Ecological Succession Investigated Through Food-Web Flow Networks

Succession is the orderly process of ecosystem development which involves changes in species composition and community processes over time (Odum, 1969;Ulanowicz, 1986). Patterns to be ascribed to an ideal sequence for this process have been searched for. Odum provided a list of features that would accompany ecosystem evolution. His view was criticized following observational studies that showed that changes in structural and functional characteristics often did not conform to the proposed generalizations. To investigate the consistency of trends expected in ecosystems during succession we investigated the developmental trajectories of a lacustrine ecosystem using a network approach. Data about species and dietary habits that were collected throughout 6 years of intense sampling activity were used to build up the food web of the lake: links and their magnitude. The topology and intensity of the links were converted into indices of growth and development according to Ulanowicz (1986). These indices were used as proxies for some of the Odum’s attributes of ecosystem development. Furthermore, some of the classical paramters, those for which a network counterpart could not be found, were calculated (i.e. Production, Biomass, P/B, Shannon index) to be used as benchmark for comparison. Trends observed for network indices seem to confirm some of the expectations but not all. The overall picture that emerges in this study reveals that for certain indices the Odum’s scenario seems to hold but further long term studies will be necessary to confirm predicted generalizations.