Ecosystems: Ecological Succession and Climatic Climax

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Ecosystems: Change and Challenge
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 e.g. 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

e.g. leaves fall from tree-> when they decompose nutrients are 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, in reality, 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 etc.

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(green plants)
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