6. Stability in an ecosystem is a balance between competing effects. As a basis for understanding this
concept:
a. Students know biodiversity is the sum total of different kinds of organisms and is affected by alterations of
habitats.
Biodiversity refers to the collective variety of living organisms in an ecosystem. This structure is influenced by
alterations in habitat, including but not limited to climatic changes, fire, flood, and invasion by organisms from
another system. The more biodiversity in an ecosystem, the greater its stability and resiliency.
e. Students know a vital part of an ecosystem is the stability of its producers and decomposers.
An ecosystem’s producers (plants and photosynthetic microorganisms) and decomposers (fungi and
microorganisms) are primarily responsible for the productivity and recycling of organic matter, respectively.
Conditions that threaten the stability of producer and decomposer populations in an ecosystem jeopardize the
availability of energy and the capability of matter to recycle in the rest of the biological community
f. Students know at each link in a food web some energy is stored in newly made structures but much energy
is dissipated into the environment as heat. This dissipation may be represented in an energy pyramid.
The energy pyramid illustrates how stored energy is passed from one organism to another. At every level in a
food web, an organism uses energy metabolically to survive and grow, but much is released as heat, usually
about 90 percent. At every link in a food web, energy is transferred to the next level, but typically only 10
percent of the energy from the previous level is passed on to the consumer.
Notes:
Ecology is the study of relationships between organisms and their environment.
The Biosphere
Certain areas, especially surfaces where water is plentiful, are more amenable to life than others. Nevertheless living
things can be found several miles up in the atmosphere to a kilometer or more deep in solid rock and from the icy
deserts of the arctic to super heated water near volcanic vents at the bottom of the ocean.
All organisms are intimately linked to their environment for survival. Most are dependent on one or more
organisms in a unique way to supply some essential substance. Any close relationship between two organisms is
called symbiosis which you will learn more about later.
The environment is everything an organism will come in contact with in its surroundings. This includes both the
nonliving or abiotic factors and the living or biotic factors.
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abiotic factors include such things as:
1. temperature
2. soil
3. moisture
4. light
5. minerals
6. air
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biotic factors may include most if not all of the other living things in the organisms habitat. Some important
general categories of organisms essential for a complete ecosystem are:
1. producers such as plants and algae to supply the energy needed by other organisms
2. decomposers such as bacteria and fungi to help recycle important minerals and nutrients.
Ecosystems
Every functioning ecosystem is composed of both biotic and abiotic factors which work together as a system -- the
ecosystem. The biotic factors combine to form a community. Each community is a collection of populations
composed of each species. The ecosystem therefore is the intimate fusion of a community with its environment.
The environment for an individual species may be described in terms of two ecological states. The organisms:
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Habitat: the environment in which an organism or biological population lives or grows: and its
Niche: (pronounced NITSH) the role a species plays in its community which depends on both where it lives
and well as what it does.
We will investigate only the larger ecosystems but an ecosystem has no size limitations -- it can be as large as the
worlds oceans; the marine ecosystem or as small as a pool of water in the cup of a tropical leaf.
A stable ecosystem has reached a state of equilibrium. In order to remain stable three conditions must be satisfied:
1. it must have a constant source of energy
2. the energy must be available in a usable form
3. organic and inorganic materials must be recycled constantly
Biotic Relationships
Symbiotic Relationships involve close physical contact between two different species. These interactions can be
classified in terms of who is benefited, harmed or unaffected in each case. We will look at the 4 most common
symbiotic relationships which are:
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Mutualism -- both organisms are benefited
Commensalism -- one organism is benefited the other is relatively unaffected
Parasitism -- one organism is benefited while the other is harmed.
Some examples of mutualism are:
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Bees and Flowers
Termites and intestinal protozoan
Some examples of Parasitism include:
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Fleas and Mammals (dogs, cats, etc.)
Viruses and probably every form of life
Pathogenic bacteria and their hosts
Possible examples of commensalism are:
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Barnacles attached to whales
Epiphytic plants on larger branches of a tree
Remora hitching a ride on sharks or other large fish
Feeding Relationships follows the path nutrients take through an ecosystem. These relationships can be described
in three ways.
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What individual organisms use for food
How nutrients are transferred through the community
Trophic (energy) levels
Organisms may be classified by the type of food they use or obtain into tree groups:
Producers (plants an algae) obtain their food from sunlight -- they are sometimes referred to as autotrophs
Consumers (all other organisms) get their food by eating other organisms. For example:
1. herbivores are primary consumers -- eating only plants or other producers
2. carnivores are secondary consumers -- they eat only other animals
3. some carnivores -- especially fish -- can be tertiary consumers -- animals that eat animals that eat animals
Decomposers (mostly bacteria and fungi) help breakdown complex organic molecules produced by other living
things.
How nutrients are transferred from one organism to another is outlined in one of two ways:
Food chains -- each organism, starting with plants and other producers, that eats, absorbs, or decomposes another
is part of a linear sequence called a food chain. This represents only a single thread in a larger more complex set of
relationships called a food web.
Food webs -- represents a network of food chains. The more extensive the food web found in a community the
more stable that community should be.
Food chains and food webs have three common threads:
Nutrients are transferred from producers to consumers
Organisms feed on several different tropic levels
Both end with decomposers.
Trophic (energy) levels
Trophic levels in a community are limited to no more than 5, but may often be less. Each trophic level represents
the amount of energy available to levels above it. Because energy is always lost from one level to the next the
trophic levels in any ecosystem can be represented as a pyramid -- widest at the bottom -- and narrow at the top.
Notice that the amount of energy transferred to the next higher level is only about one-tenth of the original amount.
This is due to several factors including:
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Energy is lost as waste
Friction and inefficiencies occur during the transfer process
Some parts of the original organism can not be recycled
This is called the 10% rule -- as energy moves through trophic levels in an ecosystem, only about 10% of the total
energy at one level is stored in the tissues of organisms in the next level.
Pyramid models emphasize 4 important ecological principles which include:
All food chains begin with producers
Consumers depend, directly or indirectly on producers for their energy
The amount of energy available at each trophic level is directly related to the number of links in a food chain
Solar energy is required as the ultimate energy source (for nearly every living thing on earth)
Remember that energy does not cycle but rather it flows through ecosystems.