A Multi-Faceted Approach to Understanding Drivers and Consequences of Aquatic Invasive Species Impacts

Understanding factors regulating the abundance and impact of invasive species is a major management and research challenge. I examine invasive species and their impacts on a variety of scales. In Chapter 1, I quantify the landscape-level abundance patterns of aquatic invasive species from a variety of taxonomic groups. Invasive species follow similar distributional patterns as native species; all species are rare in most locations. However, invasive species on average reach higher abundances than their native counterparts. Chapters 2--4 focus on the experimental removal of rusty crayfish (Orconectes rusticus) from a north temperate lake. Rusty crayfish were removed from Sparkling Lake, Wisconsin from 2001--2008, and monitoring of crayfish and other ecosystem parameters continued through 2011. In Chapter 2, I quantify the relationship between rusty crayfish, removal trapping, water level, Lepomis spp., and other fish predators using multispecies autoregressive models. Model results predict that rusty crayfish exclude Lepomis spp. under high water conditions, Lepomis spp. exclude rusty crayfish under low water conditions, and at intermediate water levels alternative stable states exist whereby each species can exclude the other. Bootstrapped parameter estimates show that the existence of alternative states is uncertain, but rapid transitions from Lepomis spp. to rusty crayfish domination as water level increases were predicted under all parameter sets. In Chapter 3, I quantify the population and ecosystem-level effects of the removal of the rusty crayfish from Sparkling Lake. Rusty crayfish declined in abundance by two orders of magnitude. Native (O. virilis) crayfish increased by two orders of magnitude, and Lepomis spp. and macrophyte cover also increased throughout the experiment. The benthic macroinvertebrate response was variable among taxonomic groups and habitat types, reflecting the multitude of indirect effects through which rusty crayfish can influence littoral communities. In Chapter 4, I use a qualitative food web modeling approach to evaluate the importance of community interactions in determining the response to the rusty crayfish removal. Rusty crayfish strongly interact directly with gastropods and macrophytes in both habitat types, but interactions between Lepomis spp. and other littoral taxa are critical in determining the community structure, particularly in macrophyte habitat.