Biological control methods adopted in agricultural pest control are an example of which interaction?

$A$ sedentary sea anemone gets attached to the shell lining of a hermit crab. The association is:

Which of the following characteristics is described by Gause's competitive exclusion principle?

$A$ bird enters the mouth of a crocodile and feeds on parasitic leeches. The bird gets food and the crocodile gets rid of blood-sucking leeches. Both partners can live independently. Such an association is:

Which of the following is an ectoparasite?

The graph below shows the changes in two populations of herbivores in a grassy field. $A$ possible reason for these changes is that