A functional comparison of earthworms and termites as ecosystem engineers

Dr Paul Eggleton (P.Eggleton@nhm.ac.uk)and Prof. Rod Blackshaw (University of Plymouth)

Project description
In most terrestrial soils, either termites or earthworms are an ecologically dominant invertebrate group. Both can be classified as ecosystem engineers because of the significant effects they have in modifying not only their own environment but also the environment of many other organisms. The two groups have overlapping distribution patterns, but globally their distributions are broadly complementary. Both groups feed on dead plant material at different stages of decomposition in the form of leaf litter, humus, or the soil below the humus layer. However, there is evidence to show that, physiologically, they process the feeding substrate in different ways.

A major research question, then, is: are these groups functional analogues? Functional classifications exist for each taxon separately, but the objective of this project is to develop a common (guild) framework to facilitate functional comparisons.

The student will:

(1) Use museum specimens of key earthworm (and for some analyses termite) species to examine gut contents, describe the comparative gut anatomy and mouthpart morphology, and so make direct comparisons with work carried out on termites in an earlier NHM-funded studentship. Gut content analysis will include classical microscopical techniques as well as those employing X-ray diffraction, stable isotope profiling and (funds permitting) carbon-age dating.

(2) From these data the student will develop a combined functional classification that includes both termites and earthworms, predominantly by examining the degree of overlap of functional groups within the two clades across eco-morphological space. The remaining parts of the project will test the biological reality of this classification experimentally.

(3) Develop experimental work using British earthworm species as model organisms. The British fauna includes representatives of all three of the currently recognized functional groups: anecic (surface or near surface dwellers), epigeic (litter feeders with permanent vertical burrows to the surface) and endogeic (subsoil feeders). An experimental mesocosm approach will be developed at Plymouth University to investigate the effects that each of these (old) functional groups has on a number of pre-defined important soil processes (e.g. clay mineral weathering, nutrient cycling, soil pH) and their relation to the new functional classification. This will enable direct comparison to be made with previous work on both termite-soil and earthworm-soil interactions (e.g. pore size, biogenic structures).

(4) Use the developed mesocosm approach in Cameroon, West Africa, where earthworm and termite functional diversity is very high. A comparative study of a small number of termites and earthworm species - belonging to the full range of putative functional classes – will be made examining key ecosystem effects to test the biological value of the new joint functional classification.

The student will gain a working knowledge of the morphology, morphometrics, taxonomy and functional ecology of earthworms (Ms Emma Sherlock, Zoology Dept) and termites. He or she will also receive training in a range of techniques for the analysis of soil physical and chemical characteristics (Dr William Dubbin, Mineralogy Dept; Dr Roland Boll, IGER). Within the project he or she will also need to develop skills for the analysis of experimental data using morphometric and ordination techniques. The student will also gain experience of experimental procedures (Dr Sarah Donovan, Plymouth) and tropical field ecology (Dr Stefan Hauser, IITA, Mbalmayo, Cameroon). The student will be obliged to attend training sessions, provided by the University of Plymouth’s Graduate School, on literature searching, literature database management, statistics, scientific writing, and project management. Opportunities also exist for the student to attend relevant taught modules.