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How beetles and crabs help forests spread seeds
When we think about how forests grow and regrow, we often think about colorful birds carrying berries or monkeys dropping fruit seeds. For a long time, these animals have been known as nature's seed dispersers, carrying seeds far from the parent plant and helping forests grow.
But beneath the forest floor another team of hard-working helpers has been quietly doing the same job for millions of years. Tiny ground-dwelling invertebrates are emerging as unlikely allies in forest regeneration, from modest earthworms and slugs to beetles, crickets and even freshwater crabs. Though often ignored due to their small size, these beings play a key role in helping plants reproduce and sustaining biodiversity.A new review by researchers from the School of Biological Sciences at The University of Hong Kong (HKU) published by Phys Org, suggests that these small animals contribute much more to seed dispersal than we previously believed. The researchers, by pooling together evidence from studies worldwide, argue that invertebrates should be given more recognition in ecological research and conservation planning.
A secret network of seed dispersers
According to scientists, seed dispersal is one of the most critical processes in nature.
Plants rely on animals, wind or water to disperse their seeds away from the parent plant, decreasing competition for sunlight, water and nutrients whilst increasing the chance of successful germination. Most scientific research has so far concentrated on birds and mammals because they can carry seeds over long distances after eating fruits.
But the new review highlights another important mechanism, called invertebrate endozoochory.
This occurs when small invertebrates ingest whole seeds that pass through their digestive systems undamaged. Later, the seeds are deposited elsewhere, where they are still able to germinate. This kind of seed dispersal is likely to be widespread across a range of ecosystems, rather than isolated observations, the review suggests.
What the scientists discovered
43 peer-reviewed scientific studies documented internal seed dispersal by at least 51 invertebrate species and 186 plant species.
In this new research, the review was led by Professor Si-Chong Chen of HKU and involved scientists from the Chinese Academy of Sciences, Durham University in the United Kingdom and Kobe University in Japan, where the team looked at the results of 43 peer-reviewed scientific studies that documented internal seed dispersal by at least 51 invertebrate species and 186 plant species.
The evidence came from ecosystems in Oceania, Asia, Europe and North America.
The study highlights that scientists found that many small animals, like slugs, earthworms, beetles, crickets and freshwater crabs, often eat the seeds and then defecate them in suitable places to grow. The results showed that invertebrates disperse seeds significantly more often than scientists believed.
Why seeds have to travel through the gut
To the untrained eye, being eaten might appear to be the end of a seed’s journey.
Surprisingly, it actually can improve its odds of becoming a healthy plant. Invertebrates that eat seeds can scarify their surface coating during digestion. This softens the tough seed coat slightly, allowing water to penetrate and begin germination. Many seeds are then deposited in moist microhabitats such as leaf litter, soil or in burrows underground.
Such environments often offer good conditions for germination whilst protecting seeds from drying out or being eaten by other animals.
Although invertebrates tend to move seeds shorter distances than birds or mammals, such small movements can reduce competition near the parent and increase survival rates.
Plants may be tuned to miniature helpers
If we go by the scientists, the review highlights the concept of invertebrate endozoochory syndrome, which is one of the most interesting ideas.
If we go by the scientists, the review highlights the concept of invertebrate endozoochory syndrome, which is one of the most interesting ideas. It is found that some plants have evolved features that are particularly adapted to invertebrates that dwell on the ground.
Typically, these plants produce small, hard seeds inside tiny, dull-colored fruits that grow near the forest floor. These fruits are easily found by slugs, beetles and other small animals searching for food, unlike the bright-colored fruits that attract birds.
This implies an evolutionary partnership between plants and invertebrates that had not been previously appreciated.
Small animals, big ecological footprint
Because of their size, invertebrates have traditionally been far less studied than larger animals.
But they are one of the most prolific creatures in the forests. Invertebrates that live on the ground are constantly moving seeds through leaf litter, soil and forest floors into small pockets where environmental conditions are good for growth. This continuous movement provides a huge opportunity for plant regeneration that would otherwise be missed.
It is reported that many forests around the world are losing birds and large mammals due to habitat fragmentation, hunting, urban expansion and climate-related pressures.
Many plant species rely on animals to disperse their seeds, and the loss of these larger animals threatens natural forest regeneration.
Forest conservation reconsidered
Scientists believe that conservation efforts should pay more attention to these animals, which are often ignored. Ecological restoration projects tend to focus on trees, birds and mammals, while the huge number of invertebrates living under our feet are comparatively overlooked Also, further work could determine the relative importance of invertebrate-mediated seed dispersal in different habitat types, identify which plant species benefit most from these interactions and provide information that can be used to improve biodiversity management.Images Courtesy: istock
