Burt Kotler | Ben Gurion University of the Negev (original) (raw)

Papers by Burt Kotler

Physiology & Behavior, Jun 1, 2023

Ethology Ecology & Evolution, Dec 3, 2018

Reducing predation risk is fundamental to many animals. Among those, social animals are studied f... more Reducing predation risk is fundamental to many animals. Among those, social animals are studied for one type of anti-predator defense. They aggregate in certain habitats to dilute risk, share vigilance, defend each other, and reduce their chances of being attacked. However, this tendency is not necessarily unique: solitary animals may also benefit from the presence of conspecifics. Thus, we hypothesize that even solitary animals should aggregate whenever there is safety in numbers. Additionally, this tendency to aggregate should create a “risk pump”, a positive feedback in aggregation because more individuals bring more safety, which brings more individuals. We also analyzed if they will aggregate in resource-rich or resource-poor environment. Aggregation in a richer and thus crowded environment implies risk pump is a stronger mechanism than competition. Aggregation in a resource-poor environment indicates the presence of risk pump, but one weaker than competition. To test the existence and direction of a “risk pump” in non-social animals, we compared quality between patches at different distances and population densities in three experiments. We used the most abundant gerbils of the Negev Desert: Gerbillus andersoni and G. pyramidum. Results supported the hypothesis of aggregation in the resource-poor patch for both species.

Ecological Modelling, Apr 1, 2019

Density-dependent habitat selection is a central theme in ecology. Empirical studies collect data... more Density-dependent habitat selection is a central theme in ecology. Empirical studies collect data with increasing resolution and provide greater opportunities for its testing. However, several different density-dependent habitat selection models exist in the literature incorporating many different scenarios. We attempt to unify some of these models in a single framework, to increase our predictive power, and assist researchers in making predictions from combinations of these models. To achieve this, we created the generalized ideal free distribution, an expansion of the ideal free distribution model. With this model, we synthesize many of the previous theoretical developments in habitat selection to better incorporate temporal dynamics. By using community matrices to represent the interaction between individuals, we demonstrated that thirteen scenarios represented in other studies can be combined into a single model. In addition, for four of these scenarios, our predictions are similar to the original studies that developed these scenarios. Additionally, we derived four novel predictions that take advantage of using community matrices to represent distribution. We discuss how this model creates a connection between community interactions and the distribution of individuals, and its uses in other subjects in ecology.

Israel Journal of Ecology & Evolution, Mar 21, 2019

We studied the influence of manipulating predation risk on Allenby’s gerbil ( Gerbillus andersoni... more We studied the influence of manipulating predation risk on Allenby’s gerbil ( Gerbillus andersoni allenbyi) held in a large, outdoor enclosure. We measured giving up densities (GUDs), apprehension, time allocation to foraging, harvest strategy (grab and go (GAG) vs. eat at tray (EAT)), and fecal cortisol concentration. First we established the time necessary for cortisol and corticosterone concentrations to change significantly from baseline after a stressful experience. To do this we collected feces from gerbils 2, 4, 6, or 8 hours after being handled (treatment) or not (control). After 8 h, fecal cortisol, but not corticosterone, concentration was significantly higher in treatment animals. We used the results from the hormone time course experiment to design the predation experiment. We used a dog, trained to harass gerbils, to increase predation risk for the gerbils. We predicted that fecal cortisol concentrations would increase directly in the face of predation risk, or indirectly, due to reduced foraging time because of perceived predation risk that, in turn, leads to increased hunger levels. As predicted, in the presence of a predator, GUDs were higher, time allocation lower, and GAG foraging was used more in treatment animals than in controls, but we found no change in apprehension. There was no difference in cortisol concentration between predator present and no-predator treatments. However, individuals that tended to have higher average fecal cortisol concentrations also tended, on average, to spend more time foraging. This indicates a relationship between stress hormones and optimal foraging. This relationship is potentially causal. While nightly changes in behavior may not be related to stress hormones, over course time scales, stress hormones may be driving gerbils to forage more.

Ethology Ecology & Evolution, Aug 16, 2017

Rodent anti-predator behavior has been documented in many different habitats across the world. Mo... more Rodent anti-predator behavior has been documented in many different habitats across the world. Most studies found that rodents seek shelter in bushes. However, there is little evidence for this from the tropics, and existing evidence is ambivalent. Thus, we studied rodent anti-predator behavior in a new tropical system: the rodent Thrichomys fosteri in the Pantanal wetlands. We tested two hypotheses: (1) patch use decreases with distance to caraguatá (Bromelia balansae) bushes, as it would be expected if they were shelters; (2) canopy cover increases patch use, as it is also a form of cover. To test those hypotheses, we set eight 6 × 4 grids of patches composed of 200 mL of sand and 20.5 g of peanuts. We measured giving-up densities, the leftover food in patch, which is inversely proportional to time in habitat. We found support for hypothesis 1, but also evidence in contradiction of hypothesis 2. We suggest that open areas may be dangerous to the predators of T. fosteri, making these habitats safer than the forests for this rodent. We conclude that this tropical species adheres to global patterns, but only at microhabitat level.

Ethology Ecology & Evolution, Jun 18, 2018

For prey individuals, predation risk constitutes an important cost of foraging. They respond by a... more For prey individuals, predation risk constitutes an important cost of foraging. They respond by altering their foraging behaviour in risky areas that involves a trade-off between energy intake and safety. In particular, prey can vary the amount of time they spend in safe and risky foraging patches in response to the level of perceived predation risk. Using Giving up Densities (GUDs), we examined foraging behaviour decisions of goldfish groups foraging in open and cover habitats. We specifically compared the foraging behaviour of goldfish in the two habitats in the presence and absence of a predator (little egret). In the absence of a predator, the goldfish equalised GUDs between open and cover habitats. However, in the presence of a predator, the GUDs were significantly lower in the cover microhabitat than in the open. The goldfish spent almost twice the time foraging in the open GUD trays in the absence of the predator. The number of visits and time spent per visit to the foraging patch were significantly higher in the absence of a predator. However, the goldfish group harvested food pellets at a similar rate in both risky and non-risky environments, suggesting that in risky environments they forego apprehension and instead rely on time allocation to manage risk.

Evolutionary Ecology Research, 2002

Predator-prey interactions constitute a foraging game when prey individuals manage risk from pred... more Predator-prey interactions constitute a foraging game when prey individuals manage risk from predators and predator individuals manage fear in their prey. As tools for managing risk, clever prey can use time allocation and apprehension (redirecting attention from foraging to predator detection). One such foraging game occurs between gerbils and their predators on the sand dunes of the Negev Desert. Here, interacting species of gerbils compete for patches of seeds that renew daily by afternoon winds. In such circumstances, gerbils are expected to deplete resource patches over the course of the night, the predators are expected to hunt when gerbil activity is highest, and gerbils are expected to be most apprehensive when predators are most active and most deadly. We tested these predictions for gerbils in two field experiments using seed trays to measure resource depletion, gerbil activity and apprehension over the course of the night, between the bush and open microhabitats and at four moon phases (new, half waxing, full and half waning). Gerbils depleted seed resources more quickly in the bush microhabitat than the open and more quickly at new moon than at other moon phases. Gerbil activity at new moon was high throughout most of the night, but decreased towards dawn. In contrast, activity at full moon was generally low, but increased towards dawn. The two gerbil species Gerbillus andersoni allenbyi and G. pyramidum partitioned the night, with G. pyramidum visiting resource patches earlier in the night and encountering a richer, but more risky environment, and G. a. allenbyi foraging later in an environment characterized by fewer seed resources, but lower risk. The same pattern extended over moon phases, with G. pyramidum foraging relatively more at full and waning half moon. Apprehension by gerbils was higher early in the night than later and higher at full moon than new moon. Schedules of apprehension changed according to moon phase and may have differed between the two gerbils. Finally, apprehension was higher in the open microhabitat, although the opposite was true at the beginning of the night. This foraging game affects three trophic levels, including the effect of the gerbils on the availability and

Ethology Ecology & Evolution, Nov 17, 2021

Evolutionary Ecology Research, 2018

Question: What is the adaptive significance of the heteromyid cheek pouch? Organisms: Two heterom... more Question: What is the adaptive significance of the heteromyid cheek pouch? Organisms: Two heteromyid rodents (Merriam's kangaroo rat, Dipodomys merriami, and desert pocket mouse, Chaetodipus penicillatus) from the Mojave Desert, and two gerbils (greater Egyptian gerbil, Gerbillus pyramidum, and Allenby's gerbil, Gerbillus andersoni allenbyi) from the Negev Desert, Israel. Site: An outdoor vivarium on the Sede Boqer campus of Ben-Gurion University of the Negev, Israel. Methods: We measured foraging time in seed trays for heteromyids and gerbils. We also measured the number of trips to food patches, and giving-up densities (GUDs, the amount of seed left behind when an individual left a seed tray). Predictions: We expected cheek pouches to confer improved heteromyid foraging efficiency by reducing the number of trips between food patches and caching sites. We further expected that, compared with the other species, kangaroo rats would be less inhibited by barn owls, by moonlight, and by risky microhabitats. Results: The two heteromyid species harvested more food per trip than the two gerbil species. Kangaroo rats had lower GUDs than any other species, particularly in risky microhabitats and at the full moon. Harvest rate curves for greater Egyptian gerbils and kangaroo rats indicated that these two larger bodied species were more vigilant than the two smaller bodied species. Conclusion: Adaptations such as body size and the external cheek pouch appear to allow kangaroo rats to manage risk and harvest food more effectively than smaller and nonheteromyid rodents.

Israel Journal of Ecology & Evolution, May 18, 2016

Derring-do is how aggressive a predator is in stalking and capturing prey. We model predatorÀprey... more Derring-do is how aggressive a predator is in stalking and capturing prey. We model predatorÀprey interactions in which prey adjust vigilance behavior to mitigate risk of predation and predators their derring-do to manage risk of injury from capturing prey. High derring-do increases a predator's likelihood of capturing prey, but at higher risk of injury to itself. For fixed predator derring-do, prey increase vigilance in response to predator abundance, predator lethality, and predator encounter probability with prey and decrease vigilance with their own feeding rate; there is a humped-shaped relationship between prey vigilance and effectiveness of vigilance. For fixed prey vigilance, predators increase derring-do with the abundance of prey and predator lethality and decrease it with benefit of vigilance to prey and level of prey vigilance. When both prey and predator are behaviorally flexible, a predatorÀprey foraging game ensues whose solution represents an evolutionarily stable strategy (ESS). At the ESS, prey provide themselves with a public good as their vigilance causes predators to decrease derring-do. Conversely, predators have negative indirect effects on themselves as their derring-do causes prey to be more vigilant. These behavioral feedbacks create negative intra-specific interaction coefficients. Increasing the population size of prey (or predators) now has a direct negative effect on the prey (or predators). Both effects help stabilize predatorÀprey dynamics. Besides highlighting a common way by which predators may experience a food-safety tradeoff via dangerous prey, the model suggests why natural selection favors even small defensive measures by prey and hulky predators.

Israel Journal of Zoology, Feb 1, 2004

Oxford University Press eBooks, Jan 6, 2005

Despite their apparent simplicity, arid environments can be quite heterogeneous. From small-scale... more Despite their apparent simplicity, arid environments can be quite heterogeneous. From small-scale variation in substrate and slope to large-scale geographic variation in solar input and productivity, drylands and deserts provide organisms with a tremendous range of ecological challenges (Schmidt-Nielsen 1964, Huggett 1995). Any single species is unable to meet all of these challenges equally well. A species will do better in some environments than others because evolution in heterogeneous environments is constrained by fitness tradeoffs. Such tradeoffs prevent the evolution of a versatile species, competitively superior to all other species across the entire spectrum of heterogeneity (Rosenzweig 1987). Although fitness tradeoffs may hinder species’ evolution in heterogeneous environments, they are a blessing for biodiversity. The source of biodiversity that we address in this chapter is the interplay of heterogeneity, tradeoffs, and density dependence. While we focus on species interactions at the local scale, our presentation includes a model that predicts changes in local diversity as a function of climate. The model’s predictions are based on changes in the nature of competition wrought by changes in productivity levels and climatic regimes. Cast in terms of evolutionary stable strategies (ESSs), the predictions refer to evolutionary as well as ecological patterns. A mechanism of coexistence consists of an axis of environmental heterogeneity together with an axis that indicates a tradeoff in the abilities of species to exploit different parts of the axis. In the absence of some kind of heterogeneity, there is only one environmental type, and whatever species is best adapted to it will competitively exclude others. In the absence of a tradeoff, one species could evolve competitive superiority over the full range of heterogeneity, again resulting in a monomorphic community. Consider some examples of mechanisms of species’ coexistence from dryland communities (Kotler and Brown 1988, Brown et al. 1994). For many taxa, spatial heterogeneity in predation risk is a consequence of the pattern of bushy and open areas common in drylands. In certain rodent communities, some species are able to exploit the relatively riskier open microhabitats by virtue of antipredator morphologies (Kotler 1984).

Oecologia, May 1, 1985

The method of estimating interactions proposed independently by Pimm and Schoener is studied usin... more 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.

African Journal of Ecology, Nov 19, 2016

Due to their direct dependence on wildlife products for subsistent use, people living in poverty ... more Due to their direct dependence on wildlife products for subsistent use, people living in poverty are often viewed as being in conflict with wildlife conservation. We studied the attitudes of local people towards mountain nyala (Tragelaphus buxtoni) in Munessa, Ethiopia. A household survey (n = 214) was used to examine the socio‐economic characteristics and beliefs of local people from three peasant associations and one village. Generally, the study revealed that local people had positive attitudes towards mountain nyala, its conservation and population increase, which is consistent with our predictions. For example, a greater percentage of the respondents had positive (62.5%) rather than negative (37.5%) attitudes towards mountain nyala and its conservation. Moreover, the larger proportion of the respondents had positive (66.67%) rather than negative (33.3%) attitudes towards an increase in mountain nyala population. However, compared to socio‐economic characteristics, beliefs towards mountain nyala were more powerful and consistent predictor of attitudes and explained much of the variances of the two groups of the dependent variables. Thus, informing local communities about the value of mountain nyala (e.g. recreational and economic) through conservation education, advocating the need for sustainable utilization and introducing an economic benefit sharing may improve positive attitude and increase participation of local people in conservation and management of the mountain nyala population in Munessa.

Israel Journal of Ecology & Evolution, Apr 27, 2021

Bacterial infections can have both direct (physiological) and indirect (ecological) costs for the... more Bacterial infections can have both direct (physiological) and indirect (ecological) costs for their hosts. The direct costs of infection may include nutritional deficiencies, which reduce body condition over time, and result in the hosts modifying their foraging behaviour to compensate for any losses. Allenby’s gerbils are commonly infected with the Mycoplasma haemomuris-like bacteria, which may induce choline (essential vitamin) and arginine (amino acid) deficiencies. Gerbils should therefore alter their behaviour to make up for any shortfalls in nutrient production and retention. We tested two predictions. 1) infected gerbils would compensate for nutrient losses by spending more time foraging in patches, including, during riskier periods of owl presence, and in riskier open microhabitats. Furthermore, infected gerbils would preferentially forage from patches supplemented with choline and arginine enriched food over control food. 2) Alternatively, if infection did not create a nutrient deficiency, then infected individuals would display a similar pattern of patch use to uninfected individuals, and harvest similar amounts of food from supplemented and control patches. Our findings supported the second prediction. There was no observed difference in foraging behaviour between infected and uninfected individuals. Moreover, infected gerbils did not selectively forage more intensively from food patches enriched with either choline or arginine seed over the control patches. These results suggest that this bacteria-gerbil interaction does not result in a nutrient deficiency as observed for other Mycoplasma-rodent systems.

Behaviour, Sep 9, 2022

Prey animals must attempt to optimize foraging success while reducing the probability of being ca... more Prey animals must attempt to optimize foraging success while reducing the probability of being captured. Within social prey groups, intrinsic differences in bold-shy personality among individuals influence their respective risk-taking tendencies. We examined the foraging and refuge use behaviour of mixed groups of goldfish (Carassius auratus) containing half bold individuals and half shy individuals under variable levels of predation risk from a live avian predator (Egretta garzetta). At the group level, the fish groups significantly decreased their foraging time by spending more time under the refuge when the predator spent more time at the focal pool. As expected, the bold fish tended to be the first to leave the refuge, and foraged outside the refuge more often than shy fish under control conditions and at lower risk levels. However, the behavioural differences between bold and shy fish disappeared under higher risk conditions. In terms of mortality, the predator captured significantly more bold fish than shy fish. Our study illustrates how bold individuals in social groups often take greater risks to achieve foraging success, but demonstrates that innate differences in boldness can be diminished in times of elevated predation risk.

Oecologia, May 30, 2019

In a heterogeneous environment containing multiple patches that may deplete and renew, a forager ... more In a heterogeneous environment containing multiple patches that may deplete and renew, a forager should be able to detect the quality of food resources within and among patches and choose to exploit them to best maximize returns. From the predator's perspective, the behavioral responses of the prey in a patch will be perceived as depletion when they retreat to refuge and renewal when they reemerge. A predator encountering responsive prey should manage predation risk, and thus behavioral resource depression, by optimally timing its return time to the patch based on prey behavior. We evaluated the foraging decisions of a predator that encountered patches differing in size of the refuge and prey density. We used little egrets and goldfish as predators and prey in an environment that contained three patches (pools). We manipulated prey density and refuge size and availability (using covers) and observed predator foraging behavior. When the egret had previously caught a fish it did not discriminate between the pools, and the return time was similar for all cover types. The fish densities also did not affect the egret decisions to return to pools. However, when it failed to catch fish, it returned sooner to the pool containing the small cover than the larger one. Additionally, after failing to catch fish in patches containing the highest prey density, the egrets subsequently preferred to return to such patches sooner. We show experimentally that previous failures influence the foraging decisions of a predator choosing how quickly to return to a previously visited patch.

Ethology Ecology & Evolution, 2021

Prey individuals vary in their body size even within groups and are often scattered heterogeneous... more Prey individuals vary in their body size even within groups and are often scattered heterogeneously in patchy environments. A foraging predator has to evaluate and select the patches where it can maximize its energetic gains. We studied the foraging behavior of a predator (little egret, Egretta garzetta) hunting prey groups (goldfish, Carassius auratus) that differed in body size and composition across three different patches (one large, one mixed, and one small). We quantified predator’s stay time, return time and size-specific kills of the prey. The egret spent a similar amount of total time foraging in the three patches; however, it spent more time per-visit in pools containing large-bodied fish and also returned to those pools soonest after leaving to forage elsewhere, suggesting that the predators employ a time management strategy to maximize energetic returns. Furthermore, the egret preferentially killed larger individuals. Such size-selective predation can shift the prey size...