Ecosystems are dynamic entities composed of the biological community and the abiotic environment. An ecosystem's abiotic and biotic composition and structure is determined by the state of a number of interrelated environmental factors. Changes in any of these factors (for example: nutrient availability, temperature, light intensity, grazing intensity, and species population density) will result in dynamic changes to the nature of these systems. For example, a fire in the temperate deciduous forest completely changes the structure of that system. There are no longer any large trees, most of the mosses, herbs, and shrubs that occupy the forest floor are gone, and the nutrients that were stored in the biomass are quickly released into the soil, atmosphere and hydrologic system. After a short time of recovery, the community that was once large mature trees now becomes a community of grasses, herbaceous species, and tree seedlings.
Energy Flow
The SUN is the source of all energy, providing heat and light to ecosystems and biomes. The first phase in the energy flow process is PHOTOSYNTHESIS whereby the LIGHT ENERGY from the sun is stored in green plants and converted into CHEMICAL ENERGY. This energy is used by the plants for growth and repair and is then passed along through the ecosystem on a FOOD CHAIN or in, complex ecosystems, a FOOD WEB.
Trophic Levels
The transfer of energy is not 100% efficient, as energy is lost via respiration, dead organisms, decay, excreta, and heat given off. As energy is passed through an ecosystem several processes occur:
The diagram above (right) shows where and when energy lost in an ecosystem.
- Energy passes through different trophic levels.
- The amount of energy there is decreases
- Fewer species and biomass exist at each level (Above left).
The diagram above (right) shows where and when energy lost in an ecosystem.
Trophic LevelLevel 1 Level 2 Level 3 Level 4 |
Producer/
|
Name/ExampleAutotrophs/Green Plants Herbivores/Primary Consumers/Caterpillars Carnivore/Secondary Consumer/ Blackbird Omnivores/Hawks |
ActionPlants are capable of producing all their own food. Eat the green plants Carnivores feed upon herbivores. Fewer secondary consumers than primary Omnivores have two source of of food (both plants and animals) |
energy transferSun-Plant Sun-Plant-Caterpillar Sun-Plant-Caterpillar-Blackbird Sun-Plant-Hawk or Sun-Plant-Caterpillar-Blackbird-Hawk |
The Nutrient Cycle
In 1976 P.F. Gersmehl attempted to model the nutrient cycle by mapping the transfer and storage of nutrients in an ecosystem. In all nutrient cycles there are interactions between the atmosphere and soil that incorporate many food chains.
Put simply the nutrient cycle works as such:
Plants take in those nutrients where they are built into new organic matter. Nutrients are taken up when animals eat plants and they returned to the soil when animals die and the body is broken down by decomposers.
Nutrient cycles vary greatly between ecosystems, as the rate of nutrient transfer is dependent on the amount of moisture, heat, vegetation and the length of the growing season.
Plants take in those nutrients where they are built into new organic matter. Nutrients are taken up when animals eat plants and they returned to the soil when animals die and the body is broken down by decomposers.
Nutrient cycles vary greatly between ecosystems, as the rate of nutrient transfer is dependent on the amount of moisture, heat, vegetation and the length of the growing season.
- The more moisture in the ecosystem the higher the rate of leaching
- The warmer the ecosystem the higher the rate nutrient transfer.
- The cooler the ecosystem the shorter the growing season, and therefore a lower biomass.
- The type of vegetation can affect nutrient transfer e.g. needle like coniferous tree leaves decompose slower.
Rainforest ecosystem and nutrient cycle
Extremely rapid rates of nutrient transfer, due to high temps, rainfall and humidity. Biomass is the largest store of nutrients due to the vast arrays of plants found in the Rainforest. Few nutrients are in the litter, due to their rapid decomposition as a result of high temperatures. Leaching is rapid and more so in areas of rainforest clearance.