ENERGETICS A N D A N I M A L P R O D U C T I V I T Y
99
Because of the division of labor within the colony, the marking technique was not successful for estimating the total number of individuals
in the hill. Data for net production were also difficult to evaluate, because the authors took the top birth production figures rather than
averages; yet they had no estimate for deaths of adults or young during
their life span. Net production, in this case, requires estimates for both
parameters because most of the individuals lived more than one year.
The important point is, however, that maintenance metabolism required 99.6% of the total assimilated energy. No estimate of ingestion
was attempted and, therefore, we have no information on the total
number of calories consumed annually by the population. The data presented by Golley and Gentry indicated that, in the “old field”, the
harvester ant was an important herbivore converting most of its assimilated energy into maintenance and very littlo energy into net production.
Odum et al. (1962) worked in the abandoned fields (“old fields”)
associated with the Savannah River Plant of the U.S.A. Atomic Energy
Commission, Georgia. The authors concentrated on two grasshopper
species (Melanoplus femur-rubrum, and M . biliteratus), the tree cricket
(Oeconthus nigricornis), a mouse (Peromyscw polionotus), and a sparrow
(Passerculus sandwichensis). The mice were live-trapped, the sparrows
captured with mist nets, and the Orthoptera were captured with sweep
nets and in cages after the procedures originated by Smalley. Caloric
equivalents were obtained by Parr bomb cdorimetery . Metabolism was
measured both in terms of caged animals sad by respirometry.
The field energy was assumed to be twice maintenance energy (an
assumption questioned by McNab, 1963). The authors estimated that
gross production of the sparrow was 3.6 kcal/m2/year. However, since
Southern Georgia is the wintering range for these birds, there was
virtually no net production (0.04 kcal/m2/year). Gross production for
the mouse was 6.7 kcal/m2/year, with average net production at only
0.12 kcal/m2/year. Gross production for the Orthoptera was 25-6 kcal/
mZ/year and net production was 4-0 kcal/m’a/year. Once the authors had
determined the total amount of each food consumed, they could find
out how much of the standing crop of peen plants the herbivores
utilized. The gramnivorous birds and mice used from 10% to 50% of
the seeds consumed, whereas the herbivorous Orthoptera utilized only
2% to 7% of the plant foliage. Golley and Gentry estimated that the
ant, P. badius, consumed the equivalent of 64% to 213% of the seed
crop on these same fields. Thus it would appear that from 74% to 263%
of the seed crop produced on each m2 was used by these three species
during the year. This can only imply that ei1;her the seed crop was underestimated or the animal utilization overestimated, or both.
Analysis of droppings of vesper and field oparrows in Michigan showed
99
Because of the division of labor within the colony, the marking technique was not successful for estimating the total number of individuals
in the hill. Data for net production were also difficult to evaluate, because the authors took the top birth production figures rather than
averages; yet they had no estimate for deaths of adults or young during
their life span. Net production, in this case, requires estimates for both
parameters because most of the individuals lived more than one year.
The important point is, however, that maintenance metabolism required 99.6% of the total assimilated energy. No estimate of ingestion
was attempted and, therefore, we have no information on the total
number of calories consumed annually by the population. The data presented by Golley and Gentry indicated that, in the “old field”, the
harvester ant was an important herbivore converting most of its assimilated energy into maintenance and very littlo energy into net production.
Odum et al. (1962) worked in the abandoned fields (“old fields”)
associated with the Savannah River Plant of the U.S.A. Atomic Energy
Commission, Georgia. The authors concentrated on two grasshopper
species (Melanoplus femur-rubrum, and M . biliteratus), the tree cricket
(Oeconthus nigricornis), a mouse (Peromyscw polionotus), and a sparrow
(Passerculus sandwichensis). The mice were live-trapped, the sparrows
captured with mist nets, and the Orthoptera were captured with sweep
nets and in cages after the procedures originated by Smalley. Caloric
equivalents were obtained by Parr bomb cdorimetery . Metabolism was
measured both in terms of caged animals sad by respirometry.
The field energy was assumed to be twice maintenance energy (an
assumption questioned by McNab, 1963). The authors estimated that
gross production of the sparrow was 3.6 kcal/m2/year. However, since
Southern Georgia is the wintering range for these birds, there was
virtually no net production (0.04 kcal/m2/year). Gross production for
the mouse was 6.7 kcal/m2/year, with average net production at only
0.12 kcal/m2/year. Gross production for the Orthoptera was 25-6 kcal/
mZ/year and net production was 4-0 kcal/m’a/year. Once the authors had
determined the total amount of each food consumed, they could find
out how much of the standing crop of peen plants the herbivores
utilized. The gramnivorous birds and mice used from 10% to 50% of
the seeds consumed, whereas the herbivorous Orthoptera utilized only
2% to 7% of the plant foliage. Golley and Gentry estimated that the
ant, P. badius, consumed the equivalent of 64% to 213% of the seed
crop on these same fields. Thus it would appear that from 74% to 263%
of the seed crop produced on each m2 was used by these three species
during the year. This can only imply that ei1;her the seed crop was underestimated or the animal utilization overestimated, or both.
Analysis of droppings of vesper and field oparrows in Michigan showed