74
MANFRED D. ENGELMANN
terrestrial energetics at this point in its history. The task is by no means
a small one. Even though the accumulated literature a t present is
rather limited, the studies that have been reported are recorded in many
different journals covering diverse approaches to ecological research.
In this article, the subject of field estimation of productivity will be
approached in three ways: first, the historical and theoretical bases
which undergird terrestrial productivity studies will be considered;
second, the various works in the field will be reviewed, with particular
emphasis upon the relationships of the papers to one another and the
type of data each yields; finally, the progress of terrestrial energetic
studies as a whole will be evaluated and areas wherein critical research
is needed will be indicated. I must admit that I face some difficulty performing the task set before me with necessary thoroughness, especially
with respect to the final point. However, I hope that my efforts will
give others further insight into the problems in the field and thus
enhance its progress.
11. THREE APPROACHES TO ENERGETICS STUDIES
There are probably three main approaches to the problem of field
estimates of animal production. The preceding statement is qualified
because the word productivity has various interpretakions. Not one of
the definitions given in Webster’s Unabridged Dictionary would suitably
characterize the highly specialized nature of “production” as used in
the field of energetics. The cattlemen and farmers use the word to mean
such measurements as number of head or bushels per acre, the biologist
refers to number of individuals born per unit time as “production”.
Most of the time, the ecologist also employs the latter meaning when
constructing life tables or dealing with other aspects of population.
However, when the term calorie is considered, the terms production and
productivity take on more restricted meanings. The restricted meaning,
moreover, was not immediately recognized, but evolved slowly through
the 1930’s and 1940’s. Variations in the use of these terms by different
authors are eloquently summarized by Macfadyen, 1963a, pages 160
and 161. His table, clearly demonstrates why the term productivity
provokes a confused response from “production scientists”. To avoid
many of the difficulties raised, I wish to sidestep the issue by stating
the two definitions of productivity used in this paper. They are: (1) net
productivity, the number of calories represented by the new individuals
and the increase in weight of the population per unit of time; and,
(2) gross productivity, the total number of calories expended by the
population in maintenance, i.e. respiration, plus the calories represented
by numbers produced and increase in population weight or biomass. In
referring to the three main sources of productivity information, then, I
MANFRED D. ENGELMANN
terrestrial energetics at this point in its history. The task is by no means
a small one. Even though the accumulated literature a t present is
rather limited, the studies that have been reported are recorded in many
different journals covering diverse approaches to ecological research.
In this article, the subject of field estimation of productivity will be
approached in three ways: first, the historical and theoretical bases
which undergird terrestrial productivity studies will be considered;
second, the various works in the field will be reviewed, with particular
emphasis upon the relationships of the papers to one another and the
type of data each yields; finally, the progress of terrestrial energetic
studies as a whole will be evaluated and areas wherein critical research
is needed will be indicated. I must admit that I face some difficulty performing the task set before me with necessary thoroughness, especially
with respect to the final point. However, I hope that my efforts will
give others further insight into the problems in the field and thus
enhance its progress.
11. THREE APPROACHES TO ENERGETICS STUDIES
There are probably three main approaches to the problem of field
estimates of animal production. The preceding statement is qualified
because the word productivity has various interpretakions. Not one of
the definitions given in Webster’s Unabridged Dictionary would suitably
characterize the highly specialized nature of “production” as used in
the field of energetics. The cattlemen and farmers use the word to mean
such measurements as number of head or bushels per acre, the biologist
refers to number of individuals born per unit time as “production”.
Most of the time, the ecologist also employs the latter meaning when
constructing life tables or dealing with other aspects of population.
However, when the term calorie is considered, the terms production and
productivity take on more restricted meanings. The restricted meaning,
moreover, was not immediately recognized, but evolved slowly through
the 1930’s and 1940’s. Variations in the use of these terms by different
authors are eloquently summarized by Macfadyen, 1963a, pages 160
and 161. His table, clearly demonstrates why the term productivity
provokes a confused response from “production scientists”. To avoid
many of the difficulties raised, I wish to sidestep the issue by stating
the two definitions of productivity used in this paper. They are: (1) net
productivity, the number of calories represented by the new individuals
and the increase in weight of the population per unit of time; and,
(2) gross productivity, the total number of calories expended by the
population in maintenance, i.e. respiration, plus the calories represented
by numbers produced and increase in population weight or biomass. In
referring to the three main sources of productivity information, then, I