X Donate or Adopt

We live in a world where obliging scientists who endlessly research animals borrow from other disciplines to describe animal functions. This is where the concept of rhinos as eco-engineers comes from.

A rhino does not simply act as one of the most efficient grazers of grass and maintainers of the savanna, it is described as an eco-engineer. The big words and concepts don’t stop there as the rhino is not only an eco-engineer but it is also a megaherbivore i.e. any animal which weighs more than 1000kg, and to round off the building analogies, it is described as a keystone species. The latter describes any animal which has a disproportionately large effect on the ecosystem relative to its abundance.

The one thing we know about rhinos is that they are no longer in abundance. Whereas they were once found in a more or less continuous stretch from Burkino Faso in West Africa through central Africa and as far as Somalia in the east down to Southern Africa, where they were once found right down to Cape Town, there are now only remnant populations in most of Africa with South Africa having become their last remaining stronghold.  In the past the most abundant rhino was the black rhino which is about half the size of a white rhino but in terms of temperament it is far more aggressive. It’s temper however did not prevent it from being decimated. From the 1960s when the population of black rhinos was around 100,000 it dropped by the 1990s to only 2,415. Poaching accounted for the 96% loss in black rhinos. Fortunately according to WWF the species has made a comeback and current estimates of the population numbers is between 5,000- 5,455. What the impact on the environment is of the overall decline is hard to gauge however, as black rhinos are primarily browsers feeding on trees and shrubs within their height range of approximately 1-1.5 m one can assume that a great many plants were not effectively pruned and so the passage through trees and shrubs for smaller species was harder, seed might not have spread and many smaller plants would not have had access to enough light to grow. The loss of their dung would also have had a negative impact on soil fertility and the creatures that process dung.

Unlike black rhinos, white rhinos graze primarily on grasses. They weigh anything upwards of 2,300 kg and are the most perfect lawnmower imaginable doing a job that appears to have been part of their co-evolution with grasses. They maintain grasses at a nutritious level making grazing better for other animals and they do it on a scale that no other animal other than a hippo and Indian rhino achieves. They prefer lawn grasses rather than clump grasses which not only gives better groundcover but also creates natural fire barriers, as lawn grasses don’t catch fire as easily as clump grasses do.  One of the grasses favoured by rhinos is rooigras (Themeda triandra) which if not overgrazed is known to be resistant to fire, so not only does the rhino maintain the lawn but it’s helped by some of its favourite grasses in managing fires. It is helped by buffalos who graze grass to a height that makes it particularly convenient for rhinos to graze. However it takes quite a few buffalo to cover the area that one rhino can manage which underlines the definition of rhinos as megaherbivores.

In Hluhluwe game reserve in KZN South Africa, rhinos account for approximately 25% of the animal biomass in the park. It was found that when rhino were removed from an area the grazing for impala, wildebeest and impala declined. The nutritional value of grass is critical but one of the features of a megaherbivore is that they can often tolerate less nutritious grass than other smaller species. It is not only their mowing that is a major component of their impact on their environment, but also their abundant fertilising of the soil. In a study conducted in an area where soil degradation due to overgrazing had occurred, the introduction of rhino dung saw a radical change in the soil. The electrical conductivity increased as phosphorus and organic nitrogen in the soil became more available.

While rhinos eating habits shape the flora and affect the lives of animals around them, they also have their own ecosystem which has its own inherent balance. Rhinos host a fascinating collection of parasites, insects and birds which are all intimately connected to them. The biggest fly species in Africa known as Gyrostigma rhinocerontis is now a rare and endangered species due to the loss of its favourite host. The fly’s life cycle is directly linked to that of the rhino. The eggs are laid directly onto the head of the rhino near the nostrils and horn. The larvae hatch after 6 days and begin a migration into the belly of the rhino where they feed on blood and tissues. Large numbers of larvae in all different stages of development attach to the wall of the stomach and develop there until they are ready to be nymphed when they leave the host during defecation. They then leave the dung and bury themselves in the nearby ground until they emerge as adults six weeks later. After that long journey through the belly of the beast its astonishing to read that the adult flies lives for only 3-5 days, as they die soon after copulation.

You probably are not weeping over the demise of a botfly or other parasites which rely on rhinos like the Dermacentor rhinocerinus tick. These ticks are restricted to the rhinos range and are a delicious food source for opportunistic oxpeckers which are common companions of rhinos. In a normal ecosystem the ticks which are disease vectors would also help sort out the fit from the less fit of the species, so that only the strongest and healthiest of rhinos survived. That option has long been lost, so ticks still hang in but when the rhino goes, so will they.

Oxpecker birds love blood and feast not only on ticks but also on blood from wounds on rhinos. There is some questioning of the relationship between rhinos and oxpeckers as mutualistic because oxpeckers actually delay the healing of wounds by pecking at scabs to release fresh blood which is their favourite food. It might however be that they keep wounds clean in the process so the jury is out on whether the relationship isn’t a mutually supportive one. The belief that oxpeckers also act as an alarm system for rhinos who are notorious for their poor eyesight, has also come into question as it appears they fly away mainly when humans approach rather than when other animals do. Drongo birds and other birds have less contentious relationships with rhinos because all they rely on them for, is to disturb insects as they browse. The opportunistic birds swoop down and pick off the many insects conveniently revealed by the rhino as it bumbles along.  Another little rhino hitchhiker is the Cape dwarf gecko (Lygodactylus capensis) which also appreciates the free meals and the free ride.

Veritable swarms of dung beetles of feast on rhino dung in the rainy season and many species of  both the roller and tunneller varieties are present at any fresh dung pile, with different species arriving at different times performing different services.  Butterflies also enjoy the moisture from the dung and congregate to drink it during the day while moths have been observed doing the same at night. The fact that both the rhino botfly and rhino tick will die out if rhinos become extinct, is hardly likely to bother many, but we don’t fully understand all the workings of nature so it would be foolhardy in the extreme to consider their loss as a good thing.

On a broader scale, the maintenance of the African savanna and its grasses which are vital to ungulates, is a job for which there is no other equivalent candidate. In these times of climate change, the value of the rhino maintaining natural fire breaks is even greater. As the earth heats up and the game reserves become drier, being able to manage and inhibit the spread of fire by creating natural fire breaks will become an even more central task.

Rhinos perform specific and important functions in maintaining the remaining wild areas of Africa. As humans occupy more and more land and the animal world shrinks even further the soil becomes less fertile and the landscape less biodiverse. Rhinos have evolved over centuries into some of the largest and most enigmatic vegetarians on earth who whether we call them eco-engineers or lawnmowers are vital to the health and maintenance of the eco-system.