82
L. B. S L O B O D K I N
communication theory does not have temperature as a significant
parameter nor can the complete array of states be specified so as t o
permit a statistical mechanical definition of entropy to be operationally
evaluated in any biological system. I n short, while certain analogies
between parts of ecological energetics and parts of thermodynamics
can be verbalized, there is no evidence whatsoever that these are necessary or even fruitful for the advance of ecological comprehension.
Not only are thermodynamic analogies current in the literature but
circuit diagrams and hydrostatic flow diagrams are also taken as
analogies. All of these violate common sense. Note the statement by
H. T. Odum (1960) in discussing an analogy between electric circuits
and ecological communities : “The validity of this application may
be recognized when one breaks away from the habit of thinking that
a fish or bear, etc. takes food and thinks instead that accumulated
food by its concentration practically forces food through the consumers.” To my knowledge this sort of analogy has produced neither
suggestions for practical experiments nor significant syntheses.
IV. LINDEMAN’S THEORETICAL FORMULATION
The classical initial study of energy-passage through a natural community is that of Lindeman (1942).
The framework into which Lindeman fitted his data was essentially
the following. Assume all organisms in a natural community t o belong
t o one and only one of the trophic levels designated by Al, A2, A , . . . A ,
such that any organism at trophic level A,,, is nourished by eating
organisms of trophic level Ai-,. Trophic level A , consists of autotrophs
deriving their energy from the sun. The energy passed per unit time
from trophic level A i t o trophic level Ai+l is designated as Ai and is
referred t o as the productivity of level Aie A problem has risen in the
literature about whether the food consumption or the protoplasm synthesis of Ai+l should be called its production but this problem is not of
fundamental importance for our immediate purpose. I’ll try to keep the
concepts clear as we proceed. A i is a standing crop with a dimension
of calories, X i has a dimension of calories per time and both are calculated per cmz of surface.
There is a relation between the concept of trophic levels and that of
food chains but the two concepts are not identical, the first being a
simplifying assumption while the second is purely descriptive. If a
diagram of the passage of all high-energy molecules through an ecological community is made, it w i l l be found that the potential energy
of any given molecule will either have dissipated as heat in or near the
body of some organism or been transferred to some other organism. The
individual organisms can be arranged by drawing arrows t o a point
L. B. S L O B O D K I N
communication theory does not have temperature as a significant
parameter nor can the complete array of states be specified so as t o
permit a statistical mechanical definition of entropy to be operationally
evaluated in any biological system. I n short, while certain analogies
between parts of ecological energetics and parts of thermodynamics
can be verbalized, there is no evidence whatsoever that these are necessary or even fruitful for the advance of ecological comprehension.
Not only are thermodynamic analogies current in the literature but
circuit diagrams and hydrostatic flow diagrams are also taken as
analogies. All of these violate common sense. Note the statement by
H. T. Odum (1960) in discussing an analogy between electric circuits
and ecological communities : “The validity of this application may
be recognized when one breaks away from the habit of thinking that
a fish or bear, etc. takes food and thinks instead that accumulated
food by its concentration practically forces food through the consumers.” To my knowledge this sort of analogy has produced neither
suggestions for practical experiments nor significant syntheses.
IV. LINDEMAN’S THEORETICAL FORMULATION
The classical initial study of energy-passage through a natural community is that of Lindeman (1942).
The framework into which Lindeman fitted his data was essentially
the following. Assume all organisms in a natural community t o belong
t o one and only one of the trophic levels designated by Al, A2, A , . . . A ,
such that any organism at trophic level A,,, is nourished by eating
organisms of trophic level Ai-,. Trophic level A , consists of autotrophs
deriving their energy from the sun. The energy passed per unit time
from trophic level A i t o trophic level Ai+l is designated as Ai and is
referred t o as the productivity of level Aie A problem has risen in the
literature about whether the food consumption or the protoplasm synthesis of Ai+l should be called its production but this problem is not of
fundamental importance for our immediate purpose. I’ll try to keep the
concepts clear as we proceed. A i is a standing crop with a dimension
of calories, X i has a dimension of calories per time and both are calculated per cmz of surface.
There is a relation between the concept of trophic levels and that of
food chains but the two concepts are not identical, the first being a
simplifying assumption while the second is purely descriptive. If a
diagram of the passage of all high-energy molecules through an ecological community is made, it w i l l be found that the potential energy
of any given molecule will either have dissipated as heat in or near the
body of some organism or been transferred to some other organism. The
individual organisms can be arranged by drawing arrows t o a point