ON THE EFFECTIVENESS OF ARTIFICIAL SHELTERS IN THE STUDY OF POPULATION ATTRIBUTES OF SMALL TERRESTRIAL GASTROPODS

The proportions of replicated, artificial populations found adhering to the lower surfaces of shelters (squares of masonite) from May-July averaged 20% for Discus cronkhitei and 33% for Euconulus fulvus. Variation between inspections in the numbers of both species recorded adhering to the shelters was influenced by both temperature (fewer snails were recorded when mean temperatures for the preceding 24 h were <7.5°C and >17.5°C), and precipitation (fewer snails were recorded when >2 mm of precipitation were recorded in the previous 48 h than when <2 mm fell). Numbers of individuals of each species on each plot declined annually over the 3-month period, from an initial density of 50 to a final average density of 5 individuals/m2. This loss was related to mortality in situ (c12% in each species over 1987 and 1988), the remainder disappearing from the plots probably as the result of dispersal during periods of heavy precipitation. -from Author