- 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,
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.