Chapter 22

21.1: The Biological Species Concept
Something that changes over time
The species is the fundamental evolutionary unit
Species clusters on the basis of two characteristics
Fundamental biological unit
Reflection of ability to exchange genetic material by producing fertile offspring
Species become extinct and give rise to other species
Reproductive isolation is the key to the biological species concept (BSC)
Species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups
Offspring must be fertile to pass on genetic material
Potential to mate- example of elephants
The BSC is more useful in theory than in practice
On a day-to-day basis biologists often use the morphospecies concept
Same species usually look alike
Fallible
Species can look different one another
Different species can look alike
The BSC does not apply to asexual or extinct organisms
Based on sexual exchange of genetic information
Ring species and hybridization complicate the BSC
Reproductively isolated populations but not genetically isolated because of gene flow
Hybridization occurs in plants
Ecology and evolution can extend the BSC
Ecological niche gives rise to the ecological species concept (ESC)
One-to-one correspondence between a species and its niche
Evolutionary species concept (EvSC)
Idea that members of species all share a common ancestry and a common fate

22.2: Reproductive Isolation
Pre-zygotic factors prevent fertilization from taking place
Post-zygotic factors result in the failure of the fertilized egg to develop into a fertilie individual
Pre-zygotic factors occur before egg fertilization
Behaviorally isolated
Membrane proteins on sperm and egg in marine species
Incompatibility of pollen and flower
In some insect the genitalia can only fit with the same species
Lock and key systems
Temporal and ecological separation
Post-zygotic isolating factors occur after egg fertilization
Genetic incompatibility

22.3: Speciation
Speciation is a by-product of the genetic divergence of separated populations
Unable to interbred
Spontaneous mutations
May be partially reproductively isolated at first
Allopatric speciation is speciation that results from the geographical separation of populations
Subspecies formed
Dispersal- colonize a different place
Vicariance- geographic barrier
Dispersal is important in peripatric speciation
A few individuals from a mainland population disperse to a new location
Island population
Classically small and often in