Intraspecific competition in temporally autocorrelated environments

Background/Question/Methods

Many abiotic and biotic factors exhibit stochastic dynamics with some degree of temporal autocorrelation. This autocorrelation is known to influence several ecological processes in important ways. One particular consequence that has drawn recent interest is the so-called ‘inflationary effect’; populations that fluctuate between positive and negative growth due to environmental variation (aka intermittent-sinks) can experience an ‘inflation’ in abundance when these fluctuations are positively autocorrelated in time. The inflationary effect is corroborated by much theoretical and empirical evidence, but less is known about how this inflationary effect influences competition, especially among variant strategies within a population. We developed a continuous-time model of Lotka-Volterra-type competition between two different intermittent-sink phenotypes within the same population in order to ascertain when environmental autocorrelation determines the outcome of competition. Environmental variation was incorporated by assigning growth parameters to each competitor that vary over time according to a common, dynamic environment. We ran simulations covering a wide range of environmental autocorrelations and competitive scenarios (i.e., specific responses in each competitor to environmental change). Competitive outcomes were then compared to identify specific instances in which coexistence depends upon the amount of autocorrelation in the environment.

Results/Conclusions

Our results indicate that the coexistence of intraspecific competitors can indeed depend on the degree of temporal autocorrelation in the environment. In particular, we highlight an instance in which the exclusionary effect of competition can be erased by temporal autocorrelation in the environment. However, this effect is only observed when the competitors’ fitness responses to environmental variation are negatively correlated. Also, the data suggest a common theme of coexistence in highly autocorrelated environments and exclusion in weakly autocorrelated environments. Exactly how the influences of competition and the inflationary effect combine to produce a gradient of coexistence across differently autocorrelated environments depends sensitively on the particulars of the competitive scenario in question. This work exposes interesting competitive effects attributable to the temporality of the environment which have important implications for competitive coexistence among variant strategies within a population and, therefore, the maintenance of intraspecific variation.