AGGRESSION
IN
ANIMALS
Animals Response to the biotic
Environment
Responses of animals to other animals can be
intraspecific or interspecific
They can be further classed as aggressive or
co-operative behaviours
Aggression
 Animals often
display aggressive
acts towards one
another.
 Aggression
increases during
times of stress.
Classification of aggressive behaviours
Intra-specific aggression:
Intraspecific Aggressive
Responses
•Agonistic behaviour is aggressive behaviour
towards another member of the same species
involving threats, submissions, chases and
physical combat. Agonistic behaviour is a
contest to determine who gains access to a
resource.
(Does not include predatory aggression for
obtaining food)
•Conflicts between members of the same
species are usually resolved with ritualistic
behaviour. This prevents serious injury to the
combatants.
•Fighting to the death is non-adaptive to most
animals. Only occurs when eliminating a
stranger from another group.
•The more scarce the resource the more
intense the fighting.
Reasons for Aggressive Behavior
• Defense of territory
Usually connected with reproduction
Sometimes to keep food source
• Defense of brood
• Repelling competitors for mates
(dominance)
Features of Aggressive Behaviour
•Belligerent behaviour by an animal that threatens to harm or kill
another animal with which it is competing.
•Combat is more likely to be physical if it is essential to the survival and
reproductive success of the competitors.
•Natural selection favours a quick end to combat to prevent the winner
from becoming too injured, to be able to take advantage of the
resources won.
•Fighting between males for mates is common. Winner mates with
female and passes on genes for successful fighting. Selection may cause
males to become larger than females (sexual dimorphism).
Types of Aggression
Lair or Nest
Territory
Home range
 Hierarchical aggression
Territories
•A territory is an area defended against other members of the
same species.
•It provides food, water supplies, nesting areas, and refuges
from danger.
•Ownership of a territory is signalled by vocalisations, scent
marking, visual displays.
•Boundary marking warns against accidental intrusion by others
of its species.
•Another animal (rival) is only likely to attempt to dislodge the
owner of the territory if it has a chance of being successful.
•Territories help to regulate the population to a size that can be
supported by the available resources.
These New Zealand gannets maintain their
individual nesting territories by calling and
pecking at each other
These New Zealand gannets maintain their individual nesting territories by
calling and pecking at each other
Dominance -Hierarchies
•Many animals that live in social groups have a dominance
or social hierarchy
•It is established and maintained by agonistic behaviour.
•Once established it is maintained by ritualised displays
unless a new animal enters the group or a low ranking
individual challenges a higher ranking animal. Cuts down
competition and tension in the group.
•Body postures are common dominance signals
Types of Aggression
Dominance Hierarchy
Dominance aggression
Defensive aggression
Chickens establish a “peck order”
Types of Aggression
Abberant Aggression -Cannibalism
Tadpoles exhibit cannibalism for avoiding competition for food and space
Aggression for mate
 Rutt in male deers (stags)
Resource defense
Resource defense
Aberrant aggression
E.g.: Aggressive Behavior in Fish
• Direct charges
Often includes biting
Ritualistic displays
Modified swimming
Flaring gill covers
Color changes
Threatening movements
Cannibalism
Levels of aggression
Predator – Prey
•Not truly an aggressive relationship.
•Predators can limit a population to a healthy level.
•Most predators tend to catch the least well-adapted
animal, sick or old.
•Keeps the gene pool of the prey strong.
•The 2 species are dependent on each others wellbeing.
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