Cong Chen, Rieta Gols, Arjen Biere and Jeffrey A. Harvey
Understanding effects of Anthropogenic Global Warming (AGW) on species interactions is essential for predicting community responses to climate change. In particular, AGW-related events, like heatwaves and droughts, may have significant consequences for the biology and ecology of species-interactions in food webs. However, while the effects of AGW on resource (plant) –consumer (insect herbivore) interactions (i.e. first and second trophic level) have been relatively well studied, much less is known about effects on interactions involving insects at higher trophic levels at the top of food chains (e.g. in the third and fourth trophic levels). We examined the effects of temperature variability through a simulated heatwave on functional responses of two species in the fourth trophic level (hyperparasitoids: species that parasitize other parasites) that parasitize host species in the third trophic level (parasitoid cocoons). Even under average conditions, the temporal window of susceptibility of parasitoid cocoons to hyperparasitism is short (e.g. only a few days). We found that host cocoons developed faster under simulated heatwave conditions, decreasing the temporal window of susceptibility of the host cocoons to parasitism by the two hyperparasitoids, and consequently hyperparasitism declined with temperature. However the effects of a simulated heatwave markedly differed among the two hyperparasitoid species; temperature and host quality had a much stronger effect on early reproduction in the less fecund generalist Gelis agilis, than in the more fecund specialist Acrolyta nens. Our results suggest that exposure to heatwaves, which are expected to increase in frequency, will affect the ability of species in higher trophic levels to exploit transient resources whose suitability is temperature-dependent. In turn, the observed effects of AGW on the functional responses of the hyperparasitoids may disrupt trophic interactions and have profound impacts on population dynamics and ecological processes.