5.1.1 Population Size

Which of the following is not a factor in determining population size? A) the food supply B) birth rate C) available niches D) detritivore activity

D) detritivore activity

Migration is __________. A) the movement of organisms from a native location to a foreign location B) the movement of organisms from a foreign location to a native location C) the movement of organisms from their water supply to their food supply D) the seasonal movement of organisms between locations

D) the seasonal movement of organisms between locations

Which of the following is an example of an even population distribution? A) corn planted in a field B) flocks of birds C) people in a park D) deer in a forest

A) corn planted in a field

journal activity How have advances in medicine, industry, and education affected birth rates, death rates, and population growth?

Advances in medicine, industry, and education have lead to a decrease in death rates, causing an increase in the population. The average lifespan has increased as well, and due to this population increase, birthrates have gone up in general. People are better educated, in better health, and live much more safely than previously. It's easier to treat diseases and keep people alive for longer. This is why the population has increased.

Which of the following species is an R-selected species? A) Giant tortoises B) Mosquitoes C) Elephants D) Redwoods

B) Mosquitoes

Which of the following statements about population distribution is not true? A) Population distribution can be even, clumped, or random. B) Population distribution applies only to animals. C) A population distribution shows where organisms are located. D) A population distribution shows the arrangement of organisms in a location.

B) Population distribution applies only to animals.

When two species compete for the same ecological niche, they cannot coexist because they are competing for the exact same resources. One species is always slightly better adapted for the niche than the other, so over time the disadvantaged species will either go extinct or shift to a different ecological niche. This situation highlights the concept of __________. A) carrying capacity B) competitive exclusion C) limiting factor D) biotic factor

B) competitive exclusion

Lions live in groups called prides. Lion populations would most likely fall in which category of population distribution? A) even B) random C) clumped D) density

C) clumped

In a particular environment there is plenty of food, water, cover, and space to support a large population of pheasants, but a larger quantity of predators are introduced. The predators become the __________ for pheasants in that environment. A) carrying capacity B) abiotic factor C) limiting factor D) biotic factor

C) limiting factor

Which of the following factors would have the smallest impact on a population's size? A) the total number of organisms B) the available water supply C) the variety of organisms D) adequate shelter

C) the variety of organisms

Identify the abiotic limiting factor from the choices below. A) biodiversity B) food C) water D) plant cover

C) water

online content Compare and contrast genetic drift, the founder principle, and the bottleneck effect. (Site 1)

Genetic drift is the idea that random events change the gene pool. It effects populations of any size, but will impact smaller ones more. It can lower the gene pool of a population over time. The founder principle is a specific type of genetic drift where a smaller portion of the population is separated, limiting their gene pool. Finally, the bottleneck effect is what happens when a population decreases rapidly due to a sudden event. This will limit the gene pool greatly, just like the other processes we've described. It is a specific type of genetic drift. The founder principle and the bottleneck effect are both specific types of genetic drift where a population's gene pool is limited. The difference is in how they occur.

lab lecture In our Gizmo today we're going to take a look at how different limiting factors can affect the size of a population within an ecosystem.

Lab Lecture Section 1 00:00:00 PROFESSOR: Hi. Welcome to class today. In our Gizmo today we're going to take a look at how different limiting factors can affect the size of a population within an ecosystem. What I mean by limiting factor is anything that has control over the size of a population, so for example shelter, predation, weather conditions, food availability, land 00:00:24 availability. Any of these things would be considered limiting factors because they have an effect on the size of a population within an ecosystem. In our Gizmo today we're going to take a look at a rabbit population and we're going to test two of the limiting factors that I mentioned, land availability and weather conditions. 00:00:43 So we're going to be able to manipulate the amount of land available and also the types of weather conditions that the rabbits are subjected to. And we're going to see what type of effect does that have on the rabbit population over time. So let's go ahead and open up our Gizmo and get started. All right, so right now as you can see, we have our land for our rabbits. 00:01:08 Our land right now is set to moderate. And for weather conditions, we haven't selected any of the weather conditions. So right now we're saying it's just typical weather conditions, nothing out of the ordinary. What I'm going to do is I'm going to allow this simulation to run under just moderate conditions to see what will happen with the rabbit population over a number of 00:01:29 years under just typical conditions with a moderate amount of land available. Now we can also, as our simulation is running, if you click on Table it's going to show you over time how many rabbits do we have. And also, there's different seasons. Notice our clock here is going from spring, summer, fall, to winter. So you are going to notice there's a pattern to the 00:01:50 fluctuations in the rabbit population depending on which season we're in. Bar chart, right now we're starting with a rabbit population of 50. So we're going to see what happens to that number under moderate typical conditions. And then our graph will help us to analyze the data even further and to see, as I was mentioning, over the seasons 00:02:13 what is the natural fluctuation in our rabbit population. So what I'm going to do is, I'm going to go ahead and click play. I'm going to allow about 10 years to go by. So on the table here, notice our time's counting down, our rabbit population is listing for all the different seasons as they occur. 00:02:32 If we look at our bar chart, again, there's going to be some fluctuations with the seasons. So that's why we're seeing the bar going up and down, up and down. And our graph is really where we're going to see what the pattern is over time and if this ecosystem starts to stabilize and when it starts to stabilize. So notice at first it was increasing but then once we 00:02:53 get to about year three it looks like we're starting to see the same pattern over and over again. So let's go. We're already past year 10 so I'm going to click pause. So it looks like the pattern started to be that we got to a population of around 300 rabbits. And it looks like the population would increase in the spring, be increased for the summer, and then start to 00:03:18 decrease as the weather cooled off for fall and winter. Which would make sense, right? Living conditions are going to be more difficult during the cooler months. So it looks like over time we had a rabbit population of about 300 with the same natural fluctuations with the seasons, moderate land available, typical weather conditions. 00:03:38 So again remember we started with 50 rabbits, we're up to about 300 in a stable ecosystem with moderate land available, typical weather conditions. So let's go back. Let's reset. Well now we're going to do is we're going to actually test one of our limiting factors. Instead of there being moderate land available, I'm 00:04:01 going to say that there's little land available. Well what is that going to do to our rabbit population? Let's do the same kind of test. Let's allow a number of years to go by and find out. So I'm going to click play. Again, if you look at your table here it's showing over time what's happening with the number of rabbits. The bar chart, notice our bar is way down around 100. 00:04:23 Remember with moderate land we were up to 300. So already I'm noticing a difference here. Let's look at our graph. Looks like over time I'm starting to see the same type of pattern. But again, we're down at the 100 mark instead of being up at the 300 mark like we were with moderate land. So let's go ahead and pause our graph. 00:04:44 OK, so have we proven that land availability is a limiting factor on the rabbit population? Yes, we definitely have. Moderate land we were up to 300 rabbits, little land we're down to 100. OK, so definitely we have proven that that is a limiting factor in this case. Let's reset. Land available is back to moderate. 00:05:07 Well now we're going to test one more thing. We're going to say OK, if these rabbits are subjected to a harsh winter is that weather condition going to be a limiting factor? Let's find out. Let's run the simulation again and see what happens. So again we click play. We're allowing time to go by just as we did before. 00:05:26 You can see that by looking at your table. Now if we look at our bar chart, looks like our rabbit population is around the 200 mark. If we go to our graph, looks like it increased to about the 200 mark and it looks like it's staying right around that level over time. So remember, moderate land with typical weather conditions, we were at about 300. 00:05:49 Moderate land with a harsh winter, I'm going to go ahead and pause it, looks like we're down to 200. So again, have we proven that the weather condition of a harsh winter a limiting factor? Yes, our rabbit population is down from 300 to 200. So for the remainder of the Gizmo, what you're going to do, you're going to continue to test these different factors to prove that they are limiting factors and how big 00:06:14 of an effect do they have on the rabbit population. That is the goal in the Gizmo today.

section one So in this section, we're going to discuss population size. We'll identify biotic and abiotic factors that limit population growth.

Section 1 00:00:02 PROFESSOR: What types of factors you think might affect a population size? We have several things that we consider and they're called limiting factors. So this is a picture of a spruce forest. Now forests have organisms that are adapted specifically for surviving in that area. Some forests, such as a tropical rainforest, have 00:00:20 many, many resources. While others, such as the spruce, might not have as many. This would be a limiting factor. So in this section, we're going to discuss population size. We'll identify biotic and abiotic factors that limit population growth. 00:00:33 Looking ahead, we'll evaluate the effect of various factors on population size. And analyze population patterns within ecosystems. Biotic and abiotic factor. Well, let's really quickly review what biotic and abiotic factors are. Remember, bio means life, so a living factor would be a biotic factor. 00:00:53 Abio is the opposite of life, so an abiotic factor would be a non living factor. So examples of a biotic factor would be organisms, anything that's alive. Abiotic factor, things like air temperature, water, soil, things like that that affect an ecosystem but do not live. So all members of one species that live together, in the same habitat, are considered a population. 00:01:18 So that's what we're talking about. What affects their population growth? So we have some pictures here. These would both examples of populations. Here we have a population of some fish. Here we have a population of some mountain goats. They're consider populations because they're the same species living in one area. 00:01:36 They're affected by biotic and abiotic factors, so not only can a population be affected by biotic factors such as predators, but abiotic factors, such as temperature, the amount of water, things like that, can really affect the population of organisms. So limiting factors. Food, water, space, shelter, weather, climate, and temperature are all things that we want to consider when 00:02:02 we're looking at limiting factors. So let's talk about these each individually, just a little bit. We have food. Well, if there's not enough food, you cannot feed yourself or your children. You're not going to be able to reproduce any offspring. Water. 00:02:15 Same thing. If we don't have enough water, organisms are simply not going to survive. They're going to compete for it. Whoever is the most fit is going to win. Space. When organisms start living in crowded conditions, like humans. 00:02:29 When humans are living in very crowded conditions, disease becomes much more prominent. Organisms need a certain amount of space to survive. Now these fish show that they can survive very well living close to one another. In fact, they probably survive better when they live in schools, because they're not as prone to things like predators. 00:02:46 However, some organisms, if you live in too crowded conditions, it can cause more problems than anything. Shelter. Organisms need to be able to find shelter to stay away from certain weather conditions or maybe even predators. Weather and climate. If you cannot live in the climate, you cannot survive. If it is too cold or too hot, you will not survive. 00:03:07 So for instance, a polar bear could not survive in the desert. And we couldn't take a saguaro cactus to the arctic and have it survive. And temperature, which is different than just weather and climate, because it just refers to the air temperature, not the actual weather conditions. The effects of limiting factors. 00:03:26 The tolerance range. Every organism has a range of tolerance that it can survive, so the range of abiotic factors an organism can tolerate. So for instance, an organism that lives in the rainforest would not be able to survive in the arctic, most likely. Because that is out of its tolerance range. It is not adapted to live in that area. 00:03:45 Now human beings are kind of an exception to this rule. We are not adapted to survive in areas other than very mediocre temperatures. We're not supposed to survive in very dry deserts. We're not adapted to survive in very cold conditions. However, since we have been able to solve problems the way we do, we can change our environment so we are able to survive there. 00:04:08 So for instance, you go to a cold area, you put on a jacket you are changing the conditions that you're putting your body in. You have a heater in your house. You go into a very hot area. We have plenty of water supply. We have air conditioners. We're not adapted to living in those areas. 00:04:26 They are kind of out of our tolerance range, but we are able to change those conditions and make them tolerable for us. So a polar bear could not go to the desert and survive in this type of situation. Carrying capacity. So we're talking about a carrying capacity. A carrying capacity is the most number of organisms that 00:04:48 can be supported by an ecosystem. So if you pass that carrying capacity, you now have more individuals in a population than the ecosystem can support. So your population can be expected to decline. If you have not yet reached your carrying capacity, you can expect your population to continue to increase. Competitive exclusion. 00:05:08 If you have a number of organisms trying to get the same niche, or similar niches, they're going to compete with each other. And eventually, one of them is going to nudge the other one out of the entire equation. The other weaker, or less fit, organism, the one that's less adapted to the environment, needs to either find a new niche in that ecosystem, move to a different 00:05:29 ecosystem, or die. Those are the only three choices. Human impact on population size. Habitat destruction is a huge problem with the impact of population size in the rainforest. With our cutting of the rainforest to create lands for cattle grazing and farming, all of this causes populations to decrease because they simply don't have the resources they need to 00:05:53 survive and to support their population. Wetlands are another very important thing that we have a problem with losing a lot of our habitat. Wetland, as we mentioned, is described as an area that is covered with water for all or part of the year, including the growing season. And is not covered with more than six feet of water. So a wetland would also be an example of something that, if 00:06:13 we damage those resources, a lot of organisms are going to be hurt, such as fowl that are migrating. They use a lot of wetlands along the way of the migratory patterns to rest and feed in those long flights that they do every year. So getting real with science. Protecting natural habitats. Remediation. 00:06:32 How can we fix certain things that we have already messed up? If we have damage in ecosystem in some way or another, how can we actually bring that back to the way it was? Wildlife refuge creation. There are certain areas that we will protect the wildlife in certain areas to allow their populations to increase. Rather than keeping them in areas that are frequented by 00:06:52 humans and hunted and things like that. Wetland conservation. Wetland conservations are very endangered. And as I mentioned, many organisms rely on them for their survival in the population increasing. So if we keep our wetlands healthy, and keep plenty of them around, for animals, like our water fowl that use them for migratory patterns, we can really help to improve their 00:07:14 chances of increasing their population. So thinking ahead to the next section. What kinds of popular patterns do you think each of these organisms might have? How would they increase in population? Do you think they happen fast? Do you think they happen slow? Do you think they happen at all?

section two Now we're going to evaluate the effect of various factors on population size.

Section 2 00:00:00 PROFESSOR: Imagine spending every penny you had on a passage ticket on a ship that crossed the ocean from Europe to America, and this was the welcome that you saw when you got here. Well, many people have immigrated into this country over the years. And many people have emigrated out of this country over the years. 00:00:23 We're going to talk about how things like that can affect population size in any ecosystem. Population size section two. We've already identified biotic and abiotic factors that limit population growth. Now we're going to evaluate the effect of various factors on population size. And looking ahead, we're going to analyze population patterns 00:00:47 within ecosystems. Factors of population size. Population size is determined by birth rate and death rate, so how many organisms are born and how many die? We're going to talk about this in a minute. Animal migration. Do animals leave temporarily and then come back? Immigration and emigration. 00:01:08 Do organisms leave permanently or come in permanently? Available niches, is there any available ways of making a living in that ecosystem? So just like this bee and this flower he has a very specific niche, or she has a very specific niche. So when you look at an ecosystem is there room for another organism in that ecosystem? And resource supply. 00:01:34 In a place where these camels live there's not a lot of resources. So is there enough resources to go around to allow populations to increase? Birth and death rates. All right the birth rate of an organism is how many organisms are born in a certain time period, the number of births that occur in relation to the overall population per year. 00:01:56 The death rate is the number of deaths that occur in relation to the overall population per year. So if you want to figure out if your population is increasing or decreasing all you have to do is look at the ratio between these two numbers. If you have more deaths than births your population is going to decline. If you have more births than deaths your population is 00:02:18 going to increase. So if you have the same deaths and births your population is going to stay level. So the growth rate is birth rate compared to the death rate. So by looking at that we can see if the population is actually increasing or decreasing. r-selected and K-selected species. 00:02:37 These are two different types of species that use difference strategies for survival in the population growth. r-selected species have a short lifespan. They produce a large number of offspring in a short period of time And they have relatively low biomass because they reproduce so frequently. Insects are an example of this. House flies, fruit flies, algae, those are all examples 00:02:59 that reproduce very, very rapidly, and that's their strategy for survival. If they produce in very large numbers and they produce often enough they're going to be able to keep their population large even though their lifespan is very, very short. K-selected species are exactly the opposite. They have a very long lifespan. They produce very few offspring. 00:03:21 So here's an example of something that's a K-selected species, a Galapagos tortoise. They have a very long lifespan, and they do not reproduce very frequently. In fact, some species of sea turtles don't even start reproducing until they're about 15 years old. So when we had a population decline in like the Hawaiian green sea turtle for instance, now that they've been 00:03:44 protected they still have not started-- we haven't seen an increase in their population because a lot of those organisms that have survive due to that protection are still not at the reproduction age yet. So elephants, giant tortoise, et cetera, those are examples of organisms that are K-selected species, that have a long lifespan and reproduce very few times in their life. Migration is the seasonal movement of 00:04:14 organisms between locations. It occurs because there's a change in food or water supply, a change in the climate, so winter and summer, and reproduction. So here's some examples of migrations. On the savanna in Africa we have many organisms that move from area to area throughout the year to follow the resources. 00:04:34 If it's dry in an area they have to go to an area where there's more moisture and more food. We have gray whales that migrate from the Arctic. They migrate all the way-- basically across the globe following the food from place the place and for migratory patterns. We already talked about the Monarch butterfly. We said that amazing little butterfly can fly 1,800 miles 00:04:55 just so it can get to an area where the weather is favorable for reproduction. Immigration and emigration is the permanent movement of an organism from a native location to a foreign location. So it's a permanent movement in or out. So immigration would be into an area. Emigration would be out of an area. 00:05:15 So emigrate is from a native location and immigrate is to a foreign location. So here we have some pictures of people coming to the United States. Here we have Europeans going through Ellis Island and here we have some Asians going through Angel Island on the West Coast. So immigration is different than migration because it's 00:05:35 permanent where migration is just a temporary movement, and they will come back year after year. So Ellis Island in the United States is towards the East Coast and has been open from 1892 to 1954, and processed over 12 million immigrants into the United States. Angel Island on the West Coast, open from 1910 to 1940, processed 175,000 immigrants in that time period. So when you look at our population of the United 00:06:04 States does it only increase because we reproduce more? No. It's also going to be increasing because we have a lot of immigration. Let's say we had some emigration from the United States also. As long as our emigration wasn't higher than the immigration we're still going to have an increasing 00:06:22 population. So thinking ahead to the next section. What might the following terms refer to in regards to population, age, structure, distribution, density, and size? If we look at this little graph here, we'll see that this graph shows the populations of different countries in the world. 00:06:45 However, their population density is much different in China than say it would be in the United States. We have less people per square mile than they would in China. So how do those following things affect a population?

section three Now we're going to analyze population patterns within an ecosystem.

Section 3 00:00:02 PROFESSOR: Looking at the picture in front of you, would you say that that is a high population density or a low population density? Well, since population density is defined as the number of organisms per unit of area, I would say it's pretty high density. There are a lot of people packed into a really small space. 00:00:20 That is one of the factors that can affect population growth. How dense is that population? Population Size, section three. We've already identified biotic and abiotic factors that limit population growth and evaluated the effects of various factors on population size. Now we're going to analyze population 00:00:39 patterns within an ecosystem. Population patterns-- age structure. There are certain ways we can look at the population by looking at how many organisms are in each age range of that population. So here's a chart that shows the age of individuals in Belize in 2006. 00:01:02 So if you look at this graph here, this little visual aid, there are more people age zero to four than there are 80 and over. In fact, it's a very consistent curve as it goes from large to small. So there are much more young people than there are old people in Belize, at least in 2006. Now, countries go through different stages. 00:01:32 And as they go through these different stages of population growth, these charts or these distributions are going to also change as that country goes through those different stages. So the distribution of age groups within a population are shown in that graph. Population distribution-- how and where organisms are located. 00:01:52 So if you look at a map, where does everybody live? Well, in the United States, most people live in cities. So here is another visual aid that might show how organisms might distribute themselves in an area. This might be an example that shows how squirrels live in an area. They're going to space themselves out evenly in trees surrounding a certain area. 00:02:14 It might be completely random, where organisms don't care where they are, they just want to live somewhere and survive as long as they can get the resources. This might be another example of how humans might live. Although we do spread ourselves out, we do often live in houses with families, so we would be in more of a clumped scenario rather than a random scenario or perfectly even distributions. 00:02:40 Population densities, the amount of organisms per unit of area. So we might measure the population density of a state, one of the 50 states, and we would find that places like Alaska have a very low population density, because there's such a large volume of land and not as many people, whereas a place like New York City is going to have a much higher population density, because it's not as much area 00:03:04 and there's a lot more population. So here's a map that shows how the population is distributed in the United States. And if you look here, the yellow areas are going to be the areas that have less population, and the blue areas have more population. One thing that really jumps out at you right away is that in a lot of the coastal areas, we have higher populations. 00:03:30 People love to live along the coast. There are a lot of resources there. It was a good place to settle when people started first living in this country. Now, when we come out here into this yellow portion, we might notice that the populations go down. Well, this is a lot of agricultural area where we can grow a lot of food, so it makes sense. 00:03:48 If we're using a lot of land for food, for growing resources, then we can't have as many people because a lot of that land is being used up for supplying our country with food. So population size is the number of members of a species in a given population. So if we look at this graph that shows the population increasing from 1950 to 2010, we'll see that it is a 00:04:12 steadily growing population. So the population size is increasing in this situation. Getting real with science. Madagascar is something that we've mentioned before, but it's a very interesting subject when you're looking in environmental science. 75% of the species in Madagascar are only found there. 00:04:32 What that means is they are endemic to that island. They are found nowhere else in the world. So a couple of the animals I want to talk about today are very unique. The first one is called an aye-aye, which is an animal that is a primate, and is the largest nocturnal primate in the world, which means it's the largest primate that comes out at night. 00:04:54 It's interesting because it has teeth like a rodent, but it is also like a primate, and it has a very extended middle finger. If you look at his hands right here, there is a very long middle finger. And what it does is it uses that finger and those teeth to fill the niche of a woodpecker. So it goes around on trees and it taps on trees until it can 00:05:15 find a place where a grub is. It uses its teeth to chew through the wood, and then it sticks its very long middle finger in that tree to pull out that grub and eat it. Very well-adapted for that niche on Madagascar. The other one is a fossa. Now a fossa, you might think, looks a lot like a cat, and it does look a lot like a cat. 00:05:33 But actually it's related to a mongoose, and it is a predator on the island of Madagascar, endemic to just that island, nowhere else in the world. So once again, I'd say we accomplished our mission. Population growth is affected by factors such as available food sources, water space, as well as weather, climate, and temperature. Population size is determined by birth and death rates, 0:05:58 migration patterns, and reproductive strategies. So if you have more birth than death rates, your population is going to increase, but it's not just that that affects population sizes. If we have more immigration than emigration, your population is also going to increase. And migration, which is a temporary change when organisms go from one place to another on a yearly or 00:06:21 a cycle, it's going to change your population from time to time throughout that year. And patterns seen within a population include age structure, distribution, density, and size.

A) An increase in the amount of land available

What is the most likely cause of the change in population size in year 6 shown in the graph below? A) An increase in the amount of land available B) A decrease in the amount of land available C) A cold spring D) A hot summer

C) hot summers

Which of the following conditions best match this graph? A) normal conditions B) cold springs C) hot summers D) harsh winters

D) ample land, harsh winters

Which of the following conditions will result in the rabbit population pictured in the graph below? A) ample land, cold springs B) little land, normal conditions C) moderate land, hot summers D) ample land, harsh winters