Self-organised pattern formation promotes consumer coexistence by fluctuation-dependent mechanisms

Abstract

1. In spatially extended ecosystems, habitat heterogeneity facilitates coexistence of species if each competitor experiences environmental conditions in a particular habitat that provide a growth advantage compared to other species, thereby making it locally competitively superior. If the competitive hierarchy among species is the same everywhere, heterogeneity-facilitated coexistence is possible provided that superior competitors disperse maladaptively towards unfavourable habitats or if they hedge insufficiently against fluctuating environmental conditions. 2. We use a generic two-patch metacommunity model to show that the latter mechanisms also operate in metacommunities with homogeneous habitat quality when heterogeneous biomass distributions emerge from self-organised pattern formation. The model consists of an abiotic resource, an autotroph producer and two competing heterotroph consumer species of which one is always competitively inferior to the other, irrespective of resource availability. 3. If the induced biomass patterns are static in time, a lower dispersal rate can allow the inferior competitor to avoid competitive exclusion by retaining most of its biomass in the patch with the higher resource density. However, if the biomass patterns fluctuate spatio-temporally, the inferior competitor must adopt a higher dispersal rate than the superior competitor to persist. This increased movement enables the inferior competitor to effectively distribute its biomass across space, thereby achieving a higher growth rate during periods of recovery from local population minima. 4. Strikingly, we find a novel coexistence mechanism that emerges if the competitors differ in their abilities to induce pattern formation. Similar to relative nonlinearity in resource use (based e.g. on a gleaner–opportunist trade-off), the dominant species modifies the spatial or spatio-temporal variation in the distribution of the resource in a way that favours its competitor. This prevents competitive exclusion due to differently effective dispersal strategies. 5. We conclude that while temporal instabilities that cause, for example, predator–prey oscillations are usually regarded as jeopardising species' persistence, spatial instabilities that give rise to self-organised pattern formation should be interpreted more positively, as they provide a generic mechanisms for maintaining diversity in metacommunities without requiring a priori habitat heterogeneity.