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Evolution, Biodiversity, and Population Ecology

Evolution as the Wellspring of Earth’s Biodiversity

AP Environmental Science

Mr. Grant

Lesson 27

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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.

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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.

Define the terms evolution and natural selection.

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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

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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.

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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.

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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

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Extinction is a natural process, but …

• Humans profoundly affect rates of extinction

• Biodiversity loss affects people directly

- Food, fiber, medicine, ecosystem services

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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

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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

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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

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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

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The geologic record

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Macroevolution