Population Growth Sharks Fish Objective 5.01: Investigate and analyze the interrelationships among organisms, populations, communities and ecosystems.

Population Growth

Sharks

Fish

Objective 5.01: Investigate and analyze the interrelationships among organisms, populations,

communities and ecosystems

A Population is a group of organisms that belong to the same species and live in a

particular place at the same time

Population size refers to the number of individuals in the population.

Populations are usually too large and widespread to count directly, so sampling

techniques are usually used.

Sampling is when a small sample is counted and used to estimate the larger population (100 plants x 1,000)

Population density measures how crowded a population is and is always

expressed as the number of individuals per unit of area

Population Densities

Japan 337 people per square km

United Kingdom 254 people per square km

Kenya 69 people per square km

Mexico 55 people per square km

United States 32 people per square km

Russia 8.3 people per square km

Over time, all populations change in size and composition due to changes in

birth rates, mortality rates, and life expectancy.

Age structure refers to the distribution of individuals among different ages. Populations with more young

people tend to increase more rapidly.

Survivorship Curves show the life expectancy rate at different ages of a population.

Type IMortality increases

later in life

Type IIMortality probability

doesn’t change

Type IIIMortality probability is high early but low

later in life

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

Population Growth = Birth Rate - Mortality Rate

An increase in birth rate or a decrease in mortality rate will cause an increase in population growth

Population growth can also be affected by immigration, individuals moving in, or

emigration, individuals moving out

Immigration and emigration affect a local population’s size but not the world

population

Graphs are used to analyze population growth

1900 1910 1920 1930 1940 1950 1960 1970 1980 20000

5

10

15

20

25

X axis - Years

Y axisNumber

of Churches

Number of Churches in Ramseur

Linear Growth is when the numbers increase steadily by the same amount (2, 4, 6…)

1900 1910 1920 1930 1940 1950 1960 1970 1980 20000

5

10

15

20

25

X axis - Years

Y axisNumber

of Churches

Number of Churches in Ramseur

Exponential Growth is when the numbers increase by a larger amount each time (2, 4, 16, 256…)

19001910192019301940195019601970198020000

1000

2000

3000

4000

5000

6000

X axis - Years

Y axisNumber

of Churches

Number of Churches in Raleigh

Populations tend to increase exponentially in that as they grow larger they begin increasing faster

Slow Increase Rapid Increase

The J – Curve Shows Exponential Population Growth

All ecosystems have a limited amount of resources to support populations

All organisms need water, food, space for habitats, and sanitary conditions

As populations increase, there is more competition for the same resources

Populations begin to die out due to disease, starvation, or thirst

Therefore, any ecosystem can only support a certain amount of individuals

Carrying Capacity refers to the

maximum number of individuals an ecosystem can

support

The S – Curve shows logistic growth where a population begins to stabilize

as it reaches its carrying capacityThe carrying capacity

is determined by limiting factors such

as amount of available resources or

ability to fight off diseases

Limiting factors that restrain population growth and do not depend upon the initial

size of the population are called Density-Independent Factors

FloodsFires

EarthquakesCold SpellsHot SpellsDrought

Limiting factors that restrain population growth and do depend upon the initial size

of a population are called Density-Dependent Factors

Food ShortagesWater Shortages

DiseasesHabitat Space

Competition between species that compete for the same resources can also affect population growth

Gray Seal

Sabel Island

Lance Fish Harbor Seal

One population will out compete the other causing a decline in the other population

Harbor Seal in

Grey Seal in mixed

Months

Predator – Prey Relationships also affect Population Growth

Increase in predators cause a decrease in prey

Decrease in prey causes a decrease in predators

Decrease in predators cause an increase in prey

Increase in prey causes an increase in predators

There is always a delayed relationship in growth and decline between the two populations

The Lesson of the Kaibab

Kaibab National Forest in Arizona

1906, President Teddy Roosevelt created the Grand Canyon National Game Preserve to protect the

“finest deer herd in America”

1905, there was about 4,000 deer on almost 300,000 hectares of

land.

The carrying capacity was estimated to be about 30,000 deer

By this time though, over grazing by cattle, sheep, and horses had eliminated most of the tall perennial grasses

The first step to protect the deer was to ban all hunting of deer as well as extermination of the predators of the deer

1907 – 1939816 mountain lions, 20 wolves, 7,388 coyotes, and 50 bobcats

were killed

The Kaibab Deer Investigating Committee recommended that all livestock not owned by local residents be removed immediately from the range and that the number of deer be cut in half as quickly as possible. Hunting was reopened, and during the fall of 1924, 675 deer were killed by hunters. However, these deer represented only one-tenth the number of deer that had been born that spring. Over the next two winters, it is estimated that 60,000 deer starved to death.

Today, the Arizona Game Commission carefully manages the Kaibab area with regulations geared to specific local needs. Hunting permits are issued to keep the deer in balance with their range. Predators are protected to help keep herds in balance with food supplies. Tragic winter losses can be checked by keeping the number of deer near the carrying capacity of the range.

Human Population Growth

Early humans were hunters and gathers and their populations grew very slowly due to high

mortality rates.

The initial increase in population began when people started civilizations that farmed food together during the agricultural revolution.

The Bubonic Plague, around 1400’s, led to a sharp decline in the population

Europe lost 25% of its population

The current trend of human population growth is that of exponential growth. In other words, as the population gets larger, it is increasing faster.

Industrial revolution, that began in the 1800’s, made obtaining resources even easier.

The discovery of antibiotics, vaccines, and other medical improvements lowered the mortality rate

Current World Population6,815,052,967

World Population 19703,912,211,699

World Population 2050

10,299,634,568

Carrying Capacity

When ?

How ?

Who ?

Developing nations are those nations that are not fully industrialized and still use primitive means to farm and live. The average income is far below poverty level.

Developing nations include India, those in the Mid-East, Africa, South America, and Asia

The developing nations are growing faster in populations than the developed nations. Their faster

growth places a much larger strain on their natural resources.

China’s Population Growth

The End