Evaluating the sampling bias in pattern of subterranean species richness: combining approaches |
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Authors: | Maja Zagmajster David C Culver Mary C Christman Boris Sket |
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Institution: | (1) Oddelek za biologijo, Biotehniška fakulteta, Univerza v Ljubljani, Večna pot 111, p.p. 2995, 1000 Ljubljana, Slovenia;(2) Department of Environmental Science, American University, 4400 Massachusetts Ave, NW, Washington, DC, 20016, USA;(3) Department of Statistics—IFAS, University of Florida, PO Box 110339, Gainesville, FL 32611-0339, USA |
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Abstract: | We investigated the pattern of species richness of obligate subterranean (troglobiotic) beetles in caves in the northwestern
Balkans, given unequal and biased sampling. On the regional scale, we modeled the relationship between species numbers and
sampling intensity using an asymptotic Clench (Michaelis–Menten) function. On the local scale, we calculated Chao 2 species
richness estimates for 20 × 20 km grid cells, and investigated the distribution of uniques, species found in only one cave
within the grid cell. Cells having high positive residuals, those with above average species richness than expected according
to the Clench function, can be considered true hotspots. They were nearly identical to the observed areas of highest species
richness. As sampling intensity in a grid cell increases the expected number of uniques decreases for any fixed number of
species in the grid cell. High positive residuals show above average species richness for a certain level of sampling intensity
within a cell, so further sampling has the most potential for additional species. In some cells this was supported by high
numbers of uniques, also indicating insufficient sampling. Cells with low negative residuals have fewer species than would
be expected, and some of them also had a low number of uniques, both indicating sufficient sampling. By combining different
analyses in a novel way we were able to evaluate observed species richness pattern as well as identify, where further sampling
would be most beneficial. Approach we demonstrate is of broad interest to study of biota with high levels of endemism, small
distribution ranges and low catchability. |
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