Chapter 24
Section 2
Competition
I.
Animals compete for food and space.
◦ Competition occurs when 2 or more
organisms seek the same resource at the
same time
◦ Ex. Gila woodpecker lives in Arizona and
Mexico. They live in holes in saguaro cactus.
Competition
I.
Competition limits population size
If nesting spaces are limited some
woodpeckers won’t be able to raise their
young
II.
If food becomes scare some
woodpeckers might not survive to
reproduce
Competition
I.
Limits on population growth are food,
living space, or other resources
II.
The most intense competition comes
from individuals of the same species
They need the same type of food
They need the same type of shelter
III.
Competition also occurs among
different species
Population Size
I.
Ecologists often need to measure the
size of a population.
Counts of the population can indicate if a
population is healthy and growing or in
danger of disappearing.
Population Size
I.
Ways to measure population size
1. Trap-mark-release
a)
b)
c)
d)
e)
Trap the animals without injuring them
Mark the animal and release
Later another sample of animals is captured
Some of the animals will have marks and others
will not
By comparing the marked animals to the
unmarked ecologists can estimate the population
size
Population Size
I.
To measure rabbits in a large population
Ecologists use sample counts
1. Determine the area of the population (Ex.
100 acres)
2. Count the number of rabbits in 1 acre
3. Multiple it by 100 to estimate the
population size
Population Size
I.
Limiting Factors:
Anything that restricts the number of
individuals in a population.
Can be living and non-living features
Can affect more than one population
Population Size
Example:
Lack of rain limits plant growth in a
meadow
Fewer plants = fewer seeds
For seed eating mice this causes less food
availability
Fewer mice means less prey for hawks and
owls
Population Size
I.
Carrying Capacity
Largest number of individuals of one species
that an ecosystem can support
When the population begins to exceed the
carrying capacity some individuals will NOT
have enough resources
With a lack of resources animals die or
move out of the population
Population Size

What would happen if there were no
limiting factors that restricted the growth
of a population?
◦ The highest rate of reproduction under ideal
conditions is a population’s biotic potential
◦ The larger the number of offspring produced
by parent organisms = a higher biotic
potential of the species
Population Size

Biotic Potential Example
◦ Compare an avocado tree to a tangerine tree
◦ Each avocado = 1 large seed
◦ Each tangerine fruit = a dozen seeds or more
◦ Because the tangerine produces more seeds
per fruit it has a higher biotic potential than
the avocado tree
Changes in Populations

Birthrate and Death rate influence the
size of a population – also affects the rate
of growth

A population gets larger when the # of
individuals born is greater than the # that
die.

http://www.worldometers.info/
Changes in Populations

How does a population get smaller then?
◦ There are more deaths than births

Ex: In Central Park one year 900 squirrels
were born and 800 died
◦ This shows the population increasing by 100

If the next year 400 squirrels were born
and 500 die then the population is
decreasing by 100 squirrels
Changes in Population

The same is true for human populations

Look at Table 1 on page 692

What is happening in Zimbabwe?

What is happening in Germany?
Moving Around

Animals moving from place to place can
affect population size

Why would animals move from place to
place?
◦
◦
◦
◦
Food
Mates
Space
Natural disaster or human causes
Moving Around

Birds move during annual migrations
◦ Orioles live in eastern North America during
the summer and migrate to Central America
for the winter
◦ Move due to temperature and food resources
Moving Around

Plants and Microscopic organisms move too
◦ Wind
◦ Water
◦ Being carried by animals
Seeds and spores are carried by the wind
 Spine-covered seeds cling to the fur of animals
and clothing on humans
 Others are carried by water currents

Exponential Growth

What happens when a species moves
somewhere with a lot of available food,
living space, and other resources?
◦ The population grows quickly

What type of growth do we call this?
◦ Exponential Growth
Exponential Growth

Exponential growth means that the larger
the population is the faster it grows

What happens when it reaches its
carrying capacity?
◦ The population can’t support any more
animals
◦ The better adapted survive and reproduce
◦ Some move to different area
Exponential Growth

Do you think that the Earth has a carrying capacity?
◦ Yes
◦ By the year 2050 our population could be over 9 billion
◦ As our population grows we are forced to live closer together
◦ Diseases spread faster
◦ http://www.worldometers.info/world-population/
◦ http://www.census.gov/main/www/popclock.html