Managing Earthworms as a Resource in Australian Pastures - Earthworm Ecology - page 253

rain falling during the winter months. Further east in Victoria and southern N.S.W., rain falls more
evenly throughout the year, and perhaps the resulting moister soils for more months in the year
are more suitable for building up earthworm communities. Intriguingly, native earthworms were

rare when total earthworm populations were highest in Victoria and vice versa ( Figure 14.1b ) . The

sites with the highest total earthworm population corresponded with the regions with the highest
rainfall and included a predominance of dairy pastures rather than sheep pastures, which were the
norm elsewhere. Whether the geographical switch in bias of the earthworm communities reflects
the abilities of exotic and native earthworm species to cope with climatic or agricultural management
variables or whether the patterns (in particular for the native species) relate to preagricultural habitat
types is not known. The possible role of competition among different earthworm species in
determining the observed distribution patterns is also not understood.
Although exotic species tend to dominate earthworm communities in pastures in southern
Australia, many pastures totally lack exotic species. It may be that such absences of exotic species
simply reflect a lack of opportunity to colonize them to date rather than that they are unsuitable
habitats. Environmental factors that determine the geographic distribution and population of the
earthworm fauna are poorly understood. Many autocorrelated variables (climatic, edaphic, land
use) are related weakly to earthworm abundance. Rainfall and soil particle size, somewhat under-
standably, may explain most of the variance (Baker 1998a).
Baker et al. (1997a) conducted a national survey, ÑEarthworms Downunder,Ò involving school-
children in 1992. This survey included sampling urban gardens as well as agricultural land.
Lumbricid earthworms predominated in both habitat types in southern Australia, but north of the
Tropic of Capricorn they were rare and were replaced by other introduced species such as

Pon-

(Glossoscolecidae). Thus, the most common earthworm species in disturbed
land in Australia are the peregrine lumbricid species identified by Lee (1985) and are similar to
those occurring in comparable habitats elsewhere in the world.
The common earthworm species in agricultural soils in southern Australia are endogeic, feeding
predominantly on decomposing organic matter that is already incorporated into the mineral soil
layer. These earthworms are active in the top 10 cm of soil for about 4 to 5 months of the year
(early winter to early spring), when the soils are moistest (Baker et al. 1992a, 1993c,d; Garnsey
1994b). During the drier summer months, most earthworms are inactive and deep in the soil. There
are very few anecic species in the earthworm fauna (i.e., species that feed at the soil surface and
burrow deeply during the active season). Such species have the potential to influence soil properties

toscolex corethrurus

markedly at depth (e.g., porosity) (see Chapter 10 , this volume), thus encouraging deeper penetration

of water, nutrients, and rooting of plants. In contrast to this paucity of anecic earthworm species
in pasture soils in southern Australia, earthworm communities in similar habitats in other parts of
the world are commonly dominated by anecic species (e.g., 70% of the earthworm biomass) (Lavelle
1983). One anecic species,

Aporrectodea longa , is common in pastures in northern Tasmania (Baker

1998a) (see further comments on the potential of extending the distribution of this species Ñ Intro-
ductions of Earthworm Taxa to New Areas Ò). Epigeic earthworm species, those that live near the

soil surface and feed on recently produced dead organic matter, are patchy in distribution and
abundance in southern Australia, but Lumbricus rubellus can be very abundant under moist con-

ditions. is more widespread but rarely abundant. It survives summer as resistant

cocoons (i.e., eggs) in the dry surface soil (Doube and Auhl 1998).
Several of the rarer native species of earthworms that occur in pastures are probably anecic,
but little attention has been paid to the ecology and behavior of these species. The giant Gippsland
earthworm

Microscolex dubius

(Megascolecidae) is perhaps the best-known native earthworm
in Australia because of its size and protected status, but even this species has been poorly studied
(van Praagh 1992).

Megascolides australis