Biomes OCR 7.35-6
Temperate deciduous forest
Temperate deciduous forest
There are 2 types of cycle Energy Nutrients
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.
Tertiary consumers / top predators Secondary consumers OCR 7.31 Primary consumers Primary producers
Trophic Pyramids Trophic level 3 Secondary consumer (Carnivore) Loss of energy Trophic level 2 Trophic level 1 Primary consumer (Herbivore) Loss of biomass Primary producer (Plants) Total biomass
Why does each successive Trophic level get smaller? • Energy is lost by: respiration, movement, reproduction and growth. • 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 • level and some is lost via defecation, removed by detritivores.
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. 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.
The addition of mink to a woodland ecosystem The massive increase in the number of carnivores will lead to the reduction in the number of herbivores Secondary consumer (Mink added) Loss of energy Primary consumer (Herbivore) Loss of biomass Primary producer (Plants) Total biomass
The addition of mink to a woodland ecosystem 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 primary consumers will continue to decrease and this will lead to an increase in the total biomass of the plants. Secondary consumer (Mink added) Primary producer (Plants) Total biomass
The addition of mink to a woodland ecosystem Mink will eventually run out of food and a) die of starvation or b) move to another ecosystem 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. Most herbivores will be killed Total biomass
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
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
The size of the arrows and the circles indicates the amount of nutrients in that store or transferred in flows in the system Biomass (total mass of living material) There are 3 types of store 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 Precipitation Biomass Dead matter Uptake by plant roots Litter Soil Decomposers Runoff Removal of minerals Leaching
biomass is main store • rapid transfer between stores and environment Tropical rain forest
Nutrient Cycle The nutrient cycle is easily disrupted here – it is a closed system Once the vegetation is removed, nutrients are quickly removed from the system - creating infertile conditions - even deserts
Human Impact: Rainforest Ecosystem after deforestation Trees removed and logged Harvest Precipitation Crop Biomass The removal of trees decreases interception and increases runoff Litter Ash Depletion of nutrients in soil Increased leaching Increased runoff
Case Study Tropical Rainforest Ecosystem Human Impact: 200 million people live in rainforests Demand for timber / cleared land 1 Acre of rainforest is lost per second – 74 species are Lost every day Eg 5-15% of Madagascar’s GNP is lost each year through soil erosion, flooding of rice paddies and silting of electricity turbines