The way predators control their prey populations is determined by the interplay between predator hunting mode and prey antipredator behavior. It is uncertain, however, how the effects of such ...interplay control ecosystem function. A 3-year experiment in grassland mesocosms revealed that actively hunting spiders reduced plant species diversity and enhanced aboveground net primary production and nitrogen mineralization rate, whereas sit-and-wait ambush spiders had opposite effects. These effects arise from the different responses to the two different predators by their grasshopper prey--the dominant herbivore species that controls plant species composition and accordingly ecosystem functioning. Predator hunting mode is thus a key functional trait that can help to explain variation in the nature of top-down control of ecosystems.
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 bottom-up 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.
When studying the responses of food web dynamics to climate change, shifts in resource nutrient content are frequently overlooked, although they generally occur along with shifts in consumer physiology and behavior
Studying the simultaneous effects of both processes on food webs is necessary because they are interdependent and have the potential to produce ecological surprises
Nutritional ecology (NE) provides a convenient organizing principle on which to build understanding of the interdependent nature of the two processes because NE allows one to track the macronutrient connections between trophic levels
By integrating top-down (shifts in consumer physiology and behavior) and bottom-up (shifts in resource nutrient content) responses to climate change into one conceptual framework, we can improve the realism of climate change ecology experiments and predictive accuracy
We present a framework to explain how prey stress responses to predation can resolve context dependency in ecosystem properties and functions such as food chain length, secondary production, ...elemental stoichiometry, and cycling. We first describe the major nonspecific physiological stress mechanisms and their ecologically relevant consequences. We next synthesize the evidence for prey physiological responses to predation risk and demonstrate that they are similar across taxa and fit well within the general stress paradigm. We then illustrate the utility of our idea by applying our understanding of the ecological consequences of stress to explain how herbivore‐prey physiological antipredator responses affect ecosystem dynamics. We hypothesize that stressed herbivores should forage on plant species with higher digestible carbohydrates than should unstressed herbivores to meet heightened energy demands. Increased consumption of carbohydrate‐rich plants should reduce their relative abundance in the community, hence altering the quantity and quality of plant litter entering the detrital pool. We further hypothesize that stress should change the elemental composition and energy content of prey excreta, egesta, and carcasses that enter the detrital pool. Finally, prey stress should lower energy and nutrient conversion efficiency and hence the transfer of materials and energy up the food chain, which should, in turn, weaken the association between ecosystem productivity and food chain length.
The process of nutrient transfer through an ecosystem is an important determinant of production, food-chain length, and species diversity. The general view is that the rate and efficiency of nutrient ...transfer up the food chain is constrained by herbivore-specific capacity to secure N-rich compounds for survival and production. Using feeding trials with artificial food, we show, however, that physiological stress-response of grasshopper herbivores to spider predation risk alters the nature of the nutrient constraint. Grasshoppers facing predation risk had higher metabolic rates than control grasshoppers. Elevated metabolism accordingly increased requirements for dietary digestible carbohydrate-C to fuel-heightened energy demands. Moreover, digestible carbohydrate-C comprises a small fraction of total plant tissue-C content, so nutrient transfer between plants and herbivores accordingly becomes more constrained by digestible plant C than by total plant C:N. This shift in herbivore diet to meet the altered nutrient requirement increased herbivore body C:N content, the C:N content of the plant community from which grasshoppers select their diet, and grasshopper fecal C:N content. Chronic predation risk thus alters the quality of animal and plant tissue that eventually enters the detrital pool to become decomposed. Our results demonstrate that herbivore physiology causes C:N requirements and nutrient intake to become flexible, thereby providing a mechanism to explain context dependence in the nature of trophic control over nutrient transfer in ecosystems.
Animals and the zoogeochemistry of the carbon cycle Schmitz, Oswald J; Wilmers, Christopher C; Leroux, Shawn J ...
Science (American Association for the Advancement of Science),
12/2018, Volume:
362, Issue:
6419
Journal Article
Peer reviewed
Predicting and managing the global carbon cycle requires scientific understanding of ecosystem processes that control carbon uptake and storage. It is generally assumed that carbon cycling is ...sufficiently characterized in terms of uptake and exchange between ecosystem plant and soil pools and the atmosphere. We show that animals also play an important role by mediating carbon exchange between ecosystems and the atmosphere, at times turning ecosystem carbon sources into sinks, or vice versa. Animals also move across landscapes, creating a dynamism that shapes landscape-scale variation in carbon exchange and storage. Predicting and measuring carbon cycling under such dynamism is an important scientific challenge. We explain how to link analyses of spatial ecosystem functioning, animal movement, and remote sensing of animal habitats with carbon dynamics across landscapes.
The recognition that predators play important roles in ecosystems has prompted research to resolve how combinations of predator species influence ecosystem functions. Interactions among predator ...species and their prey can lead to a host of linear and nonlinear effects. Understanding the conditions causing these effects is critical for assigning predator species to functional groups in ways that lead to predictive theory of predator diversity effects on trophic interactions. To this end, I provide a synthesis of experiments examining multiple-predator-species effects on mortality of single shared prey. I show how experimental design and experimental venue can determine the conclusion about the importance of predator diversity on trophic interactions. In addition, I link natural history insights on predator species habitat and hunting behavior with linear and nonlinear multiple-predator effects to derive a new concept of predator diversity effects on trophic interactions. This concept holds that the nature of predator diversity effects is contingent upon predator species hunting mode plus predator and prey species habitat domain (defined as the spatial extent to which a microhabitat is used by a species). This concept allows the classification of multiple-predator effects into four broad functional categories: substitutable, nonlinear due to predator species interference, nonlinear due to intraguild predation, and nonlinear due to predator species synergism. Experimental evidence so far provides ample and comparatively equal support for substitutable, interference, and intraguild effects, and equivocal support for nonlinear synergisms. The paper closes by discussing ways to further a research program aimed at using the building blocks presented here to understand predator functional diversity and trophic interactions in complex ecological systems.
Functional traits are useful for characterizing variation in community and ecosystem dynamics. Most advances in trait‐based ecology to date centre on plant functional traits, although there is an ...increasing recognition that animal traits are also key contributors to processes operating at the community or ecosystem scale.
Terrestrial invertebrates are incredibly diverse and ubiquitous animals with important roles in nutrient cycling. Despite their widespread influence on ecosystem processes, we currently lack a synthetic understanding of how invertebrate functional traits affect terrestrial nutrient cycling.
We present a meta‐analysis of 511 paired observations from 122 papers that examined how invertebrate functional traits affected litter decomposition rates, nitrogen pools and litter C:N ratios. Based on the available data, we specifically assessed the effects of feeding mode (bioturbation, detritus shredding, detritus grazing, leaf chewing, leaf piercing, ambush predators, active hunting predators) and body size (macro‐ and micro‐invertebrates) on nutrient cycling.
The effects of invertebrates on terrestrial nutrient cycling varied according to functional trait. The inclusion of both macro‐ (≥2 mm) and micro‐invertebrates (<2 mm) increased litter decomposition by 20% and 19%, respectively. All detritivorous feeding modes enhanced litter decomposition rates, with bioturbators, detritus shredders and detritus grazers increasing decomposition by 28%, 22% and 15%, respectively. Neither herbivore feeding mode (e.g. leaf chewers and leaf piercers) nor predator hunting mode (ambush and active hunting) affected decomposition. We also revealed that bioturbators and detritus grazers increased soil nitrogen availability by 99% and 70%, respectively, and that leaf‐chewing herbivores had a weak effect on litterfall stoichiometry via reducing C:N ratios by 11%.
Although functional traits might be useful predictors of ecosystem processes, our findings suggest context‐dependent effects of invertebrate traits on terrestrial nutrient cycling. Detritivore functional traits (i.e. bioturbators, detritus shredders and detritus grazers) are more consistent with increased rates of nutrient cycling, whereas our currently characterized predator and herbivore traits are less predictive. Future research is needed to identify, standardize and deliberately study the impacts of invertebrate functional traits on nutrient cycling in hopes of revealing the key functional traits governing ecosystem functioning worldwide.
This is the first meta‐analysis to investigate the impacts of invertebrate functional traits on terrestrial nutrient cycling. The findings are of interest to a broad readership, including those interested in the influence of animals on ecosystem functioning and those interested in the evolutionary ecology of organismal traits’ impacts.
Large carnivores face serious threats and are experiencing massive declines in their populations and geographic ranges around the world. We highlight how these threats have affected the conservation ...status and ecological functioning of the 31 largest mammalian carnivores on Earth. Consistent with theory, empirical studies increasingly show that large carnivores have substantial effects on the structure and function of diverse ecosystems. Significant cascading trophic interactions, mediated by their prey or sympatric mesopredators, arise when some of these carnivores are extirpated from or repatriated to ecosystems. Unexpected effects of trophic cascades on various taxa and processes include changes to bird, mammal, invertebrate, and herpetofauna abundance or richness; subsidies to scavengers; altered disease dynamics; carbon sequestration; modified stream morphology; and crop damage. Promoting tolerance and coexistence with large carnivores is a crucial societal challenge that will ultimately determine the fate of Earth's largest carnivores and all that depends upon them, including humans.
Recent reports on the state of the global environment provide evidence that humankind is inflicting great damage to the very ecosystems that support human livelihoods. The reports further predict ...that ecosystems will take centuries to recover from damages if they recover at all. Accordingly, there is despair that we are passing on a legacy of irreparable damage to future generations which is entirely inconsistent with principles of sustainability.
We tested the prediction of irreparable harm using a synthesis of recovery times compiled from 240 independent studies reported in the scientific literature. We provide startling evidence that most ecosystems globally can, given human will, recover from very major perturbations on timescales of decades to half-centuries.
Accordingly, we find much hope that humankind can transition to more sustainable use of ecosystems.
Predators are predominantly valued for their ability to control prey, as indicators of high levels of biodiversity and as tourism attractions. This view, however, is incomplete because it does not ...acknowledge that predators may play a significant role in the delivery of critical life-support services such as ecosystem nutrient cycling. New research is beginning to show that predator effects on nutrient cycling are ubiquitous. These effects emerge from direct nutrient excretion, egestion or translocation within and across ecosystem boundaries after prey consumption, and from indirect effects mediated by predator interactions with prey. Depending on their behavioural ecology, predators can create heterogeneous or homogeneous nutrient distributions across natural landscapes. Because predator species are disproportionately vulnerable to elimination from ecosystems, we stand to lose much more from their disappearance than their simple charismatic attractiveness.
PDF
