The association between a suckerfish $(Remora)$ and a shark is an example of:

In an aquarium,two herbivorous species of fish are living together and feeding on phytoplanktons. As per the Gause's Principle,one of the species is to be eliminated in due course of time,but both are surviving well in the aquarium. Give possible reasons.

Match the Column-$I$ and Column-$II$:

Column-$I$	Column-$II$
$(P)$ Lichens	$(i)$ Parasitism
$(Q)$ Abingdon tortoise and goat	$(ii)$ Commensalism
$(R)$ Sea anemone and clown fish	$(iii)$ Competition
$(S)$ Human and liver fluke	$(iv)$ Mutualism

In commensalism,

For a limited resource, two closely related species compete for the same resource, which is known as $.........$, which keeps them in check in the environment.

Match the following columns:

Column-$I$	Column-$II$
$P$. Calotropis	$I$. Special chemical
$Q$. Cactus and Acacia	$II$. Camouflage
$R$. Monarch butterfly	$III$. Thorns
$S$. Some species of insects and frogs	$IV$. Glycosides