Evolution of mobbing antipredator behavior is found in many evolutionarily distinct clades such as birds, mammals, and fish. This leads to a theory of the convergent evolution of cooperation among these species in response to predation (Lorenz 1966). Communal living often precedes cooperation and mobbing behavior is just one way in which groups of animals can expand the benefits and mitigate the costs of communal living (Gaston 1978).
The evolution of mobbing behavior stems from individuals trying to maximize their inclusive fitness. Since fitness isn’t limited to the number of offspring produced by an individual, but also includes the number of kin that survive to reproduce, we begin to see the potential benefits of cooperation among kin. Mobbing can therefore be seen as a form of altruism among kin where individuals work together in attacking potential predators and thereby protecting their kin group from predation (Gaston 1978). Hamilton’s rule postulates that an individual will take risks to help another individual as long as the amount of genetic material shared by the two individuals exceeds the cost. The rule is rB>C where r is the relatedness of the two individuals, B is any other benefits the recipient might receive and C is the cost to the actor performing the altruistic act (Hamilton, 1964). Thus we see that altruism is in fact grounded in the drive to increase individual fitness.
Ecological factors may also favor selection for group territorial behavior when adult survival is high and there is saturation of suitable habitat. In territorial animals, an individual can take over the territory of its kin when they die so cooperating with their kin (often their parents) can help them to establish a territory and its corresponding access to resources that are essential for successful reproduction (Gaston 1978). Staying with parents and kin may also increase an individual’s chances of survival since the individual can receive a prolonged period of parental care, allowing the individual to learn important information and strategies for survival as well as gaining important experience and increasing in physical size (Stankowich 2010) . Additionally, potential prey are able to mitigate risks from predators by assessing the level of threat that the predator may pose and appropriately adjusting their behavior (Griesser 2009). These risk management strategies may include making alarm calls, attacking in groups, or evaluating potential environmental dangers. Mobbing may have many potentially life-threatening costs, but when benefits exceed costs, this apparently altruistic behavior may actually help to optimize an individual’s fitness.
The evolution of mobbing behavior stems from individuals trying to maximize their inclusive fitness. Since fitness isn’t limited to the number of offspring produced by an individual, but also includes the number of kin that survive to reproduce, we begin to see the potential benefits of cooperation among kin. Mobbing can therefore be seen as a form of altruism among kin where individuals work together in attacking potential predators and thereby protecting their kin group from predation (Gaston 1978). Hamilton’s rule postulates that an individual will take risks to help another individual as long as the amount of genetic material shared by the two individuals exceeds the cost. The rule is rB>C where r is the relatedness of the two individuals, B is any other benefits the recipient might receive and C is the cost to the actor performing the altruistic act (Hamilton, 1964). Thus we see that altruism is in fact grounded in the drive to increase individual fitness.
Ecological factors may also favor selection for group territorial behavior when adult survival is high and there is saturation of suitable habitat. In territorial animals, an individual can take over the territory of its kin when they die so cooperating with their kin (often their parents) can help them to establish a territory and its corresponding access to resources that are essential for successful reproduction (Gaston 1978). Staying with parents and kin may also increase an individual’s chances of survival since the individual can receive a prolonged period of parental care, allowing the individual to learn important information and strategies for survival as well as gaining important experience and increasing in physical size (Stankowich 2010) . Additionally, potential prey are able to mitigate risks from predators by assessing the level of threat that the predator may pose and appropriately adjusting their behavior (Griesser 2009). These risk management strategies may include making alarm calls, attacking in groups, or evaluating potential environmental dangers. Mobbing may have many potentially life-threatening costs, but when benefits exceed costs, this apparently altruistic behavior may actually help to optimize an individual’s fitness.
Figure 4. Phylogentic construction depicting the effect of convergent evolution on mobbing behavior (taken from Alcock, 2005).
The comparative method can be used to investigate the evolution of mobbing behaviour. The comparative method says that if another phylogenetically distinct group is subject to the same selective pressure, the adaptation should evolve again. This is shown above in Figure 4, where convergent evolution has allowed ground-nesting gulls and colonial swallows to both evolve mobbing behavior due to the similar selective pressure of accessible nest sites. However, the Kittiwake gull only nests on inaccessible cliffs and doesn’t display mobbing behavior, showing divergent evolution due to a change in selective pressures. (Alcock 2009).