Symposium conclusions 26th of February 2007

Conclusions of the 5^th environment symposium of the Maj and Tor Nessling Foundation

Alien Species – environment, biorisks, future

Prof. Erkki Korpimäki, Symposium Convener, Section of Ecology, Department of Biology, University of Turku, Finland
Prof. Erkki Leppäkoski, Chairman, Environmental and Marine Biology, Department of Biology, Åbo Akademi University, Turku, Finland
Prof. Pekka Niemelä, Chairman, Faculty of Forestry, University of Joensuu, Joensuu, Finland
Dr. Mikael Nordström, Symposium Convener, Metsähallitus, Natural Heritage Services, Turku, Finland
PhD Stud. Pälvi Salo, Symposium Secretary, Section of Ecology, Department of Biology, University of Turku, Finland

Alien species are considered as one of the main factors causing biodiversity loss in both terrestrial and aquatic ecosystems. However, most evidence consists of observations that alien species invade and native species decline more or less synchronously, which does not conclusively show that alien species are the principal factor of environmental change. Therefore experimental approach is needed to answer the question whether alien species are the “drivers”, i.e. a major force of ecological changes, or whether alien species are merely “passengers” who take advantage of ecosystem changes, such as habitat disturbance, caused by human activity (Didham et al. 2005).

The answer to this question is species- and context-specific, and it has great conservation value. To prevent any additional species from becoming extinct we must be able to identify the real causes of population declines, not only to treat the symptoms but the disease itself. Alien species may have significant ecological, economic and even social impacts on ecosystems and human societies. Together with other major changes like global warming, their impact may be even more wide-spread and serious. Research on the biology, distribution and impacts of alien species is needed to be implemented by authorities, NGO’s and managers fighting against harmful aliens. This therefore is a field where multidisciplinary research is recommended and important as well as the collaboration between academic and non-academic institutions.

We attempted to evaluate the main outcomes of the symposium in the light of this driver-passenger framework. We agreed that alien predators have clearly been shown to induce major changes in the ecosystems and communities of their new environment (see Salo et al. 2007 for a review). Therefore, they can be considered as drivers of ecological change. The case of alien herbivores is perhaps not so clear, but they also have been shown to have major impacts on native communities (Donlan et al. 2002) and can thus be considered as drivers rather than passengers. Alien plants are showing characteristics of both drivers and passengers: in many cases alien plants seem to depend on human-modified environments, and are thus not affecting undisturbed communities. On the other hand, some species are able to invade pristine habitats and cause changes in the local ecosystems.

In the cases of alien soil organisms and pathogens it is clear that there is not enough information to make any conclusive judgements. Soil organisms, whether alien or native, are still very poorly known. The same holds for alien pathogens, although there is much research going on as far as their impacts are of concern to our well-being.

Overall, we find that the effects of alien species are complex indeed. The complexity of the target food web and the number of other alien species already present in the system make the effects of new alien invasions even less predictable. In practice this may mean that each case should be evaluated separately to find a targeted and successful management of the problem. Therefore, there is a plethora of needs and opportunities for the future research into invasion biology which include:

1) opportunities to study rapid evolutionary processes possibly induced by alien species invasions,

2) establishment of landscape-level long-term experiments to tease out the impacts of different agents,

3) new insight into biogeography (patterns of invasions, vectors, invasion corridors),

4) application of modern methods, e.g. molecular genetics, to track the origin of invasive species and their pathways, and hybridisation processes,

5) involving not only biological and ecological but also technical and socio-economic aspects of alien species on the multidisciplinary biodiversity research agenda.

and

6) possible bio-risks and bio-security problems caused by alien species, and how these will be affected by, for example, the global climate change and other major drivers of bioinvasions (trade, transport, and travel), which are and will continue to increase as a byproduct of globalization.

References

Didham, R. K., Tylianakis, J. M., Hutchinson, M. A., Ewer, R. M. & Gemmell, N. J. 2005. Are invasive species the drivers of ecological change? Trends Ecol. Evol. 20: 470-474.

Donlan, C. J., Tershy, B. R. & Croll, D. A. 2002. Islands and introduced herbivores: conservation action as ecosystem experimentation. J. Appl. Ecol. 39: 235-246.

Salo, P., Korpimäki, E., Banks, P. B., Nordström, M. & Dickman, C. R. 2007: Alien predators are more dangerous than native predators to prey populations. Proc. R. Soc. Lond. B (in press).