Vertical stratification of leaf-beetle assemblages (Coleoptera: Chrysomelidae) in two forest types in Panama
Journal of Tropical Ecology
To study vertical gradients of arthropod species richness in tropical forests, adult chrysomelids were surveyed with similar sampling effort by beating in four plots of 0.8 ha, representative of the canopy and understorey of one wet and one dry forest in Panama. Samples included in total 4615 individuals representing 253 species, and were of similar species richness at the two study sites. At both sites, chrysomelids were significantly more species-rich in the canopy than in the understorey. The proportion of species shared between the two study sites was 24%, whereas 16% and 28% of species were shared between the canopy and understorey of the wet and dry sites, respectively. Mature trees supported more and different chrysomelid species than conspecific saplings. A higher proportion of liana feeders vs. tree feeders occurred at the dry site than at the wet site. Multivariate analyses confirmed the faunal differences between the wet and dry sites and that stratification was more marked at the wet site than at the dry site. The latter observation may relate to differences in forest physiognomy (a tall and closed canopy at the wet site) and to the high interconnectivity via lianas between the understorey and canopy at the dry site. "Tropical herbivores may be less specialized with regard to resource use (i.e. use of different host-plants), but more specialized with regard to habitat use (i.e. use of host-plants in different forest strata) than temperate herbivores - Basset et al. 2003, Novotny et al. 2002) Herbivores such as leaf beetles (Chryomelidae) represent suitable test organisms to study vertical gradients in tropical forests, since they are dependent on the presence of young foliage with high protein content. Every beetle collected was placed in a plastic vial in a laboratory with a portion of young leaf, mature leaf or flower from the plant it was collected on. Evidence of feeding or frass was recorded for a period of up to 305 d and each specimen was eventually classified as feeding or not feeding.