Mechanisms of species coexistence in polyrhythmic environments

Background/Question/Methods

While environmental polyrhythms – biological fluctuations ranging from diel to annual to decadal cycles – may play a fundamental role in structuring species interactions, there is surprisingly very little theoretical research on how polyrhythmic forcing may impact species coexistence. In some environments, competing species have adapted trade-offs in response to these environmental fluctuations that may allow for spatial-temporal differentiation, thus reducing direct competition within a cycle. With alarming evidence that suggests climate change is fundamentally altering these environmental signals across temporal scales, the mechanisms by which these trade-offs promote species coexistence need further exploration. We argue that altering polyrhythmic signals in response to climate change may influence the competitive outcomes between species with different adapted trade-offs. Here, we extend the classic Lotka-Volterra competition model to incorporate environmental polyrhythmic forcing and biological constraints to match differentially adapted species and examine how climate change may influence future competitive outcomes.

Results/Conclusions

We develop a simplified isocline approximation that follows numerical simulations remarkably well and most importantly, allows us to determine analytical solutions for competitive outcomes. Specifically, this elegant approximation allows us to analytically explore the bifurcation structure of our model and determine the interacting roles of polyrhythmic forcing and biological trade-offs. Our results illustrate that polyrhythmic forcing, in and of itself, can mediate coexistence, competitive exclusion, and contingent coexistence. As species densities and competitive outcomes appear to be incredibly sensitive to the change in environmental polyrhythms, climate change has the potential to drastically impact future competitive outcomes in the natural world. Understanding these mechanisms may help provide early warning signals for possible extinction and help tip the scale in favour of vulnerable species.