Oswald Schmitz - Academia.edu (original) (raw)
Papers by Oswald Schmitz
Ecology, Mar 11, 2019
The inability of species to adapt to changing climate may cause ecological communities to disasse... more The inability of species to adapt to changing climate may cause ecological communities to disassemble and lose ecological functioning. However, theory suggests that communities may be resilient whenever populations within species exhibit variation in thermal plasticity or Accepted Article This article is protected by copyright. All rights reserved. adaptation whereby thermally tolerant populations replace thermally sensitive ones. But will they maintain the functional roles of the populations being replaced? This study evaluated whether "like replaces like" functionally by measuring how four populations of a grasshopper herbivore and its co-occurring spider predator cope with environmental warming. The study occurred across a latitudinal gradient bounded by southerly, warmer Connecticut and northerly, cooler New Hampshire, USA. The study compared the survival rates, thermal performance, habitat usage, and food chain interactions of each grasshopper and spider population between its home field site (field of origin) and a Connecticut transplant site, and the native Connecticut population. Three grasshopper populations exhibited physiological plasticity by adjusting metabolic rates. The fourth population selected cooler habitat locations. Spider populations did not alter their metabolism, and instead selected cooler habitat locations thereby altering spatial overlap with their prey and food chain interactions. Grasshopper populations that coped physiologically consumed plants in different ratios than the fourth population and the Connecticut population. Hence "like may not replace like" whenever populations adapt physiologically to warming.
PLoS biology, 2018
Carnivore predation on livestock often leads people to retaliate. Persecution by humans has contr... more Carnivore predation on livestock often leads people to retaliate. Persecution by humans has contributed strongly to global endangerment of carnivores. Preventing livestock losses would help to achieve three goals common to many human societies: preserve nature, protect animal welfare, and safeguard human livelihoods. Between 2016 and 2018, four independent reviews evaluated >40 years of research on lethal and nonlethal interventions for reducing predation on livestock. From 114 studies, we find a striking conclusion: scarce quantitative comparisons of interventions and scarce comparisons against experimental controls preclude strong inference about the effectiveness of methods. For wise investment of public resources in protecting livestock and carnivores, evidence of effectiveness should be a prerequisite to policy making or large-scale funding of any method or, at a minimum, should be measured during implementation. An appropriate evidence base is needed, and we recommend a coa...
Ecological Applications, 2014
Niche theory is a well-established concept integrating a diverse array of environmental variables... more Niche theory is a well-established concept integrating a diverse array of environmental variables and multispecies interactions used to describe species geographic distribution. It is now customary to employ species distribution models (SDMs) that use environmental variables in conjunction with species location information to characterize species' niches and map their geographic ranges. The challenge remains, however, to account for the biotic interactions of species with other community members on which they depend. We show here how to connect species spatial distribution and their dependence with other species by modeling spatially explicit predator-prey interactions, which we call a trophic interaction distribution model (TIDM). To develop the principles, we capitalized on data from Canada lynx (Lynx canadensis) reintroduced into Colorado. Spatial location information for lynx obtained from telemetry was used in conjunction with environmental data to construct an SDM. The spatial locations of lynx-snowshoe hare encounters obtained from snow-tracking in conjunction with environmental data were used to construct a TIDM. The environmental conditions associated with lynx locations and lynx-hare encounters identified through both SDM and TIDM revealed an initial transient phase in habitat use that settled into a steady state. Nevertheless, despite the potential for the SDM to broadly encompass all lynx hunting and nonhunting spatial locations, the spatial extents of the SDM and TIDM differed; about 40% of important lynx-snowshoe hare locations identified in the TIDM were not identified in the lynx-only SDM. Our results encourage greater effort to quantify spatial locations of trophic interactions among species in a community and the associated environmental conditions when attempting to construct models aimed at projecting current and future species geographic distributions.
International Philosophical Quarterly
Accounts of flourishing have been employed in many disciplines. Aristotelian moral philosophers h... more Accounts of flourishing have been employed in many disciplines. Aristotelian moral philosophers have developed accounts of flourishing based on the characteristic forms of life of living things. In this paper we develop an Aristotelian account of flourishing for living things in general as part of a larger Aristotelian natural philosophy. We relate accounts of flourishing to evolutionary theory, behavioral studies, and ecology as well as to what flourishing is for individual organisms in their parts and activities. We distinguish between contingent and determinate activities by arguing that the behavior of living things are their contingent activities. We consider the structure of cognitive capacities in living things and their relation to flourishing, and we follow out the implications of the distinctively human capacities of cognition. Our consideration of humankind alloww us to show that the study and practice of human flourishing entail stewardship of nature.
Rates of survival for spiders and grasshoppers from mesocosms spread across five sites in New Englan
Carbon and nitrogen content of goldenrod and grass leaves from five sites in New Englan
Locations (height above ground) of grasshoppers and spiders inside terrariums recorded over the p... more Locations (height above ground) of grasshoppers and spiders inside terrariums recorded over the period of one da
Ecology Letters, 2020
This is the author manuscript accepted for publication and has undergone full peer review but has... more This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Evolutionary Ecology, 1997
A comparatively recent focus in consumer–resource theory has been the examination of whether adap... more A comparatively recent focus in consumer–resource theory has been the examination of whether adaptive foraging by consumers, manifested through the functional response, can stabilize consumer–resource dynamics. We offer a brief synthesis of progress on this body of theory and identify the conditions likely to lead to stability. We also fill a gap in our understanding by analysing the potential for adaptively foraging herbivores, which are constrained by time available to feed and digestive capacity, to stabilize dynamics in a ...
F1000 - Post-publication peer review of the biomedical literature, 2017
One contribution of 17 to a theme issue 'Biodiversity and ecosystem functioning in dynamic landsc... more One contribution of 17 to a theme issue 'Biodiversity and ecosystem functioning in dynamic landscapes'.
Ecology, Jan 6, 2017
Community ecology was traditionally an integrative science devoted to studying interactions betwe... more Community ecology was traditionally an integrative science devoted to studying interactions between species and their abiotic environments in order to predict species' geographic distributions and abundances. Yet for philosophical and methodological reasons it has become divided into two enterprises: one devoted to local experimentation on species interactions to predict community dynamics; the other devoted to statistical analyses of abiotic and biotic information to describe geographic distribution. Our goal here is to instigate thinking about ways to reconnect the two enterprises and thereby return to a tradition to do integrative science. We focus specifically on the community ecology of predators and prey, which is ripe for integration. This is because there is active, simultaneous interest in experimentally resolving the nature and strength of predator-prey interactions as well as explaining pattern across landscapes and seascapes. We begin by describing a conceptual theor...
Ecology letters, 2017
Approaches to quantifying and predicting soil biogeochemical cycles mostly consider microbial bio... more Approaches to quantifying and predicting soil biogeochemical cycles mostly consider microbial biomass and community composition as products of the abiotic environment. Current numerical approaches then primarily emphasise the importance of microbe-environment interactions and physiology as controls on biogeochemical cycles. Decidedly less attention has been paid to understanding control exerted by community dynamics and biotic interactions. Yet a rich literature of theoretical and empirical contributions highlights the importance of considering how variation in microbial population ecology, especially biotic interactions, is related to variation in key biogeochemical processes like soil carbon formation. We demonstrate how a population and community ecology perspective can be used to (1) understand the impact of microbial communities on biogeochemical cycles and (2) reframe current theory and models to include more detailed microbial ecology. Through a series of simulations we illus...
Trends in Ecology & Evolution, 2016
Climate change ecology has focused on climate effects on trophic interactions through the lenses ... more Climate change ecology has focused on climate effects on trophic interactions through the lenses of temperature effects on organismal physiology and phenological asynchronies. Trophic interactions are also affected by the nutrient content of resources, but this topic has received less attention. Using concepts from nutritional ecology, we propose a conceptual framework for understanding how climate affects food webs through top-down and bottomup processes impacted by co-occurring environmental drivers. The framework integrates climate effects on consumer physiology and feeding behavior with effects on resource nutrient content. It illustrates how studying responses of simplified food webs to simplified climate change might produce erroneous predictions. We encourage greater integrative complexity of climate change research on trophic interactions to resolve patterns and enhance predictive capacities. Bottom-Up and Top-Down Processes in Climate Change Ecology Understanding how environmental drivers impact trophic interactions is key to predicting food web responses to global climate change. Research has enhanced such understanding largely along two fronts. The first deploys biophysical and thermal energetic principles to predict temperature dependence of consumer-resource trophic interaction strengths [1-3]. The second uses life-history principles to predict the temperature dependence of trophic interaction strengths caused by climate-driven mismatches in the life-cycle timing of interdependent consumers and resources [4-6]. In both cases, it is assumed that shifts in trophic interactions are driven largely, if not entirely, by the thermal energetics of species. This leads to predictions that changing temperatures primarily alter resource quantity ingested by consumers as they strive to meet elevated energetic demands. A less explored, but equally important, research front is how climate change alters trophic interactions through shifts in resource quality (i.e., nutrient content [7-9]). At the plant level, nutrient content is influenced by environmental variables such as temperature, water availability, and CO 2 , all of which are affected by climate change. Shifts in plant nutrient content can propagate upward in food webs by altering feeding rates, assimilation efficiencies, and growth rates of consumers [10-12]. Indeed, theory predicts that altered primary-producer nutrient content and abundance will change fundamental attributes of food webs, such as 'steepness' (i.e.; consumer:plant ratio [13]) and frequency of multichannel omnivory [14], which could alter food web stability [3]. In addition, temperature-dependent shifts in consumer metabolism can create plasticity in consumer nutrient requirements [15], which can determine the types of resource (i.e., protein, lipid, or carbohydrate) that are consumed, as well as their quantity [7,9].
Trends in ecology & evolution, Nov 20, 2016
Few concepts in ecology have been so influential as that of the trophic cascade. Since the 1980s,... more Few concepts in ecology have been so influential as that of the trophic cascade. Since the 1980s, the term has been a central or major theme of more than 2000 scientific articles. Despite this importance and widespread usage, basic questions remain about what constitutes a trophic cascade. Inconsistent usage of language impedes scientific progress and the utility of scientific concepts in management and conservation. Herein, we offer a definition of trophic cascade that is designed to be both widely applicable yet explicit enough to exclude extraneous interactions. We discuss our proposed definition and its implications, and define important related terms, thereby providing a common language for scientists, policy makers, conservationists, and other stakeholders with an interest in trophic cascades.
Ecology, 2016
Prey at risk of predation may experience stress and respond physiologically by altering their met... more Prey at risk of predation may experience stress and respond physiologically by altering their metabolic rates. Theory predicts that such physiological changes should alter prey nutrient demands from N-rich to C-rich macronutrients and shift the balance between maintenance and growth/reproduction. Theory further suggests that for ectotherms, temperature stands to exacerbate this stress. Yet, the interactive effects of predation stress and temperature stress on diet, metabolism, and survival of ectotherms are not well known. This knowledge gap was addressed with a laboratory study in which wild juvenile grasshoppers were collected, assigned to one of three groups, and raised at three different temperatures. All grasshoppers had access to equal quantities of two diets composed of opposite carbohydrate:protein ratios. Half of the individuals in each temperature group were exposed to predation risk cues from spider predators, while the other half were kept in risk free conditions. Grasshoppers consumed more carbohydrates when exposed to predation risk, but consumption favored greater protein intake as temperature increased. Moreover, the difference in carbohydrate intake between risk cue and risk free treatments diminished as temperature increased. Furthermore, variability between individual consumption patterns both within and between treatments decreased markedly as temperature increased, suggesting that higher temperatures promote more consistent individual consumption behaviors. Grasshoppers grew faster and larger as temperature increased, which translated into higher survival rates at higher temperatures. Warmer grasshoppers also did not alter their metabolic rates in response to predation risk cues, in contrast to colder grasshoppers. Digestive efficiency increased with temperature as well, further indicating that lower temperatures were much more stressful than higher temperatures for grasshoppers. The study shows that physiological responses of ectothermic herbivores to predation stress are highly plastic and temperature dependent, with higher temperatures promoting increased protein intake, growth, Accepted Article This article is protected by copyright. All rights reserved. development, survival, and digestive efficiency relative to colder temperatures. These findings help to reconcile why dietary responses (proportion of protein vs. carbohydrate intake) to predation stress may vary among different prey taxa studied previously.
Ecology and evolution, 2015
Understanding the impacts of invasive species requires placing invasion within a full community c... more Understanding the impacts of invasive species requires placing invasion within a full community context. Plant invaders are often considered in the context of herbivores that may drive invasion by avoiding invaders while consuming natives (enemy escape), or inhibit invasion by consuming invaders (biotic resistance). However, predators that attack those herbivores are rarely considered as major players in invasion. Invasive plants often promote predators, generally by providing improved habitat. Here, we show that predator-promoting invaders may initiate a negative feedback loop that inhibits invasion. By enabling top-down control of herbivores, predator-promoting invaders lose any advantage gained through enemy escape, indirectly favoring natives. In cases where palatable invaders encounter biotic resistance, predator promotion may allow an invader to persist, but not dominate. Overall, results indicate that placing invaders in a full community context may reveal reduced impacts of ...
Proceedings of the Royal Society B: Biological Sciences, 2015
Trophic interactions in multiprey systems can be largely determined by prey distributions. Yet, c... more Trophic interactions in multiprey systems can be largely determined by prey distributions. Yet, classic predator–prey models assume spatially homogeneous interactions between predators and prey. We developed a spatially informed theory that predicts how habitat heterogeneity alters the landscape-scale distribution of mortality risk of prey from predation, and hence the nature of predator interactions in multiprey systems. The theoretical model is a spatially explicit, multiprey functional response in which species-specific advection–diffusion models account for the response of individual prey to habitat edges. The model demonstrates that distinct responses of alternative prey species can alter the consequences of conspecific aggregation, from increasing safety to increasing predation risk. Observations of threatened boreal caribou, moose and grey wolf interacting over 378 181 km 2 of human-managed boreal forest support this principle. This empirically supported theory demonstrates h...
Encyclopedia of Life Sciences, 2007
ABSTRACT Food webs are a way of describing the lines of dependency among species in Nature. Such ... more ABSTRACT Food webs are a way of describing the lines of dependency among species in Nature. Such interdependencies are basic to all ecological processes in that species consume resources and are themselves consumed by their predators.Keywords:complexity;connectance;feeding link;food chain;trophic interaction
Ecology and evolution, 2015
Innovative conservation tools are greatly needed to reduce livelihood losses and wildlife decline... more Innovative conservation tools are greatly needed to reduce livelihood losses and wildlife declines resulting from human-carnivore conflict. Spatial risk modeling is an emerging method for assessing the spatial patterns of predator-prey interactions, with applications for mitigating carnivore attacks on livestock. Large carnivores that ambush prey attack and kill over small areas, requiring models at fine spatial grains to predict livestock depredation hot spots. To detect the best resolution for predicting where carnivores access livestock, we examined the spatial attributes associated with livestock killed by tigers in Kanha Tiger Reserve, India, using risk models generated at 20, 100, and 200-m spatial grains. We analyzed land-use, human presence, and vegetation structure variables at 138 kill sites and 439 random sites to identify key landscape attributes where livestock were vulnerable to tigers. Land-use and human presence variables contributed strongly to predation risk models...
Ecology, Mar 11, 2019
The inability of species to adapt to changing climate may cause ecological communities to disasse... more The inability of species to adapt to changing climate may cause ecological communities to disassemble and lose ecological functioning. However, theory suggests that communities may be resilient whenever populations within species exhibit variation in thermal plasticity or Accepted Article This article is protected by copyright. All rights reserved. adaptation whereby thermally tolerant populations replace thermally sensitive ones. But will they maintain the functional roles of the populations being replaced? This study evaluated whether "like replaces like" functionally by measuring how four populations of a grasshopper herbivore and its co-occurring spider predator cope with environmental warming. The study occurred across a latitudinal gradient bounded by southerly, warmer Connecticut and northerly, cooler New Hampshire, USA. The study compared the survival rates, thermal performance, habitat usage, and food chain interactions of each grasshopper and spider population between its home field site (field of origin) and a Connecticut transplant site, and the native Connecticut population. Three grasshopper populations exhibited physiological plasticity by adjusting metabolic rates. The fourth population selected cooler habitat locations. Spider populations did not alter their metabolism, and instead selected cooler habitat locations thereby altering spatial overlap with their prey and food chain interactions. Grasshopper populations that coped physiologically consumed plants in different ratios than the fourth population and the Connecticut population. Hence "like may not replace like" whenever populations adapt physiologically to warming.
PLoS biology, 2018
Carnivore predation on livestock often leads people to retaliate. Persecution by humans has contr... more Carnivore predation on livestock often leads people to retaliate. Persecution by humans has contributed strongly to global endangerment of carnivores. Preventing livestock losses would help to achieve three goals common to many human societies: preserve nature, protect animal welfare, and safeguard human livelihoods. Between 2016 and 2018, four independent reviews evaluated >40 years of research on lethal and nonlethal interventions for reducing predation on livestock. From 114 studies, we find a striking conclusion: scarce quantitative comparisons of interventions and scarce comparisons against experimental controls preclude strong inference about the effectiveness of methods. For wise investment of public resources in protecting livestock and carnivores, evidence of effectiveness should be a prerequisite to policy making or large-scale funding of any method or, at a minimum, should be measured during implementation. An appropriate evidence base is needed, and we recommend a coa...
Ecological Applications, 2014
Niche theory is a well-established concept integrating a diverse array of environmental variables... more Niche theory is a well-established concept integrating a diverse array of environmental variables and multispecies interactions used to describe species geographic distribution. It is now customary to employ species distribution models (SDMs) that use environmental variables in conjunction with species location information to characterize species' niches and map their geographic ranges. The challenge remains, however, to account for the biotic interactions of species with other community members on which they depend. We show here how to connect species spatial distribution and their dependence with other species by modeling spatially explicit predator-prey interactions, which we call a trophic interaction distribution model (TIDM). To develop the principles, we capitalized on data from Canada lynx (Lynx canadensis) reintroduced into Colorado. Spatial location information for lynx obtained from telemetry was used in conjunction with environmental data to construct an SDM. The spatial locations of lynx-snowshoe hare encounters obtained from snow-tracking in conjunction with environmental data were used to construct a TIDM. The environmental conditions associated with lynx locations and lynx-hare encounters identified through both SDM and TIDM revealed an initial transient phase in habitat use that settled into a steady state. Nevertheless, despite the potential for the SDM to broadly encompass all lynx hunting and nonhunting spatial locations, the spatial extents of the SDM and TIDM differed; about 40% of important lynx-snowshoe hare locations identified in the TIDM were not identified in the lynx-only SDM. Our results encourage greater effort to quantify spatial locations of trophic interactions among species in a community and the associated environmental conditions when attempting to construct models aimed at projecting current and future species geographic distributions.
International Philosophical Quarterly
Accounts of flourishing have been employed in many disciplines. Aristotelian moral philosophers h... more Accounts of flourishing have been employed in many disciplines. Aristotelian moral philosophers have developed accounts of flourishing based on the characteristic forms of life of living things. In this paper we develop an Aristotelian account of flourishing for living things in general as part of a larger Aristotelian natural philosophy. We relate accounts of flourishing to evolutionary theory, behavioral studies, and ecology as well as to what flourishing is for individual organisms in their parts and activities. We distinguish between contingent and determinate activities by arguing that the behavior of living things are their contingent activities. We consider the structure of cognitive capacities in living things and their relation to flourishing, and we follow out the implications of the distinctively human capacities of cognition. Our consideration of humankind alloww us to show that the study and practice of human flourishing entail stewardship of nature.
Rates of survival for spiders and grasshoppers from mesocosms spread across five sites in New Englan
Carbon and nitrogen content of goldenrod and grass leaves from five sites in New Englan
Locations (height above ground) of grasshoppers and spiders inside terrariums recorded over the p... more Locations (height above ground) of grasshoppers and spiders inside terrariums recorded over the period of one da
Ecology Letters, 2020
This is the author manuscript accepted for publication and has undergone full peer review but has... more This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Evolutionary Ecology, 1997
A comparatively recent focus in consumer–resource theory has been the examination of whether adap... more A comparatively recent focus in consumer–resource theory has been the examination of whether adaptive foraging by consumers, manifested through the functional response, can stabilize consumer–resource dynamics. We offer a brief synthesis of progress on this body of theory and identify the conditions likely to lead to stability. We also fill a gap in our understanding by analysing the potential for adaptively foraging herbivores, which are constrained by time available to feed and digestive capacity, to stabilize dynamics in a ...
F1000 - Post-publication peer review of the biomedical literature, 2017
One contribution of 17 to a theme issue 'Biodiversity and ecosystem functioning in dynamic landsc... more One contribution of 17 to a theme issue 'Biodiversity and ecosystem functioning in dynamic landscapes'.
Ecology, Jan 6, 2017
Community ecology was traditionally an integrative science devoted to studying interactions betwe... more Community ecology was traditionally an integrative science devoted to studying interactions between species and their abiotic environments in order to predict species' geographic distributions and abundances. Yet for philosophical and methodological reasons it has become divided into two enterprises: one devoted to local experimentation on species interactions to predict community dynamics; the other devoted to statistical analyses of abiotic and biotic information to describe geographic distribution. Our goal here is to instigate thinking about ways to reconnect the two enterprises and thereby return to a tradition to do integrative science. We focus specifically on the community ecology of predators and prey, which is ripe for integration. This is because there is active, simultaneous interest in experimentally resolving the nature and strength of predator-prey interactions as well as explaining pattern across landscapes and seascapes. We begin by describing a conceptual theor...
Ecology letters, 2017
Approaches to quantifying and predicting soil biogeochemical cycles mostly consider microbial bio... more Approaches to quantifying and predicting soil biogeochemical cycles mostly consider microbial biomass and community composition as products of the abiotic environment. Current numerical approaches then primarily emphasise the importance of microbe-environment interactions and physiology as controls on biogeochemical cycles. Decidedly less attention has been paid to understanding control exerted by community dynamics and biotic interactions. Yet a rich literature of theoretical and empirical contributions highlights the importance of considering how variation in microbial population ecology, especially biotic interactions, is related to variation in key biogeochemical processes like soil carbon formation. We demonstrate how a population and community ecology perspective can be used to (1) understand the impact of microbial communities on biogeochemical cycles and (2) reframe current theory and models to include more detailed microbial ecology. Through a series of simulations we illus...
Trends in Ecology & Evolution, 2016
Climate change ecology has focused on climate effects on trophic interactions through the lenses ... more Climate change ecology has focused on climate effects on trophic interactions through the lenses of temperature effects on organismal physiology and phenological asynchronies. Trophic interactions are also affected by the nutrient content of resources, but this topic has received less attention. Using concepts from nutritional ecology, we propose a conceptual framework for understanding how climate affects food webs through top-down and bottomup processes impacted by co-occurring environmental drivers. The framework integrates climate effects on consumer physiology and feeding behavior with effects on resource nutrient content. It illustrates how studying responses of simplified food webs to simplified climate change might produce erroneous predictions. We encourage greater integrative complexity of climate change research on trophic interactions to resolve patterns and enhance predictive capacities. Bottom-Up and Top-Down Processes in Climate Change Ecology Understanding how environmental drivers impact trophic interactions is key to predicting food web responses to global climate change. Research has enhanced such understanding largely along two fronts. The first deploys biophysical and thermal energetic principles to predict temperature dependence of consumer-resource trophic interaction strengths [1-3]. The second uses life-history principles to predict the temperature dependence of trophic interaction strengths caused by climate-driven mismatches in the life-cycle timing of interdependent consumers and resources [4-6]. In both cases, it is assumed that shifts in trophic interactions are driven largely, if not entirely, by the thermal energetics of species. This leads to predictions that changing temperatures primarily alter resource quantity ingested by consumers as they strive to meet elevated energetic demands. A less explored, but equally important, research front is how climate change alters trophic interactions through shifts in resource quality (i.e., nutrient content [7-9]). At the plant level, nutrient content is influenced by environmental variables such as temperature, water availability, and CO 2 , all of which are affected by climate change. Shifts in plant nutrient content can propagate upward in food webs by altering feeding rates, assimilation efficiencies, and growth rates of consumers [10-12]. Indeed, theory predicts that altered primary-producer nutrient content and abundance will change fundamental attributes of food webs, such as 'steepness' (i.e.; consumer:plant ratio [13]) and frequency of multichannel omnivory [14], which could alter food web stability [3]. In addition, temperature-dependent shifts in consumer metabolism can create plasticity in consumer nutrient requirements [15], which can determine the types of resource (i.e., protein, lipid, or carbohydrate) that are consumed, as well as their quantity [7,9].
Trends in ecology & evolution, Nov 20, 2016
Few concepts in ecology have been so influential as that of the trophic cascade. Since the 1980s,... more Few concepts in ecology have been so influential as that of the trophic cascade. Since the 1980s, the term has been a central or major theme of more than 2000 scientific articles. Despite this importance and widespread usage, basic questions remain about what constitutes a trophic cascade. Inconsistent usage of language impedes scientific progress and the utility of scientific concepts in management and conservation. Herein, we offer a definition of trophic cascade that is designed to be both widely applicable yet explicit enough to exclude extraneous interactions. We discuss our proposed definition and its implications, and define important related terms, thereby providing a common language for scientists, policy makers, conservationists, and other stakeholders with an interest in trophic cascades.
Ecology, 2016
Prey at risk of predation may experience stress and respond physiologically by altering their met... more Prey at risk of predation may experience stress and respond physiologically by altering their metabolic rates. Theory predicts that such physiological changes should alter prey nutrient demands from N-rich to C-rich macronutrients and shift the balance between maintenance and growth/reproduction. Theory further suggests that for ectotherms, temperature stands to exacerbate this stress. Yet, the interactive effects of predation stress and temperature stress on diet, metabolism, and survival of ectotherms are not well known. This knowledge gap was addressed with a laboratory study in which wild juvenile grasshoppers were collected, assigned to one of three groups, and raised at three different temperatures. All grasshoppers had access to equal quantities of two diets composed of opposite carbohydrate:protein ratios. Half of the individuals in each temperature group were exposed to predation risk cues from spider predators, while the other half were kept in risk free conditions. Grasshoppers consumed more carbohydrates when exposed to predation risk, but consumption favored greater protein intake as temperature increased. Moreover, the difference in carbohydrate intake between risk cue and risk free treatments diminished as temperature increased. Furthermore, variability between individual consumption patterns both within and between treatments decreased markedly as temperature increased, suggesting that higher temperatures promote more consistent individual consumption behaviors. Grasshoppers grew faster and larger as temperature increased, which translated into higher survival rates at higher temperatures. Warmer grasshoppers also did not alter their metabolic rates in response to predation risk cues, in contrast to colder grasshoppers. Digestive efficiency increased with temperature as well, further indicating that lower temperatures were much more stressful than higher temperatures for grasshoppers. The study shows that physiological responses of ectothermic herbivores to predation stress are highly plastic and temperature dependent, with higher temperatures promoting increased protein intake, growth, Accepted Article This article is protected by copyright. All rights reserved. development, survival, and digestive efficiency relative to colder temperatures. These findings help to reconcile why dietary responses (proportion of protein vs. carbohydrate intake) to predation stress may vary among different prey taxa studied previously.
Ecology and evolution, 2015
Understanding the impacts of invasive species requires placing invasion within a full community c... more Understanding the impacts of invasive species requires placing invasion within a full community context. Plant invaders are often considered in the context of herbivores that may drive invasion by avoiding invaders while consuming natives (enemy escape), or inhibit invasion by consuming invaders (biotic resistance). However, predators that attack those herbivores are rarely considered as major players in invasion. Invasive plants often promote predators, generally by providing improved habitat. Here, we show that predator-promoting invaders may initiate a negative feedback loop that inhibits invasion. By enabling top-down control of herbivores, predator-promoting invaders lose any advantage gained through enemy escape, indirectly favoring natives. In cases where palatable invaders encounter biotic resistance, predator promotion may allow an invader to persist, but not dominate. Overall, results indicate that placing invaders in a full community context may reveal reduced impacts of ...
Proceedings of the Royal Society B: Biological Sciences, 2015
Trophic interactions in multiprey systems can be largely determined by prey distributions. Yet, c... more Trophic interactions in multiprey systems can be largely determined by prey distributions. Yet, classic predator–prey models assume spatially homogeneous interactions between predators and prey. We developed a spatially informed theory that predicts how habitat heterogeneity alters the landscape-scale distribution of mortality risk of prey from predation, and hence the nature of predator interactions in multiprey systems. The theoretical model is a spatially explicit, multiprey functional response in which species-specific advection–diffusion models account for the response of individual prey to habitat edges. The model demonstrates that distinct responses of alternative prey species can alter the consequences of conspecific aggregation, from increasing safety to increasing predation risk. Observations of threatened boreal caribou, moose and grey wolf interacting over 378 181 km 2 of human-managed boreal forest support this principle. This empirically supported theory demonstrates h...
Encyclopedia of Life Sciences, 2007
ABSTRACT Food webs are a way of describing the lines of dependency among species in Nature. Such ... more ABSTRACT Food webs are a way of describing the lines of dependency among species in Nature. Such interdependencies are basic to all ecological processes in that species consume resources and are themselves consumed by their predators.Keywords:complexity;connectance;feeding link;food chain;trophic interaction
Ecology and evolution, 2015
Innovative conservation tools are greatly needed to reduce livelihood losses and wildlife decline... more Innovative conservation tools are greatly needed to reduce livelihood losses and wildlife declines resulting from human-carnivore conflict. Spatial risk modeling is an emerging method for assessing the spatial patterns of predator-prey interactions, with applications for mitigating carnivore attacks on livestock. Large carnivores that ambush prey attack and kill over small areas, requiring models at fine spatial grains to predict livestock depredation hot spots. To detect the best resolution for predicting where carnivores access livestock, we examined the spatial attributes associated with livestock killed by tigers in Kanha Tiger Reserve, India, using risk models generated at 20, 100, and 200-m spatial grains. We analyzed land-use, human presence, and vegetation structure variables at 138 kill sites and 439 random sites to identify key landscape attributes where livestock were vulnerable to tigers. Land-use and human presence variables contributed strongly to predation risk models...