Abstract
Abstract Understanding the effects of anthropogenic global warming (AGW) on species interactions is essential for predicting community responses to climate change. However, while effects of AGW on resource–consumer interactions at the first and second trophic level have been well studied, little is known about effects on interactions at higher trophic levels at the terminal end of food chains (e.g. in the third and fourth trophic levels). Here, we examined the effects of temperature variability by simulating heatwaves on functional responses of two species at the fourth trophic level (hyperparasitoids) that parasitize host species at the third trophic level (parasitoid cocoons). 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 parasitism 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 hyperparasitoid Gelis agilis, than in the more fecund species Acrolyta nens. Our results suggest that exposure to heatwaves, that are expected to increase in frequency, will affect the ability of species at 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 impact on population dynamics and ecological processes. A plain language summary is available for this article.
Highlights
Rising atmospheric concentrations of greenhouse gases driven by a suite of anthropogenic processes has resulted in rapid warming of the planet's surface since the Industrial Revolution and over the past three decades (IPCC, 2014)
We found that host cocoons developed faster under simulated heatwave condi‐ tions, decreasing the temporal window of susceptibility of the host cocoons to parasitism by the two hyperparasitoids, and parasitism declined with temperature
We examine the effects of different temperature re‐ gimes, including simulated heatwave conditions, on host exploitation and early reproduction in the idiobiont hy‐ perparasitoids Acrolyta nens Hartig (Hymenoptera: Ichneumonidae) and Gelis agilis Fabricius (Hymenoptera: Ichneumonidae) in the fourth trophic level
Summary
Rising atmospheric concentrations of greenhouse gases (primarily CO2) driven by a suite of anthropogenic processes has resulted in rapid warming of the planet's surface since the Industrial Revolution and over the past three decades (IPCC, 2014). Exposure to higher temperatures may shorten the development time of insect herbivores, reducing their tem‐ poral window of exposure to natural enemies such as predators and parasitoids (the “slow‐growth‐high‐mortality hypothesis” (Clancy & Price, 1987; Benrey & Denno, 1997). Parasitoids are much more specialized than most insect predators and attack a limited number of host species in nature and spe‐ cific host stages such as eggs, larvae or pupae (Godfray, 1994) This makes them highly susceptible to changes in the availability of hosts caused by warming that either disrupt the temporal phenology of the host–parasitoid interaction or else reduce the temporal window of accessibility of parasitoids to specific host stages (Harvey, 2015; Jeffs & Lewis, 2013). These tem‐ peratures reflect the lowest to highest mean average day and night summer temperatures in the Bilt in the Netherlands measured from 1981 to 2010 (https://www.knmi.nl)
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