Influence of Habitat, Predation, and Spatial and Temporal Scales on Species Diversity and Distributions: Interactions Involving Crayfishes in the Laurentian Great Lakes and Inland Lakes

The discipline of ecology seeks to understand the abiotic and biotic factors that influence species diversity and distributions. Specific factors include interactions with other species and humans, habitat characteristics, and the position of these interactions and habitats within the landscape. My research examines species diversity and distributions in fresh waters. Historically, relatively little research has focused on benthic invertebrates in the littoral zone of lakes. However, because of the isolated nature of lakes, the increased impacts of non-native species in aquatic systems, and the diverse habitats of littoral areas, such systems are ideal for studying the drivers of species diversity and distribution. Additionally, by combining general ecology and invasion biology principles, I provide new management and conservation recommendations. My research uses crayfishes, focusing on the invasive rusty crayfish (Orconectes rusticus), as model organisms to examine the importance of predation, habitat heterogeneity and species spread, on species coexistence and ecological impacts. Doing so provides guidance to improve native species conservation and invasive species management within the littoral zone of lakes. Using a snapshot survey across multiple lakes, I show that habitat heterogeneity and predation are major drivers of where crayfish occur in the littoral zone. When exposed to multiple predators, crayfish distribute themselves across the three main littoral habitats (unvegetated cobble, unvegetated sand, and vegetated sediments) to minimize their risk of predation.Invasive crayfish can alter littoral zone food webs through herbivory and interactions with native crayfish. In one lake, I used a field experiment to demonstrate that invasive crayfish selectively remove aquatic vegetation, which can have cascading effects on the physical, chemical and biological dynamics of lakes. I used long-term data sets and surveys across multiple lakes, combined with field experiments in one lake, to demonstrate that the availability of the three littoral habitats influences whether native virile crayfish (O. virilis) are displaced by or coexist with invasive rusty crayfish. My combination of within-lake and between-lake analyses revealed that habitat availability and niche partitioning permitted long-term coexistence of native and invasive crayfish species. Considering cobble habitats (a habitat not affected by crayfish) across multiple lakes, results suggest that managers should target lakes with littoral areas comprised of Ì¢'¡å´ 25% cobble habitats for efforts to prevent the introduction of rusty crayfish. Such lakes (with abundant cobble), and the native crayfish they contain, stand to suffer the most if invaded by rusty crayfish. Finally, I provide a regional assessment of crayfish diversity and distribution at the Great Lakes scale over the past 100 years and the corresponding policies targeting invasive crayfish. The rate that rusty crayfish, the most wide-spread invasive crayfish in the Great Lakes, have been found in new locations significantly differs between lakes, reflecting the differences in near shore fish communities and human movement of crayfish. Although my baseline data demonstrate rusty crayfish have been in all Great Lakes for the past 20-30 years (and >100 years in Lake Erie), policies to prevent introductions of invasive species have been reactive rather than proactive. In addition, the effectiveness of policies that have targeted invasive crayfish in the Great Lakes region are limited by a lack of consistency across the states/province in the region to address the vectors that are moving non-native crayfish species.Overall, by combining small-scale experiments, surveys, and long-term datasets, I examined the underlying mechanisms that influence crayfish diversity and distribution, document crayfish dynamics, and develop management and conservation recommendations at lake, multi-lake landscape, and regional scales.