96
MANFRED D. ENOELMANN
tools, Smalley could collect data on numbers of individuals, and size
categories of individuals. Weights were assigned to the size categories
by weighing representative individuals from each size category. A
simple constant pressure respirometer was used to measure respiration
rates. Observations on caged individuals were used in making estimates
of egestion rates. Calorific values for various biological materials were
determined in a Parr bomb calorimeter. Ingestion was figured as the
sum of respiration, “production” and defecation. “Production” in this
case then refered to net production which included estimates of new
nymphs produced and numbers of individuals lost to the population
through death. Estimates were lacking on numbers of eggs produced by
the population. Smalley calculated that a biomass equivalent to 10.8
kcal/m2 respired 18.6 kcal of oxygen annually. Gross production by the
population equaled 29.4 kcal/m2/year. Assimilation efficiency averaged
2’7.4% and ranged from 20.8 to 35.4%. Smalley estimated that the
grasshoppers ingested 107 kcal of the 5 200 kcal produced annually
on each square meter of the marsh. The grasshoppers consumed only
2% of the net amount produced by the flora available to them.
It is of interest that the net productivity of this population was estimated entirely from the data on calories lost to the population via
death. This population, as in the case of many insects, overwintered in
the egg stage and, thus, the adults died off at the end of the season, their
bodies going directly to the decomposer system. The net production
estimate of the grasshopper, however, was still short, for Smalley did not
have data on the number of deaths for every stage in the life cycle.
The paper by Odum and Smalley (1959) summarized energetics data
for grasshopper and snail populations living in the salt marsh on Sapelo
Island off the coast of Georgia. The data for this study were collected
by Smalley. The authors calculated that the grasshopper, Orchlimum,
ingested 48 kcal/m2/year of Spartinu grass. Thirty-six per cent of the
food ingested was assimilated. The gross production of the grasshopper
was 28 kcal/m2/year. The snail (Littorina) feeding upon the decaying
grass stems and algae, etc., was 45% efficient in assimilating its food and
yielded a gross productivity of 290 kcal/m2/year. No ingestion figure was
given for the snail. Since the organism was 45% efficient in assimilating
food, it must have egested 55% of the material, or 354 kcal/m2/year.
Thus, the Littorina population ingested annually a total of 644 kcal/m2.
Littorim used only 14% of its assimilated energy for production of new
individuals, while the grasshopper utilized 37% of its energy in reproduction. These figures can give us a minimal estimate of net productivity in the two species, but losses due to death were not stated in this
paper. Net production in the grasshopper was 10.4 kcal/m2/year, and
in the snail, 40.6 kcal/m2/year. The major point Odum and Smalley
MANFRED D. ENOELMANN
tools, Smalley could collect data on numbers of individuals, and size
categories of individuals. Weights were assigned to the size categories
by weighing representative individuals from each size category. A
simple constant pressure respirometer was used to measure respiration
rates. Observations on caged individuals were used in making estimates
of egestion rates. Calorific values for various biological materials were
determined in a Parr bomb calorimeter. Ingestion was figured as the
sum of respiration, “production” and defecation. “Production” in this
case then refered to net production which included estimates of new
nymphs produced and numbers of individuals lost to the population
through death. Estimates were lacking on numbers of eggs produced by
the population. Smalley calculated that a biomass equivalent to 10.8
kcal/m2 respired 18.6 kcal of oxygen annually. Gross production by the
population equaled 29.4 kcal/m2/year. Assimilation efficiency averaged
2’7.4% and ranged from 20.8 to 35.4%. Smalley estimated that the
grasshoppers ingested 107 kcal of the 5 200 kcal produced annually
on each square meter of the marsh. The grasshoppers consumed only
2% of the net amount produced by the flora available to them.
It is of interest that the net productivity of this population was estimated entirely from the data on calories lost to the population via
death. This population, as in the case of many insects, overwintered in
the egg stage and, thus, the adults died off at the end of the season, their
bodies going directly to the decomposer system. The net production
estimate of the grasshopper, however, was still short, for Smalley did not
have data on the number of deaths for every stage in the life cycle.
The paper by Odum and Smalley (1959) summarized energetics data
for grasshopper and snail populations living in the salt marsh on Sapelo
Island off the coast of Georgia. The data for this study were collected
by Smalley. The authors calculated that the grasshopper, Orchlimum,
ingested 48 kcal/m2/year of Spartinu grass. Thirty-six per cent of the
food ingested was assimilated. The gross production of the grasshopper
was 28 kcal/m2/year. The snail (Littorina) feeding upon the decaying
grass stems and algae, etc., was 45% efficient in assimilating its food and
yielded a gross productivity of 290 kcal/m2/year. No ingestion figure was
given for the snail. Since the organism was 45% efficient in assimilating
food, it must have egested 55% of the material, or 354 kcal/m2/year.
Thus, the Littorina population ingested annually a total of 644 kcal/m2.
Littorim used only 14% of its assimilated energy for production of new
individuals, while the grasshopper utilized 37% of its energy in reproduction. These figures can give us a minimal estimate of net productivity in the two species, but losses due to death were not stated in this
paper. Net production in the grasshopper was 10.4 kcal/m2/year, and
in the snail, 40.6 kcal/m2/year. The major point Odum and Smalley