ENERGY I N ANIMAL ECOLOGY
89
values of Richman, computed growth-efficiency and reproductiveefficiency by a least squares fit t o the energy budget:
calories ingested
(13)
calories of growth
calories reproduction
+
-
- gross efficiency of growth gross efficiency of reproduction ’
finding growth-&ciency as 7% and reproductive-efficiency as 5%.
Armstrong estimated the mean cell concentration in his populations
as approximately 104/cms. As indicated above, efficiency may be
expected to decrease at sufficiently low algal concentrations.
Building on the work of Richman, Armstrong (1960) has made a
particularly interesting analysis of growth-efficiency and age in Daphnia
in which he considers the origin of age t o be at the onset of production
of the egg which will give rise to the animal in question.
Armstrong assumed that the growth-efficiency determined for the
period immediately prior t o the onset of reproductive activity persisted into reproductive life but that the total amount of energy available for growth had been reduced in favour of reproduction. The total
energy associated with growth during reproductive life is, therefore,
the total calorific content of the growth-increment divided by the
growth-efficiency a t the termination of pre-reproductive life.
The cost of producing a single young animal is calculated by Armstrong as the calorific content of newborn divided by reproductive
efficiency. This cost is added t o the food consumption during free life
to form the denominator of Armstrong’s growth-efficiency calculation.
The calculated relation between growth-efficiency, animal size and
algal cell concentration as calculated by Armstrong is summarized in
Fig. 2.
Using the calorific determinations of ‘Richman, Slobodkin (1959)
could state with reasonable accuracy for twenty-eight Daphnia populations the calorific equivalent of the food, standing crop and, for
twenty-three of these populations, the yield in calories of young,
adults, and eggs. Slobodkin assumed that all of his populations ( P F )
were related t o the size of a control population ( P o ) by Eq. (12). It
had previously been demonstrated by Slobodkin (1954) that Daphnia
population-size is linearly related t o food supply when food consumption equals food supply. Further, all food supplied. is consumed by a
Daphnia population in the absence of predation.
At high values of F, food was left unused in Slobodkin’s populations.
The amount of food consumed by each population was, therefore,
estimated for each population P, by substituting F a n d P, in Eq. (12),
solving for Po’, the theoretical size of a population with food consumption identical to PF but with F = 0. The food consumed by Pp was
89
values of Richman, computed growth-efficiency and reproductiveefficiency by a least squares fit t o the energy budget:
calories ingested
(13)
calories of growth
calories reproduction
+
-
- gross efficiency of growth gross efficiency of reproduction ’
finding growth-&ciency as 7% and reproductive-efficiency as 5%.
Armstrong estimated the mean cell concentration in his populations
as approximately 104/cms. As indicated above, efficiency may be
expected to decrease at sufficiently low algal concentrations.
Building on the work of Richman, Armstrong (1960) has made a
particularly interesting analysis of growth-efficiency and age in Daphnia
in which he considers the origin of age t o be at the onset of production
of the egg which will give rise to the animal in question.
Armstrong assumed that the growth-efficiency determined for the
period immediately prior t o the onset of reproductive activity persisted into reproductive life but that the total amount of energy available for growth had been reduced in favour of reproduction. The total
energy associated with growth during reproductive life is, therefore,
the total calorific content of the growth-increment divided by the
growth-efficiency a t the termination of pre-reproductive life.
The cost of producing a single young animal is calculated by Armstrong as the calorific content of newborn divided by reproductive
efficiency. This cost is added t o the food consumption during free life
to form the denominator of Armstrong’s growth-efficiency calculation.
The calculated relation between growth-efficiency, animal size and
algal cell concentration as calculated by Armstrong is summarized in
Fig. 2.
Using the calorific determinations of ‘Richman, Slobodkin (1959)
could state with reasonable accuracy for twenty-eight Daphnia populations the calorific equivalent of the food, standing crop and, for
twenty-three of these populations, the yield in calories of young,
adults, and eggs. Slobodkin assumed that all of his populations ( P F )
were related t o the size of a control population ( P o ) by Eq. (12). It
had previously been demonstrated by Slobodkin (1954) that Daphnia
population-size is linearly related t o food supply when food consumption equals food supply. Further, all food supplied. is consumed by a
Daphnia population in the absence of predation.
At high values of F, food was left unused in Slobodkin’s populations.
The amount of food consumed by each population was, therefore,
estimated for each population P, by substituting F a n d P, in Eq. (12),
solving for Po’, the theoretical size of a population with food consumption identical to PF but with F = 0. The food consumed by Pp was