Baboons, like macaques and vervet monkeys, are remarkable for their ecological and behavioral flexibility and their ability to use changing environments in new ways. As a result, they are affected differently by human population expansion compared to less flexible, more habitat-limited primates such as guenons (e.g., blue monkeys or samangos), mangabeys, or bushbabies. Human population growth results in increased contact with wild animals – in suburban environments, alongside agriculture, and during recreational activities outside of urban areas. Many wild animals simply never get used to contact with humans and continue to avoid human habitation. With habitat destruction and fragmentation, these species will likely go extinct. Baboons instead easily adapt to these changes and start exploiting human-derived resources to their own benefit. One of the consequences of baboon flexibility, therefore, is a level of contact between humans and baboons that does not occur in many other animals.
When increased contact between two species results in the exploitation of one species by another, e.g., when baboons start incorporating human-derived foods into their diet, we call this commensalism. Commensalism is the result of many interacting factors, most notably the ecological flexibility of the species in question (which is high for baboons and many other monkeys) and the enabling behaviour of the species being exploited (i.e., our own behaviour and failure to prevent commensalism from occurring).
It is important to realize that behavioral features of baboons also play a role in the development of commensalism and conflict with humans. Baboons, like vervet monkeys, become easily habituated to contact with humans and eventually lose their natural fear of people. If this loss of fear is combined with easy access to human-derived foods (e.g., via tourists feeding monkeys to encourage them to come closer for photo opportunities), these animals will begin to form an association between people and food, and thus whenever they see people they will expect to receive food. As their fear of humans decreases further, they may start taking the food from people even when it is withheld. These negative interactions are particularly likely in socially complex species such as baboons and vervets in which dominance rank determines priority of access to resources; i.e., if a monkey discovers it can take food from a human, it will perceive itself to be dominant over that human and will likely assume it can continue to take food at will. Once this process has begun, it is difficult to stop because it involves behavioural changes in the animals themselves, i.e., a learning process that cannot be easily reversed.
Commensalism and increased contact between humans and wildlife can lead to baboon-human conflict in a number of ways. One way in which this increased contact leads to increased mortality for baboons (as well as their close relatives, drills and mangabeys) is via hunting by humans. Hunting of nonhuman primates by humans as a source of food is most common in West and Central Africa (Gonzalez-Kirchner and Sainz de la Maza 1996; Paterson 2006; Fischer et al 1999-2000). Even when hunting does not occur, wherever humans and baboons live in close proximity and there are no inhibitory cultural factors (e.g., Bishop et al 1981; Wolfe and Fuentes 2007), people generally regard baboons as pests and often kill them either to eliminate raiding behavior or for sport. In South Africa, human-induced mortality is often biased towards males, as they are typically more aggressive and also larger and more conspicuous, thus more easily identified and shot. In some areas of East Africa, where hunting of baboons more commonly occurs with spears and dogs rather than guns, human-induced mortality is biased towards females and juveniles, who are more easily captured in these ways.
Even when baboons are not directly targeted and shot on a regular basis, the ways in which they adapt to expanding human populations leads to commensalism and conflict with humans. The most widely cited form of commensalism in baboons (and other primates) is crop-raiding, which occurs virtually everywhere that baboons are found adjacent to agricultural areas (Maples et al 1976; Forthman Quick 1986; Strum 1986, 1987; Else 1991; Biquand et al 1992a, 1994; Naughton-Treves et al 1998; Hill 2000, 2005; Zinner, et al 2001; Higham et al 2009b). Baboons also raid garbage dumps (Altmann and Muruthi 1988; Biquand et al 1992a, 1994; Zinner, et al 2001; Okecha and Newton-Fisher 2006) and even resort to the direct theft of food from homes, game lodges, and picnic spots in national parks (Else 1991; Kansky and Gaynor 2000; van Doorn 2009). In some cases, humans deliberately provision baboons (Biquand et al 1992a, 1994; Boug et al 1994b; Kamal et al 1997), thereby reinforcing the baboons' perception of an association between humans and food and further attracting baboons to human-frequented areas. This, of course, only exacerbates the problem.
Commensalism in and of itself affects the biology and behavior of baboons, even without direct conflict with humans. For example,
- Commensalism increases feeding efficiency, which influences activity budgets. Olive and yellow baboons that feed on human-derived foods spend far less time foraging and feeding and more time resting than neighboring wild-foraging troops (Forthman Quick 1986; Altmann and Muruthi 1988; Muruthi et al 1991; Bronikowski and Altmann 1996). In addition to activity budget changes, a concentration of high-quality food in one area leads to reduced home range sizes and travel distances (Forthman-Quick and Demment 1988; Altmann and Muruthi 1988).
- The availability of human-derived food to nonhuman primates can also have cascading effects on reproductive parameters, life history variables, health, mortality, and social organization (Bishop et al 1981). At Amboseli, baboons with regular access to food from a garbage dump experience higher infant growth rates, earlier maturation, higher infant survival, and reduced interbirth intervals compared to wild-foraging troops (Altmann and Alberts 2003b), and crop-raiding olive baboons in Nigeria have shorter inter-birth intervals than wild-foraging baboons (Higham et al 2009b). Moreover, baboons at Amboseli that subsist largely on food from garbage dumps are 50% heavier with 21% more body fat (Altmann et al 1993) and higher concentrations of serum insulin and cholesterol compared to wild-foraging troops, suggesting a greater risk of cardiovascular disease (Kemnitz et al 2002).
One of the best examples of baboon commensalism can be found in the Cape Peninsula of South Africa, where an expanding human population and heavy tourism have dramatically impacted the ecology and behavior of the baboon population (Kansky and Gaynor 2000; van Doorn 2009). Virtually every troop in the Cape Peninsula has some contact with humans and human-produced food, whether it be along the highways, in urban areas, or in the Table Mountain National Park. Commensalism in the Cape Peninsula has led to extensive research on baboon-human conflict, the establishment of a ‘Baboon Management Team’, and the employment of ‘baboon monitors’ to herd baboons away from towns and other human-frequented areas (Kansky and Gaynor 2000; van Doorn 2009).
As human populations continue to expand, nonhuman primate commensalism will become increasingly common. Baboons are not the only primates to which the above issues apply: the types of human-wildlife conflict described above, as well as the associated behavioral changes, are also found in other omnivorous and behaviorally flexible primates such as vervet monkeys (Brennan et al 1985; Lee et al 1986) and macaques (Fa 1991; Schlotterhausen 2000). One role of conservation efforts, in addition to habitat preservation and education, should thus be to continue to devise and refine management solutions to conflict between humans and nonhuman primates, especially such highly flexible primates as baboons (Strum 1986, 1987, 1994, 2005; Biquand et al 1994; Hill 2000; Forthman et al 2005; Webber et al 2007; van Doorn 2009).
Content contributed by:
Dr Larissa Swedell
|Thanks to the following reviewers:
Dr Susan Alberts
Dr Cliff Jolly
photographs by L. Swedell
For a more scholarly version of the information on these pages, see:
Swedell, L (2011) African Papionins: Diversity of Social Organization and Ecological Flexibility. IN Primates in Perspective, Second Edition (Campbell CJ, Fuentes A, MacKinnon KC, Bearder SK, Stumpf, RM, eds). New York: Oxford University Press, pp. 241-277.
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