76
MANFRED D. ENGELMANN
level of the system in the form of food or sunlight; A,, the energy found
in the bodies of individuals which make up the trophic level, i.e. the
standing crop energy; R,, the energy lost to the trophic level in respiration; D,, the energy lost to the trophic level by way of the decomposers;
and Adl, the energy lost to the trophic level from consumption by
the next trophic level (see diagram). The flow diagram is in turn based
upon several laws and assumptions. They are as follows: (1) the laws of
thermodynamics hold for plants and animals; (2) plants and animals
can be grouped together into trophic levels according to their feeding
habits; (3) there are at least three trophic levels (there may be more)
which are: (a) producers (green plants) ; (b) herbivores (animals feeding
upon the green plants); and (c) ca.rnivores (animals feeding upon the
herbivores); and (4) the system is in equilibrium; and ( 5 ) calories are
the basic units of the trophic scheme. From these assumptions, it can
be deduced that: (1) each succeeding trophic level will have fewer calories than the preceding one, and (2) that there is a finite number of
trophic levels. In a steady state condition, A, , will equal the sum of
R, + D, + Adl . For increasing or decreasing populations, A, will equal
R, + D , + hdl + AA,, where AA, is the increase or decrease in energy
of the standing crop. However, the Lindeman model is not designed to
TO NEXT TROPHIC
LEVEL
Fra. 1. Schematic representation of the Lindeman Model. The drawing depicts a single
trophic level with the energy flow indicated by the arrows. For a complete representation of the trophic levels of an “old-field’’ community see Engelmann, 1961, p. 236.
MANFRED D. ENGELMANN
level of the system in the form of food or sunlight; A,, the energy found
in the bodies of individuals which make up the trophic level, i.e. the
standing crop energy; R,, the energy lost to the trophic level in respiration; D,, the energy lost to the trophic level by way of the decomposers;
and Adl, the energy lost to the trophic level from consumption by
the next trophic level (see diagram). The flow diagram is in turn based
upon several laws and assumptions. They are as follows: (1) the laws of
thermodynamics hold for plants and animals; (2) plants and animals
can be grouped together into trophic levels according to their feeding
habits; (3) there are at least three trophic levels (there may be more)
which are: (a) producers (green plants) ; (b) herbivores (animals feeding
upon the green plants); and (c) ca.rnivores (animals feeding upon the
herbivores); and (4) the system is in equilibrium; and ( 5 ) calories are
the basic units of the trophic scheme. From these assumptions, it can
be deduced that: (1) each succeeding trophic level will have fewer calories than the preceding one, and (2) that there is a finite number of
trophic levels. In a steady state condition, A, , will equal the sum of
R, + D, + Adl . For increasing or decreasing populations, A, will equal
R, + D , + hdl + AA,, where AA, is the increase or decrease in energy
of the standing crop. However, the Lindeman model is not designed to
TO NEXT TROPHIC
LEVEL
Fra. 1. Schematic representation of the Lindeman Model. The drawing depicts a single
trophic level with the energy flow indicated by the arrows. For a complete representation of the trophic levels of an “old-field’’ community see Engelmann, 1961, p. 236.