Community (ecology)

In ecology, a community consists of all the living organisms within an ecosystem. The organisms comprising the community interact with and affect one another through their behavior. Scientists study communities in part because learning about organisms’ interactions helps them better understand individual organisms. It also helps scientists learn more about other subjects, such as evolution. Some scientists study community ecology, which is the branch of ecology focusing mainly on the relationships among organisms within an ecosystem. Scientists classify organisms into groups to help explain their role in an ecosystem. Studying community ecology is important because it helps people better understand how to maintain and improve biodiversity and the overall health of the world’s ecosystems.

Background

Ecology is a branch of science focusing on the interactions among living and nonliving organisms in the environment. Ecologists organize organisms into groups to better understand the elements of ecosystems and their organization. The broadest category of organization is an ecosystem, which is a system of living (biotic) and nonliving (abiotic) organisms. What constitutes an ecosystem varies, depending on what scientists want to study and learn about. For example, a scientist might categorize a single tree and the community of organisms living in and on it as an ecosystem. Another scientist might categorize an entire lake, including the living and nonliving creatures in it, as an ecosystem.

The next broadest level of organization is a community. A community consists of the living organisms in an ecosystem. The organisms in a community may all impact one another and have different types of relationships. Populations are groups of the same type of organism in a community. A community in a woodland ecosystem might have a population of oak trees and a population of rabbits. An organism is an individual within a population; an individual oak tree in a woodland ecosystem is an organism.

Organisms, populations, and communities are the biotic parts of ecosystems and are connected because they affect one another. Living organisms in ecosystems require energy and nutrients to live, and the energy and nutrients in an ecosystem cycle around various organisms at different times. The amount of energy and nutrients in an ecosystem is called a limiting factor. A limiting factor is a change in a system that affects the input or output of a part of the system. In other words, if an ecosystem begins giving away more energy than it produces, it will limit the number of living organisms in the ecosystem. However, if the ecosystem produces more energy than it gives away, an ecosystem will likely attract or create more living organisms to use this energy. For example, if a forest grows fewer berry bushes, the number of birds that eat those berries will decrease. If more berry bushes grow in the forest, more birds will live in the forest.

Overview

Communities are groups of organisms and populations that interact with other organisms and populations. Communities do not include non-biological materials—such as water, toxins, and minerals—but rely on these materials for survival. Since all members of a community are alive, they require energy to survive. Not all populations and organisms get energy in the same way. How organisms get energy greatly influences their interactions with one another. For example, a plant that gets energy from the sun interacts differently with a grasshopper than a bird that preys on the grasshopper for its energy. Organisms fill ecological niches in their communities based on how they obtain energy and other materials, such as water. An ecological niche is a role that an organism plays in an ecosystem.

Scientists label organisms based on how they get energy and the niches they fill in an ecosystem. Producers are the most important living organisms in an ecosystem because they create their food using energy. Most producers are green plants that use energy from the sun to make food. Producers are vital to the existence of an ecosystem because they turn energy from the sun into energy that other organisms can consume and use.

Primary consumers are another type of organism in an ecosystem. They get energy from eating producers such as herbivores (organisms that eat only plants) or omnivores (organisms that eat plants and animals). Primary consumers cannot make their own food and instead get energy from eating other organisms. Secondary and tertiary consumers are animals that eat other animals. For example, foxes eat rabbits. A rabbit is a primary consumer that eats plants, and a fox gets its energy from eating the rabbit. A bobcat is an example of a tertiary consumer because bobcats eat foxes.

Decomposers are the third category of organisms in an ecosystem. These organisms, which include bacteria and fungi, break down nonliving and decaying material, such as dead plants. Decomposers release nutrients from the dead plants back into the soil. Decomposers are vital to energy flow and the nutrient cycle.

Different types of organisms within a community compete for the same nutrients and energy because an ecosystem has a limited amount of both. Scientists call the interactions among living things symbiosis. The five types of symbiosis are predation, mutualism, commensalism, parasitism, and competition.

Predation is a relationship in which one organism eats another organism. For example, a tiger is a predator that preys on zebras. The predation relationship keeps the tiger alive but kills the zebras. While the term predation is most often used to describe an animal eating another animal, it can also be used to describe an animal eating a plant, such as a bear eating berries.

Predation is one of the most influential types of relationships in terms of evolution because evolution occurs when a genetic difference leads to one organism in a population having an advantage over other organisms. For example, the fastest lions are able to catch and eat prey, so these lions are able to survive and reproduce. Over time, faster lions will make up a larger portion of the population.

Mutualism describes a relationship in which both organisms in the relationship benefit from the relationship. One well-known example of mutualism is the relationship between flowering plants and pollinators, such as honey bees. Flowering plants need pollen to be moved from one flower to another flower on the plant to fertilizer it. Honey bees and other pollinators fly from flower to flower, carrying and depositing pollen that will fertilize some of the flowers, helping the plant reproduce. The honey bee also benefits from the relationship because it gets to drink nectar from the flowers.

Commensalism describes a relationship in which one organism benefits from the relationship and is not affected either positively or negatively by the relationship. The relationship between whales and barnacles is an example of commensalism. The barnacles benefit from growing on the whale and being moved to different places. The whale is not harmed by the barnacles but also does not receive any benefits from them.

Parasitism is a relationship in which one organism benefits and the other is harmed. Parasitism can often cause one of the organisms to die. However, the host organism does not die immediately as prey does. Often, a host gets sick or weak and dies over time. An example of parasite is a leech. The leech can attach to a fish and feed on the fish’s blood, making the relationship parasitic. Sometimes the leech can kill a small or weak fish.

Competition describes a relationship in which two organisms compete for the same resources. Sometimes individuals of the same species compete for resources. Other times, individuals from different species compete for resources. If one of the organisms is better suited to getting the resources, that organism is more likely to survive and the other organism is more likely to die. In this way, competition is also an important factor in evolution. An organism with a trait that makes it faster or better at accessing resources will most likely allow that organism to survive long enough to reproduce; in that way, that trait will become more common in the population over many generations.

Bibliography

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