Einstein is best known as a visionary physicist, but he was also passionately interested in all the complexities and interactions of the natural world. Nature is indeed an intricate web of many interconnected threads, and I am always amazed that the more I look, the more remarkable and unlikely are the relationships I discover…
Images: Will Jansen & Lorraine DoyleThe time before the arrival of the first rains is a stressful period for many bushveld animals, as food is often in short supply after the dry winter season. Vegetation growing along river courses is frequently the only source of nutritious browse for animals such as giraffe (Giraffa camelopardus), and even that may be insufficient. These uniquely beautiful creatures, with their long eyelashes, necks and legs, require some 30kg of food per day − a tall order at a time when many trees do not yet have their summer foliage.
One tree, the Knob thorn (Senegalia [Acacia] nigrescens), has evolved a strategy that meets both its own needs and those of the Giraffe – early flowering. The lovely creamy-white flowers appear in abundance during late August, a time when most other trees are still naked. Rich in protein, the flowers, as well as any foliage that may be present, are readily eaten by giraffe. While feeding, the giraffe is dusted with pollen on its head and neck, and when it moves on to the next tree, it deposits its pollen load. Smaller mammals such as bats are known to pollinate many trees, including the Sausage pod tree (Kigelea africana) as well as the iconic Baobab tree (Adansonia digitata), but the inclusion of a large mammal pollinator appears to be specific to the Knob thorn.
Giraffe are not only unusual pollinators; they are also tree sculptors. Males, with their longer necks, tend to feed at a higher level than females, thus avoiding direct competition for food. However, both sexes still feed within a relatively small section of the overall crown, creating the characteristic hour-glass shape of many of their favourite browse trees.
If one is in no doubt that Giraffe are ‘vegetarian’, it comes as something of a shock to come across one happily chewing away at a bone in its mouth. Bizarre? …Perhaps. Unusual? …Not really. Giraffe require large amounts of phosphorous and calcium to sustain the growth and maintenance of their skeletons. Although most calcium can be obtained from browse, phosphorus levels may be insufficient in leaf-matter alone – especially in nutrient-poor soils. Although the scientific jury is still out on exactly how significant the concentration of phosphorus obtained from this practice of osteophagia (literally bone loving) is, it is a common enough practice to suggest that some benefit is derived by the giraffe.
The Leopard Tortoise (Stigmochelys pardalis) has evolved yet another ingenious method of obtaining the calcium that it needs to maintain its shell and to lay hard-shelled eggs. Unable to chew bones easily with its beak-like mouth, it nibbles on the scat of Spotted Hyaena (Crocuta crocuta), which are able to crush bones easily with their extremely powerful jaws and, as they are equipped with an equally strong digestive system, process them effortlessly. As a result, their scat contains very high levels of calcium with which the tortoise is able to supplement its diet.
Although I am very grateful to be able to obtain my vitamin and mineral supplements by swallowing a tablet, the fact that herbivores will feed on the bones or droppings of other animals demonstrates the extraordinary complexity of the interrelationships between organisms. So, the next time you are out in the bush and are fortunate enough to watch a lion feeding on a carcass, spare a moment to consider that what you are witnessing may have, as its end point, the provision of much-needed minerals for tortoises and giraffes and the ongoing pollination of Knob thorn trees…
Lorraine Doyle is the owner of Africa Nature Training. This is the first article in a series on bush lore and the wonders of the African Bushveld.