Computational protocol: Complexity of the prey spectrum of Agaronia propatula (Caenogastropoda: Olividae), a dominant predator in sandy beach ecosystems of Pacific Central America

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[…] Between November 2011 and April 2017, the intertidal zone of Playa Grande, Costa Rica (10°20′N, 85°51′W), was patrolled during opportunistic trips to search for A. propatula with filled metapodial pouches. Searches were performed during daylight, usually within the six hours around the time of low tide. Filled pouches almost always contained a prey item, indicating a successful predation attempt. Successful predators were picked up while burrowing into the sediment or sailing seaward in the backwash, and the prey was released by gently pressuring the metapodial pouch between fingertips (). The size of the predator and its prey were measured to the nearest 0.1 mm either using calipers or on images taken of predator and prey next to a ruler using ImageJ (https://imagej.nih.gov/ij/). Size was defined in gastropods as the shell length from apex to base, in bivalves as the longest axis across the shell, and in crustaceans as the anterior–posterior body length. All animals were released immediately after being measured or photographed at the same location where they had been collected. The handling period between capture and release was shorter than two minutes. A small number of predation events involving mole crabs, Emerita sp., which were observed on the beach of El Cuco, El Salvador (13°10′N, 88°06′W), in May 2011, were included in our analyzes for comparative purposes, as specified in the Results section.The original data is available online as ; gives an overview. When the coefficient of determination (r2) suggested a possible correlation between predator size and prey size, the relationship was described by the geometric mean functional relationship (also known as standardized major axis) following . This was necessary since neither of the two parameters (predator size and prey size) could be considered independent variables (i.e., free of significant statistical error); in such cases conventional regression analysis does not yield meaningful descriptions of the relationship between the parameters. Binomial probability calculations and χ2 tests were performed using online tools available at http://vassarstats.net/.In a subset of the documented predation events, shelled prey items (21 O. semistriata, 14 Donax sp.) that had been removed from pouches were placed in small tanks containing sand and water immediately. Any activities of the released prey were recorded over the following 5 min.Field studies were performed under the research permits ACT-OR-D-015 and ACT-OR-DR-064 to W.S.P. from the Ministerio de Ambiente y Energia de Costa Rica. […]

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