Lauren Fuge
The phrase ‘animal architect’ may conjure up an image of a beaver adding one last stick to its dam, or a termite scurrying inside its 3-metre-tall mound. The feats of these individual species are impressive – but a new way of interpreting animal impact has resulted in a calculation which adds up the combined engineering efforts of animals around the world, showing that they help shape the planet itself.
A paper published in the Proceedings of the National Academy of Sciences (PNAS) conducted the first global synthesis of animal architects. It looked at data from 513 prior studies to understand how species influence the processes that shape the surface of the Earth.
“Based on our list of 500 species we estimated that animals collectively offer at least 76,000 Gigajoules of energy to landscape forming processes globally in a given year,” says Gemma Harvey, a physical geographer at Queen Mary University London (QMUL).
“This is equivalent to the energy of 500,000 extreme flood events, or 200,000 monsoon seasons.
“This tells us that animals are far more influential in shaping landscapes than previously recognised and their collective energy can rival some geophysical processes.”
This research sits within the little-known field of zoogeomorphology – let’s delve into what that means.
Local architects
From underground burrows to sandy seafloor nests, animals have long built structures across the Earth. Fossils show that animals have constructed shelters and other structures for hundreds of millions of years, like the tiny aquatic creatures that created one of Earth’s oldest reefs 550 million years ago.
Vertebrates and invertebrates alike build architectural creations, although invertebrates tend to be the premier engineers in terms of the size and complexity of structures.
Termites are a well-known example. Throughout northern Australia, compass termites (Amitermes meridionalis) build towers that average 3m tall. They are constructed with a north-south orientation which keeps the temperature inside consistent as the sun moves across the sky.
Other insects create structures using their own bodies. Army ants (Eciton burchellii) display a remarkable capacity for self-assembling into temporary living structures. During mass foraging raids over the uneven jungle floor, they combine to form bridges to allow fellow workers to cross gaps, as well as highways and scaffolds to prevent others from slipping and falling.
Back in the land of vertebrates, the list of architects is extensive. Naked mole rats construct intricate tunnel systems. Male puffer fish make geometric sand circles to attract females, working sometimes for more than a week. Beavers build dams that are more efficient at their job than human constructions. Bower birds make elaborate, often whimsical structures to court females, using a mix of foraged and stolen goods.
Many of these animal architects are also called ecosystem engineers – because their creations change the world for not just themselves but for other animals too.
Ecosystem architects
The term ecosystem engineer has been around in ecology since the 1990s, applied to animals (and plants) that shape the landscapes in which they live.
“Beaver dams represent a conspicuous example,” says Dartmouth College biologist Mark Laidre, in a review article in Current Biology. “By modifying the pattern of water flow in rivers, beaver dams ultimately create large ponds, which contain an altered abundance and composition of plants and animals.”
Laidre compares beavers to hydraulic engineers, as they can regulate water levels through changing their dams.
In southern Africa, chacma baboons (Papio ursinus) flip over high volumes of rocks to feed on the invertebrates beneath – approximately 11,000 kg of rocks per hectare per year – thus sculpting the landscape around them.
Other animal engineers can destroy ecosystems, like bark beetles, which reproduce by tunnelling under bark and so can kill trees en masse.
On the other hand, termites on the African savannah create ‘islands’ of enriched soil around their mounds. These are used by plants as refuge zones.
“These social insects thereby enhance drylands’ resistance to and recovery from drought, helping prevent catastrophic ecosystem shifts and buffering against the negative effects of anthropogenic climate change,” Laidre writes.
The new study in PNAS synthesises examples like these to understand how animals collectively influence the Earth’s processes.
Lead author Harvey notes that many species are overlooked due to being smaller and less charismatic – “particularly those that live underground or underwater, including insects,” she says.
“Although their individual effects may be small, they can be present in high densities and have significant cumulative effects.
“Silk-producing caddisfly larvae are a good example. They are tiny insects that live in the stream bed and their silk nets and retreats bind sediments together, making them more difficult for the river to erode.”
The research from Harvey and team adds to the emerging field of zoogeomorphology, which recognises that to fully understand our planet, we need to understand how its ecological and geophysical processes work together.
“The geomorphic energy of animals is far more influential than previously recognized and future losses, dispersal and introductions of zoogeomorphic species may induce substantive landscape changes,” the authors write.
Undersea architects
The study focuses on terrestrial and freshwater animals, but sea critters are also impressive engineers.
In another paper released this month, a European-Japanese research team reveals how deep-sea creatures are architects of the ocean floor.
They took X-rays of sediment cores that came from the Pacific Ocean’s Japan Trench, 7.5 km below the surface in the hadal zone – among the most poorly understood ecosystems on Earth.
In the sediment, they found fossil evidence of burrowing and feeding behaviour that indicated how animals had colonised the nutrient-rich, oxygenated sediment and changed it over time through feeding and burrowing.
These behaviours are part of the process of bioturbation, in which living creatures affect the cycling of nutrients and the functioning of the ecosystem.
The future of architecture
Understanding the Earth’s landscapes also requires understanding the cumulative effect of the activities of animals. But this isn’t just the case now – animals have influenced the planet for hundreds of millions of years, and Harvey and team are keen to expand their research into the past.
“[In this study] we focused on species still in existence, but during our searches we found some interesting examples of landscape shaping effects associated with extinct animals, including dinosaurs,” she says. “Past changes in biodiversity have doubtless altered the influence of animals on landscape processes over time.”
And the field will also need to look to the future.
“We may be entering a period when large-scale zoogeomorphic effects will increase in intensity and extent,” warns fluvial geomorphologist Stephen P Rice, in a perspective paper on zoogeomorphology.
Climate change will likely have multiple different effects on landscape-shaping behaviours. For example, seasonal shifts in water temperatures will affect the behaviours of ectotherms (cold-blooded animals) like fish. Other species will shift their ranges as the climate of their current habitat changes, changing the distribution of invasive species. Humans are also increasingly changing the natural ranges of animals, either deliberately or inadvertently.
“Non-native species are prone to be significant zoogeomorphic agents because they encounter landscapes that have not coevolved to be resilient to them,” Rice explains.
The introduction of beavers to Patagonia in 1946, for example, profoundly affected the region by moving thousands of cubic metres of sediment to build dams, often drowning existing ecosystems and triggering massive invasions of exotic planet species.
As global temperatures continue to increase – largely due to humans burning fossil fuels – researchers are asking how ecosystem engineers will be affected, and in turn how this will influence the Earth’s geomorphic processes.
“We can expect to see a combination of extinctions and population declines, species introductions and range shifts under climate change,” Harvey says.
“All of these will influence the role of landscape-shaping animals in future environments. “It is important that we understand the nature and significance of these effects to inform conservation and environmental management.”