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Lecture 16

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Biology 1001A
Tom Haffie

Biology 1001A Lecture 16: Species and Speciation Defining Species (Macroevolution)  Morphological Species Concept (MSC)  Biological Species Concept (BSC)  Phylogenictic Species Concept (PSC)  Without speciation, there would be no tree of life.  There is NO consensus regarding which Species Concept is the best  None are perfect, each have their own problems Speciation  Isolation  Divergence  Secondary Contact Defining Species: Species Concept  Why does it matter whether two populations are one species, or two? o African Elephant and Asian Elephant are TWO, DIFFERENT species.  One is smaller, ear shape is different  Location of habitat is different (environment)  Other cases it can more arbitrary o Other than the African Elephant, another type of elephant species live in Africa  Population is a lot smaller  Not very widespread, live in Congo and surrounding areas  Body is smaller, tusks are shorter and different color  Live in small families, compared to large herds  Live in forest, compared to African elephant which lives in open areas o Both elephants considered members of same species  Therefore there was no special conversation status for these smaller elephants. African elephants were NOT endangered, but the other kind was.  When we considered both of these the same species, they were not considered endangered. There was very little protection for the smaller elephants. Morphological Species Concept (MSC)  Identify species by morphological similarity  Distinct clusters in phenotypic space o Most widely applied species concept o Species are defined as a group of individuals that look the same as one another. If they look different, they are a different species.  Distinct Clusters in phenotypic space, not overlapping with other clusters  In example above, both birds have different throat colour, don’t look the same, so different species o Problems:  What happens when there is a lot of variation in a phenotype, in a population  MSC is very problematic in this case  Where do we ‘draw the line’ in variation for different species  When there isn’t much variation in population, MSC again becomes problematic Biological Species Concept (BSC)  Group of actually or potentially interbreeding organisms, reproductively isolated from other such groups o Species concept is not based on how species ‘look’ different from each other o However, it defines species of a group actually or potentially interbreeding organisms, reproductively isolated from such other groups  In other words, based on who you have sex with, who you have FERTILE offspring with o More explanatory power than MSC (shared gene pool)  MSC doesn’t explain members of a species look like each other o More objectively testable than MSC (when members of a Population A encounter Population B in the wild, what happens?)  Do they interbreed?  If they do, are their offspring fertile? Or not?  Are the populations reproductively isolated from one another, if they are, then there are 2 distinct species.  If there’s no reproductive isolation; if there’s free interbreeding with each other producing offspring, then they are the same species o Ex. Lion and Tigers  Liger  Zoo, if animals are couped up, and there are no other members, they may interbreed with each other and reproduce a hybrid Liger offspring.  The BSC doesn’t consider Tigers and Lions to be the same species for 2 reasons:  It’s important to notice that they would never interbreed outside of the zoo, in the natural environment.  The offspring, liger, cannot reproduce and have offspring of their own, since they are sterile. o Ex
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