Warming Strengthens the Ecological Role of Intraspecific Variation in a Predator

Abstract

Recent work shows communities and ecosystems can be shaped by predator intraspecific variation, but it is unclear whether the magnitude and direction of these influences are context-dependent. Temperature is an environmental context of strong ecological influence and widespread relevance given global warming trends. Warming should increase per capita predator effects on prey through increases in predator metabolic rate, potentially exacerbating intraspecific differences in ecological effects. Here, we used two populations of the potent pelagic freshwater predator, WesternMosquitofish (Gambusia affinis), to test how experimental pond temperature mediates the differences between their ecological impacts. Mosquitofish introduction induced a strong pelagic trophic cascade, causing a large reduction of crustacean zooplankton biomass, an increase in phytoplankton biomass, and changes to ecosystem-level response variables. Warming (+/- 28 degrees C above unwarmed treatments) exacerbated fish-induced reduction of zooplankton biomass, but moderated the cascade to phytoplankton, primary productivity, and nutrient concentrations. Effects of intraspecific variation were apparent only on zooplankton, and only at warmed environmental temperatures. The traits underlying this divergence may be related to the population source thermal environments. Overall, results show that warming may increase the ecological importance of predator intraspecific variation. In general, extrinsic environmental drivers, such as those associated with climate change, may reshape the effects of intraspecific trait variation on ecosystems.