Symbiosis refers to a protracted relationship between two species where one species may benefit from the association while the other is affected positively or negatively of is not affected at all. There are three kinds of symbiotic relationships: Mutualistic, Commensialistic and Parasitic. In a mutualistic relationship both parties benefit from being in a natural relationship with one another, where as in a commensialistic relationship only one party benefits, while the other remains unaffected. In a parasitic relationship, one party is gains from the relationship, while the other is negatively impacted. Symbiotic relationships are widespread in nature and only a few examples will be discussed.
Mutualism—Mother Nature’s version of “you scratch my back and I’ll scratch yours”
Birds and Grazers
Large herds of grazers are often associated with various bird species. These bird species include Yellow- and Red-billed Oxpeckers. Both oxpecker species provide a benefit to these large grazers. Oxpeckers greatly reduce the parasite load (mainly ticks) of herbivores increasing their competitive advantage. The ticks are removed from all parts of the body including the eye, ears, under the tail and the groin area. In return the large grazers provide the oxpeckers with food and fur material to line their nests. Oxpeckers will even use the dung of their hosts to fill in the cracks in their nesting cavities. Although oxpeckers are more beneficial than not, they do sometimes become parasites preventing wounds from healing. Oxpeckers continuously irritate the edges of the wounds, keeping them open and more susceptible to secondary infection. In addition to reducing the ectoparasite load of the host, oxpeckers also provide an early warning system that warns their hosts of any predators approaching.
In areas where large grazers, like buffalo, occur but oxpeckers are absent the role of tick removal is taken over by Red-winged Starlings and Common Mynas. These birds are not effective tick removers in areas underneath the belly and in the groin area. This is due to the bird’s size and its weak perching foot structure. Oxpeckers have short legs and sharp claws that enable them to cling onto the fur of their host.
Mongooses and Hornbills
Yellow- and Red-billed Hornbills are also in a mutualistic symbiotic relationship with dwarf mongoose and are often seen together while foraging. Dwarf mongoose live in groups of up to 12 individuals and will forage for scorpions and invertebrates under stones. While foraging several prey items escape or to large an amount is flushed out from their hiding places for the individual to cope with. The hornbills will quickly swoop down catching item of prey that the mongoose misses. In return for the food that the hornbills get, they provide an alarm system that warns the mongooses if there is an aerial threat.
The relationship between these two species is believed to be so successful that the hornbills will wait at the entrance of their burrows in the morning. It is also thought that if the mongooses take too long to rise, the hornbills will continuously call at the entrance of the burrow. The relationship is not obligatory and both species are able to survive on their own.
Crocodiles and Plovers
Crocodiles are often seen sunbathing on the banks of rivers and dams with their mouth open, but very few people know that a small bird, the Egyptian Plover, will take the opportunity to feed on the debris stuck in the teeth of the crocodile. This brave little bird will peck the crocodile’s teeth clean allowing them to remain healthier and in exchange the birds receive needed nourishment.
Honey Badgers and Honeyguides
There is a very important mutualistic relationship between honey badgers and honeyguides. The honeyguides often feed on the wax that is inside a bee hive. The honeyguide is however unable to gain entrance to the hive by itself. There are various animals, including the honey badger, that have learnt that where there is a honeyguide there is bound to be honey. Honey badgers will follow honeyguides to hives, where the badger will open the hive and take its fill. The honeyguide will sit and wait to get its share after the honey badger has finished.
Acacia trees and Ants
There is a fascinating mutualistic relationship between Acacia trees and ants that benefits both species greatly. Acacia trees are fed on by several animals in the bush and despite their thorns they need extra protection. This is where a colony of ants living in your thorns can be beneficial. Some Acacia trees have long, hollow thorns with a bolbous swelling at the base of the thorn. The ants make a small hole in the area that is swollen in which they will live. The Acacia trees also provide the ants with a form of nectar on which they feast, in return, the ants provide protection. The ants will protect here home fiercely and will attack any browser attempting to feed on the leaves of the Acacia tree.
Trees and Wasps
There is a fascinating relationship between fig trees and a minute wasp species. This wasp species are specific to a certain species of fig. The Ficus species fig has flowers on the inside the fruit and is only pollinized by wasps of the Agaonidae family. Inside the fruit a female wasp will lay her eggs and die. The eggs with the male wasps hatch first and mate with the females while still in the egg. After the fertilized female hatched they will burrow to the surface of the fruit, taking pollen with her and takes flight. The male wasps are flightless and will never leave the fruit. The females however will fly between fruits in search of males. The female will lose her wings when she finds a fruit, burrow into the fruit pollinating the flowers and lay her eggs.
Lichen is a symbiotic relationship between a fungus and an alga or cyanobacterium that gives rise to a new organism. The fungus body normally completely surrounds the alga. Most lichens reproduce asexually when conditions are good they will simply expand across the surface of the rock or tree. In dry conditions, they become crumbly- small pieces break off and are dispersed by the wind. The fungal component of many lichens will sometimes reproduced sexually by producing spores. The spore must meet up with an algal partner to form new lichens. The algae and cyanobacteria are able to photosynthesise to produce food like plants that is beneficial for the fungus. The fungus in return protect the photosynthetic part of the relationship. The fungi provides an attachment substrate and gathers water and nutrient from the environment that is used in the photosynthetic process of the algae. Lichens are among the oldest organisms on earth. Due to the fungi parts taking up nutrients and minerals from the environment, lichens can be used as an indication of the health of the environment.
A bird building its nest in a tree is essentially the simplest form of commensalisms. When a bird makes its nest in a tree, the bird benefits greatly from the tree as the tree shelters and protect the nest. In this relationship, the tree is neither benefited nor harmed.
Red winged-Starlings, cattle egrets and little egrets are often seen in the presence of large grazers, following them and even siting on their backs. These birds associate with the grazers as they catch the insects that are disturbed when the grazers move through the grass and foraging. In this relationship, the birds have no impact on the life of the large grazers. The same relationship exists between grazers and birds like Fork-tailed Drongo, Burchell’s and Cape Glossy Starling.
Predators and Scavengers
A commensalistic symbiotic relationship occurs between all predators and scavengers. To describe the association between them lions (predator) and brown hyenas (scavengers) will be used. Brown hyenas are known to be fairly strict scavengers and will only occasionally hunt small animals, birds and rodents. Due to their strict scavenging behaviour they benefit greatly from living in the same area as lions. The brown hyena will commensally benefit from lions (and other predators) by feeding on the carrion that is left over after the pride had their meal. Brown hyenas will have no direct impact on the lions. Brown hyenas may also be considered to be in a parasitic relationship with smaller predators like wild dog, leopard and cheetah as they will steal prey from these predators.
Apart from the relationship between the fig trees and their minute wasp pollinators another fig tree species is considered to be a parasite. The strangler fig tree or common wild fig parasitizes several species of trees including marula and the knobthorn. Baboons, birds, monkeys and fruit bats will feed on the seed-bearing fruit. The seeds in the dung of these animals are deposited in the forks of the host tree. As the seed germinate, a root system will tap into the bark of the host tree anchoring it in place. The root system will then slowly grow down to the ground. The young tree will produce large leaves to produce loads of food which help the young fig to grow as quickly as possible. When the roots reach the ground, the roots will thicken and wrap themselves around the trunk of the tree preventing the host tree to grow laterally. The fig tree will grow several meters above the extant tree and will soon be higher and bigger than the host. The canopy of the fig tree will reduce the amount of sunlight that reaches the host tree as the photosynthetic process is compromised. The host will start to die and eventually rot away leaving the fig tree with a hollow trunk.
Nature is full of fascinating friendships and these examples are only a few of them. Several species coexist in the same environment. Species are always fighting for survival and as a response some species have evolved intricate associations with others to ensure their survival. Most of these associations are beneficial; some have negative impacts on others. This is usually to ensure the survival of the fittest and that the species affected negatively will adapt to fit in a specific niche.
Emmett, M. and Pattrick, S. 2013. Game Ranger in your Backpack. All-in-one interpretative guide to the Lowveld. Briza Publications. P. 178—179.
Gutteridge, L. 2012. The Bushveld including the Kruger Lowveld. 30° South Publishers. p. 6 –10.