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6a-c, Population ecology

Fixing a declining snake population.

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Video transcript

- 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.