Population and

CommunitiesCHAPTER 21

Populations

How do populations and communities interact?

What will happen to a population if food in the area becomes less plentiful?

What is a limiting factor?

How do populations change?

Why do human populations change?

Organisms

Populations

Communities

Biosphere

Food

Water

Air

Shelter

Completion

Limiting Factor

Population Density

Biotic Potential

Carrying Capacity

Resource

Overpopulation

Birthrate

Death Rate

Extinct Species

Endangered Species

Threatened Species

Migration

Estimate

The Biosphere and Ecological Systems

Biosphere

Can be defined as, the parts of Earth and the surrounding atmosphere where there is

life.

The biosphere includes all the land of the continents and islands, as well as, Earth’s

oceans, streams, lakes, and the ice caps located at the North and South Pole.

Parts of the biosphere with large amounts of plants or algae often contain many other

organisms. These locations are represented by the chlorophyll distribution on the

biosphere.

Recall…

What is an ecosystem?

An ecosystem is a group of organisms that live in an area at one time, in

addition to, the climate, soil, water and non living parts of the

environment.

Ex: Kalahari Desert in Africa

The study of all ecosystems on Earth is referred to as ecology.

What is a population?

A variety of species reside in the Kalahari Desert including: meerkats,

spiders, snakes, insects, zebras, etc.

Together, all the plants, animals, and other organisms form a community.

A community is all the population s of different species that live together

in the same area at the same time.

However, all the meerkats would form a population.

A population is all the organisms of the same species that live in the

same area at the same time.

Quick Check

What defines a population?

Competition

There are going to be times where not enough food is available for every

organism in a community.

This will require members of a population, to compete with other populations and

each other for enough food to survive.

Competition is the demand for resources, such as food, water, and shelter, in

short supply in a community.

Competition to survive increases, as the resources become less available.

Population Sizes

Changes in environmental factors can result in population size

changes.

Populations can be effected by:

Limiting factors

Population density

Biotic potential

Carrying capacity

Overpopulation

Population Sizes

Limiting Factors

Anything that restricts the size of a population.

Includes environmental factors, such as water, food, shelter, sunlight, and

temperature.

Sunlight acts as a limiting factor when green plants do not receive enough to

carry on the process of photosynthesis.

Therefore, those organisms that eat plants will be affected if little food is

available.

Diseases, predators, and natural disasters can also act as a limiting factor.

Population Sizes

Population density

Is the size of a population compared to the amount of space available.

Two ways to measure population size are

Sample count

Capture-mark-and release method

Biotic potential

Is the potential growth of a population if it could grow in perfect conditions with no

limiting factors.

No population on Earth ever reach this limit, due to no ecosystem has an unlimited

supply of natural resources.

Population Size

Carrying capacity

The largest number of individuals of one species that an

environment can support.

Populations grow until they reach this limit within their

environment.

Factors that have the potential to limit a carrying

capacity within an ecosystem include: disease, space,

predators, and food.

However, this amount is never constant, due to the

continuous increase and decrease amount of available

resources.

Quick Check

What is carrying capacity?

Population Size

Overpopulation

This happens once a population becomes

larger than the carrying capacity of the

ecosystem.

Overpopulation has the capability to can

problems for other organisms within the

ecosystem.

Ex: The overpopulation of meerkats can

have a negative impact on the

population of birds and other animals, as

a result of them both feeding on spiders.

Quick Check

Give me an example, in your own words, of how overpopulation

can affect a community.

Changing Populations

How Populations Change

Describe how spiders can go through a population change.

Population Change

Population changes can be measured by the birthrate and death

rate of a population.

Birthrate is the number of offspring produced over a given time period.

Death rate is the number of individuals that die over the same time

period.

If the birthrate is higher than the death rate, the population

increases. However, if the death rate is higher than the birthrate, the

population is decreases.

Population Change

Exponential Growth

When a population is in ideal conditions with unlimited resources, it grows in a pattern called exponential growth.

The larger a population gets, the faster it grows.

Exponential growth cannot continue for long, eventually, limiting factors will stop population growth.

Population Change

Population Size Decrease

Population size decrease can be caused by:

Natural disasters (floods, fires, or volcanic eruptions)

Diseases

Predation

Shortage of food

If the population continues to decrease in numbers, the organisms can either become an/a

Extinct species “a species that has died out and no individuals are left”

Endangered species “a species whose population is at risk of extinction”

Threatened species “a species at risk, but not yet endangered”

Population Change

Movement

Populations have the ability to change when organisms move from

place to place.

When populations become overcrowded, some individuals might

move to find more food or living space.

With regards to plants, these organisms can be moved by wind or

animals.

Often, an entire population might more from one place to another

and later return to the original location.

This is referred to as migration, “the instinctive seasonal movement of a

population of organisms from one place to another”.

Quick Check

List three ways populations change.

Human Population Changes

Although human population is affected by the same three factors of

all population, humans have developed ways to increase the

carrying capacity of their environment.

Things such as improved crop yields, domesticated farm animals,

and timely methods of transporting foods and other resources have

enable people to do this.

However, human population growth affects the growth of other

species.

Destruction of living space, food, and other resources.

Increase of pollution

Human Population Change

Population Size Increase

Today, people in the United States are living

longer than in previous generations. This can be contributed to;

Food

Resources

Sanitation

Medical care

Human Population Change

Decreases in Human Population

Human population in some parts of the world are

decreasing in size due to factors including:

Diseases

Severe drought

Floods, earthquakes, and other natural disasters

Damage from disasters

Human Population Change

Population Movement

The size of a human population changes as people move from

place to place.

Just like other organisms, population of humans might move when

more resources become available in a different place.

Most population is descended from people who immigrated from

other countries.

Give an example of a type of move…

Communities

Communities, Habitats, and Niches

Reminder: A community is made up of all the species that live in the same ecosystem at the same time.

Habitats are the places within an ecosystem where an organism

lives.

These places provide all the necessary resources an organism would

need, including food, and shelter.

Habitats also have the right temperature, water, and other conditions

the organism needs to survive.

Each species that reside in that particular habitat typically use the area

in different ways.

This is referred to as a niche, “what a species does in its habitat to survive”.

Communities, Habitats, and Niches

Quick Check

What organisms in a community need energy?

Energy Roles

All living things use energy and carry out life

processes such as growth and

reproduction.

How organisms obtain energy is an

important part of its niche.

Almost all the energy available to life on

Earth originally came from the Sun.

However, other organisms that live near

deep-sea vents, obtain energy from

chemicals such as hydrogen sulfide.

Energy Roles

Producers

Organisms that get energy

from the environment, such

as sunlight, and make their

own food.

They use the process of

photosynthesis and make

sugar molecules that they us

for food.

Producers near deep-sea

vents use hydrogen sulfide

and carbon dioxide and

make sugar molecules.

Energy Roles

Consumers

Are organisms that get energy by eating other organisms.

These organisms are typically classified by the type of organisms they

eat.

Herbivores -Producers

Carnivores -Consumers

Omnivores -Producers and Consumers

Detritivores -Dead organisms

Quick Check

Identify a producer, an herbivore, and an omnivore.

Relationship in Communities

The population that make up a community interact with each other

in a variety of ways.

While some species have feeding relationships, some species interact with another species to get the food or shelter they need.

Types of relationships:

Predator- Prey Relationships

Cooperative Relationships

Symbiotic Relationships

Predator-Prey Relationships

Predators hunt other animals for food, while the prey are the animals

being hunted.

Predators help prevent prey populations from growing too large fro the carrying capacity of the ecosystem.

Predators often target weak or injured animals, this leaves more

resources for the remaining members, and helps keep the prey

population healthy.

Quick Check

Why are predators important to a prey population?

Cooperative Relationships

The members of some populations work together in cooperative

relationships for their survival.

These organisms cooperate as they hunt for food and watch for

danger.

Symbiotic Relationships

Some species have such close relationships that they are almost

always found living together.

Symbiosis is “a close, long-term relationship between two species that usually involves an exchange of food or energy”.

There are three types of symbiosis

Mutualism

Commensalism

Parasitism

Symbiotic Relationships

Mutualism

Symbiotic relationship in which both partners benefit.

Ex: carbs and sea anemones

Commensalism

Symbiotic relationship that benefits one species but does not

harm or benefit the other.

Ex: epiphytes and trees

Parasitism

A symbiotic relationship that benefits one species and harms

the other.

Ex: tapeworms and humans

Quick Check

List five ways species in a community interact.