Agriculture Reference
In-Depth Information
different environmental factors. These include the availability and the quality of food as well as
physical and chemical factors that can affect the earthworms directly or indirectly, modifying the
availability of food and other biotic factors like competition. Finally, life histories depend on the
different components of the life cycle of each earthworm species.
Different species of earthworms have quite different life histories, behaviors, and environmental
requirements occupying different ecological niches. They have been formally classified into three
major ecological categories based primarily on their feeding and burrowing strategies (Bouch
1977): epigeic, endogeic, and anecic.
species are essentially litter dwellers; they live in organic horizons in or near the surface
litter and feed primarily on coarse particulate organic matter, ingesting large amounts of undecom-
posed litter. These species produce ephemeral burrows into the mineral soil for periods of diapause,
so most of their activities and effects are limited primarily to the upper few centimeters of the soil-
litter interface. They are essentially Ñlitter transformers.Ò They are typically small, uniformly
pigmented species with high metabolic and reproductive rates, which represent adaptations to the
highly variable environmental conditions at the soil surface. In habitable tropical regions, earth-
worms in this category can be found aboveground in microbially rich accumulations of soil and
water in the axils of plants such as Bromeliaceae (Lavelle and Barois 1984). When the environmental
conditions within heterotrophic decomposition systems are unsuitable or food is limited, epigeic
species are difficult to find, despite their great potential for rapid reproduction. This group of epigeic
species includes
Epigeic
Lumbricus rubellus, Eisenia fetida, Eisenia andrei, Dendrobaena rubida, Eudrilus
eugeniae,
Perionyx excavatus,
and
Eiseniella tetraedra
.
earthworm species live deeper in the soil profile and feed primarily on both soil and
associated organic matter. They have little pigmentation, and they generally construct horizontal,
deep-branching burrow systems that fill with cast material as they move through the organic-mineral
layer of the soil. Earthworms of this type can burrow deep into soils, and unlike r-selected epigeic
species of earthworms, they are k-selected species (Satchell 1980; Lavelle 1983) that require a
much longer time to achieve their maximum weight and appear to be more tolerant of periods of
starvation than are epigeic species (Lakhani and Satchell 1970). These species are apparently of
no major importance in litter incorporation and decomposition because they feed on subsurface
soil material; they are important in other soil formation processes, including root decomposition,
soil mixing, and aeration. Species such as
Endogeic
Allolobophora caliginosa, Aporrectoedea rosea,
and
Octolasion cyaneum
are included in this endogeic group of species.
earthworm species live in more or less permanent vertical burrow systems that may
extend several meters into the soil profile. The permanent burrows of anecic earthworms create a
microclimatic gradient, and the earthworms can be found at either shallow levels or deep in their
burrows, depending on the prevailing soil environmental conditions. They cast at the soil surface
and emerge at night to feed primarily on surface litter, manure, and other partially decomposed
organic matter, which they pull down into their burrows. Some anecic species also may create
heaps of cast material termed
Anecic
at the burrow entrance; these consist of a mixture of cast,
soil, and partially incorporated surface litter. Characteristically, these earthworms are large in size
as adults and dark in color anteriorly and dorsally; their reproduction rates are relatively slow.
Anecic species of earthworms, intermediate on the r-k scale (Satchell 1980; Lavelle 1983; Lavelle
and Barois 1988), are very important agents in organic matter decomposition, nutrient cycling, and
soil formation, accelerating the pedological processes in soils worldwide.
middens
Lumbricus terrestris
,
Aporrectodea trapezoides,
and
Allolobophora longa
are included in this ecological anecic group
of earthworms.
EARTHWORM SPECIES SUITABLE FOR VERMICOMPOSTING
Looking at this general ecological grouping, it is obvious that only epigeic species can be expected
to be suitable for vermiculture and vermicomposting. Moreover, to consider a species suitable for
