Fuzzy Mating Behavior Enhances Species Coexistence and Delays Extinction in Diverse Communities

Abstract

Current theories about mechanisms promoting species co-existence in diverse communities assume that species only interact ecologically. Species are treated as discrete evolutionary entities, even though abundant empirical evidence indicates that patterns of gene flow such as selfing and hybridization frequently occur in plant and animal groups. Here, we allow mating behavior to respond to local species composition and abundance in a data-driven meta-community model of species co-existence. While individuals primarily out-cross, they also maintain some small capacity for selfing and hybridization. Mating choice is treated as a 'fuzzy' behavior, determined by an interaction between intrinsic properties affecting mate choice and extrinsic properties of the local community, primarily the density and availability of sympatric inter-fertile species. When mate choice is strongly limited, even low survivorship of selfed offspring (<10%) can prevent extinction of rare species. With increasing mate choice, low hybridization success rates (~20%) maintain community level diversity for substantially longer periods of time. Given the low species densities and high diversity of tropical tree communities, the evolutionary costs of competition among sympatric congeneric species are negligible because direct competition is infrequent. In diverse communities, many species are chronically rare and thus vulnerable to stochastic extinction, which occurs rapidly if species are completely reproductively isolated. By incorporating fuzzy mating behavior into models of species co-existence, a more realistic understanding of the extinction process can be developed. Fuzzy mating strategies, potentially an important mechanism for rare species to escape extinction and gain local adaptations, should be incorporated into forest management strategies.