Environmental Engineering Reference
In-Depth Information
Heterotroph sizes range over eight orders of magnitude, from the numerous micro-
bial decomposers to the largest marine mammals (blue whales,
Balaenoptera mus-
culus
, with maximum lengths of more than 30 m).
The term
zoomass
is used much less frequently than phytomass and easily evokes
images of thousands of cattle packed in America's beef feedlots or large herds of
migrating wildebeests and caribou or multiple V-shaped l ocks of high-l ying Canada
geese—but not of bacterial decomposers or insects. But the total fresh-weight
zoomass density of different termite species can add up to more than twice as much
(on the order of 100 kg/ha) as the biomass of elephants (Inoue et al. 2001). The
term zoomass is used infrequently when referring to zooplankton or to insect
biomass and is usually reserved for vertebrates. The abundance of small-scale studies
of microbial and fungal biomass contrasts with the still very rare zoomass estimates
on large (biome, continental) scales.
Quantii cations of invertebrate and vertebrate zoomass have similar limitations:
i eld data make it easy to calculate the resident zoomass of lions or wildebeests
within their respective home ranges in some national parks, but there are no reliable
accounts of the total zoomass of wild ungulate herbivores or top carnivores in a
biome or at the global level. The only possible, and very minor, addition to hetero-
trophic biomass could be made by including viruses: they have, of course, no intrin-
sic metabolism, but they exert enormous inl uence on the survival and productivity
of cellular organisms, especially in the ocean, where recent research has shown them
to be the most abundant entities containing nucleic acids (Fuhrman 1999; Brum
2005).
Biomass Carbon
An excellent alternative to using absolutely dry mass is to use
carbon
as the common
denominator for all phytomass comparisons (I will explain the inevitable complica-
tions and uncertainties associated with this choice when taking a closer look at
specii c harvests). Life's structural unity means that all biomass is made up of the
same kinds of carbon-based macromolecular
polymers,
which must be synthesized
from a limited number of
monomers
(their simpler subunits): more than 90% of
biomass is made up of only about 50 different compounds, including 21 amino
acids, 15 monosaccharides, 10 fatty acids, and i ve nucleotides. Dry biomass is
mostly composed of just four kinds of polymers, two of an aperiodic kind (nucleic
acids and proteins) and two classes of periodic polymers (carbohydrates and lipids)
that act as long-term energy stores and structural components.
