commentary: Towards an efficient management of biological invasions

ISSN 1948-6596 news and update commentary Towards an efficient management of biological invasions Biological invasions are a current conundrum for the management of worldwide biodiversity. Inter- national transportation networks have facilitated the connection of distant regions, and eased the movement of exotic species historically confined to their native areas by natural barriers and dis- persal constraints. Some of these species have the capacity to establish and spread successfully in newly occupied biogeographic regions, becoming a real problem for the hosting ecosystems and the humans that depend on them. They compete with native species and alter the functioning of ecosys- tems, threatening the services provided by these ecosystems and in some cases having direct ef- fects on human health. The management of biological invasions and/or ecosystems hosting them is becoming ever more relevant, as the number of exotic plant and animal species increases worldwide. Management actions range from preventive measures to avoid the introduction of exotic species, to control op- erations of entire ecosystems after establishment of invasive organisms. To facilitate the manage- ment of these novel ecosystems (sensu Hobbs et al. 2006), it is necessary to expose and develop appropriate data on the ecology and distribution of invasive species, as well as tools to assist in pri- oritizing actions for control of alien plants. In this vein, two papers have been published recently that shed some light into these issues. The first study was conducted by several plant ecologists from Europe, and has been pub- lished in Diversity and Distributions under the leadership of Milan Chytrý from the Masaryk Uni- versity (Czech Republic). Chytrý et al. (2009) pro- vide the first spatially explicit quantification of the level of alien plant invasion at a regional level for Europe. Combining quantitative data on the pro- portion of alien species that invade different habi- tat types with a land-cover map, they produced a map that estimates the levels of invasion across Europe. Their utilization of habitats as a basis for mapping levels of invasion was justified by a previ- ous study (Chytrý et al, 2008), in which habitat types were shown to be better predictions of inva- sion levels than other variables, such as environ- mental characteristics or propagule pressure. Their results predict that the highest levels of alien plant invasions occur among arable land, urban and industrial areas, whereas the lowest levels occur in sclerophyllous vegetation, peat- bogs and heathlands. The spatial distribution of the level of invasion suggests that the highest lev- els of invasion are in lowland areas of western Europe and in agricultural regions in central and eastern Europe. In contrast, low levels are pre- dicted in boreal regions and mountainous zones, except along coastlines, irrigated agricultural land, and rivers of the Mediterranean region. Even though the approach used to elaborate the map is coarse and although there is potential for further improvements, this study provides a first look at the level of plant invasion in Europe and permits the identification of areas susceptible to donate/ receive exotic species. In parallel with this study mapping levels of invasion, Andrew J. Tatem from the University of Florida (USA) examined the potential dispersal of exotic species in a new study published in Ecogra- phy. Tatem (2009) provides a framework to pre- dict biological invasion risks through the world- wide airline network, and assesses future changes due to human and environmental variations. The growth of air travel increases the propagule pres- sure and rate of exotic species introductions, but the establishment of such organisms in new re- gions will depend upon whether they find climatic conditions similar to those at their origin. Build upon a previous study (Tatem and Hay 2007), he examines the spatial and seasonal distribution of incoming traffic volume to individual airports, and combines this information with climate scenarios for the period 2007-2010 to identify potential in- vasion risk routes. His results suggest that changes in global climate will be relatively small during the near fu- ture, but increases in incoming traffic from China, India, Russia and eastern Europe are expected to frontiers of biogeography 1.1, 2009 — © 2009 the authors; journal compilation © 2009 The International Biogeography Society