Grasslands: from poo to predators

Grasslands are the stage for a real A-list animal cast.

When it comes to the Earth’s most glamorous habitats, you may think grasslands lack the kudos of a tropical rainforest or lofty Himalayan pass. But dig a little deeper and the wonder of this remarkable habitat, covering about a quarter of all land on Earth, begins to emerge.

For a start, grasslands are the stage for a real A-list cast.

Think 270kg lions perfectly camouflaged against the dry African savannah, hairy battalions of bison roving the prairies, or herds of wildebeest wandering the Serengeti in their millions.

Go back a few millennia, and even then grasslands were home to the big players. Elasmotheriums were enormous rhinos endowed with 6-foot horns, that grazed steppe grasses alongside mighty woolly mammoths. Even the biggest land animal ever was a grasslander: the Indricotherium was a 20 tonne hornless rhino who stood some 5 metres tall, and roamed plains that stretched from Europe to China 30 million years ago.

Another animal that owes a debt to the grasslands is Homo sapiens: that’s us. Recent studies have found that our key human traits of bipedalism, large brains, flexible diets and complex social structures may have evolved as tricks to survive in newly colonised open grasslands.

So what makes this habitat tick? In short, grasslands are nature’s halfway house. When an ecosystem lacks sufficient water or nutrients to support high-maintenance forests, grass comes into its own. Even the Sahara enjoyed a brief spell as verdant grassland around 10,000 years ago, when a rainier climate meant that giraffes, rhinos, and even humans moved in.

There is one key ingredient that makes this limbo-land productive and that ingredient is a load of crap. Herbivores that feed on grasses produce an astronomical amount of excrement- excrement that is still rich in undigested nutrients. And through the tireless efforts of specialist recyclers known as dung beetles, this rich fertiliser gets spread out and buried, returning these nutrients to new-growth grass ready for the grazers.

Article continues below

More on Nature

© BBC NHU 2016

There are some 8000 species of dung beetle around the globe, and they are found on every continent except Antarctica. What most of them have in common is their taste for droppings, usually of herbivores, as these contain plenty of undigested vegetable matter. But dung beetles are picky, and won’t tuck in to just any old pooey morsel. This fact became abundantly clear to Australian cattle farmers in the 1960s. The local dung beetle, partial to marsupial faeces, was simply not interested in the pats of imported cows. Dung piled up, biting fly populations boomed, and pasture began to wilt, starved of light and nutrients. It wasn’t until bovine-specific beetles were imported that the pastures were able to return to some sort of normality.

Shifting biblical amounts of poop is all very well, but the world’s dung beetles would be up the proverbial creek if they weren’t supplied with fresh fodder every day. One of the plains’ most forthcoming providers is the African elephant. An adult elephant can produce over 70kg of dung daily.

Incidentally, it’s not just dung-beetles that get involved; people put this to various uses too, including repelling mosquitoes, making paper, producing prize-winning artworks and even brewing beer!

All that defecation is powered by a lot of eating. The elephant’s iconic trunk can weigh 200kg, but finger-like protrusions on its tip are so dainty that they can pluck a single blade of grass from the ground. With this facial cutlery set they can shovel up to 300kg of vegetation into their mouths each day; that’s around four times the weight of your average Brit.

© BBC NHU 2016

Elephants have excellent memories, and old matriarchs are fonts of information when times get tough in the plains. Their repository of mental maps, accumulated over their lifetime, means they can lead the herd to pastures new when their usual stomping grounds are stricken by drought.

Elephants’ size and, in some places, inch-thick skin, means they are rarely bothered by the formidable carnivores that stalk the savannah. And there are some serious meat-eaters in grassland ecosystems.

Lions’ four-inch teeth and muscular build mean they can take down fully-grown buffalo. And few prey can outrun a cheetah in full 60mph sprint.

Not all grassland predators carve out such an honest living. Many grassy ecosystems go through natural cycles of wildfire and regrowth, as witnessed in the Australian outback. The inferno is usually started by lightning, and sends frogs, insects and other undergrowth inhabitants running for their lives. But some birds of prey seem to be attracted to these bush fires.

Many grassy ecosystems go through natural cycles of wildfire and regrowth. © BBC NHU 2016

They make hay while the pyre blazes, and catch birds and small mammals as they flee the flames. There are even reports of both brown falcons and black kites picking up burning branches to start new fires to flush out their prey.

However familiar this habitat may seem, the planet’s grasslands still hold secrets waiting to be discovered. As recently as last year, scientists finally got an insight into the thousands of mysterious mounds carpeting the Llanos plains around the Orinoco River in Colombia and Venezuela. Close inspection revealed that these weird knolls were made largely from the manure of metre-long earthworms that forage in shallowly flooded soil, only coming to the surface to breathe and deposit their dung.

The Llanos grasslands hold a lesson for us all: scrape the surface, and you may find more than you bargained for. Home to giants, beetle-horticulturalists, and even playing a critical role in our own evolution, it seems grasslands aren’t as ‘plain’ as we give them credit for.

Featured image © Chadden Hunter | BBC NHU 2016