Climate warming experiments generally test the ecological effects of constant treatments while neglecting the influence of more realistic patterns of environmental fluctuations. Moreover, organisms experience multiple stress events during their life and several stressors may interact non-additively with each other leading to complex influences on physiological rates and life history traits. Thus, little is known regarding how the temporal interaction between multiple episodes of thermal stress influences biotic interactions. We measured the sensitivity of predation rate in a keystone intertidal sea star (Pisaster ochraceus) to changing levels of temporal coincidence of underwater and aerial thermal stress events. This sea star feeds preferentially on mussels on the North American West coast. We used biomimetic dataloggers to measure the aquatic and aerial body temperatures of this sea star in the field in California. Based on these field measurements, we designed laboratory trials to measure the influence of aquatic and aerial body temperatures on predation rate under constant and fluctuating conditions. We controlled for intensity (whole average), variance and temporal patterning of both underwater and aerial body temperature, as well as the level of temporal coincidence of elevated aquatic and aerial temperatures.
Results/Conclusions
We found that predation rate decreased when aerial body temperature increased from 16°C to 27°C. By contrast, feeding rate was higher at intermediate underwater body temperature (13°C) in the range 10°C-16°C. Under constant conditions, cold water tended to buffer partially the impact of high aerial thermal stress. However, experiments under constant conditions were a poor predictor of more complex environmental scenarios because of strong temporal interactions. Increasing thermal variance depressed predation rate while the temporal pattern of fluctuations did not matter when only one of the two variables was varying. Surprisingly, predation rate decreased as underwater and aerial thermal stress episodes became temporally non-coincident, despite a similar mean and variance among treatments. Therefore, considering the precise timing of stressful events relative to each other is essential when addressing the effects of global change on organismal responses, and ultimately species interactions and distributions. Temporality appears to be a critical parameter in ecological systems including multiple interacting stressors. Such temporal interactions may be widespread in various ecosystems, suggesting a strong need for empirical studies and models that link environmental complexity, physiology, behavior and species interactions.
Reference: Pincebourde et al. (2012). Temporal coincidence of environmental stress events modulates predations rates. Ecology Letters, in press.