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Thermal history mediates the ecological role of body size in a freshwater fish

Moffett, Emma1; Fryxell, David23; Perry, George2; Palkovacs, Eric3; Simon, Kevin2

Published Jul 03, 2025 on Dryad. https://doi.org/10.5061/dryad.qv9s4mwsd

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Abstract

Intraspecific trait variation among populations may strongly alter community and ecosystem structure and function. Body size is a fundamental trait of all organisms, affecting both organismal physiology and ecological effects, which may differ across populations. For example, body size is predicted to decline with warming. As such, in this study, we aim to determine how population differences in thermal history mediate the ecological role of body size in a freshwater fish. We conducted a mesocosm experiment in which we manipulated fish (Gambusia affinis [Baird and Girard, 1853]) source populations (ambient source vs warm source) and body size while holding their biomass constant. We monitored community and ecosystem response variables including, macroinvertebrate abundance, zooplankton biomass, phytoplankton abundance, and greenhouse gas flux. Changes in fish body size influenced most ecological responses, but these effects often depended on the thermal history of the fish population. For many responses, the effects of reduced fish body size were offset by a history of exposure to warm temperatures, suggesting that environmental factors (including thermal acclimation) and adaptation may offset the community and ecosystem effects of decreased consumer body size. Our research suggests that ecological changes will depend on changes in body size and environmental factors, as well as on other trait changes associated with warming. Experiments and models addressing the ecological effects of body-size decline alone may overestimate the ecological changes expected under warming.