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

Population size refers to the number of individuals in the population. 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 I Mortality increases later in life Type II Mortality probability doesn’t change Type III Mortality probability is high early but low later in life

Population Growth = Birth Rate - Mortality Rate 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

Number of Churches in Ramseur Graphs are used to analyze population growth Number of Churches in Ramseur Y axis Number of Churches X axis - Years

Number of Churches in Ramseur Linear Growth is when the numbers increase steadily by the same amount (2, 4, 6…) Number of Churches in Ramseur Y axis Number of Churches X axis - Years

Number of Churches in Raleigh Exponential Growth is when the numbers increase by a larger amount each time (2, 4, 16, 256…) Number of Churches in Raleigh Y axis Number of Churches X axis - Years

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

Populations begin to die out due to disease, starvation, or thirst 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 capacity The 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 Floods Fires Earthquakes Cold Spells Hot Spells Drought

Limiting factors that restrain population growth and do depend upon the initial size of a population are called Density-Dependent Factors Food Shortages Water Shortages Diseases Habitat Space

Competition between species that compete for the same resources can also affect population growth Sabel Island Gray Seal Harbor Seal Lance Fish

One population will out compete the other causing a decline in the other population Grey Seal in mixed Harbor Seal in 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

1905, there was about 4,000 deer on almost 300,000 hectares of land. 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 – 1939 816 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.

Europe lost 25% of its population 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 Population 6,815,052,967 World Population 1970 3,912,211,699 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