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 at this study here. The data from the study show that in 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, I don't know, 19 snakes were juvenile.

We see that the total population seems to be declining. The total snakes captured, which they say is an indication of the overall population, that is declining. Then they introduce the males from the outside, and it takes a couple of 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. 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 population.

When you have a small, isolated population, some things can happen that are a lot less likely than if you have a large, unisolated population. For example, you might have an uneven distribution of males and females, so not enough males. That's less likely to happen if you have a really large population, but in a small, isolated population, there's a chance that you could skew one way or the other.

If you don't have enough males, you're not going to have enough reproduction. You might have too few young snakes that are in their prime of the reproductive age. 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 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. You could have some type of mutation that is just disproportionately showing up in that population, which 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. Well, if you had not enough males, introducing males could rebalance the male-female ratio. It could have introduced some genetic diversity, so you don't have the mutation.

Once again, this is a small, isolated population. Those are triggers you head and say, "Okay, there might not be a lot of genetic diversity there." Introducing genetic diversity is one of the possibilities. The introduced male snakes might have been younger; they didn't tell us whether the males from the outside were what age they were, but these are just theories based on what they did tell us.

You only have to describe one, so you could just say it could have rebalanced the male-female ratio. In 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.

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 the population keeps growing from 1993, or especially from 1995 onward. It wouldn't happen if we had limited resources. It wouldn't have happened without abundant resources. We're done.