Warming causes contrasting spider behavioural responses by changing their prey size spectra

Predators may adapt to global warming via behavioural plasticity. However, empirical evidence showing such adaptations in terrestrial ecosystems is scarce. Here we report behavioural shifts that alter the web mesh size of two dominant predatory spider species in response to experimental warming in an alpine meadow field. Experimental large open-top chambers increased the mean annual air temperature by 0.6 °C, resulting in a decrease in the web mesh size of the large spider (−43.6%), and an increase in the web mesh size of the small spider (+79.8%). Structural equation models indicated that the changes in mesh size and web area were primarily the result of warming-induced changes in prey size spectra, which in turn were impacted by warming-induced changes in soil moisture and plant community. These results indicate that predators can adjust their behavioural responses to warming-induced changes in the physical setting and prey community. The authors show shifts in predatory spider web mesh size under experimental warming in an alpine meadow. Web mesh size decreased for a large spider species, but increased for a small species, with changes linked to altered prey size spectra following soil moisture and plant community shifts.