Transcript Applying Natural Selection

Applying a general model of
natural selection to a variety
of cases that focus on both
survival and reproduction.
We have now developed
a general natural selection model.
Initial population
1. The initial population varies in many traits.
Most individuals have one version of some
traits.
Environmental change
2. An environmental change occurs.
Some traits help
individuals survive.
3. Individuals with one version of a trait are
more likely to survive after the environmental
change. The trait is advantageous in the new
environment.
Offspring
4. The individuals that survive more
reproduce more. Their offspring vary but are
similar to them. So more offspring have the
advantageous version of the trait.
Population after many
generations
5. After many generations, the population still
varies, but most individuals have the
advantageous version of the trait.
2
Red-Bellied Black Snakes
Red-Bellied Black Snakes live in Australia,
usually in forests or woodland areas. Cane
toads are also found in Australia. These
toads are poisonous and large in size. They
were first introduced to Australia by
humans in 1935. Red-Bellied Black Snakes
feed on frogs and toads and eat them
whole.
The Red Bellied-Black Snakes’ head sizes
vary but recently scientists have found a
surprising change! In certain areas where
cain toads are found, the Red-Bellied Black
Snakes’ head sizes are smaller today, on
average, than they were in 1935.
Why are the snake’s heads smaller?
3
Answers
Initial Population: The initial population of Red-Bellied Black
Snakes varies in many traits, including head size. Most
individuals have this version of the trait: large head size.
Environmental Change: An environmental change occurs:
Poisonous cane toads are introduced to Australia.
Some traits help individuals survive: Individuals with version of
trait small head size are more likely to survive after the
environmental change. The trait is advantageous because snakes with a small head size cannot eat the cane toads.
Offspring: The individuals that survive more reproduce more.
Their offspring vary but are similar to them. So more offspring
have the advantageous version of trait small head size.
Population after many generations: After many generations, the
population sill varies, but most individuals have the advantageous
version of trait small head size.
Guppies
Trinidad is a tropical island in South America
with many streams through the forests with
many different kinds of fish in them. One fish in
these streams is the guppy. Trinidad’s male
guppies have a highly variable pattern of
colorful spots. What this means is that some
guppies are bright and have many colorful spots
on their tails. Other guppies are dull in color
and have very few spots on their tails.
Recently, a new predator, the killifish, has moved into the streams where the
guppies live. Scientists have been studying several generations of guppies since
the killifish were introduced to the stream. They have noticed that on average,
guppies are now much less colorful than they were before the killifish arrived.
Why are the guppies less colorful now than they used to be?
5
• Fill in in the table on page 3 for the
guppies.
6
Bed Bugs
In 2009, New York City had a serious problem with bed bugs. They infested many
homes and hotels throughout the city so a common pesticide called deltamethrin
was used to kill them. But the pesticides are no longer working! A researcher who
studies bedbugs did a study showing the percent of bed bugs that were killed in 2009
and 2012 by deltamethrin. His results are below:
2009
2012
Percentage of Bed Bugs killed
effectively by deltamethrin
99%
34%
Percent of bed bugs immune to
detamethrin
1%
68%
Why are bedbugs more
resistant to pesticide now
than they were in 2009?
7
• Fill in in the table on page 3 for the bed
bugs example.
8
Peacocks
At the Gir Forest National Park in India, there used to be a population of
many female peacocks and only a few male peacocks. Then, many new
males were introduced to the park because they were relocated to the park
from another area. Now, there are many males and fewer female peacocks.
There was a lot more pressure on males to reproduce.
Park rangers have recently noticed a
change in the new generations of
peacocks. Male peacocks are more
colorful now than they used to be
before.
Why are male peacocks today more
colorful than they used to be?
9
Revising the General Model
Individuals with version of trait
_______________________ are more
Some traits help
individuals survive. likely to survive after the environmental change.
The trait is advantageous because
______________________________.
Offspring
The individuals that survive more reproduce more.
Their offspring vary but are similar to them. So
more offspring have the advantageous version of
trait
_________________________________________
__ .
10
Revising the General Model
Some traits help
individuals survive /
mate more. (Circle
one.)
Offspring
Individuals with version of trait
_______________________ are more
likely to survive / mate more after the
environmental change. The trait is
advantageous because
______________________________.
The individuals that survive / mate more
reproduce more. Their offspring vary but are similar
to them. So more offspring have the advantageous
version of trait
_________________________________________
__ .
11
Complete page 7 for the peacocks.
Bacteria
Recently, doctors have found that many kinds of bacteria are becoming
resistant to antibiotics. The same antibiotics that would kill the bacteria years
ago no longer works as effectively.
MRSA is a kind of bacteria that infects people. Years ago, MRSA could be killed
by many kinds of antibiotics. Some common antibiotics that used to work on
MRSA are penicillin and amoxicillin. Now MRSA is resistant to these and many
other antibiotics.
How did this resistance occur?
13
• Fill in in the table on page 8 for the
bacteria.
14
Sage Grouse
Sage grouse is a type of bird found western North America. Their mating
rituals take place in a lek, an area where birds gather during breeding
season for courtship displays. Males “strut” to attract females over a 3
month period. This strut can be seen in the video on the next slide.
Females visit the lek for 2-3 before mating to choose their mate. Scientists
have found that females tend to choose males that attended more leks and
had a higher display rate.
15
• Fill in in the table on Page 9 for the sage
grouse example.
16