Lecture 17: Human and animal Flashcards
Define living in groups
Any set of organisms, belonging to the same species, that remain together for a period of time. They interact with one another, more so than that of other conspecifics. There is close proximity and an attraction instead of random association. Wilson 1975.
What are the benefits of living in groups?
Survival; finding food, assessing food and not being killed.
Reproducing; finding mates and assessing mates.
Protection; More vigilance, more eyes, chances of detecting a predator is higher.
Discuss in detail how living in a group can increase protection
Alarm signals can be used to warn others and transfer information. Some animals, like meerkats and pied babblers, have a watchman’s song where they give quite vocalisations whilst on guard, allowing the workers to have more foraging success and not have to worry about vigilance. It also dilutes the risk of predation as the predator won’t eat all of the group, however, it makes them more easy to spot so this creates a trade off. Groups can cause confusion as the predator will struggle to single one out, carp do this and so do pike. You can create a communal defence and be more effective at defending the group, red wing birds do this.
Discuss how living in a group can benefit foraging
There are more individuals so as a group they are more likely to find food as the group can act as an information centre. It facilitates the location of food as members will see other members gathering around it and it maximises the exploitation of the food as they will know where to find the food due to information sharing. It helps predators catch prey that are too big to catch on their own. Sometimes they adopt different roles to maximise success, for example chimps have a driver, an ambusher and a chaser when catching prey.
Discuss how living in a group can benefit mating
This is especially evident in primates, it’s beneficial as members of the group don’t have to travel far to find a mate. Some groups temporarily form for this purpose alone, for example, lekking.
Discuss how living in a group can benefit energy usage
Groups can be used to conserve heat and water, for example penguins huddle in the cold in order to keep warm as their surface area exposed to the surroundings is reduced. It can also reduce the cost of movement as some animals attain specific formations to maximise speed with less force and less energy usage. Geese do this, as well as some crayfish.
List the direct and indirect costs of living in a group
Direct costs: Being eaten by a predator as you’re more easy to spot and it’s easier for predators to catch prey.
Indirect costs: Spending energy to avoid the direct cost, e.g. more time being vigilant resulting in less time for feeding.
Discuss how living in a group can be bad in terms of competition
The more individuals at a resource, the less food there is to share. The ideal free distribution occurs where the first arrivals go to the rich habitat with lots of resources and as more arrive, the resource becomes depleted. Then, the rich habitat becomes as equally as attractive as the poor habitat, resulting in no benefit. If many people are at a resource, there is also an increased risk of aggression as more individuals are competing for the same resource. It also increases the risk of kleptoparasitism which is when one steals the food of another, this can be beneficial if you’re stealing more than you’re being stolen from but it also increases the risk of injury. Retten 2010 found this.
Discuss how living in a group can be bad in terms of parasite load
They’re more likely to collect contact transmitted parasites which can have a really strong cost like reduced body mass.
Discuss how living in a group can be bad in terms of misdirected parental care
Cuckoldry: If males are involved in parental care then it can be costly as they spend time and energy bringing up an offspring that isn’t their own and therefore doesn’t bring any fitness benefits. This happens a lot with birds because of EPCs and EP fertilisations. It can also happen with primates as well. So even though mating can occur easily, there is more competition involved.
Brood parasitism: Cuckoo birds do this, if birds are living in groups then it’s easier for the cuckoo bird to observe many nests and spot the best parents, so living in groups doesn’t always increase protection against predation.
How do animals find the optimal group size?
Living in a group can have many benefits that come with many costs as the benefits aren’t mutually exclusive. The optimal group size should be when the benefit is highest but the cost is still lower. However, this is rarely found in nature as their group sizes are usually to big. This is because they want to maximise their relatives’ fitness as well as their own, so relatives might be more tolerant to costs if there is an increased group size. This follows Hamilton’s rule. However, sometimes members of a group leave because the environment can’t sustain the group so individuals will be better off on their own if they avoid competition with the previous group.
