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.