Critical Analysis of Arthropod Project

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Hypothesis: there are more ground-dwelling arthropod species in closed canopy rainforest than in gaps. Leaf litter under the forest canopy is less likely to be affected by environmental disturbance and temperature extremes, thereby providing a more stable habitat.

H0: there are no differences in the diversity of ground dwelling arthropods found in the rainforest compared with those found in gaps.


1. What were our results?

More in RF or Gaps - was it significant?

  • If significant or not significant - what does this mean?


2. Did we sample ‘ground-dwelling arthropod diversity’?

  • Could other sampling methods add anything to our results?
  • Different size pitfalls - some arthropods may be too big to fit in the pitfall
  • Arrays of 9, 13, 17, etc., instead of 5
  • Pitfalls with ethanol rather than detergent
  • Guided pitfall traps
  • Baited pitfall traps (bait suspended over pitfall)
  • Sticky traps
  • Bait traps (honey, faeces, fruit – buried or on the surface)
  • Yellow pan
  • Deeper soil samples
  • Winkler sorting
  • Tolgren or Berlese funnels
  • Is the arthropod community variable? [different times of year]

Should our hypothesis be more specific in referring to ground-dwelling arthropods? - no! but sampling should be qualified in the methods.


3. What human variables could bias the results?

  • Bias in selecting the exact sample site within each habitat type?
  • Bias in selecting sample position [no! Randomization]
  • Experience – how well were the traps set?
  • Different people setting traps – how consistently were the traps set? (Dave and I split the trap setting so that both groups did a forest and a gap – we did not have one group setting gap traps and a different group setting rainforest traps).
  • Order in which we set the traps – different time span, different time of day.
  • Sampling effort (enthusiasm, time expended)
  • Did we disturb the site where we set the pitfall traps?

- would this affect our results? - would this bias our results? i.e. was the disturbance consistent? - If all sites were equally disturbed then it may not be a problem.

  • How consistent was the leaf litter sampling?

Have we controlled for these variables (bias with different people setting traps)? Could we control for all these variables?


4. Was there error in gathering our data?

  • Pseudoreplication [If we took all three samples in the same large gap – would this be acceptable?]
  • How long did each trap remain - did we take down in same order (so that traps remained in the field for the same amount of time)?
  • Emptying pitfall traps - OK?
  • Pre-sorting leaf litter – time expended, consistency of disturbance, thoroughness of emptying bag
  • Sub-sampling consistency (maybe not applicable)
  • Were we consistent in sorting the samples
  • Accuracy identifying arthropods
  • Enthusiasm – of course everyone gave undivided attention to the sorting!
  • Counting, accuracy!
  • Recording data – KEEPING TRACK OF THE DATA! Did any samples get mixed or lost?


5. We hypothesized that different disturbance/temperature regimes were the cause of variation? What other ecological variables could contribute to the results?

  • soil type
  • age of the gap
  • size of the gap
  • slope
  • aspect
  • altitude
  • soil pH
  • weather (rain, temperature, humidity, wind speed/direction, nebulosity)
  • season
  • mass fruiting
  • how far from the edge should we sample in the rainforest (edge effect)
  • diversity of tree species (litter type)
  • length of time for sample (consistent?)
  • time of day (when did we take the litter sample)
  • with three replicates, noise (variation) could be a factor in our results - maybe more samples to reduce noise
  • After we get home we realise we did not take a soil pH measurement - could we direct someone else to the site?
  • MAP or RECORD THE COORDINATES for sample sites – so we know what trees, soil type, etc., occur (in the plot).


6. If there is variability in ‘rainforest’ and ‘gap’ habitats then this variability could affect ground-dwelling arthropods and our results.

  • How could we get around this problem in a study?

- Sample large number of gaps so we cover all variability - Define our treatment (gap) type more explicitly


7. Is the hypothesis well written (or practical)?

  • What is primary rainforest?

- should we specify Bornean or dipterocarp or Old World?

  • What are gaps?

- We need to define the terms in the methods section.

  • Is there any literature to support our assumption?


8. Does the sampling design really test our hypothesis?

  • Have we controlled for any of these variables?
  • Could we control for these variables?
  • Do we need to control for all of these variables?
  • Limited sampling of arthropods was OK
  • Comparing species diversity between habitats was OK
  • Assigning the reason for differences - NO!


9. Could we extrapolate our results to some general rule?

  • Will our results hold true at all times (e.g. every season, every year, El Nino, during mass fruiting)?
  • Will our results hold true in all cases, in all rainforest types, in all places (e.g. Neotropical)


10. What other tests could we do with our sample design and results?

  • Partition by site (since samples were paired)
  • Partition by order in which we set up the traps
  • Partition by group (Dave vs Rod)
  • Partition by sampling method
  • Partition by different taxa
  • Other?


What practical application could such a study have?