Phylogenetic and morphological relationships between nonvolant small mammals reveal assembly processes at different spatial scales

Abstract

The relative roles of historical processes, environmental filtering, and ecological interactions in the organization of species assemblages vary depending on the spatial scale. We evaluated the phylogenetic and morphological relationships between species and individuals (i.e., inter- and intraspecific variability) of Neotropical nonvolant small mammals coexisting in grassland-forest ecotones, in landscapes and in regions, that is, three different scales. We used a phylogenetic tree to infer evolutionary relationships, and morphological traits as indicators of performance and niche similarities between species and individuals. Subsequently, we applied phylogenetic and morphologic indexes of diversity and distance between species to evaluate small mammal assemblage structures on the three scales. The results indicated a repulsion pattern near forest edges, showing that phylogenetically similar species coexisted less often than expected by chance. The strategies for niche differentiation might explain the phylogenetic repulsion observed at the edge. Phylogenetic and morphological clustering in the grassland and at the forest interior indicated the coexistence of closely related and ecologically similar species and individuals. Coexistence patterns were similar whether species-trait values or individual values were used. At the landscape and regional scales, assemblages showed a predominant pattern of phylogenetic and morphological clustering. Environmental filters influenced the coexistence patterns at three scales, showing the importance of phylogenetically conserved ecological tolerances in enabling taxa co-occurrence. Evidence of phylogenetic repulsion in one region indicated that other processes beyond environmental filtering are important for community assembly at broad scales. Finally, ecological interactions and environmental filtering seemed important at the local scale, while environmental filtering and historical colonization seemed important for community assembly at broader scales. Taxa co-occurring in neotropical non-volant small-mammal assemblages show high ecological and phylogenetic similarities, which makes them useful for studying the coexistence mechanisms of ecologically related taxa. We evaluated the phylogenetic and morphological structures through species and individual approaches in a local grassland-forest ecotone, and on landscape and regional scales. We used a phylogenetic tree and morphologic traits as indicators of niche similarities between species and individuals. Our results highlight a balance between organism's tolerances in face of environmental filtering and the decrease in niche overlap due to ecological interactions limited phylogenetic relatedness and morphological similarities between taxa at the local scale. At the landscape scale, environmental filtering seemed to be an important process structuring the small-mammal assemblages. Finally, the phylogenetic and morphological structure of the small-mammal assemblages revealed the influence of both environmental filtering and historical processes at the regional scale.