Limits on Populationcan the world be taken over by one organism?

Consider this…

Mouse litters are 6+

It takes a mouse 6 weeks to reach sexual maturity

Mice can reproduce every 6 weeks

So… why hasn't the world been covered in mice?

Limits on all populations!

Each Population is LIMITED

Because there are a limited number of resources available in an ecosystem, not every organism born survives

These factors are known as LIMITING FACTORS (because they limit populations)

Organisms basically need 3 things to survive:FoodWaterShelter

Biotic Potentialmaximum number of offspring a species

could produce with unlimited resources

Controlled by 4 factors

1.Birth potential

2.Capacity for survival

3.Procreation

4.Length of reproductive life

Factors That Determine Biotic Potential

Birth Potential

maximum number of offspring per birthe.g. whooping crane females lay 2 eggs

per year and only 1 chick survives

Capacity for Survival

number of offspring that reach reproductive agee.g. female sea turtle lays many eggs,

but only a few offspring even reach the sea, and few still reach sexual maturity

Factors That Determine Biotic Potential

Procreation

The number of times that a species reproduces each year e.g. elk mate only once per year (during the fall)

while farm animals will breed more than once a year

Length of Reproductive Life

The age of sexual maturity and the number of years the individual can reproduce e.g. African elephants reach sexual maturity at about

15 years of age, but may reproduce until they are 90

Limiting Factors

An environmental factor that prevents an increase in the number of organisms in a population or prevents them from moving into new habitats

Example: Fern

Ideally, ferns should produce 50,000 spores per year

Abiotic FactorDrier weather reduces

population

Biotic FactorGrazing animals reduces

population

Carrying Capacity

maximum number of individuals of a species that can be supported indefinitely by an ecosystem i.e. the “room” available in the

ecosystem

determined by the availability of resources (food, shelter, water)

communities tend toward stability

achieved when an ecosystem is in equilibrium (i.e. balance)

Carrying CapacityPopulation can exceed carrying capacity for a short

time

If more organisms come in, there is more competition for space and resourcesAll available food eaten

As resources disappear, organisms die off because they can’t get resources needed

Lack of food leads to illness

Easier prey

Population decreases again to or below carrying capacity

THEREFORE, IF THE CARRYING CAPACITY IS

REACHED, THERE CAN BE A MASSIVE POPULATION

CRASH!

Density

Density refers to the number of organisms in a certain space

Low Density

BIG SPACE

Big space to spread out

SMALL SPACE

Small space with a few organisms

High Density

BGI SPACE

Crowded

SMALL SPACE

Crowded

Limits of Tolerance

Living organisms need certain level of nutrients and conditions to survive

Law of Minimum:nutrient in LEAST supply limits growth

Law of Tolerance:organism can survive within a certain

range of an abiotic factor (above and below this limit… the organism cannot)

Law of Tolerance

• population of fish likely increases as water temperature is close to optimum• no fish survive when it’s too hot or too cold

Density Independent Factors

Affect members of population regardless of population density… kill organisms randomly, regardless of how many are around

e.g. fires, floods, tornados, pesticides, temperature, lack of rain, habitat destruction

Density Dependent Factors

Affect population because of a large population density

e.g. food supply, water quality, mates, sunlight, territory, increase predators and disease (easier to catch a disease in a crowded place)

Lower food supply means energy lost to competition

Definitions

Limiting Factors

Birth Potential

Capacity for Survival

Procreation

Reproductive Life

Carrying Capacity

Density

Law of Minimum

Law of Tolerance

Density Dependent Factors

Density Independent Factors

Homework

1. Suppose that there is a forested park in which squirrels are reproducing very quickly because there is so much food available. In this situation, the population will grow until it reaches the carrying capacity. What will define the carrying capacity of the squirrel population?

2. Identify the following limiting factors as either abiotic or biotic Wind blows the seeds of a dandelion into a pond. The seeds fail to grow. A population of grasshoppers eats all the available food and their numbers

drop dramatically. A bacterium causes a deadly disease in a herd of reindeer and some of them

die. Plants growing beneath the trees in a forest are unable to get enough

sunlight.

3. Cockroaches are insects that reproduce very rapidly. Suggest reasons why the world is not covered in cockroaches.

4. Limiting factors normally control a population from expanding past its carrying capacity in a specific area. Most of the limiting factors that would normally control the human population have been removed through various technologies. How does this affect your quality of life? How might it affect your children’s or grandchildren’s lives?