Interspecific interactions can be categorized by whether each species in the interaction benefits, is harmed, or is neither nor harmed. competition is a –/– interaction, meaning that it has a negative effect on both species. mutualism, parasitism, and commensalism are types of interspecific interactions in which at least one species benefits. three examples of symbiosis are epiphytic orchids and trees, hookworms and humans, and rumen bacteria and cows. epiphytic orchids are plants that live on the branches or trunks of trees. the trees supply the orchids with space, and the orchids (which are autotrophs) do not appear to affect the tree. human hookworms live in human intestines and eat blood. rumen bacteria allow for digestion of cellulose in the cow's diet; in turn, the bacteria are supplied with nutrients. categorize mutualism, parasitism, and commensalism as either +/–, +/0, or +/+. also select the correct definition and example for each interaction.