Multiple factors affect invasions: An overview and a case study

The success of an invader depends on its interactions with the invaded community.  Numerous theories (e.g. biotic resistance, enemy release) explore the expected impacts of different components of the community on invaders, but their relative importance under diverse circumstances is poorly understood.   The relative impacts of, and interactions between, different community components were addressed for two invasive thistle species, Carduus nutans and C. acanthoides.  Bottom-up factors, in particular competition, strongly affect local population growth of the thistles, while natural enemies are less important.  However, a complex interplay of both top-down and bottom-up mechanisms appears to determine the success of dispersal to new locations.  Simultaneously addressing multiple processes allows a deeper understanding of invasion and provides insight of use in mitigation.