Vernal Pools IV: Effects of Depth and Temperature on Pelagic Community Composition
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SubjectScholarship Sewanee 2011; University of the South, Sewanee, Tennessee; Undergraduate research; Vernal pools; Species abundance and diversity; Temperature; Depth
AbstractVernal pools, in broad terms, are rain-fed wetlands that develop in shallow depressions over impervious surfaces (Keeley and Zelder 1998) and are a hot spot for invertebrate, salamander, and bird diversity (Scheffers, et al. 2005). Without established fish populations, vernal pools host a prolific range of “avoider” and “tolerator” species, many of which remain vulnerable to even the slightest variations in water temperature and depth regardless of their specializations (Colburn 2004). Because of the pools’ relative isolation, only these highly specialized organisms are capable of inhabiting them. The Southeastern United States, known for its pronounced granite outcroppings, has unique vernal pools that differ hydrolytically and temporally from other regions in the U.S. (Keely 1991). In particular, the period between late winter and late spring contains the highest levels biotic and abiotic change throughout the year (Colburn 2004). One notable consequence of being primarily rain-fed is that most vernal pools are nutrient poor. Because of the high surface to volume ratio of the mostly shallow vernal pools, most experience high daily variations in temperature (Keely 1991). It is unknown how localized variance in temperature and precipitation will affect the already delicate balance of vernal pool life histories in Sewanee, Tennessee. For this study, several crustacean species were examined for their direct life history relations to documented trends in vernal pool abiotic change. Copepods are small crustaceans that inhabit nearly every freshwater habitat in the United States. Their life history can range from between one week and one year, depending on the species. Huntley and Lopez (1992) showed that temperature alone explains over 90% of the variance in growth rates between the 33 species of copepod. Copepods are not the only contributor to vernal pool community structures, but are good indicators of overall ecosystem health. Uye (1981) showed that maximum copepod longevity decreases with increasing temperature, likely due to higher metabolic demands at higher temperatures. To observe these communities, we chose to take measurements of pelagic crustacean diversity and abundance. Our study sites spanned six well-documented vernal pools on the Cumberland Plateau in Sewanee, Tennessee. We hypothesized that vernal pool depth and temperature would affect pelagic morphospecies abundance and diversity over time.
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