Research on island species–area relationships (ISAR) has expanded to incorporate functional (IFDAR) and phylogenetic (IPDAR) diversity. However, relative to the ISAR, we know little about IFDARs and IPDARs, and lack synthetic global analyses of variation in form of these three categories of island diversity–area relationship (IDAR). Here, we undertake the first comparative evaluation of IDARs at the global scale using 51 avian archipelagic data sets representing true and habitat islands. Using null models, we explore how richness‐corrected functional and phylogenetic diversity scale with island area. We also provide the largest global assessment of the impacts of species introductions and extinctions on the IDAR. Results show that increasing richness with area is the primary driver of the (non‐richness corrected) IPDAR and IFDAR for many data sets. However, for several archipelagos, richness‐corrected functional and phylogenetic diversity changes linearly with island area, suggesting that the dominant community assembly processes shift along the island area gradient. We also find that archipelagos with the steepest ISARs exhibit the biggest differences in slope between IDARs, indicating increased functional and phylogenetic redundancy on larger islands in these archipelagos. In several cases introduced species seem to have ‘re‐calibrated’ the IDARs such that they resemble the historic period prior to recent extinctions.
Aim: Research in island biogeography has long focused mainly on present-day island configurations. Recently, there has been an increasing focus on islands' past histories of land connection, shape and size. Moreover, continental islands (=shelf islands) have received less attention than oceanic islands, and species inventories from extremely small islands are lacking in many datasets. We examine the effects of sea-level rise since the Last Glacial Maximum (LGM) on bird species diversity and composition of tropical shelf islands in Southeast Asia. Location: Sundaland.Taxon: Birds. Methods:We compiled avifaunal island inventories for 94 islands using an exhaustive literature review of historic surveys of larger islands combined with our own comprehensive island surveys from both small and large islands. Using generalised least-squares models with spatial autocorrelation, we assessed the importance of traditional biogeographical parameters including area, maximum elevation, distance from mainland and geographical isolation, along with post-LGM effects of change in island area and duration since isolation. We also compared the species composition on similar-sized shelf islands from two categoriesrecently submerged and unsubmerged-using non-metric multidimensional scaling.Results: Post-LGM effects on species diversity are minimal and insular diversity is instead well explained by present-day island characteristics, such as area, distance to mainland and proportion of land surrounding an island within a 10 km radius (Cox and Snell Pseudo-R 2 = 0.803). Avifaunal diversity is similar across recently submerged and unsubmerged small shelf islands.Main conclusion: Avifaunal diversity on tropical shelf islands equilibrates rapidly after isolation, indicating that both extinction and immigration rates are high. In particular, a high immigration rate of dispersive species maintains diversity, especially on small islands. Over-water dispersal is generally restricted to short distances among Sundaic birds. Consequently, the diversity of an island can be maintained by the presence of large or stepping-stone islands near it.
The common paradise-kingfisher, Tanysiptera galatea, species complex comprises 19 taxa distributed across New Guinea and Wallacea. Owing to its highly conserved morphological features, the lineage has been taxonomically confused, with 15 similar-plumaged taxa currently treated as conspecific. To shed light on species limits, we analysed eight bioacoustic parameters across 107 sound recordings using principal component analysis and the Isler criterion, among other methods. Our results show that multiple geographical entities of Tanysiptera paradise-kingfishers form discrete bioacoustic clusters across several vocal parameters, suggesting that species diversity of the common paradise-kingfisher complex has been greatly underestimated. Based on our results, we propose splitting T. galatea into six species: (1) Obi paradise-kingfisher, Tanysiptera obiensis; (2) Rossel paradise-kingfisher, Tanysiptera rosseliana; (3) Papuan paradise-kingfisher, T. galatea; (4) Halmahera paradise-kingfisher, Tanysiptera margarethae; (5) Morotai paradise-kingfisher, Tanysiptera doris; and (6) Amboyna paradise-kingfisher, Tanysiptera nais. Our work highlights that the non-invasive collection of avian vocal data is a crucial taxonomic tool and adds to increasing evidence that bioacoustic analyses are effective in elucidating cryptic diversity.
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