EVOLUTION

Chapter 11

CH. 11 THE PROCESS OF SPECIATION

I. SpeciationA. Speciation - the formation of new

species.B. Species - is a group of organisms

that breed with one another and produce fertile offspring.

CH. 11 THE PROCESS OF SPECIATION

1. This means that individuals in the same species share a common gene pool.

2. A genetic change that occurs in one individual can spread through the population.

3. If the genetic change increases fitness, that allele will eventually be found in many individuals of that population.

CH. 11 THE PROCESS OF SPECIATION

II. ISOLATING MECHANISMSA. The gene pools of two populations

must become separated for them to become new species.

1. As new species evolve, populations become reproductively isolated from each other.

CH. 11 THE PROCESS OF SPECIATION

a. reproductive isolation - when the members of two populations cannot interbreed and produce fertile offspring.

b. Populations respond to natural selection or genetic drift as separate units.

B. Reproductive isolation can develop in a variety of ways, including behavioral isolation, geographic isolation, and temporal isolation.

CH. 11 THE PROCESS OF SPECIATION

1. BEHAVIORAL ISOLATION – occurs when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior. Example: eastern and western meadowlarks use different songs to attract mates.

CH. 11 THE PROCESS OF SPECIATION

2. GEOGRAPHIC ISOLATION – two populations are separated by geographic barriers such as rivers, mountains, or bodies of water. Example: the Abert squirrel and the Kaibab squirrel.

3. TEMPORAL ISOLATION – two or more species reproduce at different times. Example: three species of orchids release pollen on different days.

Concept Map

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Reproductive Isolation

Isolating mechanisms

Behavioral isolation Temporal isolationGeographic isolation

Behavioral differences Different mating timesPhysical separation

Independentlyevolving populations

Formation ofnew species

CH. 11 THE PROCESS OF SPECIATION

IV. SPECIATION IN DARWIN’S FINCHESA. Natural selection can lead to speciation 1. Speciation in the Galapagos finches

occurred by founders forming a new population, geographic isolation, changes in the new population’s gene pool, reproductive isolation, and ecological competition.

CH. 11 THE PROCESS OF SPECIATION

B. FOUNDERS ARRIVE 1. Many years ago, a few finches

(species A) flew and high winds transported them from South America to the Galapagos islands.

2. Once they arrived, they managed to survive and reproduce.

CH. 11 THE PROCESS OF SPECIATION

C. SEPARATION OF POPULATIONS 1. Later a few finches flew to another

island.2. They became isolated from each

other because finch do not fly over open water.

3. They no longer share the same gene pool.

CH. 11 THE PROCESS OF SPECIATION

D. CHANGES IN THE GENE POOL – 1. Over time, populations on each

island became adapted to their local environments.

2. Food supplies may have been different and one group developed larger beaks forming a separate population.

CH. 11 THE PROCESS OF SPECIATION

E. REPRODUCTIVE ISOLATION 1. Finches mate with other finches

that have bills the same size as their own.

2. Even if the finches wind up on the same island, the gene pools of the two bird populations remain reproductively isolated.

3. The two population then become separate species.

CH. 11 THE PROCESS OF SPECIATION

F. ECOLOGICAL COMPETITION1. If the two types of finches wind up

on the same island there will be competition for food.

2. The more specialized birds have less competition for food.

3. Over time, species evolve in a way that increases the differences between them.

CH. 11 THE PROCESS OF SPECIATION

G. CONTINUED EVOLUTION 1. The process of isolation on different

islands, genetic change, and reproductive isolation probably repeated itself time and time again across the entire Galapagos island chain.

2. Over many generations it produced 13 different finch species.

Patterns of Evolution

I. Macroevolution- large-scale evolutionary patterns and processes that occur over long periods of time

II. ExtinctionA. Extinctions happen for reasons

Darwin proposed1. Species compete for resources and

environments change

Patterns of Evolution

2. Some species adapt and survive, and others gradually become extinct in ways that are often caused by natural selection

3. Many paleontologists think mass extinctions were caused by several geological factors

Patterns of Evolution

4. Each disappearance of so many species left habitats open and provided ecological opportunities for those organisms that survived.

Ex: the extinction of dinosaurs cleared the way for the evolution of modern mammals and birds

Patterns of Evolution

III. Adaptive RadiationA. Adaptive radiation - a single species

or a small group of species has evolved into diverse forms that live in different ways

1. Ex: Darwin’s finches -more that a dozen species evolved from one single species

Patterns of Evolution

IV. Convergent EvolutionA. Convergent evolution - the process by

which unrelated organisms come to resemble one another

1. caused by similar environmental demands, such as moving through air, moving through water, or eating similar foods

2. Ex.: the streamlined body and various appendages of a shark (fish), a penguin (bird), and a dolphin (mammal)

Patterns of Evolution

V. CoevolutionA. coevolution - the process by which

two species evolve in response to changes in each other over time

1. caused by the ecological interactions between organisms

2. Ex.: shape of flower and moth’s feeding tube

Patterns of Evolution

VI. Punctuated EquilibriumA. Evidence suggests that evolution

has often occurred at different rates for different organisms at different times during the history of Earth

B. punctuated equilibrium - pattern of long, stable periods interrupted by brief periods of more rapid change

Flowchart

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Species

Unrelated Related

Inter-relationshiops

Similar environments

Intense environmental

pressure

Small populations

Different environments

Coevolution Convergent evolution

ExtinctionPunctuated equilibrium

Adaptive radiation