Environmental Engineering Reference
In-Depth Information
yields rates of 50-300 kg/km
2
for eland (
Taurotragus oryx
), about 70 kg/km
2
for
zebra (
Equus zebra
), and 30-200 kg/km
2
for wildebeest (
Connochaetes gnu
). The
African elephant (
Loxodonta africana
), the largest surviving terrestrial mammal, has
its highest densities (in excess of 3,000 kg/km
2
) on natural grasslands in the eastern
part of the continent; the rate can be an order of magnitude lower on transformed
grassland and in most parts of West Africa (Sinsin et al. 2002). But even the smaller
forest elephant (
L. africana cyclotis
) can have a biomass of 2,000-3,000 kg/km
2
(White 1994; Morgan 2007). In contrast, the biomass density of all small mammals
(mostly rodents) in temperate grasslands and forests rarely surpasses 3 kg/ha, and
their most common biomass densities are less than 1 kg/ha (French et al. 1976;
Smith and Urness 1984).
Finally, the zoomass densities of chimpanzees (
Pan troglodytes
), mammals that
are genetically closest to humans: in Tanzania's Gombe Stream National Park there
are more than i ve animals/km
2
(Pusey et al. 2005), but this community, habituated
to humans, is now surrounded by densely inhabited and cultivated areas. Its former
chimpanzee densities were between 1.29 and 1.93 individuals/km
2
, in line with
typical counts in the forests of East and Central Africa: 1.45-2.43 and 1.45-1.95
in, respectively, Uganda's Kibale National Park and Budongo Forest Reserve, and
2.2 in Congo's Odzala National Park (Bernstein and Smith 1979; Ghiglieri 1984;
Bermejo 1999; Williams et al. 2002; Plumptre and Cox 2006).
Chimpanzee densities are lower in northern Congo (0.33-1.75 individuals/km
2
),
while a long-term mean in Côte d'Ivoire's Taï National Park was 2.8-3.2 animals/km
2
between 1982 and 1996 (Boesch and Boesch-Achermann 2000); more recent numbers
have ranged between 1.03 and 2.14 (Lehmann and Boesch 2003; Devos et al. 2008).
There are both interannual and seasonal density variations in all studied populations.
The population structure of chimpanzee groups is dominated by smaller females
and infants, resulting in an average body mass of only about 25 kg/animal, compared
to about 40 kg/adult male and 34 kg/adult female. This results in average zoomass
densities ranging from highs of more 100 kg/km
2
to lows of less than 25 kg/km
2
.
Inevitably, aggregate mammalian densities decline when expressed as averages
for large regions or for biomes: at those scales, only savannas and some tropical
forests harbor in excess of 2 g/m
2
, while the mammalian zoomass in most equatorial
and montane rain forests as well as in temperate woodlands is below 1 g/m
2
(Prins
and Reitsma 1989; Plumptre and Harris 1995), and totals for avifaunas usually do
not surpass 0.05 g/m
2
(Edmonds 1974; Reagan and Waide 1996). Continental
zoomass means are less than 1 g/m
2
, and hence their actual precise rates make little
difference in counting the planetary biomass: unavoidable errors in estimating the
