AlienImpacts

January 29, 2026

Neighbours Matter More Than Herbivores in Grassland Chemistry

How competition, not consumers, shapes plant chemistry

Plants are chemical powerhouses.

They make a huge range of chemicals. Some help them grow, others protect them from pests or stress. For years, scientists have thought these chemicals mainly evolve because of herbivores and diseases. But new research suggests something different: the plants growing next to you might matter more than who is eating you.

A study looked at two species in a long-term grassland experiment in Minnesota: Andropogon gerardi (also known as big bluestem, which is a tall grass) and Lespedeza capitata (roundhead bush clover; a nitrogen-fixing legume).

The team tested how these plants’ chemistry changed when they grew alone or in mixed communities, and when insect and fungi enemies were either present, or reduced with pesticides.

The findings were surprising. Both species grew better when pests were reduced, but their chemical make-up didn’t always change.

For A. gerardi, the chemistry stayed almost the same no matter the treatment. This suggests the grass relies on built-in defences rather than changing its chemistry when stressed.

L. capitata, on the other hand, reacted strongly to its neighbours. When surrounded by other species, it produced more amino acids and phenolic compounds – signs of stress – and less sugar. This means competition, not herbivory, was the bigger challenge.

Why does this matter?

First, it questions the old idea that herbivores are the main reason plants have such diverse chemistry. At least in the short term, who you grow next to can be more important. Second, it shows species respond differently. The grass seemed to thrive in mixed plots, while the legume struggled – both in growth and in chemical balance.

These differences could affect whole ecosystems, from nutrient cycling to how plants interact with insects.

The study also shows how complex plant responses are. Chemicals that dissolve in water and those that dissolve in fats behaved differently, and overall pest damage was low in the year studied. Even so, the evidence points to neighbours as key drivers of chemical change.

For ecologists and land managers, predicting how plants respond to climate change and biodiversity loss means looking beyond herbivores. As plant communities shift, their chemistry will shift too – and that could change how ecosystems work.

Future research should test more species and sample over time to catch short-term changes. For now, this study offers a simple lesson: in the chemical lives of plants, competition can matter more than consumption.

Read more:

Joshua I Brian, Adrien Le Guennec, Elizabeth T Borer, Eric W Seabloom, Michael A Chadwick, Jane A Catford, Plant neighbours, not consumers, drive intraspecific phytochemical changes of two grassland species in a field experiment, AoB PLANTS, Volume 17, Issue 6, December 2025, plaf071, https://doi.org/10.1093/aobpla/plaf071

Article originally posted on KCL’s Spheres of Knowledge

January 22, 2026

When Scale Shapes Ecological Truths

Rethinking Darwin’s Naturalisation Conundrum through Spatial Lenses

Darwin’s naturalisation conundrum has long puzzled ecologists. Two competing ideas – preadaptation and limiting similarity – offer contrasting explanations for why some introduced species thrive while others fail.

The former suggests that invaders succeed when they resemble native species, benefiting from shared traits suited to local conditions. The latter argues that similarity breeds competition, so success favours difference. Both sound plausible, yet evidence has remained inconsistent.

A recent study led by Maria Perez-Navarro and colleagues at King’s College London sheds light on why. The team examined 33 years of grassland succession data in Minnesota, testing these hypotheses at two unusually fine spatial scales: neighbourhood plots of 0.5 m² and site transects of 40 m². This methodological choice proved decisive.

At the neighbourhood scale, where plants interact directly, practical features such as height and leaf structure mattered most. Species that differed in these traits were more abundant, supporting the limiting similarity hypothesis. Competition, it seems, rewards difference. Yet at the larger site scale, environmental filtering dominated. Here, species more similar to the community – those sharing traits suited to local conditions – were favoured, aligning with preadaptation.

Intriguingly, evolutionary closeness told a different story. Introduced species that were close to natives in the “family tree” thrived at both scales, reinforcing preadaptation even where trait-based analyses suggested otherwise. This disconnect between evolutionary lineage and physical features highlights a key insight: these two measures are not interchangeable.

The study also revealed nuanced differences between native and introduced species. Introduced plants tended to prosper with lighter seeds, higher leaf dry matter content, and in nitrogen-rich soils, suggesting distinct strategies for colonisation and resource use.

What does this mean for invasion ecology? First, spatial scale matters – profoundly. Analyses at tens of metres, often deemed “local”, may obscure competitive dynamics evident only at sub-metre scales. Second, relying on a single measure of similarity risks misleading conclusions. Evolutionary relationships and practical traits capture different dimensions of ecological reality.

Beyond its technical findings, this research invites reflection on how ecological theory grapples with complexity. Darwin’s conundrum endures not because the underlying hypotheses are flawed, but because nature resists simple binaries. Community assembly is shaped by overlapping forces – competition, environmental filtering, evolutionary history – whose influence shifts with scale and context.

For practitioners, the message is clear: management strategies for invasive species must consider both the traits that confer advantage and the environments that filter them. For theorists, the challenge remains to integrate these insights into models that embrace, rather than flatten, ecological nuance.

In the end, the study reminds us that scale is not a backdrop but an active player in ecological processes. To understand why species succeed or fail, we must look closely – sometimes as closely as half a square metre.

Read more:

Perez-Navarro, Maria A., Harry E. R. Shepherd, Joshua I. Brian, Adam T. Clark, and Jane A. Catford. 2025. “ Evidence for Environmental Filtering and Limiting Similarity Depends on Spatial Scale and Dissimilarity Metrics.” Ecology 106(11): e70244. https://doi.org/10.1002/ecy.70244

Article originally posted on KCL’s Spheres of Knowledge

January 19, 2026January 19, 2026

Understanding Alien Plant Invasions

Alien plants are everywhere – but not all invaders behave the same

a group of yellow flowers — Photo by Brittany Lee on Unsplash

Alien plant invasions are accelerating worldwide, posing serious threats to biodiversity and costing billions in management. A recent study – led by David Gregory as part of his Masters at King’s and in collaboration with Matt White from the Victorian government – sheds light on how these invasions unfold across landscapes and why growth form matters when predicting and managing risk.

The research, conducted in Victoria, Australia, analysed data from more than 7,600 vegetation surveys spanning five decades. It found that 69 per cent of surveyed plots contained alien species, which made up 22 per cent of all recorded plant species. Forbs (broad-leaved herbs) were the most common invaders, followed by graminoids (grasses and similar) and woody plants. Yet the patterns of invasion were far from uniform.

Using boosted regression trees – a machine-learning approach well suited to ecological data – the team modelled how environmental, biotic and human factors influence both the presence and dominance of alien plants. Abiotic conditions, particularly temperature and rainfall, emerged as the strongest drivers overall, explaining up to 76 per cent of variation in invasion risk. Summer maximum temperature was a consistent predictor across all growth forms, with occupancy rising sharply above 23°C.

Human activity also played a major role. Areas with intensive land use, such as urban centres and agricultural zones, showed the highest levels of invasion. Alien forbs and graminoids were especially prevalent in these disturbed landscapes, often reaching more than 70 per cent cover in towns and cities. Alien woody plants were less widespread but still more likely to occur in urban areas than in intact forests.

Interestingly, the relationship between vegetation cover and invasion differed by growth form. Alien forbs and graminoids were more likely to occupy sites with high vegetation cover, but their proportional cover tended to decline as native vegetation increased – a sign of strong competition. Woody invaders, by contrast, were negatively associated with woody vegetation cover, suggesting that dense tree cover offers resistance to colonisation.

Spatial predictions confirmed these trends. Alien forbs had a high probability of occurring almost everywhere, even at higher elevations, though their cover remained low in alpine regions. Alien graminoids were largely confined to lowland areas dominated by human activity, while woody invaders were the most restricted, reflecting lower seed dispersal and availability and lower habitat suitability.

A global challenge

These findings resonate far beyond Australia. Invasive alien plants are among the top five drivers of biodiversity loss globally, according to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES).

They disrupt ecosystems, alter fire regimes and threaten food security. Economic costs are staggering – estimated at more than US$400 billion annually worldwide – and rising as trade and travel expand. Climate change compounds the problem by creating conditions that favour invaders, while land-use change accelerates their spread.

Understanding invasion dynamics at scale is therefore critical for global conservation strategies.

The implications for management are clear. Maintaining and restoring native vegetation is critical to limiting alien plant dominance, particularly after disturbances such as wildfire – a growing risk under climate change. Urban expansion and agricultural intensification will likely increase invasion pressure, making strategic land-use planning essential. Grouping species by growth form, as this study does, offers a practical way to prioritise control efforts without building hundreds of single-species models.

Alien plant invasions are complex, shaped by climate, land use and ecological interactions. But by recognising both shared drivers and growth-form-specific patterns, we can design more effective strategies to protect ecosystems. Growth-form-based models provide a tractable, widely understood tool for science and policy – a step towards smarter, landscape-scale management of one of the most pressing environmental challenges of our time.

Read more:

Gregory D, White M, Catford JA (2025) Similar drivers but distinct patterns of woody and herbaceous alien plant invasion. NeoBiota 103 31–52. https://doi.org/10.3897/neobiota.103.164914

May 14, 2024May 14, 2024

2024 fieldwork preparations underway!

Preparations are underway for field season 2024, promising to be the biggest one yet in the project!

Both Harry and Josh will be spending 3 months over the summer at Cedar Creek Ecosystem Science Reserve conducting plant surveys, plant trait measurements along with a whole host of other sampling to undertake.

Josh will be largely be focusing on his mechanistic enemy release or “MechER” experiment, which is in its final year. The experiment examines the role of plant pathogens in regulating plant populations and whether release from these pathogens can explain the success of non-native species. The first year of results from this experiment were excitingly published in Journal of Ecology last month.

Harry will be largely focusing on a monoculture experiment set-up two years ago on the grounds of the big biodiversity experiment. In this experiment, we have planted a range of commonly found species at the field site in single-species plots that we will now use to measure a whole host of different aboveground and belowground traits. This data will be essential as we look to further develop models that can predict the impact of non-native species on native biodiversity.

Alongside these experiments, we also have our sights set on some additional data ‘goodies’, including measures of soil functioning and fungal communities across the different experiments. There will also be a resurvey of E275, an experiment set up by Jane in 2012 to explore the drivers of plant colonisation, the first results of which were published last year.

All in all it promises to be a busy but exciting summer of fieldwork!

November 30, 2023

New article published in the Conversation

Earlier this month, an article I wrote was published in the Conversation discussing the implications of a recently published meta-analysis highlighting the risk extreme weather events pose to native biodiversity.

Extreme weather events are predicted to increase in regularity in the coming century under human-driven climatic change, posing increasing challenges for the protection of native biodiversity. Interactions between extreme weather events and invasive species have been observed in a number of recent studies (such as in this study), and could exacerbate impacts of non-native introductions on native biodiversity.

The study, published in Nature Ecology and Evolution, examined the responses of native and non-native animals to a range of extreme weather events (such as storms, wildfires, droughts) across the globe. They found that non-native species are in general more resistant to extreme weather events, and may therefore be better placed to capitalize and out compete native biodiversity following such events.

Studies such as this highlight how interactions between non-native species and other global change drivers may combine to threaten native biodiversity in the Anthropocene, and how we may not yet be able to see the full scale of these interactions and the threats they pose. Developing predictive models, such as in WP5 of AlienImpacts, that allow forecasting of species responses under new environmental conditions and to changing climatic conditions is therefore crucial to identify areas of native biodiversity most at risk and implement preventative and restorative measures that can protect native diversity in the future.

The Conversation article can be found here.

November 22, 2023

A mechanistic framework of enemy release

Biological invasions are one of the five biggest threats to global biodiversity. On the face of it, this doesn’t make sense: how can exotic species with no previous history in a given location do so well and outcompete native species? The most popular hypothesis to explain this is the Enemy Release Hypothesis (ERH). This hypothesis states that exotic species leave their natural enemies behind when being introduced beyond their home range, releasing them from top-down regulation and enhancing performance in their invaded range. Despite this intuitive basis, evidence for the ERH is inconsistent. Further, while many studies demonstrate that exotic species lose enemies, they do not explicitly link this loss with increases in exotic performance. We therefore still do not understand whether enemy release can explain high exotic performance, and under what circumstances if so.

A semi-eaten plant in our MechER experiment…

To address this, we have proposed a new framework for the ERH (Fig. 1), that has just been published in Ecology Letters. Our framework emphasises exotic performance as the key outcome of the ERH (Fig. 1a), with three factors – enemy impact, enemy diversity, and host adaptation – that influence performance (Fig. 1b). We then explore seven contexts that modulate the effect of these factors (Fig 1c): (i) time since introduction; (ii) resource availability; (iii) phylogenetic relatedness of exotic and native species; (iv) host–enemy asynchronicity; (v) number of introduction events; (vi) type of enemy; and (vii) the strength of growth–defence trade-offs.

We argue that our framework is more mechanistic and predictive, enabling better understanding of how and when enemy release can facilitate invasion. Our approach helps explain the ‘context-dependence’ in previous support for the ERH (something which is important to grapple with!). The framework also shows that many different enemy-related invasion hypotheses just represent different factor/context combinations, bringing theoretical clarity – we don’t need a new hypothesis for every new set of observations. We hope that our paper will encourage more explicit testing and reporting of the factors and contexts of the ERH in future studies on enemy release. This will enable effective synthesis, and more mechanistic insights into the role of enemy release in global invasions.

Full paper: Brian, J. I., & Catford, J. A. (2023). A mechanistic framework of enemy release. Ecology Letters.

Figure 1: A mechanistic reframing of the enemy release hypothesis. The enemy release hypothesis as an explanation for (a) increased exotic performance is the product of (b) three factors, which are modulated by (c) seven contexts. Three factors: 1) the difference in per-capita effect of enemies (compare damage on leaves); 2) the difference in enemy diversity, which incorporates enemy abundance (number of individuals) and richness (number of species); and 3) host adaptation, which involves changes in exotic growth (plant size) and defence (shield size). The influence of these factors and our ability to detect them changes with seven contexts. Each panel in (c) shows two hypothetical studies that examine different levels of a given context, and so would give contrasting support for the ERH.

July 3, 2023November 22, 2023

Exciting guests and engaging science to kick off 2023

A jam-packed first half of 2023 with a host of visitors and exciting science keeping us busy!

Things kicked off with Marc Cadotte visiting the lab for a month back in March. During his time with us, Marc gave a departmental seminar at KCL, along with an interactive session exploring the use of green space in cities to the Political Ecology, Biodiversity and Ecosystem Services (PEBES) group.

Adam Clark was also able to join for a few days in April to share his research to the group and work on an ongoing meta-community modelling collaboration with Jane and Laura Graham, who could only join virtually as heavy snowfall brought midland trains to a standstill!

We were then joined by Elizabeth Borer, Eric Seabloom, and Sophia Turner along with Marc for a 2-day workshop aimed at disentangling invasive species as drivers or passengers of environmental change and biodiversity loss. The workshop was crammed full of brainstorming and discussions, but we still found time for a few dog walks and some evening meals together.

Dinner and drinks following the culmination of the AlienImpacts workshop

In mid-June we set off for our annual AlienImpacts lab retreat, this time in Ashdown Forest in East Sussex. The retreat offered a welcome break from the London heat, and a chance to reflect on the work completed over the last year and focus on areas at which we could better collaborate to achieve our scientific goals for the project.

Finally, in late June David Tilman joined us as chair of the AlienImpacts scientific advisory committee and a key collaborator in the project. Despite Dave battling jet lag, we discussed the many ongoing components of AlienImpacts and got valuable feedback on the project thus far.

All-in-all an exciting first 6 months for the team!

David Tilman (center) and members of the AlienImpacts team in June 2023

February 13, 2023March 14, 2023

Beyond Triffids: Plants without Prejudice – collaboration with artist Léonie Hampton

We’re excited to welcome Léonie Hampton from the artist collective Still Moving to our group and department for a 6-month artist residency.

Together, we will develop a project exploring perceptions of human and plant “nativeness” to perceive ourselves in relation to biodiversity and climate crises.

_{Activate from the series ‘Beyond Triffids: Plants without Prejudice’ 2023 by Léonie Hampton.}

Beyond Triffids: Plants without Prejudice

Invasive alien species are recognised as one of the greatest threats to global biodiversity, their invasion facilitated by, and compounding impacts of, climate change.  Within ecology and conservation biology there is a heated debate about whether alien plant invasions are good or bad for biodiversity. Do human-introduced alien species increase diversity and compensate for native species loss? Or are alien plants a major threat to biodiversity, warranting active management and restrictions on trade and travel?

Through the lens of alien plants we will particularly focus on perceptions of “nativeness” – both human and plant. Our interdisciplinary approach – co-created between arts, science and humanities – will challenge and interrogate understandings and value judgements, and how these values may need re-evaluation in light of biodiversity loss and migration.

Just as speculative fiction creates the potential, far off in space, where we might see ourselves more clearly, this creative collaboration will work with the perceptions and values of plants to perceive ourselves in relation to our urgent biodiversity and climate crisis.

Our first public outreach event through this collaboration will be held at the Thelma Hulbert Gallery in Honiton on 4 March: Climate Conversations & Honiton Seed Swap. This will take place on the final day of Léonie’s exhibition “A Language of Seeds“.

The residency is funded by King’s Culture and supported by our ERC project AlienImpacts. More about this collaboration and five others supported by King’s Culture can be found here.

January 30, 2023

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.”

https://www.kcl.ac.uk/invasive-species-the-critical-yet-complex-group-driving-biodiversity-loss

December 2, 2022December 2, 2022

NEOBIOTA conference 2022

This year the 12^th 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!