부산대학교 도서관

We developed mathematical models that simulate community dynamics derived from a series of perturbation experiments. These experiments were performed in an Atlantic Forest stream. The three trophic level community was submitted to two combinations of press perturbation experiment. In the first, the top trophic level was removed by electrical exclusion. In the second configuration, the top trophic level was still excluded plus a group of species from the second trophic level was inhibited, also by electrical pulses. Experiments were repeated at different times to increase confidence in the observed mechanisms. Community responses indicated the existence of cascading interactions similar to a classic trophic cascade. The community was composed of Macrobrachium shrimps at the top trophic level, Ephemeroptera and Chironomidae larval insects at the second trophic level and periphyton (= epilithon = biofilm) at the first trophic level. The shrimp exclusion caused an increase in ephemeropterans and chironomids and led the periphyton to decrease in the exclusion zone. When ephemeropterans were inhibited together with the exclusion of shrimps, the chironomids and the periphyton increased. We modelled the community interactions by means of differential equation systems, simulating the three configurations: 1. natural condition, 2. shrimp exclusion condition and 3. shrimp-exclusion-plus-ephemeropteran-inhibition condition. All parameters were calculated via experimental results and the stability of the models was determined by their matrix eigenvalues. The models successfully reproduced the qualitative responses of the community. They proved to have attraction points, which enables us to predict that the system has some ability to return to its previous condition after local perturbation.
Comment: 28 pages, 11 figures and 5 tables