Influence of Stream Permanence, Predation, and Invasive Species on Crayfish in the Ozark Highlands with an Emphasis on Species of Greatest Conservation Need (Orconectes marchandi, Orconectes eupunctus and Cambarus hubbsi)

Due to the ecological importance of crayfish and the increasing vulnerability of freshwater systems due to habitat loss, invasive species, and hydrologic alteration, understanding crayfish-environment relationships is crucial in the context of aquatic species conservation. I sought to examine the influence of hydrologic variation among intermittent and permanent streams on crayfish occupancy, abundance, predation risk, and potential vulnerability to invasive species effects. I conducted crayfish and environmental data sampling during two consecutive summers across 20 Ozark streams of differing permanence levels (10 intermittent, 10 permanent). In these same streams, I conducted fish and scat surveys over the course of four seasons. In addition, I performed population modeling based on previously collected data to understand the population dynamics of three crayfish species of greatest conservation need (Orconectes eupunctus, Orconectes marchandi, and Cambarus hubbsi) in the Spring River drainage of Arkansas and Missouri and assess their risk of invasive species and drought effects. I determined that occupancy of all crayfish species collected in my study was related to stream permanence. In most cases, crayfish abundance was largely related to stream permanence rather than local habitat. I documented that two species of conservation concern (i.e., Orconectes williamsi, Orconectes meeki) appear dependent on intermittent streams. Stream permanence, however, did not appear to influence crayfish predation by riparian mammals in my study. Crayfish predation pressure by mammals appeared to be determined by season and was strongest in spring and summer. The prevalence of fish prey in mammalian diets appeared to be strongly influenced by a season by stream permanence interaction, and this may be the first study to document such an observation. Lastly, my population modeling procedure indicated the potential of the Spring River to serve as a refuge for O. eupunctus and C. hubbsi when invasion and drought effects are strong in the surrounding area. Conversely, the Spring River appears to serve as a barrier to dispersal for O. marchandi which could result in high extinction risk of the population under invasive species effects. This thesis adds to the knowledge of flow-ecology relationships and invasive species effects in the Ozark Highlands