Spatial turnover of insect communities at rainforest edges

Abstract

Rainforest fragmentation is leading to huge increases in the quantity of forest in close proximity to edges. Edge effects may cause multiple alterations to ecological processes, however we do not know their impacts on the spatial turnover of communities, β-diversity. Using a dung beetle community in the north-east Brazilian Amazon, I addressed the problem in four, systematic steps. First, as β-diversity is spatially dependent it is essential to sample at small through to broad scales, presenting us with a limitation of sampling over large areas at fine scales. I present a scalable sampling design based upon a fractal series of equilateral triangles that proved in simulations to be more efficient at recovering accurate estimates of β-diversity than classical sampling designs. Second, I investigated optimal bait choice for accurately sampling the dung beetle community. A human-pig dung mix was found to be as effective as pure human dung baits, whilst removing possible dung source limitations. Third, I investigated the drivers of β-diversity based upon traits that govern foraging strategies. Wing and body morphology was found to be a significant predictor of the spatial scales at which species populations were structured. I then partitioned the variation attributed to environment and space for each morphological subset at three spatial scales. The drivers, and the scales at which they were most important, were dependent upon morphological traits, which further interacted with habitat modification. Finally, I investigated if β-diversity was greater in dung beetles at the forest edge. Linearising the fractal design, I estimated turnover within communities at set distances from the edge. Results were mixed: there was no elevation at a primary-Eucalyptus forest edge, but significantly higher turnover within communities at a primary-secondary forest edge than interior communities. This work increases our knowledge of how fragmentation and edge effects impact the underlying processes governing diversity.