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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