In macroecological studies, accurate species distribution information and reliable methodologies are essential to illustrate the accurate geographical distribution of organisms. The available distribution data sources are generally limited to a particular geographical region and studied taxa and often contain some degree of sampling bias that caused a misrepresentation of species distribution. This study investigates how the different distribution data, methods, and spatial resolution affect the amphibian distribution pattern in the Malay Peninsula. Five types of distribution data, namely point-based (simple point occurrences and rarefied point occurrences) and range-based (expert-drawn range map, modelled range map and hybrid range map), were assembled from the published checklist, GBIF, natural history museum collections information, and digital range maps. Species richness was point-to-grid mapped by overlaying each distribution data with spatial resolutions of 100 km, 75 km, 50 km, 25 km and 15 km square grid and were evaluated with descriptive and quantitative-based approaches. Overall results show that richness maps created from range-based maps well-performed both descriptive and quantitative. Spatial autocorrelation was present in all distribution data; however, it is significantly reduced in 50 km resolution in range-based maps. When mapped with different spatial resolutions, the hybrid range map showed less variability in spatial relatedness and structure and executed a better predictive performance. The findings suggested that integrating the information from other distribution sources reduces the erroneous information in particular distribution data and can also evaluate the effects of spatial resolutions before developing species distribution maps.

Kin Onn Chan

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Most new cryptic species are described using conventional tree- and distance-based species delimitation methods (SDMs), which rely on phylogenetic arrangements and measures of genetic divergence. However, although numerous factors such as spatial population structure and gene flow are known to confound phylogenetic and species delimitation inferences, the influence of these processes on species estimation is rarely evaluated. Using large amounts of exons, introns, and ultraconserved elements obtained using the FrogCap sequence-capture protocol, we compared conventional SDMs with more robust genomic analyses that assesses spatial population structure and gene flow to characterize species boundaries in a Southeast Asian frog complex (Pulchrana picturata). Our results showed that gene flow and introgression can produce phylogenetic patterns and levels of divergence that resemble distinct species (up to 10% divergent in mitochondrial DNA). Hybrid populations were inferred as independent (singleton) clades that were highly divergent from adjacent populations (7–10%) and unusually similar (<3%) to allopatric populations. Such anomalous patterns are not uncommon in Southeast Asian amphibians, which brings into question whether the high cryptic diversity observed in other amphibian groups reflect distinct cryptic species—or, instead, highly structured and admixed metapopulation lineages. Our results also provide an alternative explanation to the conundrum of divergent (sometimes non-sister) sympatric lineages―a pattern that has been celebrated as indicative of true cryptic speciation. Based on these findings, we recommend that species delimitation of continuously distributed “cryptic” groups should not rely solely on conventional SDMs but should necessarily examine spatial population structure and gene flow to avoid taxonomic inflation.