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Population

ecology is the

study of how

populations

interact with their

environments.

Chapter 14: Population Ecology

Populations can grow quickly for a while, but not forever.

There is no exception to the rule that every organic being naturally increases at so high a rate that, if not destroyed, the Earth would soon be covered by the

progeny of a single pair.

—Charles Darwin, The Origin of Species

In stable populations,

How many of the five million eggs that a female cod might lay over the course of her life will, on average, survive and grow to adulthood?

Who leaves more surviving offspring, a pair of elephants or a pair of rabbits?

Figuring Out How a Population Grows (or Shrinks)

Two pieces of information are needed:

• Growth rate, abbreviated as “r”

• Number of individuals in the population (N)

• r * N

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Population Growth Rate Calculation

500 individuals in a population

Over the course of the year, 125 offspring are born, so the birth rate is 125/500, or 0.25, births per person.

If 25 out of the 500 individuals die during the course of the same year, the death rate is 25/500 or .05 deaths per person.

The growth rate is 0.25 − 0.05, or 0.20, individuals per person.

A population’s growth is limited by its environment.

Density-dependent FactorsThe limitations on a population’s growth

that are a consequence of population density

Food, space, disease, predation

This ceiling on growth is the carrying capacity, K, of the environment.

The Carrying Capacity of an Environment Influences a Populations Growth

r * N

Multiply by [(K – N)/K]• Varies between 0 and 1

If the new term, [(K – N)/K], is close to 1, population growth is essentially unchanged.

If the new term, [(K – N)/K], is close to 0, the environment is nearly full to capacity, and population growth reduces to almost zero.

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Density-independent Forces

Factors that strike populations without regard for the size of the population

Mostly weather-based

How many people can Earth support?

Some populations cycle between large and small.

Do lemmings jump off cliffs committing suicide when their populations get too big?

“Maximum sustainable yield” is a useful (bogus) but impossible-to-implement concept.

We don’t know K.

What We Often Do Not Know…

Population carrying capacity

Number of individuals alive

Stability of carrying capacity from year to year

Which individuals to harvest

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• A life history is like a species summary.

– Life histories are shaped by natural selection.

Why all the variation?

Is one strategy better than others, evolutionarily?

There are many possible responses to the challenge of:• When to reproduce • How often to reproduce• How much to reproduce

Life History

The vital statistics of the species

Includes: age at first reproduction, probabilities of survival and reproduction at each age, litter size and frequency, and longevity

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Reproductive Investment

The material and energetic contribution that an individual will make to its offspring

Single episode of reproduction

Repeated episodes of reproduction

Which life history strategy is best?

1. What is the cost of reproductive investment during any reproductive episode?

2. What is an individual’s likelihood of surviving to have future reproductive episodes?

Natural selection favors lifetime reproductive success.

We put off mating much longer than cats or mice

Populations can be described quantitatively in life tables and survivorship curves.

Life Tables and Survivorship Curves

Life table

• Allow biologists to predict an individual’s likelihood of either dying within a particular age interval or surviving the interval.

Life Tables and Survivorship Curves

Survivorship curves

• Graphs of the proportion of individuals of a

particular age that are alive in a population

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Designing an OrganismTo structure its life history for maximum fitness, create one that could:

produce many offspring,

beginning just after birth,

continuing every year,

while growing tremendously large, to reduce the predation risk

and living forever.

There are tradeoffs between reproduction and longevity. Evolutionary Constraints

These traits are not all possible because selection that changes one feature tends to adversely affect others.

Evolutionary tradeoffs

Three areas to which an organism can allocate its resources:

Growth

Reproduction

Survival

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Physiological Deterioration over Time

Aging: an increased risk of dying with increasing age.

Things fall apart: What is aging and why does it occur?

Many genetic diseases kill old people, but almost none kill children.

Mutations That Arise and Cause Their Carrier to Be More Likely to Die Later in Life

Such mutations include those that increase the risk from cancers or heart disease or other types of ailments.

Do not affect reproductive output

Consequently, these mutants are never cleaned out of a population.

Hazards

High-risk worlds

• Death from external sources

• Reproduce early

Low-risk worlds

• Death from external sources low

What determines species longevity?

Age at Time of Reproduction

A key factor determining longevity

Early reproduction will also favor early aging.

Later reproduction will also favor later aging.

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Can we slow down the process of aging?

What is the baby boom?

Is it bad news for young people today?

The human population is growing:

Age pyramids reveal much about a population.

Describing Populations

In terms of the proportion of individuals from each age group

The population age distribution

Age groupings called cohorts

Population growth is alarmingly slow in Sweden and alarmingly fast in Mexico.

As less-developed countries become more developed, a demographic transition often occurs.

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How high can it go?!

Very difficult to assess just how many resources each person needs

Ecological footprints

• Evaluating how much land, how much food and water, and how much fuel, among other things, are necessary

Learning Objectives

Be able to explain the following:

What are ecosystems?

How is weather created?

How do energy and chemicals move through

ecosystems?

Chapter 15: Ecosystems and Communities

Learning Objectives

Be able to explain the following:

How do species interactions influence the structure of communities?

How do communities remain stable or change over time?

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What are ecosystems?

A community of biological organisms plus the non-living components with which the organisms interact.

Ecosystems

have living and

nonliving

components.

Which list below likely describes an ecosystem?

1. Grasses, flowering plants, bees, ants, deer, wolves.

2. A fast flowing stream filled with aquatic plants, crayfish, water striders, trout, and water snakes.

3. Bacteriodes, Clostridium, Peptococcus, Escherichia, and Lactobacillus living in the human gut.

4. 2 and 3

5. All of the above

BiomesWhat is the average temperature?

What is the average rainfall (or other precipitation)?

Is the temperature relatively constant or does it vary seasonally?

Is the rainfall relatively constant or does it vary seasonally?

A variety of biomes occur around the world, each determined by temperature and rainfall.

Biomes

Temperature and precipitation dictate:

• Primary productivity levels

The amount of organic matter produced

The numbers and types of primary producers are the chief determinants of the amount and breadth of other life in the region.

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What type of biome are we in?

1. Temperate deciduous forest

2. Savannah

3. Temperate grassland

4. Chaparral

5. Desert

6. Coniferous forest

Global air circulation patterns create deserts and rainforests.

At around 30o north and south around the

world, there is very little rainfall, the ground

is very dry, and deserts form

Around what latitude(s) would we expect rainforests (tropical

and temperate)?

1. 60oN and 60oS

2. 30oN and 30oS

3. 0o, 30oN, and 30oS

4. 0o, 60oN, and 60oS

5. All of the above

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Local topography influences the weather

Is it warmer or cooler in urban areas relative to nearby rural areas?

“Urban Heat Islands”

Ocean currents affect the weather.

Beaches on the east coast of the United States have warmer water than west coast beaches at the same latitudes.

Why?

Beach communities have milder weather than more inland communities?

Water’s capacity to absorb and hold heat

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Which weather experienced by people living in Washington, DC, is most directly caused

by humans?

1. It is warmer in DC than in the surrounding suburbs.

2. DC is on average warmer than cities in Maine.

3. DC experiences more moderate summers and winters than cities further inland.

4. It is warmer in DC than at the peak of the mountains west of it.

Energy flows from producers to consumers.

Chains or Webs?

Food chain

• Pathway from photosynthetic producers

through the various levels of animals

Food web

• Involve harvesting energy from multiple stops in the food chain

A grasshopper eats a plant. A mouse eats the grasshopper. A snake eats the mouse. A hawk could eat the snake or the mouse. In this food

web, how would we categorize the mouse?

1. Producer

2. Primary consumer

3. Secondary consumer

4. Tertiary consumer

5. Quaternary consumer

6. 2 and 3

Biomass

10% rule

Where does the rest go?

Expended in cellular respiration or lost as feces

Energy pyramids reveal the inefficiency of food chains.

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In humans, why is vegetarianism more energetically efficient than meat-eating?

The 10% rule in application

Big, predatory animal species are rare in the world?

The Three Most Important Chemical Cycles

1. Carbon

2. Nitrogen

3. Phosphorus

Essential chemicals cycle through ecosystems.

The recycling of molecules

Chemical Reservoirs

Each chemical is stored in a non-living part of the environment.

Organisms acquire the chemical from the reservoir.

The chemical cycles through the food chain.

Eventually, the chemical is returned to the reservoir.

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Global CO2 levels are rising in general, but they

also exhibit a sharp rise and fall within each year.

Why?

Why are global CO2 levels rising?

Fossil fuels

Plants take in more CO2 during warm periods

– Plants are trying to save us!

Nitrogen is like a bottleneck limiting plant growth.

Fertilizers

Species

interactions

influence the

structure of

communities.

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Interacting species evolve together.Natural Selection

Causes organisms to become better adapted to their environment

Does not distinguish between biotic and abiotic resources as selective forces

Which interaction between two species likely arose by coevolution?

1. Cheetahs (predator) are really fast, and gazelles (prey) are fast and very agile.

2. The relationship between bacteria living in the human gut and humans is mutually beneficial.

3. Garter snakes can eat a type of moth that has

developed a neurotoxin as a defense mechanism.

4. All of the above

Each species’ role in a community is defined by its niche.

More than just a place for living, a niche is a complete way of living.

“You can’t always get what you want.”

Fundamental niche

• The full range of environmental conditions

under which a species can live

Realized niche

• Where and how a species is actually living

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Competition can be hard to see, but it still influences community

structure.

Why is competition hard to see in nature?

The “ghost of competition past”

Predation

One of the most important forces shaping the composition and abundance of species in a community

Predation produces adaptation in both predators and their prey.

Why do exotic species often flourish when released into novel habitats, even though natural selection has not adapted them to this new environment?

Prey Adaptations for Reducing Predation

There are two broad categories of defenses against predators:

• Physical

• Behavioral

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Predator Adaptations for

Enhancing Predation

Why don’t predators become so efficient at capturing prey that they drive the prey to extinction?

The “life-dinner hypothesis”

A chameleon can easily change the color of its skin to blend into its surroundings. What does this suggest about

the types of predator that eat chameleons?

1. They are visual hunters that primarily track the movement of prey.

2. They are visual hunters with color vision.

3. They track prey using primarily scent.

4. They track prey using primarily infrared vision to sense body heat.

Parasitism is a form of predation.

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Parasite Predators

Parasites have some unique features and face some unusual challenges:

• The parasite generally is much smaller than its host and stays in contact with the host for extended periods of time.

• Complicated life cycles as means of getting from host to host

The three case studies we just discussed illustrate how parasites can

move between hosts and could be explained by…

1. Competitive exclusion principle

2. Competition

3. Coevolution

4. Exclusive interactions between predator and prey

Not all species interactions are negative: mutualism and commensalism.

In commensalism, one species benefits

and the other is neither harmed nor helped.

Pollinators

Mutualism, in which both species benefit

from the interaction, is widespread and

critically important to all ecosystems.

Buffalo and cattle egrets

Which answer is an example of mutualism?

1. Bacteria in the human gut

2. Fleas on a dog

3. Wolves and coyotes preferring the same prey

4. Insects being attracted to and digested by carnivorous plants

Communities change over time.

In primary succession, the process begins in an area with no life and no soil.

Secondary succession

Much faster than primary succession

• Life and soil are already present.

Succession is the change in the species

composition of a community over time,

usually after a disturbance

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Which answer below will involve primary succession to establish a community?

1. Regression of a glacier

2. Eruption of a volcano that covers the land with lava

3. Plowing a field and letting it lie fallow

4. 1 and 2

Some species are more important than others within a community.

Learning Objectives

• Explain what biodiversity is

• Explain how extinction reduces biodiversity

• Describe how human interference generally reduces biodiversity

• Discuss strategies we can develop for effective conservation

Chapter 16: Conservation and Biodiversity

Vinblastine and vincristine Cancer treatments: from snail

AncrodDissolves blood clots: from pit viper

Epibatidine Pain reliever: From frog

Biodiversity benefits humans in many ways.

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It is important to protect the biodiversity of our planet.

1. Strongly agree

2. Agree

3. Neutral

4. Disagree

5. Strongly disagree

Biodiversity is not easily defined.

Defining biodiversity

is difficult because it

can be considered at

multiple levels, from

entire ecosystems to

species to genes and

alleles.

If we choose to protect a specific parcel of land, say the one from the last slide, we are

protecting…

1. Genetic biodiversity

2. Species biodiversity

3. Habitat biodiversity

4. All of the above

Why are there more species in an acre of tropical rain forest than in an acre farther from the equator, such as in a temperate forest or prairie?

Latitudinal Biodiversity Gradient

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Island biogeography helps us understand the maintenance and loss of biodiversity.

The theory of island

biogeography generates

predictions about the

patterns of species diversity

in isolated habitats.

Island Recolonization

1. The closer islands were recolonized more quickly than the distant islands.

2. On all of the islands, the number of insect species after fumigation returned to about the same number of insect species prior to fumigation.

3. The composition of insects on each island changed over the course of the study, even on the two control islands.

According to MacArthur and Wilson, which island would experience the

highest extinction rate?

1. Large island, close to mainland

2. Small island, close to mainland

3. Large island, far

from mainland

4. Small island, far from mainland

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There are multiple causes of extinction.

Extinction

reduces

biodiversity. Mass extinctions are

more the result of bad luck

than particulars of a

species’ biology.

Background extinctions

tend to be a consequence

of one or more features of

the species’ biology.

Which type of organism below is least likely to become extinct?

1. Dandelions

2. Pine trees

3. Lions in Africa

4. Polar bears

Current rates of extinction in every well-studied group of plants and animals support the hypothesis that a mass extinction is underway.

Seems to be the result of the activity of one species—humans.

We are in the midst of a mass extinction.

Which answer below is the chief cause of the loss of biodiversity

on our planet?

1. Invasive species

2. Overexploitation of natural resources

3. Habitat destruction

4. Answers 1, 2, and 3 have equal impact on loss of biodiversity.

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Some ecosystem disturbances are reversible, others are not.

Human interference

generally reduces

biodiversity.

Biodiversity on Mt. St. Helens is recovering. How is this possible after such a cataclysmic event?

1. New species are evolving from scratch.

2. Species are repopulating the area from distant reservoirs of species.

3. Species are repopulating the area from nearby reservoirs of species.

4. All the species became extinct after the eruption, now the area consists of mainly invasive species.

Disruptions of ecosystems can be disastrous.

1. Introductions of exotic species

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WHOOPS!

How can introduced species outcompete native species?

1. They are stronger and bigger.

2. They have no natural food source in the area, so they eat the weaker species.

3. They have no natural pathogens or predators in the area to hold their population in check.

4. They fit into an ecological network shaped by adaptive evolution of multiple species.

Disruptions of ecosystems can be disastrous.

2. Acid rain and the burning of fossil fuel

Rain is usually close to pure

water.

What can turn it to acid?

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The effects of acid precipitation can be direct or indirect.

Direct effects result from contact of living tissues with acidic water.

Indirect effects are produced by interactions between non-living and living systems.

Which state has the most acidic precipitation?

1. Florida

2. California

3. Texas

4. Pennsylvania

5. Kansas

Disruptions of ecosystems can be disastrous.

3. Global warming and the greenhouse effect

Carbon dioxide and

methane are called

“greenhouse gases”because they trap heat

in the atmosphere.

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Biological systems are also showing the effects of climate change.

Trees and flowers

Blooming earlier

Migratory birds

Heading north sooner

Birds and butterflies Extending range northward

Increased global temperatures are most likely caused by…

1. Increasing levels of carbon dioxide and ammonia in our atmosphere

2. Burning of fossil fuels

3. Deforestation

4. Humans

5. All of the above

Disruptions of ecosystems can be disastrous.

4. Depletion of the ozone layer

Ozone Hole

Ozone in the stratosphere prevents short-wavelength ultraviolet light (UVB) from reaching the earth’s surface, but for many decades the amount of ozone has been decreasing.

Synthetic chemicals, the chlorofluorocarbons (CFCs), are largely responsible for the destruction of ozone.

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Disruptions of ecosystems can be disastrous.

5. Deforestation of tropical rain forests

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Destruction of tropical rain forests has two serious environmental impacts:

1. Reducing biodiversity

2. Increasing greenhouse gases

How can global warming be linked to deforestation?

1. Trees that remove CO2 from the air are cut down and burned, releasing CO2.

2. Trees add CO2 to the air and are cut down releasing sulfuric acid.

3. Trees that remove nitrogen and sulfur from the air are cut down and burned, releasing sulfur and nitrogen.

4. 1 and 3

We can develop

strategies for

effective

conservation.

With limited conservation resources, must we prioritize which

species should be preserved.

Goals

Effective conservation requires the setting of goals on the elements of biodiversity (genes, species or ecosystems) to be conserved and setting priorities among those elements.

The Endangered Species Act has focused much conservation effort on the preservation of species.

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There are multiple effective strategies for preserving biodiversity.

Landscape Conservation

World Wildlife Fund’s “Global 200”

Geared toward conserving not just species, but habitats and ecological processes

Modern Preserve Design

Larger

Circular

Corridors

Buffer zones

Efforts Focusing on Individual Species

1. Flagship species

– Charismatic, from a human stand point

2. Keystone species

– Disproportionate effect in biodoversity

3. Indicator species

– Presence/absence indicate habitat quality

4. Umbrella species

– Large habitat needs – thus acts to save them influence lots of other species

Captive breeding programs and habitat restoration

Bringing back biodiversity from the brink of extinction

Zoos and botanical gardens

Restoration Ecology

• Natural habitat is essential

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The presence or absence of amphibians (frogs) in an ecosystem is a sign of its

health. Therefore, amphibians would be categorized as a(n)…

1. Flagship species

2. Umbrella species

3. Keystone species

4. Indicator species

It is important to protect the biodiversity of our planet.

1. Strongly agree

2. Agree

3. Neutral

4. Disagree

5. Strongly disagree