Natural ecosystems are changing rapidly in the face of fragmentation and degradation through land-use and climate change. However, the impact of environmental change on the structure and functioning of ecosystems is poorly understood. To address this problem, we study the role of vertebrates, focusing on birds as key components of top-down or mutualistic processes (predation, pollination, seed dispersal). We also prefer to work on tropical systems, as these are suffering the fastest rates of development and change, as well as being home to over 85% of terrestrial species, including the vast majority of threatened taxa. Moreover, because of habitat clearance and rising temperatures in lowland and montane tropical forests supporting large numbers of endemic lineages, tropical landscapes are by far the most likely setting for mass extinction or functional collapse caused by environmental change.
We are working as part of international multidisciplinary teams to quantify biophysical processes and functionally important components of biodiversity across “natural” and experimental gradients of land-use intensity in tropical forests (Brazil, Panama, Malaysia). We are using these systems to explore a range of questions, such as: What is the relative importance of top-down versus bottom-up processes in ecosystem function and resilience? What is the role of stochastic versus deterministic processes in community disassembly? How do dispersal ability, habitat choice and habitat connectivity influence the impact of land-use change? What is the impact of land-use and climate change on key ecosystem processes such as seed dispersal? What are the tipping-points beyond which ecosystem processes are significantly impaired, and what land-use practices relax these thresholds?
Finally, to focus in detail on the key mechanisms of ecosystem resilience, we are interested in community re-assembly: the recovery of species and interactions in habitat regenerating after land-use change. Recent studies have demonstrated the potential ecological impacts of species extinctions, but we still know very little about the forces governing community re-assembly. We are compiling occurrence, abundance and functional trait data across systems of secondary forest plots with known age: 2–80 years old. We are applying a range of models to test whether trait re-assembly is random or explained by species interactions. For example, we are asking whether intrinsic factors (e.g. dispersal limitation) or species interactions (e.g. competition) shape the dynamics of trait re-assembly in the frugivore community, and whether this in turn generates non-random re-assembly in their fruit-bearing food-plants.
- Yadvinder Malhi (OUCE)
- Toby Gardner (SEI)
- Jos Barlow (Lancaster)
- Alex Lees (Cornell)
- Alexandre Aleixo (Belem)