Factors Limiting Population Growth - Online Tutor, Practice Problems & Exam Prep

Population growth is influenced by two main types of limiting factors: density dependent and density independent. Density dependent factors, such as competition, predation, and disease, intensify as population density increases, affecting birth and death rates. In contrast, density independent factors, like natural disasters, impact populations equally regardless of density. Understanding these factors is crucial for grasping concepts like carrying capacity, which represents the maximum sustainable population size in an ecosystem.

Factors Limiting Population Growth

This video, we're going to briefly talk about factors limiting population growth. And so what's important for you to realize is that in the absence of ecological factors that limit population growth, theoretically, any population will grow exponentially. However, these conditions are rarely met in nature since in most cases, there are factors that limit population growth that are present. And so these limiting factors on population growth that are usually present can be separated into 2 distinct types. The first type are density dependent factors, and the second type are density independent factors.

Now moving forward, we're going to talk about each of these in their own separate videos starting with density dependent factors. So I'll see you all there.

Density-Dependent Factors

This video, we're going to talk about density-dependent factors and how they limit population growth. Density-dependent factors, as their name implies with the term dependent, are going to have limiting effects on population growth that are directly dependent on population density. If you change the population density, then you'll also change the effects that these density-dependent factors have on limiting the population's growth. Often, these density-dependent factors will have an impact that intensifies as population density increases. Most, but not all, of these density-dependent factors are going to be biotic in nature, meaning they're associated with life.

Notice that down below in our image, we're showing you just a few examples of density-dependent factors, which includes things such as resource or water availability, predation, disease, competition, waste accumulation, and limited space. As an example to help you better understand how the impact intensifies as population density increases, you can imagine a scenario where as population density increases, the resources in the environment, such as food and water, become exhausted and depleted. This means that there won’t be enough resources for all of the individuals in the population, leading to increased death rates and decreased birth rates. In a graph, like the one that you can see down below right here, which has population density on the x-axis and mortality rate on the y-axis, you might expect this graph to look something like this for density-dependent factors. As the population density increases, the impact on the population's growth intensifies, so the mortality rate is going to increase as well. It's important to note that as population density increases, the population will approach what's known as its carrying capacity, which is often abbreviated with the letter K and represents the theoretical maximum population that an area can sustain at any given time.

As the population density increases, it approaches the carrying capacity and the impact of these density-dependent factors will intensify. This conclusion concludes our lesson on density-dependent factors. In our next lesson video, we'll talk about density-independent factors. I'll see you all there.

Density-Independent Factors

This video, we're going to talk about density independent factors and how they limit population growth. Density independent factors, as their name implies with the term independent, have limiting effects on population growth that are completely independent of population density. Unlike density dependent factors, changing the population density here is not going to change the effect that these density independent factors have on limiting the population's growth. These density independent factors are often random ecological events that are random with respect to population density, and usually, they are abiotic in nature, meaning that they're associated with nonliving things, such as natural disasters like hurricanes, floods, and fires. The big takeaway here is that these density independent factors limit population growth equally, regardless of the population density.

In a graph like this one on the right side, where we have population density on the x-axis and mortality rate on the y-axis, for density independent factors, we might expect this graph to look something like this: just a straight horizontal line. Regardless of what the population density is, the impact on the population's growth limitation is going to be equal. This here concludes our lesson on density independent factors, and moving forward, we'll be able to apply these concepts and problems. So I'll see you all there.

Factors Limiting Population Growth Example 1

So here we have an example problem that wants us to label each of the following 5 factors that we have numbered down below as either a density-dependent factor using the letter 'd' or as a density-independent factor using the letter 'i'. Now, of course, recall from our previous lesson videos that both density-dependent and density-independent factors will have limiting effects on a population's growth. The difference between these two is whether the impact of the factor depends on population density or not. With density-dependent factors, the impact does depend on population density. But with density-independent factors, the impact does not depend on population density at all.

Keeping that in mind, notice option 1 says, a disease epidemic among the African elephant population. In this case, the disease is the factor, and the question is, does the impact of the disease depend on the population density of the African elephant? The answer to that question is yes; it does depend on it. Because if we were to increase the population density of the African elephant, that would allow the disease to spread faster into more individuals so that the disease has a greater and more significant impact on limiting the population as the population density increases.

So that's consistent with a density-dependent factor, and so we can put a 'd' here. Now next, what we have is a severe flash flood in northern India. In this case, does the impact of the flash flood change with population density? The answer to that is no. The flash flood is going to have the same impact on a population regardless of its density. And so for that reason, we can label this as a density-independent factor.

Next, what we have is number 3, which says an increase in the number of predators that prey on squirrels. In this case, the factor is predation, and looking at these predators and how they impact the squirrels. So the question is, does changing the population density of these predators have an impact on the predation of these squirrels? The answer to that is yes. As we increase the population density of the predators, that's going to increase the predation effect and therefore limit the population of the squirrels more significantly, and so this is a density-dependent factor for that reason.

Next, what we have is severe wildfires in Californian forests during the summer, and the question is, does the impact of the wildfires depend on population density? The answer to this question is no; regardless of what the population density is, the wildfire would have the same impact. And so for that reason, this is a density-independent factor.

Now, last but not least, we have number 5, which says overcrowding at a watering hole in Kenya's Aberdare National Park. In this case, the limiting factor is space, and so we can see here that it's overcrowding. The question is, does the impact of the amount of space depend on the population density? The answer here is yes. It does depend because if we increase the population density, that means there's going to be less space available. And so, that's going to impact or increase the effect of this factor. And so that means it's a density-dependent factor.

This here concludes that example problem, and I'll see you in our next video.

Which of the following is a density-independent factor that limits a population’s growth?

• A. Disease.
• B. Drought.
• C. Lack of food availability.
• D. Predation.

Density-Dependent vs. Density-Independent Factors

In this video, we're going to compare both of these population growth limiting factors, which are density-dependent factors and density-independent factors, side by side in this table that you can see down below, starting with their definitions. A density-dependent factor is a factor whose impact depends on population density. On the other hand, a density-independent factor is a factor whose impact does not depend on population density. In terms of its relation to population density, the impact of density-dependent factors is proportional to population density, which means that the impact increases or intensifies as population density increases. On the other hand, with density-independent factors, the impact is constant regardless of population density.

Now in terms of the impact on small and large populations, for density-dependent factors, there's a higher or greater impact on high-density populations that approach the carrying capacity, which recall is the theoretical maximum population that an area can sustain at any given time. These density-dependent factors will actually have a lower impact on low-density populations. On the other hand, density-independent factors will have equal impacts on low and large density populations. In terms of common effects, density-dependent factors, because they have a higher impact on high-density populations approaching the carrying capacity, they somewhat help to establish the carrying capacity, and therefore, it helps to regulate the maximum population size of an area. On the other hand, density-independent factors can cause sudden and drastic changes in population size.

In terms of the nature of the factor, density-dependent factors are typically, but not always, biotic in nature, meaning that they're associated with living things, whereas density-independent factors on the other end are typically abiotic. Notice down below, we have a few examples of each of these factors. For density-dependent factors, we show things such as competition, predation, disease, water availability, waste accumulation, and limited space in nutrients. Whereas, for density-independent factors, we show things such as hurricanes, floods, wildfires, droughts, earthquakes, temperature extremes, and seasonal changes. Ultimately, what we're saying here is that all of these factors depend on the population density, and as the population density increases, so will the impact of these factors.

For all of these factors over here, they do not depend on population density and they will have an equal impact regardless of what the population density is. This here concludes our side-by-side comparison, and I'll see you all in our next video.