Why is a species hard to define?

A collection of organisms that are able to reproduce with one another is referred to as a species.

While certain groups of organisms rarely reproduce with one another, they can when given the right circumstances or habitats.

There are numerous examples. For example, there are two populations of squirrels on either side of the Grand Canyon. It is likely that these were once engaged in interbreeding; however, the canyon has since divided the populations, preventing interbreeding. The two populations differ significantly in terms of phenotype; they are now classified as two distinct species, but they can still interbreed if brought together.

Because they occupy distinct niches on the islands, Darwin Finches are thought to comprise thirteen different species; however, hybridization—the intermarriage of members of one species with those of another—has been regularly observed.

While lions and tigers are thought to be distinct species in the wild, they interbreed in wild animal parks.

The definition of a species is complicated by the question of whether two populations can interbreed or not.

A species is hard to define because there are different criteria used by biologists to classify organisms, including morphological, genetic, ecological, and evolutionary factors. Additionally, there are cases where hybridization, geographic variation, and asexual reproduction blur the boundaries between species.