ENERGETICS AND ANIMAL PRODUCTIVITY
109
productivity and maintenance metabolism (see Fig. 2). It is important
to remember that the relationship (Log Rp == 0-62 + 0-86 Log p ) waa
obtained from data provided by 5 different authors, working on several
species of animals and using markedly different techniques to make
energetics estimates. The majority of the points on Fig. 2 represent
single species populations. Point 7, however, represents all of the oribatid mites in the “old field” soil (Engelmann, 1961). While working with
the plot, I questioned the position of point 7, for it represents data from
about eighteen species. Yet this point lies near a regression line derived
mostly from points representing single species data. I used the new
formula to check further the position of the oribatid data on Fig. 2 as
well as to make a preliminary check on the plausibility of this formula.
In my original analysis (Engelmann, 1961) the productivity estimates
came from two independent sources, one based on egg production in
three species of mites (particularly Oppia nova and Scherloribates leuigatus) in cultures, and the other from the deduced death rate of the
adult population. This net production figure, then, was not compiled
from individual production rates for each population. By using the net
productivity formula for poikilotherms listed ,tbove, I was able to calculate from the annual respiratory metabolism the net production for each
species of oribatid found on the “old field’’ (Table IX). The immature
individuals were not reproducing and thus were not included in the
calculation. Certain other populations (marked with asterisks) were not
originally separated into groups of adults and young, because all stages
were readily identified as belonging to the mme species. Thus, I arbitrarily assumed that one-third of the population were adults, capable
of reproduction, and two-thirds were immatures. The total net productivity as calculated by the net productivity e quation for poikilotherms
(using the above-mentioned omissions and assumptions) was 428 cal/
m2/yr while the net productivity calculated by oviposition data and
turnover rate was 430 cal. If no assumption were made about the mixed
populations (*), the total would have been 568.3 cal/m2/yr. In the first
case the agreement would be phenomenal and in the second instance
there would still be reasonable agreement. Thus, I feel that the new
equation has great potential, but should be more fully tested.
If we are concerned with predicting net productivity of a community,
we cannot use the simple equation for respiration and net productivity.
As more data on species respiration are added, the calculations deviate
further from the true figure, e.g. if we take the total respiration data
from Macfadyen’s (1963b) Grassland No. 1 and use it in the equation,
net productivity is estimated at 650 kcal/m2/yr. If the productivity is
then calculated for each trophic level and taxon listed, an estimate of
only 470.7 kcal/m2/yr results (some 27% lower than the estimate based
109
productivity and maintenance metabolism (see Fig. 2). It is important
to remember that the relationship (Log Rp == 0-62 + 0-86 Log p ) waa
obtained from data provided by 5 different authors, working on several
species of animals and using markedly different techniques to make
energetics estimates. The majority of the points on Fig. 2 represent
single species populations. Point 7, however, represents all of the oribatid mites in the “old field” soil (Engelmann, 1961). While working with
the plot, I questioned the position of point 7, for it represents data from
about eighteen species. Yet this point lies near a regression line derived
mostly from points representing single species data. I used the new
formula to check further the position of the oribatid data on Fig. 2 as
well as to make a preliminary check on the plausibility of this formula.
In my original analysis (Engelmann, 1961) the productivity estimates
came from two independent sources, one based on egg production in
three species of mites (particularly Oppia nova and Scherloribates leuigatus) in cultures, and the other from the deduced death rate of the
adult population. This net production figure, then, was not compiled
from individual production rates for each population. By using the net
productivity formula for poikilotherms listed ,tbove, I was able to calculate from the annual respiratory metabolism the net production for each
species of oribatid found on the “old field’’ (Table IX). The immature
individuals were not reproducing and thus were not included in the
calculation. Certain other populations (marked with asterisks) were not
originally separated into groups of adults and young, because all stages
were readily identified as belonging to the mme species. Thus, I arbitrarily assumed that one-third of the population were adults, capable
of reproduction, and two-thirds were immatures. The total net productivity as calculated by the net productivity e quation for poikilotherms
(using the above-mentioned omissions and assumptions) was 428 cal/
m2/yr while the net productivity calculated by oviposition data and
turnover rate was 430 cal. If no assumption were made about the mixed
populations (*), the total would have been 568.3 cal/m2/yr. In the first
case the agreement would be phenomenal and in the second instance
there would still be reasonable agreement. Thus, I feel that the new
equation has great potential, but should be more fully tested.
If we are concerned with predicting net productivity of a community,
we cannot use the simple equation for respiration and net productivity.
As more data on species respiration are added, the calculations deviate
further from the true figure, e.g. if we take the total respiration data
from Macfadyen’s (1963b) Grassland No. 1 and use it in the equation,
net productivity is estimated at 650 kcal/m2/yr. If the productivity is
then calculated for each trophic level and taxon listed, an estimate of
only 470.7 kcal/m2/yr results (some 27% lower than the estimate based