Geographic Impact on Communities - Online Tutor, Practice Problems & Exam Prep

Species diversity in communities is influenced by latitude and area. Generally, species diversity decreases with increasing latitude, particularly away from the equator, due to factors like climate and historical glaciation. Conversely, larger areas support more species due to greater resources and habitats. The island equilibrium model illustrates that species numbers stabilize when immigration equals extinction, influenced by island size and distance from the mainland. Larger, closer islands have higher species richness, while smaller, distant islands experience lower immigration rates and higher extinction rates.

Geographic Impact on Communities

This video, we're going to switch our focus over to geographic impact on communities, more specifically focusing on 2 biogeographical factors that have a significant impact on a community's species diversity. And those two factors are latitude and area. Now latitude actually has an inverse relationship with species diversity, which means that species diversity typically decreases with increasing latitude further from the equator. Now this is for several different reasons including the fact that the climate near the equator fosters more biological productivity, which can support a greater range of species. And this is because the equator receives more direct angles of sunlight throughout the year and more annual precipitation than any other latitude on Earth.

And, also, tropical communities tend to be older than communities at higher latitudes, and this is because glaciation events during ice ages have somewhat hit the reset button on communities that are at higher latitudes. But communities that fall on tropical regions near the equator haven't been impacted as much, and so they've simply had more time for speciation to occur, creating a greater species diversity along the equator. Now in terms of area, it actually has a directly proportional relationship with species diversity, which means that species diversity typically increases with increasing area. And this is simply because larger areas have more resources available for a greater range of species. They offer more habitats and more microhabitats, which can support a greater range of species.

And also, larger areas are simply more likely to be found by migrating species than smaller areas are. So let's take a look at our image down below, which is really just a visual representation of the same exact ideas we just talked about. So on the left hand side, we're focusing on latitude and its relationship to species diversity. So notice that we've got this graph here that has species richness for mammals on the x axis, and recall that species richness is simply just the total number of different species in the community. So it's just a simple count, if you will.

And what you'll notice is that these species richness bars here are at their highest right along the equator. And so this is suggesting a greater species diversity along the equator. And notice that as you get further and further away from the equator towards higher latitudes on earth, the species richness drops off, indicating that the species diversity also drops off. And this tends to be the case for most species. Now on the right hand side, we're focusing on area.

So notice that we have island area on the x axis and species richness for birds on the y axis. And notice that when the island area is really, really small, this creates relatively low species richness and low species diversity. But notice that as the islands get larger and larger and larger, that they have greater species richness, which corresponds with greater species diversity. So this here concludes this lesson, and we'll be able to apply these concepts moving forward. So see you all in our next video.

Geographic Impact on Communities Example 1

So here we have an example problem that asks, which of the following statements explains why tropical communities tend to have more species diversity than communities at higher latitudes? And we've got these 5 statements and the 4 potential answer options down below. Now, statement 1 says tropical communities tend to be larger and therefore have more habitats and resources available. Now this is not something that we've said in our previous lesson videos, and it's simply not true that tropical communities are always larger than communities at higher latitudes. So we can eliminate statement 1 here for that reason.

Now, statement 2 says that there are fewer predators and parasites in tropical regions, allowing more species to thrive. Once again, this is not something that we've said in our previous lesson videos, and it's simply not true that there are fewer predators and parasites in tropical regions. In fact, there are more predators and parasites in tropical regions. And, for that reason, we can eliminate statement number 2. Now moving on, statement number 3 says that tropical communities have been around for longer, allowing more time for evolution and speciation to occur.

Of course, recall from our last lesson video that this statement number 3 is a true statement. And so it is true that tropical communities have not been impacted as much by glaciation events during ice ages, whereas communities at higher latitudes are more impacted by those glaciation events. So the tropical communities, because they weren't impacted as much, were able to remain around for longer periods of time, giving it more time for evolution and speciation, and that helps to explain why there's more species diversity in tropical communities. Now statement number 4 says, tropical regions tend to receive more precipitation and sunlight. And, of course, we know that this is also a true statement, and having more precipitation and sunlight in tropical regions is going to allow for more biological productivity in tropical regions, which can support a greater diversity of species.

So statement number 4 is also a true statement. Now statement 5 says, tropical regions experience fewer disturbances. And this is not something that we've said in our previous lesson videos. In fact, tropical regions can experience a pretty good amount of disturbances as they can get hurricanes, flooding, and fires. And so, also recall that the intermediate disturbance hypothesis tells us that it's actually a moderate or intermediate amount of disturbances that fosters the greatest species diversity.

And so even if it did have fewer disturbances, that would not explain why it has more species diversity. So, for that reason, we can eliminate statement 5. And so notice that the only option that indicates that statements 3 and 4 are the true statements is option c, 3 and 4 only. And so we can go ahead and indicate that answer option c is the correct answer to this example problem, and I'll see you all in our next video.

Which of the following communities would likely have the highest species diversity?

• A. A large island in the tropics.
• B. A small island in the tropics.
• C. A large island in a temperate region.
• D. A small island in a temperate region.

What is the Island Equilibrium Model?

This video, we're going to answer the question, what is the island equilibrium model? Well, the island equilibrium model tells us that the number of species on an island eventually reaches an equilibrium number of species and is maintained somewhat stable at this equilibrium, where the immigration rates of new species arriving to the island become exactly equal to the local extinction rates of species already on the island. And if a disturbance happens that changes the number of species on the island, well, over time, the number of species on the island is naturally going to drift its way back to this equilibrium number of species. And so the number of species at this equilibrium actually depends on two factors, which are the size of the island and the distance that the island is from the mainland or the source of species arriving to the island. Now in terms of the size of the island, as we already know from our previous lesson videos, the larger the island size is, the more species are going to be present at this equilibrium.

And this is because we know from previous lesson videos that larger areas not only offer more resources, but they also offer more habitats and more micro-habitats that can support more species. And also, larger islands are simply more likely to be found by species migrating off of the mainland. Now in terms of the distance, what you should know is that the closer the island is to the mainland or the source of species arriving to the island, the more species are present at equilibrium. And once again, this is because islands that are closer to the mainland are more likely to be found by species migrating off of the mainland. So let's take a look at our image down below where we can piece this together a little bit better.

And notice on the left-hand side, we're focusing on island size where we have these three different sized islands that are all equally distant from the mainland or the source of species. And on the right-hand side, we focus on island distance from the mainland, where we have three islands of equal size, but they are different distances from the mainland. And so what you should know is that as the island size decreases and gets smaller and smaller, and as the island distance gets greater and greater from the mainland, there are three important effects that you can gather from this image. The first effect is that immigration rates will decrease, indicated by the decreasing thickness of these immigration rate arrows. The second effect is that the species diversity decreases, indicated by the decreasing number of species on the island.

And the last effect is that the local extinction rate increases, indicated by the increasing number of local extinction symbols on these islands. And really, that's all there is to the island equilibrium model. Now the last thing that I'll leave you all off with is that this island equilibrium model actually applies to any isolated patch of habitat. And so although we've only been focusing on these oceanic islands or these islands in the oceans, the island equilibrium model again applies to any isolated patch of habitat, such as, for example, lakes, mountain peaks, caves, ect. And so this here concludes our lesson on the island equilibrium model, and moving forward, we'll be able to apply these concepts and problems.

So I'll see you all there.

Geographic Impact on Communities Example 2

So here we have an example problem that asks, according to the figures below, which of the following options likely has the highest extinction rate? Notice that we've got these three figures or graphs and four potential answer options below. In all three graphs, we have the species richness on the x-axis, which, recall, is the total number of species in the community, just a simple count. On the y-axis, we have both the immigration rate and the extinction rate, where immigration rates are color-coded in blue and extinction rates are color-coded in red.

This first graph tells us that the equilibrium number of species in a community is indicated by the intersecting point of these immigration and extinction curves.

The next graph has curves that correspond with a large island, which I'm highlighting here, and it has curves that correspond with a small island, which I'm highlighting here. Notice that the number of species at equilibrium for the small island is lower than the number of species at equilibrium at the large island. This is consistent with our previous lesson videos, as we know larger islands offer more resources, habitats, and micro-habitats to support more species at equilibrium. Also, larger islands are simply more likely to be found by species migrating off the mainland, giving them a higher number of species at equilibrium.

The final graph focuses on distance from the mainland. We have curves that correspond with near shore islands that are close to the mainland, and curves that correspond with remote islands that are far from the mainland. Notice that the equilibrium number of species for remote islands is smaller than the equilibrium number of species for near shore islands, close to the mainland. Again, this is consistent with our previous lesson videos. Islands that are near shore and close to the mainland are more likely to be found by species migrating off of the mainland, giving them a higher number of species at equilibrium.

Given this context, the problem asks us which of these options likely has the highest extinction rates. Islands that are small have higher extinction rates than islands that are large because the extinction rates are colored red. Islands that are remote and far from the mainland have higher extinction rates than islands that are near shore and close to the mainland. If we aim for the highest extinction rates, then a small island that is remote or far from the mainland is the target. This corresponds with answer option b, which states that the island is small and far from the mainland. Thus, answer option b is the correct response to this example problem.

Option a is incorrect because it says an island that is small and near the mainland; being near shore results in slightly lower extinction rates, explaining why it does not have the highest extinction rates. Option c, which states an island that is large and near the mainland, would actually have the lowest extinction rates, not the highest, so we eliminate option c. Finally, option d also fails because, although being far from the mainland raises extinction rates, being large does not maximize them. Consequently, option b is the correct answer to this example, and I will see you all in our next video.

Which of the following graphs best corresponds with a small island that is distant from the mainland?

• A. Graph #1
• B. Graph #2
• C. Graph #3

Which of the following statements correctly describes the graph below?

• A. Point A represents a large island close to the mainland.
• B. Point D represents a large island close to the mainland.
• C. Point B represents an island with higher species diversity than point C.
• D. Point D represents an island with higher extinction rate than point A.