Ecological patterns of the small mammal communities at El Cielo Biosphere Reserve, Tamaulipas, Mexico

Scarce knowledge of Neotropical small mammal communities prevents experimental inquiry on the mechanisms structuring these communities. In this study, I examined patterns of local assembly of the small mammal communities on the eastern slopes of El Cielo Biosphere Reserve (ECBR) in Tamaulipas, Mexico, at two spatial scales. At the landscape level I tested patterns of species co-occurrences between four sites with a null model. At the local level I addressed floor microhabitat use, vertical structure use and temporal partitioning. I studied these niche axes at two adjoining forest types, Tropical Subdeciduous Forest (TSDF) and Cloud Forest (CF), that had different structural complexity. Total trapping effort consisted of 19,712 trapnights distributed over three years. In 1,365 capture events I recorded 789 individuals representing 14 species. Abundant species, mostly Peromyscus species that are of intermediate body size, co-occurred less often than expected by chance, whereas rare species, mainly Reithrodontomys species of small size, occurred at random over study sites. This pattern suggests that species interactions might be responsible for this non-random structure. Both the TSDF and CF had striking differences in both microhabitat use and temporal partitioning. In the TSDF common species (>8 individuals) organized along a microhabitat gradient from grassy/open areas to closed forest areas. Temporal partitioning for the whole community was less than expected by chance with use of an ad hoc null model. Species from ecotone/open areas avoided use of middle portions of the night whereas the single forest species concentrated activity in this period. So, it is plausible that predator avoidance strategies might have higher impact on temporal partitioning as compared to competitive interactions. In high contrast the CF community was codominated by two Peromyscus species that overlapped heavily in both their microhabitat use and diel activity patterns. Ecological separation of these two species probably occurs along a niche axis not considered in my study or might be facilitated by their body mass difference. Overall, I provide the first account of community patterns for small mammals at ECBR. These patterns can provide the basis for experimental manipulations to ascertain mechanisms responsible for structure at these communities.