Suppose that a plant disease kills all the fruit. the change could become a on the birds.

reason of selective pressure

Explanation:

Selective pressure is due to the factors that hinders the survival of any living being. These limiting factors could be non-availability of food, Mating issues, any natural calamity etc. Here, the selective pressure on birds is due to the lack of food as it is given that all the fruits were effected by a disease and hence cannot be fed upon by the birds.

it takes hundreds of years to become stable.

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