Population Growth Sharks Fish Objective 5.01: Investigate and analyze the interrelationships among...
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Transcript of Population Growth Sharks Fish Objective 5.01: Investigate and analyze the interrelationships among...
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