Connectivity and complexity in landscapes and ecosystems

The connectivity of sites in a landscape affects both species distribution patterns and the dynamics of whole ecosystems. Dispersal tends to produce clumped distributions, which promote species persistence and provide a possible mechanism for maintaining high species richness in tropical rainforests and other ecosystems. Simulations of multi-species systems show that, below a critical rate, disturbance regimes have little impact on species richness. With super-critical rates of disturbance the rate of decrease in species richness depends on the balance between the rate of disturbance and dispersal range. Theoretical and simulation studies discussed here reveal that landscape connectivity falls into three distinct classes: connected, disconnected, and critical. Landscape processes are inherently unpredictable when connectivity lies within the critical range. Critical levels of connectivity lead to phase changes in the behaviour of many ecosystem processes. For instance epidemics, fire spread and invasions by exotic plants or animals are all suppressed if inter-site connectivity is too low. Conversely, genetic drift within individual populations is an order of magnitude greater if connectivity is sub-critical.