Single-island Endemics Research Articles

Biogeography of the Caribbean Cyrtognatha spiders

Island systems provide excellent arenas to test evolutionary hypotheses pertaining to gene flow and diversification of dispersal-limited organisms. Here we focus on an orbweaver spider genus Cyrtognatha (Tetragnathidae) from the Caribbean, with the aims to reconstruct its evolutionary history, examine its biogeographic history in the archipelago, and to estimate the timing and route of Caribbean colonization. Specifically, we test if Cyrtognatha biogeographic history is consistent with an ancient vicariant scenario (the GAARlandia landbridge hypothesis) or overwater dispersal. We reconstructed a species level phylogeny based on one mitochondrial (COI) and one nuclear (28S) marker. We then used this topology to constrain a time-calibrated mtDNA phylogeny, for subsequent biogeographical analyses in BioGeoBEARS of over 100 originally sampled Cyrtognatha individuals, using models with and without a founder event parameter. Our results suggest a radiation of Caribbean Cyrtognatha, containing 11 to 14 species that are exclusively single island endemics. Although biogeographic reconstructions cannot refute a vicariant origin of the Caribbean clade, possibly an artifact of sparse outgroup availability, they indicate timing of colonization that is much too recent for GAARlandia to have played a role. Instead, an overwater colonization to the Caribbean in mid-Miocene better explains the data. From Hispaniola, Cyrtognatha subsequently dispersed to, and diversified on, the other islands of the Greater, and Lesser Antilles. Within the constraints of our island system and data, a model that omits the founder event parameter from biogeographic analysis is less suitable than the equivalent model with a founder event.

Phylogeography of western Mediterranean Cymbalaria (Plantaginaceae) reveals two independent long-distance dispersals and entails new taxonomic circumscriptions

The Balearic Islands, Corsica and Sardinia (BCS) constitute biodiversity hotspots in the western Mediterranean Basin. Oligocene connections and long distance dispersal events have been suggested to cause presence of BCS shared endemic species. One of them is Cymbalaria aequitriloba, which, together with three additional species, constitute a polyploid clade endemic to BCS. Combining amplified fragment length polymorphism (AFLP) fingerprinting, plastid DNA sequences and morphometrics, we inferred the phylogeography of the group and evaluated the species’ current taxonomic circumscriptions. Based on morphometric and AFLP data we propose a new circumscription for C. fragilis to additionally comprise a group of populations with intermediate morphological characters previously included in C. aequitriloba. Consequently, we suggest to change the IUCN category of C. fragilis from critically endangered (CR) to near threatened (NT). Both morphology and AFLP data support the current taxonomy of the single island endemics C. hepaticifolia and C. muelleri. The four species had a common origin in Corsica-Sardinia, and two long-distance dispersal events to the Balearic Islands were inferred. Finally, plastid DNA data suggest that interspecific gene flow took place where two species co-occur.

Biodiversity and Extinction of Hawaiian Land Snails: How Many Are Left Now and What Must We Do To Conserve Them-A Reply to.

Pacific islands, with their incredible biodiversity, are our finest natural laboratories for evolutionary, ecological, and cultural studies. Nowhere, in relation to land area, does land snail diversity reach that of the Pacific islands, with more than 6000 species, most of which are single island endemics. Unfortunately, land snails are the most imperiled group with the most recorded extinctions since the 1500s, and Pacific island snails make up the majority of those extinctions. In 1990, Dr. Alan Solem, a well renowned malacologist, with expertise in Pacific island land snails, posthumously published a plea to save the remaining Hawaiian land snails before they vanish forever. Now, more than 25 years later, we have finally begun to make inroads into answering the questions "How many Hawaiian land snails remain?" and "What will we need to save them?". Here we provide a belated reply to Solem (1990) and address these questions about Hawaiian land snails. We conclude by building on the actions suggested by Solem and that we feel are still needed to realize his hope of conserving Hawaii's remaining land snails specifically, but also our hope of conserving invertebrates more broadly.

A revision of the Neotropical spider genus Nops MacLeay (Araneae: Caponiidae) with the first phylogenetic hypothesis for the Nopinae genera.

The spider genus Nops MacLeay is revised, with redescriptions of 22 previously known species and descriptions of 12 new species. A new diagnosis for the genus is provided and keys to separate the species are proposed. After this revision Nops includes 34 extant species, thereof 15 (44%) occur in the Caribbean Islands, four (12%) in Central America and 15 (44%) in South America. Females of Nops meridionalis Keyserling and Nops gertschiChickering are found and described for the first time. Three new synonymies are proposed: Nops virginicus Sánchez-Ruiz with Nops blandus Bryant, Nops craneae Chickering with Nops maculatus Simon and Nops proseni Birabén with Nops farhati Prosen. Four species are considered inquerenda: Nops anisitsi Strand, Nops bellulus Chamberlin, Nops branicki(Taczanowski) and Nops glaucusHasselt. The following new species are described: N. jaragua n. sp., N. navassa n. sp., and N. pallidus n. sp. from the Caribbean region; N. campeche n. sp. and N. tico n. sp. from Central America, and N. alexenriquei n. sp., N. amazonas n. sp., N. bahia n. sp., N. ipojuca n. sp., N. itapetinga n. sp., N. minas n. sp. and N. pocone n. sp. from South America. New geographical records and distribution maps are provided for all species, with illustrations and reviewed diagnoses. The Nops species are restricted to the Neotropical region, from the Caribbean Islands and Mexico to the north of Argentina. The highest species richness is concentrated in the Wider Caribbean Region, including Central America and the north of Colombia and Venezuela where 64.7% of the species occur. Endemism in the Caribbean islands is very high; most of these species are single island endemics. A cladistic analysis, based on morphological data, was executed to test the monophyly of the genus. This is the first cladistic analysis of Caponiidae, and it includes besides the Nops species, 1) the six other species that were transferred from Nops, now in the genera Orthonops, Cubanops, Tarsonops and Medionops, and 2) Nopsides ceralbonus Chamberlin and Nyetnops guarani Platnick Lise. Therefore, representatives of all known Nopinae genera are included in the ingroup. The data matrix comprises 41 taxa scored for 47 morphological characters. The analyses under equal weights resulted in six equally parsimonious trees of 99 steps. All these trees are congruent with a unique hypothesis for Nopinae genera. Thus, all topological differences among the most parsimonious trees were the consequence of different hypotheses of relationships within Nops. The same result was also found under implied weighting with constants of concavity k = 2 to 13, where the topology of all trees was congruent for a single Nopinae genera hypothesis, but relationships within Nops were not resolved. All analysis under equal and implied weights recovered the monophyly of Nops with high support values, but internal clades within the genus showed low branch supports. Our results thus suggest that to resolve the internal relationships of Nops, studies based on molecular evidence are necessary to counteract the deficit of morphological data. The hypothesis obtained for Nopinae showed high branch support values for most of clades, corroborating all the transfers made from Nops. Medionops was recovered as the sister group of Nops with high support values. Nops, Medionops and Nopsides form a closely related, distinct spider group among nopine, supported by five unambiguous synapomorphies. Two of these synapomorphies could be functionally related: the presence of an arolium on the anterior pretarsi and the elongated and dorsally reflexed unpaired claw on the anterior legs. Nopsides appears to be a genus with apomorphic characters, presenting highly modified legs, but lacking the crista and gladius, and gaining a pair of anterior lateral eyes. Nyetnops is sister to all other nopine genera. Our results identified the necessity of further studies on nopine leg structures (arolium, crista, gladius and adesmatic joints) to improve understanding of the phylogenetic relationships of Nopinae genera.

Revision of the Hawaiian psyllid genus Swezeyana, with descriptions of seven new species (Hemiptera, Psylloidea, Triozidae).

The endemic Hawaiian genus Swezeyana Caldwell, 1940 is highly distinctive due to the extremely long genal processes. In addition, some of the immatures are ornamented with extraordinary tubercles and tentacles. Two Swezeyana species are redescribed, and seven new species are described, bringing the total number of species in the genus to nine. All species are hosted by a single, endemic host plant, Planchonella sandwicensis (Sapotaceae), which is distributed across all major islands in the archipelago. The majority of Swezeyana species are single island endemics. A sister taxon pair is found sympatrically on the same individual plants on Kauai, and putative sister or at least closely related species are also found sympatrically on Oahu and Hawaii, suggesting these taxa may have diversified in sympatry. However, there is no observed ecological niche partitioning, despite some striking morphological diversity, as all Swezeyana species have free-living immatures that are found on the leaf surface, and therefore no apparent biological shifts are coincident with occupying the same host plant. Two species groups are represented by strikingly different female terminalia structure and endoskeletal development, although ovipositor structure is very similar between the two groups. Mitochondrial DNA barcodes (COI and cytB) are provided for eight of the nine species. A phylogenetic analysis of the mitochondrial barcode regions indicates species relationships within Swezeyana and provides a comparison of genetic divergence with other Hawaiian endemic genera.

Species conservation profile of moths (Insecta, Lepidoptera) from Azores, Portugal.

BackgroundThe few remnants of Azorean native forests harbour a unique set of endemic moths (Insecta, Lepidoptera), some of them under severe long term threats due to small sized habitats or climatic changes. In this contribution, we present the IUCN Red List profiles of 34 endemic moths to the Azorean archipelago, including species belonging to two diverse families: Noctuidae (11 species) and Crambidae (eight species). The objective of this paper is to assess all endemic Azorean moth species and advise on possible future research and conservation actions critical for the long-trem survival of the most endangered species.New informationMost species have a large distribution (i.e. 58% occur in at least four islands), very large extent of occurrence (EOO) and a relatively large area of occupancy (AOO). Only nine species are single-island endemics, three of them from Flores, three from São Miguel and one from Pico, São Jorge and Faial. Most of the species also experience continuing decline in habitat quality, number of locations and subpopulations caused by the ongoing threat from pasture intensification, forestry, invasive plant species and future climatic changes. The lack of new records may indicate that one of the species previously named is extinct (Eupithecia ogilviata). Therefore, we suggest as future conservation actions: (1) a long-term species monitoring plan and (2) control of invasive species.

Multiple origins of the Phaenonotum beetles in the Greater Antilles (Coleoptera: Hydrophilidae): phylogeny, biogeography and systematics

The systematics and the phylogenetic position of the Caribbean representatives of Phaenonotum Sharp (Coleoptera: Hydrophilidae) are investigated in order to understand the composition of the Caribbean fauna and its origin. Phylogenetic analysis based on mitochondrial and nuclear genes has revealed the Caribbean species to be situated in three deeply nested clades, inferring multiple colonization of Caribbean islands from the continent. Time-tree analysis and BioGeoBEARS analyses of ancestral ranges estimated the oldest clade, consisting of wingless single-island endemics of Cuba ( P. delgadoi ), Jamaica ( P. ondreji sp. nov. ) and Hispaniola ( P. laterale sp. nov. ), to have diverged ca. 46.6 Ma from the South American ancestor and subsequently colonizing the Caribbean most likely via the GAARlandia land bridge connecting South America with Greater Antilles. The remaining three Caribbean species, including the Puerto Rican endemic, P. borinquenum sp. nov. , are of more recent (Miocene to Pliocene) origin and colonized the Greater Antilles by over-water dispersal. All the Caribbean species are illustrated and diagnosed and three new species are described. The genus Phaenonotum , excluding P. caribense Archangelsky, is confirmed as a monophylum. We demonstrate that species-level taxonomy of Phaenonotum is difficult to solve by morphology alone, and ideally requires the combination of morphology and molecular markers.

An island view of endemic rarity—Environmental drivers and consequences for nature conservation

AbstractAimRarity—an important measure for conservation biogeography—can vary over many orders of magnitude. However, it is unclear which regional‐scale abiotic conditions drive processes affecting rarity of endemic species on islands. To support conservation efforts, we (1) assess the main abiotic drivers of endemic rarity, (2) determine how well existing protected areas (PAs) coincide with hotspots of endemic rarity and (3) introduce and evaluate a new hypervolume‐based rarity estimator.LocationLa Palma (Canary Islands).MethodsWe recorded all present endemic vascular plant species in 1,212 plots covering the entire island. We calculated endemic rarity (corrected range‐rarity richness for endemics) using a rarity estimation approach based on kernel density estimations (hypervolume approach). We performed a sensitivity analysis based on multiple linear regressions and relative importance estimations of environmental drivers to estimate the performance of the hypervolume‐based rarity estimation compared to standard methods (occurrence frequency, convex hulls, alpha hulls).ResultsClimate variables (mean annual temperature, climatic rarity, precipitation variability) best explained archipelago endemic (AE) and single‐island endemic (SIE) rarity. Existing PAs covered the majority of AE and SIE rarity, especially national and natural parks as well as the Natura 2000 sites. In our study system, hypervolumes performed better than standard measures of range size.Main conclusionBoth AE and SIE rarity on La Palma show a clear spatial pattern, with hotspots of endemic rarity found at high elevations and in rare climates, presumably owing to geographical and climatic constraints and possibly anthropogenic pressure (e.g., land use, introduced herbivores, fire). Areas of high rarity estimates coincide with the distribution and extent of PAs on La Palma, especially since the recent addition of the Natura 2000 sites. The hypervolume approach is a promising tool to estimate species range sizes, and can be applied on all scales where point/plot data are available.

A molecular phylogeny of the Pacific clade of Cyrtandra (Gesneriaceae) reveals a Fijian origin, recent diversification, and the importance of founder events

Cyrtandra (Gesneriaceae) is among the largest genera of flowering plants in the remote oceanic islands of the Pacific, with an estimated 175 species distributed across an area that extends from the Solomon Islands, east to the Marquesas Islands, and north to the Hawaiian Islands. The vast majority of species are single-island endemics that inhabit upland rainforests. Although previous molecular phylogenetic studies greatly advanced our understanding of the diversification of Pacific Cyrtandra, a number of uncertainties remain regarding phylogenetic relationships, divergence times, and biogeographic patterns within this large and widely dispersed group. In the present study, five loci (ITS, ETS, Cyrt1, psbA-trnH, and rpl32-trnL) were amplified and sequenced for phylogenetic reconstruction of 121 Cyrtandra taxa. Maximum likelihood and Bayesian inference confirmed that C. taviunensis from Fiji is sister to the remaining members of the Pacific clade. Dating analyses and ancestral area estimation indicates that the Pacific clade of Cyrtandra originated in Fiji during the Miocene ca. 9mya. All major crown lineages within the Pacific clade appeared < 5mya, coincident with the emergence of numerous Pacific islands and a subsequent increase in available habitat. The biogeographic history of Cyrtandra in the Pacific has been shaped by extinction, dispersal distance, and founder events. Biogeographic stochastic mapping analyses suggest that cladogenesis within Pacific Cyrtandra involved a combination of narrow (within-area) sympatry and founder events. A mean of 24 founder events was recovered between Pacific archipelagos, while a mean of 10 founder events was recovered within the Hawaiian archipelago.

Unpaid extinction debts for endemic plants and invertebrates as a legacy of habitat loss on oceanic islands

AbstractAimThe majority of documented extinctions world‐wide in the last four centuries are of species endemic to islands. However, the phenomenon of delayed extinctions as a result of habitat loss has rarely been assessed on oceanic islands. In this study, we tested whether extinction debt (ED), in general, occurs on islands and for which taxonomical groups this phenomenon is most pronounced by assessing ED for multiple endemic taxa and for each of the main altitudinal ecosystems in a well‐studied oceanic archipelago.LocationCanary Islands.MethodsWe characterized habitat preferences for all endemic species of several taxonomic groups (vascular plants, ground and darkling beetles, flies and land snails). Using generalized linear mixed models and available data about habitat distributions, we tested for all taxa and habitat types to determine whether past habitat area better explained current richness of habitat specialists than current habitat area. If so, an extinction debt can be assumed.ResultsFor all five major habitat types and five taxonomic groups studied, present‐day richness of habitat specialists fitted better with past than current habitat area, evidencing habitat‐ and taxon‐specific extinction debts. This pattern was consistent for both long‐lived vascular plants and short‐lived invertebrates. Single island endemics in each taxonomic group showed steeper slopes of the species–area relationship (SAR) compared to archipelago endemics indicating higher sensitivity to habitat loss which might increase sizes of ED.ConclusionDespite differences in species’ generation times, plants and invertebrates showed delayed extinctions after habitat destruction in the Canary Islands. Our SAR approach suggests that a considerable number of Canary Island endemics will eventually become extinct in the future without further habitat loss. The case of the Canary archipelago is probably not unique. Hence, we interpret our results as a warning for island conservationists that the worst of the extinction crisis on oceanic islands might be yet to come. Conservation actions should focus on habitat restoration to attenuate or reverse current extinction processes.

A new endemic psyllid genus, Stevekenia gen. nov. (Hemiptera: Psylloidea, Triozidae), from the Hawaiian Islands with two new and rare species on threatened host plants in the endemic genus Nothocestrum (Solanaceae)

A new endemic psyllid genus from the Hawaiian Islands, Stevekenia gen. nov., is described. Two new species, both single island endemics, feed on host plants in the endemic genus Nothocestrum (Solanaceae). Stevekenia nothocestri sp. nov. is found on Nothocestrum longifolium on the island of Oahu and Stevekenia aiea sp. nov. is found on N. peltatum on the island of Kauai. The host plants are montane rainforest species and both are on the IUCN Red List of Threatened Species. In particular, N. peltatum, which is endemic to the island of Kauai, is considered critically endangered, and therefore a similarly endangered status for these host-specific insects is likely. Only a few specimens of each Stevekenia species have been found, suggesting occurrence at low abundance. The host plants survive either as isolated individuals or small fragmented populations, which may already constitute less than the required critical host plant density for the long term survival of this psyllid genus. Unique morphological characters distinguish Stevekenia from other Hawaiian genera, and the placement of this genus within Triozidae is discussed. Mitochondrial DNA barcodes for the new species are provided.

Morphology, ultrastructure and phylogenetic affinities of the single-island endemic Anthoceros cristatus Steph. (Ascension Island)

Oceanic islands, due to their geographical isolation, number, precisely defined boundaries and their geomorphological and climatic diversity, have provided enormous insights into speciation, dispersal, adaptive radiations and macroecological processes. One of the key components of these island studies is the role of single-island endemics (SIEs) as, in many instances, island biogeography models use the proportion of SIEs to infer evolutionary processes. It is, therefore, imperative to undertake critical taxonomic revisions to evaluate SIEs because changes in the number of SIEs have a key impact on downstream biogeographic analyses. We revise the special case of a putative SIE Anthoceros cristatus on Ascension Island using light and electron microscopy, as well phylogenomic tools. A. cristatus lies within the A. agrestis/A. punctatus complex but differs from the sister species A. agrestis and A. punctatus in spore morphology and gametophytic lamellae fringed with caducous marginal cells. The present confirmation, from both molecules and morphology, of the SIE status of Anthoceros cristatus and its restricted distribution on the Island makes the preservation of its habitat a conservation priority. Ascension Island is the tip of an undersea volcano that is thought to have emerged from the ocean 1 million years ago with an area of approximately 91 km2, with Green Mountain as the highest elevation (∼859 m a.s.l.). Ascension has a relative low bryophyte species diversity of 87 spp but this includes 12 endemics (∼14%); a much higher level of endemism than on the far more speciose Macaronesian Islands.

Ancient biogeography of generalist predators on remote oceanic islands

Aim Remote islands are known for providing spectacular examples of adaptive radiation, with ecological divergence across a lineage giving rise to multiple species, each specialized for a particular niche. These isolated environments also provide some of the best examples of recent colonization, often human-mediated, with a single generalist taxon distributed over vast regions. Highlighted by this dichotomy is a tendency of taxa to become more specialized over time. The current study focuses on two spider taxa (family Uloboridae) each occupying a broad range of habitats: Tangaroa tahitiensis in the Austral and Society islands of French Polynesia and Daramulunia gibbosa in Fiji. We ask whether the generalist tendency of each is associated with recent colonization of widespread species or, rather, maintained over extended evolutionary time. Location South Pacific: Fiji (18° S, 175° E), Society (18° S, 150° W), and Austral (23° S, 150° W) archipelagoes. Methods Mitochondrial COI and nuclear 18S rDNA were sequenced and analysed using maximum likelihood (RAxML) and Bayesian approaches with concurrent divergence dating calibrated with a general arthropod molecular clock. Ancestral ranges were reconstructed independently for French Polynesia and Fiji (RASP). Results While both T. tahitiensis and D. gibbosa occur broadly from sea-level to cloud forest, each has a separate and ancient origin within their respective archipelagoes, the pattern of colonization matching the geographical arrangement of the islands. Main conclusions Populations of two spider species, T. tahitiensis in the Australs and Societies and D. gibbosa in Fiji, are extreme generalists with broad physiological tolerances throughout their respective ranges. Yet, every population displays single island endemism and deep genetic divergences between islands indicating a long history on individual landmasses, a finding that contradicts the tendency for organisms to show increasing specialization associated with endemism.

Surviving in isolation: genetic variation, bottlenecks and reproductive strategies in the Canarian endemic Limonium macrophyllum (Plumbaginaceae).

Oceanic archipelagos are typically rich in endemic taxa, because they offer ideal conditions for diversification and speciation in isolation. One of the most remarkable evolutionary radiations on the Canary Islands comprises the 16 species included in Limonium subsection Nobiles, all of which are subject to diverse threats, and legally protected. Since many of them are single-island endemics limited to one or a few populations, there exists a risk that a loss of genetic variation might limit their long-term survival. In this study, we used eight newly developed microsatellite markers to characterize the levels of genetic variation and inbreeding in L. macrophyllum, a species endemic to the North-east of Tenerife that belongs to Limonium subsection Nobiles. We detected generally low levels of genetic variation over all populations (H T = 0.363), and substantial differentiation among populations (F ST = 0.188; R ST = 0.186) coupled with a negligible degree of inbreeding (F = 0.042). Obligate outcrossing may have maintained L. macrophyllum relatively unaffected by inbreeding despite the species' limited dispersal ability and the genetic bottlenecks likely caused by a prolonged history of grazing. Although several factors still constitute a risk for the conservation of L. macrophyllum, the lack of inbreeding and the recent positive demographic trends observed in the populations of this species are factors that favour its future persistence.

Pseudoscorpion diversity and distribution in the West Indies: sequence data confirm single island endemism for some clades, but not others

The Caribbean Islands are a biodiversity hotspot harboring high levels of endemic biodiversity. In an effort to contribute to the characterization of invertebrate diversity in the region, we present an assessment of pseudoscorpion (Arachnida: Pseudoscorpiones) diversity and distribution with a focus on the superfamily Chthonioidea and the family Olpiidae. We used three markers (cytochrome c oxidase subunit I, histone H3 and 28S rRNA) to infer the first molecular phylogenies for each lineage and identified 32 putative new species in need of taxonomic assessment. These new records include the documentation of the genera Pseudochthonius Balzan, 1892 Lagynochthonius Beier, 1951, Tyrannochthonius Chamberlin, 1929 (Chthoniidae), Antillolpium Muchmore, 1991, Novohorus Hoff, 1945, and Pachyolpium Beier, 1931 (Olpiidae) on various islands. Chthonioid genera are strongly structured geographically, suggesting that many Caribbean species may be short-range endemics and excellent candidate systems for testing biogeographic hypotheses. The olpiid genus Pachyolpium is less geographically structured, which is consistent with the hypothesis that olpiids are better dispersers than chthonioids. This study aims to provide a foundation for taxonomic and biogeographic work on Caribbean pseudoscorpions, revealing a diversity that is far richer than is documented in the literature.

Phylogeography of a good Caribbean disperser: Argiope argentata (Araneae, Araneidae) and a new 'cryptic' species from Cuba.

The Caribbean islands harbor rich biodiversity with high levels of single island endemism. Stretches of ocean between islands represent significant barriers to gene-flow. Yet some native species are widespread, indicating dispersal across oceans, even in wingless organisms like spiders. Argiope argentata (Fabricius, 1775) is a large, charismatic, and widespread species of orb-weaving spider ranging from the United States to Argentina and is well known to balloon. Here we explore the phylogeography of Argiope argentata in the Caribbean as a part of the multi-lineage CarBio project, through mtDNA haplotype and multi-locus phylogenetic analyses. The history of the Argiope argentata lineage in the Caribbean goes back 3-5 million years and is characterized by multiple dispersal events and isolation-by-distance. We find a highly genetically distinct lineage on Cuba which we describe as Argiope butchko sp. n. While the argentata lineage seems to readily balloon shorter distances, stretches of ocean still act as filters for among-island gene-flow as evidenced by distinct haplotypes on the more isolated islands, high FST values, and strong correlation between intraspecific (but not interspecific) genetic and geographic distances. The new species described here is clearly genetically diagnosable, but morphologically cryptic, at least with reference to the genitalia that typically diagnose spider species. Our results are consistent with the intermediate dispersal model suggesting that good dispersers, such as our study species, limit the effect of oceanic barriers and thus diversification and endemism.

Why do different oceanic archipelagos harbour contrasting levels of species diversity? The macaronesian endemic genus Pericallis (Asteraceae) provides insight into explaining the 'Azores diversity Enigma'.

BackgroundOceanic archipelagos typically harbour extensive radiations of flowering plants and a high proportion of endemics, many of which are restricted to a single island (Single Island Endemics; SIEs). The Azores represents an anomaly as overall levels of endemism are low; there are few SIEs and few documented cases of intra-archipelago radiations. The distinctiveness of the flora was first recognized by Darwin and has been referred to as the ‘Azores Diversity Enigma’ (ADE). Diversity patterns in the Macaronesian endemic genus Pericallis (Asteraceae) exemplify the ADE. In this study we used morphometric, Amplified Length Polymorphisms, and bioclimatic data for herbaceous Pericallis lineages endemic to the Azores and the Canaries, to test two key hypotheses proposed to explain the ADE: i) that it is a taxonomic artefact or Linnean shortfall, ie. the under description of taxa in the Azores or the over-splitting of taxa in the Canaries and (ii) that it reflects the greater ecological homogeneity of the Azores, which results in limited opportunity for ecological diversification compared to the Canaries.ResultsIn both the Azores and the Canaries, morphological patterns were generally consistent with current taxonomic classifications. However, the AFLP data showed no genetic differentiation between the two currently recognized Azorean subspecies that are ecologically differentiated. Instead, genetic diversity in the Azores was structured geographically across the archipelago. In contrast, in the Canaries genetic differentiation was mostly consistent with morphology and current taxonomic treatments. Both Azorean and Canarian lineages exhibited ecological differentiation between currently recognized taxa.ConclusionsNeither a Linnean shortfall nor the perceived ecological homogeneity of the Azores fully explained the ADE-like pattern observed in Pericallis. Whilst variation in genetic data and morphological data in the Canaries were largely congruent, this was not the case in the Azores, where genetic patterns reflected inter-island geographical isolation, and morphology reflected intra-island bioclimatic variation. The combined effects of differences in (i) the extent of geographical isolation, (ii) population sizes and (iii) geographical occupancy of bioclimatic niche space, coupled with the morphological plasticity of Pericallis, may all have contributed to generating the contrasting patterns observed in the archipelagos.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0766-1) contains supplementary material, which is available to authorized users.

The biodiversity of the United Kingdom’s Overseas Territories: a stock take of species occurrence and assessment of key knowledge gaps

Limited financial resources for conservation and growing environmental problems make it vital to base conservation on sound scientific evidence. Small islands hold a disproportionately large amount of the worlds threatened biodiversity but it is among the least well-documented. This paper reports on the most extensive collation and synthesis of biodiversity data to date for the 14 United Kingdom Overseas Territories (UKOTs). A process of literature review and consultation produced 65,259 species records, including 32,216 native species of which 1549 were endemic to a single UKOT. The extent of knowledge of species occurrence varied both between islands and taxonomic groups. It was higher for vertebrates and vascular plants than small bodied invertebrates and non-vascular and for non-Caribbean compared to Caribbean islands, a difference that largely reflects knowledge of invertebrates. Global Red List assessments exist for 2606 species and document 111 of endemic species, 75 % of those assessed, and 291, 12 % of non-endemics, as globally threatened. Using the data to estimate true species richness suggests a further 70,000 native species, including 1800 single island endemics, remain to be documented suggesting the UKOTs as a whole may support over 100,000 native species including 3300 single island endemics.

Transferring and implementing the general dynamic model of oceanic island biogeography at the scale of island fragments: the roles of geological age and topography in plant diversification in the Canaries

AbstractAimThe general dynamic model (GDM) of oceanic island biogeography integrates rates of immigration, speciation and extinction in relation to a humped trajectory of island area, species carrying capacity and topographic complexity through time, based on a simplified island ontogeny. In practice, many islands have more complex ontogenies, featuring surfaces of varying age. Here, we extend the GDM to apply at a local scale within islands, and test the predictions analytically within individual islands.LocationEl Hierro, La Palma and Tenerife (Canary Islands).MethodsFollowing the GDM logic, we derive predictions for the distributions and richness of single island endemics (SIEs) across island landscapes of different age. We test these predictions by means of generalized linear models and binominal tests using gridded species occurrence data for vascular plant SIE species and a set of climatic, topographic and terrain age variables. We also examined phylogenetic divergence times for a subset of endemic lineages.ResultsGeological age, in interaction with slope, and topographic variables, best explained SIE richness at the landscape scale. About 70% of SIEs had ranges strongly biased to, or largely restricted to old terrain. Available phylogenetic divergence times of SIEs of radiated plant lineages suggested an origin on the older parts of the islands. Metrics of anthropogenic disturbance and habitat availability were unrelated to the observed SIE pattern.Main conclusionsOur findings support the hypothesis that SIEs have evolved and accumulated on older and topographically complex terrain, while colonization processes predominate on the youngest parts. These results imply that evolutionary processes shape species distributions at the landscape scale within islands. This opens the perspective of extending the GDM framework to understand processes at a local scale within individual islands.

Using species abundance distribution models and diversity indices for biogeographical analyses

We examine whether Species Abundance Distribution models (SADs) and diversity indices can describe how species colonization status influences species community assembly on oceanic islands. Our hypothesis is that, because of the lack of source-sink dynamics at the archipelago scale, Single Island Endemics (SIEs), i.e. endemic species restricted to only one island, should be represented by few rare species and consequently have abundance patterns that differ from those of more widespread species. To test our hypothesis, we used arthropod data from the Azorean archipelago (North Atlantic). We divided the species into three colonization categories: SIEs, archipelagic endemics (AZEs, present in at least two islands) and native non-endemics (NATs). For each category, we modelled rank-abundance plots using both the geometric series and the Gambin model, a measure of distributional amplitude. We also calculated Shannon entropy and Buzas and Gibson's evenness. We show that the slopes of the regression lines modelling SADs were significantly higher for SIEs, which indicates a relative predominance of a few highly abundant species and a lack of rare species, which also depresses diversity indices. This may be a consequence of two factors: (i) some forest specialist SIEs may be at advantage over other, less adapted species; (ii) the entire populations of SIEs are by definition concentrated on a single island, without possibility for inter-island source-sink dynamics; hence all populations must have a minimum number of individuals to survive natural, often unpredictable, fluctuations. These findings are supported by higher values of the α parameter of the Gambin mode for SIEs. In contrast, AZEs and NATs had lower regression slopes, lower α but higher diversity indices, resulting from their widespread distribution over several islands. We conclude that these differences in the SAD models and diversity indices demonstrate that the study of these metrics is useful for biogeographical purposes.