Assessing Biodiversity and Ecosystem Functioning in Fragmented Tropical Landscapes Michael James Montgomery Senior
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Assessing biodiversity and ecosystem functioning in fragmented tropical landscapes Michael James Montgomery Senior Doctor of Philosophy University of York Biology April 2014 Abstract Agricultural expansion and logging are resulting in habitat degradation and fragmentation, especially in tropical regions. In Southeast Asia oil palm agriculture and commercial logging are the main threats to rainforest biodiversity, and I assessed the impacts of forest disturbance and land-use change on species composition and ecosystem functioning. I explored the role of the High Conservation Value (HCV) approach for biodiversity conservation in tropical agricultural landscapes and concluded that better knowledge exchange between scientists and HCV users is needed to improve biodiversity conservation in managed landscapes. I carried out a meta-analysis to examine the responses of birds, ants and beetles to the conversion of rainforest to oil palm which revealed that species in plantations were generally small-bodied species from lower trophic levels that had low abundances in forest. I collected new field data from Sabah (Malaysian Borneo) on dung beetle diversity and ecosystem functioning in undisturbed forest, selectively logged forest and forest fragments (5-3,529 ha). Dung beetle diversity was adversely affected by forest fragmentation, but not by selective logging. Larger fragments with better quality forest supported similar species assemblages to continuous forest, including functionally important dung beetle species. Dung removal, seed burial and seed dispersal were maintained in selectively logged forest, but were reduced by >50% in forest fragments. Dung removal in forest fragments was dependent on a few large, disturbance-tolerant species, which resulted in highly variable rates of functioning in fragments. Consistently high rates of dung removal and seed dispersal required high species richness as well as high biomass of dung beetles. Overall, forest fragmentation adversely affected diversity and ecosystem functioning, although fragments >100 ha maintained some dung beetle diversity and ecosystem functions. By contrast, degraded logged forest was functionally similar to undisturbed forest and thus should receive higher protection. 2 Contents Abstract 2 Contents 3 List of Tables 12 List of Figures 13 Acknowledgments 17 Author’s declaration 19 Chapter 1 - Introduction 20 1.1 Biodiversity 20 1.1.1 Defining and measuring biodiversity 20 1.1.2 Global biodiversity 21 1.1.3 Southeast Asian biodiversity 22 1.2 Ecosystem functioning 23 1.3 Dung beetles 24 1.4 Threats to tropical biodiversity 27 1.4.1 Land use change in Sabah, Malaysia 28 3 1.4.2 Oil palm agriculture and the Roundtable on Sustainable Palm Oil 29 1.5 Understanding and addressing the ecological impacts of land use change 30 1.5.1 Habitat fragmentation 30 1.5.2 Habitat quality and complexity 31 1.5.3 Conservation strategies 32 1.6 Thesis rationale and objectives 33 Chapter 2 - Improving the effectiveness of the ‘High Conservation Value’ (HCV) process for biodiversity conservation in managed tropical landscapes 36 2.1 Abstract 36 2.2 Introduction 37 2.3 What is the HCV approach? 40 2.4 Advantages of the HCV approach 43 2.5 Improving the HCV approach for conserving tropical biodiversity 44 2.6 Knowledge sharing between HCV users, scientists and policy makers 45 2.7 Solutions to improve the HCV evidence base 48 2.8 Acknowledgements 49 4 Chapter 3 - Trait-dependent declines of species following conversion of rain forest to oil palm plantations 50 3.1 Abstract 50 3.2 Introduction 51 3.3 Methods 53 3.3.1 Traits examined and guild classification 55 3.3.2 Analyses 57 3.4 Results 60 3.4.1 Selection of best models and model confidence 60 3.4.2 Best predictors of sensitivity to conversion 63 3.4.3 Similarity of responses among taxa 66 3.4.4 Influence of phylogeny 66 3.6 Discussion 68 3.6.1 Conserved trait declines 68 3.6.2 Drivers of trait declines 68 3.6.3 Hyper-abundance of species on plantations 70 3.6.4 Conclusions 71 3.8 Acknowledgments 72 Chapter 4 - Sampling dung beetles and their ecosystem functions in fragmented and degraded rainforest 73 5 4.1 Abstract 73 4.2 Study location 74 4.2.1 Local Fauna 77 4.2.2 Climate 77 4.2.3 Management history 81 4.3 Sampling protocols 86 4.3.1 Dung beetle sampling 86 4.3.2 Species identification and biomass calculations 87 4.3.3 Robustness of sampling 90 4.3.4 Comparing bait types in assessment of dung beetle assemblages 96 4.3.5 Measuring ecosystem functions of dung beetles 100 4.3.5.i Dung removal 100 4.3.5.ii Secondary seed dispersal 102 4.3.5.iii Experimental exclusion of Catharsius species 104 4.3.6 Vegetation structure and microclimate measurements 108 4.3.6.i Quantifying forest quality 111 4.4 Statistical Analyses 114 4.4.1 Calculating site characteristics 114 4.4.2 Measures of species richness 115 4.4.3 Information theory and linear mixed models 116 Chapter 5 - The response of dung beetle assemblages to forest fragmentation: effects of fragment area, forest quality and isolation 119 6 5.1 Abstract 119 5.2 Introduction 120 5.3 Methods 126 5.3.1 Study sites 126 5.3.2 Dung beetle sampling 128 5.3.3 Analysis 129 5.3.3.i Differences in dung beetle diversity between twice-logged and pristine continuous forest (Hypothesis 1) 130 5.3.3.ii Differences in dung beetle diversity between continuous forest and fragments (Hypothesis 2) 130 5.3.3.iii Effects of fragment area, forest quality, and isolation on dung beetle diversity (Hypothesis 3) 132 5.3.3.iv Turnover of dung beetle species assemblages among sites (Hypothesis 4) 133 5.4 Results 135 5.4.1 Differences in dung beetle diversity between twice-logged and pristine continuous forest (Hypothesis 1) 135 5.4.2 Differences in dung beetle diversity between continuous forest and forest fragments (Hypothesis 2) 136 5.4.3 Effects of fragment area, forest quality, and isolation on dung beetle diversity (Hypotheses 3) 140 5.4.4 Turnover of dung beetle species assemblages among sites (Hypothesis 4) 150 5.5 Discussion 156 5.5.1 Differences in dung beetle assemblages between continuous forest and fragments 156 7 5.5.2 Differences in dung beetle assemblages among forest fragments 158 5.5.3 Conservation management implications 160 5.5.4 Possible impacts on ecosystem functioning 162 5.5.5 Conclusion 163 Chapter 6 - Ecosystem functioning in fragmented rainforest 165 6.1 Abstract 165 6.2 Introduction 166 6.3 Methods 170 6.3.1 Study sites 170 6.3.2 Dung removal 172 6.3.3 Seed burial and horizontal seed dispersal 172 6.3.4 Analysis 172 6.3.4.i Differences in ecosystem functions between unlogged continuous forest, twice-logged continuous forest and forest fragments (Hypothesis 1 & 2) 172 6.3.4.ii Effects of fragment area, forest quality, and isolation on ecosystem functions (Hypothesis 3) 174 6.4 Results 175 6.4.1.i Differences in ecosystem functions between unlogged continuous forest, twice-logged continuous forest and forest fragments (Hypothesis 1 & 2) 175 6.4.1.ii Effects of fragment area, forest quality, and isolation on ecosystem functions (Hypothesis 3) 180 6.5 Discussion 187 8 6.5.1 Impacts of fragmentation on dung beetle functions 187 6.5.2 Within site variation in dung beetle functions 189 6.5.3 Altered functional requirements in forest fragments 190 6.5.4 Plant composition and the viability of HCV fragments 191 6.5.5 Conclusion 193 Chapter 7 - Relating species richness to ecosystem function in fragmented tropical landscapes: the importance of functionally dominant species 194 7.1 Abstract 194 7.2 Introduction 195 7.3 Methods 199 7.3.1 Comparing the impacts of biomass and species richness on dung removal, seed burial and seed dispersal (Hypothesis 1) 200 7.3.2 Comparing the importance of Catharsius spp. for dung removal in unlogged continuous forest, twice-logged continuous forest and forest fragments (Hypotheses 2-3) 201 7.3.3 Assessing the contribution of non-Catharsius spp. to dung removal (Hypothesis 3) 203 7.4 Results 204 7.4.1 Comparing the impacts of biomass and species richness on dung removal, seed burial and seed dispersal (Hypothesis 1) 206 7.4.2 Comparing the importance of Catharsius spp. for dung removal in unlogged continuous forest, twice-logged continuous forest and forest fragments (Hypotheses 2-3) 211 9 7.4.3 Assessing the contribution of non-Catharsius spp. to dung removal (Hypothesis 3) 215 7.5 Discussion 220 7.5.1 The biodiversity-ecosystem function relationship 220 7.5.2 Interspecific differences in dung beetle functional contributions 222 7.5.3 Resilience of ecosystem functioning following disturbance 223 7.5.4 Conclusion 224 Chapter 8 - General discussion 225 8.1 Summary of thesis findings 225 8.2 Impacts of selective logging, fragmentation and oil palm expansion on biodiversity 228 8.3 Maintaining ecosystem functioning following land-use change 231 8.4 Wider applicability of findings 233 8.5 Conservation in managed tropical landscapes 236 8.6 Conclusions 237 Appendix 1 239 Appendix 2 241 Appendix 3 242 10 Appendix 4 255 References 256 11 List of Tables Table 3.1. Bird feeding guilds 56 Table 3.2. Best models selected based on AICc values 62 Table 4.1. Summary of field site characteristics 76 Table 4.2. Summary of mean vegetation measurements across sites 110 Table 4.3. Contribution of the 10 vegetation variables to all principal components with eigenvalues >1 113 Table 5.1. List of response variables analysed 132 Table 5.2. Table comparing means and 95% confidence intervals of species richness, abundance and biomass in continuous forest and fragments 137 Table 5.3.