Chapter 24: The Origin of Species

speciation

one species splits into two species

Microevolution

consists of changes in allele frequency in a population over time

Macroevolution

refers to broad patterns of evolutionary change above the species level

species

-a group of populations whose members

-Have the potential to interbreed in nature

-Produce viable, fertile offspring

Reproductive isolation

results when biological barriers impede members of two species from interbreeding and producing viable, fertile offspring

hybrids

offspring that result from interspecific mating

Prezygotic barriers

block fertilization from occurring by:

 Impeding different species from attempting to mate

 Preventing the successful completion of mating

 Hindering fertilization if mating is successful

Habitat Isolation

Two species that occupy different habitats within the same area may encounter each other rarely, if at all

Temporal Isolation

Species that breed at different times of the day, in different seasons, or different years cannot mix their gametes

Behavioral Isolation

Courtship rituals and other behaviors unique to a species are effective barriers to mating

Mechanical Isolation

Mating is attempted, but morphological differences prevent its successful completion

Gametic Isolation

Sperm of one species may not be able to fertilize eggs of another species

Postzygotic barriers

prevent hybrid zygotes from developing into viable, fertile adults through

 Reduced hybrid viability

 Reduced hybrid fertility

 Hybrid breakdown

Reduced Hybrid Viability

Genes of different parent species may interact in ways that impair the hybrid’s development or survival in its environment

Reduced Hybrid Fertility

Meiosis may fail to produce normal gametes, resulting in sterility, if the parent species have chromosomes of different number or structure

Hybrid Breakdown

First-generation hybrids are viable and fertile, but offspring in the next generation are feeble or sterile

biological species concept

emphasizes the separateness of different species due to reproductive barriers

morphological species concept

distinguishes a species by its structural features

ecological species concept

defines a species by its ecological niche, the sum of its interactions with the nonliving and living parts of the environment

Allopatric speciation

-populations are geographically isolated

-gene flow is interrupted when a population is divided into geographically isolated subpopulations

Sympatric speciation

populations are not geographically isolated

gene pools of isolated populations

may diverge through mutation, natural selection, and genetic drift