Scientists' warning on invasive alien species

Abstract

Biological invasions are a global consequence of an increasingly connected world and the rise in human population size. The numbers of invasive alien species - the subset of alien species that spread widely in areas where they are not native, affecting the environment or human livelihoods - are increasing. Synergies with other global changes are exacerbating current invasions and facilitating new ones, thereby escalating the extent and impacts of invaders. Invasions have complex and often immense long-term direct and indirect impacts. In many cases, such impacts become apparent or problematic only when invaders are well established and have large ranges. Invasive alien species break down biogeographic realms, affect native species richness and abundance, increase the risk of native species extinction, affect the genetic composition of native populations, change native animal behaviour, alter phylogenetic diversity across communities, and modify trophic networks. Many invasive alien species also change ecosystem functioning and the delivery of ecosystem services by altering nutrient and contaminant cycling, hydrology, habitat structure, and disturbance regimes. These biodiversity and ecosystem impacts are accelerating and will increase further in the future. Scientific evidence has identified policy strategies to reduce future invasions, but these strategies are often insufficiently implemented. For some nations, notably Australia and New Zealand, biosecurity has become a national priority. There have been long-term successes, such as eradication of rats and cats on increasingly large islands and biological control of weeds across continental areas. However, in many countries, invasions receive little attention. Improved international cooperation is crucial to reduce the impacts of invasive alien species on biodiversity, ecosystem services, and human livelihoods. Countries can strengthen their biosecurity regulations to implement and enforce more effective management strategies that should also address other global changes that interact with invasions.

Keywords: biological invasions; biosecurity; environmental impacts; global change; invasion dynamics; invasion hotspots; naturalization; policy; protected areas; socioeconomic impacts.

Fig 1

Hotspots and coldspots of cross‐taxon established alien species richness across eight taxonomic groups: vascular plants, ants, spiders, freshwater fishes, amphibians, reptiles, birds, and mammals, calculated as in Dawson et al. (2017). Cross‐taxon values were calculated as averages of established alien species richness per taxonomic group (scaled according to the maximum value) in a region with data available. Only TDWG level‐4 regions (countries, federal states and islands/archipelagos) that were modelled by Dawson et al. (2017) were included (N = 439). Cross‐taxon established alien species richness of grey‐bordered regions was calculated from three or fewer taxonomic groups, and of black‐bordered regions from four or more taxonomic groups. Cross‐taxon established alien species richness is displayed in percentile categories; upper and lower 2.5% and 10% regions are indicated separately from the remaining upper and lower 50% regions. Regions filled in grey lacked information on established alien species (Antarctica was excluded from the analysis).

Fig 2

Increase in cumulative established alien species richness across six taxonomic groups in four regions of the world. Time series are based on the year of first record of those alien species that later became established in the given region (based on Seebens et al., 2017).

Fig 3

Examples of invasive alien species representing various taxonomic groups and environments. (A) Invasion of Pinus pinaster in the mountains of South Africa's Cape Floristic Region, transforming species‐rich fynbos shrublands into species‐poor pine forests and dramatically reducing streamflow from water catchments (photograph: A. Turner). (B) Phormium tenax invasion on St Helena (photograph: Helen Roy). (C) Forests defoliated by the gypsy moth (Lymantria dispar) in the USA (photograph: Karl Mierzejewski). (D) Japanese black pine (Pinus thunbergii) dying due to infestation by the pine wood nematode (Bursaphelechus xylophilus) (photograph: B. Slippers). (E) Harlequin ladybird (Harmonia axyridis) overwintering aggregation (photograph: Gilles san Martin). (F) Japanese buoy washed ashore in Maui, Hawaiian Islands, with living Asian species, including the rose barnacle (Megabalanus rosa) (photograph: Cheryl King). (G) Rose‐ringed parakeet (Psittacula krameri) (‘Parakeets in London in the Snow’ by David Skinner, licensed under CC BY 2.0). (H) Wels catfish (Silurus glanis) attacking a pigeon at the Tarn river in Albi, France (photograph: Camille Musseau). (I) Invasive silver carp (Hypophthalmichthys molitrix) jumping in the Fox River, Wisconsin (provided by Asian Carp Regional Coordinating Committee).