The organisms spending most of the time in the transitional area between two communities are called:

In most animals,the metabolic reactions proceed in a $A$ temperature range (in humans,it is $37^{\circ} C$). But there are microbes (archaebacteria) that flourish in hot springs and deep sea hydrothermal vents where temperatures far exceed $B$. Choose the correct option for $A$ and $B$.

In ecology,what is referred to as a 'niche'?

Assertion : Biotic community has higher position than population in ecological hierarchy.
Reason : Population of similar individuals remains isolated in the community.

$A$: Aquatic organisms do not experience mechanical shocks while swimming in water.
$R$: Water is a liquid medium for swimming.

Give scientific reasons: Mango trees do not grow in countries like Canada and Germany.