Population studies on the land planarian Artioposthia triangulata (Dendy) at natural and horticultural sites in New Zealand

Abstract

Morphometric data and general observations of habitat conditions are presented for populations of the land planarian Artioposthia triangulata at natural and horticultural sites in New Zealand. A considerable variation in size structure was apparent, the overall weight range for egg capsules being 86 and 396 mg fwt (up to a 4-fold difference), and that for flatworms being 28–2316 mg fwt (juveniles to adults). The number of hatchlings emerging per egg capsule ranged from 1–14. Densities as high as 16 flatworms m −2 and 70 egg capsules m −2 could be found in natural areas beneath pine logs felled just one year previously. Densities of 6 flatworms m −2 and 25 egg capsules m −2 occurred at a horticultural site in Christchurch. The mean individual weights of both egg capsules and flatworms were significantly greater at natural sites than horticultural sites, this being related to habitat conditions (prey availability and micro-climate) and the associated age structure of the population. Prey availability appears to be the main factor regulating population density. Many similarities between indigenous A. triangulata populations in New Zealand and populations resulting from accidental introduction in north-west Europe are revealed. Although this species is not considered a problem in its native land, owing to passive spread via horticultural trade and thereby introduction to high suitability habitats, it is likely to prove a threat to introduced European lumbricid populations in gardens and agricultural areas in New Zealand, so having implications for soil quality.