The earthworm fauna of pastures in south-eastern Australia is dominated by
exotic lumbricid earthworms, in particular the endogeic species,
Aporrectodea caliginosa and
A. trapezoides. Anecic species such as
A. longa are very rare. All 3 species were introduced
within cages in 10 pastures on a range of soil types within the region. Five
months later, A. longa had generally survived the best
and A. trapezoides the worst. The survivals and weights
of individual worms varied between sites for all 3 species. The survivals of
A. caliginosa and A. longa, and to
a lesser extent A. trapezoides, were positively
correlated with soil clay content. The weights of
A. caliginosa and A. longa, but
not A. trapezoides, were positively correlated with soil
P content. The survivals and weights of A. longa and
A. trapezoides and the weights only of
A. caliginosa decreased with increasing inoculation
density, suggesting increased intraspecific competition for resources,
particularly in the first two species. A. longa reduced
the abundance and biomass of the exotic acanthodrilid earthworm,
Microscolex dubius, at one site, and the total biomass
of 3 native megascolecid species at another, when these latter species
occurred as contaminants in A. longa cages. The addition
of lime had no effect on the survivals and weights of
A. caliginosa, A. longa, and
A. trapezoides, although the soils were acid at the
sites tested. The addition of sheep dung increased the survival and weights of
some species at some sites. Mechanical disturbance of the soil within cages
reduced the survivals of A. longa and
A. trapezoides. A. longa was
released without being caged at 25 sites within one pasture in South
Australia. Four years later, it was recovered at all release points.
A. longa has the potential to colonise pastures widely
throughout the higher rainfall regions of south-eastern Australia.
Nonlinear Soil Change by Exotic Earthworms: Organisms as a Soil Forming Factor
