the formation of new species SPECIATION the formation of new species

Speciation follows the results of DIVERGENT (branching) EVOLUTION

Phylogenetic Tree for all living things Time ---------------------------------------->present Nodes indicate most recent common ancestor of two branches

What is a SPECIES? Biological Species Concept: A group of naturally or potentially interbreeding organisms that can produce fertile offspring.

How Do New Species Form? Take 2 minutes to think about how it might happen…

Steps of Speciation: Reproductive isolation of two populations Allopatric speciation – due to a geographic barrier that prevents gene flow Squirrels and the Grand Canyon Birds and the Rocky Mountains Galapagos Finches separated from the mainland Sympatric speciation – two populations in same place, but behavior or niche prevents interbreeding Cichlid Fish Polyploidy in plants

Genetic barriers to reproduction arise. 2) Genetic divergence The gene pools become more and more different due to selection and/or drift. Genetic barriers to reproduction arise. The two populations are no longer able to interbreed, due to genetic differences in habitat preference, mating behavior, or physical compatibility. Now there are two separate species!

What can make a population reproductively isolated? Pre-zygotic isolating mechanisms (before the zygote is formed) Geographic isolation Habitat isolation Behavioral isolation Temporal isolation Mechanical isolation Chemical isolation

Post-zygotic isolating mechanisms Hybrid inviability (zygote or offspring dies) Hybrid inferiority (hybrid is weak and sickly) Hybrid sterility (offspring can’t reproduce)

Ring Species

Ligers and tigons and geeps (oh my!)

Speciation results in PATTERNS in EVOLUTION: Adaptive radiation Stasis Gradualism Punctuated equilibrium

How can we describe the RATE OF EVOLUTIONARY CHANGE? Two opposing theories: Gradualism – slow and steady change. Punctuated equilibrium – change is relatively rapid, interspersed with periods of stasis

Gradualism vs. Punctuated equilibrium

Punctuated equilibrium happens when… The environment changes quickly A barrier arises quickly One mutation enables a large shift in the population Evidence: fossils, experiments

A long period of little or no Evolutionary STASIS A long period of little or no evolutionary change

The development of many species from a common ancestor ADAPTIVE RADIATION The development of many species from a common ancestor

Adaptive radiation may result from: 1 Adaptive radiation may result from: 1. New Environments with diverse habitats

…especially on islands Fruit fly evolution in Hawaii

Galapagos finches

2. New traits that then diversify Example: Flowering plants – once flowers emerged as a strategy, it worked so well in so many different niches that flowering plants diversified greatly.

3. New Communities of Organisms Example 1: One new organism allows other to diversify – e.g. flowering plants and insects Example 2: Extinction of one group allows diversification of another – e.g. dinosaurs and mammals

Phylogenetic Tree for all living things Time ---------------------------------------->present Nodes indicate most recent common ancestor of two branches