15.1: New Species Evolve Vocabulary Objectives: Biological Species concept Macroevolution Speciation Reproductive Isolation Geographic Isolation Adaptive Radiation Punctuated Equilibrium Objectives: Describe the biological species concept. Distinguish b/w micro and macroevolution. List types of reproductive barriers b/w species. Explain how geographic isolation and adaptive radiation contribute to species diversity. Summarize models for the tempo of speciation.

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

Homo erectus 1.8 - 1.3m.y.a Homo Habilis 2.3 - 1.4 m.y.a Australopithicus, 3.2 m.y.a “Lucy”

SPECIATION = formation of new species. Species = a group of organisms that breed with one another and produce fertile offspring. The gene pools of two populations must become separated. When the members of two populations cannot interbreed and produce fertile offspring, reproductive isolation has occurred and speciation 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 One species gives rise to many species Also known as adaptive radiation Many species with common ancestor Many homologous structures Convergent Similar looking species that do not have a common ancestor Similar behavior and appearance due to environmental similarities Many analogous structures

Divergent Evolution (Adaptive)

Convergent Evolution (Adaptive)

Coevolution: The evolution of one species is directly influenced by the evolution of another

Gradualism v. Punctuated Equilibrium Rate of Speciation Two Models Gradualism v. Punctuated Equilibrium

Punctuated Equilibrium Slow background evolution (stasis) is interrupted by rapid bursts of change Rapid/Abrupt bursts of change usually occur after a mass extinction Abrupt : w/in a few thousand years Seen in fossil record after mass extinctions.

Speciation in Darwin's Finches 20

Speciation of Darwin’s Finches founding of a new population geographic isolation changes in new population's gene pool reproductive isolation ecological competition

STEP 1: Founders Arrive A few finches, “species A”, travel from S. America to one of the Galápagos Islands. There, they survive and reproduce. Speciation in the Galápagos finches occurred by founding of new populations, geographic isolation, gene pool changes, reproductive isolation, and ecological competition. Small groups of finches moved from one island to another, became reproductively isolated, and evolved into new species. 22

STEP 2: Geographic Isolation Some birds from species A cross to a second island. The two populations no longer share a gene pool. Speciation in the Galápagos finches occurred by founding of new populations, geographic isolation, gene pool changes, reproductive isolation, and ecological competition. Small groups of finches moved from one island to another, became reproductively isolated, and evolved into new species. 23

STEP 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. Speciation in the Galápagos finches occurred by founding of new populations, geographic isolation, gene pool changes, reproductive isolation, and ecological competition. Small groups of finches moved from one island to another, became reproductively isolated, and evolved into new species. 24

STEP 4: Reproductive Isolation If population B birds cross back to the first island, they will not mate with birds from population A. Populations A and B are separate species. 25

STEP 5: Ecological Competition As species A and B compete for available seeds on the first island, they continue to evolve in a way that increases the differences between them. A new species—C—may evolve. 26