A three-way tradeoff maintains functional diversity under variable resource supply

Background/Question/Methods

The resources that organisms depend upon often fluctuate over time, and a variety of common traits are thought to be adaptations to variable resource supply. To understand the trait structure of communities, it is necessary to understand the functional tradeoffs that determine what trait combinations are possible and which species can persist and coexist in a given environment. We compare traits across phytoplankton species, in order to test for proposed tradeoffs between maximum growth rate, competitive ability for phosphorus (P), and ability to store P. We then use empirical trait covariation to parameterize a mechanistic model of competition under pulsed P supply. 

Results/Conclusions

We find evidence for a three-way tradeoff between maximum growth rate, competitive ability for P, and ability to store P. The model shows that different strategies are favored under different conditions of nutrient supply regime, productivity, and mortality. Furthermore, multiple strategies typically coexist, and the range of traits that persist in the model is similar to the range of traits found in real species. These results suggest that mechanistic models informed by empirical trait variation, in combination with data on the trait structure of natural communities, will play an important role in uncovering the mechanisms that underlie the diversity and structure of ecological communities.