Chapter 24Chapter 24Section 2

CompetitionCompetitionI. 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.

CompetitionCompetition

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

CompetitionCompetitionI. 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 foodThey need the same type of shelter

III. Competition also occurs among different species

Population SizePopulation 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 SizePopulation Size

I. Ways to measure population size1. Trap-mark-release

a) Trap the animals without injuring themb) Mark the animal and releasec) Later another sample of animals is

captured d) Some of the animals will have marks

and others will note) By comparing the marked animals to

the unmarked ecologists can estimate the population size

Population SizePopulation SizeI. 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 SizePopulation 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 SizePopulation SizeExample:

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 SizePopulation Size

I. Carrying CapacityLargest 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 SizePopulation SizeWhat 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 SizePopulation SizeBiotic 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 PopulationsChanges in PopulationsBirthrate 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 PopulationsHow 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 PopulationThe same is true for human

populations

Look at Table 1 on page 692

What is happening in Zimbabwe?

What is happening in Germany?

Moving AroundAnimals 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 AroundBirds 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 AroundPlants 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 GrowthWhat 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 GrowthExponential 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 GrowthDo 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