7 Traits Associated with Invasiveness in Alien Plants : Where Do we Stand ?

Any organism must be equipped for life in a given environment, otherwise it will die. The fundamental question is how well does an organism need to be “equipped”, or what syndrome of traits must it possess to survive and flourish at a given locality. In the current human-mediated biodiversity crisis, where alien species play an important role, we need to know whether some species are inherently better equipped to become invasive when moved to new areas by humans. If so, we can identify such species and consider management options to prevent, or at least reduce the damaging effects of biological invasions. Despite the importance of chance and timing in the establishment and spread of alien plants (Crawley 1989), invasions are clearly not entirely random events (Crawley et al. 1996). Much of the early work on invasions was directed at collating traits associated with invasiveness (Booth et al. 2003). The question of whether is it possible to determine a set of traits that predispose a species to be invasive has been a central theme since the emergence of invasion ecology as a discrete field of study (Richardson and Pyšek 2006). Many studies have attempted to profile successful invaders, starting with Herbert Baker’s attempt to identify the traits of an “ideal weed” (Baker 1965), an idea now considered simplistic (Perrins et al. 1993). Baker defined as a weed a plant growing “entirely or predominantly in situations markedly disturbed by man (without, of course, being deliberately cultivated plants)”. To him, weeds included plants that encroached onto agricultural land (agrestals), and those occurring in waste places (ruderals; Baker 1965). There was no explicit reference to the status of the species as being native or alien. Perhaps it was the two species pairs he used to document different traits of “weedy”