Interference competition: consequences for individuals and populations

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Wild populations fluctuate in size over time, but typically between upper and lower limits. A fundamental goal of population ecology is to determine the factors that provide these limits. While population regulation is clear from the census of numerous populations over time, the actual mechanisms responsible for the regulation are less obvious, perhaps due to a paucity of large-scale field experiments. ******Salmonid populations in streams have emerged as important model systems for studying population dynamics, both for their tractability as experimental systems, and their importance to the economic and cultural lives of Canadians. Long-term observational studies suggest density-dependent population regulation in freshwater environments and density-independent regulation in marine environments. Our previous work has described how the territory size of individual juveniles in streams change in response to key environmental factors. In particular, we showed that territory size decreases towards an asymptotic minimum size with increasing population density, potentially providing the ultimate limit to the number of individuals that a stream can produce. However, there is a lack of experimental evidence to link what happens at the individual level to the dynamics at a population level. ******In this proposal, we take a field, experimental approach to address the gap in our understanding between the behavioural ecology of individuals and the dynamics of salmonid populations. In a series of field experiments, we will determine the relative importance of the three primary mechanisms of population regulation in stream salmonids: density-dependent mortality, emigration/dispersal, and individual growth rate. We will manipulate the density and size structure of young brook trout in small sections of streams to describe the population dynamics and infer the mechanisms of competition in replicate streams in Cape Race, Newfoundland. In collaboration with fisheries biologists with the U.S. Fish & Wildlife Service, we will manipulate the number of young Atlantic salmon that are stocked into multiple stream reaches in a Lake Champlain watershed to determine the behavioural mechanisms responsible for dispersal, and whether dispersal is density dependent or not. At our long-term field sites in New Brunswick, we will test whether adding boulders to streams is a viable long-term method for restoring habitat complexity and increasing the density of juvenile Atlantic salmon in streams. ******This proposal will provide fundamental insight into the population dynamics of a model vertebrate system. Our results will also have practical implications for how to manage, harvest and restore these valuable fish populations. My students will receive training in pure and applied ecology, allowing them to pursue careers in academics, fisheries biology and conservation science.