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Population
Population Members of the same species living in a specific
geographic area.
Species – A group of similar organisms that can
breed and produce fertile offspring
Factors that effect population size:
• Availability of Food
• Weather conditions
• Space
• Breeding Patterns
Population• When studying a population boundaries are set to
limit or make a study easier
Population Density – The number of individuals of a
particular species per unit
area or volume
• Can be expressed as a formula:– Individuals / Unit Area– 1000 Trees / 50 km² = 20 Trees/km²
• 20 Trees per km²
Limits to Growth “Factors”Exponential Growth – Population multiplies by a constant factor at constant time intervals• A populations ability to grow depends partly on the
rate at which an organism can reproduce.Reproduction – the formation of new individuals.
– Bacteria reproduce very fast– Rabbits fast– Panda – S L O W – one reason they are critically
endangered – fewer than 1000 in the wild
Exponential Growth
• Exponential growth is usually represented by a J – shaped curve
Limiting FactorsA condition that can restrict a population growth
• Space – “Normal” cells stop dividing when they run out of
room to grow• Cancer cells do not; they loose this restriction and continue
to grow beyond available space.
Lung Cancer Cells
Limiting Factors• Food• Disease• Carrying Capacity – The number of organisms in a population that the environment can maintain or “carry” with no net increase or decrease.• As you near the Carrying Capacity death rate may
increase or birth rate may decrease or BOTH– Continues till about equal
Carrying Capacity
• It is usually represented by an S – shaped curve.
Factors Affecting Population GrowthDensity – Dependent Factors – A factor that limits
a population more
as population
density increases.
• Availability of food
• Disease that spreads easier among organisms in a dense population; than one that is less dense.
Factors Affecting Population GrowthDensity – Independent Factors – Factors that limit
populations but are
unrelated to population
density.• Extreme Weather: Hurricanes, blizzards, droughts• These conditions have the same effect on population
regardless of its size• Fires, floods, habitat changes like deforestation
Factors Affecting Population Growth
Growth Cycles
“boom-and-bust” Growth Cycles• A rapid increase in population for a period of
time; followed by a rapid decrease in number– An uncontrolled growth cause a hormonal secretion
making animals sterile (rodent)• A limit to food
Human Population: Birth Rate vs. Death Rate
History
• As with all other species, the human population growth depends on birth and death rates.– Birth rates go up and death rates go down population
goes up
Human Population: Immigration & Emigration
Immigration – individuals move into an area
from elsewhere
• Increase the population
Emigration - individuals move out of the
population
• Decrease a population
Human Population
• 10,000 years ago farming replaced hunting and gathering– Provided a consistent food supply– More food = increase population
• Death rates over the last few centuries have decreased.
Predicting Population Growth
Age Structure – the proportion of people in
different age groups• In the U.S. age groups are balanced• Some nations (Sweden) have a declining growth rate
– Low birth rates and a top heavy age structure
Sweden’s Growth RatesBlue – Certified Birth Rates
Red – Certified Birth Rates
Age Population Pyramids
Predicting Population Growth
Species interact in Biological Communities Populations do not live in isolation; they interact
with other populationsThey do not live in isolationIn some cases they compete for resources such as food,
water, or shelter.
Competition
Community – all inhabitants living in a particular area.• From the organisms in the soil all the way up the food
chain
Interspecific Competition – competition between species• This competition within a single species limits the
growth of the population• This happens when two or more species rely on the
same limited resource
Disturbances and Communities• Communities change continuously
– Natural disturbances:• Fires• Volcanic Eruption• Floods• Storms• Droughts
– Changes not always negative– Some plants require extremely hot temperatures (in a
forest fire) to sprout
• Destroy Organisms
•Change resources such as shelter and water
Disturbances and Communities
• Man made disturbances:
Disturbances and Communities
• Positive “man made” natural disturbances:
Human Activities / Species Diversity
Humans have the greatest impact on Humans have the greatest impact on communities world widecommunities world wide
Land ClearingLand Clearing
• Areas cut down for lumber, planting crops, building (homes)