Predator-Prey Interactions

Our lab has a longstanding interest in predator-prey relationships, as well as related interactions between parasites and hosts, and herbivores and plants.  We address questions in predator-prey ecology either using experimental studies involving tadpoles and their predators, or through field studies with a variety of mammal, bird and reptile species.

Phenotypic plasticity

Prey have the well-known ability to detect predation risk via signals transmitted by the predator. In aquatic systems, such information is released through chemical cues, of which surprisingly little is known.  We have identified the unique chemical structure of some predator chemical cues, and have quantified how they affect behaviour and morphology of tadpole prey.  We are in the process of examining prey fitness tradeoffs activated by these cues, whether cues originate exclusively from predators or prey rather than being released as by-products of prey digestion, and how prey-mediated cues may help increase their inclusive fitness.  Of particular interest are questions related to how prey can balance behavioural and morphological adaptations to predation risk by means of these cues, and how the proper balance between behaviour and morphology may affect responses to other challenges faced by prey, such as malnutrition or disease.

Predation risk avoidance

Individual prey exhibit behaviours that might go unnoticed except for the fact that they contribute to increased vulnerability to predation, either directly or through interactions with other factors.  Central to this area of research is the starvation-predation risk tradeoff hypothesis, which addresses how prey should balance ongoing and conflicting demands of food acquisition vs. predation avoidance.  We are examining how prey assess the various risks they are faced with and how they adjust their behaviour to conform to such risks.  We are especially interested in how prey decisions related to the starvation-predation risk gradient can be altered dramatically by varying the spatial or temporal distribution of risks and rewards in the environment.

Prey selection and mortality patterns

Predators can have profound effects on prey survival, and prey that are killed by predators are not exclusively sick and lame individuals as was formerly thought.  A variety of subtle conditions and behaviours predispose individual prey to predation risk, but prey selection patterns tend to be quite variable among different populations or time periods, making it difficult to develop general rules of thumb about who will get killed.   In addition, prey selection patterns can be strongly influenced by the hunting tactics employed by the predator involved in the encounter, leading to the logical question of how prey selection and risk are shaped by prey attributes vs. predator hunting tactics.  We are also interested in the impacts of selective prey mortality on prey populations; this work usually involves monitoring prey survival and cause-specific mortality, and making population-level inferences about likely outcomes of prey selection.  Inevitably, this research takes us down the path of assessing subtle prey risk determinants, predator functional responses, prey refuge use patterns, and predator hunting strategies.

Predator-prey population cycles

Our longstanding interest in the role of predation on prey populations has led us to study predator-prey population cycles via analysis of numerical time series.  However, as ecologists we are primarily driven by an interest in studying the animals themselves rather than simply their numbers, leaving us at a loss for observing fluctuations in  mammal species that only cycle every 10 years or so. This frustration has prompted new research into predator-prey population dynamics using a model system involving microscopic prey and predators.  The advantage of this system is that generation times are measured in days rather than years, and simple perturbations that are fundamental to the predator-prey interaction can reveal profound changes in population trajectories. Using this system we aim to address broad questions related to the source of time lags in predator numerical responses and how these lags affect prey population instability, as well as the role of alternate prey or habitat heterogeneity in stabilizing prey populations and dampening cycles.

Population Ecology

Our work in population ecology broadly encompasses assessment of the sources of population growth and decline. This research involves a range of methods and systems to estimate survival and productivity, as well as analysis of population time series towards understanding patterns of numerical growth and regulation.

Patterns of density dependence

It is well understood that animal populations are regulated by density dependent forces, but there are different patterns by which density dependence can be manifest on population growth.  Currently, there is considerable controversy regarding appropriate statistical models to describe growth and regulation in single-species populations.  Moreover, it is not clear how density dependence may vary in space and time in populations inhabiting complex environments.  Using breeding waterfowl survey data, we are examining why patterns of density dependence in numbers of breeders has varied fundamentally through time.  We suspect that environmental change promoting increased nest predation by generalist predators is driving the waterfowl system to a state of increased stochasticity.  We are extending this work to gauge whether large-scale changes in landscape or climate features contribute to variability in density dependence, population asynchrony, and numerical stability. We are further developing this area of research using algae grown in experimental microcosms, to test in a more controlled manner questions addressing population responses to perturbation and density-dependent regulation.

Vital rate estimation

Demographic rates are the metrics by which populations grow and decline, and it is important not only to estimate these rates accurately but also to understand the sources of their variability.  We work on questions related to vital rate estimation in a range of mammal species, and we assess the role of biotic and abiotic factors in causing changes in those rates.  Of particular interest is the estimation of survival and competing risks in species such as wolves and snowshoe hares, and towards this end we have been at the forefront of adapting time-to-event statistical methods to analyze survival data obtained from wildlife telemetry data.  Among the novel inferences made available via these analytical methods are whether anthropogenic factors play an additive or compensatory effect on mortality patterns, and how different predator species may select unique types of individuals from the prey population. 

 Conservation Biology

A fair bit of our research involves questions of applied relevance, both for logistical reasons (it is easier to find funds to work on wolves than tadpoles!), as well as because for many of us our interest in ecology grew directly out of a desire to make a difference for populations and species under duress.  Not surprisingly, our research in the realm of conservation biology involves mostly the big furry species. 

Population viability assessment and species range limits

We have been involved in assessing the status of several populations, and currently we are active in population viability analysis and range limit determination towards understanding why some populations are imperiled. These efforts tend to be multidisciplinary and involve several collaborators, a range of study systems, and include work such as population genetics, landscape ecology, population ecology, climate analysis, habitat and nutritional ecology, and anthropogenic disturbance assessment. 

For instance, we recently completed a comprehensive study of a declining moose population in Minnesota, and showed that the combined effects of climate change, parasitism, and poor nutrition are involved in the dieoff, and in the foreseeable future these factors likely will drive the population to extinction.  Consequently, we predict that over the next decades a widespread northward push of the distributional limit for moose will occur.

Currently, we are undertaking assessment of the causes of range recession and numeric decline in Canada lynx populations.  Several factors may be implicated in this decline, including isolation of southern populations due to habitat fragmentation and loss of population connectivity, climate change and its effects on winter snow cover and snowshoe hare abundance, and hybridization with bobcats or competition with coyotes. Our work involves the analysis of genetic samples, landscape attributes, as well as population time series for lynx, their prey, and their competitors.  Because lynx are listed in the contiguous United States and populations in several Canadian provinces also are faced with decline, this work has notable conservation relevance.

Our second effort in this area concerns the viability of an introduced red wolf population in North Carolina, and the southern extent of eastern wolf distribution in south-central Ontario.  In both cases, hybridization with coyotes appears to be a driving factor affecting the range and abundance of wolves.  Near the southern edge of Algonquin Provincial Park, we are studying wolves along a hybrid zone with coyotes and documenting differences in population and habitat ecology of the two groups.  We suspect that coyotes act as a ‘hybrid swarm’, and that over the long term hybridization could impose a major threat to the genetic integrity of the wolf population in the Park.  Because the Park holds the closest genetic remnants to the original eastern wolf species, this research will be critical in understanding the likelihood of the species’ long-term viability both in the Park as well as across its range in Ontario and Quebec.

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