Agriculture Reference
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In woodlands in Alberta (Canada), Hassall et al. (1986) have related vertical migra-
tions in populations of Onychiurus subtenuis to moisture conditions in the litter layers.
Populations that were concentrated in the deeper litter horizons during dry periods
returned to the surface liner layers within a few hours after summer rain storms and
remained there until the litter dried out again. These movements were instigated by
the development of populations of highly palatable micro-organisms in the surface
litter, including yeasts and the fungus Cladiosporum.
The horizontal distribution of Collembola is often highly aggregated at small spatial
scales, as some species may form colonies of 8 to 30 cm diameter (Kühnelt, 1961).
There is some evidence that this aggregation may be caused by the production of chemical
signals (pheromones) which attract the animals to the most suitable micro-environments
(Joose, 1970; Verhoef and Nagelkenke, 1977). At a meso-scale, local variation in litter
abundance and quality and/or microclimate may affect population distribution. Where
cushion-like vegetation forms or tussocks occur (see e.g., Stanton and Tepedino, 1977;
Garay, 1981b; Athias, 1976), Collembola generally accumulate in these structures. At a
regional scale such factors as land use practices (see, e.g., Massot and Cancela da Fonseca,
1986; Lagerlöf, 1987), humus type (Ponge, 1983) and local differences in soil moisture
status, depth, light and soil type (Ponge, 1980) influence the abundance and composition
of collembolan communities.
Seasonal variation
Seasonal variation has been observed on many occasions and in Swedish grasslands at
Spiboke, density was at a maximum in winter and a minimum in summer
(65,800) (Persson and Lohm, 1977). However, most euedaphic and hemiedaphic species
may reproduce during any favourable period throughout the year. Consequently, in soils
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