2015 AP Biology free response 6

- In an attempt to rescue
a small isolated population

of snakes from decline,

a few male snakes

from several larger populations

of the same species were introduced

into the population in 1992.

The snakes reproduce sexually,

and there are abundant
resources in the environment.

The figure below shows the results

of a study of the snake population

both before and after the introduction

of the outside males.

In the study, the numbers
of captured snakes

indicates the overall population size.

So, let's look it, let's look
at this, at the study here,

the data from the study.

So 1989, they captured a bunch of snakes,

the total snakes captured,

but a small fraction
of them were juveniles.

It looks like about five of
the 19 snakes were juvenile

and we see that the total
population seems to be declining.

The total snakes captured,
which they say is a...

is an indication of overall population.

That that is declining, and
then they introduced the males

from the outside and then
it takes a couple years

but then the population
seems to increase again.

So, let's see what the questions are.

Describe one characteristic
of the original population

that may have led to
the population's decline

in size between 1989 and 1993.

So, we can only theorize,
they haven't told us a lot,

they have told us it's a small population.

So they say small and it's a small,

isolated, small isolated population.

So when you have a small
isolated population,

some things can happen
that are a lot less likely

than if you have a large
un-isolated population.

For example, you might have,

actually I'll just answer it right here.

You might have an uneven distribution

of males, females so not enough males.

Not enough males.

That's less likely to happen if you

have a really large population,

but a small isolated population,

well, you know, there's a
chance that you could skew

one way or the other and if
you don't have enough males

you're not going to have
enough reproduction,

you might have

too few young snakes in their prime

of their reproductive age,

so, too, too few young,

young reproducing snakes,

reproducing snakes,

and there could be a bunch of reasons why

this maybe happened, maybe
there was some type of

calamity that happened, you know, in 1988,

where a lot of the young snakes died

or some type of a predator
and so all the snakes

that are left are the ones that are older

and they're not as viable
in terms of reproduction,

but that's one possibility there.

You could have some type
of, it's a small population,

you could have, because of the lack,

you could have a mutation
that is just disproportionatly

showing up in that population which makes

it less likely to reproduce.

So, mutation,

mutation in population,

that makes it less likely to reproduce.

For the actual test, you
just have to describe

one characteristic and these are

all possible characteristics.

Then in part b, they
say, propose one reason

that the introduction of the outside males

rescued the snake population from decline.

So, for part b, I'll do
that right over here.

Part b, well, if you had not enough males,

introducing males, so it could re-balance,

could re-balance

male female ratio,

male female ratio,

it could have introduced
some genetic diversity

so you don't have the mutation,

could introduce,

introduce genetic diversity

Once again this is a
small, isolated population,

those are triggers in your heads, okay,

there might not be a lot
of genetic diversity there.

Introduce genetic diversity.

The introduced male snakes
might have been younger.

So, could...

introduce...

younger,

younger snakes.

They didn't tell us whether
the males from the outside,

what age they were but
these are just theories

based on what they did tell us

that that's one of the possibilities,

and once again, you only
have to describe one,

so you could just say,
could have re-balanced

the male female ratio, and then part c,

part c, describe how the
data support the statement

that there are abundant
resources in the environment.

Well, you know, if you just saw this data

you could have said, well
maybe one of the reasons

for even part a is that you
didn't have abundant resources,

but notice when you introduce
males from the outside,

now all of a sudden, the
population keeps increasing.

So, the fact that the
population keeps increasing

and actually goes above
where it was in 1989,

well, that's a pretty good indication

that you have abundant
resources, there's nothing

that's putting a ceiling
on this growth once you

somehow fix the problem by
introducing these outside males.

So, I could say, population,

population

keeps growing

from '93, or especially from '95,

1995 onward, onward,

wouldn't happen if we
had limited resources,

wouldn't have happened

without abundant resources.

Wouldn't have happened,

happened...

without abundant resources.

Abundant resources.

And we're done.