Biology_Today_-_October_2016

(iv) Echolocation Producing high frequency sound which produce echoes after striking

various objects, it helps to locate path and predators.

Bats, whales

(v) Hibernation Undergo winter sleep, body temperature drops, breathing and heartbeat

become slow.

Northern ground squirrels

(vi) Aestivation Avoid heat by spending dry-hot period in a torpid state into burrows. Ground squirrels of south western

deserts

(vii) Behavioural adaptations Desert lizards lack the physiological ability that mammals have to deal

with the high temperature. They keep their body temperature fairly

constant by behavioural means. They enjoy in the sun and absorb heat

when their body temperature drops below the comfort zone, but move

into shade when the surrounding temperature starts increasing.

Desert lizards

(viii) Physiological

Adaptations

At high altitudes, the body does not get enough oxygen due to

low atmospheric pressure, known as altitude sickness. The body

compensates low oxygen availability by increasing red blood cell

production, decreasing the binding capacity of haemoglobin and by

increasing breathing rate.

Humans going to mountain regions

POPULATIONS

s Population is the total number of interbreeding individuals of a species found in a geographical area, who share and compete
for similar resources.

s A population has certain characteristics that an individual organism does not have:

• A population has birth rate and death rate, while an individual may have birth or death.


• An individual has sex (male or female) but a population has sex ratio.

Age Pyramids

s Graphic representation of different age groups found in a population with pre-reproductive groups at the base, reproductive ones
in the middle and post-reproductive groups at the top is called age pyramid.

Age Pyramids

Urn shaped Age Pyramid

Proportion of reproductive age group is higher

than the individuals in pre-reproductive age group.

Number of post-reproductive individuals is also

sizeable. It is declining or diminishing population

with negative growth.

Bell shaped Age Pyramid

The number of pre-reproductive and

reproductive individuals is almost equal. Post-

reproductive individuals are comparatively

fewer. The population size remains stable,

neither growing nor diminishing.

Triangular Age Pyramid

The number of pre-reproductive individuals is

very large, number of reproductive individuals

is moderate while post-reproductive individuals

are fewer. Population is growing. Rate of

growth depends upon the comparative size of

pre-reproductive population.

Fig.: Various types of age pyramids

s Population Density: Number of individuals of a species per unit area/space at a given time.

Population density (D) =

Number of individuals (N)

Space (S)