Browsing by Author "Emberson, Rowan M."

External threats from agricultural intensification, fire encroachment, species invasion and illegal harvesting present major conservation challenges in isolated tropical forest remnants. These processes can greatly exacerbate the magnitude of edge effects as the degree of patch to matrix contrast increases. Theory suggests that mitigation of these effects should be possible through conservation strategies that remove external threats and restore adjacent matrix structure, but this has not been tested experimentally. In the rapidly-dwindling Afromontane rainforests of Nigeria, where nature reserves have the least protection of all African conservation areas, we created an experimental matrix restoration treatment in which we excluded livestock by fencing, maintained a fire-exclusion break, and passively revegetated a 200 m buffer zone in the surrounding matrix at replicated edges. After three years, dung beetle communities in remnant forests showed a 53% increase in abundance at sites adjacent to the restored matrix. Over 90% of the common dung beetle species differed in the magnitude of their edge responses between forest-to-restored versus forest-to-degraded matrix sites. Moreover, a significant difference in species richness across the forest-to-degraded matrix edge became non-significant following matrix restoration, and there was also a significant decrease in community dissimilarity across the edge gradient in these regenerating sites. Just three years after excluding threatening processes from comparatively small areas of matrix habitat, we found that these efforts not only reduced edge effects, but also (1) enhanced dung beetle populations in the adjacent reserve, (2) led to an increase in dung beetle capture rates in the regenerating matrix, and (3) facilitated re-establishment of species that were absent due to matrix degradation. Therefore, regenerating buffers can substantially increase effective reserve size and restore invertebrate communities in landscape mosaics where remnant habitats are embedded within anthropogenic landscapes. (C) 2013 Elsevier Ltd. All rights reserved.

New Zealand biodiversity has often been viewed as Gondwanan in origin and age, but it is increasingly apparent from molecular studies that diversification, and in many cases origination of lineages, postdate the break-up of Gondwanaland. Relatively few studies of New Zealand animal species radiations have as yet been reported, and here we consider the species-rich genus of carabid beetles, Mecodema. Constrained stratigraphic information (emergence of the Chatham Islands) and a substitution rate for Coleoptera were separately used to calibrate Bayesian relaxed molecular clock date estimates for diversification of Mecodema. The inferred timings indicate radiation of these beetles no earlier than the mid-Miocene with most divergences being younger, dating to the Plio-Pleistocene. A shallow age for the radiation along with a complex spatial distribution of these taxa involving many instances of sympatry implicates recent ecological speciation rather than a simplistic allopatric model. This emphasises the youthful and dynamic nature of New Zealand evolution that will be further elucidated with detailed ecological and population genetic analyses.

Reversing anthropogenic impacts on habitat structure is frequently successful through restoration, but the mechanisms linking habitat change, community reassembly and recovery of ecosystem functioning remain unknown. We test for the influence of edge effects and matrix habitat restoration on the reassembly of dung beetle communities and consequent recovery of dung removal rates across tropical forest edges. Using path modelling, we disentangle the relative importance of community-weighted trait means and functional trait dispersion from total biomass effects on rates of dung removal. Community trait composition and biomass of dung beetle communities responded divergently to edge effects and matrix habitat restoration, yielding opposing effects on dung removal. However, functional dispersion-used in this study as a measure of niche complementarity-did not explain a significant amount of variation in dung removal rates across habitat edges. Instead, we demonstrate that the path to functional recovery of these altered ecosystems depends on the trait-mean composition of reassembling communities, over and above purely biomass-dependent processes that would be expected under neutral theory. These results suggest that any ability to manage functional recovery of ecosystems during habitat restoration will demand knowledge of species' roles in ecosystem processes.