Abstract
The insular limestone karsts of northern Vietnam harbor a very rich biodiversity. Many taxa are strongly associated with these environments, and individual species communities can differ considerably among karst areas. The exact processes that have shaped the biotic composition of these habitats, however, remain largely unknown. In this study, the role of two major processes for the assembly of snail communities on limestone karsts was investigated, interspecific competition and filtering of taxa due to geographical factors. Communities of operculate land snails of the genus Cyclophorus were studied using the dry and fluid‐preserved specimen collections of the Natural History Museum, London. Phylogenetic distances (based on a Bayesian analysis using DNA sequence data) and shell characters (based on 200 semilandmarks) were used as proxies for ecological similarity and were analyzed to reveal patterns of overdispersion (indicating competition) or clustering (indicating filtering) in observed communities compared to random communities. Among the seven studied karst areas, a total of 15 Cyclophorus lineages were found. Unique communities were present in each area. The analyses revealed phylogenetic overdispersion in six and morphological overdispersion in four of seven karst areas. The pattern of frequent phylogenetic overdispersion indicated that competition among lineages is the major process shaping the Cyclophorus communities studied. The Coastal Area, which was phylogenetically overdispersed, showed a clear morphological clustering, which could have been caused by similar ecological adaptations among taxa in this environment. Only the community in the Cuc Phuong Area showed a pattern of phylogenetic clustering, which was partly caused by an absence of a certain, phylogenetically very distinct group in this region. Filtering due to geographical factors could have been involved here. This study shows how museum collections can be used to examine community assembly and contributes to the understanding of the processes that have shaped karst communities in Vietnam.
Highlights
The limestone karst outcrops of Southeast and East Asia, such as those of northern Vietnam, are inhabited by exceptionally large numbers of plant and animal taxa (Clements et al, 2008; Do, 2001; Sterling, Hurley, & Le, 2006)
A relatively high number of different Cyclophorus species have been reported from northern Vietnam (Dang, 2008; Kobelt, 1908), and several taxa can be found on each of the larger karst outcrops (Vermeulen & Maassen, 2003), with individual communities being present in different limestone karst areas (P.V. and K.C.M. von Oheimb, personal observation)
For studying Cyclophorus communities in limestone karst habitats in northern Vietnam, study areas were defined a priori based on the following three criteria: (1) Each area must be located in a region where limestone karst is present (based on Dang (1996) and satellite imagery available via Google Earth Pro 7.1.8.3036; Google Inc., Mountain View, CA, USA); (2) each area must be characterized by a distinct and homogeneous Cyclophorus fauna; and (3) for each area, a comprehensive number of Cyclophorus samples must be present in the NHM collections, to ensure that the entire community has been sampled
Summary
The limestone karst outcrops of Southeast and East Asia, such as those of northern Vietnam, are inhabited by exceptionally large numbers of plant and animal taxa (Clements et al, 2008; Do, 2001; Sterling, Hurley, & Le, 2006). A relatively high number of different Cyclophorus species have been reported from northern Vietnam (Dang, 2008; Kobelt, 1908), and several taxa can be found on each of the larger karst outcrops (Vermeulen & Maassen, 2003), with individual communities being present in different limestone karst areas (P.V. and K.C.M. von Oheimb, personal observation). Related camaenid land snail taxa from the Bonin Islands in the Pacific Ocean, for example, have evolved different shell shapes, which correspond to different habitats (Chiba, 2004) Such mechanisms can cause a loss of correlation between phylogenetic relationship and ecology and may remain unnoticed when relying solely on data from molecular phylogenetics. This allows clarification of the assembly processes that have shaped Cyclophorus communities among northern Vietnam’s limestone karsts
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