Nudibranch feeding biogeography: ecological network analysis of inter-and intra-provincial variations

Timed nudibranch-density studies were performed in four different central and eastern Pacific zoogeographic provinces: Hawaiian, Oregonian, Sea of Cortez and Mexican. Densities and relative percentages of species and specimens observed were compared with all known species recorded from each faunal province to determine the functional structures of nudibranch community networks. There were greater correlations of nudibranch abundances by feeding preference between provinces than from sites within a province. Diversity (Shannon-Wiener H’ and Pielou’s J’ evenness) indices revealed contrasting patterns for bryozoan, cnidarian and sponge feeder abundances. At all levels, variation varies, resulting in complexly different relationships. INTRODUCTION Traditional marine biogeographic analyses have emphasized the occurrence of genera or species in faunal provinces. Key components of ecological differences between provinces include endemism, barriers, latitudinal gradients, and vertical/horizontal distributions (summaries in, e.g., Pielou, 1979; Briggs, 1974 and 1995; Cox & Moore, 2010). Historical biogeography has viewed these themes over time (e.g., Rex et al., 2005; Jablonski et al., 2006), analyzed abundance data in the fossil record (Kidwell, 2001, and other thanatocoenoses), and used phylogenetic and molecular methodologies (e.g., Dick et al., 2003; Rocha et al., 2007). Opisthobranch biogeographic studies have also mainly emphasized genus/species biodiversity patterns in faunal regions (e.g., Marcus & Marcus, 1967; Gosliner, 1992; Bertsch, 1993, 2009 and 2010; Jensen, 2007; Garcia, Dominguez & Troncoso, 2008; Garcia & Bertsch, 2009; Trowbridge, 2002; Trowbridge et al., 2010). Broad thematic zoogeographic comparisons have been published on developmental modes (Clark & Goetzfried, 1978; Jensen, 2003; Goddard & Hermosillo, (1) Instituto de Investigaciones Oceanologicas, Universidad Autonoma de Baja California, Ensenada,