© 2011 Pearson Education, Inc. Lecture Outlines Chapter 3 Environment: The Science behind the Stories 4th Edition Withgott/Brennan.

© 2011 Pearson Education, Inc.

Lecture Outlines

Chapter 3

Environment:The Science behind the Stories

4th Edition

Withgott/Brennan


This lecture will help you understand:

• Natural selection

• How evolution influences biodiversity

• Reasons for species extinction

• Ecological organization

• Population characteristics

• Population ecology

• Conserving biodiversity


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


Extinction is a natural process, but …

• Humans profoundly affect rates of extinction

• Biodiversity loss affects people directly

- Food, fiber, medicine, ecosystem services


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


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


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


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


The geologic record


Macroevolution


Ecology is studied at several levels

• Ecology and evolution are tightly intertwined

• Biosphere = the total living things on Earth

- And the areas they inhabit

• Community = interacting species living in the same area

• Ecosystem = communities and the nonliving material and forces they interact with


Levels of ecological studies

• Population ecology = investigates the dynamics of population change

- The factors affecting the distribution and abundance of members of a population

- Why some populations increase and others decrease

• Community ecology = focuses on patterns of species diversity and interactions

• Ecosystem ecology = studies living and nonliving components of systems to reveal patterns

- Nutrient and energy flows


Each organism has habitat needs

• Habitat = the environment where an organism lives

- It includes living and nonliving elements

• Habitat use = each organism thrives in certain habitats, but not in others

- Results in nonrandom patterns of use

• Habitat selection = the process by which organisms actively select habitats in which to live

- Availability and quality of habitat are crucial to an organism’s well-being

- Human developments conflict with this process


A specialized frog

• Epiphytes grow on trees for support

- Obtaining water from the air

- They collect pools of rainwater and pockets of leaf litter

- Frogs lay their eggs in these rainwater pools


Habitats vary

• Habitats vary with the body size and needs of species

- A soil mite vs. an elephant

• Species have different habitat needs at different times

- Migratory birds use different habitats during migration, summer and winter

• Species use different criteria to select habitat

- Soil, topography, vegetation, other species

- Water temperature, salinity, prey

• Species survival depends on having suitable habitat


Organismal ecology: niche

• Niche = an organism’s use of resources - Along with its functional role in a community- Habitat use, food selection, role in energy and

nutrient flow, interactions with other individuals• Specialists = have narrow niches and specific needs

- Extremely good at what they do- But vulnerable when conditions change

• Generalists = species with broad niches - They use a wide array of habitats and resources- They can live in many different places


Population characteristics

• All populations show characteristics that help scientists predict their future dynamics

• Population size = the number of individual organisms present at a given time

- Numbers can increase, decrease, cycle or remain the same



• Population density = the number of individuals in a population per unit area

• Large organisms usually have low densities

- They need many resources and a large area to survive

• High densities make it easier to find mates

- But increase competition and vulnerability to predation

- Increased transmission of diseases

• Low densities make it harder to find mates

- But individuals enjoy plentiful resources and space



• Population distribution (dispersion) = spatial arrangement of organisms

• Random = haphazardly located individuals, with no pattern

• Uniform = individuals are evenly spaced

- Territoriality, competition

• Clumped = arranged according to availability of resources

- Most common in nature


• Sex ratio = proportion of males to females

- In monogamous species, a 1:1 sex ratio maximizes population growth

• Age distribution (structure) = the relative numbers of organisms of each age in a population

- Age structure diagrams (pyramids) = show the age structure of populations

• In species that continue growing as they age

- Older individuals reproduce more (i.e. a tree)

- Experience makes older individuals better breeders



Birth and death rates

• Type I: more deaths at older ages

• Type II: equal number of deaths at all ages

• Type III: more deaths at young ages

Survivorship curves = the likelihood of death varies with age


Four factors of population change

• Natality = births within the population

• Mortality = deaths within the population

• Immigration = arrival of individuals from outside the population

• Emigration = departure of individuals from the population

• Births and immigration add individuals

- Deaths and emigration remove individuals

• Crude birth (death) rates: number of births (deaths) per 1000 individuals per year


Population growth rate

• Natural rate of population growth =

(Crude birth rate) – (crude death rate)

- Population change due to internal factors

• Population growth rate =

(Crude birth rate + immigration rate) – (Crude death rate + emigration rate)

- Net changes in a population’s size/1000/year

• Growth rate as a percent =

- Population growth rate * 100%

- Populations of different sizes can be compared


Exponential population growth

• Exponential growth- A population increases by a

fixed percent- Graphed as a J-shaped

curve• Exponential growth cannot

be sustained indefinitely• It occurs in nature with a:

- Small population- Low competition- Ideal conditions


Limiting factors restrain population growth

• Limiting factors = physical, chemical and biological attributes of the environment

- They restrain population growth

• Environmental resistance = all limiting factors taken together

- Stabilizes the population size

- Space, food, water, mates, shelter, suitable breeding sites, temperature, disease, predators

- Aquatic systems: salinity, sunlight, temperature, etc.


Carrying capacity

• Carrying capacity = the maximum population size of a species that its environment can sustain

• Limiting factors slow and stop exponential growth

- An S-shaped logistic growth curve

Many factors contribute to environmental resistance and influence a population’s growth rate and carrying capacity


Population density impacts limiting factors

• Density-dependent factors = limiting factors whose influence is affected by population density

- Increased density increases the risk of predation and competition for mates

- Results in the logistic growth curve

- Larger populations have stronger environmental resistance

• Density-independent factors = limiting factors whose influence is not affected by population density

- Events such as floods, fires, and landslides


Perfect logistic curves aren’t often found


Carrying capacities can change

• Environments are complex and ever-changing

- Changing carrying capacities

• Humans lower environmental resistance for themselves

- Increasing our carrying capacity

- Technologies overcome limiting factors

• By increasing carrying capacity for humans

- We have reduced the carrying capacity for countless other organisms

- Calling into question our own long-term survival


Reproductive strategies vary among species

• Biotic potential = an organism’s capacity to produce offspring

• K-selected species = species with long gestation periods and few offspring

- Have a low biotic potential

- Stabilize at or near carrying capacity

- Good competitors

• r-selected species = species which reproduce quickly

- Have a high biotic potential

- Little parental care, populations fluctuate greatly


Population changes affect communities

• As the population of one species declines, other species may appear

• Human development displaces other species and threatens biodiversity

• As Monteverde dried out, species disappeared

- Golden toads, harlequin frogs and more had been pushed from their cloud-forest habitat into extinction

- 20 of 50 frog species, 2 lizard species went extinct

• Species from lower, drier habitats appeared

- 15 species tolerant of drier conditions had moved in


Conserving biodiversity

• Human development, resource extraction and population pressure are speeding changes

- In populations and communities

• Impacts threatening biodiversity have complex social, economic and political roots

- We must understand these factors to solve problems


Costa Rica and its environment

• Past economic and social forces still threaten Costa Rica’s species and ecological communities

- Lush forests are seen as obstacles to agriculture and for timber

- The country’s population grew to 3.34 million

- Pasture land increased from 12% to 33%

- Forests decreased from 80% to 25%

- Species were declining and becoming endangered


Costa Rica’s species were in danger

• Few people saw the need to conserve biological resources

- Until it became clear they were being rapidly lost


Costa Rica is protecting its environment

• The privately managed 10,500 ha (26,000 acre) Monteverde Cloud Forest Reserve was founded in 1972

- To protect the forest, its plants and animals

• Costa Rica created the country’s first national parks and protected areas in 1970

- Centered on areas of spectacular scenery

- Protecting valuable tropical dry forests, turtle nesting beaches, coral reef systems

• Government support remains strong

- Over 25% of its land is under some type of protection


Costa Rico’s protection is paying off• Ecotourism: tourists visit protected areas

- Providing thousands of jobs and billions of dollars to local economies

• But parks are still under-protected and underfunded

- Restoration is a step beyond preservation


Conclusion

• The fundamentals of evolution and population ecology are integral to environmental science

• Natural selection, speciation and extinction help determine earth’s biodiversity

• Understanding how ecological processes function at the population level is crucial to protecting biodiversity


QUESTION: Review

Which of the following is NOT a part of the process of natural selection?

a) Once grown, organisms generally don’t have to struggle to survive

b) Organisms produce more young than can survive

c) Individuals vary in their genetic characteristics

d) Some individuals are better suited to their environment than others


QUESTION: Review

What happens as a result of adaptation?

a) Species have lower reproductive success and lower survival.

b) Species have higher reproductive success and higher survival.

c) Species have higher reproductive success and lower survival.

d) Species have lower reproductive success and higher survival.


QUESTION: Review

Directional selection would result in which of the following?

a) Dogs with black coats evolving whiter coats in colder areas

b) Red and white flowers interbreeding, producing pink flowers

c) Fish evolving bigger eyes as the water gets muddier

d) A population of birds, some with thicker beaks that eat seeds, and others with thinner beaks that eat insects


QUESTION: Review

Allopatric speciation would occur in:

a) One population that mates in May, and another that mates in June

b) Two populations separated by the Mississippi River

c) One population that feeds in tree branches, another feeds on tree trunks

d) A population with a mutation that turns fur a different color than usual


QUESTION: Review

Which of these species is MOST vulnerable to extinction?

a) A species with a population size of 500 individuals

b) A species distributed in one county of the United States

c) A species that eats many different plant species

d) A species that has hundreds of offspring


QUESTION: Review

A community is defined as:

a) The total of living things on Earth

b) Members of the same population that can interbreed

c) Interacting species in an area

d) Species and the nonliving material they interact with


QUESTION: Viewpoints

Should we care whether a species goes extinct?

a) Yes, because all life is important and valuable.

b) Yes, because we are causing this wave of extinction, so we should fix it.

c) We should not, because it’s natural.

d) I don’t care; it really does not affect me.


QUESTION: Viewpoints

Do you think humans are subject to limiting factors and, ultimately, a fixed carrying capacity?

a) Yes, although we have raised the carrying capacity, there are limits to the number of humans Earth can support.

b) Yes, but technology will keep raising the carrying capacity, so it’s not much of a problem.

c) No, humans are no longer constrained by environmental limits, due to our technology and ability to manipulate the environment.

d) I don’t care; it really does not affect me.


QUESTION: Interpreting Graphs and Data

Which type of distribution is a result of competition between individuals?

a) Random

b) Uniform

c) Clumped

d) None of these


QUESTION: Interpreting Graphs and Data

What does this graph show?

a) The effects of carrying capacity on population growth

b) A population that keeps growing

c) The effects of exponential growth

d) The effects of increasing carrying capacity

© 2011 Pearson Education, Inc. Lecture Outlines Chapter 3 Environment: The Science behind the Stories 4th Edition Withgott/Brennan.

Documents

pearson education

genetic variation slide

mechanism of evolution

changes characteristics

characteristics traits

genetic variation adaptation

lethal fungus slide

time genetic changes