Disturbance, competition and the invertebrate predator guild of high gradient coastal streams

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Understanding the ecological and evolutionary factors that determine the biodiversity and species composition of communities is one of the most important scientific challenges today, in part because it is a pre-requisite to predicting the consequences that human activities will have on ecosystems. It is also one of the most daunting challenges. Even though disturbances (e.g. fires, hurricanes, floods) are a normal part of many ecosystems, they have variable short and long term effects on community structure. Disturbance, defined as a discrete event removing individuals or biomass, can exclude species, lead to the inclusion of more species, alter relative abundances, and/or change the physical or biotic environment of a community. In this study I look at the consequences of disturbance in streams (floods) in the light of its effect on coexistence with the guild of predatory invertebrates (stoneflies and caddisflies). Since trade-offs between competitive ability and response to disturbance can affect the number of coexisting competitors, the critical measurements are sensitivity to the disturbance and sensitivity to competition. I propose to use a 3-pronged approach to examining the role that disturbance in the form of flow variability plays in the coexistence of invertebrate predators in high gradient, coastal streams. I will determine (1) if (and how) species richness of invertebrate predators is related to disturbance regime, (2) the primary mechanisms by which disturbance affects species coexistence within the predator guild and (3) how and why disturbance varies among streams (geology, geomorphology, land use).