Agriculture Reference
In-Depth Information
Horizontal distribution
At a broad geographical scale, many species appear to be widely distributed (Swift
et al.
1979). Cryptostigmata such as
Tectocepheus velatus
(Mich.) and
Oppia nova
(Oudms)
have a world wide distribution across a wide diversity of habitats. New Zealand has a
largely cosmopolitan fauna and only the extreme habitats of Antarctica have a higher
degree of specific endemism (Anderson, 1977).
At a mesoscale, the distribution of acarine populations is influenced by (i) a frequent
tendency to population aggregation and (ii) the heterogeneity of vegetation and litter
inputs. In the moist African savannas of Lamto (Côte d'Ivoire) four groups of Acari had
highly aggregated distributions, seven were aggregated and four loosely aggregated.
Sixty six % of the individuals (in plots submitted to fire) to 81.8 % (in protected plots)
were found in soil under tussocks. In the latter case, however, the proportion varied from
36 to 88 % depending on the group. Five taxonomic groups out of 13 were significantly
associated with tussocks whereas two were significantly more numerous in bare soil
(Figure III.38).
Comparable effects of plant distribution and microtopography have been observed
in coastal Arctic tundra at Point Barrow (Alaska) (McLean, 1980) with an increasing
gradient of density from 'wet' to 'dry' areas. In general, mesoscale variations in temperature,
moisture, litter accumulation, or variation ascribed to litter quality (Garay 1981a; Asikidis
and Stamou, 1991) often influence the distributions of acarine populations. Nonetheless, a
few examples of relatively homogenous distribution patterns in field populations at the scale
of a few square metres have been reported (
e.g.,
Cancela da Fonseca
et al.,
1967).
Vertical distribution
In temperate climate forests, Acari typically inhabit the organic surface layers (L, F and
H) and the upper few centimetres of the mineral soil (see,
e.g.,
Anderson, 1971).
However, they may also penetrate much deeper into the soil (down to 40 and even
120-180 cm) in tropical and desert environments where holorganic layers are often
