Peter L Chesson
- Professor Emeritus
- Ph.D. Statistics
- University of Adelaide, Adelaide, South Australia, Australia
- Models for Animal Movements
- 5th Sun Yat-Sen Lecture in Ecology and Evolution
- Sun Yat-Sen University, Guangzhou, China, Summer 2015
- Fellow of the Ecological Society of America
- The Ecological Society of America, Spring 2015
No activities entered.
Community EcologyECOL 596F (Spring 2020)
Directed ResearchECOL 492 (Spring 2020)
Introductory Biology IIECOL 182R (Spring 2020)
ResearchECOL 900 (Spring 2020)
DissertationECOL 920 (Fall 2019)
Independent StudyECOL 399 (Fall 2019)
Intro Theoretical EcolECOL 447 (Fall 2019)
Intro Theoretical EcolECOL 547 (Fall 2019)
DissertationECOL 920 (Spring 2019)
Introductory Biology IIECOL 182R (Spring 2019)
DissertationECOL 920 (Fall 2018)
Community EcologyECOL 596F (Spring 2018)
DissertationECOL 920 (Spring 2018)
Independent StudyECOL 599 (Spring 2018)
Introductory Biology IIECOL 182R (Spring 2018)
Community EcologyECOL 596F (Fall 2017)
DissertationECOL 920 (Fall 2017)
Spatio-Temporal EcologyECOL 418 (Fall 2017)
Spatio-Temporal EcologyECOL 518 (Fall 2017)
Community EcologyECOL 596F (Spring 2017)
DissertationECOL 920 (Spring 2017)
Introductory Biology IIECOL 182R (Spring 2017)
Community EcologyECOL 596F (Fall 2016)
DissertationECOL 920 (Fall 2016)
Intro Theoretical EcolECOL 447 (Fall 2016)
Intro Theoretical EcolECOL 547 (Fall 2016)
DissertationECOL 920 (Spring 2016)
Introductory Biology IIECOL 182R (Spring 2016)
- Chesson, P. (2013). Metapopulations. In Encyclopedia of Biodiversity 2nd Edition, volume 5(pp 240-251). San Diego: Elsevier.
- Chesson, P., Huntly, N. J., Roxburgh, S. H., Pantastico-Caldas, M., & Facelli, J. M. (2013). The storage effect: definition and tests in two plant communities. In Temporal dynamics and ecological process(pp 11-40). Cambridge, Uk: Cambridge University Press.
- Chesson, P. (2012). Species competition and predation. In Encyclopedia of Sustainability Science and Technology(pp 10061-10085). Heidelberg: Springer.
- Chesson, P. (2011). Ecological Niches and Diversity Maintenance. In Research in Biodiversity: models and applications(pp 43-60). Rijeka, Croatia: InTech.
- Liu, Y., Fang, S., Chesson, P., & He, F. (2015). The effect of soil-borne pathogens depends on the abundance of host tree species. NATURE COMMUNICATIONS, 6.
- Sheue, C., Liu, J., Ho, J., Yao, A., Wu, Y., Das, S., Tsai, C., Chu, H., Ku, M. S., & Chesson, P. (2015). A VARIATION ON CHLOROPLAST DEVELOPMENT: THE BIZONOPLAST AND PHOTOSYNTHETIC EFFICIENCY IN THE DEEP-SHADE PLANT SELAGINELLA ERYTHROPUS. AMERICAN JOURNAL OF BOTANY, 102(4), 500-511.
- Stump, S. M., & Chesson, P. (2015). Distance-responsive predation is not necessary for the Janzen-Connell hypothesis. THEORETICAL POPULATION BIOLOGY, 106, 60-70.
- Yuan, C., & Chesson, P. (2015). The relative importance of relative nonlinearity and the storage effect in the lottery model. THEORETICAL POPULATION BIOLOGY, 105, 39-52.
- Holt, G., & Chesson, P. (2014). Variation in moisture duration as a driver of coexistence by the storage effect in desert annual plants. Theoretical Population Biology, 92, 36-50.More infoAbstract: Temporal environmental variation is a leading hypothesis for the coexistence of desert annual plants. Environmental variation is hypothesized to cause species-specific patterns of variation in germination, which then generates the storage effect coexistence mechanism. However, it has never been shown how sufficient species differences in germination patterns for multispecies coexistence can arise from a shared fluctuating environment. Here we show that nonlinear germination responses to a single fluctuating physical environmental factor can lead to sufficient differences between species in germination pattern for the storage effect to yield coexistence of multiple species. We derive these nonlinear germination responses from experimental data on the effects of varying soil moisture duration. Although these nonlinearities lead to strong species asymmetries in germination patterns, the relative nonlinearity coexistence mechanism is minor compared with the storage effect. However, these asymmetries mean that the storage effect can be negative for some species, which then only persist in the face of interspecific competition through average fitness advantages. This work shows how a low dimensional physical environment can nevertheless stabilize multispecies coexistence when the species have different nonlinear responses to common conditions, as supported by our experimental data. © 2013 Elsevier Inc.
- Ignace, D. D., & Chesson, P. (2014). Removing an invader: evidence for forces reassembling a Chihuahuan Desert ecosystem. Ecology, 95, 3203-3212.
- Sheue, C., Chang, H., Yang, Y., Liu, H., Chesson, P., & Hsu, F. (2014). A new classification of marginal resin ducts improves understanding of hard pine (Pinaceae) diversity in Taiwan. Flora, 209, 414-425.
- Li, L., & Chesson, P. (2016). The effects of dynamical rates on species coexistence in a variable environment: the paradox of the plankton revisited. The American Naturalist.
- Mathias, A., & Chesson, P. (2013). Coexistence and evolutionary dynamics mediated by seasonal environmental variation in annual plant communities. Theoretical Population Biology, 84(1), 56-71.More infoPMID: 23287702;Abstract: It is well established theoretically that competing species may coexist by having different responses to variation over time in the physical environment. Whereas previous theory has focused mostly on year-to-year environmental variation, we investigate how within-year variation can be the basis of species coexistence. We ask also the important but often neglected question of whether the species differences that allow coexistence are compatible with evolutionary processes. We seek the simplest circumstances that permit coexistence based on within-year environmental variation, and then evaluate the robustness of coexistence in the face of evolutionary forces. Our focus is on coexistence of annual plant species living in arid regions. We first consider environmental variation of a very simple structure where a single pulse of rain occurs, and different species have different patterns of growth activity following the rain pulse. We show that coexistence of two species is possible based on the storage effect coexistence mechanism in this simplest of varying environments. We find an exact expression for the magnitude of the storage effect that allows the functioning of the coexistence mechanism to be analyzed. However, in these simplest of circumstances, coexistence in our models is not evolutionarily stable. Increasing the complexity of the environment to two rain pulses leads to evolutionarily stable species coexistence, and a route to diversity via evolutionary branching. This demonstration of the compatibility of a coexistence mechanism with evolutionary processes is an important step in assessing the likely importance of a mechanism in nature. © 2012 Elsevier Inc.
- Sheue, C., Chesson, P., Chen, Y., Wu, S., Wu, Y., W., J., Guu, T., Lim, C., Marie, R., Razanajatovo, M. H., & Yang, Y. (2013). Comparative systematic study of colleters and stipules of Rhizophoraceae with implications for adaptation to challenging environments. Botanical Journal of the Linnean Society, 172(4), 449-464.More infoAbstract: Colleters are multicellular secretory structures found on various organs in flowering plants. Colleters on the adaxial sides of stipules have been hypothesized to play a role in protecting the developing shoot. Rhizophoraceae is a stipulate family with a broad distribution from mangrove to montane environments, which makes the family well suited for the examination of this hypothesis, but the colleters of Rhizophoraceae are not well known. We compared species from all three tribes of Rhizophoraceae, including five inland genera and all four mangrove genera. In all species, several to hundreds of colleters, sessile or stalked, arranged in rows aggregated in genus-specific shapes, are found at the adaxial bases of open and closed stipules. Pellacalyx uniquely has additional colleters at the stipule margins. Colleters are all of the standard type, comprising a central axis of core parenchyma with large vacuoles and tannins, and an outer palisade-like epidermis with organelles involved in secretory activity. An exception is Pellacalyx axillaris, in which colleters appear as extremely small epidermal protrusions. Kandelia obovata has a tracheary element in some colleters. Pellacalyx uniquely has an unusual fleshy outgrowth on the adaxial stipule base. We propose an evolutionary sequence in which Macarisia has plesiomorphic stipule and colleter traits and the mangrove Kandelia obovata with colleter vascular traces is most derived. Colleter and stipule structures are largely concordant with habitat and phylogeny, and show taxonomic value. The strong alignment of colleter and stipule patterns with habitat is suggestive that colleters have a protective function, although some components of these patterns may be phylogenetically determined. © 2013 The Linnean Society of London.
- Chesson, P. (2012). Scale transition theory: Its aims, motivations and predictions. Ecological Complexity, 10, 52-68.More infoAbstract: Scale transition theory is an approach to understanding population and community dynamics in the presence of spatial or temporal variation in environmental factors or population densities. It focuses on changes in the equations for population dynamics as the scale enlarges. These changes are explained in terms of interactions between nonlinearities and variation on lower scales, and they predict the emergence of new properties on larger scales that are not predicted by lower scale dynamics in the absence of variation on those lower scales. These phenomena can be understood in terms of statistical inequalities arising from the process of nonlinear averaging, which translates the rules for dynamics from lower to higher scales. Nonlinearities in population dynamics are expressions of the fundamental biology of the interactions between individual organisms. Variation that interacts with these nonlinearities also involves biology fundamentally in several different ways. First, there are the aspects of biology that are sensitive to variation in space or time. These determine which aspects of a nonlinear dynamical equation are affected by variation, and whether different individuals or different species are sensitive to different extents or to different aspects of variation. Second is the nature of the variation, for example, whether it is variation in the physical environment or variation in population densities. From the interplay between variation and nonlinearities in population dynamics, scale transition theory builds a theory of changes in dynamics with changes in scale. In this article, the focus is on spatial variation, and the theory is illustrated with examples relevant to the dynamics of insect communities. In these communities, one commonly occurring nonlinear relationship is a negative exponential relationship between survival of an organism and the densities of natural enemies or competitors. This negative exponential has a biological origin in terms of independent actions of many individuals. The subsequent effects of spatial variation can be represented naturally in terms of Laplace transforms and related statistical transforms to obtain both analytical solutions and an extra level of understanding. This process allows us to analyze the meaning and effects of aggregation of insects in space. Scale transition theory more generally, however, does not aim to have fully analytical solutions but partial analytical solutions applicable for circumstances too complex for full analytical solution. These partial solutions are intended to provide a framework for understanding of numerical solutions, simulations and field studies where key quantities can be estimated from empirical data. © 2011 Elsevier B.V.
- Emmerson, L. M., Facelli, J. M., Chesson, P., Possingham, H., & Day, J. R. (2012). Changes in seed dispersal processes and the potential for between-patch connectivity for an arid land daisy. Ecology, 93(3), 544-553.More infoPMID: 22624209;Abstract: Dispersal is a major and critical process in population biology that has been particularly challenging to study. Animals can have major roles in seed dispersal even in species that do not appear specifically adapted to animal-aided dispersal. This can occur by two processes: direct movement of diaspores by animals and modification of landscape characteristics by animals in ways that greatly influence dispersal. We exploited the production of large, persistent dispersal structures (seed heads, henceforth) by Erodiophyllum elderi (Asteraceae), a daisy from arid Australia, to further understand secondary dispersal. Seed head dispersal on and off animal tracks in eight E. elderi patches was monitored for 9.5 months by periodically recording the location of marked seed heads. Sites were located inside a reserve that excludes sheep but not kangaroos, and in a nearby area with both kangaroos and sheep. The distance moved and likelihood of seed head movement was higher in areas with sheep, and especially along animal tracks. There was clear evidence that seed heads were channeled down animal tracks during large rainfall events. Seed head dispersal away from patches occurred to a limited extent via their physical contact with sheep and potentially via wind dispersal. Thus, the advantages of this study system allowed us to demonstrate the two postulated effects of herbivores on dispersal via direct movement of seed heads, and two distinct indirect effects through landscape modification by herbivores from the creation of animal tracks and the denudation of vegetation. © 2012 by the Ecological Society of America.
- Sheue, C., Pao, S., Chien, L., Chesson, P., & Peng, C. (2012). Natural foliar variegation without costs? the case of Begonia. Annals of Botany, 109(6), 1065-1074.More infoPMID: 22362664;PMCID: PMC3336944;Abstract: Background and Aims: Foliar variegation is recognized as arising from two major mechanisms: leaf structure and pigment-related variegation. Begonia has species with a variety of natural foliar variegation patterns, providing diverse examples of this phenomenon. The aims of this work are to elucidate the mechanisms underlying different foliar variegation patterns in Begonia and to determine their physiological consequences. Methods: Six species and one cultivar of Begonia were investigated. Light and electron microscopy revealed the leaf structure and ultrastructure of chloroplasts in green and light areas of variegated leaves. Maximum quantum yields of photosystem II were measured by chlorophyll fluorescence. Comparison with a cultivar of Ficus revealed key features distinguishing variegation mechanisms. Key Results: Intercellular space above the chlorenchyma is the mechanism of variegation in these Begonia. This intercellular space can be located (a) below the adaxial epidermis or (b) below the adaxial water storage tissue (the first report for any taxa), creating light areas on a leaf. In addition, chlorenchyma cell shape and chloroplast distribution within chlorenchyma cells differ between light and green areas. Chloroplasts from both areas showed dense stacking of grana and stroma thylakoid membranes. The maximum quantum yield did not differ significantly between these areas, suggesting minimal loss of function with variegation. However, the absence of chloroplasts in light areas of leaves in the Ficus cultivar led to an extremely low quantum yield. Conclusions: Variegation in these Begonia is structural, where light areas are created by internal reflection between air spaces and cells in a leaf. Two forms of air space structural variegation occur, distinguished by the location of the air spaces. Both forms may have a common origin in development where dermal tissue becomes loosely connected to mesophyll. Photosynthetic functioning is retained in light areas, and these areas do not include primary veins, potentially limiting the costs of variegation. © 2012 The Author.
- Tsai, C., Li, S., Su, Y., Yong, J. W., Saenger, P., Chesson, P., Das, S., Wightman, G., Yang, Y., Liu, H., & Sheue, C. (2012). Molecular phylogeny and evidence for natural hybridization and historical introgression between Ceriops species (Rhizophoraceae). Biochemical Systematics and Ecology, 43, 178-191.More infoAbstract: Ceriops (Rhizophoraceae) is a genus comprised of five species of mangroves distributed in tropical and subtropical coastal regions. In this study, sequences from nuclear ribosomal ITS and the plastid . trnL intron are used to construct molecular phylogenies of this genus revealing two species complexes, the . C. . tagal complex (. C. tagal and . C. . australis), and the . C. . decandra complex (. C. decandra, . C. . pseudodecandra and . C. . zippeliana), each forming a distinct clade. All five species, including the newly designated species . C. pseudodecandra, are well supported. However, natural hybridization and historical introgression between . Ceriops species are also demonstrated. The ITS sequences of . Ceriops species, in contrast to their plastid . trnL intron sequences, show a great amount of homoplasy during evolution. Historical introgression originating from natural hybridization was demonstrated based on the additivity of ITS sequences from putative parents. Of the five . Ceriops species, . C. pseudodecandra is a relatively isolated species. . C. decandra and . C. zippeliana show mutual introgression in most populations. According to both the nuclear ITS sequences and the plastid . trnL intron, an intermediate form from Darwin is likely a natural hybrid, with . C. tagal and . C. australis respectively the maternal and paternal parents. © 2012 Elsevier Ltd.
- Chesson, P., & Kuang, J. J. (2010). The storage effect due to frequency-dependent predation in multispecies plant communities. Theoretical Population Biology, 78(2), 148-164.More infoPMID: 20600208;Abstract: Frequency-dependent seed predation (FDP) has been shown to be a powerful coexistence mechanism in models of annual plant communities. However, FDP undermines the competition-based coexistence mechanism called the storage effect (SEc), which relies on temporal environmental fluctuations that drive fluctuations in competition. Although environmental fluctuations also drive fluctuations in predation, a storage effect due to predation (SEp) may not arise due to a time lag between a change in the environment and the resulting change in the predation rate. Here we show how SEp can arise with multispecies FDP, and in a two-species setting with density-dependent frequency-dependence, partially compensating for the reduction in SEc, in the presence of predation. These outcomes occur when predatory behavior is flexible, and can accommodate to changes in prey abundances on a within-year time scale, leading to changes in predator preferences in response to prey abundances in a given year. When predator preferences are determined by average prey abundances over several years, FDP is still a strong coexistence mechanism but undermines SEc without creating SEp. © 2010 Elsevier Inc.
- Emmerson, L., Facelli, J. M., Chesson, P., & Possingham, H. (2010). Secondary seed dispersal of Erodiophyllum elderi, a patchily distributed short-lived perennial in the arid lands of Australia. Austral Ecology, 35(8), 906-918.More infoAbstract: We investigated secondary dispersal of propagules of Erodiophyllum elderi (Asteraceae), a short-lived perennial plant growing in small patches in the arid lands of southern Australia. In spite of its importance for population dynamics, secondary dispersal is a little understood process. We monitored the dispersal of 2280 large woody capitula (seed heads) released in six E. elderi patches for 9 months. Colour-coded seed heads were located at night using UV light and their distance and direction from the release point were measured. Over the 9-month period, more seed heads moved, and those that did, moved further in areas with high herbivore activity. Overall dispersal distance across the ground was limited to less than 30 m. Dispersal patterns were related to the topographical slope at the release site: seed heads moved further, and more dispersed on steeper slopes unless the steep slopes had sandy soil in which case seed heads were buried, caught or there was reduced sheet water flow limiting their dispersal potential. After several months, seed head dispersal virtually ceased as seed heads became stuck in the debris and soil after heavy rains or further dispersal became unlikely when seed heads reached locally low-lying areas. Secondary dispersal patterns suggest two distinctly different influences associated with the presence of herbivores: the direct movement of seed heads by trampling from sheep (an introduced herbivore) and the indirect effect of a reduced standing biomass from grazing. Reduced vegetation cover allows seed head redistribution via sheet water flow during large rainfall events. © 2010 The Authors. Journal compilation © 2010 Ecological Society of Australia.
- Kang, Y., & Chesson, P. (2010). Relative nonlinearity and permanence. Theoretical Population Biology, 78(1), 26-35.More infoPMID: 20394765;Abstract: We modify the commonly used invasibility concept for coexistence of species to the stronger concept of uniform invasibility. For two-species discrete-time competition and predator-prey models, we use this concept to find broad easily checked sufficient conditions for the rigorous concept of permanent coexistence. With these results, permanent coexistence becomes a tractable concept for many discrete-time population models. To understand how these conditions apply to nonpoint attractors, we generalize the concept of relative nonlinearity and use it to show how population fluctuations affect the long-term low-density growth rate ("the invasion rate") of a species when it is invading the system consisting of the other species ("the resident") at a single-species attractor. The concept of relative nonlinearity defines circumstances when this invasion rate is increased or decreased by resident population fluctuations arising from a nonpoint attractor. The presence and sign of relative nonlinearity is easily checked in models of interacting species. When relative nonlinearity is zero or positive, fluctuations cannot decrease the invasion rate. It follows that permanence is then determined by invasibility of the resident's fixed points. However, when relative nonlinearity is negative, invasibility, and hence permanent coexistence, can be undermined by resident population fluctuations. These results are illustrated with specific two-species competition and predator-prey models of generic forms. © 2010.
- Kuang, J. J., & Chesson, P. (2010). Interacting coexistence mechanisms in annual plant communities: Frequency-dependent predation and the storage effect. Theoretical population biology, 77(1).More infoWe study frequency-dependent seed predation (FDP) in a model of competing annual plant species in a variable environment. The combination of a variable environment and competition leads to the storage-effect coexistence mechanism (SE), which is a leading hypothesis for coexistence of desert annual plants. However, seed predation in such systems demands attention to coexistence mechanisms associated with predation. FDP is one such mechanism, which promotes coexistence by shifting predation to more abundant plant species, facilitating the recovery of species perturbed to low density. When present together, FDP and SE interact, undermining each other's effects. Predation weakens competition, and therefore weakens mechanisms associated with competition: here SE. However, the direct effect of FDP in promoting coexistence can compensate or more than compensate for this weakening of SE. On the other hand, the environmental variation necessary for SE weakens FDP. With high survival of dormant seeds, SE can be strong enough to compensate, or overcompensate, for the decline in FDP, provided predation is not too strong. Although FDP and SE may simultaneously contribute to coexistence, their combined effect is less than the sum of their separate effects, and is often less than the effect of the stronger mechanism when present alone.
- Chesson, P. (2009). Scale transition theory with special reference to species coexistence in a variable environment.. Journal of biological dynamics, 3(2-3), 149-163.More infoPMID: 22880826;Abstract: Scale transition theory is a mathematical technique for understanding changes in population dynamics with changes in spatial or temporal scale. It explains the emergence of new properties on large scales from the interaction between nonlinearities and variation on small scales. It applies statistical theory for averaging nonlinear functions to understanding this interaction. The fundamental concepts are most easily illustrated with reference to spatial models where state variables on larger spatial scales are simply defined as averages of those on smaller scales. Scale transition theory also explains the conceptually difficult topic of how species coexistence arises from temporal fluctuations. In this case, averages of per capita growth rates over time define long-term population trends and outcomes, and these averages are critically affected by interactions between nonlinear dynamics and temporal variation in state variables and environmental variables. Two general mechanisms of species coexistence, the storage effect and relatively nonlinear competitive variance, emerge.
- Chesson, P., & Chesson, P. L. (2009). Scale transition theory with special reference to species coexistence in a variable environment. Journal of biological dynamics, 3(2-3).More infoScale transition theory is a mathematical technique for understanding changes in population dynamics with changes in spatial or temporal scale. It explains the emergence of new properties on large scales from the interaction between nonlinearities and variation on small scales. It applies statistical theory for averaging nonlinear functions to understanding this interaction. The fundamental concepts are most easily illustrated with reference to spatial models where state variables on larger spatial scales are simply defined as averages of those on smaller scales. Scale transition theory also explains the conceptually difficult topic of how species coexistence arises from temporal fluctuations. In this case, averages of per capita growth rates over time define long-term population trends and outcomes, and these averages are critically affected by interactions between nonlinear dynamics and temporal variation in state variables and environmental variables. Two general mechanisms of species coexistence, the storage effect and relatively nonlinear competitive variance, emerge.
- Kuang, J. J., & Chesson, P. (2009). Coexistence of annual plants: Generalist seed predation weakens the storage effect. Ecology, 90(1), 170-182.More infoPMID: 19294923;Abstract: We investigate the effect of seed predation on the coexistence of competing annual plants. We demonstrate a role for predation that is opposite to the conventional wisdom that predation promotes coexistence by reducing the intensity of competition. In the common situation where competitive coexistence involves intraspecific competition exceeding interspecific competition, predation can undermine coexistence by reducing the overall magnitude of competition, replacing competition with "apparent competition" in a way that does not lead to differential intraspecific and interspecific effects. We demonstrate this outcome in the case where coexistence occurs by "the storage effect" in a variable environment. The storage effect arises when the environment interacts with competition to create opportunities for species to increase from low density. Critical to the storage effect is positive covariance between the response of population growth to the environment and its response to competition, when a species is at high density. This outcome prevents species at high density from taking advantage of favorable environmental conditions. A species at low density has lower covariance and can take advantage of favorable environmental conditions, giving it an advantage over a high-density species, fostering its recovery from low density. Hence, species coexistence is promoted. Here we find that density-dependent predation lowers population densities, and so weakens competition, replacing competition with apparent competition, which does not covary with the environment. As a consequence, covariance between environment and competition is weakened, reducing the advantage to a species at low density. The species still strongly interact through the combination of competition and apparent competition, but the reduced low-density advantage reduces their ability to coexist. Although this result is demonstrated specifically for the storage effect with a focus on annual plant communities, the principles involved are general ones. © 2009 by the Ecological Society of America.
- Miller, A. D., & Chesson, P. (2009). Coexistence in disturbance-prone communities: How a resistance-resilience trade-off generates coexistence via the storage effect. American Naturalist, 173(2), E30-E43.More infoAbstract: We investigate the effects of disturbance on species coexistence using a general mathematical model. The model can be applied to a variety of communities, and we show how it applies in particular to communities of shrubs in Mediterranean heathlands. Our analysis demonstrates that when species have distinct fire response strategies, disturbance allows for stable species coexistence. Furthermore, we show how the size of the coexistence region depends on fire frequency and dispersal ability. The stabilizing mechanism is classified as the spatial storage effect, which is identified by the covariance between environmental and competitive responses. This is the first time that disturbance, defined as a fluctuating mortality factor, has been definitively shown to promote coexistence via the storage effect. Moreover, we show that the biological driver is a trade-off between resistance and resilience to disturbance. The resistance-resilience trade-off is a biological mechanism of coexistence under patchy disturbance. However, the resistance-resilience trade-off has not previously featured in mathematical models of species coexistence. Although the storage effect depends on fluctuations in life-history parameters presumed to result from environmental variation, rarely are life-history parameters explicitly linked to environmental phenomena. Here the link is clear and concrete, allowing better definition of the intended application. © 2009 by The University of Chicago. All rights reserved.
- Chesson, P., & Kuang, J. J. (2008). The interaction between predation and competition. Nature, 456(7219), 235-238.More infoPMID: 19005554;Abstract: Competition and predation are the most heavily investigated species interactions in ecology, dominating studies of species diversity maintenance. However, these two interactions are most commonly viewed highly asymmetrically. Competition for resources is seen as the primary interaction limiting diversity, with predation modifying what competition does, although theoretical models have long supported diverse views. Here we show, using a comprehensive three-trophic-level model, that competition and predation should be viewed symmetrically: these two interactions are equally able to either limit or promote diversity. Diversity maintenance requires within-species density feedback loops to be stronger than between-species feedback loops. We quantify the contributions of predation and competition to these loops in a simple, interpretable form, showing their equivalent potential to strengthen or weaken diversity maintenance. Moreover, we show that competition and predation can undermine each other, with the tendency of the stronger interaction to promote or limit diversity prevailing. The past failure to appreciate the symmetrical effects and interactions of competition and predation has unduly restricted diversity maintenance studies. A multitrophic perspective should be adopted to examine a greater variety of possible effects of predation than generally considered in the past. Conservation and management strategies need to be much more concerned with the implications of changes in the strengths of trophic interactions. ©2008 Macmillan Publishers Limited. All rights reserved.
- Facelli, J. M., & Chesson, P. (2008). Cyclic dormancy, temperature and water availability control germination of Carrichtera annua, an invasive species in chenopod shrublands. Austral Ecology, 33(3), 324-328.More infoAbstract: We studied the germination of seeds of Carrichtera annua L. from a single cohort, stored in the field for up to 18 months, when retrieved at different times and subject to different combinations of temperature and water availability. Germination was affected by season of retrieval, and temperature and water availability in a complex interactive way. Germination rates were lowest when seeds were retrieved during summer or spring, but seeds germinated readily when retrieved during autumn and winter, if exposed to temperatures simulating autumn or winter conditions, and provided water equivalent to at least 50% field capacity. High temperatures and low water availability reduced germination substantially. The results indicate that this species has a combination of cyclic dormancy and germination requirements that minimizes the risk of germination during periods when the risk of prereproductive mortality is high. Given the short life of the seeds of this species, these mechanisms may be essential for the persistence of the species in the highly unpredictable arid lands of southern Australia. © 2008 The Authors.
- Kuang, J. J., & Chesson, P. (2008). Predation-competition interactions for seasonally recruiting species. American Naturalist, 171(3), E119-E133.More infoPMID: 18201119;Abstract: We investigate the interacting effects of predation and competition on species coexistence in a model of seasonally recruiting species in a constant environment. For these species, life-history parameters, such as maximum productivity and survival, have important roles in fluctuation-dependent species coexistence in that they introduce nonlinearities into population growth rates and cause endogenous population fluctuations, which can activate the coexistence mechanism termed "relative nonlinearity." Under this mechanism, different species must differ in the nonlinearities of their growth rates and must make different contributions to fluctuations in competition and predation. Both of these features can result from life-history trade-offs associated with seasonal recruitment. Coexistence by relative nonlinearity can occur with or without predation. However, predation can undermine coexistence. It does this by reducing variance contrasts between species. However, when competition is not sufficient to cause endogenous population fluctuations, predation can enable fluctuation-dependent coexistence by destabilizing the equilibrium. This model also reproduces the classic finding that coexistence can occur with selective predation provided that it causes a trade-off between competition and predation. Our model is formulated for competition between annual plant species subject to seed predation, but it also applies to perennial communities where competition and predation limit recruitment to the adult population. © 2008 by The University of Chicago. All rights reserved.
- Botkin, D. B., Saxe, H., Araújo, M. B., Betts, R., H., R., Cedhagen, T., Chesson, P., Dawson, T. P., Etterson, J. R., Faith, D. P., Ferrier, S., Guisan, A., Hansen, A. S., Hilbert, D. W., Loehle, C., Margules, C., New, M., Sobel, M. J., & R., D. (2007). Forecasting the effects of global warming on biodiversity. BioScience, 57(3), 227-236.More infoAbstract: The demand for accurate forecasting of the effects of global warming on biodiversity is growing, but current methods for forecasting have limitations. In this article, we compare and discuss the different uses of four forecasting methods: (1) models that consider species individually, (2) niche-theory models that group species by habitat (more specifically, by environmental conditions under which a species can persist or does persist), (3) general circulation models and coupled ocean-atmosphere-biosphere models, and (4) species-area curve models that consider all species or large aggregates of species. After outlining the different uses and limitations of these methods, we make eight primary suggestions for improving forecasts. We find that greater use of the fossil record and of modern genetic studies would improve forecasting methods. We note a Quaternary conundrum: While current empirical and theoretical ecological results suggest that many species could be at risk from global warming, during the recent ice ages surprisingly few species became extinct. The potential resolution of this conundrum gives insights into the requirements for more accurate and reliable forecasting. Our eight suggestions also point to constructive synergies in the solution to the different problems. © 2007 American Institute of Biological Sciences.
- Chesson, P., & Rees, M. (2007). Commentary: Resolving the biodiversity paradox. Ecology Letters, 10(8), 659-661.
- L., A., & Chesson, P. (2007). New methods for quantifying the spatial storage effect: An illustration with desert annuals. Ecology, 88(9), 2240-2247.More infoPMID: 17918402;Abstract: Recent theory supports the long-held proposition that coexistence is promoted by species-specific responses to a spatially varying environment. The underlying coexistence mechanism, the spatial storage effect, can be quantified by the covariance between response to the environment and competition. Here, "competition" is generalized to encompass similar processes such as facilitation and apparent competition. In the present study, we use a model field system of desert annual plants to demonstrate this method and to provide insight into the dynamics of the field system. Specifically, we use neighborhood competition experiments to quantify the spatial storage effect and compare it to the separate (but not mutually exclusive) process of neighborhood-scale resource partitioning. As our basic experimental design has been used frequently in community ecology, these methods can be applied to many existing data sets, as well as future field studies. © 2007 by the Ecological Society of America.
- Melbourne, B. A., & Chesson, P. (2006). The scale transition: Scaling up population dynamics with field data. Ecology, 87(6), 1478-1488.More infoPMID: 16869424;Abstract: Applying the recent developments of scale transition theory, we demonstrate a systematic approach to the problem of scaling up local scale interactions to regional scale dynamics with field data. Dynamics on larger spatial scales differ from the predictions of local dynamics alone because of an interaction between nonlinearity in population dynamics at the local scale and spatial variation in density and environmental factors over the regional population. Our systematic approach to scaling up involves the following five steps. First, define a model for dynamics on the local spatial scale. Second, apply scale transition theory to identify key interactions between nonlinearity and spatial variation that translate local dynamics to the regional scale. Third, measure local-scale model parameters to determine nonlinearities at local scales. Fourth, measure spatial variation. Finally, combine nonlinearity and variation measures to obtain the scale transition. Using field data for the dynamics of grazers and periphyton in a freshwater stream, we show that scale transition terms greatly reduce the growth and equilibrium density of the periphyton population at the stream scale compared to rock scale populations, confirming the importance of spatial mechanisms to stream-scale dynamics. © 2006 by the Ecological Society of America.
- Chesson, P., & Lee, C. T. (2005). Families of discrete kernels for modeling dispersal. Theoretical Population Biology, 67(4), 241-256.More infoPMID: 15888303;Abstract: Integer lattices are important theoretical landscapes for studying the consequences of dispersal and spatial population structure, but convenient dispersal kernels able to represent important features of dispersal in nature have been lacking for lattices. Because leptokurtic (centrally peaked and long-tailed) kernels are common in nature and have important effects in models, of particular interest are families of dispersal kernels in which the degree of leptokurtosis can be varied parametrically. Here we develop families of kernels on integer lattices with several important properties. The degree of leptokurtosis can be varied parametrically from near 0 (the Gaussian value) to infinity. These kernels are all asymptotically radially symmetric. (Exact radial symmetry is impossible on lattices except in one dimension.) They have separate parameters for shape and scale, and their lower order moments and Fourier transforms are given by simple formulae. In most cases, the kernel families that we develop are closed under convolution so that multiple steps of a kernel remain within the same family. Included in these families are kernels with asymptotic power function tails, which have provided good fits to some observations from nature. These kernel families are constructed by randomizing convolutions of stepping-stone kernels and have interpretations in terms of population heterogeneity and heterogeneous physical processes. © 2005 Elsevier Inc. All rights reserved.
- Davies, K. F., Chesson, P., Harrison, S., Inouye, B. D., Melbourne, B. A., & Rice, K. J. (2005). Spatial heterogeneity explains the scale dependence of the native-exotic diversity relationship. Ecology, 86(6), 1602-1610.More infoAbstract: While small-scale studies show that more diverse native communities are less invasible by exotics, studies at large spatial scales often find positive correlations between native and exotic diversity. This large-scale pattern is thought to arise because landscapes with favorable conditions for native species also have favorable conditions for exotic species. From theory, we proposed an alternative hypothesis: the positive relationship at large scales is driven by spatial heterogeneity in species composition, which is driven by spatial heterogeneity in the environment. Landscapes with more spatial heterogeneity in the environment can sustain more native and more exotic species, leading to a positive correlation of native and exotic diversity at large scales. In a nested data set for grassland plants, we detected negative relationships between native and exotic diversity at small spatial scales and positive relationships at large spatial scales. Supporting our hypothesis, the positive relationships between native and exotic diversity at large scales were driven by positive relationships between native and exotic beta diversity. Further, both native and exotic diversity were positively correlated with spatial heterogeneity in abiotic conditions (variance of soil depth, soil nitrogen, and aspect) but were uncorrelated with average abiotic conditions, supporting the spatial-heterogeneity hypothesis but not the favorable-conditions hypothesis. © 2005 by the Ecological Society of America.
- Facelli, J. M., Chesson, P., & Barnes, N. (2005). Differences in seed biology of annual plants in arid lands: A key ingredient of the storage effect. Ecology, 86(11), 2998-3006.More infoAbstract: We used a combination of field studies and laboratory experiments to characterize key ecological aspects of the seed biology and soil seed bank dynamics of annual plant communities in chenopod shrublands of South Australia. A sequential study of the soil seed bank demonstrated seasonal and between-year variability in numbers and composition of the soil seed bank. Soil samples incubated under different temperature and watering regimes produced different communities, indicating that species respond differentially to various environmental combinations. Emergence was extremely low at low water availability and at high temperatures, even in trays with ample water. A high percentage of seeds of four out of five species buried in the field remained viable for two years, while the fifth, Carrichtera annua, showed a sharp decline in seed viability, reaching nearly zero survivorship. Our results indicate that, in this system, annual plant communities result from germination of a fraction of seeds present in the soil seed bank, when autumn or winter rainfalls occur. Because different species have different responses to various combinations of environmental conditions, the community composition varies from year to year. This variability is likely to be a component of coexistence through the storage effect. © 2005 by the Ecological Society of America.
- Melbourne, B. A., & Chesson, P. (2005). Scaling up population dynamics: Integrating theory and data. Oecologia, 145(2), 179-187.More infoPMID: 15891847;Abstract: How to scale up from local-scale interactions to regional-scale dynamics is a critical issue in field ecology. We show how to implement a systematic approach to the problem of scaling up, using scale transition theory. Scale transition theory shows that dynamics on larger spatial scales differ from predictions based on the local dynamics alone because of an interaction between local-scale nonlinear dynamics and spatial variation in density or the environment. Based on this theory, a systematic approach to scaling up has four steps: (1) derive a model to translate the effects of local dynamics to the regional scale, and to identify key interactions between nonlinearity and spatial variation, (2) measure local-scale model parameters to determine nonlinearities at local scales, (3) measure spatial variation, and (4) combine nonlinearity and variation measures to obtain the scale transition. We illustrate the approach, with an example from benthic stream ecology of caddisflies living in riffles. By sampling from a simulated system, we show how collecting the appropriate data at local (riffle) scales to measure nonlinearities, combined with measures of spatial variation, leads to the correct inference for dynamics at the larger scale of the stream. The approach provides a way to investigate the mechanisms and consequences of changes in population dynamics with spatial scale using a relatively small amount of field data. © Springer-Verlag 2005.
- Snyder, R. E., Borer, E. T., & Chesson, P. (2005). Examining the relative importance of spatial and nonspatial coexistence mechanisms.. The American naturalist, 166(4), E75-94.More infoPMID: 16224698;Abstract: Much of the work on species coexistence has focused on the presence or absence of single mechanisms. Most theoretical frameworks, however, do not allow one to measure the strength of coexistence mechanisms, and so it has been difficult to determine the relative importance of each mechanism when multiple mechanisms are present. We present a model inspired by the California red scale system, in which two parasitoids coexist on a single, tree-dwelling host-scale insect. Previous work suggests that coexistence may be promoted both by intraguild predation (IGP) and by differing preferences for hosts on stems versus hosts on leaves (habitat preference). By applying an analytic framework that quantifies the strengths of spatial coexistence mechanisms, we are able to measure the individual contributions of IGP, habitat preference, and their interaction to maintaining coexistence. We find that habitat preference is much more effective at promoting coexistence in this model than in IGP. Furthermore, the effects of habitat preference and IGP are not independent. When the two parasitoids prefer different habitats, the coexistence-promoting effects of habitat preference are strengthened by IGP if IGP gives a moderate advantage to the inferior competitor. If IGP either confers an excessive advantage or favors the superior competitor, it can diminish the coexistence region.
- Chesson, P., L., R., Schwinning, S., Huntly, N., Wiegand, K., S., M., Sher, A., Novoplansky, A., & Weltzin, J. F. (2004). Resource pulses, species interactions, and diversity maintenance in arid and semi-arid environments. Oecologia, 141(2), 236-253.More infoPMID: 15069635;Abstract: Arid environments are characterized by limited and variable rainfall that supplies resources in pulses. Resource pulsing is a special form of environmental variation, and the general theory of coexistence in variable environments suggests specific mechanisms by which rainfall variability might contribute to the maintenance of high species diversity in arid ecosystems. In this review, we discuss physiological, morphological, and life-history traits that facilitate plant survival and growth in strongly water-limited variable environments, outlining how species differences in these traits may promote diversity. Our analysis emphasizes that the variability of pulsed environments does not reduce the importance of species interactions in structuring communities, but instead provides axes of ecological differentiation between species that facilitate their coexistence. Pulses of rainfall also influence higher trophic levels and entire food webs. Better understanding of how rainfall affects the diversity, species composition, and dynamics of arid environments can contribute to solving environmental problems stemming from land use and global climate change. © Springer-Verlag 2004.
- Dewi, S., & Chesson, P. (2004). Age-structured population growth rates in constant and variable environments: A near equilibrium approach. Theoretical Population Biology, 65(1), 75-88.More infoPMID: 14642346;Abstract: General measures summarizing the shapes of mortality and fecundity schedules are proposed. These measures are derived from moments of probability distributions related to mortality and fecundity schedules. Like moments, these measures form infinite sequences, but the first terms of these sequences are of particular value in approximating the long-term growth rate of an age- structured population that is growing slowly. Higher order terms are needed for approximating faster growing populations. These approximations offer a general nonparametric approach to the study of life-history evolution in both constant and variable environments. These techniques provide simple quantitative representations of the classical findings that, with fixed expected lifetime and net reproductive rate, type I mortality and early peak reproduction increase the absolute magnitude of the population growth rate, while type III mortality and delayed peak reproduction reduce this absolute magnitude. © 2003 Elsevier Inc. All rights reserved.
- Snyder, R. E., & Chesson, P. (2004). How the spatial scales of dispersal, competition, and environmental heterogeneity interact to affect coexistence. American Naturalist, 164(5), 633-650.More infoPMID: 15540153;Abstract: Spatial coexistence depends on a variety of biological and physical processes, and the relative scales of these processes may promote or suppress coexistence. We model plant competition in a spatially varying environment to show how shifting scales of dispersal, competition, and environmental heterogeneity affect coexistence. Spatial coexistence mechanisms are partitioned into three types: the storage effect, nonlinear competitive variance, and growth-density covariance. We first describe how the strength of each of these mechanisms depends on covariances between population densities and between population densities and the environment, and we then explain how changes in the scales of dispersal, competition, and environmental heterogeneity should affect these covariances. Our quantitative approach allows us to show how changes in the scales of biological and physical processes can shift the relative importance of different classes of spatial coexistence mechanisms and gives us a more complete understanding of how environmental heterogeneity can enable coexistence. For example, we show how environmental heterogeneity can promote coexistence even when competing species have identical responses to the environment.
- Chesson, P. (2003). Quantifying and testing coexistence mechanisms arising from recruitment fluctuations. Theoretical Population Biology, 64(3), 345-357.More infoPMID: 14522174;Abstract: Temporal fluctuations in recruitment are involved in two distinct coexistence mechanisms, the storage effect and relative nonlinearity of competition, which may act simultaneously to stabilize species coexistence. It is shown that comparisons of recruitment variation between species at high versus low densities can test whether these mechanisms are responsible for stable coexistence. Moreover, under certain circumstances, these comparisons can measure the total coexistence stabilizing effect of the mechanism. These comparisons are clearest for the situation of an invader (a species perturbed to low density) in the presence of its competitors, termed residents. Then average invader-resident differences in the variances of log recruitment, potentially weighted by adult survival rates and species' sensitivities to competition, are proportional to the overall stabilizing effect of the storage effect and relative nonlinearity of competition. Less effective comparisons are available for species naturally at high and low densities or with substantial mean differences in average fitness. These developments lead also to a technique of partitioning the long-term low-density growth rate of a species into community average measures of stabilizing mechanisms, deviations from these measures, and other factors. The community average measure is argued as most appropriate for understanding the ability of a coexistence mechanism to stabilize coexistence. Individual species' deviations from the community average indicate the ways in a which a coexistence mechanism may affect average fitness differences between species either enhancing or diminishing the ability of a given set of species to coexist, depending on other factors. This approach provides a general new tool for analyzing species coexistence. © 2003 Elsevier Inc. All rights reserved.
- Chesson, P. (2003). Understanding the role of environmental variation in population and community dynamics. Theoretical Population Biology, 64(3), 253-254.
- Dewi, S., & Chesson, P. (2003). The age-structured lottery model. Theoretical Population Biology, 64(3), 331-343.More infoPMID: 14522173;Abstract: The lottery model of competition between species in a variable environmental has been influential in understanding how coexistence may result from interactions between fluctuating environmental and competitive factors. Of most importance, it has led to the concept of the storage effect as a mechanism of species coexistence. Interactions between environment and competition in the lottery model stem from the life-history assumption that environmental variation and competition affect recruitment to the adult population, but not adult survival. The strong role of life-history attributes in this coexistence mechanism implies that its robustness should be checked for a variety of life-history scenarios. Here, age structure is added to the adult population, and the results are compared with the original lottery model. This investigation uses recently developed shape characteristics for mortality and fecundity schedules to quantify the effects of age structure on the long-term low-density growth rate of a species in competition with its competitor when applying the standard invasibility coexistence criterion. Coexistence conditions are found to be affected to a small degree by the presence of age structure in the adult population: Type III mortality broadens coexistence conditions, and type I mortality makes them narrower. The rates of recovery from low density for coexisting species, and the rates of competitive exclusion in other cases, are modified to a greater degree by age structure. The absolute rates of recovery or decline of a species from low density are increased by type I mortality or early peak reproduction, but reduced by type III mortality or late peak reproduction. Analytical approximations show how the most important effects can be considered as simple modifications of the long-term low-density growth rates for the original lottery model. © 2003 Elsevier Inc. All rights reserved.
- Snyder, R. E., & Chesson, P. (2003). Local dispersal can facilitate coexistence in the presence of permanent spatial heterogeneity. Ecology Letters, 6(4), 301-309.More infoAbstract: In the presence of permanent spatial heterogeneity, local dispersal, especially short-range dispersal, can facilitate coexistence by concentrating low-density species in the areas where their rates of increase are higher. We present a framework for predicting the effects of local dispersal on coexistence for arbitrary forms of dispersal and arbitrary spatial patterns of environmental variation. Using the lottery model as an example, we find that local dispersal contributes to coexistence by enhancing the effects of environmental variation on scales longer than typical dispersal distances, which can be characterized solely by the variance of the dispersal kernel. Higher moments of the dispersal kernel are not important.
- Chase, J. M., Abrams, P. A., Grover, J. P., Diehl, S., Chesson, P., Holt, R. D., Richards, S. A., Nisbet, R. M., & Case, T. J. (2002). The interaction between predation and competition: A review and synthesis. Ecology Letters, 5(2), 302-315.More infoAbstract: This review discusses the interface between two of the most important types of interactions between species, interspecific competition and predation. Predation has been claimed to increase, decrease, or have little effect on, the strength, impact or importance of interspecific competition. There is confusion about both the meaning of these terms and the likelihood of, and conditions required for, each of these outcomes. In this article we distinguish among three measures of the influence of predation on competitive outcomes: short-term per capita consumption or growth rates, long-term changes in density, and the probability of competitive coexistence. We then outline various theoretical mechanisms that can lead to qualitatively distinct effects of predators. The qualitative effect of predators can depend both on the mechanism of competition and on the definition of competitive strength/impact. In assessing the empirical literature, we ask: (1) What definitions of competitive strength/impact have been assumed? (2) Does strong evidence exist to support one or more of the possible mechanisms that can produce a given outcome? (3) Do biases in the choice of organism or manipulation exist, and are they likely to have influenced the conclusions reached? We conclude by discussing several unanswered questions, and espouse a stronger interchange between empirical and theoretical approaches to this important question.
- Chesson, P., & Peterson, A. G. (2002). The quantitative assessment of the benefits of physiological integration in clonal plants. Evolutionary Ecology Research, 4(8), 1153-1176.More infoAbstract: A genet of a clonal plant often has ramets persistently interconnected by living tissue capable of supporting the exchange of materials. This condition is known as physiological integration. A quantitative framework is developed for the study of the fitness benefits of physiological integration in clonal plants in spatially heterogeneous environments. We argue that the relative growth rate of the genet is a suitable approximate measure of fitness. Fitness benefits of physiological integration are then measured by comparing genet relative growth rates between heterogeneous and homogeneous environmental conditions. Fitness benefit measures are derived for both exponential and non-exponential growth of genet (clonal) fragments and for equilibrium scenarios. For short time-scales and equilibrium scenarios, we show how the fitness benefit (at the level of the genet) can be decomposed into net benefits accruing at the level of the genet fragment, which can then be further analysed in terms of costs and benefits for the parent and offspring sections of a genet fragment. Applying these benefit measures to simple models of clonal plant growth shows that net benefits of physiological integration may disappear with time and become net costs when physiological integration occurs between strictly good and poor environments. Such time dependence is predicted to result from long-term dominance of total genet growth by genet fragments in good environments. Time dependence, however, would not necessarily occur when the various environments are not strictly good or bad but have complementary attributes. Similarly, net benefits would not necessarily be time-dependent under equilibrium growth scenarios. The net benefit measures derived here allow such time dependence to be assessed in an experimental setting. Although the quantitative methods developed here focus specifically on a common experimental design in which genet fragments are divided into sections subject to different environmental conditions, these methods extend to complex scenarios that might be justified by particular circumstances in the field.
- Osenberg, C. W., M., C., Schmitt, R. J., Holbrook, S. J., Chesson, P., & Byrne, B. (2002). Rethinking ecological inference: Density dependence in reef fishes. Ecology Letters, 5(6), 715-721.More infoAbstract: We use a meta-analysis of density dependence in reef fishes to evaluate how ecologists approach detection, inference, and estimation. We compared two groups of studies: those that detected effects of density on survival and those that did not. Distinctions between these groups have spawned heated debate about the processes that affect fish dynamics. Per capita effects of density were similar between the two groups, although total effects (and hence ambient density) were greater in studies that detected density effects. The majority of the variation in effects of density was not resolved by the classification of studies based on the authors' conclusions. These results suggest (1) that standard inferences based on null hypothesis tests may miss important sources of variation in effects and give rise to unnecessary debate; and (2) that estimation of effect sizes and model parameters (including their uncertainty) is a powerful alternative to detection of ecological processes.
- Peterson, A. G., & Chesson, P. (2002). Short-term fitness benefits of physiological integration in the clonal herb Hydrocotyle peduncularis. Austral Ecology, 27(6), 647-657.More infoAbstract: We test whether physiological integration enhances the short-term fitness of the clonal herb Hydrocotyle peduncularis (Apiaceae, R. Brown ex A. Richards) subjected to spatial variation in water availability. Our measures of fitness and costs and benefits are based on the relative growth rate of fragmented genets. Physiological integration over a gradient in soil moisture resulted in a highly significant net benefit to genet growth of 0.015 g g-1 day-1. This net benefit represents a significant enhancement of the average fitness of fragmented genets spanning the moisture gradient relative to the average of those growing in homogeneous moist or dry conditions. Sections of genet fragments growing in dry conditions in spatially heterogeneous treatments had significantly higher growth than the sections they were connected to that were growing in moist conditions. Within fragments, older (parent) sections growing in moist conditions experienced significant costs from connection to younger (offspring) sections growing in dry conditions. In contrast, offspring sections with ample water did not experience any costs when connected to parent sections growing in dry conditions. However, the net benefit of physiological integration was similar for parent and offspring sections, suggesting that parent and offspring sections contributed equally to the net benefit of physiological integration to genet growth and short-term fitness.
- Shea, K., & Chesson, P. (2002). Community ecology theory as a framework for biological invasions. Trends in Ecology and Evolution, 17(4), 170-176.More infoAbstract: Community ecology theory can be used to understand biological invasions by applying recent niche concepts to alien species and the communities that they invade. These ideas lead to the concept of 'niche opportunity', which defines conditions that promote invasions in terms of resources, natural enemies, the physical environment, interactions between these factors, and the manner in which they vary in time and space. Niche opportunities vary naturally between communities but might be greatly increased by disruption of communities, especially if the original community members are less well adapted to the new conditions. Recent niche theory clarifies the prediction that low niche opportunities (invasion resistance) result from high species diversity. Conflicting empirical patterns of invasion resistance are potentially explained by covarying external factors. These various ideas derived from community ecology provide a predictive framework for invasion ecology.
- Chesson, P. (2000). General theory of competitive coexistence in spatially-varying environments. Theoretical Population Biology, 58(3), 211-237.More infoPMID: 11120650;Abstract: A general model of competitive and apparent competitive interactions in a spatially-variable environment is developed and analyzed to extend findings on coexistence in a temporally-variable environment to the spatial case and to elucidate new principles. In particular, coexistence mechanisms are divided into variation-dependent and variation-independent mechanisms with variation-dependent mechanisms including spatial generalizations of relative nonlinearity and the storage effect. Although directly analogous to the corresponding temporal mechanisms, these spatial mechanisms involve different life history traits which suggest that the spatial storage effect should arise more commonly than the temporal storage effect and spatial relative nonlinearity should arise less commonly than temporal relative nonlinearity. Additional mechanisms occur in the spatial case due to spatial covariance between the finite rate of increase of a local population and its local abundance, which has no clear temporal analogue. A limited analysis of these additional mechanisms shows that they have similar properties to the storage effect and relative nonlinearity and potentially may be considered as enlargements of the earlier mechanisms. The rate of increase of a species perturbed to low density is used to quantify coexistence. A general quadratic approximation, which is exact in some important cases, divides this rate of increase into contributions from the various mechanisms above and admits no other mechanisms, suggesting that opportunities for coexistence in a spatially-variable environment are fully characterized by these mechanisms within this general model. Three spatially-implicit models are analyzed as illustrations of the general findings and of techniques using small variance approximations. The contributions to coexistence of the various mechanisms are expressed in terms of simple interpretable formulae. These spatially-implicit models include a model of an annual plant community, a spatial multispecies version of the lottery model, and a multispecies model of an insect community competing for spatially-patchy and ephemeral food. © 2000 Academic Press.
- Chesson, P. (2000). Mechanisms of maintenance of species diversity. Annual Review of Ecology and Systematics, 31, 343-366.More infoAbstract: The focus of most ideas on diversity maintenance is species coexistence, which may be stable or unstable. Stable coexistence can be quantified by the long-term rates at which community members recover from low density. Quantification shows that coexistence mechanisms function in two major ways: They may be (a) equalizing because they tend to minimize average fitness differences between species, or (b) stabilizing because they tend to increase negative intraspecific interactions relative to negative interspecific interactions. Stabilizing mechanisms are essential for species coexistence and include traditional mechanisms such as resource partitioning and frequency-dependent predation, as well as mechanisms that depend on fluctuations in population densities and environmental factors in space and time. Equalizing mechanisms contribute to stable coexistence because they reduce large average fitness inequalities which might negate the effects of stabilizing mechanisms. Models of unstable coexitence, in which species diversity slowly decays overtime, have focused almost exclusively on equalizing mechanisms. These models would be more robust if they also included stabilizing mechanisms, which arise in many and varied ways but need not be adequate for full stability of a system. Models of unstable coexistence invite a broader view of diversity maintenance incorporating species turnover.
- Hood, G. M., Chesson, P., & Pech, R. P. (2000). Biological control using sterilizing viruses: Host suppression and competition between viruses in non-spatial models. Journal of Applied Ecology, 37(6), 914-925.More infoAbstract: 1. Research is currently underway to develop genetically engineered viruses that can sterilize pest animals. The technique, known as viral-vectored immunocontraception (VVIC), promises to control mammalian pests such as the European rabbit, the house mouse and domestic cats. 2. Using host-parasite models we explored the degree of control of the host population that can be attained when hosts that recover from infection become permanently infertile. The models assume some demographic compensation for reduced fertility in the host population, and are tailored to address issues raised by the use of the myxoma virus as an agent to sterilize rabbits. A 'pay-off' function is developed, which defines the degree to which host density is suppressed by a sterilizing agent. 3. The results show that sterilizing viruses can reduce host abundance, and that hosts with low birth rates and moderate mortality rates are the best targets for VVIC. High transmissibility increases the pay-off from VVIC, but because virulent parasites kill most of the hosts that they infect, the pay-off is highest if benign parasites are used as the vector of contraceptive antigens. We argue that appropriate pay-off functions should be developed as a basis for research and development on genetically modified organisms. 4. The host-parasite models are extended to include a competing strain of virus that does not sterilize the host. We analysed these models using a general approach to the analysis of competition, which has not often been applied to epidemiological models. The extended model shows that host sterilization per se does not affect the competitive ability of viruses, a result that applies to a broad class of models in which the per capita growth rates of competing parasites are linear functions of limiting competitive factors.
- Kerans, B. L., Chesson, P. L., & Stein, R. A. (2000). Assessing density-dependent establishment and dispersal: An example using caddisfly larvae. Canadian Journal of Fisheries and Aquatic Sciences, 57(6), 1190-1199.More infoAbstract: Density dependence in colonization is poorly understood. We studied colonization by a benthic, stream-dwelling caddisfly, Hydropsyche slossonae, through experiments varying conspecific densities and environmental conditions. A model of larval acceptance or rejection of a locality (dispersal from the locality) was developed and fitted to the data to estimate the relative strengths of density-dependent and density-independent processes underlying dispersal. In spring and fall, we varied density, substrate size, and current velocity in laboratory experiments and varied density in field experiments. In the laboratory, dispersal of fifth instars was always density dependent, but the strength of density dependence was highest in spring when the proportion dispersing was lowest. Dispersal in field experiments was density dependent only in spring. Proportion dispersing was highest under low flow. The model fit to laboratory data suggested that stronger density dependence in spring occurred because of a reduction in density-independent dispersal stimuli with no change in density-dependent stimuli. In contrast, a change in density-dependent stimuli did appear to cause differences between the proportions dispersing under the two flow regimes. The model reveals the potential for density-independent dispersal stimuli to modify the strength of density dependence detectable at the population level.
- Chesson, P. (1998). Recruitment limitation: A theoretical perspective. Austral Ecology, 23(3), 234-240.More infoAbstract: A theoretical analysis of the concept of recruitment limitation leads to the conclusion that most populations should be regarded as jointly limited by recruitment and interactions between individuals after recruitment. The open nature of local marine systems does not permit avoidance of density-dependent interactions; it simply may make them more difficult to detect. Local populations consisting of settled organisms may not experience density-dependent interactions under some circumstances, but the entire species population consisting of the collection of local populations and their planktonic larvae must have density-dependent dynamics. Any local population of settled individuals can escape density dependence if sufficient density dependence occurs among planktonic larvae or within other local populations. Common conceptions of density dependence are too narrow, leading too often to the conclusion that it is absent from a system. It is equally wrong to expect that density-dependent interactions after settlement determine local population densities independently of recruitment. Special circumstances allowing density dependence to act strongly and quickly are needed before density dependence can neutralize the effects of recruitment. Recruitment limitation and density-dependent interactions therefore should not be regarded as alternatives but as jointly acting to determine the densities of marine benthic populations. Moreover, the interaction between fluctuating recruitment and density dependence is potentially the most interesting feature of recruitment limitation. For example, this interaction may be an important diversity-maintaining mechanism for marine systems.
- Chesson, P. (1998). Spatial scales in the study of reef fishes: A theoretical perspective. Austral Ecology, 23(3), 209-215.More infoAbstract: Theoretical models imply that spatial scale derives its greatest importance through interactions between density-dependent processes and spatial variation in population densities and environmental variables. Such interactions cause population dynamics on large spatial scales to differ in important ways from predictions based on measurements of population dynamics at smaller scales, a phenomenon called the scale transition. These differences can account for large-scale population stability and species coexistence. The interactions between density dependence and spatial variation that lead to the scale transition can be understood by the process of non-linear averaging, which shows how variance originating on various spatial scales contributes to large-scale population dynamics. Variance originating below the scale of density dependence contributes less to the scale transition as the spatial scale of the variation declines, while variation originating on or above the scale of density dependence contributes independently of the spatial scale of the variation.
- Roxburgh, S. H., & Chesson, P. (1998). A new method for detecting species associations with spatially autocorrelated data. Ecology, 79(6), 2180-2192.More infoAbstract: Many organisms display patchiness in their distribution patterns over a wide range of spatial scales. Patchy distribution patterns can be caused by processes such as growth, migration, reproduction, and mortality, which result in neighboring areas being more likely to contain a species than distant areas, a phenomenon known as positive spatial autocorrelation. When species are patchily distributed, the within-species spatial randomness assumptions of the standard statistical tests for detecting species associations are seriously violated. Using these tests under such circumstances can lead to incorrect rejection of the null hypothesis. To address this problem we introduce a new test for detecting species associations-the random patterns test. This test takes into account spatial autocorrelation by including the characteristics of the spatial pattern of each species into the null model. A randomization procedure was used to generate the null distribution of the test statistic. The random patterns test is illustrated with data collected from an herbaceous understory community of a Eucalyptus forest near Canberra, Australia.
- Chesson, P., & Huntly, N. (1997). The roles of harsh and fluctuating conditions in the dynamics of ecological communities. American Naturalist, 150(5), 519-553.More infoPMID: 18811299;Abstract: Harsh conditions (e.g., mortality and stress) reduce population growth rates directly; secondarily, they may reduce the intensity of interactions between organisms. Near-exclusive focus on the secondary effect of these forms of harshness has led ecologists to believe that they reduce the importance of ecological interactions, such as competition, and favor coexistence of even ecologically very similar species. By examining both the costs and the benefits, we show that harshness alone does not lessen the importance of species interactions or limit their role in community structure. Species coexistence requires niche differences, and harshness does not in itself make coexistence more likely. Fluctuations in environmental conditions (e.g., disturbance seasonal change, and weather variation) also have been regarded as decreasing species interactions and favoring coexistence, but we argue that coexistence can only be favored when fluctuations create spatial or temporal niche opportunities. We argue that important diversity-promoting roles for harsh and fluctuating conditions depend on deviations from the assumptions of additive effects and linear dependencies most commonly found in ecological models. Such considerations imply strong roles for species interactions in the diversity of a community.
- Lavorel, S., & Chesson, P. (1995). How species with different regeneration niches coexist in patchy habitats with local disturbances. Oikos, 74(1), 103-114.
- Chesson, P. (1994). Multispecies competition in variable environments. Theoretical Population Biology, 45(3), 227-276.
- Chesson, P., & Pantastico-Caldas, M. (1994). The forest architecture hypothesis for diversity maintenance. Trends in Ecology and Evolution, 9(3), 79-80.More infoPMID: 21236779;
- Baskin, C. C., Chesson, P. L., & Baskin, J. M. (1993). Annual seed dormancy cycles in two desert winter annuals. Journal of Ecology, 81(3), 551-556.More infoAbstract: Freshly matured seeds of Eriogonum abertianum and Eriastrum diffusum and those of both species exhumed after various periods of burial in the Chihuahuan Desert, Arizona, were tested for germination in light and darkness at five thermoperiods. Seeds of Eriogonum were nondormant (ND) at maturity in autumn 1988, and thus 87% of them germinated in light at 15/6 and at 20/10°C. Seeds entered conditional dormancy (CD) in winter; germination at 20/10°C decreased to 6% in light However, a high percentage of the seeds were again ND by autumn 1990. Thus, like seeds of facultative winter annuals in humid, temperate regions, those of Eriogonum have an annual CD/ND cycle, which is characteristic of annuals in unpredictable habitats. Seeds of Eriastrum were dormant (D) at maturity in May 1989. A portion of the seeds after-ripened during summer, and in October 65 and 38% of them germinated in light at 15/6 and 20/10°C respectively. Most of the ND seeds re-entered dormancy during winter, but by the following October 92% of them were ND. Thus, like seeds of obligate winter annuals in humid, temperate regions, those of Eriastrum exhibit an annual D/ND cycle, which is characteristic of annuals in predictable habitats. -Authors
- Chesson, P. (1992). Preface. Theoretical Population Biology, 41(3), 255-256.
- Chesson, P. (1991). A need for niches?. Trends in Ecology and Evolution, 6(1), 26-28.More infoAbstract: The idea that different species must have distinct ecologies if they are to coexist has been challenged recently by the claim that some models involving stochastic factors or clumped spatial distributions permit stable coexistence of species that are identical or differ only in competitive ability. However, these models have been misinterpreted; except in rather limited circumstances, they provide further support for the notion that species must be sufficiently ecologically distinct to coexist stably. The possible, limited, exceptions to this rule involve social factors by which individuals of a species discriminate between heterospecifics and conspecifics without there being any true ecological differences between species.
- Chesson, P. (1991). Reply from Peter Chesson. Trends in Ecology and Evolution, 6(8), 263-.
- Chesson, P., & Rosenzweig, M. (1991). Behavior, heterogeneity, and the dynamics of interacting species. Ecology, 72(4), 1187-1195.More infoAbstract: In various settings the authors show how behavior can be a response to heterogeneity, introducing nonlinear density dependence and qualitatively altering population dynamics. Also, even simple behaviors can cause nonadditivity, which is an interaction between environmental and density-dependent processes. It has a critical effect on the coexistence of competing species. To understand these various joint effects of behavior and heterogeneity on population dynamics, the general effects of behavior on dynamics are discussed. The authors then consider examples of the various ways in which heterogeneity affects dynamics, and for each example consider the interaction of behavior with heterogeneity. -from Authors
- Hassell, M. P., May, R. M., Pacala, S. W., & Chesson, P. L. (1991). The persistence of host-parasitoid associations in patchy environments I. A general criterion. American Naturalist, 138(3), 568-583.More infoAbstract: For host-parasitoid interactions in a heterogeneous environment and with discrete generations, the dynamic effects of any patterns of distribution of searching parasitoids can be assessed within a common, simple framework. The populations are regulated if the distribution of searching parasitoids is sufficiently heterogeneous. The square of the coefficient of variation (CV2) of the searching parasitoids per host must exceed unity. CV2 may be partitioned into a density-dependent component caused by the response of parasitoids to host density per patch and a density-independent component. Population regulation is enhanced as much as density-independent as by density-dependent heterogeneity. -from Authors
- Butler, A. J., & Chesson, P. L. (1990). Ecology of sessile animals on sublittoral hard substrata: the need to measure varation. Australian Journal of Ecology, 15(4), 521-531.More infoAbstract: Examines assemblages of sessile animals occupying shaded, commonly vertical hard substrata in the shallow subtidal zone, proposing a conceptual model which focuses on variation in characteristics such as birth and death rates, competitive interactions and dispersal. This model may explain the coexistence of a large number of ecologically similar species in assemblages that appear in a sense "stable' (but where assemblages at different sites differ in detail). -from Authors
- Chesson, P. (1990). MacArthur's consumer-resource model. Theoretical Population Biology, 37(1), 26-38.More infoAbstract: MacArthur's consumer-resource model is reviewed and new ways of understanding it are presented. Statistical measures of association between the utilization functions of different species are developed to show how coexistence conditions can be expressed in simple and understandable ways without the need to introduce strong symmetry assumptions. It is hoped that this new analysis will encourage both the use of the model in its full form without special simplifying assumptions, and the development of competition models of similar biological richness but different basic assumptions. © 1990.
- Chesson, P. L. (1990). Geometry, heterogeneity and competition in variable environments. Philosophical Transactions - Royal Society of London, B, 330(1257), 165-173.More infoAbstract: The effects of environmental fluctuations on coexistence of competing species can be understood by a new geometric analysis, which shows how a species of low density gains an average growth rate advantage when the environment fluctuates and all species have growth rates of the particular geometric form called subadditive. This low density advantage opposes competitive exclusion. Additive growth rates confer no such low density advantage, while superadditive growth rates promote competitive exclusion. Total population growth is divided into different components, such as may be contributed by different life-history stages, phenotypes, or subpopulations in different microhabitats. A three-factor model aids the conceptual division of population growth into suitable components. There is a discussion by P.J.Grubb. -from Author
- Chesson, P. L., & Ellner, S. (1989). Invasibility and stochastic boundedness in monotonic competition models. Journal of Mathematical Biology, 27(2), 117-138.More infoAbstract: We give necessary and sufficient conditions for stochastically bounded coexistence in a class of models for two species competing in a randomly varying environment. Coexistence is implied by mutual invasibility, as conjectured by Turelli. In the absence of invasibility, a species converges to extinction with large probability if its initial population is small, and extinction of one species must occur with probability one regardless of the initial population sizes. These results are applied to a general symmetric competition model to find conditions under which environmental fluctuations imply coexistence or competitive exclusion. © 1989 Springer-Verlag.
- Chesson, P., & Huntly, N. (1989). Short-term instabilities and long-term community dynamics. Trends in Ecology and Evolution, 4(10), 293-298.More infoAbstract: Competition in a temporally variable environment leads to sequences of short-term instabilities that in some cases are the mechanism of long-term coexistence; in other cases they promote long-term instability. Recent work associates long-term stability with a positive relationship between environmental and competitive effects and with population growth rates that are buffered against jointly unfavorable environmental and competitive events. Buffered growth rates arise from population subdivision over life-history stages, microenvironments or phenotypes. A distinct but related mechanism of long-term stability relies on population growth rates that are nonlinear functions of competition. New ways of understanding and investigating species diversity follow from these results. © 1989.
- Devries, D. R., Stein, R. A., & Chesson, P. L. (1989). Sunfish foraging among patches: the patch-departure decision. Animal Behaviour, 37(PART 3), 455-464.More infoAbstract: Patch-use behaviour of small bluegill sunfish, Lepomis macrochirus, foraging for chironomid larvae, Chironomus riparius, was investigated in artificial macrophyte patches to examine search pattern within a patch and to determine the decision rule used by fish when leaving a patch. Fish were exposed to a sequence of habitats which differed in quality (i.e. total prey density); however, within a habitat all patches were of equal quality. When foraging in a single patch, fish encountered prey randomly, as evidenced by agreement between the distribution of intercapture intervals and the exponential distribution. Agreement between fish behaviour and predictions of a rate decision rule indicated that the decision to leave a patch was based on some estimate of capture rate in the patch. Predictions of how long fish should stay in a patch and how many prey they should capture during a patch visit were generated, using a giving-up time model based on an exponential distribution of intercapture intervals. Fish generally stayed longer and captured more prey than predicted by the model, using giving-up times that were longer than optimal. The relationship between rate of prey capture for the habitat and giving-up times was shaped such that fish minimized the cost, in terms of a decrease in capture rate, by overestimating rather than underestimating the optimal giving-up time. © 1989.
- Hatfield, J. S., & Chesson, P. L. (1989). Diffusion analysis and stationary distribution of the two-species lottery competition model. Theoretical Population Biology, 36(3), 251-266.More infoAbstract: The lottery model is a stochastic population model in which juveniles compete for space. Examples include sedentary organisms such as trees in a forest and members of marine benthic communities. The behavior of this model appears to be characteristic of that found in other sorts of stochastic competition models. In a community with two species, it was previously demonstrated that coexistence of the species is possible if adult death rates are small and environmental variation is large. Environmental variation is incorporated by assuming that the birth rates and death rates are random variables. Complicated conditions for coexistence and competitive exclusion have been derived elsewhere. In this paper, simple and easily interpreted conditions are found by using the technique of diffusion approximation. Formulae are given for the stationary distribution and means and variances of population fluctuations. The shape of the stationary distribution allows the stability of the coexistence to be evaluated. © 1989.
- Marschall, E. A., Chesson, P. L., & Stein, R. A. (1989). Foraging in a patchy environment: prey-encounter rate and residence time distributions. Animal Behaviour, 37(PART 3), 444-454.More infoAbstract: Small bluegill sunfish, Lepomis macrochirus, foraging among patches in the laboratory did not search systematically within a patch; their intercapture intervals did not differ from a model of random prey encounter within a patch. Patch-residence time, number of prey eaten, and giving-up time (time between last prey capture and leaving the patch) were measured for bluegills foraging in two different three-patch 'environments' (a constant environment, in which each patch began with the same number of prey and a variable environment, in which two patches began with low prey density and one patch with high prey density). When compared with three decision rules a forager may use to determine when to leave a patch, the data most closely agreed with predictions from 'constant residence time' rule. Bluegills responded to changes in the distribution of prey among patches, but not by using different decision rules. There was qualitative, but not quantitative, agreement with a model of random residence times. The total number of prey eaten by a bluegill during a foraging bout was similar to the number predicted from a model of random search and random residence times. © 1989.
- Reeve, J. D., Kerans, B. L., & Chesson, P. L. (1989). Combining different forms of parasitoid aggregation: effects on stability and patterns of parasitism. Oikos, 56(2), 233-239.More infoAbstract: Two models blend different forms of parasitoid search behavior; aggregation independent of host density, and in response to host density. In Model A parasitoid and host densities on a patch are assumed to be positively correlated, while in Model B the parasitoids have a linear regression on host density, with an associated error term. In Model A, the dynamics were least stable when host and parasitoid were perfectly correlated. In Model B, the slope of the regression had only a moderate effect on stability, while large amounts of error strongly promoted stability. Results suggest that a weak and noisy aggregative response by the parasitoid may be strongly stabilizing, while a strong relationship between parasitoid and host density can sometimes produce instability. As a strong relationship also produces spatial density-dependence in parasitism rates, such a pattern in the field need not indicate stabilizing forms of parasitoid behavior. -Authors
- Chesson, P. L., & Huntly, N. (1988). Community consequences of life-history traits in a variable environment. Annales Zoologici Fennici, 25(1), 5-16.More infoAbstract: Models of interspecific competition in a stochastic environment show that the effects of environmental fluctuations on species coexistence can be expected to vary from community to community. However, by taking account of some basic properties of the species in a community it is possible to predict whether environmental fluctuations should promote coexistence, promote competitive exclusion or have no effect on species coexistence. One such property is the way the growth rates of the species respond to the joint effects of environment and competition. In simple (additive) models the joint effect of environment and competition is the sum of their separate effects. Deviations from additivity, in either the direction of subadditivity or superadditivity, are important determinants of species coexistence in a fluctuating environment. Such nonadditive growth rates are predicted on the basis of life-history traits, heterogeneity within a population and heterogeneity in space. Nonadditive growth rates have intuitive interpretations in terms of buffers and amplifiers of the joint effects of environment and competition. -from Authors
- Chesson, P. L., & Murdoch, W. W. (1986). Aggregation of risk: relationships among host- parasitoid models.. American Naturalist, 127(5), 696-715.More infoAbstract: Models in which parasitoid density in a patch is strictly a function of host density in the patch, with no 'error' about this function, are pure-regression models. Those in which there is random variation in the number of parasitoids per patch, with no relationship between local parasitoid density and local host density, are pure-error models. The key factor in these models is not the distribution of parasitoids per se, but the distribution of the relative risk of parasitism which in the present formulation can result from variation in the number of parasitoids in a patch or from variation in host vulnerability. -from Authors
- Chesson, P. L. (1985). Coexistence of competitors in spatially and temporally varying environments: A look at the combined effects of different sorts of variability. Theoretical Population Biology, 28(3), 263-287.More infoAbstract: A stochastic model is developed for competition among organisms living in a patchy and varying environment. The model is designed to be suitable for species with sedentary adults and widely dispersing larvae or propagules, and applies best to marine systems but may also be adequate for some terrestrial systems. Three kinds of environmental variation are incorporated simultaneously in the model. These are pure spatial variation, pure temporal variation, and the space × time interaction. All three kinds of variation can promote coexistence, and when variation is restricted to immigration rates, all three kinds act very similarly. Moreover, for long-lived organisms their action is nearly identical, and their effects, when present together, combine equivalently. For short-lived organisms, however, pure temporal variation is a less effective promoter of coexistence. Variation in death rates acts quite differently from variation in birth rates for it may demote coexistence in some circumstances, while promoting coexistence in other circumstances. Furthermore, pure spatial variation in death rates has quite different effects than other kinds of death-rate variation. In addition to conditions for coexistence, information is given on population fluctuations, convergence to stationary distributions, and asymptotic distributions for long-lived organisms. While the model is presented as an ecological model, a genetical interpretation is also possible. This leads to new suggested mechanisms for the maintenance of polymorphisms in populations. © 1985.
- Murdoch, W. W., Chesson, J., & Chesson, P. L. (1985). Biological control in theory and practice.. American Naturalist, 125(3), 344-366.More infoAbstract: A stable pest equilibrium is neither a necessary nor a sufficient condition for control: satisfactory control in model systems is compatible with both local extinction of the pest and polyphagy in the natural enemy. Only one of 9 real examples of successful control is convincingly a stable interaction; the remainder show either strong evidence for instability and local extinction of the pest or are consistent with this interpretation. Two strategies by which a natural enemy may control a pest in a nonequilibrium state, termed here 'lying-in-wait' and 'search-and-destroy,' are distinguished.-from Authors
- Warner, R. R., & Chesson, P. L. (1985). Coexistence mediated by recruitment fluctuations: a field guide to the storage effect.. American Naturalist, 125(6), 769-787.More infoAbstract: For most species, a changeable environment creates a situation in which recruitment varies considerably from one breeding season to the next. If adults survive well, an occasional favorable recruitment can sustain population numbers over long periods: gains made in favourable periods are stored in the adult population. Storage is particularly important when the species is at low densities, because then the potential population growth rate is very high if a favorable period occurs. Storage mechanism can lead to coexistence of 2 species in lottery competition for space, as long as generations overlapped and there was sufficient variation in recruitment. This was true even if one species had an average competitive advantage. The storage model also operates when >2 species are competing, when resources renew independently of population sizes, and when not all the resource is used. Species with relatively long lives and high fecundities are most likely to enjoy the benefits of the storage effect. Environments that theoretically elicit these life history characteristics are relatively benign and permanent for established adults, but are such that births and/or juvenile survivorship vary widely. Trees and many marine organisms are examples of species with the proper life histories, and storage may be important in maintaining the high diversity of these communities.-from Authors
- Chesson, P. L. (1984). Persistence of a Markovian population in a patchy environment. Zeitschrift für Wahrscheinlichkeitstheorie und Verwandte Gebiete, 66(1), 97-107.More infoAbstract: An infinite system of Markov chains is used to describe population development in an interconnected system of local populations. The model can also be viewed as an inhomogeneous Markov chain where the temporal inhomogeneity is a function of the mean of the process. Conditions for population persistence, in the sense of stochastic boundedness, are found. © 1984 Springer-Verlag.
- Chesson, P. L. (1984). Variable predators and switching behavior. Theoretical Population Biology, 26(1), 1-26.More infoAbstract: Models are developed in which prey preferences vary between individual predators but the preference of an individual does not change with prey relative density. These two properties generally lead to the surprising conclusion that the aggregate preference of a population of predators does change with prey relative density. This phenomenon may result in negative or positive switching, depending on the circumstances, with negative switching being the more likely result. Such population negative switching is found in previously published experimental data. Implications are given for the analysis of ecological data, and some implications for the stability of field populations are suggested. © 1984.
- Chesson, P. L. (1982). The stabilizing effect of a random environment. Journal of Mathematical Biology, 15(1), 1-36.More infoAbstract: It is shown that the lottery competition model permits coexistence in a stochastic environment, but not in a constant environment. Conditions for coexistence and competitive exclusion are determined. Analysis of these conditions shows that the essential requirements for coexistence are overlapping generations and fluctuating birth rates which ensure that each species has periods when it is increasing. It is found that a species may persist provided only that it is favored sufficiently by the environment during favorable periods independently of the extent to which the other species is favored during its favorable periods. Coexistence is defined in terms of the stochastic boundedness criterion for species persistence. Using the lottery model as an example this criterion is justified and compared with other persistence criteria. Properties of the stationary distribution of population density are determined for an interesting limiting case of the lottery model and these are related to stochastic boundedness. An attempt is then made to relate stochastic boundedness for infinite population models to the behavior of finite population models. © 1982 Springer-Verlag.
- Chesson, P. L. (1981). Models for spatially distributed populations: The effect of within-patch variability. Theoretical Population Biology, 19(3), 288-325.More infoAbstract: This paper studies population models which have the following three ingredients: populations are divided into local subpopulations, local population dynamics are nonlinear and random events occur locally in space. In this setting local stochastic phenomena have a systematic effect on average population density and this effect does not disappear in large populations. This result is an outcome of the interaction of the three ingredients in the models and it says that stochastic models of systems of patches can be expected to give results for average population density that differ systematically from those of deterministic models. The magnitude of these differences is related to the degree of nonlinearity of local dynamics and the magnitude of local variability. These results explain those obtained from a number of previously published models which give conclusions that differ from those of deterministic models. Results are also obtained that show how stochastic models of systems of patches may be simplified to facilitate their study. © 1981.
- Chesson, P. (1976). The canonical decomposition of bivariate distributions. Journal of Multivariate Analysis, 6(4), 526-537.More infoAbstract: The ordinary notion of a bivariate distribution has a natural generalisation. For this generalisation it is shown that a bivariate distribution can be characterised by a Hilbert space H and a family Mp, 0 ≤ p ≤ 1, of subspaces of H. H specifies the marginal distributions whilst Mp is a summary of the dependence structure. This characterisation extends existing ideas on canonical correlation. © 1976.