Transcript Density-dependent factors

Populations
Populations Dynamics
Population: A group of organisms of the same
species, that in live in a specific area.
Biosphere
Biome
Ecosystem
Community
Population
Organism
Exponential Growth
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J-shaped curve- growth slow, then increases
rapidly
As the population gets larger, it grows at a
faster rate
Unchecked growth
See Fig. 4.2
Growth Limits
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Limiting factors will cause population growth
to slow
Examples: predators, food, disease, space
Can cause an S-shaped curve
See Fig. 4.3
Carrying Capacity
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Number of organisms of 1 species that an
environment can hold
Increased resources, more births than
deaths, population increases
When a population goes past carrying
capacity, limiting factors kick in --(deaths
exceed births)
Life Boat analogy…
Reproduction Patterns
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Life history pattern  organism’s
reproductive pattern
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Short life history pattern: reproduce very
rapidly; mature rapidly; produce many offspring;
unstable environment;
ex. mosquitoes
Long life history pattern: slow rate of
reproduction; mature slowly; few young produced;
more stable environments; at or near carrying
capacity; ex. elephants
Limiting Factors Continued..
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Density – the # of individuals in a given area
Limiting Factors Impacting Population
Dispersal (2 types)
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Density-dependent factors
Density-independent factors
Density-dependent factors
– increasing effect as population increases
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Disease
Competition
Predators
Parasites
Food
Crowding
Stress
Density-independent factors
– Affect populations regardless of their density
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Volcanic eruptions
Temperature
Storms
Floods
Habitat disruption
Human Population
Why is it important to know how many people
there are in the world and where they are
located? Who keeps track of this?
It took from the first existence of man to the
year 1800 for the world population to get to 1
billion… What is the world’s population now?
World Population
Demographics
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Demography – study of human population size,
density and distributions, movement, and birth and
death rates
Birthrate – number of live births per 1000 population
in a given year
Death rate – number of deaths per 1000 population
in a given year
Immigration – movement of individuals INTO a
population
Emigration - movement of individuals OUT of a
population
Calculating Population Rates
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Population Growth Rate (PGR) = birthrate –
death rate
If birthrate = death rate, then zero population
growth, but still changing.
If PGR is above zero, then more entering than
leaving the population
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Doubling time – time needed for a population
to double in size
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Slow double time: developed country (ex:
Germany)
rapid double time: developing country (ex: India)
DT = 70/percent increase
Age structure – the proportions of the
population that are in different age levels
What limiting factors should the next president
of the United States be concerned with in our
nation? Explain.