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With the help of suitable diagram describe the logistic population growth curve.

Logistic population growth curve

Unlimited resources result in exponential growth. Many countries have realized this fact and introduced various restraints to limit human population growth. In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. This limit is called as carrying capacity (K) for that species in that habitat.

A population growing in a habitat with limited resources shows initially a lag phase, followed by phases of increase and decrease and finally the population density reaches the carrying capacity. A plot of N in relation to time (t) results in a sigmoid curve. This type of population growth is called Verhulst-Pearl Logistic Growth as explained by the following equation :

S-shaped Population growth curve (Verhulst-Pearl logistic growth curve)

where N = Population density at a time t ; r = Intrinsic rate of natural increase and ; K = Carrying capacity, = Environmental resistance.

Since resources for growth for most animal populations become limiting sooner or later, the logistic growth model is concerned a more realistic one.

List the attributes that populations possess but not the individuals.

If the population growing exponentially doubles in size in 3 years, what is the intrinsic rate of increase (r) of the population?

Name important defence mechanisms in plants against herhivory.

List any three important characteristics of a population and explain.

Write short notes on :
(a) adaptations of desert plants and animals.

(b) adaptations of plants to water scarcity.

(c) behavioural adaptations in animals.

(d) importance of light to plants.

(e) Effect of temperature or water scarcity and the adaptations of animals.

Define the following terms and give one example for each:
(a) Commensalism
(b) Parasitism
(c) Camouflage
(d) Mutualism
(e) Interspecific competition

Select the statement which explains best parasitism.

How is diapause different from hibernation ?

List the various abiotic environmental factors factors.

If a marine fish is placed in a fresh water aquarium, will the fish be able to survive ? Why or why not ?

Define phenotypic adaptation. Give one example.

Most living organisms cannot survive at temperature at about 45°C. How are some microbes able to live in habitats with temperatures exceeding 100°C ?

An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree ?

What is the ecological principle behind the biological control method of managing with pest insect ?

Distinguish between the following :
(a) Hiberation and aestivation

(b) Ectotherms and endotherms.

Give an example for:
(a) An endothermic animal
(b) An ectothermic animal
(c) An organism of benthic zone

Define population and community

'Analysis of age-pyramids for human population can provide important inputs for long-term planning strategies.' Explain.

(a) List the different attributes that a population has and not an individual organism.

(b) What is population density ? Explain any three different ways the population density can be measured, with the help of an example each.

(a) Explain giving reasons why the tourists visiting Rohtang Pass or Mansarovar are advised to resume normal active life only after a few days of reaching there.

(b) It is impossible to find small animals in the polar regions. Give reasons.