Phenotypic variants formed in a population due to change in environment are called

Transition zone between two community is called

$A$ : Estuary constitutes one of the most productive ecosystem.
$R$ : It represents transition zone between two populations of a species.

Surface water of lake enrich in having

Soil is a mixture of

The figure given below is a diagrammatic representation of response of organisms to abiotic factors. What $(a), (b), (c)$ represent respectively ?

                  $(a)$              $(b)$                   $(c)$