Download What Is a Species?

CHAPTER 14
How Biological Diversity
Evolves
PowerPoint® Lectures for
Essential Biology, Third Edition
– Neil Campbell, Jane Reece, and Eric Simon
Essential Biology with Physiology, Second Edition
– Neil Campbell, Jane Reece, and Eric Simon
Lectures by Chris C. Romero
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Biology and Society:
One Troublesome Species or Two?
• Mosquitoes have assumed a more serious role in
public health since the outbreak of West Nile virus.
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Figure 14.1
• All mosquitoes look roughly alike.
– But close examination reveals many distinct
species, two of which may bite birds or people.
• DNA comparisons between North American and
European species
– Have revealed mosquito hybrids in North
America that bite both birds and people and are
more likely to spread West Nile virus.
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Macroevolution and the Diversity of Life
• Macroevolution
– Encompasses the major biological changes
evident in the fossil record.
– Includes the formation of new species.
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• Speciation
– Is the focal point of macroevolution.
– May occur based on two contrasting patterns.
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• In nonbranching evolution, a population transforms
but does not create a new species.
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Figure 14.2a
• In branching evolution, one or more new species
branch from a parent species that may continue to
exist.
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• The biological species concept defines a species as
– A population or group of populations whose
members have the potential to interbreed and
produce fertile offspring.
Figure 14.2b
The Origin of Species
• Species is a Latin word meaning “kind” or
“appearance.”
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What Is a Species?
Galápagos Sea Lion
Galápagos Tortoise
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Figure 14.3
• The biological species concept cannot be applied in
all situations, for example, with fossils and asexual
organisms.
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Reproductive Barriers between Species
• Prezygotic barriers prevent mating between
species.
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Figure 14.4
• Prezygotic barriers include
– Temporal isolation.
– Habitat isolation.
– Mechanical isolation.
– Gametic isolation.
Albatross Courtship Ritual
Giraffe Courtship Ritual
Blue-Footed Boobies Courtship Ritual
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• Behavioral isolation
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Figure 14.5
• Postzygotic barriers
– Are mechanisms that operate should interspecies
mating actually occur and form hybrid zygotes.
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• Postzygotic barriers include
– Hybrid inviability.
– Hybrid sterility.
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Figure 14.6
Mechanisms of Speciation
• A key event in the potential origin of a species
occurs when a population is somehow severed from
other populations of the parent species.
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• The two modes of speciation are
– Allopatric speciation.
– Sympatric speciation.
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Figure 14.7
Allopatric Speciation
• Geologic processes
– Can fragment a population into two or more
isolated populations.
– Can contribute to allopatric speciation.
Galápagos Islands Overview
Grand Canyon
Galápagos Marine Iguana
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Figure 14.8
• Speciation occurs only with the evolution of
reproductive barriers between the isolated
population and its parent population.
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Figure 14.9
Sympatric Speciation
• Sympatric speciation occurs if a genetic change
produces a reproductive barrier between mutants
and the parent population.
– Polyploidy, a mechanism of sympatric speciation,
was first observed by Hugo de Vries.
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Figure 14.10
• Polyploids
– Can originate from accidents during cell division.
– Can result from the hybridization of two parent
species.
• Many domesticated plants are the result of
sympatric speciation.
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Figure 14.11
What Is the Tempo of Speciation?
• Traditional evolutionary trees diagram the descent
of species as gradual divergence.
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Figure 14.12a
• Punctuated equilibrium
– Is a contrasting model of evolution.
– States that species most often diverge in spurts of
relatively sudden change.
– Accounts for the relative rarity of transitional
fossils.
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Figure 14.12b
The Evolution of Biological Novelty
• What accounts for the evolution of biological
novelty?
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Adaptation of Old Structures for New Functions
• Birds
– Are derived from a lineage of earthbound reptiles.
– Developed from flightless ancestors, but how?
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Figure 14.13
• Exaptation
– Involves a structure that evolves in one context
gradually becoming adapted for other functions.
– Is a mechanism for novel features to arise
gradually through a series of intermediate stages.
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“Evo-Devo”: Development and
Evolutionary Novelty
• A subtle change in developmental genes can have
profound effects.
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• Paedomorphosis
– Is the retention of juvenile body features in the
adult.
– Is important in human evolution.
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Figure 14.14
Figure 14.15
Earth History and Macroevolution
• Macroevolution
– Is closely tied to the history of the Earth.
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Geologic Time and the Fossil Record
• The fossil record
– Is an archive of macroevolution.
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Figure 14.16
• Geologists have established a geologic time scale
reflecting a consistent sequence of geologic
periods.
The Geologic Record
Macroevolution
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Table 14.1
• Radiometric dating
– Is the most common method for dating fossils.
– Has helped establish the geologic time scale.
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Figure 14.17a
Figure 14.17b
Plate Tectonics and Macroevolution
• The continents are not locked in place.
– They drift about Earth’s surface on plates of crust
floating on a flexible layer called the mantle.
• California’s infamous San Andreas fault
– Is at a border where two plates slide past each
other.
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Figure 14.18
• About 250 million years ago
– Plate movements formed the supercontinent
Pangaea.
– Many extinctions occurred, allowing survivors to
diversify.
Lava Flow
Volcanic Eruption
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Figure 14.19
• About 180 million years ago
– Pangaea began to break up, causing geographic
isolation.
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Mass Extinctions and Explosive
Diversifications of Life
• The fossil record reveals an episodic history,
– With long, relatively stable periods punctuated by
briefer intervals when the turnover in species
composition was much more extensive.
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• Extinction is inevitable in a changing world and
occurs all the time.
– However, extinction rates have not been steady.
• Extinctions typically eliminate various species of
organisms
– And are followed by explosive diversifications of
organisms.
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The Process of Science:
Did a Meteor Kill the Dinosaurs?
• Scientists believe that about 65 million years ago,
at the end of the Cretaceous period,
– A meteor impact contributed to the extinction of
the dinosaurs.
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Figure 14.20
Classifying the Diversity of Life
• Systematics
– Is the study of the diversity and relationships of
organisms, both past and present.
• Taxonomy
– Is the identification, naming, and classification of
species.
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Some Basics of Taxonomy
• Carolus Linnaeus
– Developed the formal naming system used today.
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Naming Species
• Each species is assigned a two-part name or
binomial, consisting of the genus and the species.
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Hierarchical Classification
• The taxonomic hierarchy
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Figure 14.21
Classification and Phylogeny
• The goal of classification is to reflect phylogeny,
the evolutionary history of a species.
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Figure 14.22
Sorting Homology from Analogy
• Homologous structures
– Are one of the best sources of information about
phylogenetic relationships.
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• Convergent evolution
– Involves superficially similar structures in
unrelated organisms based on natural selection.
• Analogy
– Is similarity due to convergence.
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Molecular Biology as a Tool in Systematics
• Molecular systematics
– Compares DNA and amino acid sequences
between organisms.
– Can reveal evolutionary relationships.
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Figure 14.23
The Cladistic Revolution
• Cladistics
– Is the scientific search for clades, distinctive
branches in the history of life.
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Figure 14.24
• Cladistics
– Has changed traditional classification of some
organisms.
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Figure 14.25
Arranging Life into Kingdoms:
A Work in Progress
• Linnaeus designed a two-kingdom system of
classification,
– Which was replaced by a five-kingdom system in
the mid-20th century.
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• In the late 20th century,
– Molecular studies and cladistics led to the
development of a three-domain system.
Classification Schemes
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Figure 14.26
Evolution Connection:
Just a Theory?
• Certain groups use the idea that evolution is “just a
theory”
– To discredit its validity and eliminate it from the
science curricula in our public schools.
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• The “just a theory” argument has two flaws:
– It fails to separate Darwin’s two main ideas.
– The term theory has a very different meaning in
science than in general use.
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