S7L4d Categorize relationships between organisms that are competitive or mutually beneficial. Each organism in an ecosystem interrelates with the other members. These relationships fall into one of three categories: 1. Symbiosis 2. Competition 3. Predation A long-term association between two members of a community in which one or both parties benefit Three types of symbiotic relationships: ◦ Commensalism ◦ Mutualism ◦ Parasitism Beneficial to both organisms Example: ◦ Protozoa living in termite intestine Protozoa break down wood the termite eats, while the termite provides food and shelter for the protozoa One member benefits and the other is unaffected ◦ Barnacles that live on a whale Barnacles don’t harm or feed on whale. They hitch a ride on the slow moving whale in order to catch plankton and other food in the water Whale is neither benefited nor harmed Benefits one organism (parasite), but harms the other (host) ◦ Tapeworms in a human are parasites ◦ Tapeworm benefits by getting its nutrition from the intestines of its human host ◦ Host is harmed because there are not as many nutrients to absorb into its body. Competitive Relationship When two or more organisms seek the same limited resource, they compete with each other. A resource could be food, water, light, ground space or nesting space Competion can be intraspecific or interspecific. ◦ Intraspecies competetion occurs between members of the same species ◦ Interspecies competition occurs between members of different species Predator is an organism that feeds off of another organism Prey is the organism it feeds on Sea lions hunt down and kill herring ◦ They harry the edges of the school of fish and eat until they have killed all the weak and sick animals ◦ Sounds cruel, but without predation, competition and disease, there would be no natural limitations on population growth • May seem brutal that organisms feed off one another and awful that organisms perish from losing resources or getting disease, but the alternative is even more disastrous: AN EVER-MORE-CROWDED WORLD IN WHICH EVERY POPULATION INCREASED UNTIL THERE WAS NO SPACE OR FOOD LEFT FOR ANYTHING OR ANYONE! • Ecological balances are important!