Climate change and habitat degradation have led to widespread biodiversity loss and perturbations of ecosystem functioning at an increasing pace since the end of the 19th century. Estimating and predicting the ecological and evolutionary responses of populations to these global changes have been two of the major goals in ecology over the last few decades. However, there is still a gap in our understanding of how they affect trophic interactions between species (e.g., predator-prey, host-parasite, host-parasitoid), which play a fundamental role in food web structure, ecosystem services and species coexistence.
We investigated how resource quality (a proxy for habitat degradation) and stochastic variation in temperature affect the dynamics of a host-parasitoid system: the Indian mealmoth Plodia interpunctella and the parasitoid wasp Venturia canescens.We carried out a 9 month population dynamics experiment during which 48 microcosoms, half with the moth alone and half with both species, were maintained under constant (26°C) or random daily temperatures (26°C ± 1.5 S. D.) at four levels of resource quality (moth diet) and monitored weekly. We also conducted a life history experiment for one generation to characterise the host and parasitoid direct life history responses to resource quality and temperature variation.
Results/Conclusions
Both experiments revealed that the host and parasitoid species differ in their responses to resource quality and temperature variation. At the individual level, juvenile stage duration and adult body size were affected by resource quality in both species. However, in the parasitoid, juvenile stage duration was also 1.5 day shorter in average under variable temperatures and adult lifespan was affected by an interaction between both factors.
At the population level, the host dynamics (number of adults) shifted from single generation cycles at high resource quality to multi-generation cycles at all levels of degraded resources but only in the host alone microcosoms. The parasitoid dynamics also differed between levels of resource quality, especially at the intermediate levels where parasitoid numbers were often much higher under constant than under variable temperatures. Higher numbers of parasitoids under constant temperatures were often coupled with lower numbers of hosts, leading to greater differences between temperature treatments than in the host alone microcosoms.
Our results demonstrate that resource quality and temperature variation can interact in complex ways to shape eco-evolutionary dynamics in a host-parasitoid system. In particular, they show that temperature variation can substantially affect host dynamics through differences in predation pressure.