82
MANFRED D . ENGELMANN
is that of the human louse, Pediculus humanus (Evans and Smith, 1952),
yet no one has yet seen fit to work out the energetics of this animal.
Complete life table data are very hard to obtain, but yield estimates of
standing crop and turnover rates, these being far superior to the estimates derived from simple field counts.
The entire field estimate depends ultimately upon the estimate of the
numbers of individuals present in the area. A large amount of literature
has accumulated concerning the many and varied techniques for sampling populations. The techniques vary with the type of terrain and the
kind of animal being sampled. Dice (1952) and Macfadyen (1963a) among
others have written good general chapters on sampling techniques. Each
investigator, however, has his own modification of some existing technique made necessary by the kinds of animals and the terrain encountered as well as by the time, materials, and money available to
him! Several other estimates (e.g. total numbers of individuals present
during a period of time, biomass, standing crop, age and/or size classifications, and total respiration per annum) are derived directly from the
number of organisms counted in the field sampling program. Thus, it is
important that these counts be as accurate as possible. When field data
on numbers are not accurate, as in the case of Bornebusch (Birch and
Clark, 1953), the study loses a good deal of its usefulness.
As previously stated, numbers of individuals, per se, are not useful’to
the energetics analysis and, thus, conversion must be made to energy
units. The information necessary for the conversion is: (1) the weight of
each individual and (2) the calories represented by the weight. Weight
or biomass, then, is the intermediate step between numbers and calories.
Under certain circumstances, weights are assigned from graphs or equations relating some aspect of size to weight. Dry weight or live weight
may be used, but dry weight is preferable because it eliminates the possible variation in water content of the individual. The weighed material
must then be burned in a calorimeter to obt9in the equivalent calories.
Lists of energy values for various animals and plants have been compiled by Golley (1961) and Slobodkin and Richman (1961). Average
values derived from such lists are often used where direct calorimetry
cannot be undertaken by the investigator. Aside from the techniques
neceasary for making energy estimates, there are also several ratios or
relationships which are useful in comparing different species, populations, or communities. Three such ratios appear to be important to the
studies of energetics of terrestrial animals. The first, relationship is more
or less characteristic of the individual, the efficiency of digestion. The
efficiency of digestion can be calculated also for a population and, thus,
can be used in a broader sense; however, it is ultimately based upon
each individual’s ability to consume and assimilate food. The ratio is
MANFRED D . ENGELMANN
is that of the human louse, Pediculus humanus (Evans and Smith, 1952),
yet no one has yet seen fit to work out the energetics of this animal.
Complete life table data are very hard to obtain, but yield estimates of
standing crop and turnover rates, these being far superior to the estimates derived from simple field counts.
The entire field estimate depends ultimately upon the estimate of the
numbers of individuals present in the area. A large amount of literature
has accumulated concerning the many and varied techniques for sampling populations. The techniques vary with the type of terrain and the
kind of animal being sampled. Dice (1952) and Macfadyen (1963a) among
others have written good general chapters on sampling techniques. Each
investigator, however, has his own modification of some existing technique made necessary by the kinds of animals and the terrain encountered as well as by the time, materials, and money available to
him! Several other estimates (e.g. total numbers of individuals present
during a period of time, biomass, standing crop, age and/or size classifications, and total respiration per annum) are derived directly from the
number of organisms counted in the field sampling program. Thus, it is
important that these counts be as accurate as possible. When field data
on numbers are not accurate, as in the case of Bornebusch (Birch and
Clark, 1953), the study loses a good deal of its usefulness.
As previously stated, numbers of individuals, per se, are not useful’to
the energetics analysis and, thus, conversion must be made to energy
units. The information necessary for the conversion is: (1) the weight of
each individual and (2) the calories represented by the weight. Weight
or biomass, then, is the intermediate step between numbers and calories.
Under certain circumstances, weights are assigned from graphs or equations relating some aspect of size to weight. Dry weight or live weight
may be used, but dry weight is preferable because it eliminates the possible variation in water content of the individual. The weighed material
must then be burned in a calorimeter to obt9in the equivalent calories.
Lists of energy values for various animals and plants have been compiled by Golley (1961) and Slobodkin and Richman (1961). Average
values derived from such lists are often used where direct calorimetry
cannot be undertaken by the investigator. Aside from the techniques
neceasary for making energy estimates, there are also several ratios or
relationships which are useful in comparing different species, populations, or communities. Three such ratios appear to be important to the
studies of energetics of terrestrial animals. The first, relationship is more
or less characteristic of the individual, the efficiency of digestion. The
efficiency of digestion can be calculated also for a population and, thus,
can be used in a broader sense; however, it is ultimately based upon
each individual’s ability to consume and assimilate food. The ratio is