Transcript Population Growth

Population Growth
What is a population
• A group of organisms of the same species
that live in the same area
Population Ecology
• The study of how and why
populations change.
• Why would the population of a herd
of zebra change?
Factors in Population Changes?
• What factors cause changes in:
• Size of population
• Density of population
• Distribution of population
• Growth of population
Once these factors are identified then
ecologists can predict how that
population may change in the future!
Exponential Growth ( J curve)
• When the population size is
doubled EVERY
GENERATION
• Requires that there be no
limiting factors
• Ex. Bacteria, Humans
Assumptions!
1. All cells live!
2. All bacteria cells reproduce!
Does this REALLY occur in nature?
Limiting Factors
• Any biotic or abiotic resource in the
environment that limits the size of a
population
• Either cause a decrease in the birth rate or an
increase in the death rate
Carrying Capacity
• The number of individuals in a population
that an environment can support over a
long period of time
Density-Dependent Limiting
Factors
• Factors that become limiting when the
number of organisms per unit of space
(density) reaches a certain level
Examples: Living Space
Disease
Competition
Predation
Limiting Factors –
Living Space
• Overpopulation – more
individuals than there is an
area for them to live
• Often this causes birth rates
to decrease
Limiting Factors –
Disease
• Spreads rapidly
when the population
is dense
• Bubonic Plague
Limiting Factors –
Competition
• The interaction when
organisms are trying
to obtain the same
limited resources
Compete for food, water,
mates, & territory
Limiting Factors –
Predation
• An interaction in which one species
(predator) feeds on another (prey)
Population Cycles –
Predator-Prey Interactions
• When hares are plentiful the lynx population
grows because more offspring survive
Cycle….
• More lynx’s means
more hares eaten….
Eventually they run
out of food and the
lynx population
decreases
Cycle….
• Now that there are
less lynx’s the
population of hares
increases
Cycle…
• Once there is more hares there’s more food
for the lynx’s and their population increases
again!
The Population Cycle!!!!
Density-Independent Limiting
Factors
• Factors that affect all populations in the same way,
regardless of their density.
• Examples:
• Weather
• Seasonal Cycles
• Natural Disasters
• Human Activities
Boom & Bust
• Period of
Exponential Growth
followed by a sudden
collapse of the
population
• Seen in areas where
there are seasonal
changes or droughts
Non-native species
• Species that are from one
area and are brought to a
new area, usually by
humans
• Usually out-compete
native species
Are purposely brought to an area, in cargo ships, etc…
Logistic Growth (S curve)
• Population grows to the
carrying capacity of the
environment
• # of individuals the
environment can support
• Limiting factors do not allow
exponential growth
• Space
• Food
• Water
Population Growth Rate
• The total change in a
population’s size over a
period of time
Growth Rate = Change in # of individuals
Time period
4 Factors of Growth Rate
1. Birth Rate
2. Immigration
3. Death Rate
4. Emigration
Birth Rate
• The amount of
individuals born
over a time period
• How many babies
are born in the
population
If the birth rate is high, then the population will increase!
Immigration
• The movement of
organisms into an
area already
occupied by an
existing population
If immigration is high, than the population will increase!
Death Rate
• The amount of
individuals that die
over a time period
An increase in the death rate will cause the population
to decrease!
Emigration
• The movement of
organisms out of an
area where a
population is
located
An increase in emigration will cause the population to
decrease!
Age
• Young population vs. Older population
• Population will increase more with a young
population