One of the most apparent ecological consequences of climate change has been the ongoing phenological shift in important life-history events among species, which has modified the timing of many species interactions. Two ways climate change may act to shift species’ phenologies in ecological communities is by altering the timing of a species’ appearance in a community or by dissimilarly changing the developmental rates of interacting species. However, understanding of the consequences of phenological asynchrony within ecological communities will require us to move beyond pairwise interactions and examine how interspecific interactions, such as resource competition, effect species-specific phenological responses to climate change. In this study, we investigated how these two mechanisms interact, and test whether pairwise and multispecies host-parasitoid interactions show similar responses. We examined how elevated temperatures and resource competition act to shift developmental schedules of the Drosophila host community and modify the outcomes of phenologically mismatched Drosophila-parasitoid interactions. Specifically, we addressed the following questions: 1) To what extent does elevated temperature influence parasitism rates of phenologically mismatched parasitoids? 2) Does resource competition among hosts help counter the effects of phenological asynchrony by extending the infection window of the host community? 3) Do the outcomes of phenological asynchrony differ between pairwise and multispecies contexts? We experimentally manipulated temperature (24C or 28C), resource competition (High or Low), species combinations (pairwise or multispecies), and levels of phenological mismatch with their parasitoid (0, 2, 4, or 6 days) in a fully factorial design.
Results/Conclusions
Parasitism rates, in general, were reduced in elevated temperatures and declined more rapidly as the mismatch between host and parasitoid advanced. However, resource competition among hosts acted to counter the affects of phenological asynchrony to some degree. Interestingly, parasitism rates did not differ between pairwise and multispecies contexts. Finally, differences in host development time interacted with phenological asynchrony to influence host survival, but not parasitism rates. Our results suggest that rising temperatures will make any degree of asynchrony between host and parasitoids worse. Furthermore, these results identified significant interactions between biotic and abiotic environments, and how they act to modify the outcomes of phenological shifts in host-parasitoid systems. Given the important role parasitoids play in influencing the abundance and dynamics of their hosts, any disruptions of synchrony is likely to reduce the top-down effects parasitoids have on structuring and organizing terrestrial ecological communities.