The influence of energy availability on population-, community-, and ecosystem-level processes in cave stream ecosystems

Detritus from surface environments supplies the energy that shapes community structure and fuels productivity in most cave ecosystems. However, only qualitative descriptions of cave energy dynamics are available, hindering development of quantitative models describing how energy availability influences cave ecosystem processes. In contrast, the importance of detritus for surface ecosystem processes has been appreciated for decades. This dissertation begins to close this knowledge gap by exploring how energy availability shapes cave stream ecosystem processes at multiple organizational levels (ecosystem-, community-, population-level) and time scales (evolutionary vs. ecological).;Chapter Two examined potential correlations between litter breakdown rates and detrital storage, but found no such relationships among four cave streams. However, surface-adapted species dominated macroinvertebrate biomass, suggesting that surface-adapted taxa can have a significant influence on cave ecosystem processes. In Chapter Three, a whole-reach litter amendment was conducted to explore the influence of enhanced detrital inputs on cave community structure and energy flow. While the litter amendment significantly increased total consumer biomass via assimilation of amended corn-litter, the response was dictated by evolutionary history. Biomass of surface-adapted taxa increased significantly following the amendment, while biomass of obligate cave species remained unchanged. As in Chapter Two, consumer biomass was dominated by surface-adapted taxa, reinforcing their role in cave ecosystem processes relative to cave-adapted taxa, the traditional focus of cave studies.;Chapters Four and Five utilized a 5+-year mark-recapture data set on the cave-adapted crayfish Orconectes australis to explore how energy availability has shaped its evolutionary history and population dynamics. Time-to-maturity, age-at-first-reproduction, and longevity of O. australis were substantially longer than those estimated for most crayfish species, indicating evolution of a K-selected life history. Chapter Five found that biomass and secondary production of O. australis were positively related to resource availability. Energetic models indicated resource deficits were not present, but that nearly all prey production is necessary to support each O. australis population. Thus, inter- and intra-specific competition for resources within caves is likely high. Collectively, Chapters Four and Five provide the first quantitative explanation of why K-selected life histories are an evolutionary advantage to obligate cave taxa like O. australis..