trophic structure Flashcards
what is trophic structure
the organisation and pattern of feeding in an ecosystem is called the trophic structure.
energy in the form of food is passed from one type of organism to the next along a food chain
however, the structure is a lot more complicated than this as some animals eat a wide range of food types, often both meet and plants. therefore, a more realistic picture is one of food chains being interconnected so producing a food web.
each stage along a food chain, where energy is exchanged between organisms, is called trophic level. plants = TL1, herbivores TL2, carnivores TL3, omnivores TL4
trophic pyramid
level 4 - tertiary consumers
level 3 - secondary consumers
level 2 - primary consumers
level 1 - producers
food pyramids (pyramids by number)
the area of the rectangle is proportional to the number of plants and animals at each trophic level. using this method most food webs are pyramid shaped, with the largest rectangle at the base. however, there are some exceptions eg the amount of caterpillars on a cabbage
producer losses
- respiration
- metabolic cell processes
- leaf fall
consumer losses
- heat
- waste
- movement
- digestion
- reproduction
food pyramids (pyramids by biomass)
these pyramids use the weight of organic matter per unit area, rather than the number of plants and animals.
they always produce a pyramid shape because one trophic level can only support a smaller biomass above it because of the energy loss across each trophic level
biomass
biomass is the amount of living organic matter (plants and animals) and is a measure of the energy stored
why does biomass decline at each level
the huge biomass decline at each level is because consumption at each level is never 100% efficient:
- animals do not eat all parts of a plant
- digestion processes do not covert all material (excretion)
thus, energy and matter are lost at each transfer between trophic levels
also, within each trophic level, energy and material is used up by life processes or respiration. this includes:
- heat energy from movement
- material lost as waste products eg shed skin, leaf fall, faeces