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Give three hypotheses for explaining why tropics show greatest levels of species richness.


The three hypothesis which explain why tropics show greater species richness are:

 1. Tropical latitudes have remained undisturbed for millions of years and thus, had a long evolutionary time for species diversification.

2. Tropical environments are constant, predictable and less seasonal, thus  promote niche specialisation and leads to greater species diversity.

3. There is more solar energy available in the tropics, which leads to more productivity and hence species diversity.

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How do ecologists estimate the total number of species present in the world?


The ecologists estimate the total number of species present in the world using the statistical methods because the number of species is too large .  They make statistical comparisons of the temperate-tropical species richness of an exhaustively studied group of insects and extrapolate this ratio to other groups of animals and plants and come up with a gross estimate of the total number of species on earth
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Name the three important components of biodiversity.


The  three important components of biodiversity are:
(i) Genetic diversity.

(ii) Species diversity.

(iii) Community and ecosystem diversity.

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The species diversity of plants (22 per cent) is much less than that of animals (72 per cent). What could be the explanations to how animals achieved greater diversification?


The diversity of animals is much more than the diversity of plants because the animals are mobile and move from one place to another. Thus they moved to different habitats and achieved more diversity. The animals have adapted themselves to the changing enviroment by developing various features like  complex nervous system, protective external layer or cuticles for better survival as compared to plants.
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Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem ?

The biotic components like plants control floods and soil erosion. The roots of the plants hold the soil and prevent soil erosion. Roots also make the soil porous and allow the infiltration of water, hence preventing floods. Dense forests slow down the water flow and keep a check on the floods and soil erosion. 
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