Environmental color neutralizes the competitive advantage of stress-tolerance
The environmental factors that challenge populations in nature often fluctuate, exhibiting varying degrees of temporal autocorrelation, commonly called ‘environmental colors’. Environmental color is already known to have important consequences for a number of ecological processes including population persistence, spatial synchrony, and trophic stability. It has also been suggested that environmental color can influence competitive dominance. Here, we develop a theoretical framework to test this idea in a situation where the environment fluctuates between ‘favorable’ and ‘stressful’ conditions and competitors exhibit phenotypes with different levels of stress-tolerance. We assume that a tradeoff exists such that more stress-tolerant phenotypes have higher survival under stressful conditions but are poor competitors under favorable conditions. Using a combination of deterministic and stochastic analyses, we calculated long-term competitive outcomes for a wide range of phenotypes, with environmental colors ranging from temporally uncorrelated (white) to highly autocorrelated (reddened) fluctuations. We compare these theoretical results to a laboratory experiment where competing viruses, which exhibit a tradeoff between ‘thermo-tolerance’ and reproduction (competitive ability), were subjected to environments with differently colored fluctuations between stressful and benign thermal conditions.
Both theory and experiment confirm that environmental color alone can reverse competitive dominance between stress-tolerant and intolerant phenotypes. In white environments, stress-tolerant phenotypes have a long-term competitive advantage because the benefit of reduced mortality during stressful conditions outweighs the cost of reduced competitive ability during benign conditions. However, in more reddened environments, the advantage of stress-tolerance becomes weaker as stressful conditions become more prolonged, causing competitive differences during benign conditions to outweigh mortality differences during stressful conditions. In this way, environmental reddening effectively neutralizes any long-term competitive advantage conferred by stress-tolerance. Additionally, we find that the relationship between environmental color and long-term competitive dominance depends on the strength of the tolerance-growth tradeoff as well as the proportion of total time spent under stressful environmental conditions. Our results suggest that environmental color can have profound impacts on competitive interactions, especially when tradeoffs constrain competitors across the environments that they encounter.