Human activities are causing the fragmentation of the Brazilian Atlantic rain forest. One result is that toucans have become extinct or nearly extinct in some of the forest fragments. Does the absence of toucans affect the forest? Toucans can eat fruits with large seeds because their large bills can open wide. Most other birds in the same forest can only eat small seeds. Ecologist Mauro Galetti and his colleagues measured the seed sizes of palms in forest fragments with and without toucans. The graphs show two of the forest populations they studied. What is the take-home message of the data?

Video transcript

Welcome back. Let's look at our next question. It says plants have evolved many traits that attract pollinators over time, such as brightly colored petals that attract butterflies with the presence of the pollinators, the blank increases between the plant populations. So let's imagine two populations of flowers and we've got flowers over here that are red and flowers are the same species over here in a different field that are yellow and without pollinators um They might self pollinate or maybe the wind could carry some pollen from one to another flower. Um But now we have some butterflies that are flying back and forth between the two fields carrying pollen from one group of flowers to the other. So we now have alleles blowing from one population to another, potentially altering the ideal frequency. Because over here we had the red alley over here we have the yellow and now genes are flowing between the two, altering the frequencies of those alleles and the different groups of flowers. And when we talk about something a little flowing from one population to another, potentially altering that a low frequency the term that refers to that is choice, choice C gene flow. So go ahead and highlight that. So let's just look at the other choices to see why they're not correct choice A is natural selection but natural selection refers to outside forces environmental forces that cause certain values to be more or less advantageous to the species, causing them to be more or less likely to reproduce. And obviously the ones that can greater likely to reproduction. Get chosen in favor of. And natural selection could take place here if red tracks more butterflies. But we're talking about the presence of pollinators increasing this thing between the two plant populations. So that's not really describing the situation as well as gene flow here. So choice B is mutation. Well, again, these the flower color gene may mutate in the future, but that doesn't describe what's happening between and increasing between the flower populations. The presence of pollinators isn't causing that to increase. So not are correct choice. And finally, genetic drift. Choice D genetic drift and genetic drift can sound very similar to gene flow, which is our correct answer. So it's a little bit confusing, but genetic drift specifically occurs in small populations. And it's the variation and genotype caused by random chance that can cause the disappearance or decreasing of certain alleles. So, first, when you've got a small isolated population and due to random chance, the balance of or the distribution of certain alleles is changed significantly because uh say there's only a single individual with a certain alittle, that individual by random chance does not reproduce. So, genetic drift is referring specifically to that small population scenario where you have such a small representation of certain aliens that you end up with a very different uh real distribution than, say, in the original source population. So that's why choice D genetic drift is not the correct answer. So once again, the presence of pollinators, the choice C gene flow increases between the populations. Thanks for watching. See you in the next.