Theoretical predictions for consumer-resource dynamics in variable thermal environments
Thermal variation through time and space are prominent features of ecosystems. This variation influences the movement patterns of organisms adjusting body temperatures to maximize fitness, particular among ectotherms whose fitness often directly linked to temperature. Yet, locations that are ideal in their thermal attributes (e.g., basking or refuge habitats) are often suboptimal for resource acquisition. As such, thermal variation can alter consumer-resource dynamics by influencing 1) consumer and resource body temperatures and subsequently temperature-sensitive ecological rates, and 2) the overlap of consumers and resources across small spatial scales. Currently, many theoretical and empirical climate change studies ignore the existence of either or both spatial and temporal thermal variability. This lack of thermal variability in climate change ecology research precludes an accurate understanding of how biological communities will respond to climate warming, and is due in part to the difficulty of incorporating thermal variability into models and experiments. Here, we develop a tractable mathematical framework that allows investigating how environmental temperatures alter consumer-resource dynamics in spatio-temporally variably thermal environments, and subsequently investigate how increases in mean temperature and thermal variability may affect consumer-resource dynamics.
Our model makes testable predictions regarding how consumer-resource dynamics should unfold in the presence of static, temporally variable, and spatio-temporally variable thermal environments experiencing climate warming. First, our model indicates that thermal temporal variability depresses consumer biomass during climate warming, but even small amounts of thermal spatial variability elevate consumer biomass. For example, climate warming magnitudes that completely extirpated consumers in the absence of spatial variability only caused a ~30% reduction in consumer biomass in spatio-temporally variable environments. Secondly, while climate warming increases the duration of time consumers spend in refuges and suspend feeding, this use of thermal refuges does not correspond with decreases in consumer biomass. Thus increased time spent in refuges by consumers does not necessarily signal an imminent population decline. Third, consumer-resource systems with fast dynamics are the most vulnerable during climate warming, and systems with slow dynamics are the least affected by the existence of thermal spatial variability. In conclusion, our modeling results indicate that thermal spatial and temporal variability mediate the response of consumer-resource dynamics as environmental temperatures and thermal variability increase, and as such, should be integrated into theoretical and empirical research addressing the ecological consequences of climate change.