Populations & Population
Growth
Populations
Random
sampling- take a
representative
sample
Population size - number of members in a population
2 ways to estimate population size:
1. Random sampling – used mainly for plants; samples and
counts organisms in random plots
2. Mark & recapture – used mainly for animals; captures,
marks, and releases animals, then samples the population
again
Populations
Population growth – an increase in the size of a
population
fluctuations
Leveling off
Exponential growth
Beginning growth
Populations
• Carrying capacity –
the maximum number
of individuals in a
population that an area
can support
Populations
• Limiting factor – anything
that limits the survival of
an organism
– Can stop an increase in the
size of a population
– Ex.: food & shelter
availability, climate,
temperature, number of
predators
– Affects carrying capacity (if
food increases, carrying
capacity increases)
Population Growth
• There are 2 types:
– Logistic growth
• Looks like an S-curve
• Levels off at carrying
capacity (K)
• At K, birth rate = death
rate
Population Growth
– Exponential Growth
• Looks like a J-curve
• Population keeps
increasing rapidly
• Birth rate and death rate
are constant
• Limiting factors stop
population from
growing indefinitely
large (ex.: food, space,
etc.)