The role of evolution in the invasion process

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Abstract
Biological invasions occur when organisms are transported and become established in a new range in which they persist, proliferate, and spread (1). The negative consequences of invasions include loss of native biological diversity and community structure (and in extreme cases, the extinction of native species) (2); modification of ecosystem processes such as nutrient cycling and productivity patterns; alteration of disturbance regimes, especially the frequency of wildfires (3); reduced agricultural productivity; human health concerns; and enormous economic costs (1, 4). Consequently, invasive species are now considered to be one of the leading contributors to global change (5) and thus have been the focus of an extensive amount of ecological and ecosystem-level research. Much of this research has focused on answering a series of questions associated with predicting invasions: Which species will become invasive? Which life-history traits contribute to invasiveness? Which communities are susceptible to invasion? What will be the ecological and ecosystem-level consequences of invasion? Unfortunately, answers to these questions remain elusive (1). It is surprising to note, however, that little research has focused on the evolutionary aspects of biological invasions and addressed how evolutionary mechanisms may contribute to the success of an invasion (2, 6, 7). In contrast, the research of Lavergne and Molofsky (8) reported in this issue of PNAS examines the factors that contribute to range expansion and the invasiveness of Phalaris arundinacea L. (reed canarygrass) in North America and provides powerful insights into the role of evolution in the invasion process. The invasion process can be viewed as a series of steps that are initiated when propagules of a species (seeds, eggs, larvae, vegetative material, mature individuals, etc.) are sampled in their native range and transported to a new area (1, 4). These immigrants probably experience high mortality rates while in transit, and …