COMMUNITY AND FOOD-WEB RESPONSES TO THE MANIPULATION OF ENERGY INPUT AND DISTURBANCE IN SMALL PONDS

We describe the effects on community and food web structure of an expe rimental manipulation of energy input and disturbance to a set of sixt een small artificial pools. Two levels of energy input (leaf litter) a nd disturbance (draining of pools) were established in a factorial des ign, and pools were inoculated at intervals with samples of invertebra tes from a range of local sites. Artificial leaf litter was used to co rrect for differences in habitat structure caused by the energy manipu lations. The experiment ran for 15 months, during which time small, bu t persistent, communities (8-19 taxa) established in the pools. In gen eral, energy treatments had a greater effect on the communities than d isturbance, though all effects were modest. Low energy treatments had slightly more species than high energy systems, this increase being di sproportionately due to predators. Abundances and biomasses of some in dividual species were affected by one or other manipulation, but rarel y both, and commonly neither. Some aspects of the structure of binary food webs constructed for each system were apparently affected by ener gy treatments, although food chains were not longer in higher energy s ystems. However, given the effect of energy on species number, and the non-independence of species number and various web characteristics, t he significance of the effects that were observed is not clear. We bri efly discuss some of the problems of methodology and interpretation as sociated with this and other similar studies.