A Multi Scale Approach To Evaluate The Effect Of The Invasive Aquatic Plant Hydrilla Hydrilla Verticillata On Littoral Zone Habitat Of Juvenile Largemouth Bass Micropterus Salmoides PDF Download

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 (italicOrconectes rusticusitalic) 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, italicLepomisitalic spp., and other fish predators using multispecies autoregressive models. Model results predict that rusty crayfish exclude italicLepomisitalic spp. under high water conditions, italicLepomisitalic 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 italicLepomisitalic 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 (italicO. virilisitalic) crayfish increased by two orders of magnitude, and italicLepomisitalic 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 italicLepomisitalic spp. and other littoral taxa are critical in determining the community structure, particularly in macrophyte habitat.