Download populations

How are Communities different
than Populations?
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A Community is an interacting population of
various kinds of as species in a common
location
A Population is all of the individuals of a
species that live together in one place at one
time.
POPULATIONS
KEY FEATURES OF POPULATIONS, con’t
Population size is limited by:
density-dependent factors
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density-independent factors
Disease
Competition
Predators
Parasites
Food
Crowding
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The greater the population,
the greater effect these
factors have.
Ex. Black plague in the
Middle Ages – more deaths
in cities
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Volcanic eruptions
Temperature
Storms
Floods
Drought
Chemical pesticides
Major habitat disruption (as
in the New Orleans
flooding)
Most are abiotic factors
KEY FEATURES OF
POPULATIONS
1. Population density
 – the number of individuals in a given area.
 – if they are too far apart they may only rarely
encounter one another resulting in little
reproduction.
KEY FEATURES OF
POPULATIONS, con’t
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2. Dispersion
– the way in which the individuals are
arranged.
Most common
PREDICTING POPULATION
GROWTH
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If a population grew at a set amount each year,
say by 10 organisms per year, then the
population has linear growth
However, populations normally do not have
linear growth. Linear growth looks like this:
PREDICTING POPULATION
GROWTH
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Nearly all populations will tend to grow
exponentially as long as there are resources
available.
Two of the most basic factors that affect the
rate of population growth are the birth rate,
and the death rate.
r(rate of growth)=birth rate – death rate
Exponential Growth
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POPULATION GROWTH
PATTERNS
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Exponential growth
curve: population growth
plotted against time.
As a population gets
larger, it also grows at a
faster rate.
This is the maximum
population growth under
ideal circumstances.
Includes plenty of room
for each member,
unlimited resources
(food, water) and no
hindrances (predators).
POPULATION GROWTH
PATTERNS
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Logistic model: This model accounts for the
declining resources available to populations as
they grow.
It assumes the birth and death rates are not
constant.
As the population grows, births decline and
death rises.
Eventually birth=death so the population stops
growing.
Carrying capacity (K): The number of
organisms of one species that an environment
can support indefinitely.
PREDICTING POPULATION
GROWTH
PREDICTING POPULATION
GROWTH
The Exponential curve (also known as a Jcurve) occurs when there is no limit to
population size.
The Logistic curve (also known as an S-curve)
shows the effect of a limiting factor (in this case
the carrying capacity of the environment).
PREDICTING POPULATION
GROWTH
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The environment has a CARRYING
CAPACITY for each population…
Carrying capacity is the number of organisms
that an environment can support.
Once a population reaches its capacity, its
growth stops.
Population Growth Strategies
There are 2 ways a population can prosper:
1. Depends on the rate of growth (r)
2. Influenced by the carrying capacity (K)
Population Growth Strategies
r-strategists: characterized by exponential growth, which
results in temporarily large populations, followed by
sudden crashes in population size. Ex. Insects,
bacteria, some plants
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live in unpredictable and rapidly changing environments
Reproduce quickly when conditions are favorable
Many offspring: small, mature rapidly, no parental care
r = rate of growth
Fast life history pattern!
Population Growth Strategies
K-strategists: characterized by a high degree of
specialization. Ex. Trees, whales, tigers, etc.
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Live in stable and predictable environments
Can compete effectively
Reproduce late in life
Few offspring: large, mature slowly, often much parental
care
K = carrying capacity
Slow life history pattern!
Organism Interactions Limit Population
Size
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Predation
 Predator consuming prey on a large
enough scale can have a drastic effect
on the size of prey population and
hence predator population
Competition
 Many individuals competing for
scarce supplies
 Density-dependent factor
Organism Interactions Limit
Population Size
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Crowding and Stress
 Also density dependant. Stress symptoms
include aggression, decrease in parental
care, decreased fertility, and decreased
resistance to disease
Predation