Small-island effect in snake communities on islands of an inundated lake: The need to include zeroes

The small-island effect (SIE), i.e. the pattern that species richness on islands below a certain threshold area varies independently of area, has become a widely accepted part of the theoretical framework of island biogeography and biodiversity research. However, because very few previously published datasets include islands without species, the role of S = 0 in generating the SIE is rarely examined. Here, we tested the role of S = 0 in generating the SIE for the first time by using snake data collected on 48 islands in the Thousand Island Lake, China. To determine the role of S = 0 in generating the SIE, we used regression analysis and path analysis to conduct separate analyses for all the islands (including islands with no snake records) and for the 29 islands inhabited by snakes. When including islands with no snakes, model selection based on AIC(c) identified the left-horizontal SIE model as the most parsimonious model. When excluding islands with no snakes, model selection based on AIC(c) identified the simple logarithm model without an SIE as the best model. Path analysis detected an SIE for the full dataset, but none for the dataset excluding islands with no snakes. Our results suggest that S = 0 plays an important role in generating the SIE and excluding islands with no snakes can lead to erroneously not detecting an SIE when in fact an SIE exists. We conclude that, for the robust detection of the SIE, islands with no species should not be excluded in future studies.