I sat down with leader of the UK Ladybirds Survey Helen Roy to talk about the stigma surrounding invasive species like this Harlequin Ladybird (Image Credit: PJ Taylor, Pixabay Licence, Image Cropped)

While climate change and habitat loss seem to keep making all the headlines when it comes to environmental damage, invasive species are still chugging along comfortably as the second biggest threat to our planet’s biodiversity. New cases are popping up all the time, with the Burmese python, Crucian carp and the emerald ash borer beetle recently reaching new levels of notoriety.

Yet the negative impact that many non-native species have on the habitats they move into have often led to stigmatisation of anything new. This can be counter-productive, as the majority of newcomers into an ecosystem won’t have a pronounced negative effect. And whilst it may seem like a smart piece of preventative management to maintain an ecosystem’s status quo by preventing species introductions, it’s often just not feasible.

With this in mind, I sat down at the recent British Ecological Society’s Annual Meeting with Professor Helen Roy of the UK Centre for Ecology and Hydrology. Helen has studied the impacts of non-native species the world over, from the UK to smaller island nations like St. Helena, and has led several projects for the European Commission on non-native species. We spoke about the importance of distinguishing between invasives and non-natives, the impact of climate change on invasive biology, and the social and cultural significance of both native and non-native species.

Sam Perrin: What are some of the challenges facing modern invasion biology?

Professor Helen Roy (HR): I think the important thing when studying invasive and other non-native species is ensuring that everyone is using the same definitions. Some modern studies conflate some of the invasive non-native species, which are the damaging ones, with all non-native species. Non-native species are those that have been introduced by humans from one part of the world to another, it’s only a small proportion which cause negative impacts and are termed invasive non-native species. But of those invasive non-native species, absolutely we shouldn’t downplay the impacts that they’re having both in terms of biodiversity and ecosystems, but also on a socio-economic level.

The other aspect that came up in [this morning’s plenary talk by Jonathan Chase] is scale. It was really interesting to hear him talk and remind us that when we’re looking at a quadrat versus an entire woodland or island or globally, we get very different pictures. So whilst species richness may be shown to decline on a small scale if an invader arrives and displaces a local species, on a larger scale there may actually be a net increase in diversity. Yet at the same time, we also need to be careful in terms of the sort of metrics that we use. Species richness is often used, yet I think it is really important that we get better at understanding interactions between species, because that is ultimately what makes up the functions that drive an ecosystem.

SP: You mentioned the semantics surrounding the invasive vs. non-native briefly. Why is that distinction important?

HR: Because otherwise we really are comparing apples and oranges. When you look at all of the non-native species, there are species within that spectrum which really have huge impacts on new or novel ecosystems or societies. But across the entire pool of non-native species there’s a huge amount of diversity and a huge spectrum in terms of what those species are doing when they arrive in a new place. And many of them are not having any adverse effects. They might even be having positive effects in some contexts. I think it’s really important from a policy perspective, that when considering prioritization of species for biosecurity or preventing species’ arrival, that the effort is focussed on those species that are going to have some sort of adverse impact. Just in the UK for instance, we have more than 2000 non-native species. Of that, about 15% are causing some kind of problems, and knowing which ones helps put resources in the right place.

SP: We are starting to deal with a new type of non-native species at the moment, those driven into new ecosystems by rising temperatures. Whilst we’re contributing to that climate change, we’re not directly moving these species. Do we need to look at these potential invaders in a different light?

HR: It’s so topical at the moment, there are so many discussions around climate-driven movement of species, and it’s great to hear. Many of us [ecologists] are interested in the distribution patterns of species at various spatial and temporal scales. And macro-ecological and biogeographical studies look at what causes the movement and the changes in distribution of species over time. And in that sense we might be interested in those that have been moved directly by humans and those moving as a consequence of indirect effects.

I think that when it comes to thinking about invasive/non-native species it is good to focus on those species that have been moved directly by human action through whatever pathway, because it does give some kind of focus to where action can be targeted for prevention and biosecurity. So those species that are moving as a consequence of climate warming for instance, they’re absolutely fascinating in terms of large scale patterns of species distributions but in terms of action, I think it’s really useful to have that distinction between species that are moving through pathways that can be more easily managed. To think of the invasive non-native species as those that have been moved directly by humans, allows us to think about the actions that can be taken around the pathways, so it has a very direct and practical application.

SP: Speaking of pathways, ecosystems like freshwater lakes and rivers often present distinct pathways between two habitat patches. In some of these systems we can theoretically keep these climate invaders out. Yet should we? I spoke to Mark Davis at Macalaster College about this issue in 2018, and his take was that you’d essentially be creating a ‘climate museum’.

HR: It’s a really interesting concept in terms of reconciling those different perceptions. I’m really fascinated by science communication and people within this whole process. I say that in part because conservation is really complex, and the decisions that people have to make will be based upon the evidence that comes from our ecological studies, but it will also be based in terms of perceptions and values that people have. Which means that ultimately there’s not just one answer.

We want people to be involved in the decisions about our natural world, and so we have to give them the best available evidence, so then they can assist in making decisions. Some people will want to conserve what has been there for a long, long time, and in that sense, perhaps their emphasis is on creating some kind of museum, and I wouldn‘t wish to downplay the importance of doing that . In other places people will be thinking more about the way the ecosystem is going to function. Ensuring that the interactions between species are maintained such that the system has some resilience going forward, and that might look very different, in terms of the species composition, to what has gone before.

I think there’s a place for all of these different viewpoints, and it’s probably very context dependent. For example, in the last couple of years I’ve been doing some work on the UK Overseas Territories, which has been an immense privilege, and visiting some quite unique places, like St. Helena . St. Helena has got its very own invasion problems, and New Zealand flax is one of those. It’s massively changed the habitats on this island which has a very high level of endemism. Some plants and insects are disappearing, but there are restoration programmes in place . And it’s really incredible what is being done by a very small number of people who are working in very basic nursery facilities to look after some of the plants which would otherwise be extinct. And in some small patches that have been restored, a couple of species of insects, one they thought was extinct, another that was critically low, have been seen again. I think that’s inspiring, and I think that’s incredibly important. And of course there are some senses in which this could be argued to be creating a museum, but I fully respect the value to communities of doing so.

SP: Often people do simply think of non-natives as negative because they represent a change to the ecosystem that has occurred in their lifetime. Is there a way to shift people away from this concept of an invasive non-native as simply something that ‘wasn’t there when I was young’?

HR: Again, here science communication is really important, as it helps people to understand the complexity and also the beauty of the way in which species interact within ecosystems. I think we have a long way to go with conveying those nuances and complexities of ecological ineractions. There was a plenary a few years ago here [at the BES Annual Meeting] by Pedro Jordano and I was really inspired by his perspectives on networks and interactions. Pedro talked about the insidious nature of the erosion of interactions between species and that being far more important than extinction of the species themselves with respect to ecosystem function.

Helping people to understand the interconnectivity between species within an ecosystem regardless of what those species are is what’s important in my mind. And I think that’s been neglected by many. Fred Pearce’s book The New Wild touches on this, with him saying essentially that invasive non-native species will be our salvation, we have such disturbed systems, and our only hope is for other species to come in an fulfil these roles. But he really misses the complexities and nuances of ecology. We have a very polarised debate on this topic at the moment, and I think what we need to do is to be thinking back to the basics of ecology, and to community interactions and ecosystem functioning. And we can do that, I’ve seen just this morning here some really exciting work going on in terms of empirical data collection in tropical systems, in freshwater systems and beyond exploring ecological interactions in relation to function. We can do it, we can meet the challenge. But I also want to reiterate that in terms of a local community, if they have a cultural attachment to a particular species, that is a very valid reason to conserve that species.

HR: Absolutely. And we shouldn’t be stigmatising them all as bad, I mean invasive non-native species are species within their own right as well. It is all very context dependent. Take for instance freshwater systems. There we may wish to worry more, because they’re essentially islands in many ways, and we know the kind of ecological cascades and loss of interactions that can take place within such closed systems following the the introduction of a non-native species. So that’s possibly a context where we need to follow a precautionary principle .

On Grand Cayman in the Caribbean the green iguana roams, which arrived as an escapee. When I visited Grand Cayman there were thought to be about 1 million green iguanas. That was 18 months ago. The population in a good year will double, in a bad year increases by 60%. So we can assume there’s now probably 2 million green iguanas there. And they’re encroaching on the endemic blue iguana’s habitat. This is a huge concern. But they’re also a societal nuisance, and are causing infrastructure problems. So in that context, that green iguana would ideally never have been released, and management action would seem to be an appropriate measure going forward.

SP: Any final thoughts on invasion biology?

HR: I think that people understand that we need evidence-based decision-making. I’ve been leading some studies with the GB Non-Native Species Secretariat and the European Commission towards making some predictions about what might be the most damaging species that are going to arrive in the next ten years. Following some rapid screening through horizon scanning, we undertake some predictive work regarding their potential impact and spread, and then for those species considered a priority, we gather evidence through a formalised process of risk assessment. We then hand the evidence to decision-makers to think about what actions are appropriate to go forward. So it is all about gathering that evidence, and we’ve done a lot of work to ensure the field of invasion biology is firmly within an evidence driven discipline.

Sam Perrin is a freshwater ecologist currently completing his PhD at the Norwegian University of Science and Technology. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.