Feeding Relationships
Organisms may interact with one another in several ways.  One example of an organism interaction is that of a producer/consumer relationship.   A producer is any organism capable of making its own food, usually sugars by photosynthesis.   Plants and algae are examples of producers.   A consumer is any organism which eats another organism.   Several different types of consumer organisms exist.    A herbivore is a consumer which eats primarily plant material.  A deer is an example of a herbivore.   A carnivore consumes primarily animal material.   An omnivore eats both plant and animal matter.   Humans are examples of omnivorous organisms.

A predator is a type of carnivore that kills its food.   The organism the predator feeds upon is called its prey.    A wolf and rabbit would provide an example of a predator/prey relationship.    Scavengers feed upon organisms that other organisms have killed.    A crow feeding off dead carrion in the highway would be an example of scavenger in this instance. 

Symbiotic Relationships
Close living associations are called symbiotic relationships.  Parasitism is an example of such a relationship.   In this situation, the parasite feeds upon the tissues or fluids or another organism, but usually does not kill the organism it feeds upon, as this would destroy its food supply.   The organism the parasite feeds upon is called the host organism.  An example of this sort of relationship would be fleas on a dog or athlete's foot fungus on a human.

Other Relationships
Some organisms such as certain pathogenic bacteria may cause disease in other organisms.  Decomposer organisms use the energy of dead organisms for food and break them down into materials which can be recycled for use by other organisms.   Bacteria of decay and many fungi are examples of decomposer organisms.