The impacts of extreme and fluctuating temperatures on trait-mediated indirect aphid-parasitoid interactions

Abstract

1. Global climate change models predict an increase in the frequency and magnitude of extreme temperature events. These temperature events, heatwaves for example, will impact a wide range of physiological and behavioural processes, particularly in ectotherms, and may therefore influence interactions between species.2. Anti-predator responses may be more costly under more severe temperature regimes and therefore trait-mediated disturbance could lead to high mortality or reduced reproduction under extreme and fluctuating temperature regimes.3. We examined the impacts of extreme and fluctuating temperatures on traitmediated indirect interactions in an aphid-parasitoid community.4. In treatments that isolated the effects of trait-mediated disturbance from the effects of foraging parasitoids we found that an increase in both the amplitude and frequency of peak temperatures reduced aphid numbers and provided evidence that the cost of trait-mediated disturbance could increase under frequent periods of high temperature. Aphid dispersal also increased with more frequent periods of high temperature.5. In treatments where female wasps were allowed to freely forage (direct + traitmediated effects), there was no evidence that extreme and fluctuating temperatures influenced the wasp's foraging ability. Exposure to extreme fluctuating temperatures did not influence the offspring production of exposed wasps or the position of the mummies within the plots.

Effects of climate warming on host–parasitoid interactions

“…These processes are frequently temperature dependent (Hance et al ., 2007), so climate change may alter the strength of host-parasitoid interactions by altering levels of parasitoid virulence and host resistance. For example, temperature can affect host physiological immune activity (Fellowes et al ., 1999), the efficacy of defensive behaviours (Bannerman et al ., 2011), and levels of parasitoid virulence (Zamani et al ., 2007).…”

Can Climate Change Trigger Massive Diversity Cascades in Terrestrial Ecosystems?

“…The studies that have examined the effects of climate change on tritrophic interactions suggest that effects on these interactions will favor outbreaks and (in some cases) associated decreases in diversity in natural and managed ecosystems, including most agriculture [151]. Probably the most important of the climatic changes for triggering massive diversity cascades will be increases in climatic variability and extreme weather events associated with climate change, because they disrupt regulation of herbivores by predators and parasitoids [124,127,150], leading to large shifts in herbivore and plant diversity. Many questions remain about how diversity cascades might intensify in response to changes of multiple climatic variables, but the following effects are clear: (1) abundances of pest herbivores will increase, due to higher temperatures; (2) increases in extreme weather events will lead to disruption of normal pest control by natural enemies; (3) carbon-based plant defenses will increase in response to warming and enhanced CO 2 ; and (4) additional, unpredictable patterns of diversity change will emerge, due to cascades and synergies [151,152].…”

“…Ecologists are making progress towards understanding the effects of rapid changes in climate and biogeochemical cycles on trophic interactions and diversity, and the effects of climate parameters on diversity via direct plus indirect pathways indicate that diversity cascades in response to specific climate change variables will be very large [122][123][124][125][126][127][128][129][130][131][132][133][134][135][136][137]. There are fewer studies that manipulate or measure the interacting effects of changes in multiple climate parameters, such as precipitation, temperature and CO 2 , on species interactions or diversity cascades [138][139][140][141][142][143][144], and the theoretical framework for studying climate change and diversity cascades or even direct biotic interactions is underdeveloped [122,[145][146][147].…”

“…It is clear that there will be strong top-down effects on diversity by direct changes to herbivore and natural enemy development and survival that can facilitate large decreases in plant richness and evenness (Figure 1, C1, C2 and C3). For example, high temperatures, higher atmospheric CO 2 and extreme weather events all have direct negative effects on survival of parasitoid wasps [124,127,149], which are extremely important sources of mortality for insect herbivores [97]. As a result of these negative effects on parasitoids, insect herbivore outbreaks can increase [150], causing decreases in herbivore evenness and subsequent decreases in plant diversity.…”

Differential responses to thermal variation between fitness metrics

“…The first factor is the incorporation of thermal variability in laboratory experiments as a way to better mimic field conditions. The importance of mean temperatures is widely recognized, but thermal variability could be a factor as important as average values, and could also be a strong selection force acting on organisms in the wild21617. Previous efforts have focused on the effects of temperature and variability through short and repeated exposures to stressful temperatures219.…”