What 2 things are necessary to define a species?

Economic Evolutionary Domain (Macroevolution)

Overall outcomes of evolution creates (and destroys/extinction) species.

These are members of different species - eastern (left) and western (right) meadowlark.

How many species is this?

.

What mode of selection leads to the development of a new species? WHY?

Disruptive/Diversifying!

Timing of speciation

Branching pattern called punctuated equilibrium (branching) is the widely accepted model called

cladogenesis. (Gradualism called anagenesis, is not supported with any evidence!)

This means that organisms are relatively static (stable) in their phenotypic expression until a drastic

environmental force occurs, then there are periods of great phenotypic change again followed by

periods of calm.

Reproductive isolation ends in speciation as if you can’t

get to each other, you can’t interbreed!

Two ways to stop gene flow. (Isolate):

Externally (extrinsic) separate meaning due to an

outside force and then once separated 2) Internally

(intrinsic) separate meaning due to reproductive

isolating mechanisms. (Which has to happen first?)

Geographic isolation (vicariances) are the causes of

extrinsic separation. There are 2 types of this;

1) Allopatric speciation- separation caused by a

physical barrier

2) Parapatric speciation–separation caused by unique

habitat adaptations. (Niches)

Allopatric Speciation

Harris’ antelope squirrel White-tailed antelope squirrel

Once populations are separated, each population/species continues to evolve

independently of the other group.

Therefore even if they were allowed physical contact, they don’t “recognize” each

other as mates. Recognition means economic or codical recognition!

The mechanisms that maintain the integrity of a species are called

Sympatric speciation mechanisms. These mechanisms preserve the 2 species

and maintain their separation. (Internal mechanisms).

Isolation can cause rapid exaptations as organisms face new challenges

in new environments.

So what happens after they are separated and enough time goes

by…..

Sympatric Mechanisms Are Always Required to MAINTAIN

Speciation

Internal mechanisms involve changes to organisms that prevent

Interbreeding, EVEN if they try!!

Once either allopatric or parapatric speciation occurs (external),

than internal mechanisms come into play. (AFTER the

populations are physically/habitat separated.)

Harris’ antelope squirrel White-tailed antelope squirrel

2 areas where sympatric speciation

mechanisms can be actively maintaining the

“separateness” of each species:

• 1) Pre-zygotic-pressures/mechanisms that

keep fertile/viable offspring from

developing BEFORE a zygote is formed

• 2) Post-zygotic-pressures that keep

fertile/viable offspring from developing

AFTER a zygote forms

4 PREZYGOTIC Mechanisms

1) Behavioral- courtship rituals do not match

up.

2) Mechanical- anatomical differences.

3) Gametic- chromosome # too different

4) Temporal- Breeding seasons do not match

http://www.youtube.com/watch?v=eI_quJRRGxk&t=138s

http://www.youtube.com/watch?v=VDhNutbXpFE

http://www.youtube.com/watch?v=L54bxmZy_NE&feature=related /

http://www.youtube.com/watch?v=VjE0Kdfos4Y&t=115s

http://www.youtube.com/watch?v=GPbWJPsBPdA

https://www.youtube.com/watch?v=1XkPeN3AWIE 1:49

POSTZYGOTIC MECHANISMS- Occur after the egg and

sperm fuse, but no new species made!

http://www.youtube.com/watch?v=1zOWYj59BXI&t=87s

Species Come and Go

Evolutionary process does NOT produce the perfect organisms for

all time. It produces the best possible for a given set of standards.

(environmental) Best estimates from the fossil record indicate that

greater than 99% of species that have ever existed are now extinct.

A typical “lifetime” for a species is

about 1 million years.

Mass Extinctions Are a Fact of Life

Gary Larson

The Cretaceous/Tertiary Mass Extinction

The Linnaean

Hierarchical

Classification System

ADD DOMAIN!

A Better Way to Classify Organisms

Ideally, classification is based on establishing the evolutionary relationships

between organisms.

Cladistics is the method

of classification based

on establishing

phylogenies (i.e. getting

at evolutionary

relationships.

The evolutionary relationship between organisms is their phylogeny.

Cladistics proceeds by

comparing shared

ancestral and shared

derived characters

between sets of

organisms.

Results of Cladistic Analyses Sometimes Run Counter to Classical

Classification Schemes

Which pair is more closely related? A lizard/crocodile or bird/crocodile?