11 Counting Populations

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1-1 Counting Populations
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What is the population density of deer if there
are 100 deer in 20 square meters?
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What are some ways that we can estimate a
population size?

• Direct Observation
• Indirect Observation
• Sampling
• Mark-and-Recapture Studies

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Direct observation counting the number of
species one by one in an area to determine the
population
Indirect observation Used to find population
when animals are small or hard to find. Ex.
Counting tracks, number of birds nests, and then
making an estimate.
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Population sampling is used when it is not
possible to count every member of a population.
Ecologists can make an estimate based on a sample
population from a given area.
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What is the estimated population for this area
based on this sample?
What possible errors could there be in this
method?
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Another way to estimate population is through
mark-and-recapture studies.
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Animals are captured, marked, and released into
the environment.
Then another group of animals is captured. The
population is based on the number of animals that
are recaptured with marks on them.
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Here you can see a shark that was tagged before
being released.
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4 factors that affect population growth
Birth Rate
Death Rate
Immigration
Emigration
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What are some limiting factors on population
growth?

• Amount of food available
• Space
• Weather

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1-3 Types of Interactions
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Natural selection - the changes that organisms go
through over time allowing them to adapt better
to their environment.
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Animals with favorable characteristics survive
and pass those characteristics on to their
offspring. Animals without favorable
characteristics do not survive, and over time
these traits tend to disappear.
What adaptations has this deer acquired over time
that help it to survive?
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Over a period of time organisms evolve in
response to their environment. These changes
that occur that make them better suited for their
environment is called NATURAL SELECTION.
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There are 3 major types of interaction among
organisms

• Competition
• Predation
• Symbiosis

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Organisms compete for a variety of things. Can
you name some of them?
Organisms that survive have adaptations that help
to reduce competition
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Predators have adaptations that help them catch
and kill their prey.
Prey have adaptations in order to help them
survive predation. Can you name some of them?
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There are 3 types of symbiotic
relationships
Mutualism, Commensalism, and parasitism
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Which relationship benefits both organisms
involved?
Mutualism
Which relationship benefits one and harms the
other?
parasitism
Which relationship benefits one organism and
neither helps or harms the other organism.
Commensalism
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THE END