Deep Invasion Ecology and the Assembly of Communities in Historical Time

A critical component of — and a limitation on — interpreting community structure is a detailed understanding of the ecological and evolutionary history of the assemblage of species in question. There are thus compelling reasons to under stand, and seek to measure, how communities have changed over both evolution ary (geological) and ecological (historical) time. Vast waves of change have swept across the Earth in the past one to two millennia as waves of humans invaded across the planet in sequential episodes of exploration, colonization, and urbanization. As an expected and inexorable result of human activity, alterations in biodiversity have impacted terrestrial, freshwater, and marine communities. These alterations include the addition of species (invasions), the deletion of spe cies (extinctions), and altered population dynamics (such as decreasing or increasing the abundance of a species, or altering genetic structure). In even seemingly “pristine” areas — such as wave-exposed high-energy rocky intertidal shores — it is no longer tenable to assume that communities and ecosystems have remained unaltered, in part because of supply-side impacts — impacts that are the indirect cascades of human activity originating outside of the area in question (e.g., Butman et al. 1995; Chap. 7, Johnston et al.).