In theory, competition among species in a shared habitat results in niche separation. In the case of small recondite mammals such as shrews, little is known about their autecologies, leaving open questions regarding the degree to which closely related species co-occur and how or whether ecological niches are partitioned. The extent to which species are able to coexist may depend on the degree to which they exploit different features of their habitat, which may in turn influence our ability to recognize them as species. We explored these issues in a biodiversity hotspot, by surveying shrew (genus Crocidura) diversity on the Indonesian island of Java. We sequenced portions of nine unlinked genes in 100-117 specimens of Javan shrews and incorporated homologous data from most known Crocidura species from other parts of island South-East Asia. Current taxonomy recognizes four Crocidura species on Java, including two endemics. However, our phylogenetic, population genetic and species delimitation analyses identify five species on the island, and all are endemic to Java. While the individual ranges of these species may not overlap in their entirety, we found up to four species living syntopically and all five species co-occurring on one mountain. Differences in species' body size, use of above ground-level habitats by one species and habitat partitioning along ecological gradients may have facilitated species diversification and coexistence.

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National Park is one of the last refuges protecting intact forest and a representative mammalian fauna in Sumatra. However, knowledge of bat diversity in the area is limited. From 2010 to 2012, 47 bat species were recorded through a series of surveys in 12 localities within and around the national park. An additional six species from the area were identified from the mammal collection of the Museum Zoologicum Bogoriense, Indonesia. At least seven of the species reported in this study are new records for Sumatra, including Kerivoula krauensis, K. lenis, K. minuta, Murina rozendaali, Myotis horsfieldii, Myotis cf. borneoensis, and Rhinolophus borneensis/celebensis. Moreover, a finding of two distinct morphs of Chironax melanocephalus coexisting in the study area indicates another possible undescribed species. With 60 species, we consider Bukit Barisan Selatan Landscape to be a Southeast Asian bat diversity hotspot and of critical importance in maintaining bat diversity in Sumatra.

Island systems are important models for evolutionary biology because they provide convenient, discrete biogeographic units of study. Continental islands with a history of intermittent dry land connections confound the discrete definitions of islands and have led zoologists to predict (1) little differentiation of terrestrial organisms among continental shelf islands and (2) extinction, rather than speciation, to be the main cause of differences in community composition among islands. However, few continental island systems have been subjected to well-sampled phylogeographic studies, leaving these biogeographic assumptions of connectivity largely untested. We analyzed nine unlinked loci from shrews of the genus Crocidura from seven mountains and two lowland localities on the Sundaic continental shelf islands of Sumatra and Java. Coalescent species delimitation strongly supported all currently recognized Crocidura species from Sumatra (six species) and Java (five species), as well as one undescribed species endemic to each island. We find that nearly all species of Crocidura in the region are endemic to a single island and several of these have their closest relative(s) on the same island. Intra-island genetic divergence among allopatric, conspecific populations is often substantial, perhaps indicating species-level diversity remains underestimated. One recent (Pleistocene) speciation event generated two morphologically distinct, syntopic species on Java, further highlighting the prevalence of within-island diversification. Our results suggest that both between- and within-island speciation processes generated local endemism in Sundaland, supplementing the traditional view that the region's fauna is relictual and primarily governed by extinction. This article is protected by copyright. All rights reserved.

Genetic and morphometric variation was examined in eleven island populations of the horse‐shoe bat, Rhinolophus affinis, at the easterly end of this widespread species’ range and encompassing the Australian–Oriental biogeographic interface. Allozyme variation revealed mean heterozygosity levels within islands of 0.047, which is near the mammalian average. However, heterozygosity tended to decline from west to east as populations approached the periphery of the species’ distribution, and was lowest in those islands that were separated by the greatest sea‐crossing from source populations. There is extensive between‐island genetic differentiation (mean FST = 0.40) and relationships between islands are associated with their arrangement in geographical space; genetic distance is correlated with geographical distance and the genetic arrangement of islands is associated with longitude. The arrangement of islands as indicated by variation in body and skull metrics is also associated with their geographical positions, and the metric and genetic measures are themselves associated. While other taxa in the region have shown genetic‐geographical concordances, R. affinis is the only one that displays concordant patterns in metrical features. These patterns in biological diversity are interpreted as arising from the sequential island population structure and clines in key biogeographic gradients.