4. Relationships Between Species

Feeding Relationships

There are many types of feeding relationships between organisms. A predator is an animal that kills and eats another animal, known as its prey. Scavengers are animals, such as vultures and hyenas, that eat organisms that are already dead. Decomposers break apart dead organisms or the waste material of living organisms, returning the nutrients to the ecosystem.

(a) Predator and prey; (b) Scavengers; (c) Bacteria and fungi, acting as decomposers.

Relationships Between Species

Species have different types of relationships with each other. Competition occurs between species that try to use the same resources. When there is too much competition, one species may move or adapt so that it uses slightly different resources. It may live at the tops of trees and eat leaves that are somewhat higher on bushes, for example. If the competition does not end, one species will die out. Each niche can only be inhabited by one species.

Some relationships between species are beneficial to at least one of the two interacting species. These relationships are known as symbiosis and there are three types:

  • In mutualism, the relationship benefits both species. Most plant-pollinator relationships are mutually beneficial. What does each get from the relationship?
  • In commensalism, one organism benefits and the other is not harmed.
  • In parasitism, the parasite species benefits and the host is harmed. Parasites do not usually kill their hosts because a dead host is no longer useful to the parasite. Humans host parasites, such as the flatworms that cause schistosomiasis.

Choose which type of relationship is described by each of the images and captions below:

(a) The pollinator gets food; the plant’s pollen gets caught in the bird’s feathers so it is spread to far away flowers. (b) The barnacles receive protection and get to move to new locations; the whale is not harmed. (c) These tiny mites are parasitic and consume the insect called a harvestman.