Seasonal variation in a diverse beetle assemblage along two elevational gradients in the Australian Wet Tropics.

Altered abiotic conditions resulting from human-induced climate change are already driving changes in the spatial and temporal distributions of many organisms. For insects, how species are distributed across elevations is relatively well known, but data on their seasonality at different elevations are lacking. Here we show seasonal variation in beetle abundance and species richness along two spatially-distinct elevational transects (350-1000 m and 100-1000 m asl) in the rainforests of northern Australia. Temperature was the best predictor of temporal abundance and species richness patterns, while rainfall had little influence. Elevation had little effect on seasonal changes in abundance or diversity. Adults of most beetle species exhibited long season-lengths (>6 months of the year) with distinct peaks in abundance during the summer wet-season. We found evidence of phenotypic variation among the more widespread species, with seasonal peaks in abundance often not coinciding across elevations or transects. Due to the wide elevational range of most species, and the lack of consistency in the seasonality of wide-spread individual species, we suggest that many beetles inhabiting the low to mid-elevation mountains in the Wet Tropics, and potentially other tropical rainforests, are not as vulnerable to extinction due to climate change as many other organisms.

Consistency of effects of tropical-forest disturbance on species composition and richness relative to use of indicator taxa.

Lawton et al. (1998) found, in a highly cited study, that the species richness of 8 taxa each responds differently to anthropogenic disturbance in Cameroon forests. Recent developments in conservation science suggest that net number of species is an insensitive measure of change and that understanding which species are affected by disturbance is more important. It is also recognized that all disturbance types are not equal in their effect on species and that grouping species according to function rather than taxonomy is more informative of responses of biodiversity to change. In a reanalysis of most of the original Cameroon data set (canopy and ground ants, termites, canopy beetles, nematodes, and butterflies), we focused on changes in species and functional composition rather than richness and used a more inclusive measure of forest disturbance based on 4 component drivers of change: years since disturbance, tree cover, soil compaction, and degree of tree removal. Effects of disturbance on compositional change were largely concordant between taxa. Contrary to Lawton et al.'s findings, species richness for most groups did not decline with disturbance level, providing support for the view that trends in species richness at local scales do not reflect the resilience of ecosystems to disturbance. Disturbance affected species composition more strongly than species richness for butterflies, canopy beetles, and litter ants. For these groups, disturbance caused species replacements rather than just species loss. Only termites showed effects of disturbance on species richness but not composition, indicating species loss without replacement. Although disturbance generally caused changes in composition, the strength of this relationship depended on the disturbance driver. Butterflies, litter ants, and nematodes were correlated with amount of tree cover, canopy beetles were most strongly correlated with time since disturbance, and termites were most strongly correlated with degree of soil disturbance. There were moderately divergent responses to disturbance between functional feeding groups. Disturbance was most strongly correlated with compositional differences of herbivores within beetles and nematodes and humus feeders within termites. Our results suggest that consideration of the impact of different forms of disturbance on species and functional composition, rather than on net numbers of species, is important when assessing the impacts of disturbance on biodiversity.

Biodiversity meets the atmosphere: a global view of forest canopies.

The forest canopy is the functional interface between 90% of Earth's terrestrial biomass and the atmosphere. Multidisciplinary research in the canopy has expanded concepts of global species richness, physiological processes, and the provision of ecosystem services. Trees respond in a species-specific manner to elevated carbon dioxide levels, while climate change threatens plant-animal interactions in the canopy and will likely alter the production of biogenic aerosols that affect cloud formation and atmospheric chemistry.

Insects in fragmented forests: a functional approach.

Insects are highly susceptible to the adverse effects of forest fragmentation. It is now beyond any doubt that fragmentation-induced changes in abundance and species richness occur in many insect groups. However, the study of insects in fragmented forests is still in its infancy and lacks real direction. Simple empirical studies are not answering the questions we most want to answer about fragmented systems. Are we in the midst of a mass-extinction crisis? What is the functional significance of the immense insect biodiversity? Does biodiversity loss affect ecosystem functioning? A more focused, functional approach to the study of forest fragmentation is required to move beyond the description of pattern and to determine how changes in insect communities affect ecosystem processes in fragmented forests.