Consequences of positive feedback for spatial assembly dynamics and restoration

Restoration can be thought of as directed community re-assembly, whereas management of exotic species invading native communities seeks to prevent undesirable community assembly. Positive feedback arising directly or indirectly from species interactions is thought to be an important mechanism promoting the invasion of exotic species and could strongly promote or hinder re-assembly efforts. In addition, while regional scale colonization dynamics are clearly important to the spread of invasive species, we have limited understanding about how it might affect spatial assembly dynamics. We present results from a spatially explicit model that explores the community dynamics of species that can modify local environments through positive feedback and differ in dispersal abilities. Because restoration efforts are inevitably constrained by limited resources, we explore the consequences of tradeoffs that managers might face between invasive species control and restoration. Using alternative invasion scenarios that are relevant to managers, we contrast community dynamics for different combinations of species' life history, feedback and dispersal strategies. Our results suggest that if management resources are limited, efforts to simply eradicate established exotic species may not be successful if native propagule limitation and legacy feedback conditions are not also addressed. In contrast, management to prevent invasion is less sensitive to feedback effects and propagule limitation, particularly when the invader does not widely disperse. Because a species' potential to generate positive feedback does not preclude high dispersal, restoration re-assembly efforts will be influenced by spatial processes at both local and regional scales.