Ecosystems and Energy Flow
- An Ecosystem is a community of living organisms of different species living together in the
same environment.
- Ecosystems contain biotic (living organisms) and abiotic (non-living things).
- The biotic factors include animals, plants, and other organisms. Abiotic factors include rocks,
weather, and water.
Interactions of Organisms and Their Environment
- Ecology is the study of the interactions of living organisms with one another and with their
physical environment (soil, water, climate, and so on).
- The place where a particular population of a species lives is its habitat.
- The many different species that live together in a habitat are called a community.
Diverse Communities in
Ecosystems
- The number of species living
within an ecosystem is a measure
of its biodiversity.
- The more biodiversity a
community has, the more stable
the community is.
Ecosystem Inhabitants
- Most ecosystems contain a few large animals and some smaller animals.
- Ecosystems tend to contain more plants than animal life.
- The most plentiful organisms in an ecosystem are usually microscopic bacteria and protists.
Change of Ecosystems over Time
- When a volcano forms a new island, a glacier recedes and exposes bare rock, or a fire burns all
of the vegetation in an area, a new habitat is created.
- This change sets off a process of colonization and ecosystem development.
- The first organisms to live in a new habitat are small, fast-growing plants, called pioneer
species.
Succession
- A somewhat gradual regular
progression of -species
replacement is called succession.
- Succession that occurs where
plants have not grown before is
called Primary succession.
- Succession that occurs in areas where there has been previous growth, such as in abandoned
fields or forest clearings, is called Secondary succession.
Glacier Bay: an Example of Succession
- A good example of primary succession is a
receding glacier because land is continually
being exposed as the face of the glacier
moves back.
- The seeds and spores of pioneer species
are carried in by the wind. Alders, grasses,
and shrubs later take over from pioneer
plants.
- As the amount of soil increases, spruce
and hemlock trees become plentiful.
Movement of Energy through Ecosystems
Primary Energy Source
- The rate at which organic material is
produced by photosynthetic organisms in an
ecosystem is called primary productivity.
- Organisms that first capture solar energy, the
producers, include plants, some kinds of
bacteria, and algae.
- Consumers are those organisms that consume plants or other organisms to obtain the energy
necessary to build their molecules.
Trophic Levels
- Ecologists study how energy moves through an ecosystem by assigning organisms in that
ecosystem to a specific level, called a trophic level, in a graphic organizer based on the
organism’s source of energy.
- Energy moves from one trophic level to another.
Trophic Levels: First Level
- The path of energy through the trophic levels
of an ecosystem is called a food chain.
- The lowest trophic level of any ecosystem is
occupied by the producers, such as plants,
algae, and bacteria.
- Producers use the energy of the sun to build
energy-rich carbohydrates.
Trophic Levels: Second Level
- At the second trophic level are herbivores,
animals that eat plants or other primary
producers. They are the primary consumers.
- A herbivore must be able to break down a
plant’s molecules into usable compounds.
Most herbivores rely on microorganisms,
such as bacteria and protists, in their gut to
help digest cellulose.
Trophic Levels: Third Level
- At the third trophic level are secondary
consumers, animals that eat herbivores. These
animals are called carnivores.
- Some animals, such as bears, are both herbivores
and carnivores; they are called omnivores.
- Detritivores are organisms that obtain their energy
from the organic wastes and dead bodies that are
produced at all trophic levels.
- Bacteria and fungi are known as decomposers because
they cause decay.
- Decomposition of bodies and wastes releases
nutrients back into the environment to be recycled by other organisms.
- In most ecosystems, energy does not follow simple straight paths because animals often feed
at several trophic levels. This creates an interconnected group of food chains called a food we
Food Chains
Loss of Energy in a Food Chain
Energy Transfer
- During every transfer of energy within an ecosystem, energy is lost as heat.
- Thus, the amount of useful energy available to do work decreases as energy passes through an
ecosystem.
- The loss of useful energy limits the number of trophic levels an ecosystem can support.
The Pyramid of Energy
- An energy pyramid is a diagram in which each trophic level is represented by a block, and the
blocks are stacked on top of one another, with the
lowest trophic level on the bottom.
- The width of each block is determined by the
amount of energy stored in the organisms at that
trophic level.
- Because the energy stored by the organisms at each
trophic level is about one-tenth the energy stored by
the organisms in the level below, the diagram takes
the shape of a pyramid.
Energy Transfer through Trophic Levels
Limitations of Trophic Levels
- Most terrestrial ecosystems involve only three or, on rare instances, four trophic levels. Too
much energy is lost at each level to allow more levels.
- The number of individuals in a trophic level may not be an accurate indicator of the amount of
energy in that level.
- Some organisms are much bigger than others and
therefore use more energy.
- Because of this, the number of organisms often
does not form a pyramid when one compares
different trophic levels.
- To better determine the amount of energy
present in trophic levels, ecologists measure
biomass.
- Biomass is the dry weight of tissue and other
organic matter found in a specific ecosystem.
- Each higher level on the pyramid has less
Biomass.
