Effects of land use and habitat fragmentation on local biodiversity

Abstract

Land use change is one of the greatest threats to biodiversity. Land-use change often results in fragmentation of the landscape, yet this aspect is rarely taken into account in models of how land use affects biodiversity. Additionally, previous biodiversity models have been restricted to large spatial scales, which may not be applicable for conservation practitioners. In this thesis I analyse datasets collated from multiple published studies of how local terrestrial biodiversity responds to human impacts. I start Chapter 2) by modelling how land use, specifically secondary vegetation and plantation forests, impacts tropical biodiversity. My results show that the biodiversity in each continent does respond differently to land use, an aspect that previous studies have not investigated. This difference is most likely due to the nature of the land use being different in each continent. In this first analysis, as is often the case, drivers of biodiversity change were focused on site-level environment, such as land use. Therefore, in Chapter 3 I investigate how the area of habitat surrounding a sampled area might influence the number and abundance of species within the sample. Theory suggests that within-sample species richness would increase with fragment area with an exponent between 0.07 and 0.20, which was found to be the case. Chapter 4 builds on the previous chapters in two ways. Firstly, it applies the previously used methods to create a biodiversity model of habitat change for a smaller area to inform decision making. Secondly, it specifically takes into account how local biodiversity responds to changes in fragment area. I estimated that the planned changes to the small urban area would result in a gain in overall biodiversity, most likely due to an increase is size and number of high diversity habitats. To consider these results at a landscape scale, my final chapter (Chapter 5) investigates how the wider context around a sampled site influences local biodiversity. By studying the impact on biodiversity across this range of spatial scales, I can ascertain the importance of taking these variables into account and determine the implications of my results for previous models of biodiversity. I found that landscape fragmentation, as well as local land use, was a necessary component of models of local biodiversity, and its inclusion greatly improved previous biodiversity models.