Invasion, Evenness, and Species Diversity in Human-Dominated Ecosystems

Abstract

Biological invasions have become a major ecological problem globally (Vitousek et al., 1997; Mooney & Hobbs, 2000) for several non-mutually exclusive reasons. From the perspective of economics, many invasive alien species have become pests, sometimes causing severe damages to crops (Mack et al., 2000; Pimenel et al., 2000). From the ecological point of view, invasive species can inflict drastic changes in the invaded community altering its structure and function (Simberloff, 1997; Mooney & Cleland, 2001), and leading to biodiversity loss (Herbold & Moyle, 1986; Clavero & Garcia-Berthou, 2005). The battle against invasions of alien species requires a great deal of efforts and resources, and yet is not always successful (Kaiser, 1999; Zavaleta et al., 2001). Whereas complete eradication of successfully established invasive species is in most cases impossible, controlling their population growth may decrease economical damages, and prevent biodiversity loss in the invaded community. Furthermore, successful eradication of one alien species may result in a worse alternative stable state (Beisner et al., 2003), where another, potentially more harmful invasive species dominates the community (e.g., Zavaleta et al., 2001). Therefore, fighting invasions should be done carefully and wisely, while taking into account multiple biotic and abiotic factors and outcomes. More importantly, such actions should emerge from a deep understanding of the evolutionary and ecological mechanisms that operate at different biological hierarchies to allow invasions, i.e., starting from the individual traits characterizing the invasive species (genetic background, morphology, physiology, behavior and life history), through its population parameters (demography, fluctuations, growth rate), and up to patterns and processes characterizing the invaded community (composition, structure, and age). The demography of many invasive species has been well documented, and their damages were explored in details (Pimentel et al., 2000). However, the ways such species enter new ecosystems and communities, and their exact effect on community structure and biodiversity are not yet fully understood (Gurevitch & Padilla, 2004). Our goal is to review the evolutionary and ecological mechanisms of bio-invasions at the species (e.g., Facon et al., 2006) and community levels (e.g., Shea & Chesson, 2002), and present some of the general effects and outcomes of invasions at both levels. We discuss various mechanisms by which invasive species manage to establish viable populations and even dominate new