Spatiotemporal variation in the impacts of biological invasions

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Nonindigenous species are being discovered in aquatic ecosystems at increasing rates worldwide. Many of these invasions appear to have minor ecological effects, while others cause substantial changes to biodiversity and food webs. Our capacity to predict which invasion will have undesirable consequences is impeded by context dependence: invader impacts vary across space and time under the influence of local environmental conditions. The long-term goal of my research program is to develop models that explain and predict the impacts of biological invasions. The aim of this proposal is to explore context dependency by testing hypotheses that explain spatiotemporal variation in impact. Three major hypotheses are the focus of this proposal: 1) the Invasion Front Hypothesis predicts that more recent invaders such as those at the front of a spreading population will exert higher impacts associated with higher feeding rates and heightened aggression, whereas individuals from longer established core populations will be less voracious and aggressive; 2) the Environmental Matching Hypothesis predicts that an invader will produce stronger per capita effects in an abiotic environment that closely matches its physiological optimum; and 3) the Resource Consumption Hypothesis predicts that the most disruptive invasive species have higher and more efficient resource consumption rates than those species without extensive invasion or impact histories. I will use a combination of lab and field experiments on fishes and crustaceans in a variety of freshwater and marine habitats as model systems. Treatments with increasing prey abundances will be offered to invasive predators, and the number of prey consumed will be related to prey supplied in a classical functional response experiment that will allow us to quantify per capita effects. Context dependency will be incorporated by comparing per capita effects across gradients of temperature, water chemistry and water velocity. These lab experiments will be complemented by field mesocosm experiments involving reciprocal transplants between the invasion front and core sites where the invader is well established. Field sites will incorporate natural environmental gradients. In testing these hypotheses, my lab will identify and develop some valuable model systems that can be used to inform invasion theory, and we will demonstrate how environmental context can be incorporated into risk assessment.