Speciation Summary Questions

All of the answers for these come from your reading or notes.  Answer them to the best of your abilities and give as many examples as you can.  

 

1. What is sympatric speciation and give an example?
2. What is allopatric speciation and give an example?
3. What is selective breeding and give an example?

 

OTHER FACTORS THAT ARE NATURAL INFLUENCES

WHY SO MANY SPECIES?

There are millions of species of living things on the planet.

• But why are there so many?
• As environments change over time, organisms must constantly adapt to those environments.
• Diversity of species increases the chance that at least some organisms adapt and survive any major changes in the environment.
  • For example, if a natural disaster kills all of the large organisms on the planet, then the small organisms will continue to survive.

 

Reproductive Isolation

There are two main ways that speciation happens naturally.

• Both processes create new species by isolating populations of the same species from each other.
• Organisms can be geographically isolated or isolated by a behavior.
• Over a long period of time, usually thousands of years, each of the isolated populations evolves in a different direction.

 

Geographic Isolation

Allopatric speciation happens when groups from the same species are geographically isolated for long periods.

• Imagine all the ways that plants or animals could be isolated from each other:

 

• • A mountain range
  • A canyon
  • Rivers, streams, or an ocean
  • A desert

 

Example:

When the Grand Canyon in Arizona formed, two populations of one squirrel species were separated by the giant canyon. 

• After thousands of years of isolation from each other, the squirrel populations on the northern wall of the canyon looked and behaved differently from those on the southern wall.
  • North rim squirrels have white tails and black bellies.
  • Squirrels on the south rim have white bellies and dark tails.
• They cannot mate with each other, so they are different species.

                     

            Northern Rim – Abert squirrel         Southern Rim – Kaibab Squirrel

 

Sympatric

Sympatric speciation happens when groups from the same species stop mating because of something other than physical separation, such as behavior.

• The separation may be caused by different mating seasons, for example.

 

Some scientists suspect that two groups of orcas (killer whales) live in the same part of the Pacific Ocean part of the year, but do not mate.

• The two groups hunt different prey species, eat different foods, sing different songs, and have different social interactions.

 

 

Watch these videos:

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HOW HAVE HUMANS IMPACTED EVOLUTIONARY TRENDS?

Natural Selection and Adaptation

The theory of evolution by natural selection means that the inherited traits of a population change over time through a process called natural selection.

• Inherited traits are features that are passed from one generation to the next.
  • For example, your eye color is an inherited trait (you inherited it from your parents).
• Inherited traits are different from acquired traits, or traits that organisms develop over a lifetime, such as strong muscles from working out.

 

SELECTIVE BREEDING (Artificial Selection)

With an understanding that some traits are more desirable than others, researchers have been studying ways to increase the presence of desirable traits in the populations of different organisms as well as decrease the presence of bad traits.

• One method that has been developed is selective breeding.
• In selective breeding, two organisms with desirable traits are crossed to produce offspring with those same traits.
• By continually crossing for the same good traits, scientists are able to improve the genetic make-up of a species.
• Purebred animals are the result of selective breeding.

 

One of the areas where selective breeding gives the most benefit is in farming and ranching.

• By selecting the best stock for reproduction, the farmer can improve the quality of his plants or animals.
• Suppose a corn farmer harvested his crop and half of the corn had huge, beautiful kernels while the other half had tiny scrawny kernels.
  • Which corn should he save for seed next year?
  • The answer would be the corn with the bigger kernels.
  • By using this corn, the farmer would increase the presence of the “big kernel genes” and improve his crop.
• Dairy cows like this Holstein are carefully bred for traits that will give them better strength and produce more milk.

 

A trait chart can be used to show stronger and weaker traits that an animal has.  This helps the farmer decide which animal to breed to produce the best stock.

 

For many years dairy farmers have practiced selective breeding to increase milk production in their cows.

• This practice has been limited in the past since the farmer can only use the cows that he has.
• He cannot change their genetics so the only control that dairy farmers have had is over which bulls to use for reproduction.
• Only bulls from the best milk producing cows are used.

 

In recent years, advances have been made in choosing only the best cows to reproduce.

• If a farmer has a high producing cow and one that does not produce much milk, the good producer can be given a drug that causes her to release several eggs from her ovaries.
• The eggs can then be harvested, fertilized, and implanted in a low producing cow.
• This way, even the lower milk producers can give birth to genetically superior calves.

 

Selective breeding is also used to increase the desirable characteristics of other animals.

• Purebred dogs are a good example.
  • Breeders identify the desirable traits of a species and cross breed in order to increase the presence of those desirable traits within the species.
  • Dogs can be selectively bred as watch dogs, hunting dogs, good swimmers, intelligence, and many other traits.
• Horses can be bred to increase desirable traits such as strength and speed.
• Even fruits and vegetables are bred selectively to increase size, flavor, and production.

 

Artificial Selection (Man Made Influences)

Artificial selection occurs when humans select which plants or animals to breed to pass specific traits on to the next generation.

• For example, a farmer may choose to breed only cows that produce the best milk and not breed cows that produce less milk.
• Humans have also artificially bred dogs to create new breeds.

 

Humans selected the genetic information of parent dogs to create these different breeds.

• Both dog breeds are descended from the same wolves, and their genes are almost identical.
• Yet there is at least one difference between their genes that determine size.