A Quantitative Study of Litter and Soil Invertebrates - Association for ...

86
Litter and Soil Invertebrates
with the frame still unmoved, place a cardboard square, approximately 9 cm × 9 cm, at that
location. Lift the sample upward, while holding the sample in the frame, resting on the cardboard.
Place another cardboard square on the upper surface of the sample and carefully move the sample
out of the frame and secure the cardboards in place with two rubber bands, all the while trying to
keep the sample oriented more or less horizontally. Place the sample in a plastic bag and tie so the
bag provides some support for the now exposed cut sides of the sample. If the sample is crumbly
put rubber bands around the outside of the bag so as to provide support to the integrity of the
sample organization. Now it can be carried in a knapsack or large pocket back to the laboratory.
Care should be taken not to compress the sample or allow desiccation.
To examine, place the sample on a paper towel on the stage of a dissecting microscope (Figure
4.3). Add adequate illumination and begin at the litter surface. Depending on the assignment and
information which the student has in hand, work down through the sample. Observe the
following: changes in color; condition of surfaces of organic matter (intact and skeletonized leaves
and fragments); evidence of bacterial and fungal activity; presence of water films and dew drops;
kinds, numbers, and sizes of invertebrates; change in space size and configuration with change in
stratum; and evidences of humification. Try to fill in the gaps as to what has happened over time
to cause the lower, older layers to assume their present condition. Where do sand grains appear?
What does this indicate? Have roots invaded any strata and, if so, what does this mean?
When the examination is completed the sample will probably be in shreds and needs to be
discarded. Care should be taken to protect the microscope from dirt and dust. Depending on the
instructions given, invertebrates may or may not have been listed, tallied, and/or preserved. I
recommend retrieving representative forms and preserving them into 70% alcohol. Among other
things, the student gains some impression of behavior and reaction to pursuit by the specimens and
an appreciation of the difference in appearance between the living and dead condition. This is
helpful when the quantitative sample is closely examined. It allows a better visual comparison
between those forms observed alive and those extracted in the funnel. The number and kinds seen
in the live 10 cm × 10 cm sample will be conspicuously fewer than one-half those extracted in the
10 cm × 20 cm sample. Why? Why the difference in the number and kinds in each sample?
The student is able to demonstrate powers of observation and knowledge in a final assignment
that may be phrased something like, “Describe what you observed in the live sample.” A more
difficult task might be the construction of a detritovore food web or the assignment of a
relationship between external morphology and role of the animal in the habitat.