Abstract

Traditionally Antarctica has been divided into three biogeographic regions, and the Chilean Patagonia and Falkland/Malvinas as a unit. However, the underlying causes of this pattern are still poorly understood. In this study we use oribatid mites to evaluate (1) biogeographic regions described for Antarctic and Patagonia, (2) the role of distance on the structuring pattern and (3) the source-sink metacommunity dynamic as an explanation for the geographic patterns of oribatologic assemblages. The study used a database compiled from oribatids literature of Chilean Patagonia, Falkland/Malvinas Islands, Scotia Arc and Antarctic Peninsula. The latitudinal structures patterns were assessed first by cluster analysis with the Sorensen index under the UPGMA algorithm, and then by similarity profile routine to statistically delimit the biogeographic regions. To evaluate the role of distance in the biogeographic structure, was correlated the similarity matrix with a distance matrix. As a final point, to evaluate if a source-sink metacommunity dynamic models the assemblages between biogeographic units, we perform a nestedness analysis (NODE) using the total matrix, Antarctica, and Patagonia. The analysis supporting 9 subdivisions within the four previously proposed biogeographic regions: (1) Temperate Zone with five units (i.e. Aysen, Ultima Esperanza, Magellanes, Beagle Channel, and Falkland/Malvinas Islands); (2) Subantarctic Region with two units (i.e. South Georgia, and South Sandwich Islands); (3) Maritime Antarctic as a single group; and (4) Continental Antarctica as another single large group. Our results shows that the geographic distance significantly restricts and structured the species turnover (i.e. isolation by distance), and consequently the distance can limit the spread of new colonizers. On the other hand, the matrix is significantly nested, which could be explained by a source-sink dynamic. Finally, the source-sink metacommunity dynamic can be modeling the species richness in the region, which would be maintained largely by the contribution of individuals colonizers from species that inhabiting areas with higher species richness.