The more time and effort obliging scientists put into researching animals, the more we realise their complexities and their impact on their surroundings. Because of their complexities, these scientists have begun borrowing terms from other disciplines to make it easier to describe the functions of animals. This is where the idea of describing certain species as “ecological engineers” comes from.
A while ago I looked into the value of African elephants in fighting global warming. As elephants wander through the landscape, they alter – or engineer – the biology around them.
This idea stuck with me and I was intrigued to dive a bit deeper into other animals who play a large role in developing our biome into what we see. Before going further, it’s important to understand the term “ecological engineering” and how it originated.
The Evolution of “Ecological Engineering”
Unsurprisingly, the first person I could find who published his observations on animals and their effect on the environment was Charles Darwin in 1881. He devoted his last scientific book to the effects of earthworms on soil formation.
It was only in 1994 – over 100 years after Darwin’s observations – that the term was proposed by Jones, Lawton and Shachak in their biological research. In their first article on the topic, they defined ecosystem engineers as
“Organisms that directly or indirectly modulate the availability of resources (other than themselves) to other species by causing…state changes in biotic or abiotic materials. In so doing they modify, maintain and/or create habitats”.
Rhinos as Ecological Engineers
It’s no secret that rhinos are no longer in abundance. They were once found all around Africa in an almost continuous stretch from Burkino Faso in West Africa through central Africa and as far as Somalia in the east down to Southern Africa, right down to Cape Town. There are now only relic populations in most of Africa with South Africa as their last remaining stronghold.
As white rhinos are generally more numerous than black rhinos, they will be the focus, although it is important to note that black rhinos play a large role in shaping the environment, too. Below we’ll dive into how white rhinos maintain the ecosystem as well as create their own.
1) Natural Lawnmowers
White rhinos graze predominantly on grasses. They weigh anything upwards of 2,000 kg, meaning that they need a substantial amount of food intake. As they eat, they become the perfect lawnmower, and they complete a job that appears to have been part of their co-evolution with grasses. They trim and maintain grasses at a nutritious level, improving grazing for other animals.
White rhinos prefer lawn grasses rather than clump grasses, creating better groundcover while also generating natural fire barriers, as lawn grasses don’t catch fire as easily as clump grasses do. One of the grasses favoured by rhinos is Red Grass (Themeda triandra) which is semi-resistant to fire if not overgrazed. So not only does the rhino maintain the lawn but it helps to manage veld fires.
2) Phenomenal Fertilisers
It is not only their mowing that is a key factor of their influence on their environment, but also their rich fertilisation of the soil. In a study conducted in an area where soil degradation due to overgrazing had occurred, the introduction of black rhino dung saw a radical change in the soil. Although the study used black rhino dung, phosphorus and organic nitrogen in the soil became more available, which also occurs with organic matter in white rhino dung.
Increasing soil fertility is quite important for other grazing animals in the area. In the Hluhluwe Game Reserve in the province of Kwa-Zulu Natal, South Africa, rhinos account for roughly 25% of the animal biomass in the reserve. It was discovered that when rhinos were removed from an area the grazing for impala and wildebeest declined, due to the lack of soil fertility and resultant grass growth.
3) Exuding Their Own Ecosystem
While rhinos’ eating routines shape the vegetation and affect the lives of animals around them, they also have their own ecosystem within them with their own intrinsic balance. They host an interesting assortment of parasites, insects and birds which are closely connected to them.
The biggest botfly species in Africa known as Gyrostigma rhinocerontis is now an endangered species due to the loss of its host. The fly’s life cycle is directly linked to that of the rhino: the eggs are laid onto the rhino’s head near the nostrils and horn; the larvae hatch and migrate into the belly where they feed on blood and tissues and develop there until they are ready to transform into a nymph. They finally leave the rhino during defecation and bury themselves in the nearby ground until they emerge as adults.
Along with the botfly, other parasites rely on rhinos like the Dermacentor rhinocerinus tick. These ticks are limited purely to living on the rhino and are a delicious food source for opportunistic Oxpeckers which are common companions of rhinos. The fact that both the rhino botfly and rhino tick will die out if rhinos become extinct is unlikely to bother many, but we don’t fully understand all the workings of nature so it would be foolish to consider their loss as a good thing.
Rhinos perform specific and important functions in maintaining the Southern African bushveld. As humans occupy more land and animal kingdoms shrink, even more, the soil will become less productive and the landscapes less biodiverse. Rhinos have advanced over centuries into some of the greatest and most inexplicable herbivores on earth who are vital to the health and maintenance of the ecosystem.