Isolation and Diversion in Allopatry Colonization events are more common on islands. When a physical barrier separates a population, a vicariance event is said to occur.

DISPERSAL AND COLONIZATION 1. Start with one continuous population. Then, a colonist floats to an island on a raft. 2. Finish with two populations isolated from one another. Island Continent Figure 23.8 left

VICARIANCE 1. Start with one continuous population. Then a chance event occurs that changes the landscape (river changes course). 2. Finish with two populations isolated from one another. River River changes course Figure 23.8 right

Phylogeny Evolutionary history of a species or group of species From Greek phylon, tribe and genesis, origin

Systematics Study of biological diversity in an evolutionary context Includes taxonomy - the naming and classification of species and groups of species The first taxonomic framework was the Scala Naturae of Linnaeus

Darwin wrote: “Our classications will come to be, as far as can be made, genealogies” In other words, our taxonomic system should reflect evolutionary relationships

Cladistics - a method for developing phylogenetic trees Conceived by the German biologist, Willi Hennig - first described in his 1951 book Phylogenetic Systematics Relies on identification of clades - a collection of an ancestral species and all of its descendant species The resultant phylogenetic tree using cladistics is called a cladogram

How we go about constructing a cladogram? Fossil record can be helpful Morphology Behavior Molecular information (DNA sequences or proteins)

Morphological similarity can be very useful in reconstructing phylogenies However, there are two problems with morphology: Not all similarity represents common ancestry Primitive characteristics are not useful in reconstructing a phylogeny