Species

Biological Species Concept (BSC)

Interbreeding populations reproductively isolated from others.

Morphological Species Concept (MSC)

Species defined by physical features (shape, color, size).

Phylogenetic Species Concept (PSC)

Smallest monophyletic group diagnosable by unique characters.

Cryptic Species

Species that look identical but are reproductively isolated.

Monophyly

A common ancestor and ALL of its descendants.

Synapomorphy

A shared, derived trait used to define a clade.

Paraphyly

A group including an ancestor but only some of its descendants.

Prezygotic Barrier

Evolutionary mechanism preventing mating or fertilization.

Temporal Isolation

Isolation due to differing mating times (day

Habitat Isolation

Isolation because populations live on different hosts

Behavioral Isolation

Isolation due to differing mating rituals or songs.

Mechanical Isolation

Reproductive organs are physically incompatible.

Gametic Isolation

Eggs and sperm fail to recognize

Postzygotic Barrier

Fertilization occurs but hybrids are inviable or sterile.

Hybrid Sterility

Offspring are healthy but cannot reproduce (e.g., Mules).

Allopatric Speciation

Speciation caused by a physical geographic barrier.

Vicariance

Population subdivision by an extrinsic physical factor.

Dispersal

A subset of a population moves to a new, isolated place.

Parapatric Speciation

Speciation between adjacent populations via isolation by distance.

Sympatric Speciation

Speciation within the same area via niche partitioning.

Adaptive Radiation

Rapid diversification into many niches from one ancestor.

Apple Maggots

Example of sympatric speciation via a host shift to apples.

Meadowlarks

Example of similar-looking birds with different songs