Population density tells the number of individual species or living beings per unit area.

C. population density

Migration generally refers to the movement of individuals between areas. The movement *out* of an area is called *emigration*, while the movement *into* an area is called **immigration**.

Both immigration and emigration can influence the growth rate of a population as individuals leave and enter a population. Other factors that can affect growth rate include births and deaths.

C

The area that is occupied by a particular population is known as its **geographical distribution** or range. It is one of the characteristics that is used to describe a population in an ecosystem.

The geographical distribution of a population can be influenced by certain factors. The amount of available resources and the intensity of competition can influence the range of a population.

B

The given graph shows a J-shaped curve, which illustrates the rapid increase in the number of individuals in a population over a period of time. This rapid growth is called **exponential growth**.

Exponential growth only occurs under ideal conditions such as when resources are unlimited, which allows for rapid population growth. In reality, however, available resources are limited.

B

Since the environment has a limited amount of resources, it could only support a certain number of individuals in a population. This maximum number is known as the **carrying capacity**.

Aside from the amount of available resources, the carrying capacity of a particular environment with respect to a population of species can also be infleunced by the intensity of competition.

B

A. Death rate may rise

Please review explanation

B. Hurricanes

Please review explanation

Density-dependent means the population growth varies with the population density. This limiting factor only controls the population growth if the density reaches a particular level.

A. density-dependent limiting factor

D. Demography

Please review explanation

A demographic transition is marked complete once the birthrate meet with the death rate. This means that the population growth stops.

A. population growth stops

**Immigration** is the movement of organisms or individuals to another location and population

**Emigration** is the movement of individuals from its orignal habitat to another area and population. It is the movement of organisms out of a population.

An exponential growth produces a J-shaped curve. An exponential growth is an increasing growth rate in which the population reproduces at a constant rate. The graph below is a sample exponential growth curve of a hypothetical population of red foxes.

**Logistic growth curve** shows the expansion of a population decreases as the resources become limited, leveling off when the carrying capacity of the environment attained and reached.

Hence, logistic growth happens when a population initially started from a slower growth rate followed by an exponential period then stops at or near the carrying capacity of the area.

**Carrying capacity** is the maximum value or number of individuals of a particular species a specific environment can sustain and support.

Example: A pond that is inhabited by 50 fishes will be sustainable for the organism’s population

. Increasing the amount of a limiting nutrient would increase the carrying capacity of the pond until it is spent, after which the carrying capacity of the pond will decrease unless the amount of the limiting nutrient is increased over and over again.

Increasing the amount of a limiting nutrient would increase the carrying capacity of the pond until it is spent, after which the carrying capacity of the pond will decrease unless the amount of the limiting nutrient is increased over and over again.

**Competition** is an ecological interaction between species in which they compete or strive for similar resources in an ecosystem. One or both species can be harmed.

It two species are competing over the same resources in a given environment, the one that has an advantage at competing will have a higher reproduction rate, hence higher birthrate than the other species. In addition, they may also displace the other species in their habitat.

**Predation** is a biological interaction where one organism called the *predator* kills another organism, the *prey*, in order to get food.

The **predator-pray relationship** can be a tool of population control for both species since the population size of the predators is limited by the amount of prey present and available to eat. In turn, the number of prey is limited by the predation relationship.

Parasitism is considered as a density-dependent limiting factor. For an instance, when parasites attach themselves to the body of the hosts, the hosts will be harmed and eventually, they will get sick and die. Given this case, parasites serve as a limiting factor to population growth because they cause a decrease in the population of the host species.

**Demographic transition** is a long-term phenomenon of declining birth and death rates. This trend can transform the age structure, hence, changing the age distribution of a given population

Demographic transition can happen in three stages:

**Stage 1:** A country has a high rate of natality and mortality

**Stage 2:** The rate of mortality stops, but the rate of natality remains high.

**Stage 3:** The natality falls to meet the mortality rate.

Hence, the correct answer is **A**

For the past 20,000 to 100,000 years or more, the growth of the population can be described as “gradually slow”. However, just about 500 years ago the human population started to grow exponentially and increased abruptly. The growth rate only slowed during the second half of the twentieth century.

The human population began expanding rapidly 500 years ago because of the various conditions that made survival more advantageous, thereby decreasing the mortality rate.

The following conditions are enough and reliable supply of food, improved sanition and medical care services.

The demographic transition was used by demographers to determine the correlation between the population growth and the social and economic development of a country and use this information to predict its economic growth. Before, the population growth had a dramatic change in the human society because of the growth spurt in either the birthrates or the death rates. Since people are more educated due to the modernization and technological advancement in the society, they now have the ability to control the population by raising the standards of living. People were educated about family planning and they were also receiving sufficient healthcare. As a result, the birthrate falls to meet the death rate.

**Age structure** is the term to define the proportion of a certain population at various age ranges.

The populations with nearly equal numbers of individuals in each age group will likely experience a slow but steady population growth for the near future. Populations with many more young individuals compared to adults will likely increase at a rapid rate.

When there are limited resources, growth rate decreases once the population reaches its maximum capacity. For an instance, a small pond is limited only for sustaining three hundred minnows. If the population of the fishes grows higher than what the pond can accommodate, there will be a competition for food. Only the fishes which are properly fed will survive, and those which are not fed will eventually die. As a result, the growth rate of the minnows will decrease. Because of this, minnows are now limited in number and those species that feed on them such as birds and other larger fishes will also be affected.

**Density-dependent factors** are population regulating factors that affect the size of the population of the organisms in response to their density

A contagious virus will be able to spread easily in crowded conditions or in area where there is a denser population, hence it is considered as density-dependent factor.

**Density-independent limiting factors** are population regulating factors that affect the size of the population in many ways *regardless* of the density of the population

In most cases, it will result in a greater impact on populations in a small ecosystem. This is because the small populations in these ecosystems are more susceptible to serious damage and destruction from density-independent factors such as floods or wildfires.

As shown in the diagram, the number of people in each age group appears to be nearly equal. Hence, this age structure predicts that the population would have a slow but steady growth rate.

In contrast, if the age-structure diagram shows that there are more young people than adults, then the age structure would predict that the population would grow rapidly in the near future.

Since the age-structure diagram predicts that the population would have a slow but steady growth rate, then the size of the population of Sweden would not change as much after 50 years.

Town A (a small town made up of mainly senior citizens)

Since the old age group is greater in numbers compared to the younger age groups, the following predictions are made:
a. There will be a higher death rate compared to birthrates.
b. The future population growth rate will decrease or slow down.

Therefore, Town A’s growth curve will show an S-shaped pattern which indicates a logistic growth.

Town B (a small town made up of mainly newly married couples in their twenties )

Since the younger age group is greater in numbers compared to the older age groups, the following predictions are made:
a. Married women will increase the fertility rate.
b. There will be a higher birth rate than the death rate.
b. The future population growth rate will increase.

Therefore, Town B’s growth curve will show a J-shaped pattern which indicates exponential growth.

Generally, a road can only accommodate a specific number of vehicles in order to have a smooth traffic flow. When there is an overflow of vehicles on the road, the traffic becomes congested. Once this happens, the road’s vehicle capacity will decrease which may lead to accidents or road closure. This situation can be compared to the carrying capacity in an ecosystem. Like a road, an ecosystem has limited resources that can only sustain a certain number of organisms. If there is an overpopulation, the ecosystem gets congested and the food supplies and space will run out. As a result, there will be a competition among the organisms and only the stronger species will survive. This event causes limitation to the population growth in the ecosystem.

**Predation** is a biological interaction where one organism called the *predator* kills another organism, the *prey*, in order to get food.

If there will be an abrupt increase in resources for the prey population we can say that their population will increase. Hence, there will be more food for the predators, which in result will also increase their population

The prey-predator and host-parasite relationships are similar in terms of the effect of their symbiotic relationship. In this case, preys and hosts are harmed during the process which eventually leads to their deaths, whereas the predators and the parasites both benefit from those organisms by acquiring their energy and nutrients.

This is because if the water levels falls, the density of the fish populations will increase. This will result in the susceptibility of the fish population to density-dependent limiting factors

A demographer may ask these questions in order to determine if a country is approaching demographic transition:

1. Birthrate
a. What is the birthrate ten years ago?
b. What is the birthrate five years ago?
c. What is the birthrate for the current year?

2. Death rate
a. What is the death rate ten years ago?
b. What is the death rate five years ago?
c. What is the death rate for the current year?

3. Compare the birthrate and death rate. Is the birth rate higher than the death rate?

4. What is the age-structure of the population?

5. Is there any child policy imposed in the country?