Download Lesson 8 Ecosystems

Ecosystems
The organization of the biosphere, from the broadest level of organization to the most
specific level of organization, is shown below:
biosphere → biome → ecosystem → community → population → organism
Biosphere
The biosphere includes any part of the Earth where organisms live. It extends from the
crust of the Earth to the atmosphere. All of the ecosystems on the Earth are included
within the biosphere.
All of the ecosystems on Earth are part of the biosphere.
The biosphere is the broadest level of ecological study. It includes interactions between
different ecosystems that can only be studied by viewing the entire Earth as one large
system. The lithosphere, hydrosphere, and atmosphere are all part of the biosphere.
Biome
A biome is a geographic region that has a distinct climate. A biome is made up of
separate (but similar) ecosystems, so it contains characteristic types of plants and
animals adapted to the region and its climate.
Deserts, grasslands, and rainforests are all examples of biomes.
Ecosystem
An ecosystem is made up of the biotic, or living, community and its abiotic, or
nonliving, environment. Abiotic factors include rocks, air, dirt, sunlight and water.
An example of an ecosystem would include all of the living and nonliving factors that are
inside a pond. The water in the pond, the algae and plants that grow in the water, the
animals and bacteria that live in the water, the dirt and rocks on the bottom of the pond,
and the sunlight that hits the water would all be considered a part of this ecosystem.
All of the living and nonliving factors of this coral reef are part of the coral reef
ecosystem.
Ecosystems can vary greatly in size and conditions. The abiotic factors that make up an
ecosystem determine what kinds of plants and animals that can live there. For example,
a desert ecosystem that is very hot and does not receive much water can only support
certain kinds of organisms, such as cacti and lizards.
Community
A community includes all of the populations that live and interact in the same area. An
example of a community is all of the plants and animals inside of a forest. All of these
organisms interact and depend on one another for survival. A community makes up
an ecosystem's living, or biotic, portion.
All of the plants and animals in this forest belong to the same community.
At the community level, interactions between organisms can be observed. For example,
predator/prey and consumer/producer interactions occur at this level. Competition and
cooperation between different species are also part of community ecology.
Population
A population is a group of individuals of the same species living in the same area at
the same time. An example of a population of organisms is a grove of orange trees.
All of the orange trees in this grove belong to the same population.
Populations can be defined at different levels of size. For example, a local population
could occupy a very small habitat, such as a puddle. A population could also include
every member of a species of monkey that occupies a large island. There is generally a
boundary between populations of the same species, such as an ocean or an area of
land that the animals do not freely cross.
Changes in Ecosystems
The survival of organisms depends greatly on physical factors in their
environment. Any changes to either the biotic or abiotic factors can impact an
ecosystem. Some changes that might appear to be minor could have a large effect. For
example, minor changes in the pH of a body of water can cause massive fish kills.
But not all changes are negative, some could be positive. By simply moving through the
soil, worms are able to help break up the soil and add air. This improves the quality of
soil, which plants benefit from.
Changes in an environment also have ongoing effects. For example, if some or all of the
plants in an ecosystem were to die, the animals that feed on the plants would have less
food, so fewer of the animals would survive.
As the population of these primary consumers becomes smaller, secondary consumers
would begin to compete with each other more for food, and this population would also
begin to shrink.
Biotic & Abiotic Factors
Factors which can affect change in a population or species are usually divided into two
types: abiotic and biotic. Abiotic refers to the nonliving environmental factors, while
biotic refers to the influence or effect created by a living organism.
Both abiotic and biotic factors can limit or enhance a population’s success in a
particular environment.
Biotic Factors
The word biotic comes from the Greek word for "life". Biotic factors include not only
living organisms but also factors from formerly living organisms.
Biotic factors include both living things and things that were once living. This means that
the cotton plant and a cotton shirt are both considered biotic.
For example, both a cotton plant and a cotton t-shirt would be considered biotic factors
because they are derived from the same living organism. Biotic factors typically
influence the viability of a community and include interactions between members of the
same species and members of different species.
Abiotic Factors
Abiotic factors include any nonliving geological, geographical and climatological factors.
Specific abiotic factors are water, air, soil, light, temperature, and natural disasters.
These things are a part of each species’ ecological niche because they influence how
populations affect, and are affected by, resources and enemies.
Abiotic factors shown here include air, water, light, soil, and even the forest fire.
Biomes
The term biome refers to a geographic region that has a distinct climate. A biome
contains characteristic types of plants and animals adapted to the region and its climate.
Characteristics of Biomes
The climate of a location determines which types of organisms are able to live there.
Climates that are very cold are home to plants and animals that have adapted to the
extreme temperatures. The same is true for climates that are extremely hot and dry.
The major biomes on Earth include: tropical rainforest, temperate rainforest, desert,
grassland, deciduous forest, coniferous forest, tundra, estuary, savanna, and taiga.
Tropical Rainforest
The climate of a tropical rainforest is hot and wet. Heavy rainfall (around 150 cm per
year) and year-round warm temperatures make it very humid. This climate is found near
the equator. A tropical rainforest is very dense with lots of large trees that block out
sunlight. Very little sunlight reaches the rainforest floor.
Tropical rainforests are very hot and wet.
Temperate Rainforest
The climate of a temperate rainforest is mild and wet. Temperatures are moderate and
change with the seasons. Rainfall amounts are very high. Like tropical rainforests,
temperate rainforests have a thick canopy of trees that block most sunlight from hitting
the forest floor. However, while tropical rainforest canopies are generally broadleaf
trees, temperate rainforest canopies may be broadleaf or coniferous trees.
Temperate rainforests commonly have coniferous canopies, with smaller broadleaf
plants in the understory.
Image courtesy of NPS.
Temperate rainforests are farther from the equator than tropical rainforests and can be
found in the U.S. Pacific Northwest, Asia, South America, Europe, and Australia.
Desert
The climate of tropical deserts is generally hot and dry. However, temperate deserts,
such as the Gobi in Asia, are much cooler. The amount of precipitation in all deserts is
less than the amount of water that could potentially evaporate. Deserts get less than 25
centimeters of rain every year. Desert plants and animals are adapted to store water
and withstand year-round hot temperatures.
Deserts are very dry and generally hot.
Succulents, snakes, scorpions, and mice are examples of organisms that live in desert
ecosystems.
Temperate Grasslands
Temperate grasslands are located in the dry temperate interiors of continents. In North
America, they are called prairies, in Asia they are referred to as steppes, and in South
America they are pampas.
Temperate grasslands receive enough rainfall to support grasses, but not enough to
support the growth of large trees. The temperatures are generally warm in the summer
and cold in the winter. Drought and wildfires are also common in this biome.
The temperate grassland is characterized by thick, mixed grasses.
Prairies are often converted into farmland due to the rich soils found there. Some of the
animals that can be found in this ecosystem include grasshoppers, prairie dogs, and
bison.
Deciduous Forest
The climate of a deciduous forest is temperate with four distinct seasons (spring,
summer, fall, and winter). Deciduous forests have warm summers and cold winters.
They have moderate precipitation throughout the year.
Deciduous forests have four distinct seasons.
During winter months, however, the precipitation is usually frozen and unavailable to the
organisms that live there. Trees in a deciduous forest usually lose their leaves during
the winter and have thick bark to conserve water and protect them from the cold.
Taiga
The taiga, known also as a boreal forest, is the largest continental biome. It experiences
long, cold winters; short, warm summers; and low precipitation. It is characterized by
coniferous forests. Taiga covers most of Canada and Siberia and is not found in the
Southern Hemisphere.
The taiga is characterized by coniferous forests; long, cold winters; short, warm
summers; and low precipitation.
Arctic foxes, wolves, and snowy owls are a few examples of the animals that live in the
taiga.
Tundra
The tundra has very low temperatures and very little precipitation. Winters in the tundra
are long and extremely cold; summers are short, mild, and cool. The animals living in
tundra ecosystems have adaptations that allow them to stay warm in the very low
temperatures. For instance, Arctic foxes, grizzly bears, and ermines (a kind of weasel)
all have thick fur that protects them from the cold.
The tundra is very cold and dry.
Tundra is characterized by its frozen subsoil, which makes only a small layer of soil
available to plant life. This limits the plants that can grow to small low growing plants
such as mosses and grasses and makes it impossible for trees to grow.
Estuary
An estuary is an area in which fresh water and salty ocean waters mix together. These
areas may include bays, mouths of rivers, salt marshes, and lagoons. These brackish
(salt mixed with fresh) water ecosystems shelter and feed marine life, birds, and other
wildlife with nutrients from the ocean.
Estuaries provide a place where young animals can grow up.
The plants in estuaries are marsh grasses and other plants that are adapted to water
levels that change with the tides. Muskrats, herons, egrets, shrimp, and crabs are
animals often found in estuaries.
Savanna
A savanna is a dry tropical grassland where trees are present but more widely
scattered than in forest ecosystems. The savanna climate has a temperature range of
68° to 86°F.
Savannas receive around 125 centimeters of rain every year, with most of the rain
falling during the summer. Because of the vast differences in precipitation, the summer
is referred to as the "wet season," and the winter is the "dry season."
The trees in a savanna are very sparse and spread out.
Zebras, giraffes, lions, and acacia trees are found in the savannas of Africa.
Ecosystems - Trophic Levels
The organization of communities is based on the use of energy from the Sun within a
given ecosystem. Organisms within a community are dependent on the survival of the
other organisms because energy is passed from one organism to another.
The Sun's energy cycles through ecosystems from producers through consumers and
back into the nutrient pool through decomposers.
A trophic level describes the feeding level of an organism. Producer, decomposer,
primary consumer, secondary consumer, and tertiary consumer are all trophic levels
that can be used to describe an organism's place in an ecosystem.
Producers
Producers are organisms that are able to
synthesize food molecules from inorganic compounds. Green plants, such as
sunflowers, are producers because they can make their own food using energy from the
Sun during a process called photosynthesis. Other producers include algae and some
kinds of bacteria and protists.
All other organisms in an ecosystem depend on producers for energy.
Consumers
Consumers are organisms that get energy by feeding on producers (e.g., plants) or
other consumers.
There are three main kinds of consumers: primary consumers, secondary consumers,
and tertiary consumers. The classification given to a consumer depends on where it is
located in a food chain.

Primary consumers are animals that eat producers. Primary consumers are also called
herbivores because they eat only plants. A deer that eats only leaves and grass is a
primary consumer and an herbivore.

Secondary consumers are organisms that eat primary consumers. Secondary
consumers can be carnivores if they eat only animals. Or, they can be omnivores if
they eat both animals and plants. A wolf that kills and eats a deer is a secondary
consumer and a carnivore.
Consumers eat other organisms. Deer are primary consumers. Wolves are secondary
consumers.

Tertiary consumers eat secondary consumers, and they may be carnivores or
omnivores. A bear that eats a fish that has fed on other fish is a tertiary consumer.
Since the bear also eats berries and other plants, it is an omnivore.
Decomposers
Decomposers are organisms that consume
dead organisms. As they break down dead organic matter, decomposers release
nutrients back into the soil, water, and atmosphere.
The role that decomposers play in an ecosystem is crucial. Decomposers are important
for the carbon, nitrogen, phosphorus, and oxygen cycles. The nutrients that
decomposers release into the soil are also used by producers to make complex organic
molecules. Fungi, such as mushrooms, are examples of decomposers. Some kinds of
bacteria are also decomposers.
The Flow of Energy Through an
Ecosystem
The ultimate source of energy for all ecosystems is the Sun. Only producers can
convert solar energy into food energy. Therefore, all other organisms depend on
producers for their energy needs.
Food Chains
A food chain describes the feeding relationships and energy flow between species
within an ecosystem.
Producers receive energy from the Sun and make food. Producers are the beginning of
a food chain because all of the other organisms in the food chain depend on the food
energy that is made by producers. The next organisms in the food chain are primary
consumers, which eat producers. Next come secondary consumers, then tertiary
consumers, and so forth until the top carnivore is reached. All organisms in the food
chain are decomposed by decomposers.
This food chain shows the flow of energy from a producer, algae, to the consumers in
the ecosystem. Minnows are primary consumers, salmon are secondary consumers,
and bears are tertiary consumers.
The arrows in a food chain or a food web represent the direction of energy flow.
The arrow points from the organism that is being consumed to the organism that is
receiving energy. For example, in the food chain above, the arrow points from the algae
to the minnow. This means that the minnow is consuming the algae and receiving
energy.
Food Webs
A food web is a group of interconnected food chains. Organisms within a food web can
belong to more than one trophic level, or feeding level. For example, in the food web
below, krill are both primary and secondary consumers. Krill are primary consumers
because they eat phytoplankton, which are producers. Krill are also secondary
consumers because they eat carnivorous zooplankton, which are primary consumers.
An Antarctic food web is shown in the picture above. Organisms in food webs can
belong to more than one feeding level.
Energy Pyramid
An energy pyramid is a diagram that shows the relative amounts of energy located
within each trophic level. The trophic levels are stacked one on top of another, with the
producers on the bottom. Each level in an energy pyramid has less energy available to
it than the level below.
Most of the stored energy in an ecosystem is in plants and other producers. This is
because most of the energy in an energy pyramid is used or lost as heat energy as it
moves up the pyramid. In fact, only about 10% of the energy produced at each level is
available to the one above it. This is the reason that consumers in an ecosystem cannot
outnumber producers and predators cannot outnumber prey.
The size of each level of the energy pyramid is determined by the amount of energy
stored in the organisms at that trophic level.
An average of only 10% of the energy from the previous level moves to the next level.
The rest is used up or lost as heat energy.
Organism Interactions
Organisms within an ecosystem interact with one another in many different ways. These
interactions play an important role in the survival of the organisms and the function of
the ecosystem.
Organisms can affect one another directly, through a shared resource, or through
common enemies. Some interactions are harmful to the organisms involved, whereas
others provide benefits for one or both of the organisms.
Energy Relationships
Food chains and food webs describe the feeding relationships between species and
represent the flow of energy through an ecosystem. The Sun provides energy to
producers, such as plants. Producers convert this energy into a form that can be eaten
by consumers. Animals that eat producers are then consumed by animals at higher
trophic levels. Eventually all organisms are broken back down into nutrients by
decomposers.
The food chain above shows the flow of energy from a producer, a plant, to the
consumers in the ecosystem. Decomposers may feed on organisms at any stage of the
food chain. Decomposers recycle nutrients back into the ecosystem.
Symbiosis
Symbiosis is an interaction between individuals of different biological species. At least
one of the organisms receives a benefit from the interaction. The other organism can
either receive a benefit, be harmed, or not be affected in any way.
A symbiotic interaction involves a close relationship between the two organisms
involved. There are three main kinds of symbiotic relationships: commensalism,
mutualism, and parasitism.
Mutualism
Bees receive nourishment from flowering plants, and plants are pollinated by the bees.
Therefore, the relationship is mutualism.
Both organisms benefit in a mutualistic relationship.
Flowers and their pollinators are one of the most common examples of mutualism
because many kinds of plants depend on insects, such as moths, bees, wasps, and
beetles, to perform pollination in order to reproduce. Plants that rely on pollinators
attract the pollinator by the shape, color, or smell of their flowers. As the pollinator feeds
on the nectar or pollen from the flower, some of the pollen sticks to its legs and body.
When the pollinator visits a second plant of the same species, the pollen from the first
plant is transferred to the reproductive organs of the second plant, and pollination
occurs. Both organisms receive a benefit from this interaction. The pollinator receives
access to a food source and the plant is able to reproduce because of their relationship.
Commensalism
Cattle egrets follow behind large grazing herbivores and eat the insects that are stirred
up. This is a form of commensalism.
One organism benefits and the other is neither helped nor harmed in a
commensalistic relationship.
Often, the benefit that the organism receives is the ability to find food more easily or
protection from other organisms.
For example, large grazing herbivores, such as cattle and horses, often stir up insects
as they graze on grass in fields and pastures. Birds known as cattle egrets often follow
behind the grazing herbivores and eat the insects that have been displaced. Since the
cattle egret benefits by being able to find food easily and the grazing herbivores are not
affected by the presence of the egrets, their interaction is an example of commensalism.
Parasitism
This mosquito is receives nourishment, while the human is harmed. This is an example
of parasitism.
Image is courtesy of the CDC.
One organism benefits and the other is harmed in a parasitic relationship.
The organism that receives a benefit is known as a parasite. The organism that is
harmed by the relationship is known as the host. The host species is usually impaired
slowly over a long period of time.
Parasites are usually smaller than the host species, but not always, and can live either
inside the body of their host or externally. Common external parasites include fleas and
mosquitoes which feed on the blood of their hosts. Internal parasites, such as
tapeworms, live inside the body of their host and absorb nutrients from the host's body.
In both cases, the parasite receives nutrients at the expense of the host and the host
can no longer use these nutrients for its own life processes.
Predation
Predation is a type of interaction in which a predator hunts, kills, and eats its prey.
Predators use the prey as a source of food. Predation is different from parasitism
because the prey is killed immediately for consumption. During parasitism, the host is
kept alive for a long period of time so that the parasite can continue to receive nutrients
from the host. An example of predation is a wolf pack hunting, killing, and consuming a
deer.
Lions kill and eat zebra. Lions are predators. Zebras are prey.
Competition
Since there are limited amounts of resources in an ecosystem, if one organism gets a
particular resource, another does not. This leads to competition as two organisms try
to access the same resources. Food, water, sunlight, and space are examples of
resources that organisms compete for.
Plants and animals of the same species may compete for resources such as food,
water, shelter, and space. Populations of different species will also compete with one
other if their needs are the same as the needs of another population in that ecosystem.
For example, trees in a forest compete for sunlight. As one tree grows taller, the shorter
trees are shaded by it, and they receive less sunlight. The shorter trees may die as a
result.
The tall tree and the shorter trees in this picture are competing for sunlight.
Cooperation
Cooperation is a type of interaction in which organisms work together. Many species
exhibit cooperative behavior, including horses, dolphins, lions, and ants. Animals that
exhibit cooperative behavior often live, travel, and/or hunt in herds or groups. Living in
these groups can provide protection for the animals and a higher success rate during
hunts.
Groups of organisms that live together cooperatively are usually part of a hierarchy of
leadership. Some members of the group have a higher status than other members of
the group. Dominant members determine what the group will do and subordinate
members follow their lead. This helps to eliminate aggression between group members
and allows the group to work together for the benefit of all.
An example of an animal that lives in a cooperative group is the wolf. Wolves live in
packs that usually include six or seven members. There are two leaders within the
group, the alpha male and the alpha female, and these two pack members determine
when the pack hunts, moves location, or stays in an area. The leaders of the pack are
usually the pack members with the most experience in hunting and defending territory.
The other pack members have roles within this pack to help the pack work effectively.