Simulating the relative effects of movement and sociality on the distribution of animal-transported subsidies

Animal sociality (i.e., conspecific attraction or avoidance) can influence how animals move (i.e., sinuous to straight) across landscapes. Active subsidies are animal-transported resources (e.g., nutrients, detritus, prey) or consumers (e.g., predators, parasites, pathogens) across ecosystem boundaries and can affect ecosystem function. Animal movement has been shown to affect the spatial distributions of active subsidies. However, there is limited research on how conspecific interaction affects active subsidy distributions through animal movement. Based on dispersal from a donor to recipient ecosystem, we constructed a spatially explicit individual-based model (IBM) to quantify the effect of variation in conspecific interaction in three scenarios (attraction, avoidance, no interaction) and movement behavior as a correlated random walk on living and dead subsidy displacement, density, and clustering. In each conspecific interaction scenario, we examined emergent subsidy distributions from varying the straightness of movement path and the settlement probability as a function of settled conspecifics within dispersers’ perceptual range. Movement behavior predicted subsidy displacement, and conspecific interaction determined subsidy density and clustering patterns. We found that avoidance spread subsidies farther and at lower densities in the recipient ecosystem, generating more spread-out dead subsidy clusters. Attraction resulted in fewer, smaller, and denser living subsidy clusters closer to the ecosystem boundary. Higher settlement probability constrained living subsidy displacement with increased subsidy density and clustering across conspecific interaction scenarios. Subsidy density and clustering increased with perceptual range in attraction scenarios, limiting subsidy displacement. Subsidy displacement increased with perceptual range in avoidance scenarios, reducing subsidy density and clustering. This work is the first systematic simulation study on the influence of animal movement interactions with sociality on spatial subsidies across a broad parameter space. Our work provides context for empirical studies of active subsidy distribution and impact for a variety of taxa and ecosystems.