what is microevolution?
the evolutionary change that occurs within populations
why is macroevolution critical?
so that popuations can persist in the face of environmental change caused by humans, and for species to shift their geographical disitribution in response to rapid global change
what is a species?
a group of populations whose members have the potential to interbreed in nature and make viable, fertile offspring, but do not productive viable and fertile offspring with members of other such groups, and must be able to be done in nature
what is reproductive isolation, and how is it seperated?
- pre zygotic reproductive barriers: preventing the formation of zygotes
- post zygotic mechanisms: impairing the survival or ultimate reproduction of the zygote
what are the 3 phases of speciation? explain
- separation of a species or a cohesive gene pool into one or more groups that are largely isolated from gene flow
- the genetic divergence of these groups
- seperated gene pools become reproductively isolated from one another
what happens if diverging populations experience different environment?
- experience different selective pressures
- directional selection will favour different traits within different populations
- will ultimately drive the populations apart
what will populations experiencing similar selective pressures result in?
- they will tend to converge on the same phenotype due to stabilizing selection
what are the two models of speciation?
- allopatric speciation
- sympatric speciation
describe the two types of speciation, and the differences between them.
- allopatric speciation: “different land”. populations that are seperated by a physical barrier. this could be a geological feature, it is believed this is relatively common
- sympatric speciation: “same land” happens without any obvious physical barrier, without this physical seperation there is a potential for gene flow, therefore this made it seem relatievly uncommon
what are two general mechanisms of allopatric speciation?
- long distance dispersal: mainland that was habitated, but an island develops (example_
- vicariance: division of a once continous geographical range of the species, into two or more ranges
what is an example of prezygotic reproductive isolation?
when you bring two sister species together, they fight each other, rather than mate
describe a possibility for when speciation occurs in sympatry, there doesn’t seem to be any obvious physical barrier to gene flow, so how they can diverge?
- the divergence of populations that specializied on different kinds of resources
- this divergence will be the fastest of the use of different resources, which somehow also includes some reproductive isolation
what is polyploidy?
- the heritable condition of possessing more than two complete sets of chromosomes
- speciation by polyploidy usually starts with the rare instance of hybridization between two divereged species
what is hybridization?
when two divergent lineages (ex. species) with independent evolutionary histories come into contact and interbreed
what is a cline?
a hybrid zone between two sepcies, where the allele frequency’s change across this hybrid zone, provides evidence for genetic exchange for species in that region
what are the three outcomes of the genetic exhange that occurs in the cline?
- the hybrid zone is stable
- genetic homogenization between the two species that are hybridizing
- reinforcement: when the hybrid progeny suffer poor viability or dramatically reduced reproduction. the production of hybrids is selected against when the two species come into contact
what does natural selection favor in terms of hybridization?
reduce the incidence of hybridization
