Effects of multiple timescales of resource supply on the maintenance of species and functional diversity

It is well known that variable resource supply can allow competitors to coexist on a single limiting resource, and this is one mechanism that may explain the maintenance of diversity in paradoxically speciose communities. Ecosystems experience fluctuations in resource supply on a range of timescales, but we have a poor understanding of how multiple frequencies of resource supply affect the maintenance of diversity and community structure. Here we explore this question using a model of phytoplankton competition for a limiting nutrient, parameterized using empirical tradeoffs between rapid growth, nutrient storage capacity and nutrient uptake affinity. Compared to a single frequency of nutrient supply, we find that multiple frequencies of nutrient supply increase functional diversity, by permitting the coexistence of strategies adapted to different frequencies of supply. Species richness is also promoted by multiple modes of nutrient supply, but not as consistently as functional diversity. Although this model is parameterized for phytoplankton, the fundamental dynamics and tradeoffs likely occur in a variety of ecosystems. Our results suggest that the spectrum of temporal variation driving communities should be further investigated in the context of the maintenance of diversity and the functional composition of communities under different environmental regimes.