Hypothesis: Grazing cattle reduces the density of Oribatid mites in a pasture.
Procedure: Collect and process Berlese samples from a pasture where cattle are grazing (treatment) and from adjacent land (e.g. other side of the fence) where cattle are excluded (control). Count the number of Oribatid mites in each sample.
Treatment Control Rep #1 25 19 Rep #2 17 14 Rep #3 34 32 Rep #4 21 28 Rep #5 13 6
Data Analysis: Calculate mean and variance for treatment and control. Use average values to estimate population density of the mites. Maximum and minimum values can establish a range. Advanced students could use a t-test to evaluate statistical significance. Increase the number or size of samples to improve precision in estimates of population density.
Conclusions: If treatment average is lower than control average, than the hypothesis is likely to be correct. Reject the hypothesis if values are similar, or if control average is lower than treatment average.
Hypothesis: Density of millipedes is lower on north-facing slopes than on south-facing slopes.
Procedure: Collect and process Berlese samples from north and south-facing slopes near the peak of a dome-shaped hill or mountain. Identify and count all Diplopoda.
North South Brown
Rep #1 3 7 Rep #2 5 8 Rep #3 2 10 - - - - - - - - - - - - - - - - - - - - - - - - Ivory
Rep #1 5 5 Rep #2 3 7 Rep #3 6 5 - - - - - - - - - - - - - - - - - - - - - - - - Banded
Rep #1 8 2 Rep #2 10 3 Rep #3 9 0
Data Analysis: Calculate mean and variance for numbers of each species in each location. Taking more samples will give a better estimate of population densities. Each species may be adapted to different environmental conditions. Advanced students could use a t-test to determine whether differences are statistically significant.
Conclusions: Higher millipede density in samples collected on south-facing slopes would support the hypothesis. Students could then speculate that the warmer microclimate favors millipede growth and development. Similar populations in both areas (or higher densities in north-facing samples) should lead students to reject their hypothesis, speculating that millipedes are not sensitive to temperature of the microclimate (or prefer conditions that are cooler and more humid).
Hypothesis: Species diversity increases with increasing distance from a highway.
Procedure: Collect and process Berlese samples at regular intervals away from a major highway. Identify and count the major taxa present.
Number of Species Present 1 Meter 2 Meters 3 Meters Chelicerata 7 6 5 Crustacea 0 0 1 Myriapoda 3 6 6 Insecta 5 14 24
Data Analysis: Calculate the total number of species at each distance from the highway. Graph number of species vs. distance. Advanced students can compute an Index of Diversity (e.g. Jaccard's Index or Mountford's Index) for comparing the two samples at opposite ends of the transect.
Conclusions: Accept the hypothesis if the number of species collected decreases in samples toward the highway. Reject the hypothesis if similar numbers are found everywhere, or if numbers increase toward the highway.
Hypothesis: The relative abundance of animal species in compost piles is affected by the source of composted materials.
Procedure: Collect and process Berlese samples from two compost piles, one containing mostly grass and the other containing mostly leaves. Identify and count all representatives of major taxa.
Number of Individuals Present Leaf Pile Grass Pile Earthworms 4 6 Spiders 6 8 Mites 18 4 Sowbugs 10 8 Centipedes 3 7 Millipedes 6 6 Symphylans 15 9 Collembola 57 43 Thrips 12 5 Ants 10 4 Beetles 7 3
Data Analysis: Rank arthropods by abundance. Determine which groups are most/least abundant. Draw pie graphs showing relative abundance of each group. Advanced students could use a diversity index to compare samples.
Conclusions: Accept the hypothesis if there is a difference in the rank order of groups between compost piles. Reject the hypothesis if the ranking is similar.
|Return to The Ground Crew or ENT 591-K HomePage||John R. Meyer|
|Last Updated: 4 January 1998||Department of Entomology|
|NC State University|