Agriculture Reference
In-Depth Information
fragments of dead grasses and forbs but will also consume leaves of the shrub
Larrea
tridentata
and the faeces of large herbivores when its preferred food is in short
supply (Whitford, 1991). Similarly, the African grass harvester
Trinervitermes trinervius
may change to feeding on dead wood during drought conditions (Lepage, 1974).
Over all environments, the wood and litter feeders are probably the most important
ecologically because of their widespread distributions and numerical preponderance in
terms of both species and individuals. In addition, with the grass harvesters, they are
the major initial processors of the dead organic matter produced by plants. Substantial
overlaps occur between the first three groups in the food materials they gather, from
their environments. However, it seems desirable to separate them since their biological
and pedological effects may differ substantially. Because of their dietary flexibility,
many economic pests are represented among the polyphagous species. No overlap in
feeding habits occurs between the soil feeders and those of the first three groups
(Noirot, 1992) although some members of the soil-wood feeder group are reported to feed
partly on relatively sound wood (Miller, 1991).
The fungus cultivators (Macrotermitinae) include both litter and wood feeders
(Darlington, 1994). As considered below, they break down their food materials in a much
more complete way than other groups and have different effects on soils. This group
may be worthy of separate categorisation because of the distinctive ecological and
pedological effects of its members.
5.2.2
BIOGENIC STRUCTURES IN THE TERMITOSPHERE
5.2.2.1
Nests and nest materials
Nest types
Termites nest in a range of locations (Chapter III.4.3.2.2 and Table IV.20). Many species
nest and feed within their foodstuffs while others build nests in locations often, but
not necessarily, closely associated with their food materials and exploit the resources
of their surrounding territories. As shown below, the nests of certain species may not
be confined to one location and a single colony may have more than one nest within
its territory.
Termite nests and other constructions are built by a combination of excavation
and construction (Noirot, 1970). Excavation in wood is considered the most primitive
since it most closely resembles the behaviour of the presumedly-ancestral, wood-feed-
ing cockroaches. Some form of construction is always present in termite nests. This may
range from a simple lining of galleries with faeces to the construction of highly-
elaborate nest structures. The materials used in the construction of termite mounds
include earthen and little-digested plant materials and these may be diluted, softened or
cemented by saliva or faecal materials. In certain types of construction, faecal materials
may comprise much of the mass.
The materials comprising nests and other termite constructions may be of four major
types (Wood, 1996):
(i)
Those built largely of repacked, orally-transported mineral soil materials with
