HKU-led Review Highlights Hidden Seed Dispersers in Forest Regeneration

A review led by the School of Biological Sciences at The University of Hong Kong (HKU) has revealed that tiny ground-dwelling invertebrates are overlooked but important seed dispersers, challenging the traditional focus on birds and mammals and offering new insights into forest regeneration and biodiversity conservation.

Led by Professor Si-Chong CHEN from the School of Biological Sciences, the review, published in Trends in Plant Science, synthesises global evidence showing that invertebrates such as slugs, earthworms, beetles, crickets and crabs can consume seeds and later excrete them while they remain viable. The findings highlight an important but underappreciated pathway of seed dispersal that may help sustain plant regeneration, especially in fragmented or degraded ecosystems where larger animal dispersers are declining.

An Overlooked Pathway for Plant Regeneration

Seed dispersal is essential for plant regeneration, forest recovery and biodiversity conservation. Scientific attention has traditionally focused on birds and mammals, which can move seeds over long distances after feeding on fruit. The HKU-led synthesis highlights another pathway: internal seed dispersal by small invertebrates, known as invertebrate endozoochory, in which seeds pass through an animal’s digestive tract and remain viable after being deposited.

Professor Chen conducted the study in collaboration with researchers from the Chinese Academy of Sciences, Durham University in the United Kingdom, and Kobe University in Japan. By consolidating evidence from 43 peer-reviewed publications, the team synthesised evidence of internal seed dispersal involving at least 51 invertebrate species across 186 plant taxa, with records spanning Oceania, Asia, Europe and North America. The review suggests that invertebrate-mediated seed dispersal is not simply a collection of isolated ecological anecdotes. Instead, it appears to be a widespread but overlooked interaction between plants and small animals.

“If you walk through a forest, you might think only birds or monkeys are spreading seeds. But beneath our feet, a hidden group of gardeners is also at work,” said Professor Kenji SUETSUGU, a key collaborator and co-author.  “One of the most fascinating examples we synthesised is a freshwater crab in Japan. A single crab can ingest over a thousand tiny seeds in a single night and later deposit them inside underground burrows. These humid burrows can protect the seeds from being eaten by rodents or drying out, giving them a better chance to grow.”

The review formalises the concept of an “invertebrate endozoochory syndrome” — a convergent suite of plant traits perfectly adapted to these small vectors. Such plants typically produce tiny, resilient seeds enclosed in dull-coloured, inconspicuous fruits at ground level. These fruits may be less attractive to birds and mammals but accessible to ground-dwelling invertebrates, whose digestive processes may scarify the seeds and enhance germination.

After ingestion, seeds may be scarified by the digestive system, which can, in some cases, improve germination. The seeds are then deposited in microhabitats such as soil, leaf litter or burrows. Although such movement may occur over shorter distances than dispersal by birds or mammals, it can still reduce competition near the parent plant and place seeds in sites that favour survival.

“These interactions have long been treated as ecological anecdotes rather than as part of a wider framework,” Professor Chen said. “Because of size bias, invertebrates were traditionally viewed as minor players compared with mammals or birds. But when we look at their abundance and the number of documented interactions, their cumulative contribution to ecosystems can be substantial. Changing our perspective helps us recognise that plant-animal partnerships are more diverse and interwoven than previously assumed.”

The findings do not replace the recognised importance of vertebrate seed dispersers. Rather, they broaden the picture of how plants recruit animal partners. Birds and mammals remain crucial for long-distance dispersal, while invertebrates may contribute through high abundance, frequent contact with the forest floor and precise seed deposition over small spatial scales.

The review also carries conservation implications. As many ecosystems lose large mammals and birds through habitat fragmentation, hunting, and other human pressures, plant species that rely on animal-mediated dispersal may face reduced opportunities for regeneration. In this context, invertebrates could provide an additional layer of resilience, particularly at microhabitat scales.

“We are losing large mammals and birds at an alarming rate globally, which threatens the future of many plant species,” Professor Chen said. “Tiny invertebrates like beetles or slugs cannot carry seeds for kilometres, but their ability to place seeds precisely at fine spatial scales is incredibly important. They reduce competition near the parent tree and deliver seeds into favourable micro-niches. In an increasingly fragmented world, these small-bodied partners offer a vital safety net, helping forest regeneration persist even as larger animals decline.”

By bringing together global evidence, the HKU-led review calls for greater attention to small-bodied animals in seed dispersal research, ecological restoration and biodiversity management. The authors suggest that future studies should examine how frequently invertebrate dispersal occurs across different habitats, how it affects seed survival and germination, and how conservation planning can better account for interactions near the ground.

For details of the research, please refer to the journal paper “Invertebrate endozoochory: An overlooked pathway of seed dispersal”: https://doi.org/10.1016/j.tplants.2026.06.004