Michael L Rosenzweig

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• Katz, M. W., Abramsky, Z., Kotler, B. P., Rosenzweig, M. L., Alteshtein, O., & Vasserman, G. (2013). Optimal foraging of little egrets and their prey in a foraging game in a patchy environment. American Naturalist, 181(3), 381-395.
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  PMID: 23448887;Abstract: We explored the behavioral game between a predator, the little egret (Egretta garzetta), and a prey, the common goldfish (Carassius auratus), in a laboratory theater containing three fish pools. We tested the hypotheses that the egrets maximize their total capture success by responding to the fish's antipredatory behavior and that the behaviors of both players respond adaptively to the density distribution of fish among the pools. One experiment presented egrets with 15 fish per pool. The second experiment used a heterogeneous environment: pools 1, 2, and 3 had 10, 15, and 20 fish, respectively. Within each pool, fish could move between a safe, covered microhabitat and a risky, open microhabitat. Only the risky habitat had food, so fish were trading off food and safety by allocating the time spent in the two habitats. Egrets spent more total time in pools with more fish and returned to them sooner. Egrets maximized the number of fish they captured by following the matching rule of the ideal free distribution. The fish used the risky but productive habitat 65% of the time during experiments without egrets, but only 9% during experiments with 15 fish and egrets present somewhere in the theater. In addition, with egrets present, fish fine-tuned their behavior by reducing their use of the risky habitat as the egrets increased the frequency of their visits. © 2013 by The University of Chicago. 0003-0147/2013/18103-54025$15.00. All rights reserved.
• Gavish, Y., Ziv, Y., & Rosenzweig, M. L. (2012). Decoupling Fragmentation from Habitat Loss for Spiders in Patchy Agricultural Landscapes. Conservation Biology, 26(1), 150-159.
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  PMID: 22136430;Abstract: Habitat loss reduces species diversity, but the effect of habitat fragmentation on number of species is less clear because fragmentation generally accompanies loss of habitat. We compared four methods that aim to decouple the effects of fragmentation from the effects of habitat loss. Two methods are based on species-area relations, one on Fisher's alpha index of diversity, and one on plots of cumulative number of species detected against cumulative area sampled. We used these methods to analyze the species diversity of spiders in 2, 3.2 × 4 km agricultural landscapes in Southern Judea Lowlands, Israel. Spider diversity increased as fragmentation increased with all four methods, probably not because of the additive within-patch processes, such as edge effect and heterogeneity. The positive relation between fragmentation and species diversity might reflect that most species can disperse through the fields during the wheat-growing season. We suggest that if a given area was designated for the conservation of spiders in Southern Judea Lowlands, Israel, a set of several small patches may maximize species diversity over time. © 2011 Society for Conservation Biology.
• Rosenzweig, M. L., Drumlevitch, F., Borgmann, K. L., Flesch, A. D., Grajeda, S. M., Johnson, G., MacKay, K., Nicholson, K. L., Patterson, V., Pri-Tal, B. M., Ramos-Lara, N., & Serrano, K. P. (2012). An ecological telescope to view future terrestrial vertebrate diversity. Evolutionary Ecology Research, 14(3), 247-268.
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  Abstract: Background: Some regions of the Earth sustain their own diversities through the processes of speciation and extinction. Theory predicts and data support the conclusion that the number of species (S) in such regions should attain a steady state whose value correlates with their areas (extents). Other data strongly suggest that climate plays a significant role in determining S. Aim: Combine the influences of area and climate in a mathematical model that fits known global terrestrial vertebrate species diversities. Data: The WildFinder terrestrial vertebrate data set of the World Wildlife Fund as it stood in January 2006 (less some data associated with islands). Each of WildFinder's 825 ecoregions is accompanied by a set of abiotic variables (area and values of climate variables), as well as a list of the resident vertebrate species it contains. Methods: Assign each ecoregion to a zoological region (sensu Sclater, 1858). Compile a list of all species that reside in each zoological region. Calculate the area of each region (A), the number of species in it (separated into the four vertebrate classes: Amphibia, Reptilia, Aves, Mammalia). Find a suitable variable to represent annual energy flow (i.e. ecological productivity). Determine the number of species endemic to each zoological region. Calculate the mean annual temperature (T) and actual evapotranspiration (AE) in each zoological region. Find the regression equations that best fit the numbers of species. Results: The land has nine zoological regions (in order of area): Palearctic, Nearctic, Sub-Saharan Africa, Neotropics, Australasia, Indo-Malaysia, Madagascar, New Zealand, and Hawaii. The number of species, S, fits area (R2 =0.84; P =6 ×10-4). Neither T by itself nor AE by itself is significantly correlated with S. However, adding either T or AE as the second variable in the regression does increase R 2 significantly. Their statistical effects on R2 are virtually identical: using logA and logAE as independent variables yields R 2 =0.974; using logA and T yields R2 =0.973. The results for the diversities of the four separate classes are quite similar to those of the total S, except that their four z-values vary from 0.53 to 1.07. Conclusion: The Earth's terrestrial vertebrates face a mass extinction of 30-96%. © 2012 Michael L. Rosenzweig.
• Davis, M. A., Chew, M. K., Hobbs, R. J., Lugo, A. E., Ewel, J. J., Vermeij, G. J., Brown, J. H., Rosenzweig, M. L., Gardener, M. R., Carroll, S. P., Thompson, K., T., S., Stromberg, J. C., Tredici, P. D., Suding, K. N., Ehrenfeld, J. G., Grime, J. P., Mascaro, J., & Briggs, J. C. (2011). Don't judge species on their origins. Nature, 474(7350), 153-154.
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  PMID: 21654782;
• O'Brien, J. M., Thorne, J. H., Rosenzweig, M. L., & Shapiro, A. M. (2011). Once-yearly sampling for the detection of trends in biodiversity: The case of Willow Slough, California. Biological Conservation, 144(7), 2012-2019.
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  Abstract: The butterfly fauna at Willow Slough, Yolo County, California has been censused for 32. years as part of a participatory citizen-science project, the Fourth of July Butterfly Count. While the utility of a once-a-year census as a monitoring tool is potentially compromised by lack of standardization in counting protocols and variation in observer skill, at Willow Slough these issues have been minimized.We examined the Willow Slough count data for trends in both faunal diversity and the probability of presence of individual species. During the study, the number of species observed at a visit declined by 39%. Regressions of per-visit species counts against time did not detect a statistically significant decline until year 24. In contrast, Fisher's α, a statistic designed to reduce sample-size bias, detected the decline as early as year 13. Twelve of the 24 species analyzed showed significant declines in probability of occurrence; a further nine exhibited negative but non-significant trends. Butterflies that overwinter as eggs or larvae were more likely to decline than those that overwinter as pupae or adults. Many species in decline at Willow Slough have also been observed less frequently at nearby sites which are monitored year-round, supporting the value of once-a-year monitoring. Although correlations with climatic data have been identified, they are too weak to account for the observed faunal decline. We suspect broader patterns of land use and habitat continuity are implicated in butterfly declines across the region.We conclude that once-a-year sampling, if properly and rigorously done, is in fact useful as a monitoring tool for butterfly faunas, and that Fisher's α is well suited to early detection of trends in repeated diversity sampling. © 2011 Elsevier Ltd.
• Rosenzweig, M. L. (2011). Comment: A new approach to relative speciation rates. Evolutionary Ecology Research, 13(8), 879-882.
• Katz, M. W., Abramsky, Z., Kotler, B., AltsteinF, O., & Rosenzweig, M. L. (2010). Playing the waiting game: Predator and prey in a test environment. Evolutionary Ecology Research, 12(6), 793-801.
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  Abstract: Optimal behaviour of a predator depends on what its prey are doing and vice versa. Yet empirical tests of optimal foraging generally take place with only one of the two species free to adjust its behaviour. Question: Do predators and prey follow predictions of optimality when they are interacting and each is free to adjust its behaviour? Organisms: Commercially purchased common goldfish (Carassius auratus) and wild-caught little egrets (Egretta garzetta). Experimental arenas: Covered circular enclosures (radius 3.5 m), each with three artificial pools (radius 0.76 m). Each pool had a habitat where the goldfish could hide, and an open habitat where they could collect their food but were exposed to predation. Methods: An egret was allowed to forage in an arena each of whose pools contained 15 goldfish (replaced daily according to the number consumed). We measured the time goldfish spent in the open and under cover; the time it took for them to emerge from cover after an egret visit (i.e. the refractory time, rf ); the number of fish eaten; and the time an egret took to return to a pool after leaving it (i.e. the return time, rt). Predictions: Qualitative: during an egret's visit to a pool, fish should spend a greater proportion of time hiding and thus become less and less vulnerable to predation. Quantitative: An egret will maximize its chance to encounter exposed fish by adopting a return time equal to fish refractory time (rt = rf ). An egret should maximize its catch of fish if rt = rf. Results: In the presence of an egret, goldfish significantly reduced the time they spent in the open (2.09% vs. 65.4%). The average goldfish refractory time was 20.31 min. The average little egret return time was 21.09 min. These values are not significantly different. Egrets catch the most fish if rt = 18.6 min (not significantly different from that observed). © 2010 Zvika Abramsky.
• Rosenzweig, M. L. (2010). On the size selectivity of extinction in late pleistocene mammals: A mini-forum based on Polishchuk. Evolutionary Ecology Research, 12(3), 403-410.
• Rosenzweig, M. L. (2009). A tribute to Tom Vincent. Evolutionary Ecology Research, 11(2), 135-.
• Tainaka, K., Yoshimura, J., & Rosenzweig, M. L. (2007). Do male orangutans play a hawk-dove game?. Evolutionary Ecology Research, 9(6), 1043-1049.
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  Abstract: Background: (1) The hawk-dove game has been invoked to explain animal fighting. (2) Orangutans (Pongo pygmaeus) have two forms of reproductively competent males: (a) The matured adult male (MA) has wide cheek pads and a well-developed throat sac used for emitting loud cries. The average weight of matured adult males is more than twice that of adult females, (b) The arrested adult male (AA), although it is old enough to be a matured adult male, remains comparable in size to an adult female and lacks the wide cheeks and throat sacs of matured adult males. Matured adult males are behaviourally dominant, whereas arrested adult males are sneakers and forcibly copulate with females. When the population density of matured adult males is low, sub-adult males develop to matured adults by the age of 5-7 years. When the density of matured adults is high, males become arrested adults. Question: Might game-theoretic models similar to the hawk-dove game explain male dimorphism in orangutans? Models: (1) A modified density-independent hawk-dove game. In each, MA is the hawk and AA is the dove. The value of winning (pay-off) for an MA is larger than that for an AA. But only MAs pay a combat cost. (2) A density-dependent hawk-dove game similar to the first but with pay-offs that decline as population size grows. Results: Density-independent: If an MA's combat cost is smaller than its payoff when it wins, then AA males always have less fitness than MAs. There should be no dimorphism. But if an MA's combat cost exceeds its pay-off when it wins, a stable mixed ESS proportion (less than 100%) of males should contain AAs (doves). In the density-dependent model, AAs are part of the ESS even in some circumstances in which the cost is smaller than the pay-off to MA. As population size increases, we see an increase in the breadth of mathematical conditions supporting a stable mixed evolutionarily stable strategy (ESS). © 2007 Kei-ichi Tainaka.
• Yaacobi, G., Ziv, Y., & Rosenzweig, M. L. (2007). Effects of interactive scale-dependent variables on beetle diversity patterns in a semi-arid agricultural landscape. Landscape Ecology, 22(5), 687-703.
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  Abstract: Understanding species-diversity patterns in heterogeneous landscapes invites comprehensive research on how scale-dependent processes interact across scales. We used two common beetle families (Tenebrionidae, detrivores; Carabidae, predators) to conduct such a study in the heterogeneous semi-arid landscape of the Southern Judean Lowland (SJL) of Israel, currently undergoing intensive fragmentation. Beetles were censused in 25 different-sized patches (500-40,000-m2). We used Fisher's α and non-parametric extrapolators to estimate species diversity from 11,125 individuals belonging to 56 species. Patch characteristics (plant species diversity and cover, soil cover and degree of stoniness) were measured by field transects. Spatial variables (patch size, shape, physiognomy and connectivity) and landscape characteristics were analyzed by GIS and remote-sensing applications. Both patch-scale and landscape-scale variables affected beetle species diversity. Path-analysis models showed that landscape-scale variables had the strongest effect on carabid diversity in all patches. The tenebrionids responded differently: both patch-scale and landscape-scale variables affected species diversity in small patches, while mainly patch-scale variables affected species diversity in large patches. Most of the paths affected species diversity both directly and indirectly, combining the effects of both patch-scale and landscape-scale variables. These results match the biology of the two beetle families: Tenebrionidae, the less mobile and more site-attached family, responded to the environment in a fine-grained manner, while the highly dispersed Carabidae responded to the environment in a coarse-grained manner. We suggest that understanding abiotic and biotic variable interactions across scales has important consequences for our knowledge of community structure and species diversity patterns at large spatial scales. © 2006 Springer Science+Business Media, Inc.
• Yaacobi, G., Ziv, Y., & Rosenzweig, M. L. (2007). Habitat fragmentation may not matter to species diversity. Proceedings of the Royal Society B: Biological Sciences, 274(1624), 2409-2412.
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  PMID: 17666380;PMCID: PMC2274973;Abstract: Conservation biologists worry that fragmenting a bloc of natural habitat might reduce its species diversity. However, they also recognize the difficulty and importance of isolating the effect of fragmentation from that of simple loss of area. Using two different methods (species-area curve and Fisher's α index of diversity) to analyse the species diversities of plants, tenebrionid beetles and carabid beetles in a highly fragmented Mediterranean scrub landscape, we decoupled the effect of degree of fragmentation from that of area loss. In this system, fragmentation by itself seems not to have influenced the number of species. Our results, obtained at the scale of hectares, agree with similar results at island and continent scales. © 2007 The Royal Society.
• Rosenzweig, M. L. (2006). A promising cluster of contributions. Evolutionary Ecology Research, 8(4), 575-.
• Abramsky, Z., Rosenzweig, M. L., Elbaz, M., & Ziv, Y. (2005). Does interspecific competition from congeners cause the scarcity of Gerbillus henleyi in productive sandy desert habitats?. Journal of Animal Ecology, 74(3), 567-578.
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  Abstract: 1. We tested the hypothesis that Gerbillus henleyi (de Winton 1903), the smallest species (10 g) of a pssamophilic guild in Israel, is scarce on relatively productive dunes of the Israeli desert, due to negative interactions from the common G. allenbyi (Thomas 1918) and G pyramidum (Geoffroy 1825). 2. The alternative hypothesis was that scarcity on sand resulted from the size of its naked hind feet, that do not allow efficient locomotion on sand. 3. Despite their naked soles the weight-bearing surface of G. henleyi feet carry less mass/area than those of any other species. 4. We measured interaction coefficients with the two common species using field-manipulation experiments in two enclosures. 5. Habitat usage of G. henleyi changed from significantly preferring the stabilized sand, when alone, to significantly using the semistabilized dune, when G. allenbyi was also present. 6. We also estimated the interaction coefficients and calculated the G. henleyi's isoclines competing with the two common gerbil species using a technique we developed elsewhere. 7. The stability analysis of the isoclines of G. henleyi competing with either G. allenbyi or with G. pyramidum suggests that stable coexistence occurs when G henleyi is relatively scarce while the competitors are common. 8. Interspecific competition from either G allenbyior G. pyramidum accounts for 90.3% reduction in G. henleyi density, relative to when it is alone. 9. We concluded that the negative interactions from congeners was the major cause for the scarcity of G. henleyi on the relatively rich sand dunes of the Israeli desert. © 2005 British Ecological Society.
• Rosenzweig, M. L. (2005). Avoiding mass extinction: Basic and applied challenges. American Midland Naturalist, 153(2), 195-208.
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  Abstract: Preserving the earth's diversity of species requires that conservation biology turn much of its attention to reconciliation ecology, which is the science of sharing our habitats with wild things. Although many reconciliation projects are already working, we can extend our efforts with modern natural history research focused on species we aim to open our landscapes to. Some of this research will utilize what we already know about the principles of community ecology and niche organization and some will teach us more about those subjects. Perhaps most important will be a deeper understanding of the coevolution of niche apportionment. However, lacking perfect understanding is no reason to delay. The ecologist's motto ought to be, "Stop whining and try something".
• Abramsky, Z., Rosenzweig, M. L., Belmaker, J., & Bar, A. (2004). The impact of long-term continuous risk of predation on two species of gerbils. Canadian Journal of Zoology, 82(3), 464-474.
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  Abstract: Individuals of Gerbillus allenbyi Thomas, 1918 were subjected to artificial illumination in large field enclosures (2-ha sandy-substrate plots in the Negev Desert, Israel). The illumination was similar to that provided by a full moon and was used to mimic the elevated risk of avian predation that accompanies a full moon. We artificially illuminated the enclosures during all hours of darkness for 3 consecutive months. In some cases, we also added individuals of Gerbillus pyramidum Geoffroy, 1825 to provide a competitive challenge for the G. allenbyi. In the presence of the light source, individuals of G. allenbyi shifted their foraging activity to favor experimental areas of darkness. They also foraged less in the open and more beneath bushes. In the absence of the light source, G allenbyi shifted its activity from the subplot with G pyramidum to the subplot without the competitor. However, the competitive effect of the G pyramidum disappeared in plots that were artificially illuminated. These results closely resemble those of earlier experiments during which we increased the apparent risk of predation in brief pulses lasting only 2 h/night.
• Rosenzweig, M. L. (2003). Reconciliation ecology and the future of species diversity. ORYX, 37(2), 194-205.
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  Abstract: Species-area relationships (SPARs) dictate a sea change in the strategies of biodiversity conservation. SPARs exist at three ecological scales: Sample-area SPARs (a larger area within a biogeographical province will tend to include more habitat types, and thus more species, than a smaller one), Archipelagic SPARs (the islands of an archipelago show SPARs that combine the habitat-sampling process with the problem of dispersal to an island), and Interprovincial SPARs (other things being equal, the speciation rates of larger biogeographical provinces are higher and their extinction rates are lower, leading to diversities in proportion to provincial area). SPARs are the products of steady-state dynamics in diversity, and such dynamics appears to have characterized the earth for most of the last 500 million years. As people reduce the area available to wild species, they impose a linear reduction of the earth's species diversity that will follow the largest of these scales, i.e. each 1% reduction of natural area will cost about 1% of steady-state diversity. Reserving small tracts of wild habitat can only delay these reductions. But we can stop most of them by redesigning anthropogenic habitats so that their use is compatible with use by a broad array of other species. That is reconciliation ecology. Many pilot projects, whether intentionally or inadvertently espousing reconciliation ecology, are demonstrating that it can be done. © 2003 FFI.
• Rosenzweig, M. L., Turner, W. R., Cox, J. G., & Ricketts, T. H. (2003). Estimating diversity in unsampled habitats of a biogeographical province. Conservation Biology, 17(3), 864-874.
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  Abstract: Estimating the number of species in a biogeographical province can be problematic. A number of methods have been developed to overcome sample-size limits within a single habitat. We evaluated six of these methods to see whether they could also compensate for incomplete habitat samples. We applied them to the butterfly species of the 110 ecoregions of Canada and the United States. Two of the methods use the frequency of species that occur in a few of the sampled ecoregions. These two methods did not work. The other four methods estimate the asymptote of the species-accumulation curve (the graph of "number of species in a set of samples" versus "number of species occurrences in those samples"). The asymptote of this curve is the actual number of species in the system. Three of these extrapolation estimators produced good estimates of total diversity even when limited to 10% of the ecoregions. Good estimates depend on sampling ecoregions that are hyperdispersed in space. Clustered sampling designs ruin the usefulness of the three successful methods. To ascertain their generality, our results must be duplicated at other scales and for other taxa and in other provinces.
• Abramsky, Z., Rosenzweig, M. L., & Subach, A. (2002). Measuring the benefit of habitat selection. Behavioral Ecology, 13(4), 497-502.
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  Abstract: We used a behavioral bioassay to estimate the advantages that two species of gerbils (Gerbillus allenbyi and G. pyramidum) experienced by preferring a semistabilized dune habitat over a stabilized sand habitat. We used the magnitude of foraging effort by the gerbils to signal the difference between the two habitats. When they were foraging as much in stabilized sand as in semistabilized dune, we inferred that these habitats were providing equivalent rewards. We performed a series of experiments in two 1-ha field enclosures, each containing similar proportions of stabilized sand and semistabilized dune. Each enclosure contained a population of only one of the species. By varying the amount of seeds added (either 0.5, 1, 2, or 3 g of seeds in 18 seed trays) to each habitat and monitoring the behavior of the gerbils, we were able to fit a curve that reflected the change in habitat preference as a function of seed addition rate. We were also able to show how much seed addition had to be added to bring the two habitats into equal use. Each species required only 13 g/ha/night to entirely offset the advantage of the semistabilized dune.
• Abramsky, Z., Rosenzweig, M. L., & Subach, A. (2002). The costs of apprehensive foraging. Ecology, 83(5), 1330-1340.
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  Abstract: We used a behavioral bioassay, in the form of foraging behavior of Gerbillus altenbyi, and the ideal free distribution to estimate the costs associated with risk of predation. Experiments were conducted in two pairs of 2-ha field enclosures. Risk of predation was introduced to one 1-ha subplot of each pair of enclosures either by simulating the light of a full moon or by causing trained owls to fly over our experimental subplots. We used a titration method to estimate the energetic costs associated with risk of predation. We added seeds to the 1-ha subplot of each enclosure that experienced the risk of predation. The adjacent subplot served as a control. Without seed addition the subplot without risk of predation had more foraging activity: the foragers were avoiding the risk of predation. As the amount of seeds in the treatment increased, the gerbils responded smoothly and quantitatively and shifted their foraging activity back to the subplot with the seeds (and risk). At addition rates of 4.24-8.47 g seeds per individual per ha per night (simulated-moonlight treatment) and 4.24-5.64 g seeds per individual per ha per night (owl-flights treatment) the seed addition compensated for the extra risk. At these rates the foraging activity on the two subplots of each enclosure was the same. Our results suggested that, when challenged by the threat of predation, G. allenbyi individuals spent at least 25% of their foraging time being vigilant.
• Rosenzweig, M. L. (2002). The distraction hypothesis depends on relatively cheap extrafloral nectaries. Evolutionary Ecology Research, 4(2), 307-311.
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  Abstract: Extrafloral nectaries may have evolved because they distract insects from flowers. For this to have occurred, extrafloral nectaries must be cheaper than flowers. This requirement stands in addition to the requirement that extrafloral nectaries must reduce the rate of insect visits to flowers. In the model examined here, the cost of each extrafloral nectary divided by the cost of each flower must be less than the proportion of reproduction threatened by insect visits.
• Abramsky, Z., Rosenzweig, M. L., & Subach, A. (2001). The cost of interspecific competition in two gerbil species. Journal of Animal Ecology, 70(4), 561-567.
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  Abstract: 1. It has been shown that the two common granivorous gerbil species Gerbillus allenbyi and G. pyramidum that coexist in the sand dunes of the Israeli Negev show temporal partitioning in their time of activity. The bigger species, G. pyramidum, aggressively displaces the smaller species from early night-time. We examined the change in the activity pattern of G.allenbyi in pure and mixed populations in two 1-ha field enclosures. 2. We confirmed the temporal pattern reported by Ziv et al. (1993) and Kotler et al. (1993). 3. We also measured how much energy it takes (in g of millet seeds) to compensate for the costs, associated with interference and exploitation competition, by adding millet seeds to 18 seed trays/enclosure. We added 1, 3, 5, 7 or 9 g of seeds/seed-tray. In each seed-tray we mixed the seeds in 2 L of sand. 4. It took 3-5 g of seeds/seed-tray (1·8-3 g seeds/day/ha/individual) to completely overcome the competition by G. pyramidum. This is the cost of the interference and exploitation competition from G. pyramidum (in the currency of millet seeds). 5. The result suggests that there is a trade-off between interference competition and food to which gerbils respond behaviourally.
• Rosenzweig, M. L. (2001). Loss of speciation rate will impoverish future diversity. Proceedings of the National Academy of Sciences of the United States of America, 98(10), 5404-5410.
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  PMID: 11344286;PMCID: PMC33226;Abstract: Human activities have greatly reduced the amount of the earth's area available to wild species. As the area they have left declines, so will their rates of speciation. This loss of speciation will occur for two reasons: species with larger geographical ranges speciate faster; and loss of area drives up extinction rates, thus reducing the number of species available for speciation. Theory predicts steady states in species diversity, and fossils suggest that these have typified life for most of the past 500 million years. Modern and fossil evidence indicates that, at the scale of the whole earth and its major biogeographical provinces, those steady states respond linearly, or nearly so, to available area. Hence, a loss of x% of area will produce a loss of about x% of species. Local samples of habitats merely echo the diversity available in the whole province of which they are a part. So, conservation tactics that rely on remnant patches to preserve diversity cannot succeed for long. Instead, diversity will decay to a depauperate steady state in two phases. The first will involve deterministic extinctions, reflecting the loss of all areas in which a species can ordinarily sustain its demographics. The second will be stochastic, reflecting accidents brought on by global warming, new diseases, and commingling the species of the separate bio-provinces. A new kind of conservation effort, reconciliation ecology, can avoid this decay. Reconciliation ecology discovers how to modify and diversify anthropogenic habitats so that they harbor a wide variety of species. It develops management techniques that allow humans to share their geographical range with wild species.
• Rosenzweig, M. L. (2001). Optimality - The biologist's tricorder. Annales Zoologici Fennici, 38(1), 1-3.
• Rosenzweig, M. L. (2001). The four questions: What does the introduction of exotic species do to diversity?. Evolutionary Ecology Research, 3(3), 361-367.
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  Abstract: The breakdown of isolating barriers between biogeographical provinces will not have much effect on species diversity. In the short term, it will reduce global diversity, but increase local diversity. At steady state, the effects on global diversity disappear, but local increases remain. The real damage to diversity will come from shrinking the areas of the Earth that harbour wild species. The considerable damage exotic species have been known to do comes primarily from direct effects of particular introductions.
• Abramsky, Z., Rosenzweig, M. L., & Subach, A. (2000). The energetic cost of competition: Gerbils as moneychangers. Evolutionary Ecology Research, 2(3), 279-292.
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  Abstract: Using behavioural bioassays, we measure the cost of both inter- and intraspecific competition to a foraging gerbil, Gerbillus allenbyi. The bioassay is the amount of foraging activity in field enclosures of 2 ha, and the difference between foraging activity in an experimentally manipulated 1-ha subplot compared to the matched, unmanipulated twin hectare next to it. The bioassay depends on assuming that natural selection has fitted the gerbils to assess the comparative values of feeding opportunities and competitive pressures, although these occur in different currencies. The gerbils perform quantitatively and consistently, smoothly adjusting their foraging effort to the combination of disparate opportunities and costs. Measuring their responses as behaviour allowed us to estimate the costs of competition in the currency of energy flow, that is, the rate at which we experimentally add seeds to subplots.
• Wisheu, I. C., Rosenzweig, M. L., Olsvig-Whittaker, L., & Shmida, A. (2000). What makes nutrient-poor mediterranean heathlands so rich in plant diversity?. Evolutionary Ecology Research, 2(7), 935-955.
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  Abstract: Mediterranean heathlands with extremely low soil-nutrient concentrations (the fynbos of South Africa and the kwongan of Australia) have plant species diversities several times greater than one would expect from their areas. A combination of three factors provides a sufficient explanation for these diversities: First, poor soils favour shrubs that are killed by fire and reestablish from seed ('seeders'). Otherwise, the frequent fires in most mediterranean heathlands favour shrubs that can re-sprout ('sprouters'). Second, the numeric dominance of seeders on poor soil lowers their extinction rates. Third, seeders have relatively short generation times and thus increased speciation rates. Elevated speciation rates coupled with depressed rates of extinction lead to enhanced diversities. We elucidate this scenario and discuss evidence that favours the first factor. The evidence comes from 23 previously unanalysed sample plots surveyed by R.H. Whittaker and from two supplemental data sets. In mature fynbos and kwongan, 90 and 93% respectively of the shrub cover belongs to shrubs that re-seed after fire. In maquis (Israel), chaparral (California) and matorral (Chile), the proportion is considerably smaller. Mature strandveld, a South African shrubland superficially like fynbos but with richer soil, has only 29% seeders, although it is physically adjacent to fynbos. We suggest that nutrient-poor soil may favour seeders because the extra investment in underground organs is not worth the cost: pulses of nutrients released by fire lie mostly on top of the soil, inaccessible to new growth sprouting from subterranean lignotubers or epicormic buds.
• Rosenzweig, M. L. (1999). Heeding the warning in biodiversity's basic law. Science, 284(5412), 276-277.
• Rosenzweig, M. L., & Ziv, Y. (1999). The echo pattern of species diversity: Pattern and processes. Ecography, 22(6), 614-628.
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  Abstract: Ecologists need not despair of discovering the mechanisms that lead to large scale patterns. The search for process at higher scales has already led to enhanced confidence in the patterns and to improvements in their description. For example, species-area relationships turn out to form not one, but three patterns. Each is controlled by gain-loss dynamics at its own scale. At the macroscale, origination and global extinction reign. At the archipelagic scale, immigration and island extinction determine the results. At the local scale, metapopulation processes do. The three scales exhibit species-area curves with systematically different slopes in logarithmic space. We use the three scales of species-area to illuminate the relationship between local and regional diversity. Algebra shows that the latter pattern is an echo of species-area curves, and that those echoes ought to be nearly linear. So, we call the relationship of local and regional diversity, the Echo pattern. Ecology has long known that species-area curves within a region reflect the accumulation of habitat variety. Thus, their connection to Echo patterns argues against concluding that local diversity has little or nothing to do with population interactions. To obtain a pure Echo pattern, one should draw data from independent regions rather than separate islands. The independence allows natural selection to adjust the fundamental niches of species to diversity. Theory suggests that higher diversity should shrink niches, allowing the coexistence of more species locally. Hence, independence should tend to produce the straightest Echoes. However, archipelagic species-area curves predict that even when different islands are used as the regions, the Echoes should show only very gentle curvatures. Flouting theory, some archipelagic Echoes approach an asymptote as regional diversity increases. These must have logarithmic slopes that increase with regional pool size. We do not understand why.
• Daviddowitz, G., & Rosenzweig, M. L. (1998). The latitudinal gradient of species diversity among North American grasshoppers (Acrididae) within a single habitat: A test of the spatial heterogeneity hypothesis. Journal of Biogeography, 25(3), 553-560.
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  Abstract: The spatial heterogeneity hypothesis predicts a positive relationship between habitat complexity and species diversity: the greater the heterogeneity of a habitat, the greater the number of species in that habitat. On a regional scale, this hypothesis has been proposed to explain the increase in species diversity from the poles to the tropics: the tropics are more diverse because they contain more habitats. On the local scale, the spatial heterogeneity hypothesis suggests that the tropics are more diverse because they contain more microhabitats. The positive relationship between habitat heterogeneity and species diversity, on the local scale, is well documented. In this paper, we test whether habitat heterogeneity on the local scale can explain the latitudinal gradient of species diversity on the regional scale. We determined the latitudinal gradient of species diversity of 305 species of North American grasshoppers using published distribution maps. We compared the slope of this multihabitat (regional-scale) gradient with the slope of a withinhabitat (local-scale) gradient in the prairie grasslands. Our results show no significant difference between the slopes at the two scales. We tested the generality of our results by comparing multi- and within-habitat latitudinal gradients of species diversity for ants, scorpions and mammals using data from the literature. These results are in accordance with those from grasshoppers. We can therefore reject the local-scale spatial heterogeneity hypothesis as a mechanism explaining the regional-scale latitudinal gradient of species diversity. We discuss alternative mechanisms that produce this gradient.
• Abramsky, Z., Rosenzweig, M. L., & Subach, A. (1997). Gerbils under threat of owl predation: Isoclines and isodars. Oikos, 78(1), 81-90.
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  Abstract: We trained barn owls to fly over 2-ha field enclosures containing populations of Gerbillus allenbyi. Each 2-ha plot was divided into two equal parts by a fence with gates allowing easy passage of the gerbils. We varied the number of gerbils in the enclosure and the number of owl flights on each side of the dividing fence. Gerbil foraging activity responded within two hours to the difference ha number of owl flights over the subplots. The greater the difference, the more the gerbils shifted their foraging to the subplot with fewer flights. Gerbils did not reduce their total foraging effort but redistributed it between subplots. In the absence of owl flights, gerbils divided their foraging effort equally between the matched subplots. Thus, they appear to seek an ideal free distribution in the two halves of each plot. Therefore, based on the gerbils' distribution of activity in the presence of different numbers of owl flights over the two subplots we estimated the shapes and slopes of the gerbil victim isoclines in the middle and right hand side of the 'gerbil-activity vs number of owl flights' state space. The isoclines were parallel straight lines with slope equal to -0.57 We believe this to be the first estimate of a victim isocline for a population of vertebrates in the field. Using the isodar method of Morris, we also determined that the fitness cost of each additional gerbil, i.e., per capita intraspecific competition among the G. allenbyi, is constant. It does not depend on either owl flight frequencies or G. allenbyi densities. The isodar also shows that the fitness cost of added owl flights does not vary with G. allenbyi population densities.
• Leitner, W. A., & Rosenzweig, M. L. (1997). Nested species-area curves and stochastic sampling: A new theory. Oikos, 79(3), 503-512.
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  Abstract: We have discovered a severe problem with the current theory of species-area curves (SPARs). This theory claims that we should expect SPARs with z-values of about 0.26. However, that is wrong. The correct prediction turns out to be approximately 0.77. To make this prediction, we used a stochastic sampling scheme, and constructed species-area curves from a lognormal abundance distribution, exactly as previous theory meant to do. We arrived at our prediction using two independent methods: we performed computer simulations of the scheme and we derived its analytical equation. SPARs that result from the simulations are the same as those from the equation, validating the logic of our analysis. We explain what went awry with the previous theory. However, although logically accurate, the new theory has an empirical problem: real SPARs do not have z-values near 0.77. Rather, they tend to lie in the interval 0.1 -0.2. To obtain these, we added an assumption to the lognormal abundance distribution. We assumed that range size and abundance are positively correlated. This new assumption is qualitatively similar to Hanski's (1982; Oikos 38: 210-221) pattern. Finally, we derive a simple relation connecting average point diversity, average range size and species diversity for a province.
• Rosenzweig, M. L. (1997). Tempo and mode of speciation. Science, 277(5332), 1622-1623.
• Rosenzweig, M. L., & Abramsky, Z. (1997). Two gerbils of the Negev: A long-term investigation of optimal habitat selection and its consequences. Evolutionary Ecology, 11(6), 733-756.
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  Abstract: Optimal foraging theory has entered a new phase. It is not so much tested as used. It helps behavioural ecologists discover the nature of the information in an animal's brain. It helps population ecologists reveal coefficients of interaction and their patterns of density-dependent variation. And it helps community ecologists examine niche relationships. In our studies on two species of Negev desert gerbil, we have taken advantage of the second and third of these functions. Both these gerbils prefer semi-stabilized dune habitat, and both altered their selective use of this habitat and stabilized sand according to experimental changes we made in their populations. Their changes in selectivity agree with a type of optimal foraging theory called 'isoleg theory'. Isoleg theories provide examples of dipswitch theories - bundles of articulated qualitative predictions - that are easier to falsify than single qualitative predictions. By linking behaviour to population dynamics through isoleg theory, we were able to use the behaviour of the gerbils to reveal the shapes of their competitive isoclines. These have the peculiar non-linear shapes predicted by optimal foraging theory. Finally, when owl predation threatens, the behaviour of Gerbillus allenbyi reveals the shape of their victim isocline. As has long been predicted by predation theory and laboratory experiments, it is unimodal.
• Rosenzweig, M. L., Abramsky, Z., & Subach, A. (1997). Safety in numbers: Sophisticated vigilance by Allenby's gerbil. Proceedings of the National Academy of Sciences of the United States of America, 94(11), 5713-5715.
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  PMID: 9159138;PMCID: PMC20844;Abstract: Since 1963, nonlinear predation theory has predicted that, at low population densities, victim species may well be mutualistic rather than competitive. Theory identifies this mutualism as a principal source of dynamic instability in the interaction. Using gerbils and trained barn owls, we conducted the first (to our knowledge) field tests of the theory's prediction of mutualism. The behavior of the gerbils confirms its existence.
• Ziv, Y., Kotler, B. P., Abramsky, Z., & Rosenzweig, M. L. (1995). Foraging efficiencies of competing rodents: Why do gerbils exhibit shared-preference habitat selection?. Oikos, 73(2), 260-268.
• Abramsky, Z., Ovadia, O., & Rosenzweig, M. L. (1994). The shape of a Gerbillus pyramidum (Rodentia: Gerbillinae) isocline: An experimental field study. Oikos, 69(2), 318-326.
• Clark, C. W., & Rosenzweig, M. L. (1994). Extinction and colonization processes: Parameter estimates from sporadic surveys. American Naturalist, 143(4), 583-596.
• Rosenzweig, M. L., & Clark, C. W. (1994). Island extinction rates from regular censuses. Conservation Biology, 8(2), 491-494.
• Rosenzweig, M. L., & Abramsky, Z. (1993). How are diversity and productivity related?. Species diversity in ecological communities, 52-65.
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  Abstract: The number of species within a region usually varies unimodally with the rate of ecosystem energy flow. This hump-shaped pattern shows up in many biogeographical provinces. Plant and animal taxa, including vertebrates and invertebrates, follow it. We find it in marine and in terrestrial biomes. Most ecologists agree that the increase in diversity that occurs over low productivities comes about because the total abundance of all species together increases over that range of productivities. The authors describe and evaluate nine hypotheses to explain the decrease phase of the pattern, ie why diversity declines as productivity grows past a certain point. They discuss the relationship of the regional pattern to global patterns such as the latitudinal gradient. The effect of productivity on diversity is best studied at the regional level. -from Authors
• Abramsky, Z., Rosenzweig, M. L., & Zubach, A. (1992). The shape of a gerbil isocline: an experimental field study. Oikos, 63(2), 193-199.
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  Abstract: Fixed the numbers of Gerbillus pyramidum in six 1-ha enclosures but allowed individuals of G. allenbyi to move between adjacent enclosures and the surrounding environment over 1-yr. The resulting isocline was very similar to that obtained during a short term study (see 91L/09153). The isocline was nonlinear and agreed with the unique predictions of the theory of optimal density-dependent habitat selection in two-species, shared-preference systems. -from Authors
• Rosenzweig, M. L. (1992). Expect six issues in 1992. Evolutionary Ecology, 6(2), 95-96.
• Rosenzweig, M. L. (1992). Species diversity gradients: we know more and less than we thought. Journal of Mammalogy, 73(4), 715-730.
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  Abstract: Patterns in the diversity of species begin to make sense when we reduce them to well-known biological processes and specify the scale of the pattern. Doing this explains why diversity declines away from the tropics (the latitudinal diversity gradient). The extensive tropical regions supply more opportunities for large geographical ranges than any other biome. Allopatric speciation feeds on such large ranges. The large regions of the tropics also probably inhibit extinction. It is a mistake to explain the richness of the tropics by noting that there are more habitats in the tropics. The global scale develops in evolutionary time. On that scale, fine habitat subdivision is a coevolved property of the species in a biome. The more species, the finer they subdivide habitats. So, it is also wrong to imagine that the tropical gradient is nothing more than a species-area curve. The species-area curve is a pattern that exists on a more local scale than the latitudinal gradient, and depends on habitat variability growing as larger areas get included in a sample. Until recently, theory maintained that higher productivity should sustain more species. Evidence from poorer environments supports that theory. But most empirical evidence, including most experiments, show that diversity declines as productivity rises. -from Author
• Rosenzweig, M. L., & Vetault, S. (1992). Calculating speciation and extinction rates in fossil clades. Evolutionary Ecology, 6(1), 90-93.
• Abramsky, Z., Rosenzweig, M. L., & Pinshow, B. (1991). The shape of a gerbil isocline measured using principles of optimal habitat selection. Ecology, 72(1), 329-340.
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  Abstract: The isoclines of Gerbillus allenbyi competing with G. pyramidum in Israeli sandy deserts are negatively sloped and at least approximately parallel. They are steeper over both low and high G. pyramidum densities and only very slightly negative at intermediate densities. This nonlinearity agrees with the predictions of the theory of optimal density-dependent habitat selection in a 2-species, shared-preference system. The isocline field was measured by a new method. The species whose isoclines are being measured (the target species) is given a chance to equilibrate its per capita reproductive rate across a fence that separates 2 densities of its competitors. Equilibration requires that the target species distribute its density unequally on the two sides of the fence. -from Authors
• Rosenzweig, M. L. (1991). Habitat selection and population interactions: the search for mechanism. American Naturalist, 137(Suppl.), S5-S28.
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  Abstract: Competition within a single species forces the use of a wide variety of habitats. A second, competing species can reverse the effects of competition within a species, producing habitat selection where it would not otherwise exist. This effect is really a cluster of effects. Whether competition restores selectivity depends on the kind of competition at work and on the information-gathering abilities of foragers. So does the extent to which it is restored. Generally, the strongest separation of species by habitat selection results from distinct-preference competition between species whose individuals have very limited abilities to assess the density of food in a patch. But if individuals have much ability to assess food density, there is little or no increase likely in their selectivity compared with the single-species case. Habitat selection may stabilize predation as well as competition. The conditions required for stabilization closely resemble those predicted by optimal-foraging theory: victims need to prefer the safer habitat most when their populations are lowest or when their chance of being killed in the riskier habitat is highest. Multispecies studies emphasize the potential for differential susceptibility and optimal habitat selection to maintain diverse communities. -from Author
• Rosenzweig, M. L. (1991). Populus. Evolutionary Ecology, 5(3), 219-.
• Rosenzweig, M. L., & McCord, R. D. (1991). Incumbent replacement: evidence for long-term evolutionary progress. Paleobiology, 17(3), 202-213.
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  Abstract: Key adaptations are those that allow for improvement in at least one organismal function at a reduced fitness cost in other functions. Replacement almost certainly involves more than pure chance. It may not often involve competitive extinction. Instead, species from the new clade produce new species to replace already extinct species from the old clade. The key adaptation gives them a higher competitive speciation rate than old-clade sources of replacement. The process, termed incumbent replacement, proceeds at a rate limited by extinction rate. Thus, replacement often seems linked to mass extinction events. The incumbent-replacement hypothesis explains what we know about the replacement of straightneck turtles. (Amphichelydia) by those that can flex their necks and protect their heads in their shells. -from Authors
• Abramsky, Z., Rosenzweig, M. L., Pinshow, B., Brown, J. S., Kotler, B., & Mitchell, W. A. (1990). Habitat selection: an experimental field test with two gerbil species. Ecology, 71(6), 2358-2369.
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  Abstract: Provides experimental evidence for the isoleg theory of habitat selection in a pair of psammophilic gerbil species. Gerbillus allenbyi (mean mass: 26 g) and G. pyramidum (mean mass: 40 g) coexist in Israel's Negev Desert in areas that may contain stabilized sand fields, semistabilized dunes, and drifting dunes. When all 3 habitat types are available, coexistence between the species has been explained by a centrifugal model of community organization, untested until now. The authors conducted a field experiment in enclosures, containing similar proportions of 2 of the sandy-habitat types (stabilized sand and semi-stabilized dune), and tested the following hypotheses: 1) both species prefer the same primary habitat type; 2) G. allenbyi and G. pyramidum exhibit intraspecific density-dependent habitat selection; 3) habitat preference of both G. allenbyi and G. pyramidum is affected by the interspecific density of the other species; and 4) in the presence of the 2 habitats, habitat preferences of the 2 species should collapse from a centrifugal to a shared-preference model of habitat selection. Results supported all 4 hypotheses and allowed the construction of their isoleg graph. -from Authors
• Rosenzweig, M. L. (1990). Deem Ye Vole Love's Meed. Evolutionary Ecology, 4(3), 276-.
• Schwinning, S., & Rosenzweig, M. L. (1990). Periodic oscillations in an ideal-free predator-prey distribution. Oikos, 59(1), 85-91.
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  Abstract: Simulated the habitat selection behavior in a 3 population predator-prey system with a mid-level predator that is also prey. There were 2 habitats, one of which was a relative refuge from predation. Individuals moved to wherever they could improve their fitness, as if subject to the rules of the ideal-free distribution, but the 3 populations could generally not achieve 3 simultaneous ideal-free distributions. Instead, individuals shifted back and forth between the habitats. Such oscillations were stabilized in 3 ways: 1) increase in the protection provided by the refuge; 2) increase in intraspectific competition among the prey; 3) the presence of a threshold in fitness difference, below which individuals would not change habitats. In the presence of a threshold, population distributions became stable without having achieved a simultaneous ideal-free distribution. -Authors
• Rosenzweig, M. L. (1987). Editor's coda: central themes of the symposium. Evolutionary Ecology, 1(4), 401-407.
• Rosenzweig, M. L. (1987). Editorial. Evolutionary Ecology, 1(1), 1-3.
• Rosenzweig, M. L. (1987). Habitat selection as a source of biological diversity. Evolutionary Ecology, 1(4), 315-330.
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  Abstract: Question: What are the conditions required for natural selection to produce phenotypes specially adapted to the various habitats available in nature? Model: Assume there are two habitat types and one or two phenotypes of the same or different species. The phenotypes do not recognize any spatial differences among patches of the same habitat type. Possible evolutionary winners can do better in one habitat only by relinquishing some ability in the other. Results: If only one phenotype is present, it will be an intermediate (unless one of the two habitat types is so rare and unproductive that its effects can be ignored by natural selection). Even if two phenotypes are introduced, natural selection should generally restore monomorphism if habitat selection is not ever favored (e.g. if search costs are high). But if search costs and environmental variation are zero, dimorphism can be expected. And if they are small, then although monomorphism is stable, its basin of attraction is small, and invasion by a second form (such as a sibling species) can provide the discontinuous jump needed to put the system in the other basin of attraction. Once there, dimorphic extremism coevolves. Each successful morph is as specialized as possible on one of the habitats. Competition between the morphs is eliminated. Environmental variation may constrict the basin, but once a point is captured by it, the system approaches dimorphic extremism anyway. In general, whatever promotes the behavior of habitat selection also promotes the evolution of extreme morphologies and physiologies. © 1987 Chapman and Hall Ltd.
• Rosenzweig, M. L., Brown, J. S., & Vincent, T. L. (1987). Red Queens and ESS: the coevolution of evolutionary rates. Evolutionary Ecology, 1(1), 59-94.
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  Abstract: The Red Queen principle states that a set of interacting species reaches an evolutionary equilibrium at which all their rates of coevolution exactly balance each other. The lag-load model, which is one way of searching for Red Queens, has, by itself, previously predicted that they do not exist. But this model has assumed that infinite maladaptedness is possible. The lag-load model is improved by assuming that once the lag load of all but one species is determined, so is that of the final species. This assumption eliminates the possibility of infinite maladaptedness. Its result is to allow the lag-load model to yield Red Queen coevolution. It does this whether or not speciation and extinction rates are included. Thus the lag-load model is harmonized with the earlier Red Queen model derived from studies of predation. Because of the intercorrelation of phenotypic traits, the predatory model concluded that the eventual stable rate of coevolution must be zero (except for intermittent bursts after some correlation or compromise is successfully broken). Another model that predicts stable coevolutionary rates of zero is that of evolutionarily stable strategies (ESS). Red Queen assumes that the more extreme a phenotypic trait is, the better it is, and that there are no constraints on the growth of such a phenotypic trait value. Such traits are the key to the Red Queen prediction of progressive coevolution. ESS models make no such assumptions. Eliminating unbounded traits from the model of predator-victim evolution changed its prediction from progressive coevolution to stasis. Before this paper, no model had dealt simultaneously with both unbounded and constrained traits. To handle both sorts of phenotypic traits at the same time in the same model, we abandoned lag load as a measure of evolutionary rate (lag loads do not uniquely determine phenotype). Instead, we used the traditional assumption that rate is proportional to the slope of the adaptive landscape. A model, relying on continuous evolutionary game theory, was developed and simulated under various conditions in two or three species sets, with up to five independent traits coevolving simultaneously. The results were: (1) there was always a set of equilibrium densities eventually achieved by coevolution; if the population interaction represented by this stable coevolutionary state is also stable, then the system should persist whether it evolves further or not; (2) whenever traits were present which were unbounded and best at their most extreme values, then a Red Queen emerged; (3) whenever traits were present which were correlated with each other or constrained below infinity, then an ESS emerged; (4) if both types were present, both results occurred: Red Queen in the unbounded traits and ESS in the constrained ones. Because unbounded traits may not exist, the Red Queen may have no domain. But the domain of ESS is real. ESS should lead to the evolutionary pattern called punctuated equilibrium. The changes in design rules which punctuate stasis should lead to an ever-expanding independence of traits from each other, i.e. to more and more refined differentiation. A single set of design rules which governs a set of species is called a fitness-generating function. Such functions may help to define the concepts of adaptive zone and ecological guild. © 1987 Chapman and Hall Ltd.
• Abramsky, Z., Bowers, M. A., & Rosenzweig, M. L. (1986). Detecting interspecific competition in the field: testing the regression method.. Oikos, 47(2), 199-204.
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  Abstract: The method failed to detect the considerable negative effect of the density of Bombus flavifrons on B. rufocinctus which was observed in the manipulation experiment. -from Authors
• Brown, J. S., & Rosenzweig, M. L. (1986). Habitat selection in slowly regenerating environments. Journal of Theoretical Biology, 123(2), 151-171.
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  Abstract: Theories of density dependent habitat selection (isoleg theories) have been used to deduce community phenomena from the behavior of the individual. Previous theories assume either that at any point in geographical space representatives of a single patch type have the same resource density, or that any spatial variation in resource density is not perceived by potential foragers. We extend these theories by allowing patches of a particular type to vary perceptibly in resource density in space (as well as time). We analyze a model incorporating distinct-preference community structure: each species does best in a different habitat type. The results differ greatly from similar models with no spatial variance. First, so long as some patches achieve their maximum resource density, the isolegs (the lines in state space separating regions of qualitatively different behaviors) have negative or vertical slopes. Previous models have had positive slopes. Second, opportunistic foragers are only semi-opportunists: they exhibit partial preferences by accepting only a fraction of their secondary patches. Third, isolegs are isoclines (lines of constant per capita growth rate). Fourth, although the habitat selection promotes the coexistence of species (as it does in zero variance models), there is little likelihood of it producing "the ghost of competition past" (i.e. interaction coefficients of zero in the neighborhood of the density equilibrium). Fifth, niche shifts can behave perversely: increase of a competitor's density may actually increase niche breadth. Or it may cause niche breadth to decrease, in agreement with other theories. As might be expected, models which allow intermediate amounts of spatial variation produce conclusions intermediate between the two extremes of: (1) zero variation and (2) sufficient variation to produce some patches at resource carrying capacity no matter how low the mean resource density. © 1986 Academic Press Inc. (London) Ltd.
• Rosenzweig, M. L. (1986). Hummingbird isolegs in an experimental system. Behavioral Ecology and Sociobiology, 19(5), 313-322.
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  Abstract: Optimal foraging theory was first looked upon as a tool to study the evolution of niches in community ecology. Isoleg theory is being developed to reestablish it as such a tool. Isoleg theories are maps of isolegs in a graph whose axes are population densities. There are two kinds of isolegs: some are lines of equal optimal behavior in the graph; others mark threshold combinations of densities past which sudden shifts in behavior should occur. A technique for determining whether isolegs exist is described and applied to hummingbird data. These data were collected experimentally in the field expressly to test one isoleg model. All three species of hummingbird exhibited at least one of the sudden-shift type of isoleg. Their behaviors map onto the density graph in the predicted portions of the graph with only one exception. The data also support the prediction that behavior in the field is disjunct, i.e. subject to substantial, abrupt, discontinuous changes produced by very small continuous changes in a control variable. Some evidence for continuous control was also found, but it is ambiguous. Theory predicts that the two forms of control should be found together in some optimal systems. © 1986 Springer-Verlag.
• Rosenzweig, M. L., & Abramsky, Z. (1986). Centrifugal community organization.. Oikos, 46(3), 339-348.
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  Abstract: If the primary preference of all species is shared, but their secondary preferences are distinct, they are said to be organized centrifugally. The biological basis for centrifugal structure may be that habitats represent combinations of different environmental variables and, although the ideal combination is the same for many species in a guild, each species is adapted to tolerate relative deprivation of a different component of the mixture. The isolegs of centrifugal organization (lines of equal optimal behavior drawn in a state space) are modelled. Their principal distinguishing feature is their negative slope. Because of this, niche shifts in such communities should occur backwards; removing a competitor produces narrower niches in those left. Another feature which distinguishes it is its inability to generate a 'ghost of competition past': competition should always be a strong dynamical influence. Two species of gerbils in the Negev Desert, Israel, both exhibit negative isolegs. Other aspects of their habitat selection are consonant with a picture of centrifugal organization. -from Authors
• Abramsky, Z., Brand, S., & Rosenzweig, M. (1985). Geographical ecology of gerbilline rodents in sand dune habitats of Israel.. Journal of Biogeography, 12(4), 363-372.
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  Abstract: In Israeli sand dune habitats, 9 species of granivorous rodents are found, 8 of which belong to the family Gerbillidae. As the amount of rainfall increased, so did the number of species and their equivalent biomass, but once a certain amount of rainfall was reached, an additional increase in rainfall was followed by a decrease in species number and biomass. Mean annual rainfall was similarly correlated with % annual cover, an index of the size of the seed crop on which the rodents feed. Number of rodent species was also significantly correlated with area of the sand dune habitats.-from Authors
• Abramsky, Z., Rosenzweig, M. L., & Brand, S. (1985). Habitat selection of Israel desert rodents: comparison of a traditional and new method of analysis.. Oikos, 45(1), 79-88.
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  Abstract: Studied habitat selection in six rodent species that occur in sandy or rocky areas of the Israeli desert using two complementary quantitative techniques. A distribution method for detecting habitat selection takes cognizance of density dependence but cannot establish what properties of the environment are being selected by the species. This and the traditional regression method were equally successful in discriminating between rodent species that exhibit selection and those that do not. Only the regression method can suggest the habitat variables that are actually preferred by a species. Either temporal or spatial variation in the data may result in backward regressions (indicating the right variable but in the wrong direction), because populations at low densities may be restricted to their best habitats. At high densities, however, populations utilize both preferred and marginal habitats. When both temporal and spatial variation exist, the regression method may fail altogether to detect habitat selection even when it exists. The distribution method does not suffer from this weakness.-from Authors
• Baharav, D., & Rosenzweig, M. L. (1985). Optimal foraging in Dorcas gazelles.. Journal of Arid Environments, 9(2), 167-171.
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  Abstract: Gazella dorcas foraging in the wild appear to conform to the prediction that they should spend more time in richer patches. They do so even though what they must optimize changes greatly from the dry to the wet season. Their foraging behaviour appears to conform more closely to the Charnov model, in which foragers abandon a patch because it has been partly depleted, than the Pyke model, in which foragers leave because a patch begins by being poor compared to what is available elsewhere. -Authors
• Pim, S. L., Rosenzweig, M. L., & Mitchell, W. (1985). Competition and food selection: field tests of a theory.. Ecology, 66(3), 798-807.
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  Abstract: A graphical model describing the optimal choices of two species competing for resources in two types of habitats is tested. Both species prefer taking resources from one of the habitat types, but one of the species (the dominant), by virtue of interference competition, can gain access to the better patch more readily than the other (the subordinate). The model begins with the result of single-species optimal foraging models: at low densities of birds, only the better patch type should be selected, but as density increases, both should be used. Interspecific competition should not lead to qualitatively different behaviours for the dominant species because the effects of the subordinate are weak. For the subordinate, however, there is a 3rd class of behaviours: under the pressure of high densities of the dominant, the subordinate may totally avoid the better patch and use only the poorer. The validity of the model's predictions was tested using three species of hummingirds: blue-throated Lampornis clemenciae, Rivoli's Eugenes fulgens and black-chinned Archilochus alexandri coming to feeders.-from Authors
• Rosenzweig, M. L. (1985). Some theoretical aspects of habitat selection.. Habitat selection in birds, 517-540.
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  Abstract: Explores the relationships between habitat selection and optimal foraging theory; density-dependent habitat selection in a single species; competition and habitat selection; and population consequences of habitat selection. Problems of building a theory of community ecology are addressed, arguing that habitat selection theory-with its suite of qualitative predictions-presents a middle path between unrealistically precise prediction and valueless generalisations. -P.J.Jarvis
• Rosenzweig, M. L., & Abramsky, Z. (1985). Detecting density-dependent habitat selection.. American Naturalist, 126(3), 405-417.
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  Abstract: Develops a geometrical method for examining habitat selection using censuses, applied to a set of rodent species living in Israel's Negev Desert.-from Authors
• Rosenzweig, M. L., Abramsky, Z., Kotler, B., & Mitchell, w. (1985). Can interaction coefficients be determined from cencus data?. Oecologia, 66(2), 194-198.
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  Abstract: The method of estimating interactions proposed independently by Pimm and Schoener is studied using field data from the community of rodents which lives in the arid, rocky habitats of Israel. One important problem the method addresses is how to remove the effects of habitat heterogeneity on the estimate. We tried six different variations of the analysis scheme outlined by Crowell and Pimm, and found their results qualitatively inconsistent. This was especially true when we compared the results produced from separate habitat variables with those produced from the principal components of the habitat variation. Another problem, this one not previously addressed, is great variation in the average abundance of the different species. We discovered that the ratio of the average abundances of two species is the best predictor of the value of their coefficients of interaction. Common species appear to have weak influence on rare ones; rare ones appear to have strong influence on common ones. The statistical mechanism which produces this relationship is clear, indicating that the relationship is an artifact. © 1985 Springer-Verlag.
• Abramsky, Z., & Rosenzweig, M. L. (1984). Tilman's predicted productivity-diversity relationship shown by desert rodents. Nature, 309(5964), 150-151.
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  PMID: 6717592;Abstract: Tilman1 has developed a model to predict the number of plant species that can coexist competitively on a limited resource base. Species diversity first increases over low resource supplies, then declines as the environment becomes richer. Although Tilman's model was developed to describe interspecific interactions between plant species, it may also apply to animal species. Tilman1 questions whether animals specialize on particular proportions of nutrients. However, we believe animals probably specialize on relatively subtle microhabitat differences, especially in a multispecies competitive regime2. Thus, microhabitats may act like nutrients. We hypothesize that animal species, too, show a peaked curve of diversity over productivity. The present data provide a confirmation of the hypothesis using rodent species. We have investigated the number of rodent species along a geographical gradient of increasing rainfall. The gradient extends from extremely poor desert habitats to those with annual rainfall over 300 mm. Because of the aridity, precipitation reflects productivity. The diversity pattern in desert rodents agrees with that predicted by Tilman for plants. It even possesses similar asymmetry, rising steeply then falling slowly. The pattern is duplicated in rocky and sandy habitats, each of which has a distinct and almost non-overlapping assemblage of species. As mean precipitation is closely correlated with the variability of precipitation, the diversity pattern might also be caused by a decline in the frequency of disturbances, models for which have been proposed by several investigators. © 1984 Nature Publishing Group.
• Rosenzweig, M. L., Abramsky, Z., & Brand, S. (1984). Estimating species interactions in heterogeneous environments.. Oikos, 43(3), 329-340.
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  Abstract: Censuses the populations of a guild of psammophilic gerbils in southern Israel and simultaneously measured a set of 22 habitat variables. The goal was to test the Pimm-Schoener technique for measuring the coefficients of species interactions. The principal hurdle was correction for habitat heterogeneity.-from Authors
• Frye, R. J., & Rosenzweig, M. L. (1980). Clump size selection: A field test with two species of Dipodomys. Oecologia, 47(3), 323-327.
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  Abstract: Seed distribution (clump size) selection has been proposed as a possible mechanism of resource subdivision for competing heteromyid rodent species. To test this hypothesis, field experiments were conducted over two years during both richer and sparser seasons of the year. None of the predictions derived from the hypothesis were supported by our results. Though some selectivity was displayed by both Dipodomys spectabilis and D. merriami, the patterns of selectivity did not match the expected patterns. Our results further indicate that clump selection may be influenced by variables other than the density of seeds within a clump. These results have led us to conclude that clump size selection is unlikely to play a role in the coexistence of different species of the genus Dipodomys. © 1980 Springer-Verlag.
• Lemen, C. A., & Rosenzweig, M. L. (1978). Microhabitat selection in two species of heteromyid rodents. Oecologia, 33(2), 127-135.
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  Abstract: An experiment was conducted to determine the microhabitat preferences of two heteromyid rodents, Dipodomys ordi and Perognathus flavus. This experiment used marked seeds and the atomic absorption spectrophotometer in order to study the environment as a mosiac of microhabitats. The results of our analysis indicate that these two heteromyids are microhabitat selectors. The preferences of the rodents are D. ordi: grass habitat 0.0%, near grass habitat 22.5%, open habitat 77.4% and P. flavus: grass habitat 46.2%, near grass habitat 32.2%, open habitat 21.4%. The overlap between the two species is only 0.43. © 1978 Springer-Verlag.
• Rosenzweig, M. L. (1978). Competitive speciation. Biological Journal of the Linnean Society, 10(3), 275-289.
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  Abstract: A new mode of speciation, competitive speciation, is suggested. It assumes that fitness is depressed by the density of a phenotype's competitors, and that the adaptive landscape of phenotypes is complex. From this it follows that some intermediate forms may be fit if and only if some extreme forms are rare or absent. Subsequent to the evolution and population growth of both extreme forms, the intermediate may disappear and homogamy evolve among each of the extremes because of disruptive selection If so, sympatric speciation has occurred and niche space has been rendered into discrete segments. The limitations of the forces leading to competitive speciation are explored. Competitive speciation is discussed in relation to stasipatric speciation and host race formation. It may be responsible for both. Finally the rates of geographical speciation and polyploidy are compared to those of competitive speciation. The latter should be almost as fast as polyploidy and may be at the root of adaptive radiation. Unlike either polyploidy or geographical speciation, competitive speciation accelerates when species diversity declines. © 1978.
• Schroder, G. D., & Rosenzweig, M. L. (1975). Perturbation analysis of competition and overlap in habitat utilization between Dipodomys ordii and Dipodomys merriami. Oecologia, 19(1), 9-28.
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  Abstract: The populations of two coexisting species of Dipodomys (Heteromyidae, Rodentia) were manipulated on 10, large, unenclosed, trapping grids. These manipulations revealed that, although many kangaroo rats are established residents in an area, a large number are transient individuals who quickly occupy vacated habitats. On plots from which residents had been removed, transients settled at rates of up to 5% of carrying capacity per day. These immigrants were invariably of the same species that was removed, indicating a strong element of intraspecific competition with little or no evidence of competition between the species. Trapping records suggest that these species avoid competition through habitat selection. Dipodomys ordii prefer a grassier habitat, and D. merriami a habitat dominated by creosote bush. Apparent overlap in their utilization of habitats, based on sites of capture, predicts competition coefficients to be higher than those permitted by the theory of limiting similarity and much higher than those actually shown by the perturbation experiments. This study demonstrates the dangers of estimating alpha without experimentation. This is especially true in cases where habitat selection may be important, since organisms may travel in habitats without collecting resources therein. Our results are discussed in light of a theory which examines the optimal (rather than tolerable) amount of overlap in habitat utilization between two potential competitors in a mixed habitat. This theory predicts that the pressure of natural selection should eliminate the interspecific competition entirely. However, the conclusion that the interspecific competitive alpha is zero does not lead to the conclusion that interspecific competition is unimportant in the system. Instead, if our interpretation is correct, such competition has molded the system, and were there not a continual threat of interspecific competition, the habitat specializations would soon disappear. © 1975 Springer-Verlag.
• Gilpin, M. E., & Rosenzweig, M. L. (1972). Enriched predator-prey systems: Theoretical stability. Science, 177(4052), 902-904.
• Rosenzweig, M. L. (1972). Stability of enriched aquatic ecosystems. Science, 175(4021), 564-565.
• Rosenzweig, M. L. (1971). Paradox of enrichment: Destabilization of exploitation ecosystems in ecological time. Science, 171(3969), 385-387.
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  PMID: 5538935;Abstract: Six reasonable models of trophic exploitation in a two-species ecosystem whose exploiters compete only by depleting each other's resource supply are presented. In each case, increasing the supply of limiting nutrients or energy tends to destroy the steady state. Thus man must be very careful in attempting to enrich an ecosystem in order to increase its food yield. There is a real chance that such activity may result in decimation of the food species that are wanted in greater abundance.