Image 1. Monotropastrum humile, a representative forest-floor plant whose seeds are dispersed internally by invertebrates. Its pale flowers emerging from the shaded forest floor evoke the hidden and often overlooked nature of plant–invertebrate interactions. Photo credit: Kenji Suetsugu.
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.
Image 2. A ground-dwelling cricket feeds on the fruit of Monotropastrum humile, illustrating how small invertebrates may ingest seeds
and contribute to their dispersal across the forest floor. Photo credit: Kenji Suetsugu.
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.
How small dispersers help seeds
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.
A safety net in fragmented forests
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
由香港大學（港大）生物科學學院陳思翀教授領導，聯同中國科學院、英國杜倫大學及日本神戶大學的研究人員進行綜述研究，發現蛞蝓、蚯蚓、甲蟲、蟋蟀以至螃蟹等體型細小、棲息於地面的無脊椎動物能夠吞食種子，而種子經其消化道排出後仍能保持活性，顯示這些動物是一直被忽視但十分重要的種子傳播者。
研究結果突破過往種子研究主要聚焦於鳥類和哺乳動物的傳統框架，並凸顯一種重要但長期未獲充分重視的種子傳播途徑。尤其在生境破碎化或退化、且大型動物傳播者日益減少的生態系統中，這種途徑或有助維持植物更新，為森林恢復及生物多樣性保育帶來新的啟示。研究結果已發表於《植物科學趨勢》。
被忽略的植物繁衍途徑
種子散布對植物更新及生物多樣性保育至關重要。過去，科學界往往受「體型偏見」影響，研究主要聚焦於鳥類和哺乳動物等大型動物，甚至將無脊椎動物視為破壞種子的捕食者。然而，這項綜述闡明了另一種長期被低估的途徑——由小型無脊椎動物進行的「體內種子散布」，即種子通過動物消化道後仍保持活性，並隨排泄物散布至其他地點。
通過整合全球43篇經同儕審查的文獻，發現至少51種無脊椎動物能進行體內種子散布，涉及186個植物分類群。這些相互作用廣泛地分佈於多個大洲與島嶼，顯示這些並非零星的生態異常，而是一種廣泛存在的全球性現象。這種散布方式尤其在森林地表等影響種子存活的微生境中扮演着關鍵角色。
「如果你漫步森林，可能會以為只有鳥類或猴子在傳播種子。但在我們腳下，一群隱藏的『園丁大軍』也正在默默耕耘。」研究共同作者、日本神戶大學的末次健司教授表示：「我們綜合分析的例子中，最令人着迷之一是日本的一種淡水蟹。一隻螃蟹在一夜之間便可吞食逾千粒微小種子，隨後將種子排放於地下洞穴內。這些溫暖潮濕的洞穴提供了完美的庇護所，不僅保護種子免被齧齒類動物吃掉或因乾燥而失去活性，更為其萌發生長贏得了起跑優勢。」
機理與「無脊椎動物體內傳播症候群」
該綜述正式提出了「無脊椎動物體內傳播症候群」的概念，指植物為適應這些小型散布媒介而演化出的一系列趨同性狀。此類植物通常產生微小且具韌性的種子，藏於接近地面、色澤暗淡且不顯眼的果實中。這些果實較少吸引鳥類和哺乳動物，卻可能吸引地棲無脊椎動物取食。種子被吞食後，種子外殼可能在通過消化道期間受到磨蝕，往往能顯著提高萌發機會。
種子被排出後，會沉積在土壤、枯枝落葉層或洞穴等適宜微生境中。雖然其移動距離不及大型脊椎動物，但仍有助減少母株附近的競爭。陳思翀教授指出：「當我們考慮到無脊椎動物龐大的種群數量時，此類生物互作對生態系統的累積貢獻其實相當可觀。這有助我們擺脫『以脊椎動物為中心』的傳統觀念，認識到動植物間的夥伴關係比想像中更多樣。」
整體圖像與保育啟示
這些新發現並非要取代鳥類和哺乳動物在長距離種子散布中的重要地位，而是顯示無脊椎動物憑藉龐大的數量及精準放置種子的能力，作出獨特而互補的貢獻。
隨着全球大型哺乳動物和鳥類因棲息地破碎化、狩獵及其他人類活動而持續減少，依賴動物傳播種子的植物可能面臨更新受阻的危機。陳思翀教授補充道：「雖然微小的無脊椎動物無法將種子搬運數公里，但在大型哺乳動物和鳥類正以驚人速度消失、景觀日益破碎的世界中，牠們提供了一張至關重要的生態安全網，確保森林更新在微生境尺度上不會完全崩潰。」
團隊呼籲科學界在生態復育與生物多樣性管理中，給予棲息於地表微生境的小型動物更多關注。未來的研究應進一步探討無脊椎動物散布種子的現象在不同棲息地中的發生頻率，以及這種散布方式對種子萌發的具體影響。