ENERGETICS AND ANIMAL PRODUCTIVITY
81
The respiration rate represents the maintenamce portion of the energy
budget, that portion of the assimilated food necessary to keep the organism together and functioning. Respiration can be estimated by measuring either oxygen consumption or carbon dioxide production. There are
numerous devices which measure oxygen uptake, but they generally
fall into three major types: the constant pressure, constant volume, and
differential (Dixon, 1952). The most widely used apparatus in tissue
culture study is the constant volume type represented by the Warburg
respirometer. Yet in most of the energetic studies at present, some form
of a constant pressure apparatus is employed. The major exception to
this statement is found where very small organisms (mites, collembola,
etc.) are concerned, and then the Cartesian diver apparatus (a constant
volume type) is used. Several studies employ some method of estimating
respiration rate by CO, production. This usually involves capturing the
CO, in a standard basic solution, thus converting the base to a salt and
then titrating the remaining base with an aoid standard. It must be
kept in mind that in energetics studies the number of units of 0, respired is not so important to know as the number of calories represented
by this respiration, because it is an estimate of the amount of heat the
population loses in the process of maintenance. Conceivably, it should
be possible to measure the heat production directly via calorimetry in
the field. However, at present the technique required for direct field
calorimetry has not yet been attempted.
Growth rates are measured either in the 5eld or in the laboratory
where the animals are kept in cages or culture,g. Each approach presents
problems. In the laboratory, growth rates ca2 be measured very accurately, but the conditions under which the animals are kept are not those
of the field. Field studies, on the other hand, have the advantage of
natural surroundings, normal activities, and usual diets, but present the
problem of measuring and keeping track of the growth rates of particular individuals. Still another approach to the measurement of growth
rates is that of deducing them from the numbers of individuals found in
various size categories during successive field samplings. This approach
is particularly useful for the meiofauna and the microfauna where marking, release, and recapture techniques have not yet been worked out.
Data on death rates are obtained in the r3ame way as are data on
growth rates. Cage or culture studies, however, yield only data on deaths
resulting from physiological limitations, and the survival rate is higher
than that found in field populations due to the absence of predation.
The most reasonable approach at this time seems to be the construction of a life table (Allee ct al., 1949, page 265) from laboratory or enclosure data, and the adjustment of this table to field conditions. One
of the most complete life tables we have for ,an animal other than man
81
The respiration rate represents the maintenamce portion of the energy
budget, that portion of the assimilated food necessary to keep the organism together and functioning. Respiration can be estimated by measuring either oxygen consumption or carbon dioxide production. There are
numerous devices which measure oxygen uptake, but they generally
fall into three major types: the constant pressure, constant volume, and
differential (Dixon, 1952). The most widely used apparatus in tissue
culture study is the constant volume type represented by the Warburg
respirometer. Yet in most of the energetic studies at present, some form
of a constant pressure apparatus is employed. The major exception to
this statement is found where very small organisms (mites, collembola,
etc.) are concerned, and then the Cartesian diver apparatus (a constant
volume type) is used. Several studies employ some method of estimating
respiration rate by CO, production. This usually involves capturing the
CO, in a standard basic solution, thus converting the base to a salt and
then titrating the remaining base with an aoid standard. It must be
kept in mind that in energetics studies the number of units of 0, respired is not so important to know as the number of calories represented
by this respiration, because it is an estimate of the amount of heat the
population loses in the process of maintenance. Conceivably, it should
be possible to measure the heat production directly via calorimetry in
the field. However, at present the technique required for direct field
calorimetry has not yet been attempted.
Growth rates are measured either in the 5eld or in the laboratory
where the animals are kept in cages or culture,g. Each approach presents
problems. In the laboratory, growth rates ca2 be measured very accurately, but the conditions under which the animals are kept are not those
of the field. Field studies, on the other hand, have the advantage of
natural surroundings, normal activities, and usual diets, but present the
problem of measuring and keeping track of the growth rates of particular individuals. Still another approach to the measurement of growth
rates is that of deducing them from the numbers of individuals found in
various size categories during successive field samplings. This approach
is particularly useful for the meiofauna and the microfauna where marking, release, and recapture techniques have not yet been worked out.
Data on death rates are obtained in the r3ame way as are data on
growth rates. Cage or culture studies, however, yield only data on deaths
resulting from physiological limitations, and the survival rate is higher
than that found in field populations due to the absence of predation.
The most reasonable approach at this time seems to be the construction of a life table (Allee ct al., 1949, page 265) from laboratory or enclosure data, and the adjustment of this table to field conditions. One
of the most complete life tables we have for ,an animal other than man