Diversity patterns along ecological succession in tropical dry forests: a multi-taxonomic approach

Evaluating the diversity of multiple taxa is fundamental to understand community assembly and to assess the integrity and functionality of tropical secondary forests. In this study, we analyzed the natural regeneration of tropical dry forests (TDFs) in three regions of Brazil using Hill-Simpson diversity, abundance and beta-diversity of trees and five groups of insects (herbivores, fruit-feeding butterflies, ants, culicid mosquitoes and dung beetles). Sampling was conducted in 39 0.1 ha plots using a chronosequence approach (13 plots in early, intermediate and old-growth forests). We evaluated the contribution of three different levels to gamma-diversity: alpha (within plots), beta 1 (among plots) and beta 2 (among successional stages), and further determined the relative importance of turnover (species replacement) and nestedness (differences in species number among sites) to beta 2. Our results showed that, unexpectedly, the Hill-Simpson diversity was consistently higher in early than old-growth stages for all regions, but varied more widely in the intermediate stages. For each group separately, the same trend was observed for butterflies, ants, dung beetles and herbivores and did not differ among stages for mosquitoes. Successional differences in abundance were only detected for trees (increasing along the gradient) and for mosquitoes (decreasing). According to our expectations, the additive partitioning analysis showed that beta 2-diversity contributed more to gamma-diversity than beta 1-diversity, when all taxa were considered together and for most of them separately (except for butterflies and dung beetles). Most of the beta 2-diversity was due to species turnover, but this contribution varied among groups and regions, with the highest turnover for herbivores and the lowest for dung beetles. Our results suggest that the Hill-Simpson diversity and changes in species composition (as given by beta 2-diversity) are better indicators of forest natural regeneration than raw species richness, corroborating previous studies with plants and animals.