ENERGETICS A N D A N I M A L PRODUCTIVITY
79
different species populations could alter their importance to the community. His methods, however, were not utiltced by others working on
natural communities and his work remains a solitary landmark in the
literature. To be sure, the engine-like nature of the living organism was
elucidated by Lavoisier in 1777 and many workers through the years
turned their attention to the bioenergetics of animals. All these works,
however, were concerned with single individuals of either man or
domestic species (Atwater and Benedict, 1903; Armsby, 1903; Brody,
1945).
Ecologists of the 1940’s and 1950’s presumably had the techniques
and information available to carry out energetic studies on terrestrial
communities. Why were not these studies carried out earlier? There is
no certain answer to this question, but part of the explanation lies in the
different characteristics of the two major envJronments (terrestrial versus aquatic), as well as in the elements of human whim and communication. The aquatic environment is easily definable with rather clear-cut
boundaries. The majority of the physical components of the liquid
environment can be measured by simple chemical tests. The portions
of an aquatic environment stay relatively congtant during the die1 cycle
and have a limited range of variation during the annual cycle. Last and
by no means least, most aquatic environments have a biota which is
taxonomically well defined and not tremendously complex. On the
other hand, the terrestrial situation is very complex. For example,
moisture variation from day to day and place to place has a tremendous
influence on the biota of an area and poses a formidable measurement
problem for the investigator. Moisture can precipitate in an area in the
form of rain, snow, sleet, or dew, and can be lost in the area as run-off
or evaporation. A single aspect of the moisture content of the air can be
recorded as relative humidity, vapor pressure, saturation deficit, absolute humidity, specific humidity, and mixing ratio (Platt and Griffiths,
1964). The obvious variability of the physical terrestrial environment is
one of the deterrents to a complete energetics study.
The biological elements of this environment further complicate the
matter. Many of the taxa important to terrestrial communities are
poorly known. It has been stated in the literature that there are about
650 000 species of described insects in the world (Metcalf and Flint,
1939), and it is estimated that 2 500 000 species exist at this time.
The insects are an important component of every terrestrial community,
both from the standpoint of numbers and of ,activity. Thus, almost half
the species present in the natural community are not as yet recognized
by science. Taxonomically, the insects are well knQwn when compared
to some other taxa such as mites or nematodes. Furthermore, the number of species present in any single area may be great. Evans (1964), for
79
different species populations could alter their importance to the community. His methods, however, were not utiltced by others working on
natural communities and his work remains a solitary landmark in the
literature. To be sure, the engine-like nature of the living organism was
elucidated by Lavoisier in 1777 and many workers through the years
turned their attention to the bioenergetics of animals. All these works,
however, were concerned with single individuals of either man or
domestic species (Atwater and Benedict, 1903; Armsby, 1903; Brody,
1945).
Ecologists of the 1940’s and 1950’s presumably had the techniques
and information available to carry out energetic studies on terrestrial
communities. Why were not these studies carried out earlier? There is
no certain answer to this question, but part of the explanation lies in the
different characteristics of the two major envJronments (terrestrial versus aquatic), as well as in the elements of human whim and communication. The aquatic environment is easily definable with rather clear-cut
boundaries. The majority of the physical components of the liquid
environment can be measured by simple chemical tests. The portions
of an aquatic environment stay relatively congtant during the die1 cycle
and have a limited range of variation during the annual cycle. Last and
by no means least, most aquatic environments have a biota which is
taxonomically well defined and not tremendously complex. On the
other hand, the terrestrial situation is very complex. For example,
moisture variation from day to day and place to place has a tremendous
influence on the biota of an area and poses a formidable measurement
problem for the investigator. Moisture can precipitate in an area in the
form of rain, snow, sleet, or dew, and can be lost in the area as run-off
or evaporation. A single aspect of the moisture content of the air can be
recorded as relative humidity, vapor pressure, saturation deficit, absolute humidity, specific humidity, and mixing ratio (Platt and Griffiths,
1964). The obvious variability of the physical terrestrial environment is
one of the deterrents to a complete energetics study.
The biological elements of this environment further complicate the
matter. Many of the taxa important to terrestrial communities are
poorly known. It has been stated in the literature that there are about
650 000 species of described insects in the world (Metcalf and Flint,
1939), and it is estimated that 2 500 000 species exist at this time.
The insects are an important component of every terrestrial community,
both from the standpoint of numbers and of ,activity. Thus, almost half
the species present in the natural community are not as yet recognized
by science. Taxonomically, the insects are well knQwn when compared
to some other taxa such as mites or nematodes. Furthermore, the number of species present in any single area may be great. Evans (1964), for