Download Section_2_Studying_Populations

Scientists found that, over a period of 200 years, a
mountain pond was transformed into a meadow.
During that time, several communities of organisms
were replaced by different communities. Which of
these best explains why new communities were able to
replace older communities?
a. The original species became extinct.
b. Species in the older community died from old age.
c. The abiotic characteristics of the habitat changed.
d. Diseases that killed the older organisms
disappeared.
In order to maintain the biodiversity in an aquatic
ecosystem the water must have plenty of dissolved
oxygen. Which of the following would increase the
amount of dissolved oxygen available?
a. Use heaters to warm the water because warm water
has more available oxygen than cool water.
b. Remove obstructions within the water way so that
the water can maintain a steady flow because
flowing water has more oxygen than stagnant water.
c. Remove trees along the water way that rob the
water of oxygen.
d. Increase the amount of fertilizer run off leading to
eutrophication.
How does succession impact the biodiversity in an
area?
A.Both primary and secondary succession increases
the biodiversity after an environmental disturbance.
B.Primary succession only, increase biodiversity since
this occurs on brand new land while secondary
succession maintains the biodiversity.
C. Secondary succession only, increase biodiversity
since this occurs on brand new land while primary
succession maintains the biodiversity.
D. Both primary and secondary succession decreases
the biodiversity of an area because the disturbance
wipes out life in the area.
Determining Population Size

There are four basic Methods that ecologists
use to determine population size?
 Direct observation
 Indirect observation
 Sampling
 Mark and recapture studies
Determining Population Size

Determining the size of ant population by
knowing the number of ants that inhabit one ant
hill, and then observing how many ant hills are in
one particular area.
Indirect observation
Determining Population Size

Ecologists estimate the size of the rainbow trout
population in a lake by catching a small sample,
tagging them and then releasing them. They come
back three weeks later and catch another sample
noting how many trout have tags, and how many do
not.
Mark and recapture studies
Determining Population Size

Determining the number of frogs in a pond
by counting all of them individually.
Direct Observation
Determining Population Size

Estimating the number of daisies in a 100
square meter meadow by counting the
daisies in a 10 meter by 10 meter plot, and
then multiplying by 100.
Sampling
Putting it all together

Direct observation of a population gives you the most
accurate count of a population while indirect observation
is more of an estimate. Why would an ecologist use
indirect observation instead of direct observation.
– Because it is not always
practical to count all the
individuals in a population.
Changes in Population Size

List 2 ways a population can change in size:
When new members join the population
1. _______________________________
When members leave the population
1. _________________________________
Changes in Population Size

Birth Rate
–

Death Rate
–

Number of deaths in a population over time.
Immigration
–

Number of births in a population over time.
New members move into a population.
Emigration
–
Members leave the population.
Changes in Population Size

Which Two allow a population to increase?
– Birth Rate
– Immigration

Which two allow a population to decrease?
– Death Rate
– Emigration
Changes in Population Size

What does the population statement say?

If birth rate > death rate, population
size increases.

If death rate > birth rate, population
size decreases.
Population Density

The number of individuals in a specific area.
Population Density =
Number of Individuals
Unit Area
Limiting Factors

An environmental factor that causes a
population to decrease.
– Food and Water
– Space
– Weather
Limiting Factors

Pick one of the limiting factors and describe
how it limits population growth.

Food and Water
Space
Weather


Carrying Capacity

The largest population that an area can
support.
– Determined by the limiting factors that
are present.
Carrying Capacity
Types of population growth
Predator-Prey Relationships
• Without predators, certain species of prey
would drive other species to extinction
through competition.
• Without prey, there would be no predators
Predator-Prey Relationships
Competition
• When the population increases to a size so
that resources such as food or space
become limited, individuals in the ecosystem
must compete for resources
R strategist vs K strategist
R
K
Unstable environment, density
independent
Stable environment, density
dependent interactions
small size of organism
large size of organism
energy used to make each individual is energy used to make each individual is
low
high
many offspring are produced
early maturity
short life expectancy
each individual reproduces only once
Mouse, frog
few offspring are produced
late maturity, often after a prolonged
period of parental care
long life expectancy
individuals can reproduce more than
once in their lifetime
Whale, elephant