Invasive species: the critical yet complex group driving biodiversity loss

Here at AlienImpacts, we are focused on predicting the impacts of plant invasions on community diversity. But we also think that sometimes it is worth taking a step back and asking some bigger questions too. What do we mean by an invasive species? Is it realistic to try and manage all invasive species? Last year, in the build-up to COP15, María Ángeles and I wrote a blog for King’s College about some of these issues.

“We are currently facing a major biodiversity crisis – something the UN Biodiversity Conference (COP15), in Canada this December, intends to address. Ecologists, María Ángeles Pérez-Navarro and Joshua Brian explain why it’s so difficult to manage invasive species and how this all fits in with the global summit’s goal of living in harmony with nature.”

NEOBIOTA conference 2022

This year the 12th International conference on biological invasions took place in Tartu (Estonia) from 12 to 16 September and AlienImpacts team couldn’t miss it! This conference is biennially organized by NEOBIOTA (the European Group on Biological Invasions) since 2000 and this time it was the turn of Estonian Naturalists’ Society to host and organize it. This year it was the first face-to-face meeting since the pandemic, and around a hundred of people meet in the Library Conference Centre of the University of Tartu, while around other fifty people attended online.

From AlienImpacts’ team only Josh could attend in person while me and Jane had to attend virtually. However, it gave us the opportunity to live the conference in two different ways, and it was extremely well organised to combine the virtual and in-person talks. I can honestly say that it was the best hybrid format I have ever participated in. The sound and image were wonderful, the slides and the speaker were presented in two separate windows in the screen, the slides with more relevant information were enlarged when required and even the virtual speakers could see the applause of the whole room and the faces of the people who asked us questions! If one day I have to organise a hybrid conference, I will definitely ask the organisers of this congress!

The conference brought together experts and colleagues in the field of biological invasions, and it was a pleasure to listen and learn from the diversity of talks ranging from the more applied and management aspects to data collection and modelling aspects. It was a pity not to be able to spend time with them in person at the coffee breaks and see the poster sessions.

AlienImpacts contributions

Jane was the first speaker in the first day of talks after the keynote. She presented her recent study about context dependency in ecology, and she explained the differences between real and apparent context dependence, the main types, their causes, and potential solutions. It was a good opportunity to think about how often in ecology we attribute unexplained processes to context dependence as a generic entity and how possible it is to try to address it and attribute context dependence to specific causes and thus improve the conclusions of the studies.

Picture 1. Jane’s talk during Tartu conference. View from the Tartu Conference Centre. Photo taken by Josh Brian.

Later that day I presented some results of my last study addressing the Darwin Naturalization Conundrum across spatial scales. According to Darwin’s natural selection theory it can be expected that those introduced species more similar to natives are more successful in their establishment as they share accurate traits to survive in the new habitat (pre-adaptation hypothesis), but also that those introduced species more similar to the natives can be less successful due to competition with natives (limiting-similarity hypothesis). I showed that the relevance of these hypotheses varied across spatial scales for grasslands communities. It was great to share these results and discuss with colleges about it despite the distance.

Picture 2. Question from the audience during Maria’s talk. View for virtual attendants. Screenshots taken Jane Catford. It could be appreciated how clearly could the virtual audience and speaker follow the questions from people in the room.

Finally, Josh presented on Wednesday 13. He talked about his recent synthesis on enemy release hypothesis. Enemy release is one of the main hypotheses explaining the success of alien species in introduced ranges, and it states that during the invasion process, invasive species lose the enemies with which they interacted in their native range, and this allows them to improve their performance and outcompete natives in the new range. He did a great job on compiling such a big number of studies and present the main findings in a simple way to the audience. He explained the different processes driving enemy release, and the relevance of different enemy release hypotheses along temporal and environmental gradients. I’m sure he had great discussions with colleges in Tartu after that.

Picture 3 Josh’s talk during Tartu conference. View for virtual attendants. Screenshot taken by Josh Maria Perez-Navarro.

It was such a great experience to participate, we all enjoyed a lot the conference and we are looking forward to the next NEOBIOTA meeting in Lisbon in 2024!

A field season at Cedar Creek!

I have just returned from three months at Cedar Creek Ecosystem Science Reserve, an amazing field station run by the University of Minnesota. I was there to set up an experiment on the enemy release hypothesis, which states that alien species succeed because they are released from their native enemies (e.g. predators, parasites and pathogens) which limit them in their native ranges. Using sixteen different grassland species as our ‘invaders’, planted into two different community contexts and hand-treated with combinations of insecticide and fungicide, we will explore the contexts (if any) under which enemy release facilitates invasion success.

When a photo opportunity presents itself in BigBio you are obliged to say yes!

The season was a busy one – everything adds up fast when you are trying to establish 288 plots, or hand-paint over 1500 seedlings with pesticide! But thanks to a great team of staff and interns at Cedar Creek, we got the experiment in the ground and some great preliminary data collected. The experiment will run for another two years, to see how enemy release affects both our target invaders, as well as the wider plant communities.

Some of our plots in the early succession community in the Lawrence strips

One of the great things about Cedar Creek is the amazing community of researchers that are there alongside you, providing plenty of people to learn from, as well as have fun with! While at Cedar Creek (which was also my first time in the USA!) I tried my first smore and about fifteen different flavours of Oreo, had a blizzard from Dairy Queen (apparently a must), helped to count bison, and played many plant-related games (I will never forget the stress of Avocado Smash). I look forward to coming back next year to see everyone again and to see the progress of the experiment – watch this space!

Harry and I ‘enjoy’ some early-morning fieldwork in the rain…

Addressing context dependence in ecology

Like many ecological research projects, one of the key things we need to – and plan to – grapple with in AlienImpacts is context dependence. Using examples from biological invasions, in this paper we propose a way in which we can think about and tackle context dependence.

Ecological Change

A phrase that you are bound to hear many times at any ecology conference is “it depends”. We see context dependence – variation in the magnitude or sign of ecological relationships depending on the conditions under which they are observed (Fig. 1) – in just about every study and every system. Such variation, especially when unexplained, can lead to spurious or seemingly contradictory conclusions across studies, which can limit understanding and our ability to transfer findings across studies, space, and time. Because of the wide prevalence of observed context dependence and the critical need to tackle it, a group of us recently knocked heads (and read lots of fabulous papers!) about how it can be addressed. Our reading, thinking, talking, drawing and writing culminated in this open access paper in TREE

Figure 1: Context dependence may be invoked when the observed relationship between two variables varies in (a) magnitude (strength), (b) sign…

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