Speciation

Pattern 1: Stabilizing Selection

Natural selection favors an average phenotype over the extremes of a trait.

Example: Robin Egg Laying

Pattern 2: Directional Selection

The effect of an environmental change causes a shift in the favored phenotype to one end of the available phenotypes.

Example: Peppered Moths

Pattern 3: Disruptive Selection

Natural selection prefers two distinct phenotypes, each which has its own benefits within a specific environment. 

Example: Gray and Himalayan Rabbits

Pattern 1: Adaptive Radiation

The process by which one species gives rise to various other species, all of which take advantage of different niches. 

Example: The Hawaiian Honeycreepers are a category of birds in the tropical forest of the Hawaii islands that have undergone adaptive radiation to take advantage of various sources of food. 

Pattern 2: Convergent Evolution

The process by which very distantly related species independently evolve similar traits in response to living in similar environments.

Example: The African Yellow-throated Longclaw (left) and the American Meadowlark (right) are two species of distantly related birds that occupy similar niches.  Due to their similar niches, they evolved to look and act almost exactly the same.

Pattern 3:  Divergent Evolution

The process by which a single species evolves into two distinct species that are adapted to different environments, often due to a physical division between the individuals from the original species.

Example: The old world monkeys and the new world monkeys both evolved from a common ancestor.  These different species of monkeys evolved due to living and adapting to different environments.

Pattern 4:  Co-Evolution

The process by which two very distantly related species affect one another's evolution.  These species interact very closely with one another in their environment.

Example: Buff-tailed sicklebill hummingbirds  and Centropogon flowers coexist in the Amazon rainforest.  The hummingbird seeks out the Centropogon flower for its nectar.  When the bird sticks its bill deep within the flower to collect the nectar, it collects pollen on its head.  As the bird continues to feed on other flowers, it pollinates as it goes.  The shape of this hummingbird’s bill has coevolved with the shape of the flower, as both species benefit from this relationship.

1) Gradualism: The formation of new species occurs with small and gradual changes to a species over very long periods of time. In this pattern of speciation intermediate phenotypes can be observed, demonstrating how the species evolved gradually over time.

2) Punctuated Equilibrium: The formation of new species occurs in relatively short bursts of time followed by periods of stasis, where there is no change. There is no record of the intermediate phenotypes that lead up to the current species. 

Type 2:  Temporal Isolation

Temporal isolation occurs when different populations are ready to mate at different times of the year. For example, the spring field cricket and the fall field cricket mate during different seasons.

Type 3:  Habitat Isolation

Habitat isolation occurs when two populations occupy different habitats.  For example, the cricket (a) Gryllus pennsylvanicus prefers sandy soil, while the cricket (b) Gryllus firmus prefers loamy soil. The two species can live in close proximity, but because of their different soil preferences, they became genetically isolated.

Type 4:  Behavioral Isolation

Behavioral isolation occurs when a female cannot recognize the courtship behaviors of closely related males.  These behaviors can include courtship calls, songs, and dances. There are many different types of Birds of Paradise, all which have different mating dances.  Females will mate with males performing recognizable courtship behaviors.  Males with unrecognizable courtship behaviors will be ignored.  Over long periods of time, new species can form due to behavioral isolation.