Orca whales have inspired
and awed humans for many
thousands of years.
But did you know there is more 
than one type of orca whale?
These are called ecotypes.
An ecotype is a distinct variety that
exhibits behavioural, structural,
or physiological differences from other
 members of the species.
For example, off the coast of
British Columbia, there are
several ecotypes, including
transient whales and resident whales.
Transient whales migrate
up and down the coast,
and specialize in eating
marine mammals.
Resident whales live in
the coastal waters year round
and eat fish, primarily salmon.
Your job will be to come up with
a plausible story, or hypothesis,
to explain why there are so many
different types of orca whales,
each with their
own set of unique traits.
To begin, let's think about distribution
of a trait in a population.
This can be any trait that exists along
a continuum in a normal distribution.
Keep in mind that not all traits
follow this distribution pattern.
We are not concerned with
those at the moment.
In such a scenario,
we have fewer individuals with
the extreme values of the trait
(in this example,
small and large size),
a moderate amount of individuals
with the intermediate values
of the trait (smaller and larger),
and a lot of individuals with
the optimum of the trait
(in this case medium size).
So how might this distribution
change when the population
adapts to a new environmental
condition?
One way that a population can adapt
is by narrowing the range of the trait.
This is called stabilizing selection.
In this mode of selection,
the optimum value
is selected for and the 
extremes are selected against.
As a result, we see more
individuals with the
optimum value after the selection event.
An example of stabilizing selection is 
number of offspring born to an individual parent.
Too few offspring is a value
selected against
because not enough of them may be viable.
Too many offspring is a value
selected against because each
individual may not get enough
resources from the parent.
The optimum is selected for,
and we see an increase in the
number of individuals who
have the ideal sized clutch.
A second mode of selection
is directional selection.
In this scenario, 
the value range of
a trait in the population shifts 
one direction or the other.
We can see that the original 
population, before selection,
including some members
with an extreme value of the trait.
Individuals with one of the extremes
have been selected against,
while individuals with the other
extreme has been selected for.
As a result, the entire range of
the trait has shifted to the right.
(It could also shift to the left.)
An example of directional selection
is coloration in peppered moths.
Before the industrial revolution,
the optimum value was a
light speckled moth that could
blend in to the bark of trees.
Notice that in this original population, 
darker moths did exist,
just in low numbers.
As soot began to build up on trees, 
those dark moths
had an increasing advantage of camouflage
in this changing environment.
The light moths were no longer
camouflaged as well.
The light color was selected against
and the dark color was selected for.
A shift occurred in the range
and optimum of this trait.
The third mode of selection we will
consider is disruptive selection.
During disruptive selection, there is
selection against the original
optimum value and selection
for both extremes.
After selection, we see a bimodal
distribution of the trait.
This can have potential interesting
consequences for speciation
if members exhibiting the contrasting
values become reproductively isolated.
As an example of disruptive selection,
we can look at Darwin's
finches on the Galapagos islands.
Pre-selection finches had a
mean beak size
that enabled them to eat 
medium sized seeds.
During the selection process 
(which was strong interspecific competition
for the medium sized seeds), 
it became a disadvantage
to rely on those medium sized seeds 
and was an advantage
to be able to eat small 
or large seeds instead.
As a result, post-selection 
distribution is bimodal,
showing a population with many members
having a smaller beak
and many members having a larger beak,
and less having a medium sized beak.
What traits in the different types
of Orca whales
are the result of each of 
these modes of selection?
[Orca whale noises]
