Agriculture Reference
In-Depth Information
must have arrived with nursery stock or other plant materials used in landscaping. Species of
Lumbricidae are present in Costa Rican montane forests at an elevation of 2000 m near Heredia
and in similar habitats in Venezuela. Significantly, the peregrine Lumbricidae are now the only
earthworms currently present in large areas of glaciated North America and Eurasia, where they
are modifying soils and litter decomposition dynamics, but this subject is discussed below. A later
wave of immigrant earthworms from temperate Asia (probably Japan) is now progressing through
North American soils. The most important of these is
Amynthas hilgendorfi
Michaelsen 1892, which
may be a range of parthenogenetic morphs.
In tropical climates, a different set of exotic species is now distributed globally, dominated by
the ubiquitous
Mller 1856, a member of the South American family
Glossoscolecidae. This species is believed to have originated in northeast South America, where
the rest of its congenitors are found (Righi 1984). This earthworm is now abundant in all tropical
areas where rainfall is adequate to support earthworm activity for at least a few months each year.
It lives in lowland evergreen tropical forests up to cloud forests along elevational transects in high
rainfall areas and can maintain populations in seasonally tropical dry forests, including some with
xerophytic vegetation. It also prospers under agricultural conditions, including pastures, tree plan-
tations, row crops, and paddies (along the margins, not in flooded soils). Reforestation programs
using root-ball planting stock provide another means of dispersal of these species, and in many
places in Southeast Asia and Fiji, only the disturbance of logging and the probable movement of
Pontoscolex corethrurus
P. corethrurus
on heavy equipment was required for virtual elimination of the native species and
introduction and establishment of this exotic species.
Some other widespread tropical peregrine earthworm species are
Dichogaster
affinis, Eudrilus eugeniae, Drawida barwelli, Pithemera bicincta, Perionyx excavatus, Amynthas
corticis
Dichogaster bolaui
,
(Fragoso et al. 1999). Of these, the most important is probably
the last because it is capable of surviving in a broad range of environmental conditions and has been
blamed for degradation of soil structure in some agricultural settings (Shah and Patel 1978). Some
of the species in this list are used in vermicomposting and so are maintained in cultures even where
they cannot survive ambient winter temperatures.
, and
Polypheretima elongata
CRITERIA OF EXOTIC EARTHWORM
We have mentioned briefly some criteria for determining whether an earthworm is an exotic species.
Essentially, it requires broad knowledge of the global or regional distribution of the larger taxon
to which the species belongs. Thus, if outside South America and some neighboring areas (Central
America and a few Caribbean islands), a glossoscolecid such as
is clearly an exotic
species because that family is otherwise confined to South America and its environs (Righi 1972;
Fragoso et al. 1995). Similarly, a species of the exclusively African family Eudrilidae would be
exotic on any other continent, and even within Africa it is exotic north of the Sahara and south of
the Kalahari deserts. The problem is harder when the larger taxon has a wider global distribution,
such as the Lumbricidae, with species native to Europe and North America and a known direct
land connection prior to the opening of the Atlantic Ocean. In this case, the debate has raged longer
(Omodeo 1963) but was settled ultimately by the observation that the two genera occurring in
North America are completely absent from Europe, and there are no endemic North American
species of any, otherwise European, genera (Gates 1982). Furthermore, the same members of
European lumbricid genera that are found in North America are also found in temperate zones of
other continents. Looking in more detail at earthworm distributions in Europe, it is clear that the
peregrine species are the only earthworms in the northern regions of the continent, whereas in
southern Europe, a very diverse earthworm fauna exists. Thus, the peregrine species are only a
small subset of the total, a pattern that is repeated in all higher earthworm taxa containing peregrine
species.
P. corethrurus
