• Species - a population(s) whose members have the potential to interbreed with one another in nature to produce fertile offspring, and cannot with members of other species. • Ex: (Left) These birds look similar, but cannot interbreed with one another. Q: Are they two different species? • Yes. • Ex: Breeds of dogs look different from one another, but all can interbreed. Q: Are they all different species? • No. They are all the same species.

Species - a population(s) whose members have the potential to interbreed with one another in nature to produce fertile offspring, and cannot with members

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Page 1: Species - a population(s) whose members have the potential to interbreed with one another in nature to produce fertile offspring, and cannot with members

• Species - a population(s) whose members have the potential to interbreed with one another in nature to produce fertile offspring, and cannot with members of other species.

• Ex: (Left) These birds look similar, but cannot interbreed with one another. Q: Are they two different species?

• Yes.

• Ex: Breeds of dogs look different from one another, but all can interbreed. Q: Are they all different species?

• No. They are all the same species.

Page 2: Species - a population(s) whose members have the potential to interbreed with one another in nature to produce fertile offspring, and cannot with members

• Ex: These humans may live in

different geographical areas, and may never get together. But if they did, could they interbreed? Are they the same species?

• Yes, all humans belong to the same species.

• Q: Are humans and chimpanzees the same species?

• A: No• Q: What about dogs and

wolves?• A: No.

Page 3: Species - a population(s) whose members have the potential to interbreed with one another in nature to produce fertile offspring, and cannot with members

Q: What prevents two species from reproducing with each other?A: Reproductive Barriers!

• 2 types of Reproductive Barriers:

• I. Pre-zygotic barriers - impedes mating or hinders fertilization of eggs.

• A. Temporal isolation - time based. Ex: Western spotted skunks breed in the fall, but eastern species breed in late winter.

• B. Habitat isolation - spatially segregated. Ex: one species of garter snake lives in water, and a closely related species lives on land.

• C. Behavioral isolation - courtship rituals. Ex: in bird species, courtship is so elaborate that individuals are unlikely to mistake a bird of a different species as one of their kind.

Courtship rituals of Blue-footed boobies in Galapagos Islands. Male does “high-step,”showing bright blue feet.

Page 4: Species - a population(s) whose members have the potential to interbreed with one another in nature to produce fertile offspring, and cannot with members

• D. Mechanical isolation - male and female sex organs of different species are anatomically incompatible. Ex: 2 insects’ copulatory organs may not fit together correctly; no sperm is transferred.

• E. Gametic isolation - individuals may copulate, but their gametes are incompatible and fertilization does not occur. Ex: mammal sperm may not survive in female of a different species.

Page 5: Species - a population(s) whose members have the potential to interbreed with one another in nature to produce fertile offspring, and cannot with members

Horse + Donkey = Mule(but is sterile)

II. Post-zygotic barriers - if mating actually occurs between different species and a zygote is formed, these mechanisms affect the hybrid offspring. (baby) A. Hybrid inviability - the hybrid offspring die before reaching reproductive maturity. Ex: certain frogs B. Hybrid sterility - the hybrid offspring may become vigorous adults, but are infertile. Ex: see below