Study spotlights slugs, beetles and crabs as seed dispersers

Small animals on the forest floor may matter more than expected

Seed dispersal is one of the quiet mechanisms that shapes forests, biodiversity and ecological recovery. It determines where plants can establish, how fragmented habitats reconnect and how ecosystems respond when larger animals decline. A new review led by researchers at the University of Hong Kong argues that an overlooked group deserves much more attention in that process: small ground-dwelling invertebrates such as slugs, earthworms, beetles, crickets and crabs.

The review, published in Trends in Plant Science, synthesizes evidence showing that these animals can consume seeds and later excrete them while the seeds remain viable. That mechanism, known as invertebrate endozoochory, has received far less scientific attention than seed dispersal by birds and mammals. But according to the review, it may represent an important pathway for plant regeneration, especially in damaged or fragmented ecosystems where larger dispersers are less abundant.

Challenging a long-standing ecological bias

Ecology has traditionally focused on animals that visibly move seeds over substantial distances, particularly fruit-eating birds and mammals. That emphasis is understandable: large vertebrates are easier to observe, and their role in moving seeds across landscapes is well established. The HKU-led team argues, however, that this focus has left a major blind spot close to the ground.

Forest floors host dense communities of small animals interacting continuously with seeds, fruiting bodies and leaf litter. Because those interactions are harder to track, they have often been treated as secondary or ignored altogether. The new review suggests that assumption is too narrow. By consolidating evidence from 43 peer-reviewed publications, the researchers documented internal seed dispersal involving at least 51 invertebrate species and 130 plant species.

That does not mean slugs and beetles replace birds or mammals in ecological importance. It means seed dispersal networks may be more layered than standard models assume. In some habitats, especially where large vertebrates have declined, small invertebrates may be helping sustain regeneration in ways that are easy to miss without targeted study.

What the review found

The basic process described in the source material is simple but consequential. An invertebrate consumes seeds, either directly or while feeding on surrounding plant material, and the seeds pass through the digestive tract intact enough to germinate after deposition. The review highlights this as a viable and underappreciated mode of movement for plants across the forest floor.

The researchers say this pathway could be especially relevant in fragmented and degraded ecosystems. In such environments, traditional dispersers may be absent, reduced or behaviorally altered, making any remaining route for viable seed movement more important. Even if the distances involved are shorter than those achieved by birds or mammals, frequent local redistribution can still shape which plants persist, colonize or recover after disturbance.

The review also broadens the range of animals that ecologists may need to think about when mapping plant reproduction. The source text specifically identifies slugs, earthworms, beetles, crickets and crabs as contributors. That is a strikingly diverse group spanning very different feeding behaviors and microhabitats, suggesting the phenomenon is not limited to one unusual species or a single ecosystem type.

Why this matters for conservation

The conservation significance lies in resilience. If ecosystems depend on more dispersal pathways than previously recognized, restoration strategies that ignore those pathways may underestimate how forests regenerate or how biodiversity is maintained. The source text frames the findings as particularly relevant to forest recovery and biodiversity conservation, areas where managers often focus on canopy structure, soil health and the return of larger animals.

Recognizing invertebrates as dispersers could refine that picture. Ground-dwelling species are sensitive to humidity, leaf litter, microclimate and soil condition, all of which are influenced by logging, fragmentation and climate stress. If those animals help move viable seeds, then preserving their habitat is not only about invertebrate diversity. It may also affect plant recruitment and long-term forest composition.

This perspective is useful because it links two conservation conversations that are often separated: concern over declining small invertebrate populations and concern over impaired plant regeneration. The review implies those trends may interact. If overlooked dispersers decline, the consequences could ripple upward into vegetation recovery and habitat structure.

A hidden process with practical implications

One reason the topic stands out is that it shifts attention from spectacular long-distance dispersal to subtle, repeated movement across the ground layer. In practical terms, that could matter for restoration sites, secondary forests and edge habitats, where short-distance transport may still determine whether seeds reach suitable microsites for germination.

The review does not claim that every seed survives digestion or that every invertebrate acts as an effective disperser under all conditions. Instead, it assembles enough documented cases to argue that the process is real, widespread and insufficiently studied. For field ecologists, that may change what counts as relevant evidence in regeneration studies. For conservation planners, it suggests that preserving the ecological functions of forest floors could be more important than previously assumed.

The work also illustrates a broader scientific pattern: processes once treated as peripheral can turn out to be central when researchers collect enough comparative evidence. In this case, the hidden nature of the interaction may have delayed recognition. Tiny animals moving tiny seeds through dense litter is exactly the sort of ecological mechanism that can escape notice for decades despite occurring continuously.

What comes next

The clearest next step is more direct measurement. The review synthesizes global evidence, but its practical influence will likely depend on how future studies quantify distance, survival rates, plant establishment and habitat-specific effects. Researchers will want to know which invertebrates are the most effective dispersers, which plant traits favor survival through digestion and how these interactions change in disturbed landscapes.

Even so, the review already makes a meaningful contribution by reframing a basic ecological question: who moves seeds, and how often do scientists miss the answer because they are looking too high above the ground? By drawing together evidence across dozens of studies, the HKU-led team argues that the forest floor is not just a passive surface where seeds land. It is an active transport network maintained in part by small animals whose ecological role has been underestimated.

For biodiversity science, that is more than a curiosity. It is a reminder that ecosystem function often depends on modest, easily overlooked interactions. In an era of habitat fragmentation and ecological decline, identifying those interactions may be essential to understanding how forests persist and recover.

This article is based on reporting by Phys.org. Read the original article.