Man is a social animal.
Ever since he has started the settled life, he is much more conscious about the
habitat in which he lives and the components to which he is attached.
In the broad sense, any interaction resulting from the response of one animal
to another of the same species represents social behavior. Even a rival male
fighting another male over the possession of a female is a social interaction.
Virtually all members of
a species exist in pairs or groups for at least same part of their leaves, for
feeding, drinking or for mating and some animals spend their entire lives as
members of a cooperative interacting group. Their association typically extends
beyond the level of mating and taking care of young. Such groups form societies
and display simple to complex social organizations.
Social behavior has
evolved independently in many species of animals and complex social
organization has been found in invertebrates as well as vertebrates. The term
social organization refers to population or groups and not to individuals and
determines how members of a species interact with each other. In various social
insects the social organization is quite rigid and species specific. In many
vertebrates however, it is more flexible and may vary with changing conditions.
For instance in elephants the females may live in the same family unit for 40
to 50 years. The stability of their relationship would allow them to be called
a society. On the other hand, organization within a flock of birds or within a
social of fish would not be termed truly social even though they may live
together for months.
Benefits and Costs of
Sociality
As early as 1938,
observations on different animal groups showed that many animals are able to
face adverse environments if they live in groups. School of fish is less
vulnerable to predators because large numbers often confuse the predator. There
is safety in number and the detection of predator may be enhanced by having
several individuals on alert to warn against any intruders. For instance
meerkats (socially living mongoose) take turns to keep vigil at high look-out-
points while other individuals feed. When a predator is spotted the group can
take collective evasive action like scattering in all directions or physically
attacking the predator. A flock of birds on seeing a predatory bird usually
bunch like gulls resort to mobbing when a predator like a fox or even humans
approach their nesting sites. Thus survival of gulls that nest in large
colonies is much better than that nest alone.
On the other hand
predators too are more successful if they hunt in groups. Lion’s hyena’s
wolves’ cape hunting dogs are examples of predators that hunt together. Some
individuals in the group help to drive the prey towards other hidden members,
or help in running down the prey to exhaustion. Another advantage may be that
scavengers are kept at bay by other members of the groups.
Another advantage is
utilization of food resources found by one individual. Also living in groups
provides protection against harsh weather conditions as can be seen in penguins
that huddle together to incubate their eggs and provide a fairly decent shelter
from the cold their young are reared communally in crèches.
Rearing of young in a
group provides grater protection and safety at the same time the potential for
learning and transmitting useful information is another advantage.
Observations on a semi
natural colony of Japanese macaque monkeys in Koshima Islands revealed that
when they provided with potatoes caked with mud, they usually rubbed off the
mud before eating it. However it was noted that one day of the females washed
the potato in the nearby sea before eating. Soon the other females began to
copy her and this behavior was learnt by offspring and soon became a part of
the group’s habit.
While group living
confers clear advantages at the same there are some undoubted disadvantages.
There may be competition for resources increased risk for transmission of
parasites and diseases, greater risk of cannibalism of the young by
conspecifics and interference in mating. The balance between benefits and costs
is a fine one and the behavior that will be favored by natural selection will
be the one that favors the reproductive interests of individuals in the long
run.
Types of Social Behavior
Patterns
We have said earlier
that societies of animals vary greatly in their structure organization
complexities and types of interactions.. These insects are termed eu-social
because of the division into castes such as soldiers’ workers reproductive
individuals which are morphologically different from each other. In contrast a
social organism in vertebrates is not so rigid though there is an example of
eu-social vertebrates which we will discuss later. Most vertebrates societies
also contain genetically related individuals, but unlike insect societies all
members are capable of reproduction and competition in reproduction is one of the
main principles in determining the social system. Usually a typical vertebrates
society would consist of genetically related females and their offspring plus
unrelated males that come and join the group.
Territoriality and
Dominance Hierarchy
Social organisms
requires cooperation amongst animals of the same species but at the same time
there is competition amongst them because of limited resources like, food,
water, mates or shelter.
Much of what do to
resolve their competition is called aggression. Aggression may be defined as
offensive physical action, or threat to force others to give up what they have
or might attain. Many ethnologists consider aggression as a part of a wider
behavior known as agonistic behavior referring to any activity related to
fighting whether it is aggression or defense or submission or retreat. Most
aggressive behavior is in the same species. The symbolic ritualistic displays
of agnostic behavior are mutually understood. For example rival male poisonous
snakes engage in stylized fights where they butt each other by their heads so
that the other is tried and eventually recedes. They never bite each other. The
loser usually submits to the winner who becomes dominant. Thus agonistic
behavior is important for maintaining social order, especially establishment of
dominance hierarchies and maintenance of territories.
Territories are marked
and defended in social organisation because they contain food resources sites
for attracting mates and rearing young. They are also locations that provide
shelter. Of all the classes of vertebrates birds are the most conspicuously territorial.
Most male songbirds as you would recall establish their territories in early
spring and defend them vigorously. Many mammals have home ranges rather than
territories. It is not an exclusively defended area but is the total area
covered by the mammal in its activities. Home ranges of individuals of the same
species may overlap and may shift with seasons.
As said earlier some
sort of dominance between individuals of a social organization is established
due to agonistic behavior and is known as dominance hierarchy. Due to this a
group of animals can coexist despite competition. The group is organized in
such a way that some members of the group have greater access to resources such
as food and mates than other do. Those animals at the top of the hierarchy have
the first choice of resources and those at the bottom may do without, if
resources are scarce. Once a hierarchy is in place coexistence is possible with
occasional fights if any member tries to move up the ladder. Dominance
hierarchy was first noticed and described in chicken societies. It was seen
that when chicken are placed in a pen, they initially fight linear hierarchy of
dominance is established among them. Higher ranking chicks are the first to eat
and may peck the lower order chicks if they disturbed the feeding order. This
is known as pecking order. Though dominant individuals gain all rights over
food, space, mate, etc, the subordinates stay around because staying may be
even worse or they may in time become dominants.
Sexual Strategy
Different species show
considerable variations in their organization. One of the fundamental
influences on social organization seen in any species in the mating system
adopted by the individuals of that species. By mating system we mean the role
adopted by the two sexes in reproduction.
These sexual strategies
result in particular kinds of mating system which have profound effect on the
social organization of the species. For example where a male has to gain access
to females by defending them against rivals there is a tendency for the social
organization to be based on a harem. This is helped by females who tend to
aggregate as a defense against predators or for feeding opportunities. The
harem is a basic features of the social structure found in antelopes and deer.
Here the mating system is polygynous. Polygyny is also more common in mammals
as females are specialized to take care of the young. But where ever both males
and females are required to care for the young, monogamy is usually the more.
Most 90 percent of the bird species are monogamous. The mating pair lives
together for life on a seasonal or continuous basis. Polygyny occurs in birds
where males are not required to care for the young like in pheasants where the
young require relatively little parental care. Monogamy is not common in
mammals, however it does occur in some primate species or in jackets where
males feed the young through regurgitation.
Another kind of mating
system found in birds is based on polyandry where the females mate with two or
more males, but the male mates with only one female. In such cases the females
are more conspicuous, territorial and dominant than the male. The eggs are
incubated by the males while the female looks for other males.
(Vaibhav Rajdeep)
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