After my latest field trip to Namibia I was fortunate enough to spend a few weeks visiting some old haunts in South Africa. Even though I had very little time and no real scientific purpose other than curiosity I could not help but put out my camera traps whilst I was there. It was after all a nature reserve and surprises can happen.
One of the camera traps was located on a well used animal track that lead from the bush down to the river. The rains had not thus far been kind in that part of Africa and the bush was rather dry with little standing water so I was confident the track would offer some interesting images. As expected I had lots of images of vervet monkey, warthog, impala, nyala and waterbuck. Imagine my surprise then when I scrolled through 20 or so images of a small herd of waterbuck does with young to find this fluffy looking white thing that looked more like a sheep!
In fact it was a leucisitic waterbuck. Not to be confused with albinism, which is a condition caused by absence of melanin leading to pale skin, hair, feathers and eyes, leucism is defined as a partial loss of pigmentation that leads to an animal appearing pale or patchy but often with patterns still showing. The eyes in animals with leucism are normally coloured never the red that can occur in albinism. So albinism is a lack of melanin and leucism is a partial lack of melanin.
You can see this little waterbuck still has the distinctive bulls eye target ring around its rump that distinguish the common water buck from the Defassa waterbuck we are used to in the Serengeti proving it is leucistic not albino.
Regardless of which of the two conditions it has the young animal will have a tough time. The pale colour makes it stand out as a target to predators and it is thought that survival rates for leucistic animals are low. That’s not to say it won’t make it to adult hood, in fact the white lions of the Timbavati are a well followed case of leucism in a population that every now and then throws up a white cub or two, they are so well watched that it is known that some do survive into adult hood. From those few individuals stem most of the white lions that can be seen in captivity in zoos all be it showing all kinds of horrible traits of constant inbreeding.
After finding these images I was lucky enough to spot the herd with my own eyes. I watched the little leucistic waterbuck playing and frolicking with a like aged normal waterbuck and for all the world you wouldn’t know what all the fuss was about. The two were identical in every way except the pure chance of a mutated gene governing colour. Good luck to the pair of them.
Symbiotic relationships are common in the Serengeti. They fall into two main types, mutualism, whereby both partners benefit from one another and commensalism, whereby one partner benefits from the actions of the other but the other partner is largely unaffected or unharmed. I wrote recently of oxpeckers and large herbivores, large herbivores provide food in the form of ticks for the oxpeckers and oxpeckers provide a cleaning service for the large herbivores, a good example of mutualism. Birds such as cattle egrets that follow buffalo around to catch the invertebrates the buffalo disturb as they graze is an example of commensalism. Of course it is not just animals that have symbiotic relationships; my blog last week on termites and mushrooms was another example of mutualism.
So what about zebras and wildebeests? We see them all the time on Snapshot Serengeti in mixed herds, grazing peaceably with one another. Is this just coincidence or is this a form of symbiosis?
It is actually hard to say and of course that is why labelling things, especially behaviour is often tricky.
Zebra and wildebeest are both grazers meaning they mostly eat grasses but that doesn’t mean they share the same diet. They preferentially eat different parts of the plants that they consume. Zebras are quite content chewing longer tougher grasses where as wildebeest prefer shorter, more tender shoots. This partition of resources means they can quite happily graze side by side with out exerting pressure on each other.
Another good reason to team up is the extra safety that numbers provide. Not only do more ears and eyes provide better early warning systems but the odds of the individual being targeted by a predator are reduced when there are greater numbers to choose from. Apparently zebra have better eyesight but wildebeest have better hearing so the two complement each other.
There could be another reason. Our very own Meredith Palmer just published a paper about interspecies reaction to each other’s alarm calls, you can read it here: https://www.sciencedirect.com/science/article/pii/S0003347217304207
She found that zebra, wildebeest and impala recognise each other’s alarm calls but that they did not always respond in the same manner. When zebra sounded the alarm all three herbivores reacted strongly but when impala gave the alarm zebra where likely to ignore it, or assess the relative danger themselves. It seems that this varied response is down to predator size. Impala are prey to a wide range of smaller predators that would not be able to handle a mammal the size of a zebra, so when impala give the call it doesn’t always signal danger for the zebra. However when a zebra, the largest of the three herbivores sounds the alarm, whatever it has seen will probably be able to take down the wildebeest or the impala too so it’s prudent that all three scarper.
It is an interesting reaction and maybe wildebeest hang out with zebra because they are more trustworthy alarmists. I am not sure that the companionship of zebra and wildebeest can be classed as symbiotic I think it is more of an interaction due to a shared habitat but it seems that on some level they can benefit each other.