How recruitment, intraspecific interactions, and predation control species borders in a tidal estuary |
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Authors: | George H Leonard Patrick J Ewanchuk Mark D Bertness |
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Institution: | (1) Brown University, Department of Ecology and Evolutionary Biology, Providence, RI 02912, USA, US |
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Abstract: | We examined the relative contribution of recruitment, intraspecific species interactions, and predation in controlling the
upper intertidal border of the northern acorn barnacle, Semibalanusbalanoides, in a tidal estuary in Maine. We hypothesized that the contracted border at sites that experienced low tidal currents was
due to flow-mediated recruitment that resulted in reduced survival due to the absence of neighbor buffering of thermal stress
(i.e., positive intraspecific interactions). We tested this hypothesis by manipulating the density of recently settled barnacles
and their thermal environment in a field experiment. Counter to our original hypothesis, barnacles with neighbors suffered
severe mortality at low-flow sites. When density-dependent predation by the green crab (Carcinusmaenus) was experimentally eliminated, however, we did detect evidence for positive interactions at the low-flow sites but not at
the high-flow sites. In spite of the close proximity of the sites, maximum daily rock temperatures at the low-flow sites were
slightly, but consistently, greater than those at high-flow sites. Our findings suggest that the upper intertidal border of
S. balanoides in the Damariscotta River is limited at low-flow sites by a combination of reduced recruitment, elevated mortality from thermal
stress and enhanced predation by green crabs. More generally, our findings highlight how physical stress and predation interact
to alter the nature of density-dependent species interactions in natural assemblages.
Received: 6 August 1998 / Accepted: 11 October 1998 |
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Keywords: | Density-dependent foraging Flow-mediated recruitment New England rocky intertidal zone Positive interactions Species borders |
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