chapter 22
microevolution
evolution within a population
macroevolution
evolutionary change above a species level
the biological species concept
a species is a group of populations whose individuals can interbreed and produce viable, fertile offspring
who developed the biological species concept
ernst mayr
gene flow between populations does what
holds the phenotype of a population together
reproductive isolation
the existence of biological factors that impede two species from reproducing viable fertile offspring
prezygotic barrier
prevent fertilization
postzygotic barriers
prevent viable and fertile offspring after fertilization
habitat isolation
a type of reproductive isolation
two species encounter eachother so infrequently because they inhabit different habitats even though there is no physical barrier between them
temporal isolation
species that breed at different times cannot mix gametes
prezygotic barrier
behavioral isolation
courtship rituals and other behaviours unique to a species prevent mating
prezygotic barrier
mechanical isolation
morphological differences prevent successful mating
prezygotic
gametic isolation
incompatible gametes prevent fertilization
prezygotic
reduced hybrid variability
offspring is infertile
postzygotic barrier
hybrid breakdown
2nd generation is infertile
postzygotic barrier
limitations of the biological species concept
doesn't apply to fossils or asexual organisms
the morphological species concept
morphological similarities make a species
ecological species concept
views species in terms of its ecological niche
phylogenetic species concept
species defined by the smallest group of individuals on a phylogenetic tree
2 main types of speciation
sympatric allopatric
allopatric speciation
gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations
sympatric speciation
speciation takes place in geographically overlapping populations
polyploidy
there are an extra set of chromosomes due to a mistake in cell division
autoploidy
an individual has more than 2 chromosome sets derived from one species
alloploidy
an individual has more than two sets of chromosomes derived from different species
why cant a new polyploid individual breed with its ancestors?
because of the chromosomal mismatch
animals are generally unsuccessful reproducing tetraploid generations because
the new generation has no one to mate with because of the mismatch in chromosomal compliment
plants are successfull in producing tetraploid individuals because
they can asexually reproduce more mates for the 4n individuals
hybrid zone
a region in which members of different species mix and mate, producing at least some offspring of mixed ancestry
reinforcement
hybrids are less fit than members of their parent species, so natural selection strengthens prezygotic barriers to reproduction
fusion
barriers to reproduction may be weak when two species meet in a hybrid zone
so much gene flow occurs so the species fuse together
stability
many hybrid zones are stable in that hybrids continue to be produced
how long does speciation take
can be fast or over thousands of years
punctuated equilibria
Niles Eldredge and stephen jay gould coined the term
describes periods of apparent equilibrium punctuated by a sudden change
contrasts model of gradual change