Doctor of Philosophy / Division of Biology / Keith B. Gido / This dissertation consists of three research-based chapters which focus on habitat association of prairie stream fishes and how these fish communities influence stream ecosystem properties. Chapter one introduces important concepts used throughout the chapters, and describes my study streams. In chapter two, I identify local habitat factors associated with the diversity and density of fishes in two protected prairie watersheds. Specifically, the relative importance of habitat factors associated with fish communities were evaluated along a stream-size gradient and across multiple seasons and years. I found that species richness was positively associated with pool area and discharge. Redundancy analyses showed common prairie fish species exhibit ontogenetic habitat associations, with adults in deep and juveniles in shallow pools. Chapter 3 addresses how fish species richness in small prairie streams affects whole-stream metabolism and biomass distribution of benthic organic matter, algal and macroinvertebrates. This study was conducted by stocking experimental stream mesocosms that included pool-riffle habitats with three different communities that represent a gradient of species richness of headwater prairie streams from one to three common prairie stream fish species. I illustrated how species influence ecosystems across multiple spatial scales and found that different communities altered the distribution of algal biomass from benthic surfaces to floating mats and from pools to riffles. The objective of the fourth chapter was to quantify how two size classes of herbivorous prairie stream fish species, central stoneroller Campostoma anamolum and southern redbelly dace Chrosomus erythrogaster differentially affect stream ecosystem properties. This study was also conducted in experimental stream mesocosms, where each unit consisted of one riffle and one pool. Using ANOVAs, I found large dace were associated with longer filaments (F = 7.5, P = 0.002, df = 4) and small fishes with less benthic organic matter (F = 4.2, P = 0.02, df = 4). There was no evidence for ontogenetic shifts in diet and likely differences in energetic requirements and behavior drove the differences among treatments. My research finds that small-bodied prairie stream fishes have predictable habitat preferences and effects on stream properties are dependent on species identity, richness and size structure.

Fish can have complex life histories and use multiple habitats and resources throughout their life span. Consequently, their life histories are often poorly understood. The Atlantic Tarpon, Megalops atlanticus, is a large, typically migratory, elopomorph fish that is both ecologically and economically important. Atlantic Tarpon are under threat due to regional exploitation, loss of natal and juvenile habitat, poor water management, and offshore impacts. In addition, little is known about its lifelong habitat and resource use. In Chapter 1, I used stable isotope analysis of eye lens δ13C and δ15N values to explore patterns in trophic history and habitat use of 16 Atlantic Tarpon from West-Central Florida and Louisiana. The stable isotope chronologies showed 100% use of backcountry habitats during the early life history and an ontogenetic habitat shift to coastal waters at approximately 10 years of age and 140 cm total length. During the coastal phase Atlantic Tarpon displayed among-individual variability and within-individual consistency in basal resource use. In Chapter 2, mark-recapture data from a multi-year genetic tagging program were used to investigate survival and growth rates, ontogenetic habitat use, and migration of juvenile Atlantic Tarpon in Florida. The study found that juvenile Atlantic Tarpon take approximately 10 years to reach the length associated with maturity, and appear to have a high survival rate (~80%), possibly due to effective use of habitats with reduced competition and predation. Atlantic Tarpon underwent several ontogenetic habitat shifts throughout the juvenile phase. In addition, juvenile Atlantic Tarpon did not migrate long distances but instead showed fidelity to systems wherein only short movements were needed to shift habitat types. This work serves to fill critical gaps in our knowledge of Atlantic Tarpon life history and may aid in better management and conservation of the species.