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Navia A.F.,Fundacion Colombiana para la Investigacion | Navia A.F.,University of Valle | Navia A.F.,Centro Interdisciplinario Of Ciencias Marinas | Cortes E.,National Oceanic and Atmospheric Administration | And 2 more authors.
Ecological Modelling | Year: 2010

We built a trophic network based on a matrix of interspecific trophic relationships to assess the role of elasmobranch fishes in shaping community structure of the Gulf of Tortugas in the Colombian Pacific Ocean. We analyzed diet similarities to define trophic components (nodes) - rather than taxonomical groups - in the network. We evaluated the ecological function of species or trophic entities through topological analysis of their structural importance in trophic networks by applying one local and several mesoscale network indices. We found that top predatory elasmobranchs play an important ecological role in top-down control and in propagating indirect effects through the system owing to high values of the node degree, centrality and topological importance indices. However, invertebrates and teleost fishes had higher connectivity and topological importance than other elasmobranchs in the network before and after removal of top predators from the system. Results from our study thus suggest that elasmobranchs at intermediate trophic levels - commonly referred to as " mesopredators" - are not so important in all complex coastal ecosystems as previously reported. © 2010.

This study evaluated the relationship between body size and geographic range size, measured as extent and volume of occurrence of resident and endemic elasmobranchs of the Tropical Eastern Pacific. Data of body size, minimum and maximum depths, and latitudinal distribution of the species were obtained from the literature. Extent and volume of occurrence were measured from 3080.25-km2 quadrants, considering the northern and southern boundaries, the maximum depth, and the depth interval of the 82 species included. The relationships between body size and depth, extent of occurrence, and volume of occurrence, and between body size and bathymetric zones were evaluated using linear regression and a nonparametric analysis of variance, respectively. The relationship between body size and extent of occurrence was positive for all groups and significant only for the batoids. They occupy smaller depth intervals than sharks and are almost exclusively restricted to the euphotic zone; the resident sharks occur in the three bathymetric zones, but not the endemic sharks. The interspecific relationship of body size and volume of occurrence revealed a triangle with defined boundaries, with 22 species under the constraint line (13 sharks and 9 batoids), Pristis sp. and Manta birostris being the most prone to extinction. Although there were no factors or characteristics common to all 22 species, variables such as habits and reproductive traits influence their vulnerability, in addition to the human pressures to which they are subjected. In elasmobranchs, the triangular relationship between body size and range size is a good predictor of species susceptible to extinction, which is useful for assessing the threat status and taking action for management and prioritization of species at regional level.

The discusray has been confirmed in Colombia for the Orinoco Basin in the rivers Meta, Inírida, Tomo, Orinoco and low Arauca. This study reports this species, for first time, for the Bita River from a pregnant female captured in March 2009, therefore extending the distribution range of this species in Colombia.

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