SPECIES
RECALL: What is a

species?

A species is a group of
organisms so similar to
one another that they
can interbreed and
produce fertile offspring

Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species

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Speciation

● Speciation is the evolution of new species over time

● Speciation is the rise of two or more species from

one existing species.

● Speciation occurs most rapidly in a small population

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• The isolation of populations can lead to speciation.

• Populations become isolated when there is no gene flow.

• Isolated populations adapt to their own environments.

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Speciation

Natural Speciation by
Reproductive Isolation

● Reproductive Isolation

occurs when members
of population can no
longer mate
successfully with one
another and produce
fertile offspring

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● Reproductive isolation is when members of a

population cannot interbreed and produce fertile
offspring

● Reproductive isolation can occur in a variety of

ways, including
○ Behavioral isolation
○ Geographic isolation
○ Temporal isolation

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Natural Speciation by
Reproductive Isolation

● Behavioral Isolation occurs when populations

are capable of interbreeding but have
differences in courtship rituals or other types
of behavior

● Example: Eastern and Western meadowlarks

use different songs to attract mates

Natural Speciation by

Behavioral Isolation

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Behavioral Isolation

Meadowlarks

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Eastern Meadowlark

Western Meadowlark

● Geographical Isolation-Two populations are separated by

geographical barriers

● Geographical barriers: Mountain ranges, Deep

canyons, Bodies of water

○ Example:A population of Abert squirrels was separated

by the Colorado river and they evolved into two distinct
species

Natural Speciation by
Geographic Isolation

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Geographical Isolation

Kaibab and Abert squirrels

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● Temporal Isolation- Members of the same species

reproduce at different times

● Examples:

■ Plants that flower at different times

■ Animals that mate or nest build at different times

Natural Speciation by

Temporal Isolation

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Temporal Isolation

● Speciation often occurs in patterns

● A pattern of punctuated equilibrium exists in the fossil

record

○ Episodes of speciation occur suddenly in geologic time

○ Followed by long periods of little evolutionary change

○ Revised Darwin’s idea that species arose through gradual

transformations

Speciation

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