Biology Today - February 2018

(vii) Behavioural

adaptations

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 (Desert lizards lack

the physiological ability that mam-

mals have to deal with the high

temperature).

(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.

Tribes living in the high altitude of

Himalayas.

POPULATIONS

• A population may be defined as a group of organisms of the same species occupying a particular space in a given time.


• The basic characteristic of a population is its size or density which is affected by four primary population parameters such
  as natality (births), mortality (deaths), immigration and emigration.

Age Pyramids

• 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.

Types of age pyramids

Urn shaped age pyramid

Proportion of reproductive age group is

higher than the individuals in pre-reproduc-

tive age group. Number of post-reproductive

individuals is also sizeable. It is declining or

diminishing population with negative growth.

Post-reproductive

Reproductive

Pre-reproductive

Declining population

Bell shaped age pyramid

The number of pre-reproductive and reproduc-

tive individuals is almost equal. Post-repro-

ductive individuals are comparatively fewer.

The population size remains stable, neither

growing nor diminishing.

Post-reproductive

Pre-reproductive

Reproductive

Stable population

Triangular age pyramid

The number of pre-reproductive indivi-duals 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.

Post-reproductive

Reproductive

Pre-reproductive

Expanding population

Population Density

• It is the number of individuals of a species per unit area/space at a given time. The formula is:

Population density (D) =

Number of individuals (N)

Space (S)

• Population density in a given habitat changes due to four basic processes:

Immigration (I)

Emigration (E)

Population

density (N)

Natality (B) Mortality (D)

Number of deaths

in the population

during a given

time period.

Number of births

during a given

period in the

population.

Number of individuals of the

same species that have come

into the habitat from elsewhere

during the time period.

Number of individuals of

the population who left the

habitat and gone elsewhere

during the time period.

+

+–

• 
  

Most populous state : Uttar Pradesh

Least populous state/UT : Sikkim/ Lakshadweep

Population density : 382 persons per sq. km.

Literacy rate : 72.99%

The highest literacy rate : Kerala with 93.91 per

cent literacy rate.

The lowest literacy rate : Bihar with 63.82 per

cent literacy rate.