Defensive behaviour in animals; Living in Herds/flocks

introduction

According to evolution, flocking together or forming herd can lead to higher chances of survival, in this page how you can find a couple of ways why this

Comparing two different animals and their group behaviour

Wild cats (lions)

live in prides

Bird ( )

live in flocks

Positive and Negative sides

Positive:

there are several anti-predator functions that can be benefits of being in a group,some of them are

dilution effect:

this is when animals live in groups to "dilute"/ reduce their chance/risk of being attacked, it is proposed by George Williams and W.D. Hamilton that this behaviour evolved because it provides benefits for the individual rather to the entire group(selfish cause), although this leads to benefits to the entire group/flock. For example, the Camargue horses living in France, and their attacker the horsefly. one or a couple of horseflies do not pose any threat to a horse although a swarm may hurt or even kill one, so each individual try to form groups to reduce their chance of being attacked by the horseflies, thereby diluting the danger of the swarm onto many horses, increasing their chance of survival drastically. the same goes to fish, they shoal, forming (sometimes) enormous fish schools, which reduces the chance of the fish's predation by sharks or other creatures.

improved vigilance:

(improved vision, and being more alarmed in general)this theory stats that animal groups are able to detect threats better and sooner that in solitary individuals and alarm the other members, as the task of scanning the environment for predators can be spread out over many individuals. this mass collaboration not only "presumably" provide a higher level of vigilance, it also allows more time for individual feeding, many predators depend on the surprise element for successful attacks, so if their prey is alarmed earlier they would have an improved chance of escape and survival. for example Wild ostriches in Kenya and lions. the ostriches feed alone or in groups of up-to four in the savannas,so they are subject of predation by the lions, in general ostriches posses the capability of running at speeds exceeding that of a lion, for longer distances, therefore lions attack when ostriches's heads are down, being in groups would allow the ostriches to feed while others take the responsibility of reconnaissance to alarm the others. the same goes to bird such as the wood pigeons, they detect their predator, alarm the others and then flee utilising dilution effect in the process

Alarm calls:

Animals living in groups usually give alarm signals warning other members of attacks, for obvious reasons such as their and the groups survival. Some species have different calls depending on the type of the risk, which the others respond appropriately. for example the Vervet monkeys , for eagles: disyllabic cough , wild cats:a loud bark, and pythons: "chutter", and for each call the monkeys act differently.for the eagle look up and take cover, for wild cats climb tree branches that are too weak to hold the cats, and so on.... similar calls are found in different species of monkeys, some other animals also have developed this behaviour such as birds.

Predator confusion:

Predator confusion effect’ proposed and demonstrated by Milinksi and Heller (1978). This theory is based on the idea that it becomes difficult for predators to pick out individual prey from groups because the many moving targets create a sensory overload of the predator's visual channel in addition to the large number makes it really hard to focus on a single target, so Individuals living in large groups can be safer according to this because of this may confuse the predator by the group's size and movement, especially from longer distances. For example zebras and lions, stationary, a single zebra is easy to spot because of its sheer size and different colour to its environment. but when in herds the stripes of black and white cause confusion as well as flickering motion dazzle effect to the lions and even other predators.

Communal defence:

this is when the group/herd/flock actively defend them selves by grouping together to attack or mob the predator, instead of being passive victims or fleeing ones. mobbing predators is when the preys group around the predator(s) and harass it(them), it is usually done by animals weaker than the predator to protect the young in the social colonies. for example: the red colomus monkeys and the chimpanzees male red monkeys group together and stand between the the attacking chimpanzees and female red monkeys and their offspring to protect them and fend off the attackers. hyenas do similarly when attacked by lions, where they get their offspring hide in burrows while they get the lions's attention. even lions may do that when attacked by other lions belonging to different prides(groups)

Increased locomotion efficiency

This theory states that groups of animals moving in a fluid environment may save energy when swimming or flying together. Geese flying in a Vee formation are also thought to save energy by flying in the updraft of the wingtip vortex generated by the bird in-front of them in the formation. Ducklings have also been shown to save energy by swimming in a line.Increased efficiency in swimming in groups have also been proposed for schools of fish and Antarctic krill. this helps the animals in reserving energy and keeping the flock together

Negative:

Asymmetric aggregation of animals under panic conditions has been observed in many species, ex when panicked individuals confined in a room or a closes space with equal exits would cause the majority to favour an exit over the other, leaving the other one(s) overlooked, except for a minority.

Panic escape charactarists :

Individual attemt of moving faster whch leads to exits becoming more arched and clogged
interactions become more physical, Exit is slowed downby fallen individuals serving as obstacles
Tendency towards mass or copied behaviour,ex. alternat or less used exits are overlocked, one making a mistake would lead to others making the same.