Many predatory species have relationships that enable a wider variety of hunting strategies. These interactions can be interspecific, such as with Moray Eels and Groupers, or intraspecific, when packs of Wild Dogs work together to take down a prey item much larger than they could manage alone. Complementary cooperative hunting refers to a strategy where each participant brings a different ‘complementing’ skill or specialisation to the hunt, whereas non-complementary hunting involves individuals acting in the same way, but in a combined effort towards the shared goal. Because of this, complementary hunting tends to occur between two different species, as their contrasting abilities and morphologies provide different assets. However, in some cases, individuals of the same species have been shown to play separate complementary roles during hunting, so complementary and interspecific are not entirely exclusive.
Cooperative behaviours will persist over evolutionary time if they are beneficial to all parties, and if the success rate or general gain from such strategies is greater than the alternative. Altruism generated by kin selection is also a driver in many closely related species, such as worker ants, and if the gain from cooperative behaviour satisfies Hamilton’s rule of rB>C, then it will be selected for.
Cooperative Hunting is one strategy within cooperative foraging, which also includes defence of food, communicating food locations (seen in the Bee waggle dance), and coordinated transport of food; a clear distinction between general group foraging, and specific hunting behaviours must be made.
I will be comparing the success and ability of various cooperative hunters, using complementary and non-complementary methods as the variable for this comparison.
Interspecific cooperative hunting can enable niche expansion, as prey items that would be previously inaccessible, due to their size, speed, defence, or habitat, can now be reached due to the complementary skills of the team. This is clearly seen in the case of Groupers and Moray Eels, which is a mutualism heavily studied by Bshary, and in Vail’s study on Coral Trout and Morays. In this case, there are highly communicative and coordinated behaviours (despite limited cognitive ability), which utilise the strengths of both parties. Alone, the groupers and trout hunt in open water, thus their prey hides in coral, and the eels use their long, slender bodies to trap this prey in coral crevices, so these small fish are safe from the eels in the open water. Together, the eels and other fish can combine these complementary hunting strategies, creating a multi-predator effect that the prey cannot easily avoid. Empirical evidence on both of these relationships show that these are non-random interactions and require both parties specialised response in order for the behaviour to be initiated. This complementary hunting is highly successful, as in Bshary’s study, groupers and Moray’s were seen to catch almost 5x more prey when hunting together, meaning the mutual benefit is great.
These themes can be seen in another interspecific complementary relationship, between the Greater Honeyguide (Indicator indicator) and the local people in Kenya, Ethiopia, and Tanzania. In this interaction, there is huge mutual benefit to both parties, as the birds use specific call patterns to indicate the direction and distance of a bees nest they located, and the humans follow the honeyguide, break open the nest, and make all of the materials inside available to share. This is beneficial because evidence shows that the humans find bee nests ~4 hours faster if they are guided by the birds, and the honeyguides have access to far more nests when working with humans. Honey and beeswax are extremely valuable resources to the people, and the honeyguides can eat the brood and comb.
The instances of complementary hunting thus far have displayed how individuals of different species can use their contrasting abilities to fulfil cooperative niches for a successful hunting strategy. However, it has been observed in certain Chimpanzees groups, that members organise to play complementary roles, when hunting for challenging prey such as monkeys or other small mammals. Specifically, Christophe Boesch identified several complementary hunting roles in chimps: the ‘climber’ identifies and flushes monkeys from their treetop, the ‘driver’ tires the prey and guides it to the trap, the ‘blocker’ sits on branches to obstruct the prey, the ‘chaser’ aims to catch the prey, and the ‘ambusher’ lays in wait after predicting the escape route of the prey. If the hunt is successful, the meat is shared between all individuals who participated, creating a clear benefit to collaborating.
Five distinct hunting roles carried out by individuals of the same species shows how sophisticated these strategies can become, if the mutual benefit and success rate is high enough to drive these abilities to evolutionary fixation.
Clearly complementary cooperation is a successful strategy, as displayed from the examples discussed, but how does it compare to species who utilise non-complementary hunting?
Many predatory animals hunt cooperatively in packs, where the use of numbers is the niche expansion gained; the combined strength, endurance, and size of many individuals working together is the variable which effects hunt success rate. It is seen in many canine species, such as wolves, hyena, and dholes, that group size greatly effects success rate of hunts. There is an optimum pack number for hunting success, which weighs up the prey size and the number of hunters which the meat must be shared between. For instance, North American wolves have a much higher probability to capture a bison when hunting cooperatively with other wolves, the bison caught is more likely to be large and strong, meaning more food for each participant. This pack-hunting strategy is found in a diverse variety of species, such as lions, orca, mongooses, and ants.
Despite the lack of distinct roles, non-complementary cooperation still entails sophisticated communication and cooperation. In lionfish, Lönnstedt identified a series of movement signals, which have evolved to mediate cooperative behaviours: they can indicate initiation, agreement, and turn-taking. Similar signals have been seen in species which use pheromones, such as bees, ants, stinkbugs, and those that communicate vocally, namely Harris’ Hawks and Brown-necked Ravens.
Hunting ability and complexity of strategy does not seem correlated with either complementary nature, interspecificity, or neurological sophistication, but rather ecological need and the success rate and mutual benefit gained from such strategy. Cooperative hunting of both complementary and non-complementary strategies are successful in increasing the success rate of the activity, and in fact, these strategies would not exist and be observable in nature and empirical studies, if they did not provide a significant level of benefit to the participants. In species where cooperative hunting is seen, it will always affect the ‘inherent hunting ability’ of such species, otherwise it would not occur. I believe there isn’t a significant effect on hunting ability determined by whether it is complementary or not, because if there was more to gain from a complementary strategy than a non-complementary one, this would be adopted/developed instead. The cooperative hunting method most successful is the one which brings most benefit to all, and this varies across species.