Understanding spatial and temporal shifts in taxonomic and functional diversity: assessing dung beetles in a human-modified amazonian landscape

Abstract

Tropical forests are under anthropogenic pressure, causing the replacement of native areas by modified habitats. These landscapes are composed of natural and modified components. Knowledge of community dynamics in these modified habitats is essential to ensure long-term conservation of species and ecosystem services. Many studies had evaluated the conservation value and impacts of anthropogenic modifications on biodiversity. However, the natural variation of communities in reference sites could obscure responses of biodiversity to disturbance. I evaluated the spatial and temporal shifts in dung beetle communities in undisturbed forest, and used these results to assess the influence of inter-annual variation on the evaluation of anthropogenic changes. Soil texture was the main factor affecting spatial variation in dung beetle communities, mainly due to different responses among beetles with distinct nesting behaviour. I found high variation in almost all community metrics after a severe dry season in the previous year, which also influenced the response of the community in modified habitats. Thus, future studies should consider inter-annual variation when studying the effect of anthropogenic change on dung beetle communities and use information about factors that could influence community metrics over time. In addition, many studies evaluate community responses to change from either taxonomic or functional perspectives, but little is known about the relationship between these components of biodiversity. I also addressed this by using conceptually similar taxonomic and functional metrics to evaluate the influence of anthropogenic changes on inter-annual variation in dung beetle communities and to compare taxonomic and functional metrics responses to modifications in forest structure. I did not find strong evidence for the influence of anthropogenic change on the inter-annual variation in the studied metrics. However, functional metrics varied less among years than taxonomic. Additionally, despite similar average effect sizes of functional and taxonomic metrics in response to forest modification, I found high variation among years for each metric and among metrics within each year. I therefore suggest that using taxonomic and functional metrics concomitantly could improve studies focusing on evaluating anthropogenic changes. Finally, I assessed the factors influencing taxonomic and functional diversity of dung beetles in plantations at the local and landscape scale. Understanding the factors modulating biodiversity in modified habitats has important applications, as these areas are likely to be the main component of tropical landscapes in the near future. I evidenced that dung beetle diversity increased with the extent of native forests surrounding the plantation, but there was no relationship between beetle diversity and yield. These findings could guide discussions with policy-makers and landowners in order to achieve sustainable management strategies. My results indicate that the restoration or retention of native areas in the landscape could facilitate species movement through plantations and those native areas could also work as ‘source’ habitats for colonisation of anthropogenic habitats by native forest species. In conclusion, this thesis demonstrates that using both taxonomic and functional diversity metrics to describe changes in dung beetle communities increases our understanding of biological community responses to change in modified areas.