Biogeography has traditionally focused on the spatial distribution and abundance of species. Both... more Biogeography has traditionally focused on the spatial distribution and abundance of species. Both are driven by the way species interact with one another, but also by the way these interactions vary across time and space. Here, we call for an integrated approach, adopting the view that community structure is best represented as a network of ecological interactions, and show how it translates to biogeography questions. We propose that the ecological niche should encompass the effect of the environment on species distribution (the Grinnellian dimension of the niche) and on the ecological interactions among them (the Eltonian dimension). Starting from this concept, we develop a quantitative theory to explain turnover of interactions in space and time-i.e. a novel approach to interaction distribution modelling. We apply this framework to host-parasite interactions across Europe and find that two aspects of the environment (temperature and precipitation) exert a strong imprint on species co-occurrence, but not on species interactions. Even where species co-occur, interaction proves to be stochastic rather than deterministic, adding to variation in realized network structure. We also find that a large majority of host-parasite pairs are never found together, thus precluding any inferences regarding their probability to interact. This first attempt to explain variation of network structure at large spatial scales opens new perspectives at the interface of species distribution modelling and community ecology. 2 .
A classic measure of ecological stability describes the tendency of a community to return to equi... more A classic measure of ecological stability describes the tendency of a community to return to equilibrium after small perturbation. While many advances show how the network structure of these communities severely constrains such tendencies, few if any of these advances address one of the most fundamental properties of network structure: heterogeneity among nodes with different numbers of links. Here we systematically explore this property of "degree heterogeneity" and find that its effects on stability systematically vary with different types of interspecific interactions. Degree heterogeneity is always destabilizing in ecological networks with both competitive and mutualistic interactions while its effects on networks of predator-prey interactions such as food webs depend on prey contiguity, i.e., the extent to which the species consume an unbroken sequence of prey in community niche space. Increasing degree heterogeneity stabilizes food webs except those with the most contiguity. These findings help explain previously unexplained observations that food webs are highly but not completely contiguous and, more broadly, deepens our understanding of the stability of complex ecological networks with important implications for other types of dynamical systems. Understanding the intricate relationship between the structure and dynamics of complex ecological systems has been one of the key issues in ecology [1-4]. Equilibrium stability of ecological systems, a measure that considers an ecological system stable if it returns to its equilibrium after a small perturbation, has been a central research topic for over four decades [1, 5-15]. Empirical observations suggest that communities with more species are more stable, i.e., a positive diversity-stability relationship [16]. Yet, these intuitive ideas were challenged by
Biogeography has traditionally focused on the spatial distribution and abundance of species. Both... more Biogeography has traditionally focused on the spatial distribution and abundance of species. Both are driven by the way species interact with one another, but also by the way these interactions vary across time and space. Here, we call for an integrated approach, adopting the view that community structure is best represented as a network of ecological interactions, and show how it translates to biogeography questions. We propose that the ecological niche should encompass the effect of the environment on species distribution (the Grinnellian dimension of the niche) and on the ecological interactions among them (the Eltonian dimension). Starting from this concept, we develop a quantitative theory to explain turnover of interactions in space and timei.e. a novel approach to interaction distribution modelling. We apply this framework to host parasite interactions across Europe and find that two aspects of the environment (temperature and precipitation) exert a strong imprint on species ...
A well-known parable is that of the blind men studying an elephant each of which assert the eleph... more A well-known parable is that of the blind men studying an elephant each of which assert the elephant is the part they first hold in their hands, e.g., "rope!" says the tail holder while the leg holder asserts "tree!" The various subdisciplines of ecology appear similar in that we each engage in our enthusiastic but at least somewhat myopic study with remarkably limited agreement or even discussion about the overall system which we all study. Allometric trophic network (ATN) theory offers a path out of this dilemma by integrating across scales, taxa, habitats and organizational levels from physiology to ecosystems based on consumer-resource interactions among co-existing organisms. The network architecture and the metabolic and behavioral processes that determine the structure and dynamics of these interactions form the first principles of ATN theory, which in turn provides a synthetic overview and powerfully predictive framework for ecology from organisms to ecosystems. Beyond ecology, ATN theory also synthesizes eco-evolutionary and socio-ecological research still largely based on consumer-resource mechanisms but respectively integrated with different processes including natural selection and market mechanisms. This paper briefly describes foundations, advances, and future directions of ATN theory including predicting an ecosystem's phenotype from its community's genotype in order to accelerate more predictive and unified understanding of the complex systems studied by ecologists and other environmental scientists.
Project Goals: Our project is designed to explore the complex interactions controlling carbon (C)... more Project Goals: Our project is designed to explore the complex interactions controlling carbon (C) flow in the rhizosphere -addressing two overarching topics: 1) How multitrophic interactions control soil C dynamics, and 2) How changing precipitation regimes alter these interactions, and thus impact flow and fate of soil C. We will study interactions among key groups of soil organisms: 1) arbuscular mycorrhizal fungi (AMF), bacteria, archaea, and roots; 2) phage and their microbial hosts; and 3) rhizosphere fauna (protoand metazoan) and their prey. Primary goals of this work are to expand the knowledge of food web dynamics in the rhizosphere, how these multi-trophic interactions play a role in terrestrial C cycling, and to investigate how drought alters these interactions and the fate of soil C. The resulting data and information will substantially expand our knowledge of microbial ecology, food web interactions, and terrestrial C cycling.
AimUnderstanding how ecological and evolutionary processes together determine patterns of biodive... more AimUnderstanding how ecological and evolutionary processes together determine patterns of biodiversity remains a central aim in biology. Guided by ecological theory, we use data from multiple arthropod lineages across the Hawaiian archipelago to explore the interplay between ecological (population dynamics, dispersal, trophic interactions) and evolutionary (genetic structuring, adaptation, speciation, extinction) processes. Our goal is to show how communities develop from the dynamic feedbacks that operate at different temporal and spatial scales.LocationThe Hawaiian islands (19–22° N, 155–160° W).MethodsWe synthesize genetic data from selected arthropods across the Hawaiian archipelago to determine the relative role of dispersal and in situ differentiation across the island chronosequence. From four sites on three high islands with geological ages ranging from < 1 Ma to 5 Ma, we also generate ecological metrics on plant–herbivore bipartite networks drawn from the literature. We ...
AimTo investigate the association between hummingbird–plant network structure and species richnes... more AimTo investigate the association between hummingbird–plant network structure and species richness, phylogenetic signal on species' interaction pattern, insularity and historical and current climate.LocationFifty‐four communities along a c. 10,000 km latitudinal gradient across the Americas (39° N–32° S), ranging from sea level to c. 3700 m a.s.l., located on the mainland and on islands and covering a wide range of climate regimes.MethodsWe measured the level of specialization and modularity in mutualistic plant–hummingbird interaction networks. Using an ordinary least squares multimodel approach, we examined the influence of species richness, phylogenetic signal, insularity and current and historical climate conditions on network structure (null‐model‐corrected specialization and modularity).ResultsPhylogenetically related species, especially plants, showed a tendency to interact with a similar array of mutualistic partners. The spatial variation in network structure exhibited ...
Understanding how ecological processes determine patterns among species coexisting within ecosyst... more Understanding how ecological processes determine patterns among species coexisting within ecosystems is central to ecology. Here, we explore relationships between species' local coexistence and their trophic niches in terms of their feeding relationships both as consumers and as resources. We build on recent concepts and methods from community phylogenetics to develop a framework for analysing mechanisms responsible for community composition using trophic similarity among species and null models of community assembly. We apply this framework to 50 food webs found in 50 Adirondack lakes and find that species composition in these communities appears to be driven by both bottom-up effects by which the presence of prey species selects for predators of those prey, and top-down effects by which prey more tolerant of predation out-compete less tolerant prey of the same predators. This approach to community food webs is broadly applicable and shows how species interaction networks can inform an increasingly large array of theory central to community ecology.
This chapter presents an approach to explore the interplay of complex trophic interactions and co... more This chapter presents an approach to explore the interplay of complex trophic interactions and consumption of multiple abiotic resources among producer species, using nonlinear and nonequilibrium numerical simulations. This approach transforms simple food-web models into more general models of complex ecological networks and can be scaled up to systems with many more species and abiotic resources. Food webs traditionally specify the structure of who eats whom among species within a habitat or ecosystem. A yet-to-be realized ideal is a food web model that includes the quantity consumed and the ecological relevance of every trophic interaction among all species within a community. The exclusive focus on feeding relationships or “trophic interactions” enables models of complex food webs to also incorporate exploitative and “apparent” competition among heterotrophs. However, this focus ignores similar interactions among autotroph producers or “basal species” consuming abiotic resources, along with other “nontrophic” interactions such as many forms of facilitation and competition. Explicit models of shared nutrient consumption including competition among producers for multiple resources are largely separate from trophic ecology.
This is a self-archived version of an original article. This version may differ from the original... more This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details.
In the 'Fish life-histories and population dynamics' section of this Article the authors erroneou... more In the 'Fish life-histories and population dynamics' section of this Article the authors erroneously cited a personal communication with R. Eckmann. Dr. Eckmann did not provide any information about perch hatchery and the applied values for whitefish hatchery were modified from raw hatchery larvae records provided by him. The authors apologise for this misinterpretation. Thus, in the simulations the perch hatchery scenario was not based on empirical data but the scenario was constructed to resemble a low level of perch hatchery input as compared to whitefish hatchery input. Nonetheless, the results of the present study are robust to the assumption that perch was or was not subsidized by hatchery input as well as to variations in whitefish hatchery input. Feeding interactions among whitefish and perch are based on knowledge of the species' ecology in typical Northern hemisphere lakes where the species co-exist, but not from direct fish diet observations from Lake Constance ecosystem.
Abstract The invasion of ecosystems by nonnative species is widely considered the greatest threat... more Abstract The invasion of ecosystems by nonnative species is widely considered the greatest threat to biodiversity after habitat loss. Given limited theoretical and empirical understanding of ecological robustness to such perturbations, we simulated invasions of complex ecological networks by integrating the ‘niche model’ of food web structure and a nonlinear bioenergetic model of population dynamics. Overall, 7958 successful invasions by 100 different invaders in 150 food webs with 15–29 original species (mean 20) and 5–38% connectance (mean 16%) showed that most (61%) communities were robust to invasion in that they experienced no species loss. The distribution of robustness in terms of the fraction of native species that persisted (mean 94%) was skewed with a long tail reaching to values as low as 20%. Loss of a single species occurred less frequently (14% of cases) than ‘extinction cascades’ involving the loss of two or more species (25% of cases). These cascades were often caused by invaders with many prey species and few predator species. While low-connectance webs and webs invaded by omnivores were most likely to lose at least one additional species, high-connectance webs experiencing extinction cascades lost the most species, especially when invaded by secondary consumers. These and earlier simulation results suggest how the structure of invaded communities and the properties of invaders involve trade-offs among robustness and resistance to invasion. For example, high-connectance communities are highly resistant and robust to invasion overall but lose the most species in the relatively few cases when extinctions occur. Low-connectance webs are the least resistant and more often lack robustness but lose the fewest species in the relatively many cases when extinctions occur. Broadly speaking, these findings suggest that high connectance makes food webs rigidly resistant to invasion but more brittle once such rigidity is breached. Low-connectance webs are less rigid while more flexibly suffering fewer extinctions when extinctions occur.
Ecosystems are composed of complex networks of many species interacting in different ways. While ... more Ecosystems are composed of complex networks of many species interacting in different ways. While ecologists have long studied food webs of feeding interactions, recent studies increasingly focus on mutualistic networks including plants that exchange food for reproductive services provided by animals such as pollinators. Here, we synthesize both types of consumer-resource interactions to better understand the controversial effects of mutualism on ecosystems at the species, guild, and whole-community levels. We find that consumerresource mechanisms underlying plant-pollinator mutualisms can increase persistence, productivity, abundance, and temporal stability of both mutualists and non-mutualists in food webs. These effects strongly increase with floral reward productivity and are qualitatively robust to variation in the prevalence of mutualism and pollinators feeding upon resources in addition to rewards. This work advances the ability of mechanistic network theory to synthesize different types of interactions and illustrates how mutualism can enhance the diversity, stability, and function of complex ecosystems.
Feeding relationships can cause invasions, extirpations, and population fluctuations of a species... more Feeding relationships can cause invasions, extirpations, and population fluctuations of a species to dramatically affect other species within a variety of natural habitats. Empirical evidence suggests that such strong effects rarely propagate through food webs more than three links away from the initial perturbation. However, the size of these spheres of potential influence within complex communities is generally unknown. Here, we show for that species within large communities from a variety of aquatic and terrestrial ecosystems are on average two links apart, with >95% of species typically within three links of each other. Species are drawn even closer as network complexity and, more unexpectedly, species richness increase. Our findings are based on seven of the largest and most complex food webs available as well as a food-web model that extends the generality of the empirical results. These results indicate that the dynamics of species within ecosystems may be more highly interconnected and that biodiversity loss and species invasions may affect more species than previously thought.
Aim: How do factors such as space, time, climate and other ecological drivers influence food web ... more Aim: How do factors such as space, time, climate and other ecological drivers influence food web structure and dynamics? Collections of well-studied food webs and replicate food webs from the same system that span biogeographical and ecological gradients now enable detailed, quantitative investigation of such questions and help integrate food web ecology and macroecology. Here, we integrate macroecology and food web ecology by focusing on how ecogeographical rules [the latitudinal diversity gradient (LDG), Bergmann's rule, the island rule and Rapoport's rule] are associated with the architecture of food webs. Location: Global. Time period: Current. Major taxa studied: All taxa. Methods: We discuss the implications of each ecogeographical rule for food webs, present predictions for how food web structure will vary with each rule, assess | 1205 BAISER Et Al.
Ecosystems are composed of complex networks of many species interacting in different ways. While ... more Ecosystems are composed of complex networks of many species interacting in different ways. While ecologists have long studied food webs of feeding interactions, recent studies increasingly focus on mutualistic networks such as those of plants who exchange food for reproductive services provided by animals such as pollinators. Here, we synthesize both types of consumer-resource interactions to better understand the controversial effects of mutualism on complex ecosystems. Contrary to classic theory, we find that the dynamics of pollination mutualisms can increase the diversity, stability, and several ecosystem functions of multiplex ecological networks. These effects strongly increase with floral reward productivity and are qualitatively robust to variation in the prevalence of mutualism and pollinators feeding upon vegetation and other species in addition to floral rewards. This work advances the ability of mechanistic network theory to synthesize different types of ecological inter...
P rey rarely, if ever, give up their lives willingly to their predators. Predators overcome their... more P rey rarely, if ever, give up their lives willingly to their predators. Predators overcome their prey's resistance by being, on average, larger than their prey, yielding a systematic pattern in communities where the non-cannibalistic average ratio of predator-to-prey body mass (hereafter, body-mass ratio) is higher than unity 1,2. Notable exceptions to this include when animals cooperate to overcome larger prey (for example, pack hunters) and where consumers are parasites or parasitoids. Variation in body-mass ratios within food webs typically spans several orders of magnitude and includes some predators that are smaller than their prey 3 , but is dominated by situations of the larger feeding on the smaller. The varying body-mass ratios limit which trophic interactions are realized in a community 4-6 , and the strength of these interactions 7-9. Predators typically exert the strongest feeding pressure on prey that are 1-2 orders of magnitude smaller 1 , while weaker interaction strengths are realized with prey that are smaller or larger than this size 10,11. Specifically, interactions of predators with small prey are characterized by high body-mass ratios that yield weak interactions with slow dynamics, which play a central role in maintaining foodweb stability 12-16 and ecosystem functioning 10,17,18. Moreover, they
Biogeography has traditionally focused on the spatial distribution and abundance of species. Both... more Biogeography has traditionally focused on the spatial distribution and abundance of species. Both are driven by the way species interact with one another, but also by the way these interactions vary across time and space. Here, we call for an integrated approach, adopting the view that community structure is best represented as a network of ecological interactions, and show how it translates to biogeography questions. We propose that the ecological niche should encompass the effect of the environment on species distribution (the Grinnellian dimension of the niche) and on the ecological interactions among them (the Eltonian dimension). Starting from this concept, we develop a quantitative theory to explain turnover of interactions in space and time-i.e. a novel approach to interaction distribution modelling. We apply this framework to host-parasite interactions across Europe and find that two aspects of the environment (temperature and precipitation) exert a strong imprint on species co-occurrence, but not on species interactions. Even where species co-occur, interaction proves to be stochastic rather than deterministic, adding to variation in realized network structure. We also find that a large majority of host-parasite pairs are never found together, thus precluding any inferences regarding their probability to interact. This first attempt to explain variation of network structure at large spatial scales opens new perspectives at the interface of species distribution modelling and community ecology. 2 .
A classic measure of ecological stability describes the tendency of a community to return to equi... more A classic measure of ecological stability describes the tendency of a community to return to equilibrium after small perturbation. While many advances show how the network structure of these communities severely constrains such tendencies, few if any of these advances address one of the most fundamental properties of network structure: heterogeneity among nodes with different numbers of links. Here we systematically explore this property of "degree heterogeneity" and find that its effects on stability systematically vary with different types of interspecific interactions. Degree heterogeneity is always destabilizing in ecological networks with both competitive and mutualistic interactions while its effects on networks of predator-prey interactions such as food webs depend on prey contiguity, i.e., the extent to which the species consume an unbroken sequence of prey in community niche space. Increasing degree heterogeneity stabilizes food webs except those with the most contiguity. These findings help explain previously unexplained observations that food webs are highly but not completely contiguous and, more broadly, deepens our understanding of the stability of complex ecological networks with important implications for other types of dynamical systems. Understanding the intricate relationship between the structure and dynamics of complex ecological systems has been one of the key issues in ecology [1-4]. Equilibrium stability of ecological systems, a measure that considers an ecological system stable if it returns to its equilibrium after a small perturbation, has been a central research topic for over four decades [1, 5-15]. Empirical observations suggest that communities with more species are more stable, i.e., a positive diversity-stability relationship [16]. Yet, these intuitive ideas were challenged by
Biogeography has traditionally focused on the spatial distribution and abundance of species. Both... more Biogeography has traditionally focused on the spatial distribution and abundance of species. Both are driven by the way species interact with one another, but also by the way these interactions vary across time and space. Here, we call for an integrated approach, adopting the view that community structure is best represented as a network of ecological interactions, and show how it translates to biogeography questions. We propose that the ecological niche should encompass the effect of the environment on species distribution (the Grinnellian dimension of the niche) and on the ecological interactions among them (the Eltonian dimension). Starting from this concept, we develop a quantitative theory to explain turnover of interactions in space and timei.e. a novel approach to interaction distribution modelling. We apply this framework to host parasite interactions across Europe and find that two aspects of the environment (temperature and precipitation) exert a strong imprint on species ...
A well-known parable is that of the blind men studying an elephant each of which assert the eleph... more A well-known parable is that of the blind men studying an elephant each of which assert the elephant is the part they first hold in their hands, e.g., "rope!" says the tail holder while the leg holder asserts "tree!" The various subdisciplines of ecology appear similar in that we each engage in our enthusiastic but at least somewhat myopic study with remarkably limited agreement or even discussion about the overall system which we all study. Allometric trophic network (ATN) theory offers a path out of this dilemma by integrating across scales, taxa, habitats and organizational levels from physiology to ecosystems based on consumer-resource interactions among co-existing organisms. The network architecture and the metabolic and behavioral processes that determine the structure and dynamics of these interactions form the first principles of ATN theory, which in turn provides a synthetic overview and powerfully predictive framework for ecology from organisms to ecosystems. Beyond ecology, ATN theory also synthesizes eco-evolutionary and socio-ecological research still largely based on consumer-resource mechanisms but respectively integrated with different processes including natural selection and market mechanisms. This paper briefly describes foundations, advances, and future directions of ATN theory including predicting an ecosystem's phenotype from its community's genotype in order to accelerate more predictive and unified understanding of the complex systems studied by ecologists and other environmental scientists.
Project Goals: Our project is designed to explore the complex interactions controlling carbon (C)... more Project Goals: Our project is designed to explore the complex interactions controlling carbon (C) flow in the rhizosphere -addressing two overarching topics: 1) How multitrophic interactions control soil C dynamics, and 2) How changing precipitation regimes alter these interactions, and thus impact flow and fate of soil C. We will study interactions among key groups of soil organisms: 1) arbuscular mycorrhizal fungi (AMF), bacteria, archaea, and roots; 2) phage and their microbial hosts; and 3) rhizosphere fauna (protoand metazoan) and their prey. Primary goals of this work are to expand the knowledge of food web dynamics in the rhizosphere, how these multi-trophic interactions play a role in terrestrial C cycling, and to investigate how drought alters these interactions and the fate of soil C. The resulting data and information will substantially expand our knowledge of microbial ecology, food web interactions, and terrestrial C cycling.
AimUnderstanding how ecological and evolutionary processes together determine patterns of biodive... more AimUnderstanding how ecological and evolutionary processes together determine patterns of biodiversity remains a central aim in biology. Guided by ecological theory, we use data from multiple arthropod lineages across the Hawaiian archipelago to explore the interplay between ecological (population dynamics, dispersal, trophic interactions) and evolutionary (genetic structuring, adaptation, speciation, extinction) processes. Our goal is to show how communities develop from the dynamic feedbacks that operate at different temporal and spatial scales.LocationThe Hawaiian islands (19–22° N, 155–160° W).MethodsWe synthesize genetic data from selected arthropods across the Hawaiian archipelago to determine the relative role of dispersal and in situ differentiation across the island chronosequence. From four sites on three high islands with geological ages ranging from < 1 Ma to 5 Ma, we also generate ecological metrics on plant–herbivore bipartite networks drawn from the literature. We ...
AimTo investigate the association between hummingbird–plant network structure and species richnes... more AimTo investigate the association between hummingbird–plant network structure and species richness, phylogenetic signal on species' interaction pattern, insularity and historical and current climate.LocationFifty‐four communities along a c. 10,000 km latitudinal gradient across the Americas (39° N–32° S), ranging from sea level to c. 3700 m a.s.l., located on the mainland and on islands and covering a wide range of climate regimes.MethodsWe measured the level of specialization and modularity in mutualistic plant–hummingbird interaction networks. Using an ordinary least squares multimodel approach, we examined the influence of species richness, phylogenetic signal, insularity and current and historical climate conditions on network structure (null‐model‐corrected specialization and modularity).ResultsPhylogenetically related species, especially plants, showed a tendency to interact with a similar array of mutualistic partners. The spatial variation in network structure exhibited ...
Understanding how ecological processes determine patterns among species coexisting within ecosyst... more Understanding how ecological processes determine patterns among species coexisting within ecosystems is central to ecology. Here, we explore relationships between species' local coexistence and their trophic niches in terms of their feeding relationships both as consumers and as resources. We build on recent concepts and methods from community phylogenetics to develop a framework for analysing mechanisms responsible for community composition using trophic similarity among species and null models of community assembly. We apply this framework to 50 food webs found in 50 Adirondack lakes and find that species composition in these communities appears to be driven by both bottom-up effects by which the presence of prey species selects for predators of those prey, and top-down effects by which prey more tolerant of predation out-compete less tolerant prey of the same predators. This approach to community food webs is broadly applicable and shows how species interaction networks can inform an increasingly large array of theory central to community ecology.
This chapter presents an approach to explore the interplay of complex trophic interactions and co... more This chapter presents an approach to explore the interplay of complex trophic interactions and consumption of multiple abiotic resources among producer species, using nonlinear and nonequilibrium numerical simulations. This approach transforms simple food-web models into more general models of complex ecological networks and can be scaled up to systems with many more species and abiotic resources. Food webs traditionally specify the structure of who eats whom among species within a habitat or ecosystem. A yet-to-be realized ideal is a food web model that includes the quantity consumed and the ecological relevance of every trophic interaction among all species within a community. The exclusive focus on feeding relationships or “trophic interactions” enables models of complex food webs to also incorporate exploitative and “apparent” competition among heterotrophs. However, this focus ignores similar interactions among autotroph producers or “basal species” consuming abiotic resources, along with other “nontrophic” interactions such as many forms of facilitation and competition. Explicit models of shared nutrient consumption including competition among producers for multiple resources are largely separate from trophic ecology.
This is a self-archived version of an original article. This version may differ from the original... more This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details.
In the 'Fish life-histories and population dynamics' section of this Article the authors erroneou... more In the 'Fish life-histories and population dynamics' section of this Article the authors erroneously cited a personal communication with R. Eckmann. Dr. Eckmann did not provide any information about perch hatchery and the applied values for whitefish hatchery were modified from raw hatchery larvae records provided by him. The authors apologise for this misinterpretation. Thus, in the simulations the perch hatchery scenario was not based on empirical data but the scenario was constructed to resemble a low level of perch hatchery input as compared to whitefish hatchery input. Nonetheless, the results of the present study are robust to the assumption that perch was or was not subsidized by hatchery input as well as to variations in whitefish hatchery input. Feeding interactions among whitefish and perch are based on knowledge of the species' ecology in typical Northern hemisphere lakes where the species co-exist, but not from direct fish diet observations from Lake Constance ecosystem.
Abstract The invasion of ecosystems by nonnative species is widely considered the greatest threat... more Abstract The invasion of ecosystems by nonnative species is widely considered the greatest threat to biodiversity after habitat loss. Given limited theoretical and empirical understanding of ecological robustness to such perturbations, we simulated invasions of complex ecological networks by integrating the ‘niche model’ of food web structure and a nonlinear bioenergetic model of population dynamics. Overall, 7958 successful invasions by 100 different invaders in 150 food webs with 15–29 original species (mean 20) and 5–38% connectance (mean 16%) showed that most (61%) communities were robust to invasion in that they experienced no species loss. The distribution of robustness in terms of the fraction of native species that persisted (mean 94%) was skewed with a long tail reaching to values as low as 20%. Loss of a single species occurred less frequently (14% of cases) than ‘extinction cascades’ involving the loss of two or more species (25% of cases). These cascades were often caused by invaders with many prey species and few predator species. While low-connectance webs and webs invaded by omnivores were most likely to lose at least one additional species, high-connectance webs experiencing extinction cascades lost the most species, especially when invaded by secondary consumers. These and earlier simulation results suggest how the structure of invaded communities and the properties of invaders involve trade-offs among robustness and resistance to invasion. For example, high-connectance communities are highly resistant and robust to invasion overall but lose the most species in the relatively few cases when extinctions occur. Low-connectance webs are the least resistant and more often lack robustness but lose the fewest species in the relatively many cases when extinctions occur. Broadly speaking, these findings suggest that high connectance makes food webs rigidly resistant to invasion but more brittle once such rigidity is breached. Low-connectance webs are less rigid while more flexibly suffering fewer extinctions when extinctions occur.
Ecosystems are composed of complex networks of many species interacting in different ways. While ... more Ecosystems are composed of complex networks of many species interacting in different ways. While ecologists have long studied food webs of feeding interactions, recent studies increasingly focus on mutualistic networks including plants that exchange food for reproductive services provided by animals such as pollinators. Here, we synthesize both types of consumer-resource interactions to better understand the controversial effects of mutualism on ecosystems at the species, guild, and whole-community levels. We find that consumerresource mechanisms underlying plant-pollinator mutualisms can increase persistence, productivity, abundance, and temporal stability of both mutualists and non-mutualists in food webs. These effects strongly increase with floral reward productivity and are qualitatively robust to variation in the prevalence of mutualism and pollinators feeding upon resources in addition to rewards. This work advances the ability of mechanistic network theory to synthesize different types of interactions and illustrates how mutualism can enhance the diversity, stability, and function of complex ecosystems.
Feeding relationships can cause invasions, extirpations, and population fluctuations of a species... more Feeding relationships can cause invasions, extirpations, and population fluctuations of a species to dramatically affect other species within a variety of natural habitats. Empirical evidence suggests that such strong effects rarely propagate through food webs more than three links away from the initial perturbation. However, the size of these spheres of potential influence within complex communities is generally unknown. Here, we show for that species within large communities from a variety of aquatic and terrestrial ecosystems are on average two links apart, with >95% of species typically within three links of each other. Species are drawn even closer as network complexity and, more unexpectedly, species richness increase. Our findings are based on seven of the largest and most complex food webs available as well as a food-web model that extends the generality of the empirical results. These results indicate that the dynamics of species within ecosystems may be more highly interconnected and that biodiversity loss and species invasions may affect more species than previously thought.
Aim: How do factors such as space, time, climate and other ecological drivers influence food web ... more Aim: How do factors such as space, time, climate and other ecological drivers influence food web structure and dynamics? Collections of well-studied food webs and replicate food webs from the same system that span biogeographical and ecological gradients now enable detailed, quantitative investigation of such questions and help integrate food web ecology and macroecology. Here, we integrate macroecology and food web ecology by focusing on how ecogeographical rules [the latitudinal diversity gradient (LDG), Bergmann's rule, the island rule and Rapoport's rule] are associated with the architecture of food webs. Location: Global. Time period: Current. Major taxa studied: All taxa. Methods: We discuss the implications of each ecogeographical rule for food webs, present predictions for how food web structure will vary with each rule, assess | 1205 BAISER Et Al.
Ecosystems are composed of complex networks of many species interacting in different ways. While ... more Ecosystems are composed of complex networks of many species interacting in different ways. While ecologists have long studied food webs of feeding interactions, recent studies increasingly focus on mutualistic networks such as those of plants who exchange food for reproductive services provided by animals such as pollinators. Here, we synthesize both types of consumer-resource interactions to better understand the controversial effects of mutualism on complex ecosystems. Contrary to classic theory, we find that the dynamics of pollination mutualisms can increase the diversity, stability, and several ecosystem functions of multiplex ecological networks. These effects strongly increase with floral reward productivity and are qualitatively robust to variation in the prevalence of mutualism and pollinators feeding upon vegetation and other species in addition to floral rewards. This work advances the ability of mechanistic network theory to synthesize different types of ecological inter...
P rey rarely, if ever, give up their lives willingly to their predators. Predators overcome their... more P rey rarely, if ever, give up their lives willingly to their predators. Predators overcome their prey's resistance by being, on average, larger than their prey, yielding a systematic pattern in communities where the non-cannibalistic average ratio of predator-to-prey body mass (hereafter, body-mass ratio) is higher than unity 1,2. Notable exceptions to this include when animals cooperate to overcome larger prey (for example, pack hunters) and where consumers are parasites or parasitoids. Variation in body-mass ratios within food webs typically spans several orders of magnitude and includes some predators that are smaller than their prey 3 , but is dominated by situations of the larger feeding on the smaller. The varying body-mass ratios limit which trophic interactions are realized in a community 4-6 , and the strength of these interactions 7-9. Predators typically exert the strongest feeding pressure on prey that are 1-2 orders of magnitude smaller 1 , while weaker interaction strengths are realized with prey that are smaller or larger than this size 10,11. Specifically, interactions of predators with small prey are characterized by high body-mass ratios that yield weak interactions with slow dynamics, which play a central role in maintaining foodweb stability 12-16 and ecosystem functioning 10,17,18. Moreover, they
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