In the past few years there has been a lot of talk about invasive species, and definitely not of the good kind. We already know these species have a profound effect on native animals. The real challenge, however, is understanding how their presence affects our access to the benefits offered by the environment. To understand this, a recent study considered 7 such benefits and how the presence of 94 different invasive species is impacting them. Its findings suggest that invasive species will have a significant impact on our livelihoods, and that the risk of invasive species to areas which provide key ecosystem services will greatly increase in the coming years.
Science tells us that invasive species are bad. This is why grey squirrels are monitored and captured across Europe, and why the blue crab, introduced in the Mediterranean from North America, is being removed to prevent further damage to native ecosystems. But what exactly is an invasive species? A species becomes ‘invasive’ when it thrives in a new habitat at the expense of species that already lived there1. When this happens, not only is the native biodiversity in danger, but the overall equilibrium of an ecosystem gets shaken2.
This spells bad news for us. Our lives, in fact, depend on ecosystem services; benefits that only the surrounding ecosystem can provide us. This study considered 7 ecosystem services including our use of the outdoors to have fun (outdoor recreation) and our reliance on it to grow our food (crop provisioning). The scientists involved in this study aimed to understand how 94 invasive species could compromise our access to these benefits in the coming years. But why would their presence have a negative impact? Surely if an animal can replace another, like grey squirrels are replacing the native red squirrels, that means it not only has the same role in an ecosystem, but also that it fulfils it better, right? Unfortunately not.
In a way, invasive species work a bit like synonyms: you can certainly use ‘easy’ and ‘simple’ interchangeably in most context, but asking someone to ‘Take it simple’ would just feel wrong. In the same way, grey squirrels do behave and feed similarly to red squirrels, but their habit of stripping bark from broadleaf trees such as ash and sycamores causes great economical damage to forestry and conservation effort3. Where bark is absent, in fact, pathogens and fungi can proliferate and kill the tree. This not only means that reforesting an area gets more difficult, but that in the long run this snacking habit of theirs could compromise our access to timber and nutrients in the soil.
As different invasive species may undermine different ecosystem services, the scientists first scored the damage each of 94 species is doing now, and then predicted what degree of damage these organisms could do in the future. Such tricky calculations were done based on how likely invasive species are to thrive in different areas, and on what level of ecosystem services these areas provide. So areas subject to greater risk of invasion were given higher scores and vice versa.
The results of this study paint a complicated picture. Good news first: the study found that, across 10% of Europe, invasive species are currently unlikely to affect the 7 ecosystem services. Around 87.5% of the continent is at moderate risk of invasion, while roughly 1.5% is considered critically susceptible, and the remaining 1% could be a hotspot for invasive species. Some of the ecosystem services – such as crop provisioning, nitrogen retention in soil and outdoor recreation – are more vulnerable to the impacts of invasive species than others.
Additionally, the most vital regions for ecosystem services are currently rather safe, but their likelihood of being invaded will increase by 77% in the future. A major benefit of this study is that it tells us which areas to prioritize in conservation by identifying up to 13% of Europe as being of high value for these ecosystem services, but also at high risk.
But as much as we love blaming invasive species, the reality is that we are the reason most of them got where they are today. International commerce, travel, and exotic gardening are all to blame for the unprecedented global threat posed by invasive species4. So what can we do to protect our ecosystems? Firstly, try to plant only native species in your garden. Who knows what insects might be hiding in that fancy palm or what other seeds are present in its soil, waiting to colonise a new nation? Secondly, familiarize yourself with the local flora and fauna. This will allow you to spot anything out of the ordinary and report it before it gets out of control. And if you have doubts about whether what you are seeing is suspicious, you can join a local Facebook nature group or upload a picture to apps like iNaturalist, where experts are always happy to share their knowledge.
Article by Maria Giulia Checchi
Photos by Lukas Skoe/Unsplash, Leela Channer/Flickr, Amee Fairbank-Brown/Unsplash
References
- Hobbs, R.J. (2000). Invasive Species in a Changing World (Island Press).
- Pejchar, L., and Mooney, H.A. (2009). Invasive species, ecosystem services and human well-being. Trends in Ecology & Evolution 24, 497–504. https://doi.org/10.1016/j.tree.2009.03.016.
- Mabbett, T. (2020). Grey squirrels cause a lot of damage – and amusement. Forestry Journal. https://www.forestryjournal.co.uk/features/18944837.grey-squirrels-causing-damage-britains-native-trees/.
- Hulme, P.E. (2009). Trade, transport and trouble: managing invasive species pathways in an era of globalization. Journal of Applied Ecology 46, 10–18. https://doi.org/10.1111/j.1365-2664.2008.01600.x.
