Herbivory - organisms that directly eat producers to get energy
Predation - consumers that eat other consumers
Competition - different species can compete for any resource (e.g. shelter, food, sunlight, nutrients, etc)
Decomposition - many invertebrates, bacteria, and fungi eat dead material, which returns nutrients back into the abiotic environment
Parasitism - A parasite is physiologically dependent upon its host for nutrition
Commensalism - occurs when one organism is positively affected by the relationship while the other organism is not affected, either negatively or positively, by the interaction.
Mutualism - both partners benefit from the relationship