Local-regional richness relationships and alternative stable states in metacommunities with local facilitation

Local-regional species richness relationships have been used to infer relative contributions of local and regional forces to determining the richness of local communities. Although most previous research assumed competition as major local species interactions, growing empirical evidence suggests that facilitation is also an important driver of local community dynamics. Here, I explore how facilitation affects the shape of local-regional richness relationships, by incorporating local facilitation into a patch-occupancy model of metacommunity dynamics. I find that facilitation can generate local-regional richness relationships with the alternative stable states of mean local richness at intermediate to high levels of regional richness. These alternative stable states tend to occur in a metacommunity in moderately harsh environments. This result cautions against assuming that only competition can be primarily important local interactions when interpreting the shapes of local-regional richness relationships. Moreover, the possibility of alternative stable states suggests that gradual decline of regional species diversity might cause a sudden collapse of metacommunities with local facilitation.