Many habitats are composed of patches with organisms distributed heterogeneously among the patches. This heterogeneity is often attributed to intrinsic factors (e.g., patch quality, or the presence of conspecifics) or the surrounding matrix. When patches are located near one another, colonization also can be affected by neighboring patches: e.g., neighbors can redirect colonists away from a target patch. Previous work demonstrated that redirection creates spatial heterogeneity among otherwise identical patches in an unsaturated systems (e.g. low density dependence, limited propagule supply).
Here, we build on past models of patch colonization and post-colonization dynamics to investigate the dynamics of residents and patches when patches are comprised of biogenic habitat whose dynamics are directly affected (positively or negatively) by resident organisms. We develop models with a coral reef system in mind. Both corals (the habitat patch) and their occupants (e.g. snails and fish) have pelagic larvae that settle to a reef during pulsed settlement events. Coral growth and survival are affected by occupants, and the occupants undergo density-independent and dependent mortality. We explore how species interactions (direction and magnitude) between habitats and occupants, in combination with larval redirection, alters habitat growth, settlement rates, and spatial patterns of occupants and habitat.
Results/Conclusions
The spatial patterns of both corals and symbionts depend on the interaction between coral and symbiont as well as demographic parameters and the degree of redirection. When there is no redirection, corals and symbionts are distributed randomly throughout space, and only coral size is a predictor of symbiont abundance. However, in the presence of redirection of beneficial symbionts, corals display two distinct qualitative spatial patterns: 1) evenly dispersed patches throughout the landscape, or 2) large isolated patches with smaller clustered patches. When symbionts have negative effects on corals, clustered corals have larger sizes because neighboring corals redirect harmful symbionts. Additionally, demographic parameters influence the resulting spatial pattern. When larval supply (of corals or symbionts) is low, heterogeneity is great. The effects of redirection of symbiont larvae are greatest when density-dependent symbiont mortality is low and symbionts are short-lived.