SPECIATION

SC B-5.4: Explain how genetic variability and environmental factors lead to biological evolution.

Speciation:

formation of a new speciesSpecies: group of similar

organisms that can successfully breed & their offspring are fertile Individuals of same species share a

common gene pool genetic change in 1 member of species

can spread thru the population▪ If that change increases fitness many

members of the species

Isolating Mechanisms

When a subset of a population becomes isolated & no longer breeds with original population over time they will no longer be able to interbreed …..new species has formed

Behavioral Isolation

Occurs when 2 populations are capable of interbreeding BUT have differences in courtship rituals or reproductive strategies that involves behavior

Behavioral Isolation

Eastern & Western meadowlarks have overlapping ranges.

No interbreeding because they have different mating songs

Geographic Isolation

2 populations physically separated by geographic barriers May separate some species (non-flying

insects, small mammals) but not others (birds, flying insects)

Does not guarantee formation of new species

Geographic Isolation

Temporal Isolation

2 or more species reproduce at different times

Testing Natural Selection in Nature

Darwin’s Finches: Once Darwin

realized all the birds on the Galapagos were finches he hypothesized that they all had a common finch ancestor

Darwin’s Finches

His hypothesis relied on 2 testable assumptions:

1. Must have enough heritable variation to provide raw material for natural selection

2. These variations must produce differences in fitness

Darwin’s Finches

Variation studied by Peter & Rosemary Grant Found lots of variation in a # of traits

Darwin’s Finches

Was there differences in their fitness?

Factors Leading to Speciation

Galapagos finches: Small birds Do not usually fly over open water

Factors Leading to Speciation

1. Founder Effect a few finches from South America

made it to one of the Galapagos islandsonce there, they managed to survive & reproduce

Factors Leading to Speciation

2. Geographic Isolationonce there, birds do not move from island to island

Factors Leading to Speciation

3. Changes in the Gene Poolover time populations on different islands natural selection forces acted on the different populations…which had slightly different variations among the population…leading to development of different adaptations suited to the available food sources on each island

3. changes in the Gene Pool Over time natural selection would have

caused birds on islands with large seeds or nuts as food source to have larger and larger beaks… birds on islands with plentiful small seeds would still have small beaks

Factors Leading to Speciation

4. Reproductive Isolation if finches return to original island

after natural selection has changed their beak size they are not likely to interbreed with original population of finches

the finch is very particular about beak size when choosing a mate

So population with large beak will live in same community as small beaked finches but never interbreed

Factors Leading to Speciation

5. Ecological Competition different populations of finch on

same island will be competing for resources

during dry season when few seeds available those with more specialized beaks will have less competition from others so will be more successful ….over time differences between populations will increase

Factors Leading to Speciat

6. Continued Evolution This process of geographic

isolation..reproductive isolation…genetic change would have been repeated many times over the years on the Galapagos

Studying Evolution Since Darwin

Modern technology has confirmed Darwin’s hypothesis that living species descended with modification from common ancestors that lived in ancient past DNA, RNA, proteins

Limitations of Research

There are “holes” in the evolutionary tree intermediate fossils helpful

Why is Understanding Evolution Important?

Because it is still going on Drug-resistance in bacteria

Understanding it helps respond to changes in ways that hopefully improve human life