Ecosystems

The Structure of Ecosystems

Ecosystem: a dynamic, stable system characterised by the interaction of plants and animals with each other and with the non-living components of the environment.

The components of an ecosystem are categorised as either biotic and abiotic.

Biotic means the living environment, components include:

i). Vegetation (living and decomposing).

ii). Mammals, insects, birds and microorganisms.

Biomass-the mass of material in the bodies of animals and plants (total mass of living matter)

Abiotic means the non-living, chemical and physical components of the ecosystem and includes:

i). Climate in particular the seasonal pattern of temperature and precipitation.

ii). Soil characteristics.

iii). Underlying parent rock.

iv). Relief of the land.

v). Drainage characteristics.

Ecosystems are open systems because energy and living matter can both enter and leave the system:

Inputs – Energy from the sun, which drives photosynthesis-enabling the plants to grow, water transported into the ecosystem from precipitation and animals that arrive from elsewhere.
Outputs – nutrients are transferred out of the system by: animals can physically move out, water can leave through evapotranspiration, groundwater flow and throughflow.
Flows – nutrients can be transferred from one store to another such as capillary uptake.
Stores – stores of nutrients: vegetation, plant litter and soils.

Energy Flows and Nutrient Cycling

Energy flows – is the flow of energy through a food chain.

Energy flows flow through an ecosystem from one stage to another.
Through photosynthesis plants are able to capture light energy from the sun to make carbohydrates from carbon dioxide and water to grow and increase their biomass.
Within all ecosystems, nutrients are required for plant growth and are recycled from one store to another such as when leaves fall from tree they decompose with the nutrients returned to the soil.

Gersmehl diagram – shows the cycling of nutrients within the main stores of biome.

Circles of proportionate size represent the stores of nutrients with the biomass, litter and soil.
Nutrient transfers, inputs and outputs are represented by arrows of varying thickness.
Inputs – include nutrients carbon and nitrogen and minerals from weathered parent rock.
Outputs – loss of nutrients from the soil by; leaching and surface runoff.
Flows – leaf fall from biomass to litter, decomposition of litter, flow of nutrients to soil, uptake of nutrients by plants and trees.

The movement of energy up the trophic levels shows the food chain as each trophic level occupies a different position.
However, food chains are often more complicated than this. Some species can occupy more than one position in every food web – may be prey to more than one animal etc.
Nutrient cycles in an ecosystem take place between the biotic and abiotic components of the ecosystem. This can be shown through the Gersmehl diagram.
Nutrients have three stores – the soil, litter and biomass.
Nutrients are transferred through the three stores through fall of dead tissue, absorption through plant roots and decomposition.

Inputs of nutrients include precipitation and the weathering of parent rock.
Outputs include loss from runoff and leaching.
Flows include leaf fall from the biomass to the litter, decomposition of litter flow of nutrients to the soil.

Trophic Levels, Food Chains and Webs

Energy transfer within an ecosystem, represented by a pyramid diagram.

At each trophic level, some energy is available as food for the next level.
Each level decreases in size, 90% of energy lost through life processes-respiration, movement and excretion.
Only 10% available as food, number of living organisms decreases as trophic levels increase.

Producers/autotrophs – first layer, produce their own food through photosynthesis including green plants.
Primary consumers – eat the producers which are herbivores.
Secondary consumers – consume the herbivores are carnivores.
Tertiary consumers – top predators that eat secondary consumers.
Detrivores and decomposers operate at each trophic level:

i). Detrivore -feeds on dead material or waste products.

ii). Decomposer– an organism that breaks down dead plants, animals and waste matter such as fungi and bacteria.

There are normally 4 links in a food chain, each link feeds on and obtains energy from the previous link and is consumed by and provides energy for the proceeding link.
There are a large number of food chains that operate in ecosystems, it is also made even more complicated as animals have varied diets, this can be shown in a food web.