Rhinos, their impacts on savannah and the ghosts of ancient poos
Photos of mutilated rhino corpses have become all too familiar to conservationists lately. Sadly Rhino horn has been making a comeback on the east-Asian black market, mainly fuelled by the myth that it is effective at curing various minor ailments, such as hangovers and fevers, as well as major diseases such as cancer.
The solutions to this issue and the economics behind it are contentious (see here and here for two sides of the debate), but one thing is agreed on by all sides: at current rates of hunting, rhinos may be extinct within twenty years. This fact is terrible in itself, because rhinos are truly awesome. Obviously a conservationist such as myself is saddened by their demise: being the second largest land animals that still exists, coupled with their legendary temper, they are a fantastic embodiment of the strength and endearing wildness of nature. To lose them would be hugely distressing, for humanity would have wiped out one of the last great symbols of the wild. A great loss to the world.
But alongside this human-centred view of rhino conservation, and even ignoring the rhinos themselves, there are greater problems at stake. Rhinos are what ecologists call ‘megaherbivores’. They are so large in body size that they are rarely killed by predators, and so their numbers are limited only by the availability of food. This, combined with their long digestive tract which allows them to graze on low-quality food lets them eat huge amounts of vegetation which would otherwise not be consumed, and so gives them an unusually large impact on their surrounding plants. In turn this is expected to have a large impact on the ecology of smaller herbivores in the area.
A paper currently being prepared for publication in the Journal of Ecology, looked into the impacts reintroduced white rhinos (Ceratotherium simum simum) have on the vegetation in their home range in Kruger National Park. They went extinct in the park in 1896 due to hunting, being subsequently reintroduced in the 1960s. However due to their slow spread from the sites of reintroduction, the density of rhino populations varies through the park. This allowed the researchers in this study to compare the plant ecology of otherwise similar habitats, letting them observe the impacts rhinos have on the plant communities of African grassland.
Data on the number of rhinos in the study areas was determined using annual census data taken from aircraft, input into a geographical analysis software. They controlled for geology, and numbers of the other herbivore species found in the area, including elephants.
It was found that rhinos increased the proportion of the grass that was kept to short lengths and in doing so, they increased the numbers of plant species found in the area. White Rhino are grazing animals, so it is perhaps unsurprising that they should create patches of short grass where they feed. However this is the first realistic study which has established a causal link between rhino and these species-rich areas of habitat.
The grazing lawns created by rhinos have been shown to be important for impala and warthogs to feed on. As rhinos decrease in number, it is therefore likely that their smaller contemporaries will also fall in numbers. Impala and warthogs in turn impact their environment by grazing and in the case of warthogs; burrowing, alongside being important prey for carnivores such as lions, leopards and hyenas. With the loss of rhinos, all of these animals will suffer changes to their ecology.
This is a situation with precedent: a recent paper in Nature shows how there is correlation between the loss of flowering plants and the extinctions that took place during recent Ice-ages. This loss of plants has been implicated in the demise of horses, Woolly Rhinos and Mammoth.
We know that until the end of the Pleistocene (around 11,700 years ago) all of the earth’s continents other than Antarctica contained large groups of megafauna such as North America’s mastodons, New Zealand’s moa, and Australia’s diprotodonts; despite such giant herbivores only being found in Africa today. As the fossil record for this period is patchy the abundance of these animals is calculated using fungus spores from a solely poo-loving group (Sporormiella) using sediment cores. As Sporormiella can only grow in the dung of herbivores, the quantity of spores found at a particular layer of lake sediment gives an approximate figure of the amount of faeces in the area at the time of deposition, and so the amount of large herbivores in the vicinity can be estimated.
These ghosts of poos-past paint a disturbing picture. As the number of Sporormiella spores in non-African sediment cores dramatically reduced through recent ice ages, the amount of hardwood species pollen increased. Presumably the extinction of each continent’s large herbivores caused a reduction of grazing pressure on the plants and trees of the area, creating a new vegetational community. This is followed by a sharp rise in the amount of global fires, as highly flammable leaf litter accumulated and the monotonous forest allowed wildfires to rapidly spread. The animal species that were well-adapted to the grasslands that disappeared, will have seen their numbers reduce or have gone extinct. Some are now maladapted to the environments they find themselves in, vulnerable to extinction.
It is however unlikely that the loss of Rhino species in Africa will get the chance to cause such an extreme situation: outside of national parks deforestation is a major issue, with it still being a problem inside of park borders as well. This unnatural destruction of trees in unprotected areas will keep fire-risk to humans at a minimum. However it is evident that inside the pristine areas that remain within national parks, the loss of rhinos is likely to have a large impact. With no rhinos scrub encroachment may occur, reducing the variety of plant species, the grazers who feed upon them and the carnivores who eat the gazers. Fewer plant species will be found, and fires will be more common. The circle of life in the savannah will be intrinsically damaged.
The international rhino horn trade is barbaric, based on mafia systems and funded by a notion of medicine which is quite simply wrong. It could well rob the world of one of the most charismatic creatures walking the earth, within decades. But more than that, it could rob us of the African savannah and much of the life there too. The need to find an effective model of rhino conservation is now more urgent than ever.