1. AP Environmental Science Mr. Grant Lesson 27
Evolution, Biodiversity, and Population Ecology
Evolution as the Wellspring of Earth’s Biodiversity

2. Objectives: Define the terms evolution and natural selection.
Explain the process of natural selection and cite evidence for this process.
Describe the ways in which evolution influences biodiversity.
Discuss reasons for species extinction and mass extinction events.

3. Define the terms evolution and natural selection.
Evolution: Genetically based change in the appearance, functioning, and/or behavior of organisms across generations, often by the process of natural selection.
Natural Selection: The process by which traits that enhance survival and reproduction are passed on more frequently to future generations of organism than those that do not, thus altering the genetic make-up of populations through time. Natural selection acts on genetic variation and is a primary driver of evolution.

4. Striking gold in Costa Rica
In 1964, Golden toads were discovered in Monteverde, Costa Rica
The mountainous cloud forest has a perfect climate for amphibians
They became extinct within 25 years
Climate change’s drying effect on the forest
A lethal fungus

5. Explain the process of natural selection and cite evidence for this process.
Because organisms produce excess young, individuals vary in their traits, and many traits are inherited, some individuals will prove better at surviving and reproducing. Their genes will be passed on and become more prominent in future generations.
Mutations and recombination provide the genetic variation for natural selection.
We have produced out pets, farm animals, and crop plants through artificial selection.

6. Evolution generates biodiversity
Species = a population or group of populations
Whose members share characteristics
They can breed with one another and 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

7. Natural selection Evolution may be random
Or directed by natural selection
Natural Selection = traits that enhance survival and reproduction
Are passed on more frequently to future generations
Than those that do not

8. Evolution by natural selection
It is one of the best-supported and most illuminating concepts in all science
It is the standpoint of modern biology
We must understand it to appreciate environmental science
Knowing ecology and learning the history of life
Evolutionary processes influence pesticide resistance, agriculture, medicine, health, etc.
In 1858, both Darwin and Wallace proposed natural selection as the mechanism of evolution

9. Natural selection shapes organisms
Premises of natural selection:
Organisms struggle to survive and reproduce
Organisms produce more offspring than can survive
Individuals of a species vary in their characteristics due to genes and the environment
Some individuals are better suited to their environment and reproduce more effectively
Natural selection acts on genetic variation

10. Genetic variation
Adaptation = the process where, over time, characteristics (traits) that lead to better reproductive success
Become more prevalent in the population
Adaptive trait (adaptation) = a trait that promotes reproductive success
Mutations = accidental changes in DNA that may be passed on to the next generation
Non-lethal mutations provide the genetic variation on which natural selection acts
Sexual reproduction also leads to variation

11. Natural selection acts on genetic variation
Natural selection changes characteristics through:
Directional selection = drives a feature in one direction
Stabilizing selection = favors intermediate traits
Preserving the status quo
Disruptive selection = traits diverge in two or more directions

12. Environmental conditions affect selection
Environmental conditions determine the pressures natural selection exerts
These pressures affect who survives and reproduces
Traits evolve that allow success in that environment
But traits that promote success at one time or place may not do so at another
Natural selection weeds out unfit individuals
It also elaborates and diversifies traits that may produce new species

13. Selective pressures influence adaptation
Related species in different environments
Experience different pressures
Evolve different traits
Convergent evolution = unrelated species may evolve similar traits
Because they live in similar environments

14. 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 variety of dog breeds and food crops

15. Describe the ways in which evolution results in biodiversity.
Natural selection can act as a diversifying force as species adapt to their environments in myriad ways.
Speciation by geographic isolation (and other means) produces new species.
The branching patterns of phylogenetic trees reflect the historical pattern by which lineages of organisms have diverged.
The fossil record informs us about life’s history

16. Evolution generates biological diversity
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

17. Speciation produces new types of organisms
The process of generating new species from a single species
Allopatric speciation: species formation due to physical separation of populations
The main mode of speciation
Populations can be separated by glaciers, rivers, mountains
Each population gets its own set of mutations

18. Another type of speciation
Sympatric speciation = species form from populations that become reproductively isolated within the same area
Feed in different areas
Mate in different seasons
Hybridization between two species
Mutations

19. Speciation results in diverse life forms
How do major groups diverge over time?
Phylogenetic trees (cladograms) = show relationships among species, groups, genes, etc.
Scientists can trace how certain traits evolved

20. The fossil record Fossil: an imprint in stone of a dead organism
Fossil record: the cumulative body of fossils worldwide
The fossil record shows:
Life has existed on Earth for at least 3.5 billion years
Earlier types of organisms evolved into later ones
The number of species has increased over time
Most species have gone extinct
There have been several mass extinctions in the past

21. Discuss reasons for species extinction and mass extinction events.
Extinction may occur when species that are highly specialized or that have small populations encounter rapid environmental change.
Earth’s life has experienced five known episodes of mass extinction, which were due to asteroid impact and possibly volcanism and other factors.
Today, human impact may be initiating a sixth mass extinction.

22. Extinction 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

23. Extinction is a natural process, but …
Humans profoundly affect rates of extinction
Biodiversity loss affects people directly
Food, fiber, medicine, ecosystem services

24. Some species are more vulnerable to extinction
Extinction occurs when the environment changes rapidly
Natural selection can not keep up
Many factors cause extinction:
Severe weather, climate change, changing sea levels
New species, small populations
Specialized species
Endemic species = a species only exists in a certain, specialized area
Very susceptible to extinction
These species usually have small populations

25. Many U.S. amphibian species are vulnerable
Many U.S. amphibians have very small ranges
They are vulnerable to extinction
The Yosemite toad, Houston toad, Florida bog frog
40 salamander species are restricted to areas the size of a typical county
Some U.S. salamander species live on top of single mountains

26. Earth has had several mass extinctions
Background extinction rate = extinction usually occurs 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
Dinosaurs went extinct
End-Permian event: 250 million years ago
75-95% of all species went extinct

27. The sixth mass extinction is upon us
Humans are causing the sixth mass extinction event
Resource depletion, population growth, development
Destruction of natural habitats
Hunting and harvesting of species
Introduction of non-native species
It is 100-1,000 times higher than the background rate and rising
Amphibians are disappearing the fastest
170 species have already vanished
It will take millions of years for life to recover

28. The geologic record

29. Macroevolution