Speciation

What is a Species? Species All members of a population that can interbreed under natural conditions. Genetics helps distinguish species today Eg. There are 3 species of orca!

Speciation – the formation of a new species. Microevolution Changes in allele frequencies and phenotypic traits in a population. May result in speciation.

Reproductive Isolation Prezygotic mechanisms Postzygotic mechanisms

Prezygotic mechanisms Many mechanisms prevent fertilization Can prevent mating. Examples: Ecological isolation (different habitats or niches) Temporal isolation (even though they live in the same area, reproductive cycles differ) Behavioural isolation (different mating rituals, etc) Or can prevent fertilization. Examples: Mechanical isolation (the anatomical shapes do not match) Gametic isolation (the gametes do not reach or recognize each other)

Modes of Speciation Allopatric Speciation Sympatric Speciation New Lemur Discovered in 2005

Allopatric Speciation A single species is separated into two geographically isolated populations. Over generations the two populations diverge from each other via mutations. Eventually, they become two species.

Sympatric Speciation The evolution of populations within the same geographical area into two species. Can be caused by disruptive selection

Patterns of Evolution

Adaptive Radiation A single species evolves into a number of distinct but closely related species. Eg. Darwin’s Finches.

Divergent Evolution The large scale evolution of a group into many different forms. Eg. Evolution of Ontario rodents.

Convergent Evolution Two different species evolve to occupy similar ecological niches. Eg. Various cactus species evolved in response to hot, dry environments.

Coevolution One species evolves in response to another species. Eg. Brazil nuts have evolved hard shells to protect their seeds…..However, the agouti has evolved jaws and teeth strong enough to bite open the shell!