Causes and consequences of ecological gradients in southwestern Appalachian streams of Alabama: insights from fish, fish parasite, benthic macroinvertebrate, and crayfish assemblages

Abstract

Biodiversity in freshwaters is highly threatened by short-term and long-term anthropogenic impacts such as landuse-landcover change (e.g., resource extraction, urbanization) and climate change, respectively. One complication for biodiversity conservation is that biodiversity is patchily distributed among freshwater habitats, and thus documenting spatial distribution of biodiversity is important for prioritizing conservation efforts. On a smaller scale, biodiversity often corresponds to various environmental gradients and tends not to be evenly distributed among streams within a network. At both the community and population levels, biodiversity can be influenced by habitat characteristics and connectivity among locations. The southeastern US, including Alabama, is an aquatic biodiversity hotspot where most of this diversity occurs in streams and rivers. I studied streams in the Southwestern Appalachians ecoregion of Alabama to investigate the spatial distribution of 1) taxonomic diversity among assemblages of fishes, macroinvertebrates, and fish parasites and 2) genetic diversity in 2 species of crayfishes. In Chapter 2, I developed tools (Ecological Endpoint Curves; EEC) for resource managers to assess the biotic integrity of fish assemblages in small streams of this ecoregion and compared these to a previously developed index of biotic integrity (IBI) for stream fishes. I found that EECs may be more appropriate assessment tools than an IBI for small stream fishes because several IBI sub-metrics are strongly influenced by the low species richness of fish assemblages naturally occurring in these streams. In Chapter 3, I described the spatial distributions of fish and macroinvertebrate diversity as they related to stream size within the iii stream networks of this ecoregion. Results suggested that large streams, where fish richness was highest, are essential for conservation efforts, whereas headwater streams should be prioritized for conservation efforts targeting macroinvertebrates because taxa richness was evenly distributed among streams of different sizes and headwaters necessarily outnumber larger streams. In Chapter 4, I investigated stream size–diversity relationships in fish parasites communities and report strong stream size–parasite richness relationships, which may have important ecological and evolutionary implications for their host (Etheostoma artesiae). In Chapter 5, I investigated the association between the spatial distribution of genetic diversity and crayfish burrowing and habitat use traits using 2 sympatric crayfishes (Cambarus striatus Hay and Faxonius validus Faxon). Results suggested that crayfish burrowing behaviors and habitat use traits are useful in predicting population genetic structure, and also may reflect cryptic diversity in F. validus, which may require conservation attention.