Ecological role of environmental stress in species assemblages: developing theory using rocky intertidal systems

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Environmental stress is the negative forcing that the abiotic environment exerts on the ecological performance of organisms. It is one of the most important factors that affect species distribution and biodiversity patterns in nature. In rocky intertidal habitats (habitats between the elevations corresponding to the highest and lowest tides on rocky seashores), gradients of environmental stress occur along relatively short distances because of tide dynamics and coastal topography. Thus, such systems are excellent for experimentally evaluating the influence of abiotic stress on how species assemble in communities. Through research that students from my Marine Ecology Lab will conduct in Nova Scotia, Maine, and Germany, we will test conceptual models that predict overall species diversity and species diversity within functional groups along stress gradients in a comprehensive way not previously achieved. Using seaweed canopies, we will also test the notion that bioengineer species (species that affect habitat conditions for many other species) may switch from positive effects (facilitation) to negative effects from high to low levels of environmental stress. This is important to know because bioengineers are normally assumed to always have positive effects on biodiversity, which makes them automatic targets for conservation, despite the fact that they may actually decrease diversity depending on local stress levels. Using a plant-herbivore system composed of algae and grazing snails, we will also investigate correlative changes in defense-attack traits in such organisms along stress gradients, which are relevant to understand because such differentiation may ultimately lead to the creation of new species if directional selection is strong. To ensure the generality of our findings, we will do similar tests on Northwest Atlantic (Nova Scotia) and Northeast Atlantic (Helgoland, Germany) rocky shores. The ultimate goal of my research program is to improve our understanding of how environmental stress shapes species assemblages at various levels of ecological complexity, seeking to identify general principles that should be applicable to other biological systems.