51. Community Ecology
Community Structure
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So here we have an example problem that says, based on the image below, which of the following communities of birds, either community number 1 or community number 2, has a greater species diversity and why? And we've got these 4 potential answer options down below. Now, of course, recall from our last lesson video that species diversity is a weighted measurement of biodiversity that integrates species richness or the total number of species in the community and relative abundance or the proportion of each species relative to all individuals in the community. Now, recall that species diversity can be mathematically calculated using the tool Shannon diversity index. However, we're not given Shannon diversity indexes here in this problem, so we need to use a different approach. Now what you'll notice in comparing community 1 and community number 2 is that they both have a total of 3 species of birds. And so the species richness between community 1 and community 2 is both 3. Now, if the species richness is the same, then we need to turn to the relative abundance, the proportion of each species in the community. And so what you'll notice is in community number 1, there are 1, 2, 3, 4, 5, 6, 7, 8, 9 of these blue species of bird. Then we also have 2 species of this red bird, and we have one species of this black bird. So this comes out to a total of 12 birds, and these are the abundances, between them. Now for community number 2, what you'll notice is that there are 1, 2, 3, 4 species of the bluebird. Then we have, 1, 2, 3, 4, 5 species of the red bird. And last but not least, we have 1, 2, 3 species of the black bird. And so what you'll notice is that in both communities, there are a total of 12 birds, but we have different relative abundances for each of the species. And what you'll notice is that in community number 2, there's a more balance between, you know, the number of, individuals in each species. Whereas in community number 1, it's pretty heavily leaning on this bluebird species where, the vast majority of the birds are the blue ones. So because community number 2 has a more even balance with, its relative abundance, this is really what makes it have a greater species diversity. So we can eliminate any answer option that suggests that community number 1 has a greater species diversity, such as eliminating answer option a and eliminating answer option b. And notice that option c says that community number 2 has a greater species diversity, but it says that it's because it has 3 different species. And, really, that's not the correct answer because community number 1 also has 3 different species, so that's not correct. And this leaves answer option d, which is the correct answer, which says community number 2 has the greater species diversity because its 3 species have a more equal relative abundance than in community number 1. And so option d is the correct answer to this example problem. That concludes this example, and I'll see you on our next video.
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