Transcript Population Ecology

Population Ecology
What is a population?
• All the members of a species living in the
same place at the same time.
• Organisms usually breed with members of
their own population.
How to describe populations
• Density: number of individuals per unit
area, or volume. Ex. Number of deer/km2.
• Dispersion: The distribution or
arrangement of individuals in space.
• Dispersion may be clumped, even or
random.
Growth Rate
• A change in the size of a population over a
given period of time = growth rate.
Growth rate = births – deaths
• Populations usually stay about the same
size from year to year as factors kill many
individuals before they can reproduce.
How fast can a population grow?
• Reproductive potential: The maximum
number of offspring that each member of a
population can produce.
• Some species have much higher
reproductive potential than others.
How many bunnies?
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Rabbits can begin reproducing at 4 - 6 months
Gestation is 31 days
Litters can be up to 14
Females can become pregnant within hours of
giving birth
• Lifespan is about 7 years
• 95 billion rabbits in 7 years!
Exponential growth
• Occurs only when
there is enough:
Food
Space
Little or no competition
No predators
• Populations rarely
grow at their
reproductive potential
Carrying Capacity
• Carrying capacity is: the maximum
population that an ecosystem can support
indefinitely.
• Ecosystems change so carrying capacity
is difficult to predict or calculate precisely.
Resource Limits
• A species reaches its carrying capacity
when it consumes a natural resource at
the same rate at which the ecosystem
produces the resource.
• This resource is called the limiting
resource.
• Examples include: light, nutrients, water.
Density Dependent Population
Regulation
• Deaths occur more
quickly in a crowded
population.
• Limited resources,
predation and disease
result in higher death
rates in dense
populations.
• Ex. Emerald Ash
Borer possibly going
to invade Iowa
Density independent
• A certain proportion of a population dies
regardless of population density. Ex.
Severe weather