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
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
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
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
In example above, both birds have different throat colour, don’t
look the same, so different species
What happens when there is a lot of variation in a phenotype, in a
MSC is very problematic in this case
Where do we ‘draw the line’ in variation for different
When there isn’t much variation in population, MSC again
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
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
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
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.