(a): equation represents Exponential growth.

‘r’ represents rate of natural increase

Importance of ‘r’ in population growth:

_• This is the parameter for assessing the impacts of any biotic or abiotic factor on population growth.

(b) In nature , a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. This is called Carrying capacity (K) of a habitat.

is the equation, this logistic curve shows sigmoid curve and is called Verhulst-Pearl logistic curve.

where, N= population density at time t

r= intrinsic rate of natural increase

k= carrying capacity

The logistic growth model is considered more realistic since, resources for growth of most animal populations are finite and become limited sooner or later.

OR

(a): Energy flow in an ecosystem is always Unidirectional.

i.e: Solar radiation———>Producers———>Herbivores——->Carnivores

There is decrease in content and flow of energy with rise in trophic level. A part of energy captured by producers is used for maintenance and as food to herbivores. From herbivores it goes to carnivores.

When energy flows from a particular trophic level to the next trophic level, she energy is always lost as heat at each step.

Only 10% of energy is utilised at each tropic level, 90% of energy is lost as body heat, respiration and other activities.

Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time or annually per unit area.

(b): The two limitations of ecological pyramid are as follows:

1. It assumes a simple chain, it does not take into account the same species belonging to two or more trophic levels.Simple food chain never exists in nature, it does not accommodate a food web.

2. Saprophyte are not given any place in ecological pyramids even though they play a vital role in the ecosystem.