Date of Graduation

5-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor

Michelle A. Evans-White

Committee Member

Steven J. Beaupre

Second Committee Member

Daniel D. Magoulick

Third Committee Member

J T. Scott

Fourth Committee Member

Sally A. Entrekin

Keywords

Biological sciences; Earth sciences; Detritus; Ecological stoichiometry; Microbial ecology; Phosphorus; Stream ecology

Abstract

A widespread stressor, anthropogenic nitrogen (N) and phosphorus (P) pollution can increase resource nutrient content and alter animal community composition in freshwater ecosystems. In this dissertation, I used ecological stoichiometry theory to examine effects of diet nutrient content and leaf litter type on growth, regulation, and wastes of aquatic invertebrate detritivores. I tested effects of leaf litter diet carbon:phosphorus (C:P) on growth and stoichiometric regulation of the detritivorous caddisfly Pycnopsyche lepida and used results to determine a threshold elemental ratio of oak litter C:P=1620 that confers peak growth of this species. This empirical, growth-based approach provided a more accurate estimate of the threshold elemental ratio compared to current bioenergetics models. Subsequent experiments used 33P and 14C as microbial tracers to examine effects of diet leaf type and nutrient content, as well as taxonomic identity, on incorporation efficiency of microbial C and P by the detritivorous caddisflies Pycnopsche lepida, Lepidostoma sp., and Ironoquia sp. Results showed no effects of leaf type on incorporation efficiencies, however elevated litter P content reduced caddisfly incorporation efficiency of microbial P, and there were inverse relationships between caddisfly body C:P content and incorporation efficiencies of microbial C and P, suggesting stoichiometric links of detritivore growth rates and P requirements to reliance on litter microbial nutrients. Given the stoichiometry of growth and regulation can vary across diets and taxa to affect production and composition of animal wastes, I also examined effects of litter type and nutrient content on the stoichiometry of particulate wastes from the detritivores Pycnopsyche lepida, Lepidostoma sp., and Tipula abdominalis. Higher litter N and P content increased N and P content of particulate wastes, but the strength of effects often differed between maple and oak litter and Tipula abdominalis produced N- and P-deplete wastes compared to Pycnopsyche lepida and Lepidostoma, indicating potential taxonomically variable effects of animals on the stoichiometry of fine particulates in streams. Finally, I conducted a long-term study of C, N, and P dynamics of decomposing egesta from the detritivorous taxa Tipula sp., Lirceus sp., and Allocapnia sp. fed low- or high-P litter. Egesta from Allocapnia and Tipula decomposed faster than egesta from Lirceus, and elevated P content of egesta increased total uptake of dissolved N by egesta during decomposition. Together, my findings provide evidence that, by increasing litter nutrient content, anthropogenic nutrient pollution alters multiple species-specific functional roles of detritivorous animals in aquatic ecosystems.

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