Alien Species

Alien: an organism occurring outside its natural past or present range and dispersal potential, whose presence and dispersal is due to intentional or unintentional human action. Apomictic/parthenogenic: asexual form of reproduction without fertilization. Casual: refers to organisms that do not form self-replacing populations and rely on repeated introductions for their persistence. Cryptogenic: a term used for species of unknown origin or means of arrival, which cannot be ascribed as being native or alien [62]. Naturalization: refers to aliens that form free-living, self-sustaining (reprodu-cing) and durable populations persisting in the wild. Founder population: a new population in a region, usually consisting of a small number of (here: introduced) individuals. Introduction/introduced: direct or indirect movement by human agency, of an organism outside its past or present natural range. Invasion/invasive: refers to established alien organisms that are rapidly extending their range in the new region. (This is usually associated, although not necessarily for an organism to qualify as invasive, with causing significant harm to biological diversity, ecosystem functioning, socio-economic values and human health in invaded regions). Native: an organism that has originated in a given area without human involvement or that has arrived there without intentional or unintentional intervention of humans. Trailing edge: the boundary of distribution where a species is retreating; opposite to the expanding range margin. Voltinism: the number of broods or generations of an organism in one year.

become less resistant to invasive species or more resilient to their impacts under future climates. In extreme cases, climate-driven invasions could lead to completely trans-formed ecosystems where alien species dominate function or richness or both, leading to reduced diversity of native species [8,9].

Based on these theoretical and conceptual aspects, we present here a compilation and synthesis of the evidence for observed changes in biological invasions arising from recent climate change. We evaluate the relative import¬ance of the direct and indirect effects of climate change on the invasion process, and compare these findings with studies on climate-induced changes