Emergent intraspecific multiple predator effects shape estuarine trophic dynamics across a gradient of habitat complexity

Abstract

Estuarine ecosystems are characterized by heterogeneity in species assemblages and habitat complexity, so prey in these systems are often threatened by multiple predators across a mosaic of habitats. When several predator species or conspecifics co-occur, behavioral interactions between them can introduce non-independence to their predator-prey dynamics, which can alter the fate of shared prey. Habitat complexity may regulate these interactions and further impact prey survivorship. We conducted an experiment that manipulated the densities and identities of two ecologically similar estuarine-dependent predators, Red Drum (Sciaenops ocellatus) and Spotted Seatrout (Cynoscion nebulosus), within three habitat complexities. The resulting survivorships of two shared prey types were utilized to determine whether these predators are substitutable, to examine their inter- and intra-specific trophic interactions, and to investigate the impact of habitat structural complexity on their trophic dynamics. The predators differed in their prey preferences and predation pressures, indicating they are generally not substitutable. Interactions between conspecific predators were particularly important in shaping trophic dynamics, and often resulted in combined predation impacts that either enhanced or reduced the survivorship of shared prey as compared to expected values based on foraging rates of individuals. Minimal evidence of interspecific trophic interactions was detected. The observed emergent multiple predator effects differed among the habitats, and were generally intense in intermediate habitat complexity but were either intense or weak in high habitat complexity, depending on the predator combination. These results collectively indicate that prey regulation in this estuarine trophic system is highly dependent on the predator-prey assemblage and habitat context, and enhances our understanding of how multiple predators interactively shape their shared ecosystem.