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Populations in ecosystems (Investigating populations (Random quadrats (non…
Populations in ecosystems
Investigating populations
Random quadrats
(non-motile)
1) 2 measuring tapes are arranged at right angles to each other to form the axes of a grid, and co-ordinates are assigned
2) Coordinates are generated at
Random
using a random number generator
eg, a calculator
. A quadrat is then placed at the intersection of these coordinates
3) The number of organisms in the quadrat is then counted or percentage cover is estimated
4) repeat this
MANY TIMES
and a running mean is calculated until the mean shows little variation
5) The running mean value would the be used to estimate the total number of organisms in the whole area
HAVE TO SAY HOW DONE
eg, Mean number of organisms in a 1m2 quadrat X the area of the field
OR
mean number per quadrat X how many quadrats fit in the area.
Belt transects
(non-motile)
1) several belt transects are placed parallel across the area and are numbered
2) A transect is chosen at random using a random number generator. A quadrat is placed along the transect at regular intervals (Every 5 meters)
3) The number of organisms or percentage cover in the quadrats is then counted
4) This is repeated
MANY TIMES
and a running mean at each interval eg. 5m is calculated until the running mean at each interval shows little to no variation
5) The running mean value for each distance would then be used to determine if the abundance of species changed across the area
Mark, release, recapture
(motile)
1) A sample of animals of a particular species are captured, counted, marked and released
2) The mark should not be toxic, rub off, make the animal more vulnerable to predation
3) The animals are left long enough to reintegrate randomly into the population
4) A second sample is captured and the total number court are recorded, as well as how many of those captured are marked
5) The formula is (Number caught in first sample X Number caught in the second sample) / Number marked in the second sample. This is an estimation of the population
Factors affecting distribution of organisms
Abiotic factors
Temperature:
If too low then the enzymes wouldn't have enough kinetic energy to work, if too high the enzymes denature
Light intensity:
Light needed for photosynthesis, more light more photosynthesis less light less photosynthesis
Water availability/ humidity:
All organisms need water as it is a solvent in cells and is involved in many reactions. The lower the humidity the more water is lost by transpiration
pH:
The pH will effect extracelluar enzymes and surface proteins the more extreme the pH the less favorable the environment and in some cases the pH effects the availability of some ions
Biotic factors
Competition:
If several species share the same niche they will compete for the finite resources.
Intraspecific
is the competition within the
same
species and
inter
is between
different
species
Predation:
When an organism kills and eats another organism. An increase in prey means more food for predators so more predators are born. The more predators kill more prey leading to a decrease in the prey population then the larger predator population starves reducing the population of the predator so the population of the prey increases again restarting the cycle