The describes a species as groups of organisms that interbreed, have a shared , and are reproductively isolated from all other species.

1. Biological species concept

2. Gene pool

Explanation:

Biological species concept defines the species as a group of individuals that can interbreed to produce fertile progeny. The individuals from two different species cannot interbreed and produce viable and fertile progeny. This means that two species are reproductively isolated from each other.

The total number of genes and alleles present in the individuals of a species makes its gene pool. Each species has its unique gene pool.  

on island x the species needed to adapt because they were being subject to predators which didn't inhabit island y.