(MAE) Symbiotic Relationships Lesson

Symbiotic Relationships Lesson

Organisms in an ecosystem constantly interact. Sometimes organisms form a close relationship over a period of time. A close relationship that benefits at least one of the species is called symbiosis. There are three types of symbiotic relationships: mutualism, commensalism, and parasitism.

The relationship between nitrogen fixing bacteria and legumes is an example of mutualism. Mutualism describes a relationship in which both species benefit. Neither organism was harmed. The bacteria attached to the roots of the legume and received nutrients in the form of sugar. Because of the bacteria, the legume received nitrogen in a usable form. Another good example of mutualism involves bees and flowers. Bees feed on the nectar produced in flowers. As they feed, some of the pollen is carried with it. In this way, flowers are able to reproduce. The bees benefit by having the food source and the plants benefit because their pollen is spread to other flowers. Each benefits from the other in some way.

Commensalism is a type of symbiosis. Commensalism describes a relationship in which one species benefits. The other species is neither helped nor harmed and receives no benefit by the relationship. The relationship between barnacles and whales can be described as commensalism. Barnacles attach themselves to whales. The barnacles benefit because they have a place to live and method of transportation. The whale is neither helped nor harmed by the barnacles.

Parasitism is similar to a predator-prey relationship. One organism benefits and one is harmed. It is a relationship in which one organism lives on or inside another. The organism that benefits is called the parasite, while the organism it lives on or in is called the host. As the parasite benefits from the relationship, the host is harmed. The benefit is usually food for the parasite so the host is not usually killed in a parasitic relationship.

Unlike the predator-prey relationship in which the prey is removed from the population, the parasite often feeds on the host for long periods of time. Some parasites, such as ticks and fleas, live on their host but do not enter the body. Other parasites, such as malaria parasites and tapeworms, live inside the host's body.

The type of relationship between two organisms is not always the same. Sometimes, the nature of the relationship can change over time. Perhaps a host becomes immune to a parasite. In addition, the understanding of a relationship can change as researchers learn more about it. For example, a bird called an oxpecker rides on the backs of some antelopes and other animals. Some researchers, for example, classify the relationship between them as mutualism because the bird gets a supply of food while the animals have their ticks removed. Other researchers have discovered evidence that the bird actually cuts the skin of the animal to obtain blood. As a result, they classify the relationship as parasitism.

Cooperation is another type of interaction between members of an environment. Many animals, including horses, dolphins, lions, and ants, demonstrate social cooperation within their species. These animals live, travel, and/or hunt in herds or groups. Cooperation provides protection for the animals. They also benefit from shared food when hunting. In such groups, a hierarchy often exists. This is an order of leadership established between members of the group. Such order is often based on status. When a conflict occurs between group members; the subordinate animal backs away. This allows the dominant animal to win and eliminates aggression between group members.

 Resources are the things that organisms obtain from their environment in order to survive. Resources include food, water, shelter, and so on. Recall that in any ecosystem, some resources are limited. Competition is the struggle between organisms that attempt to use the same limited resources. Organisms that are better at competing are more likely to get and use the available resources. Competition limits population growth. Because resources in nature are limited, species will always have to compete for them. However, competitive exclusion states that organisms competing for the same resources cannot live together in the same environment forever. Eventually, one species will win. The other will either die out or leave the area.

Competition is also the cause of territorial aggression. Animals have to compete for limited resources, such as food, space, nesting areas, and mates. They will display aggressive behaviors to protect these resources from other animals.

Predator-prey relationships exist when one species eats another. An interaction in which one organism captures and feeds on another organism for food is known as predation. The organism that does the killing is called the predator. The prey is the organism that is eaten as food. Predators generally have traits that enhance their ability to capture prey, such as fast speed, keen eyesight, and sharp teeth. Prey, meanwhile, have traits that help them avoid being captured. These might include the ability to escape quickly or to hide in the environment.

Populations or predators and prey typically follow a pattern over time. At some point, the prey population grows so large that prey are easy to find, in turn, the predator population grows because predators have a good supply of food. As the predator population grows, they continue to feed on prey. This causes the prey population to decrease. As the food supply decreases, the large population of predators can no longer be supported. The predator population then decreases. With a smaller number of predators, the prey population can grow and the cycle repeats.

 

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