title: Predator Diet and Trophic Position Modified with Altered Habitat Morphology.
abstract: Empirical patterns that emerge from an examination of food webs over gradients of environmental variation can help to predict the implications of anthropogenic disturbance on ecosystems. This "dynamic food web approach" is rarely applied at the coastal margin where aquatic and terrestrial systems are coupled and human development activities are often concentrated. We propose a simple model of ghost crab (Ocypode quadrata) feeding that predicts changing dominant prey (Emerita talpoida, Talorchestia sp., Donax variablis) along a gradient of beach morphology and test this model using a suite of 16 beaches along the Florida, USA coast. Assessment of beaches included quantification of morphological features (width, sediments, slope), macrophyte wrack, macro-invertebrate prey and active ghost crab burrows. Stable isotope analysis of carbon ((13)C/(12)C) and nitrogen ((15)N/(14)N) and the SIAR mixing model were used to determine dietary composition of ghost crabs at each beach. The variation in habitat conditions displayed with increasing beach width was accompanied by quantifiable shifts in ghost crab diet and trophic position. Patterns of ghost crab diet were consistent with differences recorded across the beach width gradient with respect to the availability of preferred micro-habitats of principal macro-invertebrate prey. Values obtained for trophic position also suggests that the generalist ghost crab assembles and augments its diet in fundamentally different ways as habitat morphology varies across a highly dynamic ecosystem. Our results offer support for a functional response in the trophic architecture of a common food web compartment (ghost crabs, macro-invertebrate prey) across well-known beach morphologies. More importantly, our "dynamic food web approach" serves as a basis for evaluating how globally wide-spread sandy beach ecosystems should respond to a variety of anthropogenic impacts including beach grooming, beach re-nourishment, introduction of non-native or feral predators and human traffic on beaches.
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, Florida 33620-5200, United States of America.
authors.forename: Alexander
authors.initials: A
authors.lastname: Tewfik
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, Florida 33620-5200, United States of America.
authors.forename: Susan S
authors.initials: SS
authors.lastname: Bell
authors.affiliation: Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Kevin S
authors.initials: KS
authors.lastname: McCann
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, Florida 33620-5200, United States of America.
authors.forename: Kristina
authors.initials: K
authors.lastname: Morrow
mesh_terms: D000818:Animals; D001493:Bathing Beaches; D049872:Bivalvia / Q000502:physiology*; D003386:Brachyura / Q000502:physiology*; D002247:Carbon Isotopes; D003247:Conservation of Natural Resources; D033364:Decapoda / Q000502:physiology*; D004032:Diet; D017753:Ecosystem; D005431:Florida; D020387:Food Chain; D006802:Human Activities; D006801:Humans; D007553:Isotope Labeling; D009587:Nitrogen Isotopes; D011235:Predatory Behavior / Q000502:physiology*; D012044:Regression Analysis
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes
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