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THE ECOSYSTEM
Agriscience 381
Wildlife and Recreation Management
# 8984-A
TEKS: (c)(3)(A)
Introduction
Ecology is the study of the
relationship between living
organisms and their environment.
Environment is an organism’s
immediate surroundings.
An ecosystem is made up of levels
containing groups of organisms.
Ecological levels are as follows.
Individuals

Populations

Communities

Ecosystems

Biomes

Biosphere
Individual organisms of a single
species make up a population.
Populations of more than one
species makes up a community.
Communities make up an
ecosystem.
Ecosystems make up a biome and
biomes make up the biosphere.
Earth is made up of living
organisms and inert substances.
It is the result of millions of years
of evolution or change that is
continuous.
The Earth is a series of different
ecosystems.
Each ecosystem has its own
parameters for life.
These parameters include
temperature, pH, and rainfall.
All species of plants and animals fit
into ecosystems to which they have
adapted.
Sometimes those parameters change.
When that happens, plants must
adapt or die; animals must adapt,
move, or die.
Early in the development of Earth,
all water was fresh, including the
oceans.
Over millions of years, water moved
mineral salts through soil, down
streams and rivers, and eventually
to the oceans’ waters.
As the water evaporated back into
the hydrological cycle, the oceans’
freshwater became brackish water
and then eventually saltwater.
Photo by M. Jasek
People are part of the ecosystem.
People are the only species that can
upset the balance in an ecosystem.
What appears to be a stable
ecosystem, in fact, can be easily
upset by over-exploitation of
resources.
There is a misconception that
humans will one day destroy the
Earth.
In reality, people may destroy the
parameters needed for survival.
If the human population became
extinct, the Earth would heal itself
and life without the human element
would continue.
Ecosystem
A biotic community is a group of
plants and animals that share the
same area and environment.
In this community, plants and
animals are interdependent.
Here biotic and abiotic components
are constantly interacting.
Biotic components
are all living
organisms, from
the smallest
microbe to the
largest animal.
Photo by E. B. Forsythe courtesy of U. S. Fish and Wildlife Service.
Abiotic components are non-living
elements that include soil nutrients,
water, air, and temperature.
Photo by Lynn Betts courtesy of USDA Natural Resources Conservation Service.
An ecosystem can be as large as a
forest or ocean or as small as a river
bank or tree cavity.
Each component in an ecosystem
relies on others within the system
for sustaining life.
A simple example of interdependency
is as follows:
Herbivores eat plants.
Carnivores eat herbivores.
Both generate waste products
that feed microbes, bacteria,
and insects.
This helps feed the plants that
herbivores eat.
Biomes
Biomes are large areas with a
distinct combination of plants and
animals.
These areas are influenced largely
by latitude, soil, temperature, and
rainfall.
The number of biomes may vary
depending on how they are divided.
Biomes can be present on land or
in water.
Aquatic biomes have their own set
of characteristics.
On land, there are six major
biomes in the United States.
Terrestrial Biomes
The six major biomes in the United
States are classified as tropical,
temperate forests, grasslands and
savannas, tundra, taiga, and
desert.
Tropical
Only Hawaii and a few U. S. Pacific
Islands have this biome.
These biomes
are commonly
found along
either side of
the equator.
Photo by M. Jasek.
Tropical forests and
tropical grasslands
are part of this
biome.
Tropical forests are
in areas with more
than 90 inches of
rainfall annually.
Tropical grasslands
occur in areas with low rainfall.
Photo by M. Jasek.
Temperate Forests
Temperate forests are located in the
southern United States, mainly east
of the Mississippi Delta.
Photo by John & Karen Hollingsworth courtesy of U. S. Fish and Wildlife Service.
This area has high value conifers that
are gradually being replaced by
hardwoods.
Plant life in this biome yields a variety
of acorns, cones, berries, and fruits.
Photo by M. Jasek.
Grasslands and Savannas
This biome has low rainfall and
occupies the plains of the western
United States northward into Canada.
Photo by M. Jasek.
Vegetation consists
mainly of grasses
and forbs.
In the U. S., only
grasslands exist.
Photo by M. Jasek
Browsing animals, predators, and
small mammals, along with reptiles
and birds, make up the animal life in
this biome.
Savannas do not exist in the North
American continent.
In savannas, soil fertility is lower
than in grasslands.
Savannas are common in Brazil,
Africa, Australia, and India.
Tundra
This biome is located in the Artic
area or at high elevations.
Biomes at high elevation are alpine
tundra.
The low temperatures and
permanently frozen ground
(permafrost) of Alaska is common
to this biome.
Certain varieties of grasses and
shrubs, lichens and mosses grow in
this area.
Photo by M. Jasek.
Tiaga (Boreal Forests)
Taiga areas are not
as cold as tundra.
Conifers will grow
in taiga.
Also called boreal
forests, trees can
support heavy quantities
of snow and low temperatures.
Photo by Laura Kennedy courtesy of U. S. Fish and
Wildlife Service.
Desert
In the United States, the desert
biome is located in the western USA.
Little or no rainfall is characteristic
of desert biomes in states like
Nevada, Arizona, and California.
Photo by David McMahan courtesy of U. S. Fish and Wildlife Service.
Temperature extremes from daytime
highs to extremely cold nights are
common.
Photo by John and Karen Hollingsworth courtesy of U. S. Fish and Wildlife Service.
Aquatic Biomes
Water freshness is a measure of the
amount of salt in the water.
The four levels of freshness are:
fresh, brackish, salt, and brine.
Fresh water has less than five parts
per thousand (ppt.) salt.
Brackish water ranges from 6 to 15
ppt.
Salt water ranges from 16 to 30 ppt.
Brine is any water with more than 30
ppt. of salt.
The only area in the United States
with this level of salt (brine) is the
Great Salt Lake in Utah.
This level does not support enough
life to consider it a biome.
There are four aquatic biomes:
• Lakes and ponds,
• Streams,
• Oceans and seas, and
• Wetlands and estuaries.
Animals and plants have adjusted
to the varying levels of freshness in
each of the biomes.
Photo by Eric Engbretson courtesy of U. S. Fish and Wildlife Service.
Lakes and Ponds
Inland lakes and ponds are usually
freshwater.
Those along the coast may contain
brackish or salt waters.
Some lakes and ponds are fed by a
watershed or rainfall.
Others are fed by melting snow and
ice or by groundwater.
Photo by Craig Rieben courtesy of U. S. Fish and Wildlife Service.
The temperature of water is
determined by its water source and
by the surrounding climate.
Water also has temperature
variations within it, some as much
as 10 to 15 degrees within as little
depth as two or three feet.
These temperature levels are called
thermoclines.
Life in an aquatic biome ranges
from microscopic organisms to
large fish.
Microscopic organisms include
phytoplankton, zooplankton, algae,
insects, and small crustaceans.
Larger vegetation includes lily
pads, reeds, exposed tree roots,
and trees.
Photo courtesy of U. S. Fish and Wildlife Service.
Dead trees that fall into lakes and
ponds provide a source of shelter
for aquatic species.
Artificial structures can be added
for additional shelter.
Swamps are part of
this aquatic biome.
Swamps are
usually shallow
and more cluttered
with vegetation.
Photo by Ned Trovillion courtesy of U. S. Fish and Wildlife Service.
Streams
Streams range in size from creeks to
rivers.
Photo by J. Schmidt courtesy of U. S. Fish and Wildlife Service.
They are fresh,
flowing water moving
from higher elevation
to lower elevation.
The steeper the
change in elevation,
the faster the water
travels.
Photo by Ed Austin & herb Jones courtesy of Yellowstone Park, National Park
Service, DOI.
As water travels faster, fewer
plants grow in the water.
Rocks, coves, and holes are
sometimes the only shelter for fish.
Oceans and Seas
Oceans and seas are the largest
bodies of water.
These are normally saltwater bodies.
Along coastlines, water may become
brackish when mixed with
freshwater.
During heavy rainfall, coastal waters
may even become fresh.
Many marine species require
saltwater to reproduce, but can grow
in fresh, brackish waters or salt
waters.
Photo by Gary Stolz courtesy of U. S. Fish and Wildlife Service.
Wetlands and Estuaries
Wetlands can be either fresh or
salt waters.
They can occur near any water
source.
Land exposed to water cover for a
long period allows water-tolerant
plants to establish.
This attracts certain types of
wildlife, such as beaver, nutria, and
waterfowl.
Swamp and marsh
vegetations grow
in wetlands.
Swamp is made
up of larger
vegetation, such
as trees.
Photo by John & Karen Hollingsworth courtesy of U. S. Fish and Wildlife Service.
Marshes are wet, grassy, low-lying
areas.
Photo by George Gentry courtesy of U. S. Fish and Wildlife Service.
Estuaries are tidal areas, where the
ocean and land meet.
More than 90 percent of all species
in the oceans depend on estuaries
during some phase of their life cycle.
Photo courtesy of U. S. Fish and Wildlife Service.
Ecological Niche
Each organism in an ecosystem
performs a specific function called
a niche.
This is its job in relation to the
other organisms in the ecosystem.
In some cases, different species will
complement each other and are
dependent on each other.
Lichens are the
result of two
organisms, a fungus
and an algae, living
in a symbiotic
relationship.
Photo by M. Jasek.
Regardless of the function, they all
work to keep the system in balance.
A coyote hunting
mice represents a
predator-prey
relationship.
Photo by J. Schmidt courtesy of Yellowstone Park, National Park System, DOI.
Food Webs
A food web is the relationship of all
animals in a community and the
organisms they eat.
Plants are producers or autotrophs.
Animals are consumers or
heterotrophs.
A basic law of physics is that matter
can be changed from one form to
another; it can neither be created
nor destroyed by ordinary physical
and chemical changes.
Nutrients move from plant to animal
to animal to soil to plant.
This is the basis for a successful
ecosystem.
Illustration: Christine Stetter
Plants take nutrients from the soil
and energy from the sun to produce
glucose, which is used for growth
and reproduction.
Herbivores consume a variety of
plants.
Photo by J. Schmidt courtesy of Yellowstone Park, National Park Service, DOI.
Omnivores feed on both plants and
animals.
Photo by John Nickles courtesy of U. S. Fish and Wildlife Service.
Carnivores feed on other animals.
Photo by J. R. Douglass courtesy of Yellowstone Park, National Park Service, DOI.
The way that these organisms
interact closely resembles a spider
web and is referred to as a food web.
A food chain is a single pathway
within a food web.
However, seldom does an organism
feed on just one other organism.
A food
pyramid
illustrates the
feeding
hierarchy of
the food chain
or food web.
The pyramid directly corresponds
to the amount of food (energy)
available at each level.
As movement occurs up the
pyramid, the population of species
declines.
At the bottom of the pyramid are
plants.
An energy pyramid shows the amount of energy that is
passed from one level to the next. Some of the energy at
each level is used by the organism and some is given off as
heat. Only about 10% is passed on to the next level.
In the perfect ecosystem, the plant
population exceeds the population of
herbivores that feed on the plants.
At the next level, the population of
all herbivores is greater than the
population of all omnivores in that
ecosystem.
The smallest population of species is
the carnivores.
Any change in population at any
level in this pyramid upsets the
whole scheme.
For example, if the predator
population was reduced by hunting
due to them preying on domestic
animals, the wild rabbit population
could outgrow the food supply of
grasses on which it feeds.
Another important part of the food
web, yet much less noticeable, is the
decomposer.
Decomposers are small organisms
that break down complex organisms
into inorganic substances.
The more important of these
substances are water, carbon,
nitrogen, phosphorus, calcium, and
sulfur.
In this form, the plants (producers)
can continue the nutrient cycle in
the food chain.
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Reproduction or redistribution of all, or
part, of this presentation without written
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Instructional Materials Service
Texas A&M University
2588 TAMUS
College Station, Texas 77843-2588
http://www-ims.tamu.edu
2006