Exotic species are also called

$I.$ introduced species

$II.$ alien species

$III.$ non-indigenous species

$IV.$ non-native species

Choose the correct combination

World environment day is celeberated on

The closely related morphologically similar sympatric populations, but reproductively isolated, are designated as

Plants which behave as mesophytes in rainy season and as xerophytes in summers are called

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