SOIL ORGANISMS - Soil Ecology - page 307

nation of the termites' own enzymes (Rouland et al ., 1990), possibly enzymes acquired
from their fungal symbiont (Martin, 1984; Slaytor, 1992) and perhaps from fermentation
in the hind gut (Breznak and Brune, 1994). However, Veivers et al. (1991) found no
evidence that micro-organisms play a significant role in digestion in these termites.
The African wood-feeding termite Sphaerotermes sphaerothorax is atypical of the
Macrotermitinae in that it has lost or perhaps never developed an association with
Termitomyces (Garnier-Sillam et al., 1989). In its place, external associations with
cellulolytic and N-fixing bacteria have evolved and these are considered further in
Chapter IV.
In sum, the tripartite action of the workers' enzymes, those of the hind gut microflora
and of the fungus Termitomyces combine to effect an almost complete breakdown of
the plant materials harvested by the fungus-cultivating termites (see, for example,
Garnier-Sillam et al., 1988b). The high proportion of food material organic matter
broken down has considerable ecological and pedological implications, as shown in
Chapter IV.

Carbon and nitrogen stable isotopes in termite foods. The values of termite
tissues reflect the relative proportions of and stable isotopes in termite bodies
and this provides useful information on their feeding habits. As occurs in other consumers,
values for their tissues are normally close (within 2 units) to those of the food that
they assimilate (Fry and Sherr, 1984). This relationship has been used to discriminate
between species that feed on wood, on tropical grasses and on a mixture of both
(Figure III.52, Spain and Reddell, 1996). It has also been used to identify the proportions
of grasses and broad leaf materials present in the diets of several African litter-feeding
termites (Boutton et al., 1983; Lepage et al., 1993).
Unlike the situation in most animals, the values of termite tissues vary over
a small range in wood-feeding species because the N fixation referred to above leads to
tissue values that are relatively close to that of the air (Tayasu et al., 1994; Spain et al.,
in prep., Figure III.52). However, termites that feed on partially-decomposed
litter have slightly higher tissue values (Tayasu et al., 1997, 1998), possibly
associated with a reduced requirement for N fixation consequent on the greater N
concentrations of their food materials (Slaytor and Chappell, 1994).

4.3.2.2 Ecological categories

While it is difficult to devise non-overlapping ecological classifications, broad classifi-
cations have been proposed, based on the types and variety of food materials used and
the locations of their nesting and feeding sites.
On the basis of their feeding habits, termites may be separated into five broad, some-
what-overlapping trophic groups (Josens, 1983; Eggleton et al., 1996), n amely:
(i) grass harvesters;

(ii) surface litter feeders;

(iii) wood-feeders;

(iv) soil-wood feeders; and

(v) soil-feeders (or humivores).