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Gonzalez S.,Museo Nacional de Historia Natural CC. 399 | Carranza A.,Museo Nacional de Historia Natural | Scarabino F.,Museo Nacional de Historia Natural CC. 399 | De Mello C.,Museo Nacional de Historia Natural CC. 399 | Ligrone A.,Museo Nacional de Historia Natural CC. 399
Pan-American Journal of Aquatic Sciences | Year: 2011

The analysis of the coexistence structure in assemblages of congeneric species might provide significant insights on the mechanisms underlying community assembly rules. We evaluated the existence of co-occurrence patterns among the five species of the gastropod genus Buccinanops occurring in the inner Uruguayan shelf and Río de la Plata estuary. Presence records were gathered from published geo-referenced data, samples from research cruises onboard R/V "Aldebaran" and Museo Nacional de Historia Natural de Montevideo (MNHNM). We evaluated the predictions of two species assembly hypothesis: co-occurrence due to affinity with similar conditions (niche filtering) and segregation of species due to interespecific competition (limiting similarity). After assembling a presence-absence matrix, the coexistence structure was analyzed for three spatial scales. The co-occurrence was measured using four indexes (C-score, Checkerboard distributions, Number of species combinations and V-ratio) and contrasted with two null models obtained from two resampling methods keeping columns and rows (1) fixed and (2) equiprobable. We found support to the hypothesis that coexistence of congeneric species would be less than expected by chance. However, results were dependent on the spatial scale considered and the null model used.

Carranza A.,UNDECIMAR | Arim M.,Seccion Zoologia Vertebrados | Scarabino F.,Museo Nacional de Historia Natural CC. 399 | Defeo O.,UNDECIMAR
Oikos | Year: 2010

Community assembly rules theory attempt to understand the processes that determine the composition of local communities from a regional species pool. Nestedness and negative co-occurrence are two of the most commonly reported meta-community patterns, but almost exclusively from terrestrial and freshwater ecosystems. Here we analyzed the structure of species coexistence in six datasets containing presence/absence data for 120 marine benthic gastropod species in 249 sampling units on the Uruguayan continental shelf and Río de la Plata estuary. The ecological features of this system, such as the idiosyncratic nature of the biogeographic and oceanographic realms, are clearly different from those observed in other systems previously targeted by studies on coexistence structure. Community patterns were evaluated using null models and four structure indices. The existence of patterns in community assembly, and in particular segregated co-occurrence, was verified only when analyzing the number of checkerboard units (CH index). This indicates more mutually exclusive species pairs than expected by chance. Nestedness, on the other hand, was not detected in any dataset. Storage and rescue effects related to overall high immigration and low local extinction rates are plausible mechanisms to account for the general pattern of random species coexistence, while the segregated co-occurrence pattern depicted by the CH index may be related to differential habitat requirements within species pairs. Our study highlights the importance of analyzing metacommunity structures in alternative biological, environmental, and historical contexts in order to advance on the construction of a general ecological theory, relating patterns with the processes dominating in particular ecosystems. © 2009 The Authors.

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