All living organisms are limited by

factors in the environment

POPULATION ECOLOGYCHAPTER 3.1 & 4.1

In Chapter 2, you learned that organisms depend on one another for survival. You also learned about abiotic factors and that abiotic factors affect individual organisms.

How, then, might these factors affect communities and populations?

REVIEW TERMSCHAPTER 2

Population is a group of individuals of the same type (or species)

Species is a group of organisms that can interbreed and produce fertile offspring

Population growth = an increase in the size of a population over time

Birth rate greater than death rate population grows Birth rate equals death rate population stays the same Death rate greater than birthrate population shrinks

Factors that change population size:

1.immigration – movement of individuals into a population from another population

2. births – causes an increase in population size

3. emigration – movement of individuals out of a population and into another population

4. deaths – causes a decrease in population size

BIRTH

EMIGRATIONIMMIGRATION

DEATH

“J” curve

Under ideal conditions with unlimited resources, a population will grow exponentially.

• Exponential growth = as a population gets larger, it grows faster

EXPONENTIAL GROWTH CURVE Population growth is NOT

limited Takes on an J-shape Ideal and doesn’t normally

occur in most populations What kinds of organisms

might have exponential growth and why?

Two types of Limiting Factors:1. density-dependent2. density-independent

Limiting factor = Any biotic or abiotic factor that restricts the numbers of organisms

Examples: food, water, shelter, etc

Density-dependent limiting factors - affected by the number of individuals in a given area

• competition and availability of food, water and space• predation• parasitism and disease

Density-independent limiting factors - limit a population’s growth regardless of the density

of the population1. unusual weather2. natural disasters3. human activities (pollution or dam building)

CARRYING CAPACITYCARRYING CAPACITY

The maximum number of individuals that can be supported by the ecosystem.

The limit is determined by the availability of resources and by their interactions with other organisms.

LOGISTIC GROWTH CURVE:Occurs when population growth is limited by factors in the environment

Take on the “S” curve• As resources become less available, the growth of the population slows or stops.

• Reaches carrying capacitycarryingcapacity

J-CURVE VS. S - CURVE

All populations will eventually display an S-curve.

Human Population Growth!

REPRODUCTIVE REPRODUCTIVE PATTERNSPATTERNS

P. 98

Species of organisms vary in the number of births per reproductive cycle, in the age that reproduction begins, and in the life span of the organism.

○ R-strategist○ K-strategist

RR-strategist-strategistP. 98

Small organism (fruit fly or a mouse) Short life span Produce many offspring Strategy is to produce as many offspring

as possible in a short time in order to take advantage of some environmental factors

Populations are controlled by density-independent factors (changes in abiotic factors)

KK-strategist -strategist (also called Carrying (also called Carrying Capacity Strategy)Capacity Strategy)

P. 99

Large organism (elephant) Long life span Produce fewer offspring but invest a lot of

care Strategy is to produce only a few offspring

who have a better chance of living due the care they get from parents

Populations are controlled by density-dependent (biotic factors)

Which are you?Which are you?

R-strategist K-strategist

How do humans affect the populations of species?

Humans have played a large role in the loss of Biodiversity on the planet.

Biodiversity = the variety of life in an area

• loss of land/habitat• water and food shortage• poor sanitation

1. Effects of Human Overpopulation:

Bio NOTES: Human Impact on the Environment

• species extinction• poverty• emerging disease

4. Pesticide use – using chemicals to kill and control pests- will sometimes kill non-target species- pollutes water sources- causes health problems

5. Biological magnification – concentrations of a harmful substance increase in organisms at higher trophic levels in a food web

2. Deforestation – loss of forests- cause soil erosion, loss of habitat, and species extinction

Worldwide, about half of the area covered by forests has been cleared.

3. Threats to biodiversity – the variety of organisms is decreasing - an imbalance can cause extinction

Global Warming Acid Rain• The earth’s atmosphere keeps some heat from going out into space• Pollution in our atmosphere causes too much heat to stay on earth• Changes overall temperature/ climate• Raises sea level• Affects health of ecosystems

Rain that has been made acidicby certain pollutants in the air.

• pollutants = sulfur dioxide and nitrogen oxides from burning fossil fuels

• causes health problems• damages forests and lakes• damages buildings•Harmful to animals

Effects on Air Quality

The Greenhouse Effect:

Effects on Water Quality

The runoff of silt, soil, pesticides, and fertilizers from agriculturalland is the largest single source of water pollution.

Eutrophication:- excess fertilizers can run off into lakes and ponds- this stimulates plant and algae overgrowth- a buildup of algae can lower the levels of dissolved oxygen in the water- this leads to the dying off of the fish population- over time, lakes and ponds slowly begin to fill in

Why can’t you just clean up polluted water?- it is expensive- who pays for it?- technology not available for all types

Effects on Natural Resources

Sustainability = a way of using natural resources without depleting them for future generations

• use renewable resources that can be “restocked”• recycle and reuse products• plant tree farms• only cut down selected trees instead of clear-cutting• follow emission standards

Renewable resources - can regenerate if they are living or can be replenished by biochemical cycles if they are nonliving - ex. trees, fresh water

Nonrenewable resources - cannot be replenished by natural processes - ex. fossil fuels

The Story of Easter Island

• Humans first landed on Easter Island between 400 and 700 A.D. • Island had thick forests, rich soil, many bird and animal species• Human population grew quickly over next 1000 years• They cut down forests for lumber and boats faster than the trees could grow back• Eventually, there were no trees left….no wood for shelter or boats, rich soil washed away, habitat lost for animal species, no fishing without boats• With no food, and island resources nearly gone, the Easter Island human population crashed and the Easter Islanders disappeared.