Ch 22- The origin of species

Geographic variation

Individuals of the same species in different areas may look different but they are connected by intermediate populations

Example of geographic variation

Eastern rat snake on the eastern coast have phenotypic intermediates from black to grey to yellow

The Biological Species concept

a species is composed of populations whose members mate with each other and produce fertile offspring

Reproductive isolation

populations whose members don’t mate w each other or who can’t produce fertile offspring are members of a different species

What are the two kinds of reproductive isolating mechanisms

Prezygotic and postzygotic

What are the types of prezygotic isolating mechanisms

Ecological, behavioral, temporal, mechanical, and prevention of gamete fusion

Ecological isolation

even if species are in the same area, they may use different portions of the environment and not encounter one another

Example of ecological isolation

Tiglions don’t occur even though tiger and lion areas overlap in India because they have different behavioral and social traits, and use different habitats

Behavioral isolation

specific mating rituals between a species prevents mating w others

Example of behavioral isolations

Blue footed boobies select mates after elaborate courtship displays

What are some other examples of behavioral isolation

visual signals (mating rituals +colors), sound production (bird songs + mating calls), chemical signals (pheromones)

Temporal isolation

mating occurs at different times

Example of temporal isolation

Two species of wild lettuce grow along SE us roadsides but hybrids aren’t made bc one blooms in early spring and the other in the summer

Mechanical isolation

Species cannot physically mate

Examples of mechanical isolation

structure of male and female copulatory organs may be incompatible

Prevention of gamete fusion

chemical differences in sex cells

Example of prevention of gamete fusion

frogs who shed gametes in the water still don’t mix w other species; the sperm and eggs will not attract or fuse w each other

How does prevention of gamete fusion work

receptor proteins ensure only same species egg and sperm interact

Postzygotic isolating mechanisms

hybrids that do occur may be weak and less fit to their environment than parent species, hybrids may be sterile bc of abnormal chromosomes or sex organs

Two types of speciation

allopatric and sympatric

Allopatric speciation

geographically seperated (allopatric) populations are much more likely to have evolved substantial differences leading to speciation

Example of allopatric speciation

South rim vs North rim squirrels; geographical isolation of north rim squirrels led to evolutionary adaptations and speciation and they no longer interbreed bc of genetic + behavioral diff

Sympiatric speciation

one species splits into two wo ever having split

Gradualism

accumulation of small changes over a period of time

Punctuated equilibrium

long periods of stasis followed by rapid change

What causes punctuated equilibrium

driven by stabilizing and oscilating selection

Gradualism and punctuated eq. are at opposite ends of a ________, but there are many __ _____ ___ ______ ____

contiuum, in betweens who experience both

__ mass extinctions have occured, as many as how many of all species have perished at a given time?

5, 96%

Not all organisms are effected equally during an extinction. Name an example of this

During cretaceous period dinos dominated but went extinct and left placental animals to adapt and dominate

6th extinction is underway because

humans; number of species is decreasing at an alarming rate