1. 24.1 The Biological Species Concept emphasizes Reproductive Isolation

2. The Biological Species Concept
A species is a population or group of populations that can interbreed and produce FERTILE offspring, but cannot produce viable offspring with other groups.
Eastern meadowlark
western meadowlark

3. Reproductive Isolation
Biological species are defined in terms of reproductive compatibility.
When members of a species are isolated reproductively, the members of the now two separate populations cannot interbreed and produce fertile offspring.
Usually having some sort of barrier can on occasion lead to hybrids, many barriers can isolate an organism altogether.
Not all barriers are obvious.

4. Reproductive Barriers

5. Prezygotic/postzygotic Barriers
Prezygotic Barriers
Postzygotic barriers
Block fertilization from occurring. Typically through geographic, temporal, or behavioral isolation.
Various mishaps can prevent hybrids from being successful.

6. Limitations to the Biological Species Concept
The Biological Species Concept is defined by the absence of gene flow (meaning hybrids typically are not a viable option).
Even though gene flow can occur between to organisms (i.e. the grolar bear which is a combination of a grizzly and polar bear).
The Biological Species concept also doesn’t include asexually reproducing prokaryotes.

7. Other Species Concepts
Morphological Species Concept: categorizes a species based on its morphological characteristics.
Ecological Species Concept: Categorizes organisms based on their niche (role in the environment).
Phylogenetic Species Concept: categorizes a species as the smallest group of individuals that share a common ancestor. Compare morphology and molecular genetics.