Environmental factors influencing the presence and abundance of a log-dwelling invertebrate, Euperipatoides rowelli (Onychophora: Peripatopsidae)

Patterns of habitat selection by American mink Mustela vison within foraging areas located on the shore, were studied in a coastal environment of Scotland from November to March in 1983/84, 1984/85 and 1994/95. The abundance of prey in the intertidal zone was modelled in relation to abiotic environmental characteristics. Four factors were found to be important predictors of prey abundance: the position within the tidal zone, the abundance and size of rockpools, the nature of the substratum and the presence of fresh water streams. The model was used to predict prey abundance in different areas of the shore. We then investigated whether mink were choosing areas with higher prey abundance at different tidal levels and within, as opposed to between, core areas (areas with a relatively high density of fixes, encompassing usually one or more dens). Only when foraging at low or mid-tide and within core areas were mink found to behave selectively. They showed no significant preference for areas rich in prey when foraging at high tide and between core areas. Mink were also found to avoid areas with fresh water streams and to prefer foraging in the mid-tide zone. The findings are discussed in relation to prey abundance and competition with the otter Lutra lutra.The microenvironments of decaying logs support a large invertebrate fauna, but are vulnerable to the effects of logging and land-clearing. We present an analysis of the relationship between a number of environmental variables and the occurrence and abundance of the onychophoran Euperipatoides rowelli within decomposing logs in a forest in south-eastern Australia. Aspect of slope is strongly associated with most of the environmental variables and is a good predictor of both presence and abundance of animals in logs; south-easterly slopes show higher levels of log colonization, larger populations within logs and a larger median weight of both males and females than north-westerly facing slopes. Degradation state of logs, log length, presence of termites and shrub cover are also associated with the presence of onychophorans, while log volume shows the most marked association with abundance. Euperipatoides rowelli prefers wetter logs, although there is considerable overlap between relative water content of logs with and without onychophorans. Log degradation state, an important factor in the presence of animals, is associated with years since felling, and our data indicate that logs become capable of supporting large populations of E. rowelli after a minimum of 45 years of decay. Thus future logging practices have important implications for the maintenance of suitable log environments for this species, and this result may be generalized to other log-reliant fauna.