Ecosystems: The basics
An ecosystem is a set of relationships between all the organisms and non living factors in a particular area, for example a forest ecosystem would include the trees, animals and micro-organisms as well as the water, soil, rock and air. The organisms that live there are called the biotic factors and the non-living objects are abiotic factors. The organisms depend on physical factors and each other to survive, so relationships between organisms are important. Ecosystems vary in size and can be as small as a pond or as large as an ocean.
Energy in an Ecosystem
Energy moves between organisms in an ecosystem. Energy enters via photosynthesis and it is stored in plants and passed up for the food chain when the plant is eaten. This process continues throughout the ecosystem as one organism eats another, therefore energy flows between all organisms in an ecosystem. Food chains are used to show how energy moves through an ecosystem, each stage in a food chain is called a trophic level. There are four levels in the food chain:
1. Producers - these create their own food, for example plants.
2. Primary Consumers - these eat the producers and are either herbivores or omnivores.
3. Secondary Consumers - these eat the consumers and are called carnivores or omnivores.
4. Tertiary Consumers - these eat consumers and are called top carnivores.
The biomass is the total mass of living matter and decreases at each trophic level. Food chains are a simplified version of the relationships in an ecosystem - food webs are more complex and show that a lot of consumers feed at more than just one level.
Nutrient Cycles
Living organisms need large quantities of carbon dioxide, hydrogen, oxygen, nitrogen and sulfur amongst other things to survive. These elements are constantly being recycled through ecosystems - they are recycled between plants, animals and the atmosphere. Plants take carbon dioxide from the air and nutrients from the soil; they use these to create plant material. These nutrients get passed along food chains by feeding, when plants and animals die they are broken down by decomposers and nutrients are returned to the soil to be used again by plants. Plants, animals and decomposers all release carbon dioxide back into the air through respiration.