Intrinsic time dependence in the diversity-invasibility relationship.

Contrasting patterns in the diversity-invasibility relationship have intrigued ecologists for many years, and are now known as the "invasion paradox." Experiments usually detect negative relationships, while field surveys find them to be positive. It is widely believed that the paradox is driven by differences in spatial scale, but this is challenged by field surveys that find positive relationships at all spatial scales. If factors that determine invasion dynamics change during the invasion process, the paradox may be partially driven by differences in temporal scale. Here we used simulation (cellular automata) models to explore the generality of temporal change in the diversity-invasibility relationship. The probability of invaders colonizing an area was inversely related to the density of natives, creating a negative native-exotic correlation when invaders first arrived. Over time, native and exotic populations were both shaped by the same post-introduction processes (disturbance, dispersal, and recolonization), shifting their correlation to positive. The rate of temporal change in the diversity-invasibility relationship was mainly dependent upon the fecundity of invaders. Greater fecundity meant that invaders spread through the landscape faster and were subject to post-introduction processes sooner. We propose a unified conceptual model where the diversity-invasiblity relationship is a function of both spatial and temporal scales.