Interspecific competition, another negative interaction form symbiosis, describes a type of interaction where organisms of the same species or different species use the same limited resources in a community. Examples of limited resources can be food, a space to live, or even sunlight. Interspecific competition can result in a negative interaction if the competing species fight and kill each other for the limited resource. Interspecific competition can also have dramatic results on one or both species even if the species do not directly interact. For example, consider a grassland ecosystem in which rabbits and deer both eat grass. In a year of drought, less grass grows, meaning there is a limited food resource for both the rabbits and the deer. Even if the two species never attack each other, numbers of individuals in both species may decline, and one of the species may even die out if food becomes too scarce.
Competition can also be a type of amensalism. Amensalism is an interaction between species where one species is destroyed and the other is unaffected. For example, the mold Penicillium produces a chemical that is toxic to most species of bacteria. The bacteria die, but the mold is unaffected.