Phylogenetic community structure of ants in secondary forests in Brazil

2.1 DNA sequencing is increasingly being used to assist in species identification in order to overcome taxonomic impediment. However, few studies attempt to compare the results of these molecular studies with a more traditional species delineation approach based on morphological characters. We sequenced the mtDNA Cytochrome oxidase subunit 1 (CO1) gene, measuring 636 base pairs, from 47 ants of the genus Pheidole (Formicidae: Myrmicinae) collected in the Brazilian Atlantic Forest to test whether the morphology-based assignment of individuals into species is supported by DNA-based species delimitation. 20 morphospecies were identified, whereas the barcoding analysis identified 19 Molecular Operational Taxonomic Unit(s) (MOTUs). We found that 15 out of the 19 DNA-based clusters allocated using sequence divergence thresholds of 2% and 3%, matched with morphospecies. Both thresholds yielded the same number of MOTUs. Only one MOTU was successfully identified to species level using the CO1 sequences of Pheidole species already in the Genbank. The average pairwise sequence divergence for all 47 sequences was 19%, ranging between 0-25%. In some cases, however, morphology and molecular based methods differed in their assignment of individuals to morphospecies or MOTUs. The occurrence of distinct mitochondrial lineages within morphological species highlight groups for further detailed genetic and morphological studies and therefore we advocate a pluralistic approach using several methods to understand the taxonomy of difficult lineages. 3.1 The assessment of the effects of habitat variation on phylogenetic composition and the processes structuring communities is of major interest to community and conservation ecologists. In this study, we used ants in the genus Pheidole in evaluating the phylogenetic composition/structure and processes structuring communities along a succession gradient in the secondary forests of Brazil. Since sampling settings can influence the performance of most indices, we used standardized measures (sesPD, NRI and NTI) besides an unstandardized measure i.e.phylogenetic distinctness (Δ* – a measure of pure phylogenetic relatedness), to test their response in detecting phylogenetic community composition and structure. We also applied null models on standardized measures in order to detect potential processes generating community patterns. Pheidole ant communities showed sensitivity to habitat variation portrayed by the overall increasing trend in phylogenetic distinctness (Δ*) along the stages of forest succession. Δ* was strongly and significantly correlated to species richness as opposed to NTI which didn’t show correlation. On overall, ant communities were phylogenetically clustered regardless of the null model used, suggesting that habitat filtering is the dominant process structuring the ant communities. That Pheidole ant communities in our study likely form non-interactive assembly, is a notion which contrasts with many studies suggesting that competitive interactions structure closely related ant communities. The observed high phylogenetic diversity in old growth forests compared to other forest stages reflects the conservation importance that need to be attached to these habitats in ensuring that maximum biodiversity value is preserved. 4.1 The mechanisms leading to phylogenetic community structure in local assemblages have become a major focus in recent community studies. Studying the phylogenetic structure of an ecological community can provide insights into the relative importance of different processes structuring that community. This study aimed at measuring the phylogenetic structure of ant genera communities occurring in 12 sites along a forest succession gradient, in the tropical secondary forests of Brazil. We also determined the processes structuring the ant communities; and tested the influence of metrics used, succession and taxonomic scale on the estimates of phylogenetic community structure. On average, the phylogenetic structure of ant communities was over-dispersed, meaning that ant species were more distantly related to their neighbours than expected by chance. The observed over-dispersion and clustering across the sites depended on the metric used and to an extent the forest succession stage, although other possible explanations may include effects of the null model, variation in the strength of ecological processes among habitats or distribution of traits. We noticed that finely defined ant communities (single genus) tended to be clustered while with several ant genera, most communities showed over-dispersion, suggesting that competition is increasingly evident as ant communities are defined to include greater phylogenetic diversity. This study shows that the phylogenetic structure of ant communities depends on interplay of several factors, most of which still need to be comprehensively researched on