Abstract
When trying to predict biodiversity patterns, species absences in a community can be as informative as species presences. The concept of dark diversity considers geographical and ecological filters to set an expected species pool and to compare it with the observed species pool, through an index known as community completeness. Completeness shows no relationship with latitude, allowing the comparison of different communities and regions concerning community saturation. Here we propose the use of these methods to a better understanding of subterranean biodiversity patterns. We applied patterns of co-occurrence among phylogenetically related species to set the theoretical species pool and then compared it with the observed richness, using isopods as model taxon. Except for one cave, dark diversity was equal or higher than observed richness. Even though completeness was low in most cases, those caves with higher completeness represent a valuable sample of regional subterranean species pool and may act as a repository of diversity. Our study showed that the dark diversity approach is adaptable to studies of subterranean communities and may be coupled with other conservation tools towards more effective management decisions.
Highlights
Subterranean biodiversity patterns are marked by taxonomic and functional disharmony and by high species turnover (Gibert and Deharveng 2002) when compared to the surface fauna in the same region
In the five caves we sampled, we found six species of isopods
Most species were in the dark diversity (3.2 ± 1.3), even when a given species was distributed in other nearby caves
Summary
Subterranean biodiversity patterns are marked by taxonomic and functional disharmony (sensu Cardoso 2012) and by high species turnover (Gibert and Deharveng 2002) when compared to the surface fauna in the same region. High species turnover reflects the smaller ranges of obligate cave fauna (Barr and Holsinger 1985; Gibert and Deharveng 2002). The processes underlying these patterns are generally attributed to regional factors, such as high habitat fragmentation and long term stability (Gibert and Deharveng 2002), and to local influences, such as resource and habitat availability, competition, and predation (Culver 1981; Christman and Culver 2001; Culver 2012; Resende and Bichuette 2016). One way to understand the impact of these patterns on subterranean communities is by looking for those species whose presence was expected but are absent instead
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