Sentinel Behavior in Meerkats
Biology 342 Fall 2010
Amber Bang and Mischka Moechtar
What is adaptive value?
It is also known as function. It explains the utility of the current form of the behavior with regards to increasing an organism’s fecundity, or lifetime reproductive success. It is helpful to understand the adaptive value of a behavior or trait to understand if and why natural selection for it is occurring.
The meerkat motto: You get by with a little help from your friends
It is commonly believed that sentinels suffer higher rates of predation than other group members. Hence, the act of the sentinel is considered altruistic because they increase the lifetime reproductive success of their group, at the expense of harming themselves. In general, everyone benefits when a sentinel is present.
In the 1960s, biologists noted that individuals that do not themselves breed can propagate their genes by helping relatives breed (Clutton-Brock 2002). They take risks and spend time and effort to help other relatives breed through such behaviors, such as pup rearing and feeding (Madden 2010). Clutton-Brock believes the answer is interdependence. Overall, they depend heavily on the functioning of the group for survival.
Go Big or Go Home
Meerkats benefit from living in large groups. Smaller groups are shown to have a lower likelihood to survive, because of the lack of a sentinel. No meerkat can act as a sentinel for more than an hour or two each day. This means some small groups have to spend part of the time without sentinels. They are forced to forage without another community member watching over them. In addition, it is beneficial to have larger groups, for the reason that it allows them to divide up all the work, allowing the pups to grow faster, indicating a higher lifetime reproductive success. In addition, larger groups also enable the individual to spend less time and energy on cooperative activities because the tasks are shared amongst the group more evenly.
Me, me, me
Despite their important role in the well-being of the group, Bednekoff's model suggests that guarding individuals are selfish; instead of being costly to the sentinel, it is actually beneficial to them. Clutton-Brock et al (1999b) supported this model when they found that sentinels actually have lower predation risk than forager. Furthermore, they provided evidence that the sentinel guards position themselves at safe sites. In addition, as shown by Figure4, the guard on average stays half the distance away from the safety of their bolt-hole. So when the forager on average is over three meters away, the guard is slightly more than 1.5 meters away. Being this much closer to the bolt-hole gives the guard an advantage over the forager, who has to travel a longer distance to reach safety.
Clutton-Brock et al. (1999b) also noticed that even though they remain close to their burrows, the raised guards spend over seventy percent of their time looking away from the foraging group suggesting that they are actually looking after the foraging group. Nevertheless, Clutton-Block suggests that this is, in a way, just an act. Selfish meerkat guards, he believes, are signaling to other meerkats that they have such attractive brave qualities by taking on a risky role. They also appear altruistic because they sacrifice the time that could have been used to forage for more food, and instead, spend their time guarding the group. However, it has been demonstrated that being a guard is probably the most optimal activity when a meerkat’s stomach is full, and he is situated in a foraging group that is constantly moving (Clutton-Brock et al. 1999b). Nonetheless, for the meerkats, this selfish action actually helps the community increase their survival.
Figure 4. (A) Median proportion of the time that 20 individuals spent looking toward versus away from foraging group members when on raised guard (16, 17). Median values and IQRs calculated across values for 20 individuals are shown. (B) Mean distance to the nearest bolt-hole for guards and foraging animals (18) (Clutton Brock et al. 1999b)