On the interaction between Janzen-Connell effects and habitat partitioning in spatially structured environments

Abstract

Janzen-Connell Effects and Habitat Partitioning have both been proposed as potential stabilizing mechanisms in species-rich forest communities. Janzen-Connell Effects describe the process in which specialized predators are attracted to adult trees, which reduce the survivorship of nearby conspecific juveniles. This is thought to generate stabilizing negative frequency dependence. Habitation Partitioning describes when species exhibit different fitness responses to spatially heterogeneous environmental factors, typically causing species to aggregate into favorable habitat types. Despite substantial empirical evidence that both processes occur simultaneously in empirical systems, the theoretical implications of how their interactions shape species diversity remain underdeveloped. In this study, I examine a spatially explicit model that incorporates both processes. I show that Janzen-Connell Effects and Habitat Partitioning can act synergistically to promote coexistence such that their contribution to species coexistence is greater than the sum of their parts when environmental spatial heterogeneity is positively autocorrelated. The results of this study highlight the need to explicitly model the interaction between co-occurring spatially dependent coexistence mechanisms to understand the role they play in the maintenance of species diversity.Significance StatementA primary goal of ecology is to explain the maintenance of species diversity. However, the mechanisms that underlie the coexistence of highly diverse tropical rainforests remain contentious. Two leading hypotheses are Janzen-Connell Effects and Habitat Partitioning. Both hypotheses are based on space. Janzen-Connell Effects are based on the observation that natural enemies attracted to adult trees reduce the survival of their nearby seeds and seedlings. In contrast, Habitation Partitioning states that diversity can be maintained when species exhibit different responses to spatially varying environmental conditions such that species congregate into their preferred habitat types. In this paper, I demonstrate that these mechanisms can interact synergistiacally to promote high species diversity.