© 2011 pearson education, inc. ap environmental science mr. grant lesson 27 evolution,...

© 2011 Pearson Education, Inc.

AP Environmental Science

Mr. Grant

Lesson 27

Evolution, Biodiversity, and

Population Ecology

Evolution: The Source of Earth’s

Biodiversity


Objectives:

• Define the terms evolution and natural selection.

• Explain natural selection and cite evidence for this process.

• Describe how evolution influences biodiversity.

• Discuss reasons for species extinction and mass extinction events.


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.


Explain natural selection and cite evidence for this process.


Evolution: The Source of Earth’s 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 = change over time Biological evolution = change in populations of

organisms over generations

Genetic changes lead to changes in appearance, functioning, or behavior


Evolution: The Source of Earth’s Biodiversity Genetic changes in evolution may be random

But may be directed by natural selection

Natural selection = process in which traits that enhance survival and reproduction are passed on more frequently to future generations than those that do not Genetic makeup of future populations is changed


Evolution: The Source of Earth’s Biodiversity

Evolution is one of the best-supported and most illuminating concepts in all science It is the foundation of modern biology

We must understand it to appreciate environmental science Understanding how species change over time and

adapt to their surroundings is crucial for comprehending ecology and the history of life

Evolutionary processes influence pesticide resistance, agriculture, medicine, health, etc.


Natural selection shapes organisms and diversity In 1858, both Darwin and Wallace proposed natural

selection as the mechanism of evolution 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

Organisms with better adapted traits will produce more offspring


Natural selection shapes organisms and diversity 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


Directional selection = drives a feature in one direction


Selective pressures from the environment influence adaptation

Related species in different environments experience different pressures and evolve different traits.

Divergent Evolution - The process by which a species evolves into two or more descendant or different forms


Convergent evolution = unrelated species may acquire similar traits because they live in similar environments


Evidence of natural selection is all around us It is evident in every adaptation of every organism Artificial selection = the process of selection

conducted under human direction Produced the great variety of dog breeds and food

crops


Describe how evolution influences biodiversity.


Evolution generates biodiversity

Biological diversity (biodiversity) = the variety of life across all levels of biological organization Species

Genes

Populations

Communities

Scientists have described 1.8 million species Estimates of the total number of species that exist

range from 3 million to 100 million

Biodiversity exists nearly everywhere


Speciation produces new types oforganisms

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

Natural selection can speed the process


We can infer the history of life’s diversification by comparing organisms How did the major groups of

organisms come to be?

Phylogenetic trees = diagrams that show relationships among species, groups, genes, etc.

Scientists can trace how certain traits evolved

Some traits evolved and were passed on

Other traits evolved more than once (e.g., the ability to fly)


We can infer the history of life’s diversification by comparing organisms Knowing how organisms are related to one another helps

scientists organize and name them

Categories reflect evolutionary relationships

Scientists use physical and genetic characteristics to organize

Each species gets a two-part Latinized scientific name


The fossil record teaches us about life’s long history

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


Discuss reasons for species extinction and mass extinction events.


Speciation and extinction together determine Earth’s biodiversity

Extinction = the disappearance of a species from Earth Species last 1–10 million years

Extinction has historically been a natural occurrence The loss of a species is irreversible

Number of species in existence = speciation

extinction


Speciation and extinction together determine Earth’s biodiversity

Human activity profoundly affects rates of extinction Biodiversity loss affects people directly

Food, fiber, medicine, ecosystem services


Some species are especially vulnerable to extinction

Extinction can occur when the environment changes rapidly and natural selection can not keep up

Many factors cause extinction: Severe weather, climate change, changing sea levels

Arrival of new species

Being a small population or specialized species


Some species are especially vulnerable to extinction

Endemic species = a species that only exists in a certain, specialized area Very susceptible to extinction

Usually have small populations

Island species are often endemic and thus at risk


Some species are especially vulnerable to extinction Many U.S. amphibians have very small ranges

They are vulnerable to extinction

For example, the Yosemite toad, Houston toad, Florida bog frog

Forty salamander species are restricted to areas the size of a typical county

Some U.S. salamander

species live on top

of single mountains


Earth has seen several episodes of mass extinctions Background extinction rate = a constant, slow rate

of extinction that occurs as a part of evolution Mass extinction events = episodes that killed off

massive numbers of species at once Occurred five times in Earth’s history

50–95% of all species go 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


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

Today’s extinction rate is 100–1000 times higher than the background rate and rising

It will take millions of years for life to recover

© 2011 pearson education, inc. ap environmental science mr. grant lesson 27 evolution,...

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