Thermal preferences drive behavioural responses but not biomass responses of predatory fishes to lake morphometry

Abstract

Top predators’ responses to environmental conditions are now widely recognized as a key part of understanding how changing food web architecture influences ecosystem structure and stability, ultimately determining the fate of ecosystems with environmental change. Yet the ways that fundamental ecosystem properties like size and complexity impact top predators’ behaviour are not well understood. We examined how lake morphometry impacts the behaviour of three key fish top predators—the cold-adapted lake trout, the cool-adapted walleye, and the warm-adapted smallmouth bass—which can each strongly shape local food web structure. We used a catch-per-unit-effort database of these key fish species in nearly 500 boreal lakes of Ontario, Canada to evaluate the role of thermal preference in driving behavioural and biomass responses to lake morphometry. We found strong evidence that species’ thermal preferences influence their responses to lake size, proportion of littoral area, and mean depth, but we found limited evidence that these species respond to lake shape. However, we did not find strong evidence that lake morphology influences these species’ biomasses. Our results suggest that some aspects of lake morphometry can alter habitat accessibility and productivity in ways that influence the behaviour and biomass of these top predator species depending their thermal preferences. Our results have strong implications for how the food webs of these lakes expand and contract with lake morphometry and other key abiotic factors. We argue that several key abiotic factors likely drive top predator behaviour in ways that may shape local food web structure and play in important role in determining how ecosystems respond to global environmental change.