HiSET Science: Relationships between Species

Symbiosis
Many species share a special nutritional relationship with another species, called symbiosis. The term symbiosis means 'living together.' In symbiosis, two organisms share a close physical relationship that can be helpful, harmful, or neutral for each organism. Three forms of symbiotic relationships are parasitism, commensalism, and mutualism. Parasitism is a relationship between two organisms in which one organism is the parasite, and the other organism is the host. The parasite benefits from the relationship because the parasite obtains its nutrition from the host. The host is harmed from the relationship because the parasite is using the host's energy and giving nothing in return. For example, a tick and a dog share a parasitic relationship in which the tick is the parasite, and the dog is the host. Commensalism is a relationship between two organisms in which one benefits, and the other is not affected. For example, a small fish called a remora can attach to the belly of a shark and ride along. The remora is safe under the shark, and the shark is not affected. Mutualism is a relationship between two organisms in which both organisms benefit. For example, a rhinoceros usually can be seen with a few tick birds perched on its back. The tick birds are helped by the easy food source of ticks, and the rhino benefits from the tick removal.

Predation
Predation is a special nutritional relationship in which one organism is the predator, and the other organism is the prey. The predator benefits from the relationship, but the prey is harmed. The predator hunts and kills the prey for food. The predator is specially adapted to hunt its prey, and the prey is specially adapted to escape its predator. While predators harm (kill) their individual prey, predation usually helps the prey species. Predation keeps the population of the prey species under control and prevents them from overshooting the carrying capacity, which often leads to starvation. Also, predation usually helps to remove weak or slow members of the prey species leaving the healthier, stronger, and better adapted individuals to reproduce. Examples of predator-prey relationships include lions and zebras, snakes and rats, and hawks and rabbits.

Competition and Territoriality
Competition is a relationship between two organisms in which the organisms compete for the same vital resource that is in short supply. Typically, both organisms are harmed, but one is usually harmed more than the other, which provides an avenue for natural selection. Organisms compete for resources such as food, water, mates, and space. Interspecific competition is between members of different species, while intraspecific competition is between members of the same species. Territoriality can be considered to be a type of interspecific competition for space. Many animals including mammals, birds, reptiles, fish, spiders, and insects have exhibited territorial behavior. Once territories are established, there are fewer conflicts between organisms. For example, a male redwing blackbird can establish a large territory. By singing and flashing his red patches, he is able to warn other males to avoid his territory, and they can avoid fighting.

Altruistic Behaviors Between Animals
Altruism is a self-sacrificing behavior in which an individual animal may serve or protect another animal. For example, in a honey bee colony there is one queen with many workers (females). There are also drones (males), but only during the mating seasons. Adult workers do all the work of the hive and will die defending it. Another example of altruism is seen in a naked mole rat colony.
Each colony has one queen that mates with a few males, and the rest of the colony is nonbreeding and lives to service the queen, her mates, and her offspring.