During recent years it has become clear that rapid global warming is associated with the arrival and establishment of new plant and animal species in the Netherlands. It is largely unknown how these exotic species will cope in their new environment. Will they remain rare and find a modest place for themselves among native species? Or will they thrive and become noxious pests? Researchers at the Netherlands Institute of Ecology (NIOO-KNAW) have demonstrated that plant species that are establishing successfully in their new area escape from their natural enemies, such as herbivorous insects and soil-borne pathogens. This puts them at an advantage over native plant species and facilitates their rapid spread. One consequence could be that they might eventually replace native species. The finding that we may face more biological invasions in the near future due to climate change will be published this week in the scientific journal Nature.
The distributional ranges of many plant and animal species are shifting due to climate change, changes in land use, and other human-induced changes. Species that move faster than their natural enemies might benefit and could become plagues in their novel range. Tim Engelkes, Elly Morriën, Wim van der Putten, and colleagues from NIOO-KNAW, Wageningen University, Leiden University and the University of Florida carried out an experiment to test whether this risk is real. They compared exotic plant species that had recently established successfully in the Millingerwaard, a nature preserve near Nijmegen, The Netherlands, with related native plant species from the same area.
In a greenhouse they grew 6 exotic and 9 native plant species in pots with field-collected soil from the Millingerwaard area, allowing natural soil pathogenic microbes to accumulate in the pots. Then they removed the plants and re-planted the soils with the same plant species. Native plant species experienced a growth reduction due to the pathogenic microbes that had accumulated in the soil, but this effect was much less in the exotic species. Thus, native plant species were more vulnerable to natural soil-borne microbes than the exotic plant species. In addition, all plant species were exposed to generalist insect herbivores: a North-African locust and a cosmopolitan aphid species. These insects are not expected to have an inherent preference for either the native or the exotic plant species in the experiment. Contrary to expectation, the native plant species suffered more from the insects than the exotic species did. Thus, the exotic species were not only more resistant to soil pathogens, but they also suffered less from insect herbivores.
Half of the exotic plants from the Millingerwaard originated from Eastern or South-eastern Europe. The other exotic species are originally from South-Africa or North-America. The European exotics were almost equally resistant to the soil pathogens and insect herbivores as the exotics from other continents were. The implication of these findings is that plant species that successfully expand their distributional range due to climate change possess traits that are comparable to invasive exotic plant species that arrive from other continents. This indicates that climate change could cause biological invasions. It had been established already that climate change can lead to a decrease in biodiversity because not all species may be able to keep pace with the changing climate. Global warming-induced biological invasions represent an additional threat to biodiversity. This research finding helps to better assess the ecological consequences of climate change.
NIOO is the research institute for Ecology from the Royal Netherlands Academy of Sciences (KNAW). It consists of three centers: for marine and estuary ecology, for fresh water ecology and for terrestrial ecology. NIOO employs approximately 250 people. This research is financed in part by NWO, the Netherlands Organisation for Scientific Research, from which Wim van der Putten received a prestigious Vici-grant.