Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Mark R. Patterson


A unifying theory of community regulation in soft-bottom systems remains elusive, despite extensive field studies on factors controlling community structure. Here, I have (1) reviewed models of community regulation, (2) examined the role of predation in controlling benthic diversity along a salinity gradient, (3) examined effects of predation upon an abundant bivalve, Macoma balthica, and (4) revised a model of community regulation in an estuarine soft-bottom system. The Menge and Sutherland (MS) "consumer stress model" posits that consumers feed ineffectively in harsh environments, and the importance of physical disturbance, competition and predation varies with recruitment, environmental conditions, and trophic position. In this model, competition for resources depends directly upon the level of recruitment. I have revised the model to fit soft-bottom systems by changing the recruitment axis to a "recruitment: resource ratio." Hence, the impact of a given level of recruitment depends upon resource availability. According to the MS model, predation is most important in determining community structure when environmental conditions are not severe. I investigated the applicability of the MS model in a soft-bottom estuarine community. I quantified predator abundance, prey abundance and diversity, and the differential effect of predation on species diversity and survival of an abundant prey species, Macoma balthica, along an estuarine gradient in two tributaries of Chesapeake Bay. Benthic diversity was lower in upriver high-stress habitats than downriver low-stress habitats, in agreement with predictions of the MS model. However, the following findings are inconsistent with model predictions: (1) predator abundance was greater upriver, (2) predation intensity and its impact on benthic diversity were greater upriver, and (3) predation-induced mortality of transplanted Macoma balthica clams, and natural mortality of clams were higher upriver. An alternative community regulation model applies to this system because higher predator abundance and predation intensity in higher environmental stress is contrary to the MS model predictions. Predators aggregated upriver where carbon production was increased, and prey were abundant. Hence, a more suitable model for this soft-bottom system is one that incorporates the effects of production and predation along with recruitment, competition and environmental stress.



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