Towards a functional classification of poorly known tropical insects: The case of rhinoceros beetles (Coleoptera, Dynastinae) in Panama

The population dynamics of most tropical insects are unknown and long-term monitoring programmes are urgently needed to evaluate a possible insect decline in the tropics. In this context, functional groups can be used effectively to summarise time-series for species-rich taxa. Neotropical dung beetles have often been catalogued into functional groups, but close relatives also of ecological significance, the Dynastinae, are awaiting such a classification. Here, we examine the functional groups of Dynastinae at the regional (Panama: 147 species) and local (Barro Colorado Island, BCI: 56 species) scales. Our optimum classification of Panamanian species distinguished five groups, one of which is probably artificial and accounts for species ecologically poorly known. Ecological attributes or species traits mainly influencing the delineation of groups were geographical distribution, body length, seasonal aggregation, larval food and whether the adult may be present in decaying wood. Our analyses indicated that (1) missing trait values and the high percentage of 'cryptic' species (25%) influenced the delineation of groups; (2) the dendrogram similarity of functional groups versus phylogenetic tree was low, although some traits were phylogenetically conserved; and (3) the overall structure of functional groups was conserved when comparing regional and local data, suggesting no drastic loss of functional groups locally. To proceed with the functional classification of poorly known tropical insects, we recommend a cautious selection of traits a priori, inclusion of 'cryptic' species recognised by DNA barcoding, and building phylogenies, which may allow a careful taxonomic imputation to complete species-traits matrices.