Notes

species and speciation

species plot: indiviuals are represented as dots & are scored for 2 characteristics to graphically show how indiviudals of the same species will clsuter togehter when measured for speicifc traits

species concepts: methodds for determining if 2 organisms are members of the same species
1. biological: species are groups of interbreeding populations that are reproductively isolated from other groups; for indivudals to be members of the same species they must be reproductively compatible & produce fertile offspring
complications: some closely related species can interbreed & produce hybrid offsrping; natural selection may act against hybrids or reproductive isolation hasn't completely evolved btwn the 2 species
2. morphological: members of the same species usually look alike
3. ecological: a species can sometimes be characterized by its ecological niche (role the species plays in its environment); 2 species can't occupy the same niche due to compeititon over resources
4. phylogenetic: all members of a species share a common ancestry & fate; useful for asexually reproducing species

reproductive isolation: inability of a species to interbreed successfully /w related species
a. pre-zygotic (before fertilization) - factors prevent fertilization from taking place: indiviudals only mate /w other indiviudals based on specific behaviors (behavioral); species reproductive organs are incompatible (mechanical); incompatibilties exist btwn gametes (gametic); plants flower and animals are active at different times (temporal); species are separated by geographic features (ecological)
b. post-zygotic (after fertilization) - a zygote fails to develop & offspring are infertile

speciation: when a group within a species separates frrom others & diverges genetically due to fixed mutations over time until the 2 populations are no longer able to interbreed & produce fertile offspring
1. allopatric speciation: a population is geographically separated from e/o either by dispersal (individuals colonize a distant place) or vicariance (a geographic barrier arises within a population) & the populations genetically diverge until speciation occurs
2. peripatric speciation: individuals from a population disperse to a new location where they evolve separately; most of the change is in the smaller population due to genetic drift & new selective pressures
3. sympatric speciation: a new species develops spontaneously in a population w/o barriers; strong disruptive selection can overcome gene flow & lead to speciation in a population w/o physical barriers
ex: instantaneous speciation: occurs when 2 species hybridize & the offpsring are reproductively isoalted from both parental species bc the chromosome # in the hybrids is different from the parents

adaptive radiation: natural selection causes closely related organisms to diverge as they specialize to occupy different ecological niches
phylogeny - diagram that depicts the lines of evolutionary descent of different species form a common ancestor

co-speciation: 2 groups of organisms speciate in response to e/o at the same time
ex: host/parasite relationships; when host populations separate from e/o, so do their parasites

speciation considerations:
1. speciation can occur with or w/o natural selection
2. natural selection doesn't always elad to speciation
3. separated populations can diverge as a result of genetic drift /w no role for natural selection