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Date of Graduation
Master of Science (MS)
Department of Biology
Recent studies in perennial streams have shown that reduction of stream-side vegetation can reduce terrestrial invertebrate inputs to streams and can cause trophic cascades throughout aquatic and terrestrial food webs; however, aquatic-terrestrial food web linkages have not been studied in intermittent streams. Food webs in intermittent streams may be even more dependent on terrestrial invertebrate fluxes because of limited aquatic invertebrate resources; thus intermittent streams may represent unique systems that warrant special attention. The objective of this research was first to quantify the abundance, biomass, and energetic content of available brook trout and insectivorous stream-side predator invertebrate resources in two Appalachian intermittent streams to determine how these resources vary with environmental factors such as stream flow and canopy cover. Secondly, the consequences of experimental reductions in terrestrial invertebrate fluxes on brook trout diet and other invertebrate resources were investigated. Total food resources for brook trout and insectivorous stream-side predators appear to be lower in intermittent Appalachian streams than other systems, and stream flow was the main factor driving resource availability. Terrestrial invertebrate resources only made up 7% of available resources, but made up 50% of brook trout diet. Insectivorous stream-side predators also appeared to be largely dependent on this resource, because, in contrast to studies in perennial streams, 73%-86% of emerging adult aquatic invertebrates fell back into the stream instead of feeding surrounding forest. Experimental reductions in terrestrial invertebrate resources resulted in a 43% decrease in abundance of winged terrestrial invertebrates, which cascaded into a 55% decrease in total brook trout consumption and reduced total caloric intake by 46%. In contrast to studies of other salmonids in perennial streams, brook trout did not switch to consuming more aquatic invertebrates when terrestrial invertebrates were experimentally reduced potentially due to competition with sculpin, other brook trout, or unavailability of benthic resources. Therefore, no trophic cascades occurred when terrestrial invertebrate fluxes were experimentally reduced, but land use changes that cause reductions in terrestrial invertebrate resources may detrimentally impact already stressed brook trout populations in intermittent streams by reducing caloric intake as fish prepare for fall spawning and by decreasing over-winter survival rates.
Courtwright, Jennifer Lauren, "Food web subsidies in intermittent streams: Implications for small isolated populations of native brook trout" (2012). Masters Theses. 178.