California Sea Grant College Program

Biological invasions are among the leading causes of the loss of biodiversity worldwide. Although there are many hypotheses about traits of a good invader and characteristics of native communities that increase susceptibility to invasion, the realized success of an exotic species is likely a combination of both species and community traits. This dissertation takes a multi-stage approach to examine how behavioral traits of an invader, along with characteristics of invaded communities influence the distribution, establishment and impact of the signal crayfish (Pacifastacus leniusculus) in freshwater stream communities. I begin in chapter one by providing an overview of each stage of the invasion process along with invader traits and community characteristics important at each stage. I then describe the patterns of crayfish invasions and provide background on the systems studied in this dissertation. In chapter two, I evaluated how native species diversity, the presence of an ecologically similar species, prey availability and stream discharge influenced the distribution and abundance of signal crayfish at fine and broad spatial scales. In chapter three, I tested whether the presence of an ecologically similar species (e.g. native crayfish) influenced the aggressiveness, activity and voracity of signal crayfish. Finally, in chapter four I evaluated the consequences of high abundances of signal crayfish on native prey and the behavior of signal crayfish. Accumulated evidence suggests that signal crayfish possess the behavioral traits (e.g. a general aggression syndrome) to overcome many challenges faced during the invasion process, but that characteristics of the invaded community (e.g. prey availability and physical attributes of streams) provide some resistance against signal crayfish reaching high abundances. When native communities do not offer much resistance (i.e. abundant prey and low flood disturbances), signal crayfish often invade at high abundances that result in large impacts on native species. The patterns and results suggest that the communities with high prey availability and infrequent disturbances are most at risk of invasion, but that the aggressive nature of this invader makes most communities vulnerable to invasion.