With animals, ecosystems flourish

Damage control

Seagrasses. Getty images

Aldabra Giant Tortoises. DH photo

Pack of grey wolves. Getty images

Animals are nature’s fascinating engineers, building some of the magnificent structures known to us.

Giant termite mounds, elaborate anthills and robust dams constructed by some of these animals show their might. But animals can do much more — they can also restore ecosystems to their former grandeur, which is most likely lost due to human activities.

Humans have damaged most of the world’s ecosystems in the last few centuries, from the frigid Arctic tundra to the tropical rainforests and everything in-between. The United Nations has recognised the need to rebuild them and has declared the years 2021-2030 as the ‘Decade on Ecosystem Restoration’ to restore degraded ecosystems and fight climate change. While we have launched several efforts, here are some animal ecosystem engineers who have championed the cause without involving us.

Giant tortoises help save islands

About a thousand years ago, when humans first set foot on Mauritius, several species of giant tortoises roamed the surrounding islands, grazing on plants. These huge reptiles also dispersed the seeds of fruits they ate, helping the native ebony trees thrive. But soon after the human invasion of the islands, tortoises were hunted for food. Dogs, rats and pigs that came with humans devoured tortoise eggs and hatchlings, driving their numbers south. The island rapidly slipped from having the highest density of tortoises in the world to having none.

The vanishing of the tortoises hurt the ebony trees, whose seeds now fell close to the parent trees, and without sufficient sunlight, struggled to germinate. Humans also felled these trees for timber and firewood, and the non-native rats feasted on the seeds, making matters worse for the native tree, and threatening other dependent life forms. The island ecosystem was in turmoil.

In the year 2000, about 20 Aldabra Giant Tortoises — a close relative of the now-extinct tortoise species of the islands — entered the scene. They were introduced from Seychelles on Ile aux Aigrettes, a small islet off the coast of Mauritius. Unlike most alien species that prove detrimental to an ecosystem, these giant tortoises swung into action to save it. They began eating the critically endangered ebony fruits and dispersing the seeds in well-lit areas, giving them a good chance at survival. The seeds that passed through the gut of these reptiles also germinated better than those that did not.

Recent studies have shown that rewilding the islands with the giant tortoises, who did their job without a glitch, was a success for the entire ecosystem, and it could be replicated elsewhere.

Beavers, excellent dam builders

The creeks of Britain were once bustling with dog-sized, hardworking rodents — the Eurasian beavers — who were native to the region. They incessantly gnawed through the trees, felled them and built 'dams' across flowing streams with deadwood. By the 16th century, humans had hunted beavers to extinction for their fur, meat and castoreum (a secretion used in making perfumes and medicine).

Once the beavers were gone, the dams—temporary structures of wood they built around their living quarters — also vanished. The flow and quality of the water changed, and the risk of flash floods increased. The fantastic mosaic of dams, ponds, and canals, which these rodent engineers created, dried up. The wetlands in Britain were in peril.

Miraculously, in 2008, a small group of beavers reappeared in parts of England and Scotland, and conservationists also released a few pairs in the wild. With the return of the beavers, trees like willow, hazel, and others regrew after being chiselled by these rodents and are now a haven to numerous birds and insects.

The deadwood serves as a refuge to many insects, frogs, waterfowl, fish, birds and bats. The beaver-built dams slowed down soil erosion in the wetlands and increased ground and surface water levels. The plant diversity also improved. Inspired by the initial success, the UK government has planned to reintroduce beavers in many regions across the country. With these natural engineers doing their job, they transform degraded agricultural land into a thriving wetland ecosystem.

Grey wolves strike the right chord

Since the early 1920s, and until about 25 years ago, the Yellowstone National Park in the United States had one of its most essential inhabitants missing—the wolves.

Without any apex carnivores, the numbers of big herbivores like elks and deers were booming. As a result, they overgrazed the grass and stomped on the plants along river banks. The coyote numbers in the park also went out of control, hurting smaller mammals like rabbits. In 1995, wolves were brought back to Yellowstone to rein in the degrading ecosystem. What happened next stands as one of the most successful stories of how nature bounces back if given a chance.

An increase in apex predators in the park led to a fall in the deer and elk numbers. As the grazing habits of herbivores changed to get away from the wolves, the trees and the grassy valleys regenerated, attracting songbirds and bears with their fruits and berries. Beavers did their magic with a rise in tree numbers and growth, supporting many aquatic life forms in the process.

Wolves killed the competing coyotes and saved the vanishing rabbits and foxes, which the coyotes overpowered. The number of raptors and other scavengers increased to feed on the carcasses of elks and other animals killed by the wolves. Interestingly, the vegetation growing on the river banks stabilised, reducing soil erosion and changing the course of the rivers in the park! Thus, the wolves replenished an entire ecosystem with far more diversity of plants and animals, beating any human efforts in doing so!

Sea greens foster lives in the blue

Hidden underwater at a depth where the sun's rays can still make their way is some of the largest meadows of grass. Seagrasses, as they are called, are the only submerged flowering plants and one of the world’s most valuable yet threatened ecosystems.

Since the later 1800s, seagrasses have declined by about 30% globally due to heatwaves, hurricanes and diseases. In the 1930s, a similar calamity struck the coastal lagoons of Virginia in Australia and wiped out swathes of seagrasses. Around 20 years ago, citizen volunteers and researchers began sowing millions of eelgrass seeds in the lagoons in the hope of reviving what was lost.

Cut to now, after twenty years of that effort, mother nature has weaved her magic. A recent study found that within three years of sowing the seeds, the barren sea floors transpired into lush green meadows, storing massive carbon and nitrogen reserves inside them.

Soon, many species of fish, scallops, and other animals made the seagrasses their new home. As the grasses thrived, the quality of water improved tremendously. The once-degraded ecosystem is now showing signs of prosperity, setting an example of what successful restoration of seagrass could do to marine environments and how we could bring other destroyed meadows back to life.