The top picture shows either a belt transect or an interrupted transect (depending on whether they take their samples at intervals or not along the transect.
The bottom picture shows a point quadrat.
(Source: google.co.uk)
The top picture shows either a belt transect or an interrupted transect (depending on whether they take their samples at intervals or not along the transect.
The bottom picture shows a point quadrat.
(Source: google.co.uk)
Investigating ecosystems.
This involves looking at the abundance (number of individuals of ONE species within an area) and the distribution (where this species is in the area you’re studying). You take samples - investigating the whole area would be too time-consuming - and the samples need to be random to avoid bias.
You also need to use an appropriate technique to sample the population and to repeat the process enough times that your results are reliable. Taking an average and multiplying it by the size of the whole area will give you an estimate of the number of individuals in the whole area. Taking an average of all the samples will give you an estimate of the %cover for the whole area.
Different techniques of sampling:
- 1) FRAME QUADRAT. Placed on the ground at random points it’s a frame with a grid of 100 squares. The number of species is recorded in each quadrant and a %cover of a species is measured by ccounting how many squares are more than half covered (each square = 1%).
These are useful for quickly investigating areas with species small enough to fit into a small quadrat (about 1m x 1m). Larger quadrats can be constructed with measuring tape to investigate larger plants. - 2) POINT QUADRAT. A bar with 2 legs that stand on the ground, you place pins in the holes on the bar and every plant the pin touches is recorded. The number of needles that touch each species is the %cover of that species.
The wuadrat (again) needs to be placed at random points, these quadrats are very useful for areas with dense vegetation close to the ground. - 3) TRANSECTS. These are lines used to investigate how plants are distributed in an area. There are three type of transect:
- LINE TRANSECT = a tape measure is placed along the transect and the species that touch the tape are recorded
- BELT TRANSECT = frame quadrats are used along the transect next to each other (no gaps between the quadrats) and data is collected.
- INTERRUPTED TRANSECT = the same method as above (with the frame quadrats) except data is collected at intervals along the transect, eg. every 2m you record data from the quadrat.
showing primary succession, starting with rocks and ending in a wood. As more organisms move into the developing ecosystem, they out-compete each other (they succeed each other).
Succession.
As you should know, ecosystems are dynamic systems (they change), and the process by which they change over time is called succession.
There are two types of succession: Primary succession and Secondary succession. Primary succession starts on new areas of land with NO organic material or soil (eg. bare rock/sand), for example, new land exposed when sea level drops, or a new surface formed by a volcanic eruption. Secondary succession is when the land has been destroyed or damaged, so succession must start again; the area has been cleared of all plants and must re-develop (eg. plants growing after a forest fire).
The succession occurs in stages called seral stages. The stages for primary succession are:
1) PIONEER SPECIES COLONISE THE LAND. The abiotic conditions are harsh, there’s no soil to retain water, so these species are specialised to tolerate and survive in these conditions.
2) PIONEER SPECIES CHANGE ABIOTIC CONDITIONS. As they die, the humus (dead organic material) is decomposed by microorganisms and create a thin, basic soil.
3) NEW ORGANISMS CAN MOVE IN AND GROW. The soil means more water csn be retained and more nutrients are available for plants. As each organism arrives, dies and is decomposed, more soil is built up and larger plants can live there. Once enough and large enough plants live there, habitats emerge and animals can move in and survive.
As more species move in and live there, the ecosystem becomes more complex and diversity increases.
The final seral stage is called the complex community, this is when the ecosystem is at its largest and most complex and won’t change much more; it’s at a steady state.
Secondary succession occurs the same way, except there is already soil present so succession starts at a later seral stage.
Intense farming of cows to restrict movement and preserve heat (held together within confined spaces also keeps the animals warm with each others body heat) does increase secondary productivity, but also is subject to large debates about animal welfare.
Greenhouses, likewise, keep a warm temperature which is controlled and can increase the rate of photosynthesis (although too high and it will effect the plants enzymes).
(Source: Daily Mail)
Manipulating energy transfer (human activity).
Primary productivity is the energy captured by plants for photosynthesis, just as Secondary productivity is the energy taken in by consumers when they eat another organism. Humans can manipulate energy transfer it when farming to increase the net productivity (and hence increasing the energy that will be transferred to us when we buy the food and eat it).
FACTORS THAT EFFECT PRIMARY PRODUCTIVITY:
- LIGHT LEVELS; using light banks or planting cops early so they have a longer growing season to harvest light.
- WATER AVAILABILITY; irrigating (creating a water supply for plants by channels) and breeding drought-resistant plants
- TEMPERATURE; greenhouses provide a warmer temperate and temperature can effect the speed of chemical reactions.
- NUTRIENTS; a lack of can slow the rate of photosynthesis. Using fertilisers or crop rotation increases the nutrients in soil.
- PEST; pesticides/insecticides can kill pests which remove biomass and energy from the food chain. You can also use natural predators to remove them (releasing ladybugs to eat the aphids).
- FUNGAL DISEASES; can be defeated by fungicides. fungal infections can rot roots and and damage xylem vessels.
- COMPETITION; from weeds restricts the lights, nutrients and water that the crop can receive. Farmers can combat these with herbicides.
*
and for secondary the animals of the ecosystem…
*
FACTORS THAT EFFECT SECONDARY CONSUMPTION:
- MOVEMENT; restricting movement means less energy is wasted (although many see this as cruel and worry about animal welfare, preferring free range food), supplying food - and lots of it - means they don’t have to look for it and can store more energy.
- TEMPERATURE; keeping the organisms warm means less energy is lost through heat.
- AGE; younger animals invest more energy than adult ones, harvesting just before adulthood helps reduce energy loss.
- ANTIBIOTICS; less energy lost fighting parasites or pathogens.
- SELECTIVE BREEDING; produce larger breeds with faster growing rates for meat, more resistant breeds, breeds that produce higher quality/higher yield of milk (or meat) etc.
All these factors effect the productivity of pants and can, when controlled or removed, increase the energy transfer.
the different types of pyramids.
Measuring energy transfer.
There are two different ways to measure the energy transfer between trophic levels: you can use a pyramid of biomass, a pyramid of energy, or calculate the rate at which energy passes through each trophic level (this is called measuring productivity).
PYRAMIDS OF BIOMASS:
Not to confused with a pyramid of numbers (which displays the number of organisms at each stage, not their biomass), a pyramid of biomass measures the amount of living tissue at each trophic level. Each bar is proportional to the dry mass of al organisms at that trophic level.
Unfortunately calculating the dry mass is a weeeee bit destructive - you put all the organisms in an oven at 80°C until all the water has evaporated - so instead biologists measure the wet mass and use previously published data to calculate the dry mass. Biomass is created using energy so it’s an indicator of how much energy an organism contains. This is an indirect way of measuring the amount of energy.
PYRAMID OF ENERGY:
To create a pyramid of energy, you burn the organisms in a calorimeter and the amount of heat given off per gram - which is calculated from the temperature rise of a known mass of water - tells you how much energy is in that organism.
This is a direct way of measuring the amount of energy. The problem is this this is just as destructive and also time consuming (all a bit grim with the burning things) so ecologists tend to use pyramids of biomass instead.
-
If you want to create a pyramid of biomass/energy:
1) first calculate the amount of energy/biomass in a sample of the organisms (eg. 1 mouse, 1m² area of wheat field a mouse eats).
2) times this number by the size of the total population at that trophic level (eg. 10 000² FIELD of wheat and ALL the mice in that population which eat it)
3) this gives you the total no. of energy at that trophic level. The difference in energy of each trophic level is the energy transferred.
-
The problems with the pyramids are that usually not all the energy/biomass of that organism will have come from that particular food chain, some may have come from another organism it ate from a different food chain, and therefore a different pyramid (eg. that mouse may have eaten from a blackberry bush outside the field which will contribute to it’s energy content/biomass). This means what you calculated wouldn’t be an accurate measurement of energy transfer between those specific organisms.
so a fox will have to eat a fair amount of rabbits in order to gain as much energy as the rabbit would have had if it hadn’t lost it through respiration, meaning the lower down the food chain, the more efficient the energy transfer as less energy is lost.
Calculating net productivity.
Net productivity is the amount of energy available to the next trophic level. For those of you who are insanely bad at maths (like me ;)) this is how you calculate it: minus the respiratory loss from the gross productivity.
NET PRODUCTIVITY = GROSS PRODUCTIVITY - RESPIRATORY LOSS
so the total energy an organism takes in, minus the amount used up in respiration (leaving you with what’s left for the next trophic level).
so if rabbits in an ecosystem take in 20 000kJm-2 a year (sorry about the iffy symbols), but dont take up 12 000kJm-2 of it, they have a gross productivity of 8000kJm-2yr-1 (yr-1 means per year).
If they loose 6000kJm-2yr-1 as respiratory loss, the net productivity (amount available to the next trophic level) would be
= 8000 - 6000
= 2000kJm-2yr-1
to calculate how efficient the energy transfer form one trophic level to the next is, simply divide the net productivity by the total energy entering the ecosystem then times by 100 for a %.
EFFICIENCY OF ENERGY TRANS. = (NET PROD. ÷ TOTAL ENERGY ENT.) X 100
so in the rabbits case it’s:
(2000 ÷ 20 000) x 100 = 10%
