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How Speciation occurs during Evolution.

SPECIATION
Definition: the development of a new
species…a population of reproductively
isolated organisms
Isolating Mechanisms can be Behavioral,
Mechanical, Ecological, Temporal
Behavioral: ex. different mating rituals (blue footed
boobie)
Mechanical: parts don’t match (giraffe and a dog)
Ecological: now live in different environments-
never in the same place
Temporal: reproduce in different seasons or time of
day (nocturnal vs diurnal)
I. Divergent Evolution: the origin of new
populations from old ones, usually resulting
in 2 or more species… A genetic divergence
with a large number of trait (allele)
differences between 2 populations gene
pools. Usually occurs over a long period of
time.
Example: During the Eocene (50 mya) epoch
only 1 species of EVEN TOED mammals
existed. By the Pleistocene (1.5 mya) epoch,
multiple species existed ranging from bison,
boar, hippos, giraffe, deer, and camels!
Oreodont skeleton
Skeleton of the Eocene oreodont
Protoreodon. It was a common herd animal
42 million years ago. It is one of the
earliest oreodonts known. Oreodonts were
very successful, becoming diverse and
common. They were even toed hoofed
mammals related to deer, sheep, and pigs
From left to right:
Pig, Red Deer and Camel
A. Geographic isolation which divides
a population into 2 or more smaller
populations.
1. geographic separation habitats
which provide an isolating
opportunity
ex: islands, lakes, river, valley, mountain
ranges
2. topographic changes-
3. intermediate zonation-
geographic
separation
topographic
changes-
intermediate
zonation-
B. Without geographic barriers.
Environmental changes can result in once
isolated groups now having access to each
other.
Ex: fires, floods, climate
C. Adaptive radiation: rapid evolution of
many species from a single species.
Colonizers of geographically remote
areas which contain few competitors.
Ex: Hawaii
ADAPTIVE RADIATION
II. Parallel 2 related species that fill similar
niches in different locations and develop
similarly.
Ex: Marsupials in Australia and Placental
mammals throughout the world both developed
comparable species of wolves, cats,
anteaters, mice, etc
Parallel evolution is
the development
over time of similar
traits in unrelated
organisms due to the
constraints imposed
by similar
environments or
ways of living
III. Convergent 2 completely unrelated species
that share only similar traits…
Ex. aquatic organisms having fins include birds,
fish, and mammals which are NOT closely
related, but independently develop the best
suited traits for the environment
DIVERGENT CONVERGENT PARALLEL
IV.Coevolution - the change in one species due to
the changes in another.
Ex. Predators which change in prey capturing
efficiency will not capture all variations of
prey, which increases the variants gene pool.
Ex: flowers and pollinators
Trends of Selection: graphical representation of
gene frequency
Given a bell shape distribution of a gene (human
height, skin color), a change in the populations
frequency many skew in any of the following ways
highest frequency near
mean value
frequencies decrease
toward each extreme
value
Stabilizing selection
reduction of the extreme
variations…too tall, too short
favors the intermediate
phenotype.
Directional selection skew toward an
extreme…giraffe necks, dark skin in
Africa
favors phenotypes at one extreme.
DO YOU SEE TWO?
peppered moth
Disruptive selection toward both
extremes and reduction of
intermediates. Leads to
dimorphism in some species.
favors both extreme phenotypes.
Gradualism
Punctuated
Equilibrium
VI. Rates of Evolution -Draw