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Accounting for detectability improves estimates of species richness in tropical bat surveys
Author(s) -
Meyer Christoph F. J.,
Aguiar Ludmilla M. S.,
Aguirre Luis F.,
Baumgarten Julio,
Clarke Frank M.,
Cosson JeanFrançois,
Villegas Sergio Estrada,
Fahr Jakob,
Faria Deborah,
Furey Neil,
Henry Mickaël,
Hodgkison Robert,
Jenkins Richard K. B.,
Jung Kirsten G.,
Kingston Tigga,
Kunz Thomas H.,
Cristina MacSwiney Gonzalez María,
Moya Isabel,
Patterson Bruce D.,
Pons JeanMarc,
Racey Paul A.,
Rex Katja,
Sampaio Erica M.,
Solari Sergio,
Stoner Kathryn E.,
Voigt Christian C.,
von Staden Dietrich,
Weise Christa D.,
Kalko Elisabeth K. V.
Publication year - 2011
Publication title -
journal of applied ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.503
H-Index - 181
eISSN - 1365-2664
pISSN - 0021-8901
DOI - 10.1111/j.1365-2664.2011.01976.x
Subject(s) - species richness , environmental science , geography , ecology , econometrics , statistics , mathematics , biology
Summary 1. Species richness is a state variable of some interest in monitoring programmes but raw species counts are often biased due to imperfect species detectability. Therefore, monitoring programmes should quantify detectability for target taxa to assess whether it varies over temporal or spatial scales. We assessed the potential for tropical bat monitoring programmes to reliably estimate trends in species richness. 2. Using data from 25 bat assemblages from the Old and New World tropics, we estimated detectability for all species in an assemblage (mean proportion of species detected per sampling plot) and for individual species (species‐specific detectability). We further assessed how these estimates of detectability were affected by external sources of variation relating to time, space, survey effort and biological traits. 3. The mean proportion of species detected across 96 sampling plots was estimated at 0·76 (range 0·57–1·00) and was significantly greater for phytophagous than for animalivorous species. Species‐averaged detectability for phytophagous species was influenced by the number of surveys and season, whereas the number of surveys and sampling methods [ground‐ or canopy‐level mist nets, harp traps and acoustic sampling (AS)] most strongly affected estimates of detectability for animalivorous bats. Species‐specific detectability averaged 0·4 and was highly heterogeneous across 232 species, with estimates ranging from 0·03 to 0·84. Species‐level detectability was influenced by a range of external factors such as location, season, or sampling method, suggesting that raw species counts may sometimes be strongly biased. 4.Synthesis and applications. Due to generally high species‐specific detection probabilities, Neotropical aerial insectivorous bats proved to be well suited for monitoring using AS. However, for species with low detectability, such as most gleaning animalivores or nectarivores, count data obtained in bat monitoring surveys must be corrected for detection bias. Our results indicate that species‐averaged detection probabilities will rarely approach 1 unless many surveys are conducted. Consequently, long‐term bat monitoring programmes need to adopt an estimation scheme that corrects for variation in detectability when comparing species richness over time and when making regional comparisons. Similar corrections will be needed for other species‐rich tropical taxa.