While most visitors to the Masai Mara are blown away by the scale and beauty of this magnificent part of Africa, it is surely the spectacular diversity of life that they come to see. This is one of the last remaining large-scale natural ecosystems in the wild, nature intact and as it used to be, with little persecution and the animals living alongside the indigenous Maasai people. When the rich volcanic soils receive rain, they stimulate the production of nutrient rich grass that the herbivores love so much and result in the famous migration of wildebeest and zebras, always on the move as the rain clouds circulate around the Serengeti and always providing a fresh bite of food over the next skyline. This abundance of herbivores is fast food for the predators, but there again not every predator is the same, they all play subtle and important roles.
To an ecologist my description of the Serengeti ecosystem sounds like a simplified “bottom-up” process whereby the nutrients flow from the grass up to the herbivores that then support the predators. At one level, this is not far from reality, but the diversity of animals at each level and their role is truly bewildering with 28 species of ungulates (those are the herbivores with hooves) and 10 major carnivore species. Lions, leopards, and cheetahs are large predators and really not hard to find and then there are the serval, caracal, wild cat, wild dogs, hyaenas, several species of jackal, bat-eared foxes, not to mention the honey badger, many species of mongoose, genets and civet as well as a large diversity of raptors. With such an abundance of predators and so many species, you may well start to think that this level of predation must be exerting a “top down” pressure whereby the predators are taking so many of the herbivores that it limits their abundance. Here we focus on the black-backed jackal, a lightweight opportunistic mesopredator that scavenges and chases anything it can obtain and ask the question what role do they play in the ecosystem?
The black-backed jackal is a monogamous, territorial, fox-like animal and the pair aggressively defend their territory through scent marking, calling, and chasing intruders. The breeding season coincides with peaks in grass mice abundance and the ungulate calving, but the adults are opportunistic and will take most prey from beetles right up to the occasional adult impala. They can have up to nine pups who are guarded by the female against predators like hyaenas while the male and the offspring from previous litters do the hunting and provisioning. Young from a previous litter who remain with the parents improve pup survival significantly. There is a dominance hierarchy amongst the pups, and they can often be seen showing dominance and submissive behaviours. The adults can be killed by hyaenas and leopards and even martial eagles although this is not done so much for food as for eliminating competing predators.
The structure of the animal communities of the African Savannah
Tony Sinclair has dedicated his life to understanding the structure of the African savannah animal community and has spent more than 50 years studying the interactions between species. To get some insight into the depth and knowledge that Tony and his crew have acquired, I strongly recommend his excellent book entitled Serengeti Story (2012, Oxford University Press). Tony showed us that the small species of ungulates are eaten by just about every predator on the African plains, they are lunch to every passing predator that can catch them. The medium sized species have a smaller number of predator species that eat them and the larger ungulates like buffalo and giraffe are only occasionally taken by lions. In contrast the megaherbivores like elephants and hippos rarely if ever die from predation unless they are seriously incapacitated by disease or injury. When he looked at the density of predators in the Serengeti and then the small predators, the black-backed jackal is the most abundant of these. They can reach very high densities so that there is one predator walking around to just 3 adult small ungulates – an extremely high ratio leading us to suppose that these small ungulates are really being limited by the small predators. This seems to be borne out by observation since the small ungulates like the impala always die from predation.
Testing these ideas at large scale is logistically very difficult but back in the 1980s, northern Tanzania experienced a “natural experiment” that helped to throw light on these ideas. During a period of about 8 years poachers were throwing down poison indiscriminately and this killed off the lions, hyaenas and jackals. In contrast, across the border in Kenya, the Masai Mara predator population was protected with little poaching and a full complement of predators. During the period when the predators were effectively removed from Tanzania, the small ungulates (oribi, Thompson gazelle, warthog, Impala and topi) increased in abundance while the larger ungulate species remained stable, in contrast to what happened in the Masai Mara. Later, when the poisoning stopped, these predators returned to former levels of abundance and the density of the small ungulate species fell. So, the evidence is that the predators, and in particular the black-backed jackal is an important predator in the Serengeti system, by limiting the abundance of some of the smaller ungulates. Such a finding is not novel to the sheep farmers of South Africa where, in the absence of the top predators, the ever-opportunistic jackals take advantage of the abundant young of domestic animals and can have a serious impact on sheep farming.
Predators of predators
While the ungulates are naturally the prey that supply many of the carnivores with energy and nutrients, they are also in direct competition with each other for the same food source and consequently we see aggression and predators killing predators- referred to in ecology as intra-guild predation. Lions go out of their way to try and kill adult and young cheetahs and leopards. Similarly, leopards kill lion cubs as will cheetahs if they get the chance, and then there is the out and out warfare between lions and hyenas where hyenas will try to maim or kill lions when they out number them.
The smaller predators are often referred to as the mesocarnivores and they can play a very important role in a natural system, as we have just seen in the Serengeti, but they are always persecuted by larger carnivores. What is more, when humans remove the large carnivores, that compete or threaten them, then these mesocarnivores do well, increase in abundance and can live close to humans. Examples of this include the abundant red foxes that live in European cities, often with their dens close to our homes. Yellowstone National Park is often thought of as the Serengeti of the North American plains and following the reintroduction of the wolf as the apex predator we have seen some fascinating ecological changes. One of the biggest has been how the wolf packs have suppressed the coyote population by 50% in the northern range by killing them, outcompeting them for food and restricting them to areas of habitat where they can avoid the wolves. Since wolf numbers have started to fall again, so we have seen something of a resurgence in coyote numbers in Yellowstone. Where we live in central Pennsylvania there are no wolves and over the past few years the coyote numbers have invaded and increased in abundance.
Just last Saturday I was woken at 2am as the coyotes killed one of the last surviving deer fawns from a white-tailed deer herd, right next to my house. It took 20 minutes for the fawn to stop screaming and all that was left was small pile of intestines. Concerns have been raised that in the absence of the apex predators, the mesocarnivores dominate, increase the predation pressure on the community and this can have a negative impact on diversity and ecosystem function. In effect the mesocarnivores replace apex predators while at the same time retaining their role as mesopredators and this domination of the community means that the smaller herbivores suffer and diversity falls.
Do these patterns reflect the processes that could be happening on the plains of Africa with the black-backed jackal? While lions have been exterminated from much of their range, they have been introduced into fenced game reserves in parts of South Africa which means that ecologists have been able to compare the consequences of lion removal on black-backed jackals and their prey. While more work is needed, initial findings indicate that the general patterns observed in North America are also observed in Africa whereby with lions present, the mesocarnivores are suppressed both in terms of their behaviour and their abundance and they become opportunistic and confident in the absence of the apex predator.
I suspect that in complex animal communities such as the one we observe in the Masai Mara there really are not simple rules to say that this is a “bottom up” or a “top down” system and the black-backed jackal is caught there between the big predators and the availability of their food. They are cheeky opportunists that will grab an ungulate when it can, but if a lion makes a kill, they will be in there trying to grab every morsel of food to feed themselves and their offspring.
What I want you to do next time you are staying at the excellent Mara Trails camp (maratrsil.com) and watching the spectacle of a lifetime is to think about the jigsaw of life that unravels before your eyes and start to think about how the species connect, and I expect your photography will improve more.
