Trophic Pyramids Trophic or energy pyramids show how energy is transferred through an ecosystem. They are an easily accessible way of looking at whether there is dynamic equilibrium, or whether the system is becoming unsustainable.
Trophic Pyramids Sunlight energy fixed by green plants is passed through the ecosystem in food chains and webs form one trophic level to the next. As energy is passed through the system it is stored at various trophic levels. The storage of energy (I.e. the amount of living matter present) is referred to as Biomass or Standing Crop.
Trophic Pyramids Primary producer (Plants) Primary consumer (Herbivore) Secondaryconsumer(Carnivore) Total biomass Loss of energy Loss of biomass Trophic level 1 Trophic level 2 Trophic level 3
Why does each successive Trophic level get smaller? Energy is lost by: respiration, movement, reproduction and growth. Energy is lost by: respiration, movement, reproduction and growth. Transfer of energy is inefficient. Not everything is eaten Transfer of energy is inefficient. Not everything is eaten at each level so some is removed by detritivores. The transfer of light energy to food energy is only 1% efficient. Not all energy can be metabolised efficiently at each Not all energy can be metabolised efficiently at each level and some is lost via defecation, removed by detritivores.
Q) If we assume our trophic pyramid is a UK woodland ecosystem (although whether there are any truly natural ones left is debatable). How would the introduction of mink effect it? Make sure you refer to the changes in terms of energy transfer, and work through you example carefully. A few years ago, Animal rights protesters freed a large number of mink from a farm and let them run wild in the local woods. Mink are not indigenous to this country and have no natural predators. They are efficient killers and, like cats and foxes, kill instinctively whether they need food or not.
The addition of mink to a woodland ecosystem Primary producer (Plants) Primary consumer (Herbivore) Secondaryconsumer (Mink added) Total biomass Loss of energy Loss of biomass The massive increase in the number of carnivores will lead to the reduction in the number of herbivores
The addition of mink to a woodland ecosystem Primary producer (Plants) Secondaryconsumer (Mink added) Total biomass The primary consumers will continue to decrease will continue to decrease and this will lead to an increase in the total biomass of the plants. Q) Although the total biomass of the plants has increased. Is this likely to be sustainable and are the plants that are increasing going to be beneficial to the ecosystem?
The addition of mink to a woodland ecosystem Total biomass Mink will eventually run out of food and a) die of starvation or b) move to another ecosystem Most herbivores will be killed The balance of plants in the ecosystem will be irreversably altered. Pioneer species such as nettles which are usually kept down by the herbivores will grow shading out other less hardy plants and saplings. They will also rapidly use up nutrients and minerals from the soil for their growth. Some plants will not be able to reproduce without the herbivores eating their seeds.
What other factors will affect the Trophic Pyramid? 1) Fertilisers (NPK) could increase production beyond that which the land could manage and possibly lead to eutrophication 2) Pesticides can reduce populations of organisms which could have a knock on effect throughout the system 3) Deforestation can have a direct adverse effect on the area 4) Artificial maintenance of the ecosystem. For example burning heather to allow grouse to feed on the young shoots.
Productivity OCR 7.37 Productivity > refers to the rate of energy production, normally on an annual basis Primary Productivity > refers to plant productivity Secondary Productivity > refers to that produced by animals Gross Productivity > is the total amount of energy fixed Net Productivity > is the amount of energy left after losses of respiration and growth are taken into account Net Primary Productivity (NPP) is the amount of energy made available by plants to animals at the herbivore level
The nitrogen cycle
Gershmels Nutrient Cycles
OCR 7.39 Gershmel’s Nutrient Cycles
Gershmels nutrient cycles are a simple way of showing how nutrients are transferred around an ecosystem. They can be represented in 2 ways: STORES FLOWS
What do all these represent? Page 38
The size of the arrows and the circles indicates the amount of nutrients in that store or transferred in flows in the system types There are 3 types of store Biomass (total mass of living material) living material) t Litter Soil
Case Study Tropical Rainforest Ecosystem Look at the diagram below and explain : a) How the nutrients are being cycled b) Why the removal of the rainforest would be so Detrimental – human impact Biomass Soil Litter Precipitation Decomposers Dead matter Removal of minerals Uptake by plant roots Runoff Leaching
Tropical rain forest biomass is main store rapid transfer between stores and environment
Once the vegetation is removed, nutrients are quickly removed from the system - creating infertile conditions - even deserts The nutrient cycle is easily disrupted here – it is a closed system Nutrient Cycle
Human Impact: Rainforest Ecosystem after deforestation Trees Trees removed and logged Ash Increased Increased leaching Crop Increased Increased runoff Harvest The removal of trees decreases interception and increases runoff Depletion of nutrients in soil Litter Biomass Precipitation
Case Study Tropical Rainforest Ecosystem Human Impact: 1 Acre of rainforest is lost per second – 74 species are Lost every day 200 million people live in rainforests Demand for timber / cleared land Eg 5-15% of Madagascar’s GNP is lost each year through soil erosion, flooding of rice paddies and silting of electricity turbines
Case Study: Temperate Deciduous Forest
Case Study Temperate Deciduous Forest Explain the nutrient flow in a deciduous forest ecosystem OCR 7.40
Case Study Temperate Deciduous Forest Litter Precipitation Biomass Soil Run-off Leaching Weathering
Temperate deciduous forest balance between stores moderate transfers between stores
Case Study Temperate Deciduous Forest Why is there a large store of nutrients in the soil? 1. Slow growth in winter 2. A low density of vegetation compared with the tropical rainforest 3. Uptake of nutrients is about 25% as efficient as a tropical rainforest
Case Study Temperate Deciduous Forest Why is there a larger store of nutrients in Litter? Deciduous leaves are shed in winter to retain moisture, conserve nutrients, avoid damage by snow and ice, strong cold winter winds, conserve energy when the sun’s power is low. Decomposition is slow (by detritivores) > nutrients return to the soil
Case Study Temperate Deciduous Forest Human Impact: Clearing for agriculture - the input of leaf fall has been replaced by chemical and organic fertilizers Forests are heavily managed for recreation, conservation, economic exploitation Very few areas of natural forest remain
Conclusion You should now be able to understand the importance of the cycling of nutrients through the different types of ecosystem and also the following; b) How mans influence can radically alter the flows and stores c) How these different ecosystems can lead to, or rely on particular soil types d) which stores dominate particular ecosystems a) How a complex ecosystem can be understood using nutrients
In this way they differ from energy or trophic cycles and pyramids where the energy arrives from the sun and is eventually lost as heat energy into space. At an ecosystem level nutrient cycling is part of an open system. is part of an open system. At a global scale however the nutrients are being continually cycled and recycled.
Boreal forest (taiga) litter is main store (needles) little transfer between stores
Temperate coniferous forest A) Why is the litter store so large? B) Why are the flows so small? C) What sort of soil would you expect here?