(a) What is an age-pyramid ?

(b) Name three representative kinds of age-pyramids for human population and list the characteristics for each one of them.

OR

Discuss the role of healthy ecosystem services as a pre-requisite for a wide range of economic, environmental and aesthetic goods and services.

(a): Age-pyramid- is a graphical representation of the distribution of various age groups within a population of a region forming the shape of a pyramid when the population is growing.

(b): For Human population age pyramids generally show age distribution of Males and Females.

The shape of pyramid reflects the growth status of the population:

I. whether it is growing

II. stable

III. declining

Population having more no.of young individuals grow faster, while, population having more no.of post-reproductive members tends to be declining.

Basically, there are three types of age pyramids present in Human population;

1.Expanding or Triangular age pyramid - in this, no.of pre-reproductive individuals are moderate, it shows rapid growth i population.

2.Stable or Bell-Shaped age pyramid- in this the pre-reproductive and reproductive individuals is almost same, hence the population size remains stable, neither diminishing nor growing.

3.Declining or Urn shaped pyramid- the proportion of reproductive age group is higher than the individuals in pre-reproductive age group. It is diminishing population with negative growth.

OR

Healthy ecosystem is the base for a wide range of economic, environmental and aesthetic goods and services.The products of ecosystem processes are named as Ecosystem services, as they are helpful to the organism living within the ecosystem.

Forests are the major source of ecosystem services and are pre-requisite for environmental, aesthetic goods and and indirect economic values in the following ways:

1. Environmental values:

(a) Carbon-fixation - Huge amount of CO2 in the atmosphere is removed naturally and fixed by plants into organic molecules and energy through photosynthesis.

(b) Release of oxygen by the producers as a byproduct in the process of photosynthesis, improves the quality of air and supports the life on earth.

(c) Soil formation and soil protection- are the major ecosystem services accounting for nearly 50% of their total worth. Plant cover protects the soil from drastic changes in temperature.

(d) Nutrient cycling- there is no depletion of nutrients, but the same are repeatedly circulated.

2. Economic values:

(a) Ecosystem services provide certain economical important products also, these include paper, rubber, wax, medicines, etc……

(b) Ecosystem also provides other benefits like aid in pollination. Bees and other insects of of natural ecosystem are a source of spiritual, culture and aesthetic values.