Interdependence and Symbiosis

1.2 InterdependenceCould you carry out your day without depending on other things besides yourself?Think of things you depend on to get through just one day:

- electricity (lights, to make/preserve food, television, radio/stereo, etc)- fossil fuels (heating, transportation,

plastics, cosmetics, clothing)- other people (parents, teachers, friends,

employers, doctors, dentists, etc)- plants and animals (food, clothing, pets)

ex. Most organisms need oxygen. Plants produce oxygen as a waste product of photosynthesis and plants need carbon dioxide. Most organisms produce carbon dioxide as a waste product of cellular respiration.

ex. Bees need pollen to produce food for their colony and queen. Flowers need bees to transfer pollen grains from one flower to another, which fertilizes the plants.

Types of Interdependence1) Food Chain / Food Web Relationship

Any food chain / web demonstrates that living things rely on other living things.Herbivores consume plant life (producers)Carnivores consume herbivores

and other carnivoresOmnivores consume producers

and other consumers.Even decomposers rely on

once-living things as a food source.

2) Predator-Prey RelationshipPredators are very important to maintain a healthy balance for a population.Predators prevent the prey population from becoming too big.

- If the prey population becomes too big, it would run out of its food supply resulting in its individuals suffering from starvation.Predators also remove old, sick, or weak individuals of a population leaving the strong and healthy members to reproduce.

3) Symbiosisa type of interdependence between members of different species.One ‘species’ survival depends directly on the health and survival of another species.

There are three types of symbiotic relationships:

a) Commensalism – one of the organisms benefits from the relationship, but the other neither benefits nor suffers because it is unaffected by the relationship.

ex. a bird builds a nest in a tree. The bird benefits, but the tree is unaffected.

The barnacles benefit from the free ride, but the whale is unaffected.

ex. barnacles on a whale.

b) Mutualism – both organisms benefit from the relationship.

ex. fungus and algae make up lichen in the arctic north.

In this harsh environment, algae are able to produce their own food energy (glucose) by photosynthesis. The fungus uses this energy, too.

In return, the fungus helps the algae by preventing dehydration.

ex. Oxpeckers (tickbirds) have very short legs and sharp claws allowing themto perch on the backs of large mammals such as hippopotamus and rhinoceros. They use their beaks to pick at scabs, feed on skin parasites such as ticks and embedded larvae, and probably obtain their main nourishment from the blood of wounds rather than from the ticks. They also protect wild game from danger by setting up rattling cries, which alert the animals to the presence of predators.

c) Parasitism – one organism benefits while the other is harmed by the relationship. Parasites don’t usually kill their hosts intentionally, because it would mean the end of their food supply. Sometimes, however, the host becomes so weakened from the parasite that the host dies.

ex. a tapeworm attaches itself to the intestine of its host (any animal) and absorbs the nutrients leaving less for the host.

ex. the parasite wasp temporarily paralyses a tomato horn worm by stinging it then the wasp lays her egg on it. The hornworm then recovers and goes about its life with the newly hatched wasp larva feeding on its haemolymph (insect "blood").