Patterns of endemism in south‐eastern Pacific benthic polychaetes of the Chilean coast

Abstract

Aim In this study we evaluate patterns of endemism for benthic polychaete species along the southeastern Pacific coast of Chile. Our goals were (1) to describe latitudinal gradients of endemism and identify areas of high endemism, (2) to evaluate the effect of biogeographical limits on endemism patterns, and (3) to evaluate indirectly the role played by evolutionary dynamics on patterns of endemism.Location South-eastern Pacific coast of Chile, ranging from Arica (18°S) to Cape Horn (56°S). MethodsWe used a list of 178 species of endemic, shallow benthic polychaetes to evaluate patterns of endemism. Parsimony analysis of endemicity (PAE) and the endemism index (EI) were used to evaluate hierarchical relationships of endemism between different latitudinal bands, and to identify areas with high degrees of endemism and differences in endemism. We evaluated the effect of biogeographical limits on endemic polychaete fauna by testing for the existence of geometric constraints (mid-domain effect). The role of evolutionary dynamics on latitudinal patterns of endemism was evaluated with nestedness analysis (NA) using the temperature index. ResultsThe PAE analysis indicated two large, separate areas of endemism: (1) the northern area between 18°S and 38°S, and (2) the southern area between 39°S and 56°S. The endemism index showed a maximum value (32 species) around 39°-41°S. Species-richness curves of each 3°band of latitude showed a clear mid-domain effect (69%), but the two maximum points of species richness at mid-latitudes (36°S to 38°S and 39°S to 41°S) did not correspond to the mid-domain peak in species richness, presenting a greater number of species than expected by the mid-domain effect. The nestedness analysis showed that the number of genera reaches a maximum of 70 at mid-latitudes (36°-41°S), decreasing towards both the northern and southern areas. The spatial distribution of the entire data set of endemic species showed a nested pattern (T°¼ 24.5°, P < 0.0001). Main conclusionsOur results strongly support the existence of a latitudinal gradient of endemism for benthic polychaete species along the Chilean coast. The shape of this gradient is clearly non-linear, with a marked peak of endemism occurring at mid-latitudes (36°-41°S, endemism hotspot), which also corresponds to a peak in species richness. Furthermore, this hotspot is the midpoint separating two distinct areas of endemism to the north and south. We suggest that the observed pattern of endemism for benthic polychaete taxa of the Chilean coast can be explained by a combination of geometric constraints and historical mechanisms, such as the processes that affected the Chilean coast during the Neogene (e.g. ENSO, oxygen minimum zone, glaciations).

The Macrobenthic Ecology of the Straits of Magellan and the Beagle Channel

“…The absence of any correlating pattern in diversity in the study region is consistent with other studies (Gutt et al 1999) and may result from variation in hydrologic regime and sedimentation processes between stations and/or the low number of replicates. Moreno et al (2006) identified a pattern of decreasing endemism in benthic polychaete species of the Magellan region with increasing latitude. Although species endemic to the Straits of Magellan and the Beagle Channel are therefore less likely to have been observed, the absence of available biogeographic information in the literature prevented an assessment of endemism within the study region.…”

Análisis, síntesis y evaluación de la literatura de lagartos de la Región de Atacama, Chile

“…Este análisis está basado en datos de rangos de distribución encontrados en publicaciones y datos de campo. A la luz de los antecedentes analizados y evaluados en el presente trabajo, se carecería de la información necesaria para establecer los niveles de endemismos para la Región de Atacama, es decir el número total de especies en los cuadrantes señalados y el número de cuadrantes con cada una de las especies (Moreno et al 2006). Consideramos necesario reevaluar los niveles de endemismo de las especies de lagartos en la Región de Atacama, a la luz de más información que permita una mayor certeza de la riqueza de especies y sus rangos de distribución.…”

Riqueza e endemismo de espécies de Baptistonia (Orchidaceae), no Brasil

“…Este índice é útil para diferenciar quadrículas igualmente ricas em número de espécies, mas com diferentes graus de endemismo (Moreno et al 2006). Peterson & Watson (1998) puseram em evidência o problema de distinção entre uma definição regional do endemismo e uma definição global, porém, esse problema não interfere no presente trabalho, no qual a abrangência do estudo cobre a totalidade da área de ocorrência das espécies de Baptistonia.…”

“…A literatura é rica em dados sobre esse conceito e sobre as dificuldades de como estima-lo (Walther & Morand 1998, Hellmann & Fowler 1999, Gotelli & Colwell 2001, Ackerman et al 2007, Smidt et al 2007. O conceito de endemismo foi também amplamente discutido para diversos táxons em diversas áreas geográficas, tanto para quantificá-lo (Usher 1986, Kerr 1997) como para comparar uma régião à outra (Ron 2000, Bisconti et al 2001, Linder et al 2005, Porzecanski & Cracraft 2005, Moreno et al 2006. O presente estudo se baseia na avaliação destes dois conceitos, riqueza e endemismo, para o gênero Baptistonia Barb.…”