Aquatic insect adaptations to different flow regimes

Graduation date: 2010My thesis explored the effects of environmental variability on population\ud dynamics and community composition of aquatic insects. Environmental variability in\ud the form of flow regime in streams can limit the distribution and life-history traits of\ud aquatic insects. I used tributaries to the McKenzie River in Oregon with dramatically\ud different flow regimes to compare aquatic insect community composition (Chapter 2).\ud Runoff-dominated streams were responsive to precipitation events and had high flow\ud events in the winter and dried down in the summer. Spring-fed streams had a\ud relatively steady flow regime year round. Streams categorized as runoff-dominated\ud had distinctly different taxonomic composition of aquatic insects compared to streams\ud designated as having a spring-fed flow regime. Larval Ameletus (order\ud Ephemeroptera) and Calineuria (order Plecoptera) were prominent indicator genera\ud for runoff-dominated streams while Caudatella (order Ephemeroptera) and Yoraperla\ud (order Plecoptera) were prominent indicator genera for spring-fed streams.\ud Additionally, life-history trait indicators for spring-fed streams included\ud semivoltinism, poorly synchronized emergence, and slow seasonal development. These analyses suggested that there were community level differences between\ud seasonally fluctuating and relatively constant flow regimes.\ud My thesis investigated population-level differences in life-history traits of an\ud aquatic insect species that is found in both runoff-dominated and spring-fed streams\ud (Chapter 3). Cohort patterns of Yoraperla nigrisoma were distinctly different between\ud both stream types. At the end of the summer, spring-fed streams had three distinct\ud cohorts, while runoff-dominated streams had two distinct cohorts present. Yoraperla\ud nigrisoma in spring-fed streams have a more consistent growth rate year round, and\ud they emerge at a larger size and have more cohorts present than in runoff-dominated\ud streams. These analyses suggest that flow regime type is highly associated with these\ud life-history differences.\ud My thesis explored whether life-history trait differences at the population level\ud are phenotypically plastic to environmental conditions in the short term (Chapter 4).\ud The variability in sources of phenotypic variation may be due to the presence or lack\ud of phenotyically plastic factors. I conducted a reciprocal transplant experiment to\ud quantify the effects of environment on life-history traits of Yoraperla nigrisoma.\ud Insects from the spring-fed stream that were transferred to the runoff-dominated\ud stream sped up their development, which was measured by change in head width over\ud time. Also, newly-emerged adults showed differences in head width and biomass\ud between treatments, but the small sample sizes associated with these results should be\ud considered. Overall, both phenotypically plastic factors and factors lacking phenotypic plasticity affect life-history traits between the runoff-dominated and\ud spring-fed stream