Brainstorm

• You and the person next to you will list 3 examples of…..

• Abiotic and biotic factors that affect population growth and decrease in size.

Chapter 9

Population Unit

Population Dynamics• Studying how populations change in size,

density, age distribution, and population distribution.

• Size: number of individuals• Density: how many are in a certain area• Age distribution: proportion of each age group• Population distribution: how the organisms arrange

themselves in their habitat

Population Distribution

Clumping: Most common. Safety in numbers, social interaction, mating and caring for young, resources are clumped

Uniform: Not as common. Used because of scarcity of resources

Random: Quite rare. Can be hard to determine between truly random or largely “clumpy”

Most common.

What goes up must come down

• Increases in population: through birth or immigration

• Decreases in population: through death or emigration.

Change in Population

Births + Immigration

Deaths + Emigration

Note: You should know difference between Immigration & Emigration!

Age Structure• What is expected to happen if a large % of

the population is under the age of 10?

• What is expected to happen if a large % of the population is over the age of 65?

• What is expected to happen if there is an equal distribution in age?

Growth will remain stable, then increase in 10-20 years

Growth will decrease

Growth remain stable

What stage are you?

• Prereproductive stage: Those not through puberty; reproductively immature.

• Reproductive stage: Those who are capable of reproduction

• Postreproductive stage: Organisms that are too old to reproduce.

• Note: while males are capable of reproduction longer, “survival of the fittest” can prevent them from breeding once they are too old.

Old Bio StuffAbiotic vs. Biotic Factors

That limit population growth

• Not living• Sunlight• Temperature• Climate• Chemical

environment

• Living factors• Reproduction rates• Food supply• Habitat• Resistance to disease• Ability to adapt to

change

Abiotic Biotic

POPULATION SIZE

Growth factors(biotic potential)

Favorable lightFavorable temperatureFavorable chemical environment (optimal level of critical nutrients)

Abiotic

BioticHigh reproductive rate

Generalized niche

Adequate food supply

Suitable habitat

Ability to compete for resources

Ability to hide from or defend against predatorsAbility to resist diseases and parasitesAbility to migrate and live in other habitatsAbility to adapt to environmental change

Decrease factors(environmental resistance)

Too much or too little lightTemperature too high or too lowUnfavorable chemical environment (too much or too little of critical nutrients)

Abiotic

BioticLow reproductive rate

Specialized niche

Inadequate food supply

Unsuitable or destroyed habitat

Too many competitorsInsufficient ability to hide from or defend against predatorsInability to resist diseases and parasitesInability to migrate and live in other habitatsInability to adapt to environmental change

Biotic potential = growth

Environmental resistance = decrease

A population will increase if….

• A) Natality decreases

• B) Mortality increases

• C) Biotic potential increases

• D) The environmental resistance increases

A population will increase if….

• A) Natality decreases

• B) Mortality increases

• C) Biotic potential increases

• D) The environmental resistance increases

Favorable lightFavorable temperatureFavorable chemical environment (optimal level of critical nutrients)

Abiotic

Biotic

High reproductive rate

Generalized niche

Adequate food supply

Suitable habitat

Ability to compete for resources

Ability to hide from or defend against predatorsAbility to resist diseases and parasitesAbility to migrate and live in other habitatsAbility to adapt to environmental change

Any of these would take place for answer C.

Biotic potential = growth

Exponential or Logistic Growth Curve?

“Boom and Bust” “Boom then stable”

Logistic Growth• Will see exponential growth at first introduction

to new environment. Video to follow this lecture.

• Then, growth will be limited by environmental factors and will follow carrying capacity

• S shaped

Po

pu

lati

on

siz

e (N

)

Time (t)

Carrying capacity (K)

Environmentalresistance

Bioticpotential

Exponentialgrowth

Clearer view of “J” and “S”

Going up…

• Intrinsic rate of increase (r) is the rate the population would grow if it had unlimited resources.

• Can be seen as the “boom” of the population.

• r species: reproduce early in life, reproduce often, have many offspring each time.

Coming down…• Overshoot occurs when the population

“booms” and is too great for the resources to support

• Overshoot is followed by dieback, or the sudden decrease in population

• Reproductive time lag: the amount of time it takes for the birth rate to fall and death rate to rise. If the time lag is too long, environmental damage can occur which further limits the carrying capacity.

Population GraphsN

um

ber

of

ind

ivid

ual

s

Time

(b) Irregular

Population GraphsN

um

ber

of

ind

ivid

ual

s

Time

(a) Stable

Population GraphsN

um

ber

of

ind

ivid

ual

s

Time

(c) Cyclic

Population GraphsN

um

ber

of

ind

ivid

ual

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Time

(d) Irruptive

(

Oscillations of the Two Populations Over Time

Population Density• Density-dependent controls: Limits

populations that are too high. Examples: competition for food, shelter, water; disease; parasites, predation

• Density-independent controls: Decreases population regardless of size. Examples: weather, temperature, natural disasters, habitat destruction, chemical changes in the environment

Who’s in control here?• Top-down control: (Predator Controls Prey)

– Structure of lower trophic levels depends on effect of consumers at high trophic levels.

• Bottom-up control: (Prey Controls Predator)– Structure depends on prey availability and nutrient

content from low trophic levels

• Example: Hare population is controlled either by the lynx killing it (top-down) or by large numbers of hare using up their food source (bottom-up)

Let’s talk about sex…old bio stuff

• Asexual reproduction: does not require sperm/egg. Mitosis – cell splitting. Bacteria reproduce this way. Only 3% of all species use this form

• Sexual reproduction: requires sperm/egg, but not necessarily intercourse/copulation

• Disadvantages:– Males don’t give birth– Increased chance of genetic defect/error– Courtship and mating rituals can be complex

• Advantages: (get your mind out of the gutter!)– Genetic variety/diversity– Parents can divide responsibilities

What species are you?N

um

ber

of

ind

ivid

ual

s

Time

Carrying capacity

K species;experienceK selection

r species;experiencer selection

Remember – You are SPECIAL

Species

• Found at bottom of population curve

• Reproduce early in life• Reproduce frequently• Large numbers of offspring• Little to no parental care• Boom and bust populations• Examples:

– Frogs– Cockroach– Dandelions– Mice– Most insects

• Found at top of population curve

• Reproduce later in life• Reproduce less frequently• Have less offspring at one time• Lower infant mortality• Logistic graph (stable at top)• Examples:

– Humans– Elephants– Whales– Long-living plants (oaks, rain

forest trees)

r-selected Species K-selected Species

R-selected Species or K-selected species?

                                                                                                                                          

R-selected Species or K-selected species?

                                                                                                                                          

R-selected Species or K-selected species?

R-selected Species or K-selected species?

                                                                                                                                          

R-selected Species or K-selected species?

                                                                                                                                          

R-selected Species or K-selected species?

                                                                             

R-selected Species or K-selected species?

                                                                                                                                          

HINT: The Capybara is the largest rodent in the world

Survivorship Curves• Early loss: high

infant mortality (fish, frogs)

• Constant loss: death rate even among all ages (song birds)

• Late loss: low infant mortality (humans, elephants)

Per

cen

tag

e su

rviv

ing

(lo

g s

cale

)

100

10

1

0

Age

Early loss

Constant loss

Late loss

Isolation isn’t best…• Problems when small, isolated populations exist.

– Founder effect: small group is geographically isolated. May not have the genetic diversity to survive (coloring, fur cover, etc)

– Demographic bottleneck: only a few surviving individuals may not have the genetic diversity to rebuild the population

– Genetic drift: some individuals breed more and dominate the gene pool (wolves)– Inbreeding: related individuals in an area mate. Can increase genetic defects.

Tying in a few things from

Chapter 1

Oops! I did it again…• Past mistakes that need to be stopped:

– Reducing biodiversity by destroying, fragmenting and degrading habitats

Oops! I did it again…• Past mistakes that need to be stopped:

– Reducing biodiversity by simplifying natural ecosystems (monocultures – one type)

Oops! I did it again…• Past mistakes that need to be stopped:

– Unintentional strengthening of pest species and anti-biotic resistant bacteria

Oops! I did it again…• Past mistakes that need to be stopped:

– Elimination of natural predators (wolves, cougars, buffalo, eagles)

Oops! I did it again…• Past mistakes that need to be stopped:

– Over-harvesting renewable resources

Oops! I did it again…• Past mistakes that need to be stopped:

– Interfering with natural cycles in natural

Oops! I did it again…• Past mistakes that need to be stopped:

– Over dependence on fossil fuels

4 Guidelines for a Sustainable Future

• Our lives and economies are dependant on the earth and sun. They don’t depend on us.

• Everything is interconnected.

• You can’t change only one thing in nature

• We cannot sustain our civilization if we deplete the natural capital. We must live off the biological interest of that capital.

PRINCIPLESOF

SUSTAINABILITY

Population

ControlSolar E

nergy

Biodiv

ersi

tyNutrient

Recycling