Global hotspots of established alien plants and animals revealed

An international team of researchers, led by Durham University, UK, including two researchers from the Institute of Botany of the CAS, provides the first global analysis of the hotspots of alien species invasion across plants and animals. This study has been published in the prestigious journal Nature Ecology and Evolution. The scientists studied existing data looking at eight groups including amphibians, ants, birds, freshwater fish, mammals, reptiles, spiders and vascular plants across 186 island and 423 mainland regions. Hotspots of established alien species were found mainly in island and coastal mainland regions, the research concluded.

The top three hotspots with the highest numbers established alien species after accounting for area, were the Hawaiian Islands, New Zealand’s North Island and the Lesser Sunda Islands (Indonesia). The Hawaiian Islands have high numbers of species in every group considered. These include guppies among fish (now globally widespread) and feral pigs among mammals. New Zealand follows not far behind Hawai’i; around half of its flora is made up by established alien plants, and predatory mammals have been a real problem for naïve native bird species that have not evolved with land-based predators. Florida is the top hotspot among continental regions, with the Burmese python a well-known example among reptiles, and a large number of less well-known ant species.

Europe has a number of well-known established alien plants and animals, including parrots (the Indian rose-ringed parakeet, found across many western-European cities), many plant species like Himalayan balsam (common along rivers and streams), mammals such as the grey squirrel, and the noble false widow spider (introduced accidentally in cargoes of fruit).

A region’s wealth, density of human population, and to a lesser extent climate affected the number of established alien species, though these factors varied between species and from region to region, the study reported. Lead author Dr Wayne Dawson, in Durham University’s Department of Biosciences, said: “Our research shows that, once we take area into account, islands and mainland coastal regions contain higher numbers of established alien plants and animals, and this may be because these areas have major points of entry like ports. In general, regions that are wealthier, and where human populations are denser also have more alien species, but these effects are stronger for islands. More work is needed to understand whether these effects arise because more species are introduced to hotspot regions, or because human disturbance in these regions makes it easier for the newcomers to find vacant spaces and opportunities to thrive.”

Global efforts aimed at preventing the further introduction of alien plants and animals could be focused on islands and coastal mainland regions, the researchers said.

Petr Pyšek, one of the two authors from the Czech Republic, added: “While species have been moved around the globe throughout history, more and more species will be introduced as the world becomes ever more connected, and the human population continues to grow. Many of these incoming species are useful, and won’t establish and spread in their new homes, but some will, with varying levels of impact on resident species and ecosystems.”

“The challenge for us is to understand what the consequences are of mixing up the world’s species in this way, to decide how to deal with this change, and what measures we can put in place to try and prevent further introductions to the most vulnerable regions. This includes bolstering biosecurity measures at major points of entry to detect stowaway species, as is already done to an impressive degree in New Zealand. It should also include careful vetting of species proposed for introduction to an area, as done by organizations such as the European and Mediterranean Plant Protection Organization (EPPO), to filter out those species that are risky in terms of their potential to establish and have negative impacts,” concluded Franz Essl from the University of Vienna, senior author of the study.

Dawson W., Moser D., van Kleunen M., Kreft H., Pergl J., Pyšek P., Weigelt P., Winter M., Lenzner B., Blackburn T. M., Dyer E. E., Cassey P., Scrivens S. L., Economo E. P., Guénard B., Capinha C., Seebens H., García-Díaz P., Nentwig W., García-Berthou E., Casal C., Mandrak N. E., Fuller P., Meyer C. & Essl F. (2017) Global hotspots and correlates of alien species richness across taxonomic groups. Nature Ecology and Evolution 1: 0186 (doi: 10.1038/s41559-017-0186)

Petr Pyšek, Institute of Botany of the CAS, Průhonice,, tel. +420 271 015 266, +420 721 904 203
Jan Pergl, Institute of Botany of the CAS, Průhonice, tel. +420 271 015 236, +420 776 803 137
Wayne Dawson, Durham University’s Department of Biosciences,, tel. +4417894239884


Clockwise from top left: Alien species that are introduced to new regions and establish new populations come in many shapes and sizes, including birds (Rose-ringed parakeet from Asia, now in London), mammals (grey squirrel from North America, now in the UK), plants (Himalayan balsam, widespread in Europe), and ants (Asian needle ant, now found in SE USA). Photo credits clockwise from top left: Tim Blackburn, Tim Blackburn, Jan Čuda, Benôit Guénard.