Applying a general model of natural selection to a variety of cases that focus on both survival and reproduction.

We have now developeda general natural selection model.

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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.

Red-Bellied Black Snakes

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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?

AnswersInitial 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.

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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.

Guppies

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?

• Fill in in the table on page 3 for the guppies.

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Bed Bugs

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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?

• Fill in in the table on page 3 for the bed bugs example.

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PeacocksAt 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.

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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?

Revising the General Model

 

Some traits help individuals survive.

Individuals with version of trait _______________________ are more

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 ___________________________________________ .

 

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Revising the General Model

 Some traits help individuals survive / mate more. (Circle one.)

Individuals with version of trait _______________________ are more

likely to survive / mate more after the environmental change. The trait is advantageous because ______________________________.

Offspring  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 ___________________________________________ .

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Complete page 7 for the peacocks.

Bacteria

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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?

• Fill in in the table on page 8 for the bacteria.

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Sage Grouse

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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.

• Fill in in the table on Page 9 for the sage grouse example.

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