Living things require energy to grow, breathe, and reproduce. This energy must be available within an ecosystem, or a community that consists of all the living and nonliving things in an area, including soil, plants, and animals.
The sun is the first source of energy for almost every
ecosystem
. Plants and other living things, or organisms, convert the sun's energy, or solar energy, into biomass, which is the energy that is part of
organisms
. As
organisms
eat other
organisms
, the
biomass
, or energy, moves all the way up the food chain.A
food chain
is a path that energy takes through a certain
ecosystem
.
Producers and Consumers
Each
organism
in an
ecosystem
is part of many
food chains
. Together, these
food chains
make a food web. Within this
ecosystem
structure,
organisms
are grouped into categories calledtrophic levels.
The first
trophic level
includes
organisms
called primary producers. They make their own food, and plants and algae are a few examples.
Primary
producers
use a process called photosynthesis to create nutrientsfrom sunlight,carbon dioxide, and water. This process is how plants convert
solar energy
into
biomass
.
The second
trophic level
includes
organisms
called primary consumers. They can't produce their own food and therefore rely on eating other
organisms
to get energy.An example might be a cow (a
primary
consumer
) eatinggrass (a
producer
">
primary
producer
).
Primary
consumers
include herbivores and omnivores.
Herbivores
are
organisms
that only eat plants, and
omnivores
are
organisms
that eat both plants and animals.
This third
trophic level
includes secondary consumers. They eat
primary
consumers
. They can either
omnivores
or carnivores, which are animals that only eat other animals. An example might be a snake that eats an insect.
The fourth
trophic level
contains tertiary consumers. These
organisms
are
carnivores
or
omnivores
that eat
secondary
consumers
. An example might be an owl that eats a mouse.
Trophic levels
are best seen in a model of a
food chain
. In reality,
primary
producers
would be eaten by many different
organisms
, not just grasshoppers.
Tertiary
consumers
like the hawk would need to hunt many
organisms
to survive. Most
ecosystems
are more complex and would be better represented by an interlinked series of
food chains
called a
food web
.
Moving Energy from One Level to the Next
Only so much biomass, or energy, can move from one trophic level to the next.Energy is lost at each step along the food chain.
An energy pyramid is a good way to show energy loss between trophic levels. Each step of the pyramid represents a different trophic level. The primary producers are at the bottom level, and the tertiary consumers are at the top level.
The size of each level in the pyramid represents the rate of energy flow, or how much energy passes through each trophic level. The steps decrease in size as you travel up the pyramid because energy is lost at every level in the food chain. Eventually, the step can't get any smaller, because there is no energy left to support another trophic level.
Only a small amount, or 10 percent, of energy moves from one trophic level to the next. This is known as the 10 percent rule. It limits the number of trophic levels an ecosystem can support.For example, when a primary consumer eats a primary producer, the consumer only gets 10 percent of the producer's energy. So, if an insect eats a plant, it only gets 10 percent of the energy from the plant. The next consumer would only receive 10 percent of the energy from the insect.This continues all the way up the food chain.
