What's the colour of environmental noise?

Understanding the environmental conditions that a species can tolerate is a growing concern in ecology and evolutionary biology. Research is beginning to reveal that the environmental factors that actually challenge organisms in nature (e.g., temperature, precipitation, or even other organisms) tend to fluctuate with varying degrees of randomness, commonly known as ‘noise-colors.’ Most natural environmental variables fall somewhere along a spectrum between totally random fluctuations, known as ‘white-noise’ environments, and environments in which conditions at any point in time are likely to be very similar to previous conditions (positive temporal autocorrelation), known as ‘red-noise’ environments. The color of environmental noise can have varying effects on species persistence, depending on characteristics of the species and environmental factors involved.

In this study, we show that environmental noise-color can interact with intraspecific variation to influence species persistence. If a species exhibits phenotypic variation such that environmental conditions at any point in time are good for some individuals but bad for others (temporal niche partitioning), then this can actually increase the size of a population by decreasing the overall amount of competition among individuals in the long-term. However, this will only happen when each phenotype experiences sufficiently long periods of growth during extended periods of good conditions. Environmental reddening increases the duration of time spent in favorable conditions for each phenotype, thus increasing the abundances of each phenotype and, in turn, the size of the whole population, provided that mutations prevent phenotypes from going ‘extinct’ during extended periods of unfavorable conditions. Surprisingly, this effect, which is called an ‘inflationary effect,’ occurs even when all phenotypes have an average negative intrinsic fitness over time, in which case the population could not persist in a less autocorrelated, or white-noise, environment. This work shows that the color of environmental fluctuations can influence both the diversity and persistence of a species, which is likely to be of widespread importance for adaptation, extinction risk, and conservation, especially as species face new environmental challenges due to changing climatic conditions across the globe.