Defining Species and Zygotic Barriers

smallest set of organisms that look alike EX: eastern and western meadowlark

a set of organisms that are adapted to a specific set of resources EX: microbes

smallest distinct set of organisms that share a common ancestor

set of populations whose members potentially interbreed in nature to produce fertile, viable young and do not successfully interbreed with other such groups (humans, species)

- share the same gene pool, so there is gene flow between two populations

barriers that prevent fertilization

different habitats and adaptions prevent two members of a population from meeting and mating

isolation due to different timing. EX: different mating months of frogs, mating behaviors tied to temp changes, warmer climates

courtship rituals and other behaviors unique to species are effective barriers to mating

physical constraints that prevent fertilization. nettles can’t mate if their mating parts don’t have the right anatomy and don’t align to a female to fit together properly

sperm of one species may not be able to fertilize eggs of another species

acts after a hybrid zygote (horse + donkey = mule (the hybrid) is formed, leads to reduced hybrid viability (where an embryo fails to develop or is weak)

the hybrid survives but is sterile EX: a horse mates with a donkey and produces a mule that is lacking chromosomes

2nd generation hybrids are feeble or sterile. The initial hybrid may survive, but the 2nd generation may be weaker or infertile.

it could be many genes or as few as one. Ex: variation in one gene keeps 2 snail species from mating because their shells spiral in different directions

-fossil species, asexual species that don’t mate, sometimes hybrids happen