Presentation on theme: "Population Growth Sharks Fish Objective 5.01: Investigate and analyze the interrelationships among organisms, populations, communities and ecosystems."— Presentation transcript:
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 Japan337 people per square km United Kingdom254 people per square km Kenya69 people per square km Mexico55 people per square km United States32 people per square km Russia8.3 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 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 X axis - Years Y axis Number of Churches Number of Churches in Ramseur
Linear Growth is when the numbers increase steadily by the same amount (2, 4, 6…) X axis - Years Y axis Number of Churches Number of Churches in Ramseur
Exponential Growth is when the numbers increase by a larger amount each time (2, 4, 16, 256…) X axis - Years Y axis Number 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 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 FloodsFiresEarthquakes 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 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 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 – 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 Population 6,815,052,967 World Population ,912,211,699 World Population ,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.