The density of empty shells, not habitat cover or quality, predicts the density of live Rhagada snails

Abstract

Camaenid land snails are often the focus of targeted biodiversity surveys in Australia, but can be difficult to locate because they hibernate for most of the year. Searches would be more effective if the density of live snails could be predicted from features of the habitat, or from the abundance of empty shells from long dead individuals. In 53 populations of Rhagada, the dominant genus of land snail in the Pilbara bioregion of Western Australia, the density of live snails is not correlated with the cover or height of spinifex (Triodia), the main habitat plant occupied by Rhagada. On the other hand, the density of empty shells on the soil surface does explain snail population density, but the relationship is weak (r²=0.209). Nevertheless, the data suggest that searches for live Rhagada are more likely to succeed in areas where empty shells are most abundant.

Keywords:

• population density
• land snail
• Camaenidae
• Pilbara bioregion
• Western Australia
• short-range endemic

Acknowledgements

I thank Jeremy Feichtinger and Robert MacDonald for assistance with the fieldwork. Two anonymous reviewers provided comments that improved the manuscript. The Department of Environment and Conservation, Western Australia (Karratha) provided transport to Rosemary Island. Financial support was provided by Woodside Energy Ltd, Rio Tinto, The University of Western Australia School of Animal Biology, an Australian Postgraduate Award, and the Department of Environment and Conservation, Western Australia.