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Temperature Effects on Warmwater Stream Insects: A Test of the Thermal Equilibrium Hypothesis

Emily H. Stanley and Robert A. Short
Oikos
Vol. 51, No. 3 (Mar., 1988), pp. 313-320
Published by: Wiley on behalf of Nordic Society Oikos
DOI: 10.2307/3565312
Stable URL: http://www.jstor.org/stable/3565312
Page Count: 8
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Temperature Effects on Warmwater Stream Insects: A Test of the Thermal Equilibrium Hypothesis
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Abstract

Population density and biomass, individual size, and life cycles of mayflies were determined in two Texas (USA) streams to test predictions of Vannote and Sweeney's Thermal Equilibrium Hypothesis with warmwater stream insects. Population density and biomass patterns corresponded well with each other for most but not all species. Austral mayflies at one site (Blanco River) had high summer but low winter densities while fecundity of mature female larvae was lowest in the summer and greatest during the winter. Female size and population density were less predictable at the second site (Honey Creek). At both sites, all species had highly asynchronous, overlapping cohorts, indicating that many generations are completed within one year. Although some results were in agreement with predictions of the hypothesis, other findings were inconsistent. Dominating abiotic conditions such as flooding or intermittence may favor rapid growth and development at the expense of egg production for warmwater mayflies. Due to the prevalence of multivoltinism, thermally optimal conditions are a function of both location and time. Additionally, population level characteristics are more appropriate indicators of thermal optimality than is individual body size of mature larvae or adults.

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