ENERGY I N ANIMAL ECOLOGY
73
Frog eggs (Rana pipiens), newly fertilized, are not beyond the
calorific range for whole organisms (6.0) and newly-hatched tadpoles
(144 hours old), with yolk still present, are in the modal region (5.8).
Salamander eggs (Ambystoma punctatum) are identical with those of
frogs. We are left with the problem of the phylogeny of energy-rich eggs
in the lower vertebrates. Skate (Raja erinacea) egg yolk has an intermediate value of 5-6. Reptilian egg yolks are intermediate between
birds and amphibians ( Urosaurus ornatus, 6-9 kcallash-free g, Sceloporus
undulatus, 6-7, Pseudemys scripta, 6.7, Chelydra serpentina, 6.6).
The calorific data abundantly demonstrate the relevance of energy
analysis in ecology and actually do stimulate the formulation of evolutionary theorems and questions.
11. THEORY OF ENERGY BUDGETS
The relation between energetics and the numerical properties of
populations must be in terms of energy budget analysis in which
the population is considered as a steady-state system through which
potential energy passes. We restrict attention t o steady states since
seasonal differences in climate and physiology combined with essentially
random meteorological or biological events in short-term data collections will permit so much variance as t o obscure real constancies and
differences.
The concept of ecological steady states has been discussed by Odum
(1957) and Slobodkin (1960) and both of these authors have indicated
something of the theoretical importance of making energy measurements at or near steady-state conditions. An obvious point that neither
of them mentions is the difference in meaning between the concept of
steady state when applied t o an entire community and when applied
t o a single population.
While a population may maintsin its own standing crop in a steady
state, no population of mortal animals can maintain a steady state in
its immediate spatial environment since the process of population
maintenance requires the product,ion of a continuing stream of dead
animals and, therefore, a new accumulation of potential energy in the
physical environment of the populations.
To avoid confusion, let us establish units now. The population,
itself, is measured in units of calories ; energy income to the population
or energy expenditure by the population is generally in calorieltime
units. The term “cost” will be in units of calories per item, so that, for
example, maintenance cost, of a population will be in units of calories
per calorie-days and replacement cost of an individual organism will be
in units of calories per individual.
Efficiencies will always be dimensionless fractions. Only if the units
c2
E.R.-1
73
Frog eggs (Rana pipiens), newly fertilized, are not beyond the
calorific range for whole organisms (6.0) and newly-hatched tadpoles
(144 hours old), with yolk still present, are in the modal region (5.8).
Salamander eggs (Ambystoma punctatum) are identical with those of
frogs. We are left with the problem of the phylogeny of energy-rich eggs
in the lower vertebrates. Skate (Raja erinacea) egg yolk has an intermediate value of 5-6. Reptilian egg yolks are intermediate between
birds and amphibians ( Urosaurus ornatus, 6-9 kcallash-free g, Sceloporus
undulatus, 6-7, Pseudemys scripta, 6.7, Chelydra serpentina, 6.6).
The calorific data abundantly demonstrate the relevance of energy
analysis in ecology and actually do stimulate the formulation of evolutionary theorems and questions.
11. THEORY OF ENERGY BUDGETS
The relation between energetics and the numerical properties of
populations must be in terms of energy budget analysis in which
the population is considered as a steady-state system through which
potential energy passes. We restrict attention t o steady states since
seasonal differences in climate and physiology combined with essentially
random meteorological or biological events in short-term data collections will permit so much variance as t o obscure real constancies and
differences.
The concept of ecological steady states has been discussed by Odum
(1957) and Slobodkin (1960) and both of these authors have indicated
something of the theoretical importance of making energy measurements at or near steady-state conditions. An obvious point that neither
of them mentions is the difference in meaning between the concept of
steady state when applied t o an entire community and when applied
t o a single population.
While a population may maintsin its own standing crop in a steady
state, no population of mortal animals can maintain a steady state in
its immediate spatial environment since the process of population
maintenance requires the product,ion of a continuing stream of dead
animals and, therefore, a new accumulation of potential energy in the
physical environment of the populations.
To avoid confusion, let us establish units now. The population,
itself, is measured in units of calories ; energy income to the population
or energy expenditure by the population is generally in calorieltime
units. The term “cost” will be in units of calories per item, so that, for
example, maintenance cost, of a population will be in units of calories
per calorie-days and replacement cost of an individual organism will be
in units of calories per individual.
Efficiencies will always be dimensionless fractions. Only if the units
c2
E.R.-1