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THE INFLUENCE OF ENERGY AVAILABILITY
ON POPULATION-, COMMUNITY, AND
ECOSYSTEM-LEVEL PROCESSES IN
CAVE STREAM ECOSYSTEMS
Michael P. Venarsky
Dissertation Defense
Date: Thursday October 25th
Time: 3pm
Location: Bevill Building room 1000
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
crayfishOrconectes 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. australiswere
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 intraspecific 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