102
MANFRED D . ENGELMANN
This study had two positive aspects from the standpoint of energetics.
First, the work represented an attempt to analyze total flow of energy
through the soil. Second, all of the data in the oribatid balance sheet
were a product of separate observations; none of the figures were derived from equations. The study had several inadequacies which could
affect the significance of the results. Taxonomic identification was the
greatest deficiency. Secondly, there was a problem of questionable efficiency of the Tullgren extractor, particularly when used on dry summer
samples. Finally, temperatures of microhabitats were not known. I am
now acquiring additional new information which may increase the
figures for net and gross productivity of the Oribatei.
Let us move to another study of an “old field” habitat. The subject
of a paper by Golley (1960) was the food chain involving the bluegrassvole-least weasel. Golley obtained data on abundance, age structure,
respiration, assimilation, and egestion rates of the vole Microtus. The
least weasel (Muste&) data were largely based upon assumptions,
the majority of them reasonable! Good information was obtained on
the food of the mouse which was Kentucky bluegrass (Poa pratensis).
Golley calculated that a standing crop of 0.021-0.553 kcal of mouse on
1 m2 would release 17 kcal in respiration and produce 0.517 kcal in
young each year. As was the case in Wiegert’s study, it was difficult to
balance the ledger because of caloric transport. The mice were able to
maintain themselves in the area, although Golley found evidence of
both immigration and emigration. An estimated 1-35 kcal/m2/year of
mice moved into the area, a quantity almost twice that accounted for
by net production. Thus, on the portion of the “old field” studied, the
number of deaths was higher than the number of individuals produced
on that area. The gross productivity of the Microtus population was
17.517 kcal/m2/year. Mustejh, the least weasel, had a net productivity
of 0.013 kcal/m2/year and a gross. productivity of 5.564 kcal/m2/year.
Nicrotus used 1.6% of the total net production of the Kentucky bluegrass, while Muste& consumed 31% of the net production of the
Microtus population. Though not calculated by Golley, ecological efficiencies for the weasel and mouse would be 2.3%. This percentage represented only a portion of predation, as the weasel was not the only predator on the mouse population.
Most of Golley’s figures seemed to be reasonable. An analysis of the
food chain is a very fruitful approach to the energetics problem. He did,
however, get an unexpectedly high estimate for the assimilation rate of
Microtus (90%). Most other herbivores assimilate from 65% to 76%
of their food (Brody [1945, p. 801,McNab [1963], Pearson [1960]). If the
rate cited by Golley truly reflects the ability of the animal to absorb
food, rather than an experimental error, then, unlike most other animals
MANFRED D . ENGELMANN
This study had two positive aspects from the standpoint of energetics.
First, the work represented an attempt to analyze total flow of energy
through the soil. Second, all of the data in the oribatid balance sheet
were a product of separate observations; none of the figures were derived from equations. The study had several inadequacies which could
affect the significance of the results. Taxonomic identification was the
greatest deficiency. Secondly, there was a problem of questionable efficiency of the Tullgren extractor, particularly when used on dry summer
samples. Finally, temperatures of microhabitats were not known. I am
now acquiring additional new information which may increase the
figures for net and gross productivity of the Oribatei.
Let us move to another study of an “old field” habitat. The subject
of a paper by Golley (1960) was the food chain involving the bluegrassvole-least weasel. Golley obtained data on abundance, age structure,
respiration, assimilation, and egestion rates of the vole Microtus. The
least weasel (Muste&) data were largely based upon assumptions,
the majority of them reasonable! Good information was obtained on
the food of the mouse which was Kentucky bluegrass (Poa pratensis).
Golley calculated that a standing crop of 0.021-0.553 kcal of mouse on
1 m2 would release 17 kcal in respiration and produce 0.517 kcal in
young each year. As was the case in Wiegert’s study, it was difficult to
balance the ledger because of caloric transport. The mice were able to
maintain themselves in the area, although Golley found evidence of
both immigration and emigration. An estimated 1-35 kcal/m2/year of
mice moved into the area, a quantity almost twice that accounted for
by net production. Thus, on the portion of the “old field” studied, the
number of deaths was higher than the number of individuals produced
on that area. The gross productivity of the Microtus population was
17.517 kcal/m2/year. Mustejh, the least weasel, had a net productivity
of 0.013 kcal/m2/year and a gross. productivity of 5.564 kcal/m2/year.
Nicrotus used 1.6% of the total net production of the Kentucky bluegrass, while Muste& consumed 31% of the net production of the
Microtus population. Though not calculated by Golley, ecological efficiencies for the weasel and mouse would be 2.3%. This percentage represented only a portion of predation, as the weasel was not the only predator on the mouse population.
Most of Golley’s figures seemed to be reasonable. An analysis of the
food chain is a very fruitful approach to the energetics problem. He did,
however, get an unexpectedly high estimate for the assimilation rate of
Microtus (90%). Most other herbivores assimilate from 65% to 76%
of their food (Brody [1945, p. 801,McNab [1963], Pearson [1960]). If the
rate cited by Golley truly reflects the ability of the animal to absorb
food, rather than an experimental error, then, unlike most other animals