Beta diversity patterns in Andean rodents: current and historical factors as drivers of turnover and nestedness

The Andes are known to be one of the most species-rich regions on Earth, with their origination promoting formation of new habitats and acting as climatic barriers. This orogenic event was structured latitudinally with 3 major segments having different formation times and with different environmental and historical conditions. The Andean region has been historically important in the evolutionary history of small mammals and is considered the region of Earth with the highest values of rodent species richness and turnover. Therefore, the region provides an excellent opportunity to evaluate mechanisms involved in structuring rodent assemblages and beta diversity patterns. Here, we assessed spatial patterns of rodent beta diversity along the Andes Mountains, with specific goals of examining patterns of turnover and nestedness as 2 recognized processes that drive species composition. We explored the role of spatial, climate, and historical factors on beta diversity patterns using geographic range maps for 432 rodent species to construct a species presence-absence matrix. We used piecewise regressions to identify latitudinal breakpoints in turnover and nestedness, and conducted multiple regressions and variation-partitioning approaches to assess the contribution of each set of postulated drivers in shaping beta diversity patterns. Beta diversity decreases from north to south. The highest turnover was located at the Northern Andes (5 degrees N and 10 degrees S) and western-central Andes (20 degrees S and 35 degrees S). Nestedness was higher below 40 degrees S and in some areas of the western-central Andes between 15 degrees and 20 degrees S. Turnover and nestedness registered breakpoints coincident with the Central and Southern Andes limit. Turnover explained most of the beta diversity for all segments, although within the Southern Andes there was also some contribution of nestedness. In all segments, beta diversity was mainly explained by spatial factors with minor contributions from spatially structured climate (Northern Andes), interaction of all factors (Central Andes), and the interaction between current climate and history (Southern Andes). Beta diversity of Andean rodents decreases latitudinally, with turnover as the dominant process and nestedness with higher contribution in the Southern Andes. Beta diversity break points partially support Andean orogenic history reflected among latitudinal segments. Figure 3 of this manuscript is recommended for promoting this research. Los Andes son reconocidos como una de las regiones mas ricas en especies de la tierra, ya que su levantamiento favorecio la formacion de nuevos habitats y actuo como barrera climatica. Este evento orogenico se estructuro latitudinalmente en 3 segmentos, cada uno con tiempos de formacion caracteristicas ambientales y condiciones historicas diferentes. La region Andina ha sido un importante escenario en la historia evolutiva de los pequenos mamiferos y es considerada la region con mayor riqueza y recambio de especies. Por lo tanto, es un excelente escenario para evaluar los mecanismos que estructuran los patrones de diversidad beta del ensamble de roedores. Aqui evaluamos el patron espacial de la diversidad beta de roedores a lo largo de la Cordillera de los Andes, descomponiendolo en recambio y anidamiento, con el fin de comprender los procesos subyacentes que determinan la composicion de especies. Exploramos el papel de los factores espaciales, climaticos e historicos sobre los patrones de diversidad beta utilizando mapas de distribucion geografica para 432 especies de roedores obtenidos de la Base de Datos de Diversidad de Mamiferos y construimos una matriz de presencia-ausencia de especies (PAM). Utilizamos regresiones por tramos (picewise) para identificar los puntos de quiebre latitudinales en recambio y anidamiento, y realizamos regresiones multiples y particion de la varianza para evaluar la contribucion de cada conjunto de factores en la conformacion de los patrones de diversidad beta. La diversidad beta disminuye de Norte a Sur, con un mayor recambio en los Andes del Norte (5 degrees N y 10 degrees S) y en la zona central oeste (20 degrees S y 35 degrees S). El anidamiento fue mas alto por debajo de los 40o S y en algunas areas del centro oeste entre los 15 degrees y 20 degrees S. Tanto el recambio como el anidamiento registraron puntos de quiebre coincidentes con el limite entre el segmento Central y el Sur. El recambio explica la mayor parte de la diversidad beta para todos los segmentos, aunque el anidamiento contribuye tambien a la diversidad beta de los Andes del Sur. En todos los segmentos andinos la diversidad beta se explico principalmente por factores espaciales con una menor contribucion del clima actual (NA), por la interaccion de todos los factores (CA) y la interaccion entre el clima historico con el actual (SA).