Resource competition in seasonal environments: The early bird gets the worm

Background/Question/Methods

Competition in seasonal environments is affected by periodic fluctuations in important environmental factors, including temperature, sunlight, resource supply, and water availability. Modeling studies have previously examined how fluctuations in single factors affect competition between species. However, species must often contend with simultaneous fluctuations in multiple factors, some of which are asynchronous. This can lead to complex interactions that alter competitive outcomes, and these interactions need to be considered further.

We used resource competition models to investigate the effects of seasonal fluctuations on competitive outcomes in two specific systems and in general. We examined lakes with seasonal temperature fluctuations as well as tropical plant communities with seasonal rainfall patterns. In both systems, we examined a broad range of environmental variation to understand how these competitive outcomes change across a realistic range of parameter space. Competitive outcomes were tested for using mutual invasibility criteria.

Results/Conclusions

We show that competitive outcomes in the two systems are strongly influenced by the occurrence of a season of death (or at least reduced growth). Specifically, interactions between the factor causing mortality (viz. low temperatures, low water availability) and the limiting resource in the models has large effects on competitive outcomes. In both cases, the species with a fitness advantage early in the growing season is able to dominate over a broad range of parameter space. This occurs due to an accumulation of the limiting resource in the system during the death season, which is then monopolized by the ‘early bird’ species.

We also show that this dynamic is crucially dependent on there being a single death season; competitive outcomes are far more symmetric if communities are unable to tolerate both extremes of environmental variation. This dynamic would lead to stronger selection on performance early in the growing season, making understanding evolutionary constraints in this period an important area of study.