Warming causes contrasting behavioral responses of predators by changing their prey size spectrum

Abstract Global warming challenges predators by changing their abiotic and biotic environment. Although predators may adapt by virtue of behavioral plasticity, few studies have explored this behavior under field conditions. We conducted a field warming experiment in an alpine meadow using six large open-top chambers that increased mean annual temperature by 0.6°C. We monitored the abundance and behavior of two web-building spider species differing in size and their prey for four consecutive years. Warming reduced the prey biomass and decreased the abundance of short-bodied prey more than long-bodied ones for the larger spiders, and increased the abundance of long-bodied prey for the smaller spiders. As a consequence, warming reduced the abundance of the larger spider and increased the abundance of the small spider by an average of -47.4% and +128.3%, respectively. The web mesh-size of the larger spider decreased by -43.6%, whereas the mesh-size of the smaller spider increased by +79.8%. Structural equation models showed that the behavior of both spider species was the result of warming-induced changes in the prey size spectrum. Our data reveal that predators can behaviorally adapt to warming-induced shifts in the composition and size distribution of complex communities, which is likely to result in altered community metabolism, energy fluxes, and thus ecosystem functioning.