Question

Student to attempt either option or. (i) Explain giving three reasons why tropics show greatest levels of species diversity. (ii) Draw a graph…

Accepted Answer

(A) (i) Tropical latitudes have remained relatively undisturbed for millions of years and thus had a long evolutionary time for species diversification Tropical environments are less seasonal more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity More solar energy is available in the tropics which contributes to higher productivity which leads to greater species diversity. (ii) Alexander von Humboldt Within a region species richness increased with increasing explored area but only up to a limit. OR (B) (i) Habitat loss and fragmentation: Deforestation leads to habitat loss and ultimately causing extinction of animals and plants / When large habitats are broken into small fragments that also leads to population decline / mammals and birds with large territories and certain animals with migratory habits are badly affected. Overexploitation: Overexploitation of natural resources by humans leads to extinction of many species / For example overexploitation of Steller’s sea cow or passenger pigeon or many marine fishes led to their extinction. Alien: species invasions, When alien species are introduced unintentionally or deliberately for whatever purpose some of them turn invasive and cause decline or extinction of indigenous species/ For example Parthenium or Lantana or water hyacinth pose threat to indigenous species Co-extinctions: When a species becomes extinct the plant and animal species associated with it in an obligatory way also became extinct/ For example unique assemblage of parasites and plant pollinator mutualism where extinction of one invariably leads to the extinction of the other (Any Three Points) (ii) Ex-situ conservation: Threatened animals and plants are taken out from their natural habitat and placed in special setting where they can be protected and given special care. e.g.: Zoological parks, Botanical gardens, Wildlife safari parks, seed banks, pollen bank

Student to attempt either option (A) or (B).
(i)
Explain giving three reasons why tropics show greatest levels of species diversity.
(ii)
Draw a graph showing species-area relationship. Name the naturalist who studied such relationship. Write the observation made by him.

Marking-scheme solution

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