This goes along with the 22nd chapter of Campbell Biology in Focus AP edition!

Species

How is species defined?
There are four species concepts (or four working definitions of species- biological, morphological, phylogenetic, and ecological.

The Biological Species Concept

The Biological Species Concept defines a species as a group of populations whose members have the potential to produce viable, fertile offspring with each other, but not with the members of any other groups.

This concept is the most common, but it is weak when it comes to describing species that reproduce asexually or that are extinct. It generally works well, but there are a few gaps.

The Morphological Species Concept

The Morphological Species Concept defines a species as a group that shares similar morphological structures.

This definition is helpful because it includes species that are extinct or that reproduce asexually, but it still has limitations. Morphology can be misleading- sharks and dolphins have similar morphology, but they are not closely related. Additionally, some researchers disagree on which structures are important enough to compare.

The Phylogenetic Species Concept

The Phylogenetic Species Concept defines a species as a group with common evolutionary history.

This works well for asexual and extinct species, and it is based on actual relationships, but it requires detailed evolutionary histories.

The Ecological Species Concept

The Ecological Species Concept defines a species as a group of organisms that shares an environmental niche.

This works well if scientists have ecological data on the group of organisms.

Speciation

Speciation is the process by which one species splits into two or more different species. Speciation is broadly caused by reproductive isolation, but there are many factors that can cause two populations to become isolated.

Causes for reproductive isolation