Ecosystem

An ecosystem (ecological system) is a living community and its nonliving environment. It is a term used by life scientists to break up the biosphere (the entire living world) into smaller parts so as to more easily categorize and study those parts.

An ecosystem can be any size and has no set boundaries. The term can be applied to an entire forest, a lake, a vacant city lot, a suburban lawn, and even a crack in a sidewalk. An ecosystem is a complex system made up of communities of living organisms that interact with each other and with their nonliving surroundings. Ultimately, the entire Earth with all of its life and its physical environment can be said to make up the largest ecosystem of all—Earth's biosphere.

BIOTIC AND ABIOTIC COMPONENTS OF AN ECOSYSTEM

All ecosystems, no matter their size, have two interacting parts—the biotic (living) component and the abiotic (nonliving) component. The biotic component is made up of autotrophic organisms (self-nourishing) and heterotrophic (other-nourishing) organisms. Green plants are autotrophic since they can make their own food or nourish themselves by their ability to convert sunlight into energy. Animals are examples of heterotrophic organisms since they cannot make their own food and are able to break down other living things (plants or animals) and use their energy.

OTHER PARTS OF AN ECOSYSTEM

These biotic and abiotic components are in fact only two parts of a six-part system that ecologists use to categorize what goes on in every ecosystem. These six elements are based on the flow of energy and the cycle of nutrients within an ecosystem. These six elements are (1) the sun; (2) abiotic substances; (3) primary producers; (4) primary consumers;(5) secondary consumers; (6) decomposers. The sun of course is the ultimate source of all energy, and its light is used by green plants (as primary producers) to make food in a process called photosynthesis. Essential to this process are abiotic substances like carbon dioxide, water, and phosphorus, which the plant uses to carry out its food-making series of chemical reactions. After this, a green plant is ready to be consumed or eaten by a primary consumer called a herbivore (any plant-eating animal from a mouse to a cow or an insect) or an omnivore (any animal able to eat both plants and other animals). Primary consumers are followed, sometimes literally, by secondary consumers who are carnivores and therefore eat the primary consumers. Thus carnivores, like snakes and coyotes, generally feed on herbivores. A subset called tertiary consumers are the world's scavengers, feeding off dead animals (as vultures do) or dead organic matter (as earthworms do). Finally, the decomposers have a major role to play in every ecosystem. Decomposers such as bacteria and fungi break down dead organic matter and allow it to release its minerals and compounds back into the soil. Beginning with the sun and ending with organic material being used by green plants, the series of stages that energy goes through in the form of food is called a "food chain." The connected network of producers and consumers is called the "food web."

ENERGY FLOW AND BIOGEOCHEMICAL CYCLE

The physical environment and all of its components serve to make up the abiotic part of an ecosystem. Included in it are basic elements like air (composed mainly of nitrogen, oxygen, and carbon dioxide) and soil (containing nitrogen calcium, phosphorus, zinc, and other minerals). These and other basic elements are constantly being shifted, transferred, and otherwise moved about in an ecosystem. Ecologists identify two major aspects of this movement: the energy flow and the biogeochemical cycle.

In the food web, energy flows through an ecosystem in a series of predictable changes. First, it is changed from light energy into chemical energy by green plants that store it in their cells. Next, the primary consumers eat the plants, digest plant cell walls, and change these into their own form of chemical energy (which they too sometimes store). When a secondary consumer kills and eats a primary consumer, the energy enters the secondary consumer's body. Animals use this energy to keep their vital functions performing and to carry out actions needed for survival (such as running after and catching another animal). When an animal exerts itself like this, it loses much of its energy in the form of heat that escapes from its body and radiates off into the atmosphere. Ecologists have studied this energy flow and arrived at what they call an energy pyramid. In all ecosystems, plants form the base or the largest part of the pyramid, followed by herbivores in the middle, which is topped by the carnivores. This means that more energy passes through plants than passes through herbivores, and still less through carnivores. Creating such a pyramid allows ecologists to know roughly how many pounds of vegetation it takes to support a certain number of herbivores, and how many herbivores are necessary to support one carnivore.

Like energy flow, the biogeochemical cycle tells ecologists the routes that chemicals follow as they pass between organisms and their environment. The obvious path of water is a good example as it evaporates off the surface only to fall back as rain or snow. In the phosphorous cycle, plants take phosphorus from the soil, animals get the phosphorus from eating the plants, and the soil gets the phosphorus back from the decomposers when the plants or animals die. Knowledge of these abiotic factors is as essential as understanding biotic factors.

ECOLOGY IS A COMPLEX SCIENCE

Recognizing all of the interactions within a complex ecosystem requires a great deal of time and actual field study. If ecologists want to understand the subtle day-to-day changes as well as the major ones in an ecosystem, they must become familiar with biology, physics, chemistry, mathematics, climatology, and even geology of ecosystems. Only then can ecologists know which changes are desirable and which may pose a real threat. This knowledge is vital for ecologists if they want to preserve the well-being of all ecosystems.

[See alsoAbiotic/Biotic Environment; Food Web/Food Chain ]