Varley Gradwell 2011

Dr Tom Fayle, Imperial College, London

Report on work achieved during Varley-Gradwell Travelling Fellowship in Insect Ecology

Habitat fragmentation and the functioning of ant communities in tropical forests The world’s natural habitats are becoming degraded and fragmented, with resulting losses of species, and predicted changes in ecosystem functioning. I was awarded the Varley-Gradwell Travelling Fellowship in Insect Ecology in May 2011, to support an investigation into the way that rates of ant-mediated nitrogen pre-emption change along a gradient of habitat disturbance in Sabah, Malaysia. This gradient comprised old growth lowland dipterocarp rain forest, twice-logged rain forest, and oil palm plantation. Furthermore, collaboration with the SAFE project (Stability of Altered Forest Ecosystems), enabled me to sample in areas of continuous forest that were destined to become fragments of a range of sizes.

During August-September 2011 I conducted pre-fragmentation N pre-emption assays at sampling points across the habitat disturbance gradient. The protocol for the assays was altered slightly from that detailed in my original proposal. In order to understand how heterogeneity in resource distribution affected redistribution rates, and furthermore, how utilisation of a heterogeneous resource changes with disturbance, I used a range of earthworm bait pellet sizes, rather than the single size originally proposed (see below). These were arrayed in a 6 by 5 grid on a laminated card at each site. We conducted over 300 assays, each one lasting for 40 minutes (12,000 minutes of observations) at the sites of the pitfall traps. I have trained three SAFE research assistants in the assay protocol, which will greatly facilitate future work. Two other RAs have also been trained in (lab-based) ant identification. In the process of this training I updated the current key to ant genera for Sabah, and a colleague of mine translated it into Malay. This key is now freely available online and we hope to further refine it in the future (http://www.tomfayle.com/research%20link.htm).

Entry of the remaining pre-fragmentation removal rate data, identification of the 15% remaining pre-fragmentation ant samples, and full post-fragmentation field assays (I am now in Sabah) are all currently on-going. However, preliminary analyses of a subset of the pre-fragmentation data show that N pre-emption is faster in less disturbed forest, and that this difference is greatest for larger pellet sizes. One possible explanation for this pattern is that less disturbed forest supports higher densities of ant species with large body sizes (e.g. the giant forest ant, Camponotus gigas, which is restricted to old growth forest). If these larger ants preferentially remove larger pellets (which seems likely, given previous work on food item-body size matching in ants (J. Trop. Ecol. 22: 685-693), and can be tested later using my data), then their loss is predicted to impact the size distribution of removed pellets in the manner observed. If this response is also detected in the full dataset, then we will have made some progress towards understanding the links between habitat disturbance, resource heterogeneity and ecosystem functioning.

I would like to take this opportunity to thank the board of the fund for the award, which has enabled me to expand my research in this new direction. In particular, being able to make pre-fragmentation assays has been invaluable, since these will form the baseline for future sampling rounds. The N pre-emption assay work is also forming the basis for a grant application I am making as a PI to the Grant Agency of the Czech Republic (GACR), with a view to understanding how this redistribution of nutrients affects plant communities.