Recent Advances in Understanding Plant Invasions

Abstract

In the last two decades biological invasions have drawn increasing attention (see e.g., Drake et al. 1989; Lodge 1993; Williamson 1996; Lonsdale 1999; Alpert et al. 2000; Kolar and Lodge 2001). Compared to other subjects of ecological investigation, studies related to biological invasions have almost exploded in number during the last years (Fig. 1).

The fact that an increasing number of ecologists gets caught up in the problem of biological invasions can be attributed to several reasons. First, biological invasions are increasingly recognized as one of the most important threats to biodiversity (D’Antonio and Vitousek 1992; Vitousek et al. 1997a; Walker and Steffen 1997; Mooney 1999), i.e. biological invasions tend to homogenize the earth’s biota (Lodge 1993; Vitousek et al. 1997b; Mooney 1999; Mack et al. 2000). Second, biological invasions can also pose severe environmental, economic and sometimes even health threats (Vitousek et al. 1997a,b; Mack et al. 2000 and references therein, Pimentel et al. 2000). Invasive species affect native species and ecosystems by competing directly for resources that native species require, by altering ecosystem functions and processes such as nutrient and hydrologic cycles, and fire frequency and/or intensity. There are virtually no natural areas left that have not felt the impact of non-native invaders (Usher 1988). Third, biological invasions represent great natural experiments for the ecologist whose investigation is extremely valuable for the understanding of population spread (Sakai et al. 2001) and community- and landscape-level processes affecting the patterns and abundance of species at large spatial and temporal scales, i.e. scales which are otherwise hardly accessible for experimental ecologists.