The assembly of ecological communities: a minimalist approach

Communities develop through community assembly, in which species invade, persist, or become extinct. Community assembly is a sequence of different community states. Each state is a unique combination of species' presence or absence. The community transition graph is the directed graph of the transitions between states. The authors investigated the statistical distribution of different community transition graphs that contain varying numbers of species. Does the species composition of a community persist? Or does it cycle, and, if so, through a few recognizable states or through a complex sequence that might appear superificially random? In random transition graphs, the directions of the transitions are specified entirely at random. In a second recipe. all cycles are excluded by assigning each state a random "height'. The community transition graph moves from a "lower' state to one of its "higher' neighbours. This produces landscape transition graphs. A third recipe adds one ecological constraint to the random assembly models. The simple, ecologically implausible cycles are removed to produce minimal transition graphs. Random transition graphs most commonly have one persistent state. Landscape transition graphs commonly have many more persistent states and the number increases rapidly with the number of species in the system. Persistent cycles are rare in the random graphs and are impossible in the landscape graphs. Random graphs may best describe community restoration. If so, restoration might eventually reach its desired persistent community but only after a long period of intermediate cycling. In contrast, if landscape or minimal graphs best decribe restoration, then it would quickly reach a persistent community. Unfortunately, this persistent community may not be the desired community. -from Authors

Duke Scholars

Author Stuart L. Pimm Environmental Sciences and Policy