SOIL ORGANISMS - Soil Ecology - page 297

In the evolutionary sense, the largest and most advanced family is the Termitidae.
Members of this family are known as the 'higher' termites while those of the remaining
six families are known as the 'lower' termites. A true worker caste does not occur in the
lower termites and the digestive system also differs between the two groups. The hind
gut of most higher termites is longer, more differentiated in structure and comprises
a larger proportion of total gut length than it does in the relatively simple gut typical of
the lower and the fungus-cultivating termites (subfamily Macrotermitinae) of the higher
termites (Bignell, 1994). Lower termites possess protist gut symbionts that contribute to
their nutrition whereas those of the higher termites are mainly bacteria. In an obligate
symbiosis between the termite and the fungus, specific fungi are cultivated as a food
source within the termite mounds of species in the subfamily Macrotermitinae.
Emerson (1955) estimated that ca . 73 % of living species belonged to the family
Termitidae. However, over the last 20 years, most new genera described have been in the
higher termites (Pearce and Waite, 1994) which are therefore likely to comprise rather
more than the 73 % of existing species calculated by Emerson. Among the lower
termites, the Kalotermitidae ( ca. 16 % of species) and the Rhinotermitidae ( ca .8%of
species) are the largest families while the Hodotermitidae and the Termopsidae are small.
The Mastotermitidae and the Serritermitidae have only one living species each (Table III.14).
Termites are most prevalent in the tropics and sub tropics and are scarce or absent at
higher latitudes and at higher elevations within their normal latitudinal range of occurrence.
Within this range, both species and generic richness decline regularly with distance from
the equator in most continents. Australia appears to be an exception to this trend with no
group showing a consistent decline in species richness from the tropics to the temperate
latitudes (Abensperg-Traun and Steven, 1997b). Where it occurs, this trend may be due
to the decline of insolation and rainfall. Figure III. 48a presents estimates of species
richness for a number of sites in relation to latitude and across a range of different
environments. While collecting methods and sampling areas differed between the studies,
a clear reduction in species richness is apparent with increasing latitude. Figure. III 48b
presents the mean number of genera within five-degree latitudinal bands and shows that
generic richness also diminishes markedly with latitude but that the decline is steeper in
the northern hemisphere (Eggleton, 1994). The lower termites are best represented at
higher latitudes, most commonly by the families Termopsidae, Kalotermitidae and
Rhinotermitidae with some Hodotermitidae in the Palaearctic region. Species richness
also diminishes rapidly with increasing elevation. On a high mountain in Sarawak, the
number of species declined from 58 in the lowland Dipterocarp forest to 10 in the mon-
tane forests above 1000 m; no termites were found above 1860 m (Collins, 1983).
The termites are an ancient group and, at the family and generic levels, are unequally
represented in the various biogeographic regions of the world. Table III. 14 lists the bio-
geographic distributions of termite taxa at the family and subfamily levels (Pearce and
Waite, 1994). Members of subfamily Macrotermitinae (fungus cultivators) are distributed
through Africa, the Malagasy and the Indo-Malayan regions but are absent from the
Americas, Australia and the Palaearctic regions. Some genera are particularly widespread.
Amongst the lower termites, Coptotermes and Cryptotemes occur in all biogeographic
regions while Heterotermes is absent only from the Palaearctic region. In the higher
termites, Amitermes occurs in all biogeographic regions except the. Malagasy and