group of individuals capable of interbreeding and reproducing the same type of offspring
Reproductive isolating mechanisms
prevent interbreeding (and gene flow) between two different species even though they may live in the same area
reproductive isolating mechanisms that prevent fertilization from taking place
the two species reproduce at different times of the day, season, or year
two related species that live in the same area but live and breed in different habitats
Behavioral (sexual) isolation-
animal species exchange distinctive signals before mating. Another species would not recognize these signals and therefore would not mate
structural differences (incompatible genital organs) prevent successful mating if it is attempted
even if mating does occur
the egg and sperm of different species are incompatible
if fertilization does take place between closely related species, this increases likelihood of reproductive failure
Postzygotic barrier. genes of different species do not interact properly and embryo spontaneously aborts
Postzygotic barrier. if a hybrid animal does survive, gametes are often abnormal
if two hybrid animals survive and mate with each other, their offspring might not be able to reproduce
formation of a new species
Population is divided by a geographic barrier so that 2 populations cannot interbreed
formation of new species without the presence of a geographic barrier
Causes of speciation
Polyploidy, Hybridization, Ecology
possession of more than the normal 2 sets of chromosomes
polyploidy in plants–why does it happen?
Takes place because of nondisjunction of all tetrads during meiosis (or spontaneous doubling of chromosomes before meiosis); therefore diploid organisms produce diploid gametes.
Where does polyploidy often occur?
Occurs often in plants- can be triploid (3n), tetraploid (4n), or higher.
what can polyploid plants reproduce with?
These new species can only reproduce with other members of its group but not with its parents
two different forms of a species from different areas mate + produce offspring. This mating only occurs (and offspring can only survive) in a small overlap area called a hybrid zone.
a geographically overlapping area where two different forms of a species can mate and reproduce.
can cause 2 different species to form
can lead to speciation in which each polymorphism each variety splits off into a different species
many related species come from one ancestral species in a relatively short period
When does adaptive radiation happen?
Occurs when a species enters an area where there are many unoccupied habitats. The ancestral species then branches off to form new species as each population occupies different environments
when a species enters an area where there are many unoccupied habitats and adaptive radiation happens, those areas are called adaptive zones.
occurs when the last individual of a lineage dies. Today, only one species is alive for every 2000 that have become extinct
continuous lowlevel extinction of species
kills numerous species (last of which was 65m yrs ago when dinosaurs)
only happened 5-6 times
two or more species that originate from a common ancestor
two unrelated species that share many related traits or analogous features
bc of adaptation to similar living environments
two related species that evolved in similar ways after divergence from a
Parallel evolution–marsupial v placental
species of marsupial mammals and placental mammals, which evolved from a common ancestor, independently evolved similar adaptations when encountering similar environments
one species evolves adaptations in response to another species’ adaptations
problem: fossil record seems incomplete- does not contain any transition fossils from animals that appear to be mid-evolution. So, punctuated equilibrium states that in the history of a species, there were long periods of stasis. evolution therefore occurs in spurts
no evolutionary change followed by short periods of rapid speciation.
evolution proceeds continuously over long periods, with populations slowly changing due to natural selection in different