Past economic activity is more likely to explain the current pattern of biological invasions across Europe than recent human activities, according to a new study. It can take several decades before a newly introduced species becomes established and spreads, which may mean that recent invasions caused by current economic activities could create an `invasion debt´ for future generations.
Non-native or alien plant and animal species can have a range of negative impacts on biodiversity, ecosystems and the economy: for example, competing with native species for resources and affecting human health or infrastructure. Earlier research suggests human economic activities are more important in influencing biological invasions than either climate or geography, but there is less certainty about the role of past activities on existing patterns of invasion.
In this study, the researchers used data from the EU-funded DAISIE project1 to explore the influence of socioeconomic factors in the years 1900 and 2000 on patterns of alien invaders in 10 groups (vascular plants, bryophytes, fungi, birds, mammals, reptiles, amphibians, fish, terrestrial insects, and aquatic invertebrates) currently found across 28 European countries. Known social and economic factors that affect biological invasions were measured by: population density, gross domestic product (GDP) per person and share of exports in GDP as a predictor for the intensity or openness of trade.
Typically, the current pattern of invasive species in Europe is explained more by historical activities in 1900 than by recent activities in 2000. The rate of introduction of alien species into Europe has significantly increased over the last 50-60 years, so it is likely that there could be a delay of at least a few decades before the full impact of these invaders is seen. This is described as an `invasion debt´ for the future.
A critical threshold of individuals is needed for a species to become established and spread, which could explain the delay after introduction. The time taken to meet this threshold depends on a number of factors, including how often and how many alien species are introduced, the routes by which they are introduced, how suitable new habitats are for alien species and how species are able to adapt to new environments.
For example, some introduced birds and insects can disperse more quickly than other types of species because they can fly and are therefore more mobile and able to find suitable habitats. However, such explanations do not always fit the detected patterns of alien invaders. Further work is needed to understand the relationships between those factors that influence the delay between introduction and establishment of alien species.
Despite current preventative measures to reduce the introduction of biological invaders in Europe, globalisation is increasing socioeconomic activity which could increase the rate of introductions. Given the likely time lag between the introduction, establishment and spread of invasive species, it is recommended that existing control measures should be strengthened.