Dung beetles as indicators of tropical forest restoration success: Is it possible to recover species and functional diversity?
Tropical forest restoration is becoming increasingly more applied, but knowledge about its efficacy is still limited. An essential step is to evaluate restoration activities success using a variety of metrics to assess the condition of the restored habitat. We evaluated the efficacy of tropical forest active restoration using dung beetles (Coleoptera: Scarabaeinae) as bioindicators and combining measures of species diversity, composition and functional diversity. We assessed patterns of dung beetles community assembly along a restoration chronosequence, sampling 15 forest restoration areas of varying ages (0-18 years). We also compared restoration areas with reference (5 areas of primary and old secondary forest) and degraded ecosystems (5 areas of pasture). For each species we determined food relocation habit, biomass, diel activity and diet, and used these traits to access assemblages functional diversity. Besides functional diversity, we also evaluated: a) species composition; b) species richness, rarefied richness, number of individuals and biomass; c) proportion of species and individuals classified as forest specialists, forest generalists, open environment specialists and habitat generalists. To understand the relationship of these parameters with restoration age and compare restoration areas with reference and degraded sites, we used principal coordinates analysis, permutational multivariate analysis of variance and generalized linear models.
Species composition in the restoration areas are clearly progressing towards the preserved forests and deviating from the pasture with increasing restoration age. We also found a turnover of open environment specialists and habitat generalists to forest generalists and forest specialist species along the restoration chronosequence. However, the majority of individuals in the older restored habitats were typically forest generalists. Species richness, number of individuals, biomass and functional richness in the restored areas were similar to, or even smaller, than in pastures and substantially lower than forest reference sites. Rarefied species richness, functional evenness and functional dispersion did not vary between the habitat types. Our study demonstrates that restored areas have the capacity to host forest-restricted species, but additional recovery time is likely needed to allow for the complete recovery of all biodiversity aspects. Restored areas did not show any progress through time in relation to the starting point of the restoration, and after 18 year still harbor extremely depauperate dung beetle assemblages in terms of species diversity and functional richness. Our study also demonstrates that measures of composition, species diversity and functional diversity can complement each other and contribute to a better understanding of the efficacy of restoration practices.