Invasive Species Week: UK Invasions in a Changing Climate

Regan Early (University of Exeter) and I wrote this piece to mark Invasive Species Week for the British Ecological Society blog. In it, we discuss the possible synergies between climate change and species invasions, and some associated policy challenges.

 Vandan Patel

Whether it is parakeets streaking across the sky, grey squirrels pirouetting in your local park, or seed pods of Himalayan balsam going pop, alien species are familiar sights and sounds in the UK.

Last week’s release of the IPBES report and this week’s Invasive Species Week remind us of the serious threat posed by alien species that become invasive. Not only do they impact the economy – costing the UK some £1.8 billion each year, threaten human health and degrade cultural values, but they are the fifth biggest threat to biodiversity globally.

Together with the BES policy team, we recently responded to Parliament’s Invasive Species inquiry.

Among the questions the Inquiry posed was whether climate change would exacerbate invasions. Would the two interact to make a problem bigger than the sum of its parts?

Increasing number of invaders under climate change 

Somewhat surprisingly, the way that climate change will affect UK invasion is yet to be comprehensively assessed. Evidence suggests it’s unlikely that numbers of invasive species will increase simply because the UK climate will become suitable for species that otherwise couldn’t live here. Rather, more invaders may arrive in the UK because their populations grow in mainland Europe, and through human responses to climate change1.

If climate change makes invaders more abundant in continental Europe, the number of emigrants will increase, driving up immigration into the UK2. For example, numbers of moths migrating each year to the southern UK (but not establishing populations) has increased by 1.3 species/year, associated with warming temperatures in Spain and France3, but there is no direct evidence that climate change is the cause.

Greater use of biofuels, more intensive agriculture, and introduction of new plant species (or plant varieties) for gardens and agriculture may help us mitigate or adapt to climate change, but may inadvertently facilitate invasion4,5. New varieties of pasture plants that grow quickly and can cope with varying weather conditions are being developed; unfortunately, these are among the traits that can make species invasive6. Seaweeds are increasingly being used for biofuel production7 – many of them alien – and tests into seaweed farms are now underway across the UK. This developing aquaculture industry may pose a future invasion risk.

 Shane Stagner

Increasing impact of invaders under climate change 

Climate change will likely increase the impacts of invaders in the UK because many invaders are opportunistic generalists with wide environmental tolerances, good dispersal ability and rapid growth rates1. These characteristics mean that they’re well placed to take advantage of environmental change and of increases in disturbances like floods and storms8. Additionally, as climate change makes life tougher for natives, they will be less able to repel the advances of invaders9,10. For example, a decline in perennial native grasses with increasing temperatures has facilitated exotic annual grass invasion in California11. Under a new climate, currently successful management may become less effective, allowing invaders to proliferate and spread4,12.

The policy challenge of range-shifting species 

No matter how hard we try, a degree of climate change is inevitable, and this will drive shifts in species’ ranges and abundances13. Such range-shifting species are not being introduced directly by people, and so don’t fit into the traditional invasive species paradigm. In areas strongly affected by environmental change, species’ range shifts are likely essential for their survival, so could species native to mainland Europe that colonise the UK merit protection here? Species colonising from nearby locations are less likely to be invasive, and indeed no European native that has thus far colonised the UK is considered invasive14. On the other hand, anecdotal evidence raises concerns. St Piran’s hermit crab colonised Cornwall from Europe in 2016, and has reached extraordinarily high numbers on one beach, with no native hermit crabs to be found. Distinguishing desirable range shifts of climate-adapting “environmental refugees” from undesirable species invasions remains a key challenge.

To our knowledge, policy makers are not yet examining this issue and we predict that European native species colonising the UK will cause conflict in conservation goals. This seems like a key challenge that the invasion and conservation science communities – among others – need to resolve. Exciting times ahead!

 Shane Young

References

  1. Catford, J. A. & Jones, L. P. (2019) “Grassland invasion in a changing climate” in Grasslands and Climate Change (eds D.J. Gibson & J. Newman). Cambridge University Press, p. 149-171.
  2. Lockwood, J. L., Cassey, P. & Blackburn, T. M. (2009) The more you introduce the more you get: the role of colonization pressure and propagule pressure in invasion ecology. Diversity and Distributions 15, 904-910.
  3. Sparks, H. T., Dennis, L. H. R., Croxton, J. P. & Cade, M. (2007) Increased migration of Lepidoptera linked to climate change. European Journal of Entomology 104, 139-143.
  4. Bradley, B. A. et al. (2012) Global change, global trade, and the next wave of plant invasions. Frontiers in Ecology and the Environment 10, 20-28.
  5. Haeuser, E., Dawson, W. & van Kleunen, M. (2017) The effects of climate warming and disturbance on the colonization potential of ornamental alien plant species. Journal of Ecology.
  6. Driscoll, D. A. et al. (2014) New pasture plants intensify invasive species risk. Proceedings of the National Academy of Sciences  111, 16622–16627.
  7. Czyrnek-Delêtre, M. M., Rocca, S., Agostini, A., Giuntoli, J. & Murphy, J. D. (2017) Life cycle assessment of seaweed biomethane, generated from seaweed sourced from integrated multi-trophic aquaculture in temperate oceanic climates. Applied Energy196, 34-50.
  8. Diez, J. M. et al. (2012) Will extreme climatic events facilitate biological invasions? Frontiers in Ecology and the Environment 10, 249-257.
  9. Kraft, N. J. B. et al. (2015) Community assembly, coexistence and the environmental filtering metaphor. Functional Ecology 29, 592-599.
  10.  Catford, J. A., Downes, B. J., Gippel, C. J. & Vesk, P. A. (2011) Flow regulation reduces native plant cover and facilitates exotic invasion in riparian wetlands. Journal of Applied Ecology 48, 432-442.
  11.  Bansal, S. & Sheley, R. L. (2016) Annual grass invasion in sagebrush steppe: the relative importance of climate, soil properties and biotic interactions. Oecologia 181, 543-557.
  12.  Hellmann, J. J., Byers, J. E., Bierwagen, B. G. & Dukes, J. S. (2008) Five potential consequences of climate change for invasive species. Conservation Biology 22, 534-543.
  13.  Inderjit, Catford, J. A., Kalisz, S., Simberloff, D. & Wardle, D. A. (2017) A framework for understanding human-driven vegetation change. Oikos 126, 1687-1698.
  14.  Fridley, J. D. & Sax, D. F. (2014) The imbalance of nature: revisiting a Darwinian framework for invasion biology. Global Ecology and Biogeography 23, 1157-1166.

Species invasions and climate change: can grasslands cope?

Lizzie Jones and I contributed a chapter about grassland invasions to Grasslands and Climate Change, the latest volume of the British Ecological Society’s Ecological Reviews series. This is a blog post that Lizzie – a former MSc student of mine at Southampton – and I wrote for the Journal of Ecology blog.

Imagine a typical grassland ecosystem. You might see American prairies, rangelands of Australia, or African savannah. Either way, you’re probably thinking of wide-open spaces, dominated by resilient grass-like species. Yet, despite covering over 35% of the ice-free land surface, grasslands are an increasingly fragile ecosystem, experiencing some of the highest levels of exotic plant species invasion of all ecosystems. While there are strong links between levels of grassland invasion and human activity (as work by the Nutrient Network shows), climate change is also thought to be a key driver of such invasions.

© Getty Images

It is well established that there will be both winners and losers with climate change, where some species experience increases in range and population sizes, while other experience reductions. A key prediction nevertheless remains that exotic species invasion will increase with climate change, especially with rises in temperature and increases in extreme climatic events. Given that – like native species – individual exotic species can be helped or hindered by climate change, why does this remain a general prediction? It makes sense that some species will benefit from changes in climate regimes, and others will not, but why should some species experience an advantage simply because they are non-native?

In our chapter of Grasslands and Climate Change, we address these questions by concentrating on the effects of climate change on exotic plant invasion in global grasslands. We specifically ask whether climate change will favour exotic species, why that might be the case, and what sort of species (including their functional traits) will be favoured. In the chapter we used a systematic approach to review three key environmental changes that may give advantage to invasive species: changes in background climate conditions including temperature and rainfall; increased disturbance from extreme events such as storms and droughts; and human responses to climate change, either to mitigate its effects or to adapt to them.

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A warming and biodiversity grassland experiment at Cedar Creek Ecosystem Science Reserve: experiments like these provide insights into the impact of climate change, including species invasions. Photo by Jacob Miller.

Exotic species are well-adapted to capitalise upon change – their very invasion shows that that they are able to expand their distributions and deal with what might be unfamiliar ecological conditions. Increases in the frequency and magnitude of storm events, floods, fires and other disturbances will increase opportunities for invasion, and species that can reproduce and spread quickly will be particularly well placed. For example, some Bromus grasses can recover very rapidly when drought eases, which has allowed them to invade and convert woody scrubland areas in North America. The ability to seize opportunities and cope with a broad range of environmental conditions means that climate change will favour many exotic species – especially compared with native species, which may be less able to keep pace with changing conditions.

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Finally, humans have a huge impact on grassland invasion. In our efforts to mitigate, offset and adapt to our changing climate, we are unwittingly exacerbating the invasion of exotic species globally. A key culprit is the production of biofuel, such as Miscanthus species, now widely used in North America and Asia and predicted to spread with climate change.

So, to respond to the question “can grasslands cope with species invasions and climate change?” – native grassland species are certainly under threat not only by exotic species but by a multitude of human and climate-related issues. But, as this book shows, work towards adapting current conservation and management strategies is already underway to keep pace with our changing climate, not only in grasslands but in all other ecosystem types.

Lizzie P. Jones (Royal Holloway, University of London and Institute of Zoology, London, UK) and Jane A. Catford (King’s College, London, UK)


Grasslands and Climate Change is part of the Ecological Reviews series. BES members get 25% off all titles in the series when buying directly from Cambridge University Press. See also, David Gibson’s blog post: Grasslands and Climate Change.

New paper: Predicting novel riparian ecosystems in a changing climate

Image
A bit of a stretch, but I couldn’t resist including this image!

I was fortunate to attend a workshop hosted by the National Climate Change Adaptation Research Facility last year that focused on riparian ecosystems under climate change. Among the various discussions at the workshop, some colleagues and I started discussing how riparian ecosystems might be affected by climate change and ways in which their abiotic and biotic characteristics are likely to change. It soon became clear that envisioning future ecosystems is no easy task, so we set about trying to come up with an approach by which to do so. 

We present our approach in a paper that has recently been published in the journal Ecosystems. Based around four recommendations, we present the approach in the first part of the paper.  We then use four case studies from contrasting environments to illustrate the approach and to determine:

–        Whether certain characteristics make some ecosystems more susceptible to climate-induced shifts in community structure than others; and

–        Which aspect of climate change seems to have the greatest effect on community structure and therefore should be a research priority.

Focusing on changes in community structure, we use qualitative process models to predict likely abiotic and biotic changes in four case study systems: tropical coastal floodplains, temperate streams, high mountain streams and urban riparian zones. We concentrate on functional groups rather than individual species and consider dispersal constraints and the capacity for genetic adaptation.  Our scenarios suggest that climatic changes will reduce indigenous diversity, facilitate non-indigenous invasion (especially C4 graminoids), increase fragmentation and result in simplified and less distinctive riparian ecosystems.

Compared to models based on biota-environment correlations, process models built on mechanistic understanding (like Bayesian belief networks) are more likely to remain valid under novel climatic conditions. We posit that predictions based on species’ functional traits will facilitate regional comparisons and can highlight effects of climate change on ecosystem structure and function. Ecosystems that have experienced similar modification to that expected under climate change (e.g. altered flow regimes of regulated rivers) can be used to help inform and evaluate predictions.

While the paper centres on Australian riparian zones experiencing climate change, the approach can be applied to ecosystems in other biomes that are subject to environmental change.

The paper is now online early; you can find the abstract and link here.

Please drop me a line if you’d like a copy.

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