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MANFRED D . ENGELMANN
example, reported 1 700 species captured from the herb strata of an
“old field” in Michigan. Two hundred and sixty of these species occur
commonly and were believed to represent the resident fauna of that
field. Hairston (1959) and Hairston and Byers (1954) recorded 271
species of arthropods found in the soil of the same “old field”. For this
15-acre field in southern Michigan then, nearly 2 000 species of arthropods have been recorded, of which about 320 are part of the normal
resident fauna. The task of keeping the species categories separated
during energetics analysis is formidable.
The problems which made terrestrial communities less suitable for
energetics studies in the 1940’s are still present. The need for making
such studies is becoming more evident and more urgent, and thus these
pioneer studies set forth the first crude guides to the methods necessary
for such an endeavor and yield data which begin to define the limits of
the problem.
To make a complete energetics analysis we must have estimates on
ingestion rates, assimilation rates, egestion rates, respiration rates,
growth rates, death rates, numbers and biomass, and the calories represented by these figures. None of these parameters is directly measurable
in the laboratory or field but must be calculated from several kinds of
data. Paradoxically, a good portion of the data necessary for field estimates must come from laboratory studies.
If energetics studies are to be properly evaluated, it is essential to
understand the general procedures of obtaining the relevant data.
Measurement of ingestion rates requires knowledge of the amount of
food the animal consumes during a certain time period and the caloric
value of the food consumed. If the amount ingested cannot be measured
directly in the field, estimates must be made from ingestion data on
animals in enclosures or in culture cages.
Direct measurements of assimilation rate must be done in the laboratory, but this parameter can be estimated from an equation when ingestion and egestion rates are known. It should be noted that every rate
estimated from an equation eliminates one of the internal checks inherent in the Lindeman system. The calories egested are not important
to the particular population or trophic level which “produce” them,
but the feces are important for the decomposer system since they make
up part of the energy source of the decomposers. Energetically, feces
contribute no calories to the population for performing work and require
only that the organism expend energy to move them through the digestive tract. The animals which can move great quantities of non-utilizable
material through the digestive tract with small amounts of energy would
of course have some adaptive advantage, but present methods used in
energetics studies are not sufficiently refined to answer such questions.
MANFRED D . ENGELMANN
example, reported 1 700 species captured from the herb strata of an
“old field” in Michigan. Two hundred and sixty of these species occur
commonly and were believed to represent the resident fauna of that
field. Hairston (1959) and Hairston and Byers (1954) recorded 271
species of arthropods found in the soil of the same “old field”. For this
15-acre field in southern Michigan then, nearly 2 000 species of arthropods have been recorded, of which about 320 are part of the normal
resident fauna. The task of keeping the species categories separated
during energetics analysis is formidable.
The problems which made terrestrial communities less suitable for
energetics studies in the 1940’s are still present. The need for making
such studies is becoming more evident and more urgent, and thus these
pioneer studies set forth the first crude guides to the methods necessary
for such an endeavor and yield data which begin to define the limits of
the problem.
To make a complete energetics analysis we must have estimates on
ingestion rates, assimilation rates, egestion rates, respiration rates,
growth rates, death rates, numbers and biomass, and the calories represented by these figures. None of these parameters is directly measurable
in the laboratory or field but must be calculated from several kinds of
data. Paradoxically, a good portion of the data necessary for field estimates must come from laboratory studies.
If energetics studies are to be properly evaluated, it is essential to
understand the general procedures of obtaining the relevant data.
Measurement of ingestion rates requires knowledge of the amount of
food the animal consumes during a certain time period and the caloric
value of the food consumed. If the amount ingested cannot be measured
directly in the field, estimates must be made from ingestion data on
animals in enclosures or in culture cages.
Direct measurements of assimilation rate must be done in the laboratory, but this parameter can be estimated from an equation when ingestion and egestion rates are known. It should be noted that every rate
estimated from an equation eliminates one of the internal checks inherent in the Lindeman system. The calories egested are not important
to the particular population or trophic level which “produce” them,
but the feces are important for the decomposer system since they make
up part of the energy source of the decomposers. Energetically, feces
contribute no calories to the population for performing work and require
only that the organism expend energy to move them through the digestive tract. The animals which can move great quantities of non-utilizable
material through the digestive tract with small amounts of energy would
of course have some adaptive advantage, but present methods used in
energetics studies are not sufficiently refined to answer such questions.