Non-linear thresholds in the effect of area on three dimensions of diversity of herpetofauna in the West Indies

AimThe small-island effect (SIE) describes an anomalous feature of the species-area relationship (SAR) on smaller compared to larger islands. However, previous studies on SIEs mainly focused on taxonomic diversity and overlooked phylogenetic and functional diversity. In this study, we explored SIEs in three dimensions of diversity. We expect to see the non-linear thresholds in the effect of area on three dimensions of diversity as well as on community structures, because the dominant assembly processes vary across spatial scales.LocationThe West Indies.TaxonHerpetofauna.MethodsWe derived data on the presence/absence of 199 amphibian species on 163 islands and 614 reptile species on 748 islands in the West Indies. We built a species-level phylogenetic tree and a species-level functional tree to estimate six taxonomic, phylogenetic and functional diversity indices. Four community metrics on behalf of the phylogenetic and functional community structure of each island were calculated using a null modelling framework and was quantified using the standardized effect size (SES). We explored the non-linear thresholds in the effect of area for each of the diversity indices and SES values of community metrics by comparing six piecewise regression models with a linear regression model and a null model.ResultsWe found evidence of SIEs in four diversity indices representing all three dimensions of diversity. Besides, area thresholds were also found in the phylogenetic and functional community structure for both amphibians and reptiles. Random extinction, competitive exclusion and adaptive radiation are the dominant processes structuring reptile communities on small, intermediate and large islands respectively.Main ConclusionsTo conduct a comprehensive biodiversity conservation plan concerning taxonomic, phylogenetic and functional diversity, we suggest it is necessary to explore the SIEs in various diversity indices representing all three dimensions of diversity and apply the lowest threshold value to make management strategies.

Automated summary

This study explores the small-island effect in three dimensions of diversity and finds evidence of this effect in four diversity indices representing taxonomic, phylogenetic and functional diversity. Furthermore, there are area thresholds in the phylogenetic and functional community structure for both amphibians and reptiles.