A species is a group of organisms in which individuals can reproduce their progeny.
Population:
A population is a group of individuals belonging to the same species who live in a specific area at a specific time.
Living populations interact with other populations of their kind, populations of other species, and physical aspects of their environment.
Relationship between species and population:
Interspecies reproduction either does not occur or results in sterile progeny. Species are made up of populations that are geographically dependent.
Some species, for example, are confined to a single geographic location, such as an island or a mountain peak. In such cases, a single population represents the entire species.
This population is in grave danger of extinction. Other species can be found in a variety of habitats.
Horses, for example, can reproduce their progeny, but a zebra and horse would generate a zorse, and a donkey and a horse would produce a mule, which is not fertile and hence is not classified as a species.
As a result, we can deduce that horses and donkeys are two distinct species.