Download Evolution and Speciation

*
Chapter 3
*Central Case Study: Striking
Gold in a Costa Rican Cloud
Forest
* Golden toads were discovered in Monteverde, Costa
Rica in 1964
* 200 males in a 16-ft. area
* The mountainous cloud forest
was
ideal for amphibians
* The toads vanished from Earth
within 25
years
* Climate change caused the
dry out
* A fungus also killed them
forest to
*Evolution is the wellspring of
biodiversity
* Species: a population or group of populations …
* Whose members share characteristics and ….
* Can breed with each other to produce fertile offspring
* Population: a group of individuals of a species that live in the
same area
* Evolution: means change over time
* Biological evolution: genetic change in populations over time
* Genetic changes lead to changes in appearance, functioning, or
behavior over generations
*Natural selection
* Evolution may be random
* Or directed by natural selection
* Natural selection: The process whereby inherited characteristics
that enhance survival and reproduction …
* Are passed on more frequently to future generations than those that
do not
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• It is one of the best-supported and most illuminating
concepts in science
– It is the foundation of modern biology
• It is vital for a full appreciation of environmental
science
– Knowing ecology and learning the history of life
• Evolutionary processes influence agriculture, pesticide
resistance, medicine, health, etc.
• In 1858, both Darwin and Wallace proposed natural
selection as the mechanism of evolution
*Natural selection shapes
*
*
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organisms
Natural selection explains nature’s patterns
Premises of natural selection:
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*
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Organisms struggle to survive and reproduce
*
Some individuals are better suited to their environment and
reproduce more effectively
They produce more offspring than can survive
Individuals of a species vary in their characteristics because of
genes and the environment
Natural selection acts on genetic variation
*Species adapt to the
environment
* A parent that produces more offspring passes on more genes to
future generations
* Over time, characteristics (traits) that lead to better reproductive
success become more prevalent
* Adaptive trait (adaptation): a trait that promotes reproductive
success
* Sexual reproduction also leads to genetic variation
* Producing new combinations of genes
* Environmental conditions determine the pressures of natural
selection
* Organisms need time to adapt to changing conditions
*
* Natural selection weeds out unfit
individuals
* It also helps elaborate and
diversify traits
* Which leads to the formation of
new species
*Evidence of natural selection
is everywhere
* It is evident in every adaptation of every organism
* Artificial selection: the process of selection conducted under
human direction
* Producing the great diversity of dog breeds and crops
*
* Biological diversity (biodiversity): the variety of life across all
levels of biological organization
* Species
* Genes
* Populations
* Communities
* Scientists have described 1.8 million species
* Up to 100 million species may exist
* Tropical rainforests are rich in biodiversity
*Speciation produces new types
of organisms
* The process of generating new species
from a single species
* Allopatric speciation: species form as
a result of physical separation of
populations
* The main mode of speciation
* Populations can be separated by
glaciers, rivers, mountains
* Each population, with its own set of
mutations, diverges
*Speciation results in
diverse life forms
* How do major groups diverge over time?
* Phylogenetic trees: branching diagrams show relationships
among species, groups, genes, etc.
* Represent life’s history
*
* Fossil: an imprint in stone of a dead organism
* Fossil record: the cumulative body of fossils worldwide
* Phylogenetic trees and the fossil record show:
* Life has existed on Earth for 3.5 billion years
* Life evolved complex structures from simple ones
* Life evolved large sizes from small ones
* But natural selection can also favor simplicity and small size
*Extinction
* Most species that once lived are now
gone
* Extinction: the disappearance of a
species from Earth
* Species last 1–10 million years
* Biological diversity is now being lost at
an astounding rate
* This loss of species is irreversible
Number of species = speciation – extinction
*Some species are vulnerable
to extinction
* Extinction occurs when the environment changes rapidly
* Natural selection can’t keep up, so species can’t adapt
* Many factors cause extinction:
* Climate change, changing sea levels, severe weather
* Arrival of new species, small populations
* Specialized species
* Endemic species: exists only in a certain, specialized area
* Very susceptible to extinction
* These species usually have small populations
* Earth has had several mass
extinctions
* Background extinction rate: extinction usually occurs slowly,
one species at a time
•
Mass extinction events: killed off massive
numbers of species at once
*
*
•
Occurred five times in Earth’s history
50–95% of all species went extinct at one time
Cretaceous-Tertiary (K-T) event: 65 million years
ago
*
A gigantic asteroid caused dinosaur extinction
* End-Permian event: 250 million years ago
*
75–95% of species went extinct from unknown
causes
*
* Humans are causing the sixth mass extinction event
* Population growth, development, resource depletion
* Destruction of natural habitats
* Hunting and harvesting of species
* Introduction of non-native species
* This loss affects humans
* We need organisms for food, fiber, medicine, services
* Amphibians are disappearing faster than any other group
* 170 species have already vanished