Unit 2 Flashcards
What is the definition of an ecosystem?
a set of interacting, interdependent biotic and abiotic components
What are the three stores within a Gersmehl nutrient cycle?
soil, litter and biomass
What is the relationship between climate and the biomass store?
- as the temp increases, the bigger the biomass store
- more energy for photosynthesis
- increase precipitation = increase in the biomass store
What is the relationship between climate and rates of litter decomposition?
- warm, moist condition = optimum conditions for bacteria, fast decomposition
What are the two processes that play a role in the nutrients stored in soils?
- weathering
- leaching
What is the definition of chemical weathering?
is the decomposition of rock minerals in to new minerals
What is the definition of physical (mechanical) weathering?
is the disintegration of rocks into smaller fragments e.g. freeze thaw weathering
How does leaching happen?
removal of soluble material from the soil by percolating water
When are the rates of leaching the greatest?
precipitation levels are higher than evapotranspiration rates (positive water balance)
soil is porous and permeable allowing percolation to occur
percolating water is acidic
What is the most significant energy source for ecosystems? Why is it important for plants?
Solar radiation, plants need for photosynthesis
What are trophic levels?
energy storage layers
What are autotrophs?
(primary producers) these are plants that produce energy from photosynthesis
What are Heterotrophs?
(consumers) these are organisms which obtain energy from the consumption of other organisms
What are the three types of heterotrophs?
- Herbivores = primary consumers which feed on plants
- Carnivores = they feed on other animals
- Omnivores = feed on both plants and animals
In a food chain, what does the first trophic level consist of?
primary producers = plants
In the food chain, what does the second trophic level consist of?
primary consumers
In the food chain, what does the third trophic level consist of?
secondary consumers
In the food chain, what does the fourth trophic level consist of?
apex predators e.g. decomposers feed on all the other levels
Why do food chains rarely contain more than 5 trophic levels?
loss of energy when you go up trophic levels, not enough to sustain another level
lots of energy lost through heat and respiration
What % of energy is lost through respiration (approx.) as heat?
90%
What % of energy is passed on to the next trophic level (approx.)?
10%
What is the definition of biomass?
the total amount of organic matter in a given area, usually measured in kg of dry weight per sq km
What is primary productivity?
the rate at which energy can be converted into organic matter in an ecosystem
What are the two types of primary productivity?
- gross primary productivity (GPP)
- Net primary productivity (NPP)
What is the definition of GPP?
is a measure of all the photosynthesis that occurs within a given area of the ecosystem
What is the definition of NPP?
is the energy fixed by photosynthesis minus the energy lost by respiration (measure of the NEW biomass)
What are the two measures of NPP?
- biomass
- carbon
The levels of primary productivity are linked to the presence of limiting factors, which are?
- temp
- moisture
- light
- nutrient availability
What is the NPP range of a tropical rainforest?
2 - 3 kg meters(-2) yr1
Why is the NPP range of a tropical rainforest so high?
- found between 10 degrees N/S of equator
- temp relatively constant = 27 degrees
- high levels of biodiversity
- typically 200 species per hectare
What is the NPP range of a temperate grassland?
400 grams meters(-2) yr1
Why is the NNP range of temperate grasslands not as high as tropical rainforests?
- mid latitudes, characterised by large seasonal variations in temp and precipitation
- hot summers = 25 degrees
- mild winters = 0 degrees
- precipitation around 500mm annual
- major limiting factors = reoccurring fire, periodic drought, grazing
What is the NPP of tundra?
100 to 200 grams meters (-2) yr1
Why is the NPP of tundra so low?
- very short growing season (6 to 10 weeks)
- temps below freezing for most of the year
- low biodiversity
- contains 3% of the worlds flora
- permafrost
- low soil nutrition due to slow decomposition
