BIOL1003 Lecture Notes - Lecture 26: Shoaling And Schooling

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Living in groups
Costs of grouping
Food
oLiving in groups can reduce foraging efficiency
oOther individuals often compete for the food, so there is less food per head
oThis can also mean that animals in groups waste time fighting for food, like
vultures at carcass
oIt also may be difficult to sneak up on wary prey if you are in a group, which is
probably why tigers hunt alone
Predation and parasitism
oGroups may be more conspicuous to predators than single individuals, and
larger groups are more vulnerable to parasites and infectious diseases
oE.g. blood-sucking bugs of cliff swallows reduce nestling quality and therefore
reproductive success
Interference with reproduction
oMales may be cuckolded by others in the social group
oE.g. red-winged blackbirds
Benefits of grouping
Reduced predation
oIncreased vigilance of a group
Means that predators are spotted sooner, allowing more time to
escape
E.g. goshawks attacking pigeon flocks
oDilution and selfish geometry
The larger group, the smaller the chance that any one individual will
be killed if a predator successfully attacks
E.g. waterstriders
Individuals can reduce the chance of being nearest to an attacking
predator by keeping away from the edge of a group
E.g. Hamilton’s model of frogs around a pond
E.g. fur seals with a greater “domain of danger” are more likely to be
killed by great white sharks
Feeding
oCooperative hunting
E.g. lions hunt in groups, enabling them to catch large prey
oFinding food
Individuals might find out about the location of food from others
This might be just parasitising the efforts of good foragers, or might
be beneficial to all
E.g. ospreys get information on the location of fish schools by
watching others return to the colony
oMore time to feed
Foraging in a group reduces the time needed for individual vigilance
and so can increase the time available for feeding
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Document Summary

Predation and parasitism: groups may be more conspicuous to predators than single individuals, and larger groups are more vulnerable to parasites and infectious diseases, e. g. blood-sucking bugs of cliff swallows reduce nestling quality and therefore reproductive success. Interference with reproduction: males may be cuckolded by others in the social group, e. g. red-winged blackbirds. Reduced predation: increased vigilance of a group. Means that predators are spotted sooner, allowing more time to escape. E. g. goshawks attacking pigeon flocks: dilution and selfish geometry. The larger group, the smaller the chance that any one individual will be killed if a predator successfully attacks. Individuals can reduce the chance of being nearest to an attacking predator by keeping away from the edge of a group. E. g. fur seals with a greater domain of danger are more likely to be killed by great white sharks. E. g. lions hunt in groups, enabling them to catch large prey: finding food.

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