The origin of species

Speciation

the origin of new species, is at the focal point of evolutionary theory

Microevolution

consists of changes in allele frequency in a population over time

Macroevolution

broad pattern of evolutionary change above the species level

Biological species concept

a species ia a group of popuations whose members have the potential to interbreed in nature and produce viable fertile offspring

Reproductive isolation

existence of biological factors (barriers) that impede two species from producing viable fertile offspring

Two types of reproductive barriers

prezygotic and postzygotic barriers

Prezygotic barriers

block fertilization from occuring by impeding different species from attempting to mate, preventing the successful completion of mating, hindering fertilization if mating is successful

Prezygotic forms of isolation and definitions

Habitat isolation - two species encounter each other rarely or at all because they occupy different habitatis

Behavioral isolation - courtship rituals and other behaviors unique to a species are effective barriers

Temporal isolation - species that breed at different times cant mix gametes

Mechanical isolation - morphological differences prevent succesful mating

Gametic isolation - sperm of one species may not be able to fertilize eggs of another

Postzygotic barriers

prevent the hybrid zygote from developing into a viable fertile adult by reduced hybrid viability, fertility, and breakdown

Postzygotic hybrid viability, fertility, and hybrid breakdown definition

Reduced hybrid viability - genes of the different parent species may interact and impair hybrids development

Reduced hybrid fertility - even if hybrids are vigorous, they may be sterile

Hybrid breakdown - some first-generation hybrids are fertie, but when they make with another species the offspring are feeble or sterile

Allopatric speciation

a population forms a new species while geographically isolated from its parent population

Reproductive isolation between populations generally ____ as the distance between them _____

increases, increases

Sympatric speciation

a subset of a population forms a new species without geographic separation

Gradualism

changes occur slowly and steadily over long periods of time

Punctuated equilibrium

periods of apparent stasis punctuated by sudden change