Practical Skills Flashcards
Define: Independent Variable
The factor that is deliberately altered or measured to see if it affects the dependent factor.
Define: Hypothesis
The theory or explanation that is being investigated.
Define: Dependent Variable
The factor that may be controlled by the independent variable.
Define: Null Hypothesis
The no-link theory against which the hypothesis is being tested.
Define: Homogenous
Evenly mixed.
Define: Quadrat
An area, usually square or circular, in which samples are taken.
Define: Pitfall Trap
A method of sampling animal populations by collecting individuals that fall into traps set into the ground.
Define: Transect
A line or belt of sampling across an area.
Define: DAFOR Abundance Scale
A qualitative scale that judges the abundance of organisms.
Define: Lincoln Index
A catch, mark, release, recapture method of estimating animal populations.
Define: Surber Sampler
An aquatic invertebrate sampling frame and net that provides more quantitative data than kick sampling.
Define: Pooter
A mouth-suction device to pick up invertebrates in soil or leaf litter.
Define: Tullgren Funnel
A piece of equipment used to extract invertebrates from soil or leaf litter.
Define: Secchi Disc
A circular disc divided into four black and white segments that is used to estimate water turbidity.
What are the different methods of sampling?
- Random Sampling (areas chosen from random numbers)
- Systematic Sampling (areas chosen from patterns/spacing)
- Stratified Sampling (areas with sub-areas that influence results must be studied individually and then combine the results)
What is ‘first-hand experience’?
- Personally performing/witnessing an experiment/activity
- Working in a group is advantageous (discuss, criticise and justify options)
What does the DAFOR abundance scale represent?
D = Dominant A = Abundant F = Frequent O = Occasional R = Rare
What are the limitations of abundance scales?
- Subjective (different judgements)
- No distinction between species in same category
- Lack of quantitative data makes statistical analysis difficult
How is a sample population estimated?
Total population = (Number in 1st sample x Number in 2nd sample) \ (Number in 2nd sample that have marks)
What are the features of a population whose size can be estimated using the Lincoln Index?
- Mobile individuals can be caught
- Births/Natural mortality do not affect population
- Caught and marked does not affect mortality
- Population not affected by immigration or emigration
- Population members mix freely and not territorial
- All members equally likely to be caught
What are the limitations of kick sampling?
- Disturbance by kicking cannot be standardised
- Rock attached organisms not collected
- Organisms that swim may escape
What are the limitations of pitfall traps?
- Underground organisms cannot be collected
- Killing fluid may attract/repel organisms
- No killing fluid will allow predators to eat animals that fall in
- Active animals more likely to be trapped
What are examples of suction samplers?
- Pooter (collects small visible invertebrates)
- Backpack suction samplers (motorised sampler collects grassland invertebrates)
What are the limitations of Tullgren funnels?
- Immobile organisms not collected
- Large organisms cannot pass through mesh
What are the limitations of using irritant solutions to collect earthworms?
- Deep soil worms unaffected
- Worms escape sideways
- Different species and sizes of worms may react to chemical differently
What are the indirect methods of monitoring populations?
- Bird nests (assume two adults per nest)
- Otter sprints (droppings provide information on their food)
- Owl pellets (regurgitates pellets provide food information)
- Footprints (sand trap checks for footprints)
- Territorial marks (scratching trees, characteristic scents)
- DNA ‘fingerprints’ (identify individuals and gain information)
How can the proportions of sand, silt and clay be measured?
- Soil sieve (vertical tower of finer meshes, contents is weighed and percentage is calculated)
- Sedimentation (measuring cylinder half full with soil and water, soil suspension occurs and proportions are calculated)
What is the standard method for estimating pH of a soil sample?
1) Add 2.5cm3 of soil to test tube.
2) Add 1cm3 of barium sulphate (soil settler).
3) Add 3.5cm3 distiller water.
4) Add 10 drops of universal indicator solution.
5) Push bung on top.
6) Shake and leave for 15 minutes.
7) Compare colour above soil with colour chart.
How do you standardise a pH test with electronic pH meters?
- pH meter calibrated with solutions of known pH
- Meter left to stabilise for stable readings
- Probe inserted at certain depth
What is the method for measuring the soil water content?
1) Soil sample collected (standardised method).
2) Placed in sealed bag to prevent evaporation.
3) Large minerals/organisms removed.
4) Placed in pre-weighed evaporating basin.
5) Heated at 100 degrees (24 hours).
6) Basin reweighed.
7) Stages 5 & 6 repeated until constant weight.
How is the percentage of water content calculated?
((Wet soil mass - Dry soil mass) \ Wet soil mass) x 100
What is the method for measuring the soil organic matter?
1) Empty crucible weighed.
2) Dried soil sample placed and re-weighed.
3) Heated at 500 degrees, must not be above 550 degrees (minerals would break down, carbon dioxide released).
4) Crucible re-weighed.
5) Stages 3 & 4 repeated until constant weight.
How is the percentage of organic matter content calculated?
((Dry soil mass - Burned soil mass) \ Dry soil mass) x 100
