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Scuba Science 6 - Indirect Interactions in Subtidal Reef Communities

Russell J. Schmitt and Sally J. Holbrook University of California, Santa Barbara bio Since the emergence of scientific diving, subtidal research has tested and helped refine ecological theory, including the influence of indirect interactions on species coexistence. For example, Predator-mediated Apparent Competition was first recognized from models as a mechanism producing habitat segregation between prey shared by a predator. The first experimental study of apparent competition was done on a temperate reef, which confirmed the interaction in nature and revealed how competition for enemy-free space by ecologically distinct organisms (mobile grazers vs. sessile suspension feeders) contributed to spatial segregation. The two co-occurring grazers also were resource competitors, although they showed complementary feeding behaviors that represented a foraging tradeoff found commonly in nature. These findings motivated development of theory that revealed how foraging can create heterogeneity in an otherwise unstructured resource to promote coexistence. Multi-species models also revealed the potential for a species to simultaneously have negative and positive effects on another via direct and indirect pathways. Our studies of fishes that compete for shelter on host sea anemones revealed that a positive indirect effect of the superior competitor (via enhanced provision of space) offset its strong competitive effect and enabled coexistence. Such studies on subtidal reefs have underscored the need to include habitat structure in models of interaction webs. Simple models of Intraguild Predation (IGP), where one predator species feeds on another with which it competes for a shared prey, predict a trophic cascade. Such cascades rarely arise from natural IGP interactions, and our studies highlighted habitat structure as one reason for the mismatch between theoretical predictions and nature. Because habitat structure can reduce adverse effects of IGP on intermediate predators, refuges both preclude cascades and provide a path to coexistence. Refining models of webs of interacting species is critical for forecasting how systems will respond to short- and long-term environmental drivers. Recorded 05/24/10 11:01AM
Length: 17:46


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