Linking Rates of Diffusion and Consumption in Relationto Resources

The functional response is a fundamental model of the relationship between consumer intake rate and resource abundance. The random walk is a fundamental model of animal movement and is well approximated by simple diffusion. Both models are central to our understanding of numerous ecological processes but are rarely linked in ecological theory. To derive a synthetic model, we draw on the common logical premise underlying these models and show how the diffusion and consumption rates of consumers depend on elementary attributes of naturally occurring consumer-resource interactions: the abundance, spatial aggregation, and traveling speed of resources as well as consumer handling time and directional persistence. We show that resource aggregation may lead to increased consumer diffusion and, in the case of mobile resources, reduced consumption rate. Resource-dependent movement patterns have traditionally been attributed to area-restricted search, reflecting adaptive decision making by the consumer. Our synthesis provides a simple alternative hypothesis that such patterns could also arise as a by-product of statistical movement mechanics

Why Are We Not Evaluating Multiple CompetingHypotheses in Ecology and Evolution?

The use of multiple working hypotheses to gain strong inference is widely promoted as a means to enhance the effectiveness of scientific investigation. Only 21 of 100 randomly selected studies from the ecological and evolutionary literature tested more than one hypothesis and only eight tested more than two hypotheses. The surprising rarity of application of multiple working hypotheses suggests that this gap between theory and practice might reflect some fundamental issues. Here, we identify several intellectual and practical barriers that discourage us from using multiple hypotheses in our scientific investigation. While scientists have developed a number of ways to avoid biases, such as the use of double-blind controls, we suspect that few scientists are fully aware of the potential influence of cognitive bias on their decisions and they have not yet adopted many techniques available to overcome intellectual and practical barriers in order to improve scientific investigation

On the Scale Dependence of Foraging in Terrestrial Herbivores

Meaningful modeling of the spatial and trophic dynamics of terrestrial herbivores demands understanding of the constraints and fitness objectives that presumably underlie behavior. This is complex in terrestrial herbivores, because of scale-dependent constraints on nutrient or energy gain. Mechanistic processes of forage cropping, forage mastication, movements between feeding stations, and forage digestion each have unique constraints that apply on different time, size, and spatial scales. Moreover, competing activities are rarely taken into account. Experimental testing of foraging objectives is therefore clouded by uncertainty regarding which time scale is most relevant from the animal’s perspective, leading to confusion and misrepresentation in the foraging literature. We illustrate these arguments from both theoretical and empirical points of view, based on our work with wild ungulates as well as the contemporary literature

Characterizing DemographicParameters Across Environmental Gradients: A Case Study With Ontario Moose

Population-level demographic characteristics as estimated by standard logistic growth models (i.e., carrying capacity and intrinsic growth rate) should vary with changes in habitat quality and availability of resources. However, few published studies have tested this hypothesis by comparing population growth rates across broad bioclimatic gradients, and fewer still the carrying capacities of those populations. We used time series data on moose (Alces alces) population densities based on aerial census and hunter harvest data for 34 management units across Ontario to estimate local carrying capacities and intrinsic growth rates. These population parameters were then regressed against associated habitat covariates for each management unit to assess how moose demography changes across a broad gradient of productivity, habitat abundance, and timber harvest. Moose carrying capacity was found to increase with increasing forest productivity as measured by DNDVI and the proportion of mixedwood stands in the forest. Both variables are plausibly indicative of high quality forage abundance for moose. Moose carrying capacity decreased with the proportion of forest stands harvested for timber annually, suggesting that immediate removal of forest stands and increased access by hunters temper maximum population size. Maximum rates of population growth by Ontario moose did not vary predictably with any of the landscape covariates tested. These findings contribute to our understanding of changes in demography across broad geographic and bioclimatic gradients and suggest that crude population estimators may be derived based on known habitat preferences and resource availability without a priori knowledge of animal abundance. (PDF) Characterizing demographic parameters across environmental gradients: A case study with Ontario moose (Alces alces). Available from: https://www.researchgate.net/publication/280936410_Characterizing_demographic_parameters_across_environmental_gradients_A_case_study_with_Ontario_moose_Alces_alces [accessed Oct 29 2018]

Temperature Triggers a Non-Linear Response in Resource–Consumer Interaction Strength

Although temperature is recognized as a major determinant of many ecological processes, it is still not clear whether temperature increase caused by climate change will strengthen or weaken species interactions. One hypothesis is that interactions will respond non‐monotonically to temperature because thermal performance curves, which determine the strength of these interactions, are also non‐monotonic. To evaluate this hypothesis, we developed a temperature‐dependent consumer–resource model and tested predictions from this model in large freshwater mesocosms populated with green algae (Chlorella vulgaris) and herbivorous zooplankton (Daphnia magna). We found both in the model simulations and empirical investigations that the suppressive effect of the consumer depended non‐monotonically on the temperature. As predicted by the model, Daphnia suppressed the algal maximum per capita growth rate at the temperature that maximized algal growth rate but had little effect on resource growth at either lower or higher temperatures. This finding could help explain why effects of temperature variation on species interaction are variable in the literature and suggests that predicting the effects of temperature on the strength of food web interactions requires knowledge of the thermal performance curves for multiple traits, for multiple species and over a range of temperatures

Food Availability Modulates Temperature-Dependent Effects on Growth, Reproduction, and Survival in Daphnia Magna

Reduced body size and accelerated life cycle due to warming are considered major ecological responses to climate change with fitness costs at the individual level. Surprisingly, we know little about how relevant ecological factors can alter these life history trade‐offs and their consequences for individual fitness. Here, we show that food modulates temperature‐dependent effects on body size in the water flea Daphnia magna and interacts with temperature to affect life history parameters. We exposed 412 individuals to a factorial manipulation of food abundance and temperature, tracked each reproductive event, and took daily measurements of body size from each individual. High temperature caused a reduction in maximum body size in both food treatments, but this effect was mediated by food abundance, such that low food conditions resulted in a reduction of 20% in maximum body size, compared with a reduction of 4% under high food conditions. High temperature resulted in an accelerated life cycle, with pronounced fitness cost at low levels of food where only a few individuals produced a clutch. These results suggest that the mechanisms affecting the trade‐off between fast growth and final body size are food‐dependent, and that the combination of low levels of food and high temperature could potentially threaten viability of ectotherms

Human Activity Mediates a Trophic Cascade Caused by Wolves

Experimental evidence of trophic cascades initiated by large vertebrate predators is rare in terrestrial ecosystems. A serendipitous natural experiment provided an opportunity to test the trophic cascade hypothesis for wolves (Canis lupus) in Banff National Park, Canada. The first wolf pack recolonized the Bow Valley of Banff National Park in 1986. High human activity partially excluded wolves from one area of the Bow Valley (low-wolf area), whereas wolves made full use of an adjacent area (high-wolf area). We investigated the effects of differential wolf predation between these two areas on elk (Cervus elaphus) population density, adult female survival, and calf recruitment; aspen (Populus tremuloides) recruitment and browse intensity; willow (Salix spp.) production, browsing intensity, and net growth; beaver (Castor canadensis) density; and riparian songbird diversity, evenness, and abundance. We compared effects of recolonizing wolves on these response variables using the log response ratio between the low-wolf and high-wolf treatments. Elk population density diverged over time in the two treatments, such that elk were an order of magnitude more numerous in the low-wolf area compared to the high-wolf area at the end of the study. Annual survival of adult female elk was 62% in the high-wolf area vs. 89% in the low-wolf area. Annual recruitment of calves was 15% in the high-wolf area vs. 27% without wolves. Wolf exclusion decreased aspen recruitment, willow production, and increased willow and aspen browsing intensity. Beaver lodge density was negatively correlated to elk density, and elk herbivory had an indirect negative effect on riparian songbird diversity and abundance. These alternating patterns across trophic levels support the wolf-caused trophic cascade hypothesis. Human activity strongly mediated these cascade effects, through a depressing effect on habitat use by wolves. Thus, conservation strategies based on the trophic importance of large carnivores have increased support in terrestrial ecosystems. Read More: http://www.esajournals.org/doi/full/10.1890/04-126

Predicted Impact of Barriers to Migration on the Serengeti Wildebeest Population

The Serengeti wildebeest migration is a rare and spectacular example of a once-common biological phenomenon. A proposed road project threatens to bisect the Serengeti ecosystem and its integrity. The precautionary principle dictates that we consider the possible consequences of a road completely disrupting the migration. We used an existing spatially-explicit simulation model of wildebeest movement and population dynamics to explore how placing a barrier to migration across the proposed route (thus creating two disjoint but mobile subpopulations) might affect the long-term size of the wildebeest population. Our simulation results suggest that a barrier to migration—even without causing habitat loss—could cause the wildebeest population to decline by about a third. The driver of this decline is the effect of habitat fragmentation (even without habitat loss) on the ability of wildebeest to effectively track temporal shifts in high-quality forage resources across the landscape. Given the important role of the wildebeest migration for a number of key ecological processes, these findings have potentially important ramifications for ecosystem biodiversity, structure, and function in the Serengeti

Stabilizing effects of group formation by Serengeti herbivores on predator-prey dynamics

Predator-prey theory often assumes that potential prey individuals are solitary and evenly distributed in space. This assumption is violated in social, mobile prey, such as many ungulates. Here we use data from 80 monthly field censuses to estimate the parameters for a power relationship between herd density and population density for eight species of large herbivores commonly found in the diet of Serengeti lions, confirming a power relationship proposed from a preliminary Serengeti dataset. Here we extend our analysis of that model to demonstrate how parameters of the power function relate to average herd size and density-dependent changes in herd size and evaluate how interspecific variation in these parameters shapes the group-dependent functional response by Serengeti lions for eight prey species. We apply the different prey-specific functional response models in a Rosenzweig-MacArthur framework to compare their impact on the stability of predator–prey dynamics. Model outcomes suggest that group formation plays a strong role in stabilizing lion–herbivore interactions in Serengeti by forcing lions to search over a larger area before each prey encounter. As a consequence of grouping by their prey, our model also suggests that Serengeti lions are forced to broaden their diets to include multiple species of prey in order to persist, potentially explaining the generalist foraging by lions routinely recorded across multiple ecosystems

Learning and animal movement

Authors acknowledge the following grants for supporting this research: NSERC Discovery (ML and MA-M), NSF DMS-1853465 (WF and EG), and Canada Research Chairs Program (ML and MA-M).Integrating diverse concepts from animal behavior, movement ecology, and machine learning, we develop an overview of the ecology of learning and animal movement. Learning-based movement is clearly relevant to ecological problems, but the subject is rooted firmly in psychology, including a distinct terminology. We contrast this psychological origin of learning with the task-oriented perspective on learning that has emerged from the field of machine learning. We review conceptual frameworks that characterize the role of learning in movement, discuss emerging trends, and summarize recent developments in the analysis of movement data. We also discuss the relative advantages of different modeling approaches for exploring the learning-movement interface. We explore in depth how individual and social modalities of learning can matter to the ecology of animal movement, and highlight how diverse kinds of field studies, ranging from translocation efforts to manipulative experiments, can provide critical insight into the learning process in animal movement.Publisher PDFPeer reviewe