New study overturns long-held assumptions about how plants spread to islands | EurekAlert!
Plants that successfully leave more offspring are those with traits that allow their seeds to spread widely. That usually involves two key factors: tolerance or adaptability to new environments, and an effective way of reaching them. Over time, evolution has produced a variety of dispersal strategies—seeds can float on the wind, stick to animals, or pass through birds and end up deposited somewhere new.
Crossing the sea, though, adds another layer of difficulty. Seeds must survive what amounts to a small ocean voyage. For a long time, scientists assumed birds were the main way plants made these crossings. The idea was straightforward: birds eat fruit, fly to new islands, and excrete the seeds.
But new evidence has challenged that view. A recent open-access paper in Ecology Letters examines how plants have colonised Surtsey, the volcanic island that emerged off Iceland in 1963. This unique setting has allowed researchers to watch ecological colonisation unfold in real time.
Their findings were unexpected: most of the 78 vascular plant species that established themselves on the island weren’t fruit-bearing plants spread by birds, but grasses. While birds like geese and gulls did contribute to dispersal, most of the colonising species lacked the traits typically linked with long-distance dispersal.
Seed Dispersal Strategies.This is a clear example of how scientific understanding changes as new evidence comes to light. It also highlights how evolution works: not through intent or direction, but through natural selection acting on existing variation and opportunities. Ecosystems arise through these interactions and chance events—not through planning or design.
- Anemochory — Wind Dispersal Light, aerodynamic seeds are carried by air currents, sometimes over great distances.
- Examples: Taraxacum officinale (dandelion), Acer pseudoplatanus (sycamore maple), many orchids.
- Adaptations: Parachutes (pappi), wings (samaras), small seed size.
- Hydrochory — Water Dispersal Seeds float on water, sometimes for weeks, allowing them to reach distant shores.
- Examples: Cocos nucifera (coconut), Nymphaea alba (white water lily), mangroves.
- Adaptations: Buoyant shells, waterproof coatings, air-filled tissues.
- Zoochory — Animal Dispersal Seeds are transported externally or internally by animals.
- Endozoochory (inside): Animals eat fruit and later excrete the seeds.
- Examples: Prunus avium (wild cherry), Rubus fruticosus (bramble).
- Epizoochory (outside): Seeds attach to fur or feathers.
- Examples: Galium aparine (cleavers), burdock.
- Autochory — Self-Dispersal The plant releases seeds mechanically, often explosively.
- Examples: Impatiens glandulifera (Himalayan balsam), Ulex europaeus (gorse), geraniums.
- Adaptations: Tension in seed pods releases seeds suddenly.
- Barochory — Gravity Dispersal
Seeds simply fall to the ground beneath the parent plant. Secondary dispersal may follow via animals or water.
- Examples: Quercus robur (oak), Aesculus hippocastanum (horse chestnut), apples.
- Adaptations: Heavy seeds, often encased in nuts or fruits.
- Anthropochory — Human-Mediated Dispersal
Seeds are moved—intentionally or accidentally—by humans through agriculture, trade, travel, and habitat disturbance.
- Examples: Many crop species (wheat, maize), garden escapes, invasive plants.
- Significance: Major driver of modern plant distributions.
Note: Many plants use more than one dispersal strategy, depending on conditions. Over time, these mechanisms have shaped the global distribution of plant species.
It’s also a reminder of how deeply interconnected life on Earth is. No species can persist entirely on its own. As we continue to damage and fragment ecosystems, we undermine the web of life that ultimately sustains us. Humanity cannot thrive on a planet stripped down to a few species of our choosing.
You can read more about this research in the EurekAlert! news release.
New study overturns long-held assumptions about how plants spread to islands
A new study from Iceland’s Surtsey island shows that birds carried most of the plants that colonised the island, challenging long-held beliefs that seed or fruit shape determines how plants spread — offering fresh insight into life’s adaptation to change.
When the volcanic island of Surtsey rose from the North Atlantic Ocean in 1963, it offered scientists a once-in-a-lifetime opportunity to observe how life takes hold on a brand-new and barren land. For decades, ecologists believed that plants’ ability to reach remote and isolated places depended mainly on special adaptations for long-distance dispersal — for example, fleshy fruits thought to attract birds, which would eat the fruit and later disperse the seeds — giving those species a decisive advantage in colonising new areas.
A new study published in Ecology Letters challenges this long-standing view. Researchers from Iceland, Hungary, and Spain found that most of the 78 vascular plant species that have colonised Surtsey since 1965 lack any of the traits traditionally associated with long-distance dispersal. Instead, gulls, geese, and shorebirds have played the leading role in bringing seeds to the island — carrying them in their guts or droppings. In doing so, birds have transported a wide range of plant species, laying the foundations for Surtsey’s developing ecosystem.
Birds turned out to be the true pioneers of Surtsey — carrying seeds of plants that, according to conventional theories, shouldn’t be able to get there. These results overturn traditional assumptions about plant colonisation and show that to understand how life spreads and responds to environmental change, we must look at the interactions between plants and animals. Life does not move in isolation — it follows life.
Dr. Pawel Wasowicz, first author
Natural Science Institute of Iceland
Akureyri, Iceland.
Our findings have far-reaching implications for ecology and conservation. Animals — especially birds — are key drivers of plant dispersal and colonisation. As migration routes shift under a warming climate, birds will play a vital role in helping plants move and adapt to new environments.
Dr. Andy Green, corresponding author
Department of Conservation Biology and Global Change
Estación Biológica de Doñana (EBD), CSIC
Sevilla, Spain.
The study underscores the exceptional importance of Surtsey as a natural laboratory, where scientists can observe the fundamental processes of life — how ecosystems emerge, evolve, and respond to environmental change. It calls for new ecological models that account for real biological interactions rather than relying solely on seed traits or taxonomic classifications.Long-term research like that carried out on Surtsey is invaluable for biology. It allows us to witness ecological processes that would otherwise remain invisible — how life colonises, evolves, and adapts. Such work is essential for understanding the future of ecosystems in a rapidly changing world.
Dr. Pawel Wasowicz.
Publication:
ABSTRACTContrary to creationist claims that the peer-review process is designed to prevent scientists from publishing anything that challenges scientific orthodoxy, this paper clearly demonstrates the opposite. It directly challenges the long-standing assumptions used to predict how plants colonise new habitats and form new ecosystems — and calls for the replacement of the existing model.
Dispersal syndromes based on traits assumed to be adaptations for specific dispersal mechanisms are routinely assigned to flowering plants. Using the colonisation record from a volcanic island formed in 1963, we assess whether dispersal syndromes predict which species establish on newly formed land. We evaluated the long-distance dispersal (LDD) syndromes of the 78 plant species using three European classification systems. Syndrome assignments were inconsistent between classifications (coinciding for ≤ 13% of species). Two systems showed no evidence that LDD syndromes conferred a colonisation advantage. The third classification suggested wind syndromes were favoured, but only assigned a minority of colonisers to LDD syndromes. ‘Unassisted’ species assumed to lack dispersal adaptations were dominant. However, empirical evidence supports endozoochory via aquatic birds for 62 colonisers. This suggests bird-dispersal is a major driver of colonisation for dry-fruited plants, and underscores the need for new approaches to plant dispersal that account for overlooked plant–animal interactions.
1 Introduction
For decades, it has been widely accepted that vascular plants have ‘dispersal syndromes’ diagnosed by readily identifiable morphological traits assumed to promote dispersal by specific mechanisms (van der Pijl 1969; Howe and Smallwood 1982; Lososová et al. 2023). This perspective has shaped functional trait-based ecology, influencing how we model plant migration and species distributions (Tamme et al. 2014; Lososová et al. 2023). For example, the ‘endozoochory syndrome’ applies to plants with fleshy fruits, presumed to disperse seeds via gut passage. Empirical studies have shown that dispersal by vertebrates provides longer dispersal distances than abiotic mechanisms (Bullock et al. 2017). Therefore, if dispersal syndromes do not reliably predict real-world plant dispersal by birds, the use of trait-based approaches to infer plant movement and responses to global change may need reconsideration.
Various authors have expressed unease about the extent to which dispersal syndromes explain empirical data on dispersal mechanisms (see González-Varo et al. 2024 for synthesis), and many dispersal events over evolutionary time scales fail to match the syndrome-based expectations (Nogales et al. 2012). In particular, emerging evidence indicates that aquatic birds such as gulls, shorebirds and geese defy the syndrome paradigm and are major dispersal vectors of dry-fruited plants from the abiotic syndromes, especially via endozoochory (Green et al. 2022, 2023.1). The same is true for endozoochory and epizoochory by large herbivores (Pakeman et al. 2002; Albert et al. 2015). To date, no study has tested whether dispersal syndromes predict plant colonisation at the scale of a newly formed island—an invaluable task to confirm that syndromes are valid tools for modelling species movements in rapidly changing environments.
Few sites provide a better setting to test the dispersal syndrome paradigm than Surtsey. Located over 30 km off Iceland's southern coast, the island emerged in November 1963 (Þórarinsson 1968) and has been strictly protected and closely monitored. Annual expeditions, beginning in May 1964 (Einarsson 1963), have generated a comprehensive dataset of plant species colonising Surtsey and their precise initial location. Surtsey offers a rare opportunity to document plant arrival, establishment and expansion and therefore for testing whether dispersal syndromes explain colonisation events over the timeframe of a single human generation. If morphological syndromes reliably predict long-distance dispersal (LDD), we would expect species with traits linked to LDD syndromes to be overrepresented among colonisers, while species lacking such ‘adaptations’ should rarely establish. We would also expect the precise location of plant colonisations to match the predicted vector (e.g., a species with a sea dispersal syndrome should colonise the shoreline). If, instead, colonisation patterns contradict the syndromes, then a reassessment of how we classify and predict dispersal mechanisms is required.
We tested three key assumptions of the dispersal syndrome paradigm. (1) That plant species can be objectively assigned to a specific syndrome, such that three existing syndrome classifications for the Icelandic flora largely agree on which species belong to which syndromes. (2) That syndromes predict which species successfully colonise over long distances. If syndromes have predictive power, Icelandic species with LDD syndromes should be overrepresented among species colonising Surtsey. If they are not, then colonisation must be explained by alternative dispersal mechanisms. (3) That the location of colonisation events within Surtsey aligns with syndrome-based expectations. If syndromes accurately reflect dispersal constraints, species assigned to wind, sea, or animal dispersal syndromes should be spatially structured in accordance with their predicted dispersal pathways. Finally, we consider whether empirical evidence for plant dispersal by birds explains the colonisation of Surtsey better than morphological dispersal syndromes.
[…]
5 Conclusions
Our study challenges the long-standing assumption that morphological dispersal syndromes reliably predict plant colonisation. Instead, we demonstrate that avian (endo)zoochory is a major force that fuels plant dispersal to a volcanic island, even for species without a zoochory syndrome. Our results revealed a critical flaw in existing predictive models, which assume that dispersal can be inferred from plant morphology alone. Moving forward, we suggest that ecological research should prioritise direct empirical evidence of dispersal processes rather than relying on subjective syndrome-based classifications. In order to accurately predict plant responses to environmental change, subjective assumptions based on plant morphological traits should be replaced with mechanistic understanding of plant–animal interactions. Intensive field studies have provided important and unexpected insights into how plants actually disperse to a volcanic island. To understand plant dispersal and colonisation mechanisms on islands, classical syndromes are inadequate and fail to reflect the complexities of plant dispersal strategies. Avian endozoochory of dry-fruited plants with small seeds is a hugely important but understudied process. More research is required into these key plant–animal interactions. Frugivory is not important in all terrestrial habitats where birds are the dominant seed vectors.
Wasowicz, P., Á. Lovas-Kiss, N. Szabó, and A. J. Green. 2025.
Putative ‘Dispersal Adaptations’ Do Not Explain the Colonisation of a Volcanic Island by Vascular Plants, but Birds Can. Ecology Letters 28(10): e70234. https://doi.org/10.1111/ele.70234.
Copyright: © 2025 The authors.
Published by John Wiley & Sons, Inc. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
In reality, the accusation levelled against science by creationists is far more accurately applied to their own movement. Many creationist organisations require contributors to sign a statement of belief and prohibit the publication of anything that does not fully align with a literal interpretation of the Bible, particularly the creation account in Genesis. Any so-called “peer review” of creationist articles is, in practice, merely a check for doctrinal compliance, not scientific rigour.
The truth is that science can only advance by questioning and testing existing ideas. That is why we now have modern medicine, microelectronics, telecommunications, air travel, the Internet, high-rise engineering, and renewable energy — whereas once it was widely believed that Earth was young and flat, that mental illness was caused by demons, that disease was spread by miasmas, and that the fastest form of long-distance communication was a handwritten letter delivered on horseback.
Science thrives because it embraces reasonable uncertainty. Religion falters because it clings to unreasonable certainties.
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