Active aggregation stabilises priority effects and promotes regional coexistence

Background/Question/Methods

Inhibitory priority effects – in which species arrival order dictates competition outcome – can allow different species to win different local patches and enhance regional diversity. However, in the presence of frequent disturbance and sparse resource patches, stochastic events may result in arrival orders that favour only one species and cause the regional extinction of another. Due to this instability, many studies have sought explanations for how regional coexistence via priority effects may be stabilised. These explanations often invoke the need for environmental heterogeneity and species’ differences in environmental requirement or colonisation ability. However, these explanations fail to consider why priority effects (i.e. high interspecific competition) evolved in the first place, potentially as adaptations, because they imply that species eventually evolve differences that essentially remove priority effects. In this study, we build a metacommunity simulation model to test the hypothesis that active aggregation, in which adjacent patches with higher frequencies of conspecifics receive more immigrants, can promote regional coexistence even when initial species densities would predict otherwise.

Results/Conclusions

We found that the strength of aggregation increases the likelihood of regional coexistence, indicating that active aggregation broadens the range of initial conditions that allow for regional coexistence. Furthermore, we find that the process of aggregation creates spatial structures in which the distribution of species are fully segregated — a process akin to resource partitioning in space. We posit that these stable macroscopic spatial structures may act to buffer individual patches from stochasticity and maintain regional diversity. In summary, our study provides a proof-of-concept, showing how priority effects may be stabilised through active aggregation — a self-organised process in which species differentiate conspecifics from heterospecifics — to construct spatial heterogeneity that facilitates regional coexistence.