ES 5.3 LESSON Population Limits

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Environmental Science, 1e
SUSTAINING YOUR WORLD
G. TYLER MILLER | SCOTT E. SPOOLMAN

5

Species Interactions, Ecological

Succession, and Population

Control

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• Populations cannot grow indefinitely due to:

– Limitations on resources

– Competition among species for these resources

5.3 What Limits the Growth of Populations?

Multiple Select

Populations cannot grow indefinitely due to which TWO?

• limited resources

• unlimited resources

• competition

• mutualism

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• A population is a group of interbreeding individuals of the

same species that usually live together in the same geographic area.

• Population size can change based on:

– Immigration (arrival of individuals from outside the population)

– Emigration (departure of individuals from the population)

Populations Can Grow, Shrink, or Remain Stable

– Births/deaths

Drag and Drop

​

Placeholder

is when new organisms come into a population.

​

Placeholder

is when new organisms leave a population.

A population is a group of organisms ​

Placeholder

.

Drag these tiles and drop them in the correct blank above

Immigration

Emigration

of the same species in the same area that breed.

from different species that live in the same area

interbreeding organisms from different species

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• Age structure is the distribution of individuals among various

age groups.

– Described as pre-reproductive, reproductive, post-reproductive

– Affects how rapidly population grows or declines

Age Structure Affects Population Size

Multiple Select

What TWO factors do population ecologists use to make age structure diagrams?

• age of individuals in a population

• number of individuals of each gender (male and female)

• age of total population (how long the population has existed in an area)

• number of individuals born into the population vs number that emigrated

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• Each population in an ecosystem has a range of

tolerance—its ability to survive under various physical and
chemical environmental conditions.

– Some individuals in a population may also have different ranges of

tolerance for temperature or other physical or chemical factors due
to differences in genetic makeup, health, or age.

Some Factors Can Limit Population Size

Multiple Choice

What do ecologists call the range of its abilities in a population to survive under various physical and
chemical environmental conditions

• range of immunity

• range of resistance

• range of tolerance

• geographic range

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Range of Tolerance

Multiple Choice

All organisms in population are of the same species so they will all have the same range of tolerance.

• True

• False

Multiple Choice

Where will you find just a few organisms in a population?

• optimum range

• zone pf physiological stress

• zone of intolerance

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• Examples

– On land, precipitation is often a limiting factor.

– In aquatic ecosystems, limiting factors can be:

• Temperature, water depth, clarity (allowing for more or less sunlight),

nutrient availability, acidity, salinity, and the level of oxygen in the water

• An excess of a limiting factor can itself be limiting

– Too much water on land or too much acidity in aquatic

environments

Limiting Factors

Multiple Choice

What do we call conditions that may keep a population from growing larger?

• limiting factors

• population controls

• natural resources

• natural capital

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• Population density: the number of individuals in a given

geographic area

– Density-dependent factors become more important as a population

size increases.

• Parasites and diseases spread more easily.

• Sexually reproducing individuals can find mates more easily.

– Density-independent factors

• Drought and climate

Density-Dependent and Density-Independent Factors

Categorize

Options (8)

climate

drought

disease

parasites

competition

finding a mate

become more important as population increases

is not affected by population increases

Organize these options into the right categories

Density-Dependent

Density-Independent

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• Some species reproduce and grow

exponentially.

– J-curve shows exponential growth

– Members reproduce at an early age; many

offspring in each generation; time between
generations is short

• All species have population growth limits.

– Sunlight, water, temperature, space,

nutrients, predators, disease

Exponential Growth

Multiple Select

When members of a population reproduce at an early age, have many offspring and a short time between generations, this can lead to...

(Choose 3)

• J-curve

• exponential growth

• logistic growth

• S-curve

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• Environmental resistance:

– The sum of all factors that limit the growth of a population

• Carrying capacity:

– The maximum population of a given species that a habitat can

sustain indefinitely

– As the population approaches its carrying capacity, its J-curve

becomes an S-curve of fluctuating logistic growth.

No Population Can Grow Indefinitely

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J-Curves and S-Curves, Illustrated

Multiple Choice

What is maximum population of a species that a habitat can sustain?

• exponential growth

• logistic population

• carrying capacity

• S-curve

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• When a population overshoots the carrying capacity, the

population sharply declines

– Dieback, or population crash

• Now a population must either:

– Stabilize its population

– Switch to new resources

– Move to a new geographic area

Populations Can Crash

Multiple Choice

What might cause a population to crash?

• an increased carrying capacity

• a population that overshot the carrying capacity

• population that stabilized at the carrying capacity

• normal limited resources can cause this

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• r-selected species have a capacity for a high rate of

population increase.

– Have short life spans

– Have many, usually small offspring

– Do not provide much parental care/protection

• Offspring loss is overcome by massive offspring production, so that at least

a few will survive

• Examples: rodents, insects, weeds

Reproductive Patterns: r-selected Species

Multiple Select

Which characteristics are true of r-selected populations?

• short life spans

• many small offspring

• little to no parental care of offspring

• long lifespans of offspring

• offspring that mature slowly after birth

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• Opportunists reproduce rapidly under favorable

environmental conditions.

– Often occurs after a fire or clearing an area that opens up a new

habitats or niches for invasion of a new species

– May crash after growth or when yet another species invades the

area

– Go through irregular and unstable boom-and-bust cycles

– Examples: desert mice, tree kangaroos, finches

Reproductive Patterns: Opportunists

Multiple Choice

What may cause opportunists to reproduce rapidly?

• favorable environmental conditions

• a population at the carrying capacity

• a population above the carrying capacity

• the presence of a new predator in the environment

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• K-selected species do well in competitive conditions when

population size nears carrying capacity.

– Reproduce later in life

– Have smaller numbers of offspring with longer life spans

– Typically develop inside their mothers and are born fairly large

– After birth, mature slowly and are protected by one or both parents

– Examples: humans, whales, elephants

Reproductive Patterns: K-Selected Species

Multiple Select

Which characteristics are true of K-selected populations?

• short life spans

• many small offspring

• reproduction later in life

• long lifespans of offspring

• offspring that mature slowly after birth

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• Because different species have different reproductive rates,

they also have different life expectancies (illustrated by
survivorship graphs on next slide).

• Three kinds of survivorship curves:

– Late loss

– Early loss

– Constant loss

Species Vary in Life Expectancy

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Survivorship Curves

Multiple Choice

Which type of organism is most likely to have an early loss survivorship curve?

• r-selected

• K-selected

• neither r or K selected

• both r and K selected