15.1: New Species Evolve

Objectives:1. Describe the biological

species concept.2. Distinguish b/w micro and

macroevolution.3. List types of reproductive

barriers b/w species.4. Explain how geographic

isolation and adaptive radiation contribute to species diversity.

5. Summarize models for the tempo of speciation.

Vocabulary

Biological Species concept

Macroevolution

Speciation

Reproductive Isolation

Geographic Isolation

Adaptive Radiation

Punctuated Equilibrium

When do new species evolve?

Evolution of Human Species

Hominids

Humans Neanderthal

Most Recent Common Ancestor

Homo heidelbergenesis, 600 - 300 ka (thousands)Homosapiens and Neanderthal evolve from

Australopithicus, 3.2 m.y.a“Lucy”

Homo erectus 1.8 - 1.3m.y.a

Homo Habilis 2.3 - 1.4 m.y.a

SPECIATION

• = formation of new species.= formation of new species. SSpecies pecies = a group of organisms = a group of organisms that that breedbreed with one another and with one another and produce produce fertile fertile offspringoffspring. .

• The The gene poolsgene pools of two populations of two populations must become must become separated.separated.

• When the members of two populations When the members of two populations cannot cannot interbreedinterbreed and produce fertile and produce fertile offspring, offspring, reproductive isolationreproductive isolation has has occurred and occurred and speciationspeciation will result. will result.

Micro vs. Macroevolution

Change allele frequencies W/IN A POPULATION.

• Small changes fr. generation to generation

• Result: What species look like can change over time.

*Does NOT change branches on EVOLUTIONARY TREE

Large scale changes in biological record (fossils)

• Origin of new species

• Extinction of species

• Evolution of new features (backbones, wings, etc)

• Result: Increase in # of species

*Changes branches on EVOLUTIONARY Tree

Speciation: Reproductive Barriers

Species separate when they cannot interbreed.

Reproductive Isolation: Condition that keeps 2 species from interbreeding

1. Timing Issues: 2 species have diff. Breeding seasons

2. Behavior: Different courtship or mating behaviors

3. Habitat: Surface water v. deep water

4. Not anatomically compatable

Speciation: Geographic Barriers

Species separate when they cannot interbreed.

Geographic Isolation: Separation of populations by barriers like mountains

Over time isolated populations change through microevolution (natural selection acting on

variations to produce adaptations)

Divergent v. Convergent Evolution

DivergentDivergent• One species gives rise One species gives rise

to many speciesto many species• Also known as Also known as

adaptive radiationadaptive radiation• Many species with Many species with

common ancestorcommon ancestor• Many Many homologous homologous

structuresstructures

ConvergentConvergent• Similar looking species Similar looking species

that do not have a that do not have a common ancestorcommon ancestor

• Similar behavior and Similar behavior and appearance due to appearance due to environmental environmental similaritiessimilarities

• Many Many analogous analogous structuresstructures

Divergent Evolution (Adaptive)

Convergent Evolution (Adaptive)

Coevolution: The evolution of one species is directly influenced

by the evolution of another

Rate of Speciation Two Models

Gradualism v. Punctuated Equilibrium

Punctuated Equilibrium

• Slow background Slow background evolution (stasis) is evolution (stasis) is interrupted by rapid interrupted by rapid bursts of changebursts of change

• Rapid/Abrupt bursts Rapid/Abrupt bursts of change usually of change usually occur after a mass occur after a mass extinctionextinction– Abrupt : w/in a few Abrupt : w/in a few

thousand yearsthousand years

Seen in fossil record after mass extinctions.

Speciation in Darwin's Speciation in Darwin's FinchesFinches

Speciation of Darwin’s Finches

•founding of a new founding of a new populationpopulation

•geographic isolationgeographic isolation•changes in new changes in new population's gene poolpopulation's gene pool

•reproductive isolationreproductive isolation•ecological competitionecological competition

STEP 1: Founders ArriveSTEP 1: Founders Arrive

•A few finches, “species A”, travel from S. America to one of the Galápagos Islands.

•There, they survive and reproduce.

STEP 2: Geographic IsolationSTEP 2: Geographic Isolation

•Some birds from species A cross to a second island.

•The two populations no longer share a gene pool.

STEP 3: Changes in the Gene PoolSTEP 3: Changes in the Gene Pool

•Seed sizes on the second island favor birds with large beaks.

•The population on the second island evolves into population “B”, with larger beaks.

STEP 4: Reproductive IsolationSTEP 4: Reproductive Isolation

•If population B birds cross back If population B birds cross back to the first island, they to the first island, they will not will not matemate with birds from with birds from population A.population A.

•Populations A and B are Populations A and B are separate species.separate species.

STEP 5: Ecological CompetitionSTEP 5: Ecological Competition

• As species A and B As species A and B competecompete for available seeds for available seeds on the first island, they continue to evolve in a on the first island, they continue to evolve in a way that increases the way that increases the differencesdifferences between between them. them.

• A new speciesA new species—C—may evolve.—C—may evolve.