Eat and be eaten: Feeding relationships
Producers
Plants differ from animals in their ability to make
their own food by obtaining energy from the Sun by photosynthesis. Plants
are called "autotrophs" (from Greek: "self-eaters")
or "producers", and are the basis of all feeding relationships
on Earth.
Consumers
Animals are wholly dependent on plants for their energy source.
Animals are called "heterotrophs" (Greek: "other
eaters") or "consumers".
Types of consumers (heterotrophs)
Consumers can be further grouped depending on what they eat.
- Herbivores eat only plant foods. For example, cows and kangaroos
eat grass, caterpillars eat leaves, parrots and mice eat seeds
and possums eat fruit or nectar. To chew and digest these cellulose-rich
foods, herbivores have various specialised structures, such
as grinding teeth and multiple stomachs with cellulose digesting
bacteria in them.
- Carnivores eat only other animals for food. For example,
cats eat mice, frogs eat insects, lions eat deer, and so on.
Carnivores require sharp tearing teeth to rip through flesh,
and have relatively simpler digestive systems because animal
meat is easier to break down than cellulose.
- Omnivores can eat either plants or animals as food, but the
cellulose from the plants is usually passed out undigested with
the faeces. Being able to eat a range of foods makes an animal
less dependent on any one food source, which aids survival.
Humans are omnivores
-
Scavengers are consumers that only feed on the bodies of
dead organisms, e.g. ravens and Tasmanian Devils.
-
Parasites are consumers which obtain food from a host animal
or plant, but without killing it in the short term, e.g. tapeworms
in a dog's intestine.
- Decomposers are tiny organisms which feed on dead organisms
or waste matter and assist in the process of decay, e.g. bacteria,
fungi and slaters.
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Predator - prey
The predator - prey relationship reflects the interaction between different
consumers.
- The predator actively stalks, kills and eats its prey. Predators
are generally very swift to chase their prey (e.g. a cheetah), have
a keen sense of sight (hawk) or smell (echidna), and possess strong
limbs, sharp claws and long tearing teeth to kill their catch.
- The prey usually has a keen sense of hearing and smell to
detect the presence of a predator. As they are often herbivores
with their heads down eating plants for most of the time, they
usually have their eyes on the side of their heads to increase
peripheral vision.
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Their ears are also often large and able to be twisted
around through 360° to pick up sounds of impending danger.
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