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Chapter 15
Origins of Biological Diversity
How do biologists identify species?
How do species arise?
15.1- The Diversity of Life is Based
on the Origin of New Species
What is a Species?

Biological Species Concept: a species is a
population or group of populations whose
members can breed with one another in nature &
produce fertile offspring.

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One species cannot interbred with members of other
species.
Concept helps biologists understand the origin of new
species.
15.1 Notes…
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From Microevolution to Macroevolution
Microevolution: change in allele frequencies in a
population.
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Evolution on small scale, explains how pop. evolve.
Macroevolution: major evolutionary changes
evident in the fossil record
1.
2.
3.
Speciation- origin of new species
Extinction of species
Evolution of new features = wings or flowers
15.1 Notes…
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Reproductive Barriers Between Species
Reproductive Isolation: inability of different
species to interbreed.
Types of Barriers:
1.
2.
Timing- Different breeding seasons.
e.g. Western spotted skunks breed in fall, eastern
skunks breed in late winter. Coexist in Great Plains.
Behavior- Different courtship or mating behaviors.
e.g. Eastern & western meadowlarks coexist in central
U.S. but have different mating songs.
15.1 Notes…
3)
4.
Habitat- Different habitats in same location.
e.g. 2 species of stickleback fish in lakes in BC,
Canada. One feeds on bottom & other lives in
open water.
Reproductive Incompatibility


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Physically Impossible
In plants, insects only pollinate a single species
Hybrid zygote fails to develop
Adult offspring is infertile, e.g. mules
15.1 Notes…
Geographic Isolation and
Speciation
Geographic Isolation: separation
of populations as a result of
geographic change or dispersal
to geographically isolated places.
e.g. Grand Canyon & 2 species of
Antelope squirrels
 Isolated pop. evolves new adaptations to changed
environment. (Genetic Drift, Nat. Selection)
 Speciation occurs if pop. can no longer breed with other
pop.

15.1 Notes…
Adaptive Radiation
Adaptive radiation: evolution from common ancestor
that results in diverse species adapted to different
environments.
e.g. native species of Hawaiian islands

1.
2.
3.
4.


Species A arrives from mainland
Species B evolves from A & colonizes nearby
island
Species C evolves from B & colonizes nearby
island
↓
Due to Genetic Drift & adapting to new environment.
Geographic isolation prevents species from breeding
with parent pop.
15.1 Notes…
The Tempo of Speciation
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Punctuated Equilibrium: Model suggesting species
often diverge in spurts of relatively rapid change,
followed by long periods of little change.
Speciation can be rapid. In a few thousand
generations, GD & N. Selection can cause change
in a small population occupying a new
environment. Relatively short amt. of time
compared to the 1-5 million years a species could
last.
15.2-Evolution is Usually a
Remodeling Process

Refinement of Existing Adaptations
Some complex structures, such as eyes in mammals,
evolve in small steps of adaptation from simpler structures.
15.2 Notes…
Adaptation of Existing Structures
to New Functions

Some structures or materials
adapt for certain functions and
later fulfill different functions.


Chitin (exoskeleton for
arthropods-insects, spiders,
scorpions & lobsters)
Flippers of penguins
15.2 Notes…
Evolution and Development

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What is the genetic basis for evolutionary remodeling of
body form?
Embryology: study of the processes of multicellular
organisms as they develop from fertilized eggs to
formed organisms.
Possible Causes:


Mutations in the genes that control the early development of
the organism.
e.g. mutation causing fly to grow legs in place of antennae
Change in rate or timing of events in development.
e.g. adaptation of feet in salamander species
15.3- The Fossil Record Provides
Evidence of Life’s History
How Fossils Form


Fossils form from
remains of organisms
buried by sediments,
dust or ash.
Consist as footprints,
animal burrows or
impressions.

Rare fossils contain
organic matter.
15.3 Notes…

The Fossil Record & Geologic Time Scale
Geologic Time Scale: Earth’s history is organized
into 4 distinct ages:
Precambrian Era
Paleozoic Era
Mesozoic Era
Cenozoic Era


→
Periods
→
Epochs
Boundaries between eras show major change in the forms
of life found in the fossil record
Boundaries between eras and some periods are also
marked by extinctions
15.3 Notes
Dating Fossils

Radiometric dating: measurement of
certain radioactive isotopes in
objects.

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Half-life: the number of years it takes for 50% of
the original isotope samples to decay.
Volcanic rock layers are dated with radioactive
isotopes in order to estimate the age of the
fossils found between them.
e.g. uranium-238
“Carbon dating”-Used to date recent fossils
containing carbon-12 and carbon-14.
15.3 Notes
Continental Drift and Macroevolution
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Continental Drift: motion of continents about
earth’s surface on plates of crust floating on
the hot mantle.
Two major events in history:
1.
End of Paleozoic Era, 250mya, all land
masses moved together into a
“supercontinent” called Pangaea.

2.
Led to environmental changes, competition
between species and mass extinction.
e.g. Fossils found in West Africa & Brazil
are the same.
During Mesozoic Era,180mya, continents
drifted apart.

Species evolved independently
e.g. plants and animals of Australia
15.3 Notes
Mass Extinctions
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
Fossil records shows long
periods of stability broken by
episodes of mass extinction, or
great species loss.
5-6 periods of mass extinction
over last 600 million years.
e.g. 65mya, end of Cretaceous
period, large # of species are lost,
including dinosaurs. Possible causes
are cooling temp., shallow seas & a
meteor that struck earth.
Meteor Impact near Yucatan
Peninsula in Mexico

Surviving species undergo
adaptive radiation
15.4- Modern Taxonomy Reflects
Evolutionary History
What is Taxonomy?


Taxonomy: branch of biology that involves the
identification, naming, and classification of
species.
Goals of taxonomy


assign a universal scientific name to each know species.
Organize and classify species into larger groups of related
species.
15.4 Notes
The Linnaean System of Classification

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Most widely used system developed by
Carolus Linnaeus.
This system has binomial, or two-part
name, for each species.
 1st = the genus which species
belongs
2nd= refers to one species within
genus
e.g. Panthera pardus = leopard
It also orders species into a hierarchy
of broader groups.
15.4 Notes
Classification and Evolution
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Biologists use phylogenetic trees and classifications to represent
hypotheses about evolutionary history
Phylogenetic Tree: branching diagram, suggesting evolutionary
relationships, that classifies species into groups within groups.
Homologous structures
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e.g. bats’ wings and whales’ flippers
Function differently in different species but have basic underlying similarities if evolved from a
structure in a common ancestor
The greater # of homologous structures two species have, the more closely related.
Analogous Structures
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Similar adaptations that result from convergent evolution, or the process in which unrelated
species from similar environments have adaptations that seem similar.
e.g. wings of insects and wings of birds
Not to be mistaken for homologous structures. Structures are not inherited from a common
ancestor, they evolved independently & are built from different structures.
15.4 Notes
Molecular Data as a Taxonomic Tool

Relatedness of species can be measured by
comparing their genes & proteins.
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Provides a way to test hypotheses about
evolutionary history.
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The more sequences that match up, the more closely related
When independent types of evidence support the same
hypothesis, it is strengthened.
e.g. Fossil evidence & molecular data both suggest whales and a
group of mammals (hippos, cows, deer & pigs) are closely related.
Paired with computer technology, provides a
new way to build phylogentic trees
15.4 Notes
A Closer Look at Phylogenetic Trees
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Clade: Evolutionary branch in a phylogenetic tree.
 Clades can nest within larger clades.
 Every clade consists of an ancestral species and all its descendants.
Cladistics: Method of determining sequencing of branching in a phylogenetic tree.
 All the organisms of a clade must share homologous structures, that do not occur
outside the clade.
 Derived characters: unique features that unite the organisms as a clade.
(homologous structures)
15.4 Notes

Cladogram: phylogenetic
diagram that specifies
the derived characters of
clades.
 Used by taxonomists
to show relationships
among organisms.
15.4 Notes

Comparing Classification Schemes
Two & Three-Kingdom Schemes
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Five Kingdom scheme
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2 kingdom system divided life forms between the
plant and animal system. Prevailed for 200 years,
but had problems & was replaced.
3 kingdom system added protists as a new
category, but the model failed over time.
Includes: plants, fungi, animals, protists and
monera
Three Domains
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Based on molecular data.
Within each domain there are multiple kingdoms.