Abstract
AbstractClimate change is advancing the onset of phenological events, with the rate of advance varying among species and trophic levels. In addition, local populations of the same species may show genetic differences in their response to seasonal cues. If populations of interacting species differ in their response, then climate change may result in geographically varying shifts in the community‐level distribution of interaction strength. We explored the magnitude of trophic‐ and species‐level responses to temperature in a tritrophic system comprising pedunculate oak, insect herbivores, and their associated parasitoids. We sampled local realizations of this community at five sites along a transect spanning fifteen degrees of latitude. Samples from each trophic level at each site were exposed to the same set of five climatic regimes during overwintering in climate chambers. We then recorded the number of days and degree‐days required for oak acorns to develop and insects to emerge. In terms of dates of events, phenology differed among populations. In terms of degree‐days, we found that for two species pairs, the heat sum required to develop in spring differed by an additional ˜500 degree‐days between trophic levels when overwintering at the highest temperature. For three species, within‐population variation in the number of degree‐days required for emergence was higher at warmer temperatures. Our findings suggest that changing temperatures can modify interactions within a community by altering the relative phenology of interacting species and that some interactions are more vulnerable than others to a shift in temperature. The geographic variation in the phenological response of a species suggests that there is a genetic component in determining the phenology of local populations. Such local variation blended with interspecific differences in responses makes it complex to understand how communities will respond to warmer temperatures.
Highlights
In any habitat with temporally variable resources and climatic conditions, we expect species to have evolved a phenological match to key aspects of their environment
We explore how geographically separated populations differ in their phenological response to temperature along a temperature gradient, and how this is reflected in the community-level synchrony among trophic levels
We found the phenological distribution of a herbivore (T. ekebladella) and two parasitoids (T. auratus and T. geranii) to be extended at warmer temperatures
Summary
In any habitat with temporally variable resources and climatic conditions, we expect species to have evolved a phenological match to key aspects of their environment. Warmer spring temperatures generally advance phenology in a wide range of taxa (Roy and Sparks 2000, Menzel et al 2006, Fu et al 2013, Kharouba et al 2018), but the rate of advance can differ among species (Thackeray et al 2016, Kharouba et al 2018). Such interspecific variation could affect the phenological synchrony between interacting species. If we want to understand how species interactions will change in a warming climate, we need to elucidate both the phenological response of species and trophic levels to temperature, and the role of plasticity vs. genetic variation in determining phenology
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