Chapter 22

process that produces new and distinct forms of life

the difficulty of defining species

*the species, as an evolutionary unit, must by definition be fluid and capable of changing, giving rise through evolution to new species, but species are not fixed

fundamental evolutionary unit

*ability (or inability) to exchange genetic material by producing fertile offspring

reproductive isolation

species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups

1. reproductively compatible

2. fertile offspring

1. asexual species

2. extinct organisms

members of the same species usually look alike

1. polymorphisms (same species look different)

2. members of different species can look alike

many forms

1. ring species

2 hybridization

species that are reproductively isolated from each other but can still exchange genetic material via other linking populations

interbreeding between species

1. ecology

2. evolution

complete description of the role the species plays in its environment- its habitat requirements, its nutritional and water needs, and the like

one to one correspondence between a species and its niche

members of a species all share a common ancestry and fate

inability to produce viable, fertile offspring

1. pre-zygotic

2. post-zygotic

act before the fertilization of the egg; prevent fertilization from taking place

1. spatial isolation

2. temporal isolation

3. behavioral isolation

4. mechanical isolation

comes into play after fertilization; failure of the fertilized egg to develop into a fertile individual

individuals only mate with other individuals based on specific courtship rituals, songs, and other kinds of behaviors

*mating dances and calls

"lock and key"

physical or chemical incompatiblity

different times

1. geographic isolation (places)

2. ecological isolation (niches)

genetic incompatibility

can mate, but offspring are not viable or sterile

the more genetically similar, the less extreme the genetic incompatibility between their genomes

the genetic divergence of separated populations

not yet separate species, but the genetic differences between them are extensive enough that the hybrid offspring they produce have reduced fertility or viability compared to offspring produced by crosses between individuals within each population

speciation that results from the geographical separation of populations

"different place", physical separation

further designation after its species name

1. dispersal

2. vicariance

individuals colonize a distant place, such as an island, far from the main source population

geographic barrier arises within a single population, separating it into two or more isolated populations

a few individuals from a mainland population disperse to a new location remote from the original population and evolve separately

central population of a species

distant, isolated that is geographically remote from the initial mainland population's habitat area

1. genetic drift is stronger in smaller populations

2. environment may differ in a way that results in natural selection driving differences between the two populations

unusually rapid evolutionary diversification in which natural selection accelerates the rates of both speciation and adapation

there are many ecological opportunities available for exploitation

speciation that occurs in response to speciation in another species

speciation with gene flow between diverging populations

"same place"

genetic divergence

caused by hybridization between two species in which the offspring are reproductively isolated from both parents

double diploid

multiple chromosome sets; change in chromosome numbers between parent and offspring

produced from hybridization of two different species

derived from an unusual reproductive event between members of a single species

natural selection

1. sympatric speciation requires some form of disruptive natural selection

2. allopatric speciation may be facilitated by natural selection

reproductive isolation

natural selection act on mutations that allows individuals to identify and mate with individuals more like themselves

*strong in sympatric speciation

genetic drift