Environmental Engineering Reference
In-Depth Information
Table 2.2
Densities of Bacterial and Invertebrate Biomass
Biomass Density (g/m
2
)
Organisms
Soil bacteria
10-1,000
Earthworms
Common densities
5-10
Maxima
>
100
Millipedes
1-5
All soil macrofauna
3-15
Ants
<
0.5
Termites
Common densities
1-3
Maxima
5-10
Total soil macrofauna
5-15
Note:
For data sources, see the text.
Ferreira 2003; Vasconcellos 2010). Zimmermann et al. (1982) found peaks of more
than 4,000 termites in tropical moist forest and wet savanna: assuming 2 mg/termite,
this translates to rates between 8 and 10 g/m
2
(table 2.2).
Mass per unit area is not an appropriate measure for l ying insects, and any
large-scale averages of biomass densities of small ectothermic vertebrates (mainly
frogs and snakes) are just statistical artifacts, as their densities are highly variable.
But reptiles and amphibians can dominate the vertebrate zoomass in some tropical
rain forests, where their overall density may rival that of invertebrates (Reagan and
Waide 1996). An abundance of terrestrial mammalian zoomass correlates with
individual body mass, but the expected decline in density with increasing body
weight is not, as formerly thought (Damuth 1981), a simple log-log linear relation-
ship with the allometric exponent of -0.75. Instead, the variation is distinctly non-
linear: only the populations of intermediate-sized mammals (body masses between
100 g and 100 kg) had allometric exponents close to the expected -0.75, while
heavier animals (100 kg to 3,000 kg) had exponents close to zero (Silva and
Downing 1995).
This means that among the nearly 1,000 studied mammalian populations, the
expected density of animals weighing 10 g would be about 1,000/km
2
, while there
would be only about 10 weighing 1 kg and one with a body mass of 100 kg—but
still nearly one weighing 1,000 kg. This would be only the best-i t values as the
actual densities for every mass category range over at least two (and even three)
