The strengths of consumer-resource interactions are fundamental to food web stability. Evidence is mounting that food webs are adaptive, whereby local environmental conditions shape the consumer-resource interactions by influencing how consumers forage. Ecological theory suggests that ecosystem size might be a crucial factor in driving how consumers forage because high-trophic-level species often couple spatially distinct habitats through their foraging. This coupling of habitats may have strong stabilizing effects in large ecosystems; however, in small ecosystems, this coupling may result in strong top-down suppression of prey species, resulting in top-heavy food webs and local extinctions. There has been limited empirical evaluation of whether interaction strengths among predator and prey magnify in smaller ecosystems and whether these strong interactions impact the co-occurrence of predators and their prey. We test this idea using standardized fish catch data from 721 lakes in Ontario, Canada to examine the co-occurrence patterns of key nearshore and offshore predator-prey species pairs across a range of lake sizes.
Results/Conclusions
We found evidence that top-down interactions intensified as lake size decreased, impacting the co-occurrence of predators and prey species. We found that offshore predator-prey pairs (e.g., lake trout and cisco) occur less often than expected by chance in small lakes but about as often as expected by chance in large lakes. However, we find only limited evidence that nearshore predator-prey pairs (e.g., walleye and yellow perch) occur less often than expected by chance in small lakes. These results support the notion that ecosystem size can drive predator-prey interaction strengths and influence the co-occurrence of predators and prey, but these effects may differ between habitats. Taken together, our results suggest that ecosystem size can drive food web flexibility and shape local community structure and may be key for understanding how ecosystems adapt to changing environmental conditions.