Using biogeographical patterns of endemic land snails to improve conservation planning for limestone karsts

Abstract

Limestone karsts on tropical land masses are considered de facto habitat islands due to their isolation from one another by non-calcareous substrata; this spatial configuration limits gene flow and induces high levels of species endemism. Apart from their biological importance, karsts are also highly valued for the ecosystem services and resources they provide if left intact. Unfortunately, conservation planning for karsts has generally lacked scientific basis. Ideally, factors affecting the richness and distribution of karst-endemic taxa should be incorporated into quantitative guidelines for karst reserve selection. Using land snail data from 43 different karstic towers in Malaysia, we: (1) identified biogeographical factors (i.e., area, isolation, surrounding soil type and geological age) hypothesized to influence endemic richness; and (2) investigated how species distributions varied among karsts in different regions. Generalized linear mixed-effect models revealed the relatively important effects of surrounding soil type and karst area on land snail endemism; the most parsimonious model contributed to 63.6% of the Akaike's Information Criterion weight and explained over 18% of the deviance in karst-endemic richness (of which 10.0% was explained by surrounding soil type). Non-metric multi-dimensional scaling indicated that karsts in different regions of Malaysia had distinct malacofaunas. Therefore, conservation planners should take into account karst size, surrounding soil type and the influence of geographic barriers to maximize the protection of land snails and possibly other karst-endemic taxa, which are increasingly threatened by quarrying throughout Southeast Asia.