Geography Reference
In-Depth Information
The “chain” of events
A
food chain
is a sequence of living things through which energy and other matter move in an ecosys-
tem. That mumbo-jumbo clearly calls for a diagram — two in fact, inasmuch as there are
terrestrial
(land) food chains and
aquatic
(water) ones (see Figure 18-3). Though their specific components dif-
fer, the overall structures are quite similar.
At the base of any food chain are a number of
primary producers
that convert solar energy
to organic matter — green plants in the case of terrestrial ecosystems, and aquatic plants or
algae in the case of aquatic systems.
Any animal that feeds upon a primary producer is a
primary consumer
. This may be a rab-
bit or squirrel (any herbivore will do) in the case of a terrestrial food chain, or a small fish in
the case of an aquatic food chain.
Any carnivore that feeds on a primary consumer is a
secondary consumer
.
Any carnivore that feeds on a secondary consumer is called a
tertiary consumer,
and so
forth. Humans can be primary, secondary, tertiary, or whatever consumers depending on what
they are eating and whether that something had itself previously eaten another consumer.
Figure 18-3:
Ter-
restrial and
aquatic food
chains link di-
verse life forms.
All living things ultimately die (a major bummer) and decay.
Decomposers,
which consist
of various microorganisms and bacteria, feed on organic waste and matter at all levels in the
food chain and, as their name suggests, aid in decomposition. Ultimately, they disintegrate or-
