SOIL ORGANISMS - Soil Ecology - page 313

4.3.2.4 Community structure

Determinants of community structure
Termite communities comprise species of differing ecological strategies. Community
complexity is determined by factors operating at different spatial scales. The large scale
factors are those of biogeographic, climatic and vegetational variation, while

topographic location and soil variability are influential at more local scales.
Differences in the presence or absence of certain taxa across biogeographic regions
are clearly important since some termite groups are absent from regions where in terms
of climate, they would be expected to readily survive. Examples include the absence
of the fungus cultivating termites (sub-family Macrotermitinae) from the Australian
and Neotropical biogeographic regions referred to above and the many incidences of
the successful spread of exotic termites through commerce. The recent establishment
of Mastotermes darwiniensis in Papua New Guinea is one example of this (Watson and
Gay, 1991). However peregrine termite species equivalent to earthworms with wide
geographical distribution do not exist (except as pests of buildings).
Climate varies systematically from the equator to the higher latitudes and termite
trophic groups react to this differently. Wood-feeding species form a greater proportion
of total species as latitude increases and may be the sole strategy represented at higher
latitudes (Abe, 1987). Conversely, the grass-harvesting termites are better represented
at lower latitudes.
The distribution of vegetation is clearly important to community structure at a
range of scales. At the broadest scale, the various biomes of the world offer different
opportunities to the various ecological groupings and this also pertains across vegetation
types at a local scale. Comparison of the termites of five habitat types in the tropical
Australian sites studied by Braithwaite et al. (1988) showed a different balance of troph-
ic groups between environments that ranged from monsoon forest (a dry rainforest
facies) to open forests, woodlands and two types of rockland. Commensurate with their
vegetation structure, no grass and grass-litter feeding species occurred in the monsoon
forest and wet rockland sites and less soil-feeding species were found in monsoon forests
than in open forest and woodland environments.
A somewhat contrasting trend, however, has been observed in Africa since the abun-
dance of humivorous species tends to decline from forest to moist savannas and drier
areas; they are also most sensitive to disturbances, possibly due to their inability to fix
nitrogen (Eggleton et al., 1996; Lepage, pers. comm.).
At a regional and local scale, the physical and other properties of certain soils may
also limit termite colonisation. In northern and central Queensland, few mound-building
termite species can tolerate the expansive nature of certain vertisols which shrink on
drying and swell when re-wet (Ratcliffe et al., 1952). Mound building termites are
virtually excluded from these soils although across abrupt lines of demarcation between
the vertisols and the adjacent sandy alfisols, mounds built by grass and litter-feeding termites
are populous. However, certain mound-building species are able to tolerate the expansive
qualities of these soils and Leprun and Roy-Noël (1976) record the mounds of the fungus-
cultivating species Macrotermes subhyalinus from vertisols in Senegal. At the coarser end
of the texture spectrum, the only Eucalyptus community type from which the widespread