An Ecosystem Approach

"Whatever befalls the Earth, befalls the children of the Earth. If we spit upon the ground, we spit upon ourselves. This we know. The Earth does not belong to us; we belong to the Earth."

— Chief Seattle

What's an Ecosystem?

An ecosystem is a natural community, and it can exist anywhere on Earth. It's made up of biotic (living) and abiotic (non-living, life-supporting) elements. In any area, such as a rain forest, frog pond, or schoolyard, biotic elements (plants and animals) form an ecosystem along with abiotic elements (soil, rocks, air, and water). Your ecosystem includes the land, air, water, sunshine, food, home, schoolmates, friends, and family you need to grow up healthy and happy.

The word ecosystem combines two words: ecology and system. Eco means habitat or home; system refers to the interdependent way all biotic and abiotic elements of a natural community fit together, like pieces in a hugely complex jigsaw puzzle.

An ecosystem can be as big as a planet or as small as the palm of your hand. A tall-grass prairie or a rain forest is an ecosystem. Even your skin is an ecosystem: it has biotic elements (microscopic creatures like fungi, bacteria, and mites) that depend on each other along with the abiotic elements needed to survive. Other examples of ecosystems are mountains, swamps, meadows, and arctic tundra. The biggest of all is the ecosphere. It includes the surface of the planet, the atmosphere, the continents, the oceans, and all life on Earth.

Ecosystem diversity refers to the number, variety, and extent of ecosystems on Earth or within a given geographical area. Ecosystems occur on many different scales. The ecosphere consists of a multitude of smaller ecosystems, some of them close together but separate, others overlapping, and still others occurring inside larger ecosystems. All are interdependent, right down to the microsystem in the gut of a gnat.

As you'll see, ecosystems never stand still: in one way or another, they're constantly changing.

Ecosystem versus Habitat

Is an ecosystem the same as wildlife habitat? Not exactly. When speaking of an ecosystem, we're really concerned with the biotic and abiotic elements of a natural community and how they interact. Wildlife habitat, on the other hand, fulfils the needs of a certain species and is just one segment of an ecosystem. Among these needs are food, shelter, water, and space, which must be arranged in a way that's just right to support a particular species. Your schoolyard ecosystem could include an incredible variety of habitats, all meeting the needs of diverse plants and animals:

• Masked shrews forage through leaf litter for insects and worms.
• Spiders wait in dark corners to capture insects in intricate webs.
• Earthworms crawl beneath the soil, enriching and aerating the earth.
• Bats roost beneath the loose bark of trees.
• Mourning doves nest in the branches of coniferous trees.
• Bumblebees buzz among wildflowers.
• Squirrels nest in snags (dead trees).

Ecosystems: a World-Wide View

The view of our planet from outer space reveals a dynamically beautiful sphere, a global ecosystem made up of oceans, clouds, continents, people, and at least five million other species. It's clear that the earth does not belong to us; we belong to the Earth.

Today, we're at a critical turning-point. People all over the world are learning that we have to take care of our life-support system. We may be just one of five million species, but we are a very important one — unlike other creatures, we can control our impact on the Earth.

Profile of an Ecosystem

A beaver pond, its banks, and its surroundings teem with wildlife in summer. Take a look at a beaver pond and you'll see how an ecosystem works.

• All biotic parts of an ecosystem need energy, which comes from the sun. They also need abiotic elements: soil, air, and water. You don't have to look very far in a beaver-pond ecosystem to find these elements.
• Soil, air, and water are critical for the growth of plants. You'll find trees, such as maple, aspen, poplar, and birch, as well as aquatic plants in a beaver-pond ecosystem. Plants absorb water and nutrients from the soil and carbon dioxide from the air. Through the process of photosynthesis, the plants use the sun's energy to turn water and carbon dioxide into organic materials like carbohydrates. Plants are the centre of life in any ecosystem because they enable the animals that eat them to get nutrients from the earth and energy from the sun. Plants also produce the oxygen that most creatures need to breathe.
• After plants, the next link in the web of life belongs to herbivores, or plant-eaters. In a beaver-pond ecosystem, they include deer, moose, elk, meadow voles, a variety of insects, and, of course, beavers. The beavers eat the tender bark of trees like aspen and poplar plus aquatic plants like cattails and water lilies.
• Next in line are carnivores, or meat-eaters, such as cougars, lynx, and wolverines. All of them prey on herbivores — including beavers — so they get their food from plants second-hand. They prevent herbivore populations from getting out of control. Other carnivores in this ecosystem are frogs, toads, snakes, herons, and weasels.
• The most formidable beaver predators are river otters, which can squirm into a beaver's lodge. Otters rely on their industrious neighbours for other food (ponds are a great place to go fishing) and shelter (in bank burrows and old beaver lodges). River otters, in turn, are eaten by coyotes and wolves.
• Omnivores eat plants and animals. Omnivorous inhabitants of a beaver-pond ecosystem include song birds, waterfowl, turtles, and bears.
• Decomposers — billions of microscopic bacteria and fungi too tiny for the naked eye to see —break down dead plant and animal tissue. They change nitrogen and other elements in the soil into food that plants and trees can absorb through their roots.

Many other things happen in an ecosystem. The roots of trees and plants prevent soil from washing away. Songbirds and meadow voles scatter seeds. Trees provide food, nesting sites, and hiding places for countless creatures. Bees and butterflies help plants reproduce by transferring pollen. Creatures known as keystone species — critically linked to many other life forms — contribute essential wildlife habitat. Beavers are a keystone species because they dam off waterways, creating new ponds that support a variety of plants, amphibians, reptiles, birds, and insects. Biodiversity, or the variety of living things that depend on each other to survive, holds the whole community together, much like interlocking pieces in a puzzle. Natural processes, such as fire, also link the parts of an ecosystem together. As you can see, everything is interdependent.

We Are Linked Together

We have been hard on the planet Earth. Until recently, many of us saw the ecosphere as a never-ending supply of resources. Entire ecosystems like old-growth forests, streams, lakes, marshlands, and grasslands have been wiped out as a result.

According to this approach, the Earth belongs to human beings. Forests are cut down without a thought for their relationship to the soil, the wildlife that live there, or the streams that run through them.

Somewhere along the line, we've forgotten one basic truth: our survival depends on the fate of the Earth. In a world where thousands of species become extinct every year, there's an urgent need for us to understand that all things are interconnected.