I am a community ecologist interested in mechanisms of species coexistence. Through this I arrived at my interest in foraging theory and foraging ecology. I am especially interested in predator-prey foraging games and eco-evolutionary dynamics.
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.
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.
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.
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).
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.
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.
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...
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.
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.
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.
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).
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.
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.
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...
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Papers by Burt Kotler