The decomposition of leaf litter of terrestrial origin is a fundamental process in aquatic ecosystems in forest contexts. Little is known about what drives leaf litter decomposition in oceanic islands. We examined the relative importance of leaf litter identity (Acacia melanoxylon, Pittosporum undulatum, Morella faya) and environmental conditions on litter decomposition in seven lakes in the oceanic archipelago of Azores for 28 and 56 days. Leaf litter was incubated in coarse and fine mesh bags for the assessment of the relative contribution of macroinvertebrates to leaf litter decomposition. Leaf litter mass loss generally did not differ between mesh sizes, suggesting that in these lakes macroinvertebrates generally have a negligible role on leaf decomposition. Leaf litter decomposition was in the order M. faya < A. melanoxylon < P. undulatum. A negative correlation was found between leaf litter mass loss and lignin concentration. Mass loss of P. undulatum was related to lake elevation and chlorophyll a (taken as surrogates for water temperature and dissolved nutrient availability, respectively), whereas mass loss of M. faya was related to chlorophyll a on day 56. These results suggest that changes in the composition of the leaf litter input and environmental conditions can affect leaf litter decomposition in Azorean lakes, with potential consequences for nutrient cycling.

Abstract AimMorphological and taxonomic diversity are intuitive measures of biological diversity. Previous studies have shown discordance between these measures at large spatial and temporal scales, but the implications of this pattern for the underlying processes are not understood. Using oceanic archipelagos as spatial units, we examine potential links between the morphological and taxonomic diversity of their land snail faunas in a biogeographical framework.LocationEleven major oceanic archipelagos.MethodsFor each archipelago, we assembled lists of indigenous land snail species, classified by family and genus, with shell height and width for each species (1723 species in total). We used biogeographic and climatic variables as potential predictors of diversity patterns. We employed regression analyses to evaluate (1) whether morphological diversity scales with taxonomic diversity at the species, genus or family level, and (2) whether morphological and taxonomic diversity correlate similarly with biogeographic/climatic factors. We also assessed which taxonomic level contributes most to morphological variation within archipelagos.ResultsMorphological diversity across archipelagos was strongly related to genus but not species richness. Within archipelagos, morphological variation reflected differences among genera and families but not species. Species richness was best explained by archipelago area, but morphological diversity was not significantly related to any of the physical features of archipelagos.Main conclusionsAcross archipelagos, species richness and morphological diversity of land snail faunas are decoupled. The relationship between species richness and the available ecological space (captured mainly by area) indicates the prevalence of niche‐based processes while, for morphological diversity, the strong conservatism of morphology at the genus level suggests the presence of diversification‐based limits. Assuming genera effectively reflect diversification, our findings indicate that morphological space on oceanic archipelagos depends primarily on the number of evolutionary units that have colonized and/or diversified through time.

The relative roles of chance colonization and subsequent gene flow in the development of insular endemic biotas have been extensively studied in remote oceanic archipelagos, but are less well characterized on nearshore island systems. The current study investigated patterns of colonization and divergence between and within two wild buckwheat species (Polygonaceae), Eriogonum arborescens and E. giganteum, endemic to the California Channel Islands to determine whether geographical isolation is driving diversification. Using plastid and nuclear sequence data and microsatellite allele frequencies, we determined that gene flow in these Eriogonum spp. is restricted by isolation. The data suggest that successful colonization of and gene flow among the islands are infrequent. Colonization appears to have followed a stepping-stone model that is consistent with a north-to-south pattern across the islands. This colonization pattern coupled with relatively little post-colonization inter-island gene flow, particularly among southern islands, has generated a pattern of more divergent lineages on the isolated southern islands. These results run counter to the general expectation that all islands close to a continental source should receive a high level of gene flow. Finally, management recommendations focused on protecting the lineages from loss of private alleles and the erosion of the remaining genetic diversity are offered.

Convergent evolution, often observed in island archipelagos, provides compelling evidence for the importance of natural selection as a generator of species and ecological diversity. The Indo-Australian Archipelago (IAA) is the world's largest island system and encompasses distinct biogeographic units, including the Asian (Sunda) and Australian (Sahul) continental shelves, which together bracket the oceanic archipelagos of the Philippines and Wallacea. Each of these biogeographic units houses numerous endemic rodents in the family Muridae. Carnivorous murids, that is those that feed on animals, have evolved independently in Sunda, Sulawesi (part of Wallacea), the Philippines, and Sahul, but the number of origins of carnivory among IAA murids is unknown. We conducted a comprehensive phylogenetic analysis of carnivorous murids of the IAA, combined with estimates of ancestral states for broad diet categories (herbivore, omnivore, and carnivore) and geographic ranges. These analyses demonstrate that carnivory evolved independently four times after overwater colonization, including in situ origins on the Philippines, Sulawesi, and Sahul. In each biogeographic unit the origin of carnivory was followed by evolution of more specialized carnivorous ecomorphs such as vermivores, insectivores, and amphibious rats.

Abstract AimPhylogeographical and modelling studies have suggested that the biotas of oceanic hotspot archipelagos (such as the Hawaiian, Canary and Galápagos islands) diversify in parallel with the formation of the islands on which they live. Here, we review the phylogeography of the native terrestrial biota of the Society Islands, an archipelago formed &lt; 4.6 Ma, to test this model.LocationSociety Islands, French Polynesia (Pacific Ocean).MethodsWe reviewed 49 phylogenetic and phylogeographical studies incorporating Society Island terrestrial animal and plant taxa. We ask: (1) Where are the sister groups of Societies lineages distributed? (2) Are Societies‐endemic ‘radiations’ monophyletic or polyphyletic? (3) What between‐island barriers are seen in the phylogeography of Societies taxa? (4) What within‐island barriers are seen in the phylogeography of Societies taxa? (5) How old is the Societies biota?ResultsMost Societies lineages are closely related to those in other tropical Pacific archipelagos, particularly the Cook, Austral and Marquesas Islands (&lt; 2000 km distant). More genera show strong evidence for polyphyly (13 genera) than for monophyly (4 genera) in the Society Islands. The most common within‐archipelago phylogeographical barrier corresponds to the straits (150 km) between the Windward Society and Leeward Society Islands. Only a few groups, primarily species‐rich invertebrate radiations, show divergence among or within islands. Published divergence time estimates suggest that much of the Societies biota may be much younger than the age of the archipelago.Main conclusionsMuch of the Societies biota does not appear to have diversified in parallel with the formation of the archipelago, differing from ‘progression rule’ and general dynamic models for the diversification of oceanic archipelago biotas. Rather, many Societies ‘radiations’ may have been assembled via repeated, independent colonizations, which may have entailed extensive macroevolutionary turnover of colonizing lineages. These patterns have implications for the biogeography of other Pacific hotspot archipelagos.

Abstract Introduced species negatively impact native species through competitive and trophic interactions, particularly on oceanic islands that have never been connected to any continental landmass. However, there are few studies on the relative importance of competitive interactions (resource competition with introduced species) and trophic interactions (predation or herbivory by introduced species) with respect to the negative impacts on native organisms on oceanic islands. A literature review on introduced and native species of the oceanic Ogasawara (Bonin) Islands in the western Pacific Ocean indicated that many native species (e.g., bees, beetles, damselflies, butterflies, land snails, birds, and plants) have been negatively impacted by introduced predators and herbivores (e.g., lizards, rats, flatworms, and goats). Several native plants and bees have been negatively affected by introduced competitors. However, the native species that have competed with introduced species have also suffered from either intense herbivory or predation by other introduced species. Thus, introduced predators and herbivores have had greater impacts on native species than introduced competitors in the Ogasawara Islands.

Abstract AimEcological niche concepts, in combination with biogeographic history, underlie our understanding of biogeographic ranges. Two pillars of this understanding are competitive displacement and niche conservatism. The competitive displacement hypothesis holds that very similar (e.g. closely related) co‐occurring species should diverge, forced apart by competition. In contrast, according to the niche conservatism hypothesis, closely related species should have similar niches. If these are fundamental structuring forces, they should be detectable when comparing the climatic niches of endemic species in radiating clades in oceanic archipelagos, where closely related species exist in both sympatry and allopatry and the species' entire ranges are known. We took advantage of this natural experimental system to test whether the climatic niche relationships predicted by the two hypotheses are found.LocationCanary Islands.MethodsFor the plant clades Aeonium, Argyranthemum, Descurainia, Echium, Lotus and Sonchus, separately, we tested relationships between phylogenetic distance and climatic niche differentiation (in temperature, precipitation and their combination), using a high‐resolution dataset. We also tested for niche conservatism using Blomberg's K and Pagel's λ. We compared climatic niche differentiation between pairs of species existing in sympatry with that for pairs of species in allopatry. For each comparison, we focused on the climatic niche space available to both species.ResultsThe relationships between phylogenetic distance and climatic niche differentiation were mostly non‐significant; some weak but significant positive relationships were found, mainly for Aeonium and Sonchus. Where differences between sympatry and allopatry were found, niche differentiation tended to be greater in allopatry.Main conclusionsThe expectations from niche conservatism were frequently not met; instead our results suggest considerable climatic niche lability. All significant differences in climatic niche differentiation were opposite to the predictions from competitive displacement. These forces may be less important in structuring biogeographic ranges than is commonly thought, at least on islands.

Oceanic archipelagos are vulnerable to natural introduction of parasites via migratory birds. Our aim was to characterize the geographic origins of two Plasmodium parasite lineages detected in the Galapagos Islands and in North American breeding bobolinks (Dolichonyx oryzivorus) that regularly stop in Galapagos during migration to their South American overwintering sites. We used samples from a grassland breeding bird assemblage in Nebraska, United States, and parasite DNA sequences from the Galapagos Islands, Ecuador, to compare to global data in a DNA sequence registry. Homologous DNA sequences from parasites detected in bobolinks and more sedentary birds (e.g., brown-headed cowbirds Molothrus ater, and other co-occurring bird species resident on the North American breeding grounds) were compared to those recovered in previous studies from global sites. One parasite lineage that matched between Galapagos birds and the migratory bobolink, Plasmodium lineage B, was the most common lineage detected in the global MalAvi database, matching 49 sequences from unique host/site combinations, 41 of which were of South American origin. We did not detect lineage B in brown-headed cowbirds. The other Galapagos-bobolink match, Plasmodium lineage C, was identical to two other sequences from birds sampled in California. We detected a close variant of lineage C in brown-headed cowbirds. Taken together, this pattern suggests that bobolinks became infected with lineage B on the South American end of their migratory range, and with lineage C on the North American breeding grounds. Overall, we detected more parasite lineages in bobolinks than in cowbirds. Galapagos Plasmodium had similar host breadth compared to the non-Galapagos haemosporidian lineages detected in bobolinks, brown-headed cowbirds, and other grassland species. This study highlights the utility of global haemosporidian data in the context of migratory bird-parasite connectivity. It is possible that migratory bobolinks bring parasites to the Galapagos and that these parasites originate from different biogeographic regions representing both their breeding and overwintering sites.

In natural ecosystem, species assemblages in fragmented habitats frequently exhibit a nested subset pattern.Although nestedness has been documented for a wide range of taxa, it is rarely tested in butterfly assemblages in oceanic archipelago ecosystems.We surveyed the butterfly occupancy and abundance on 28 islands using a line-transect method in the Zhoushan Archipelago, China from July to August 2013.We determined island geographical factors (area, isolation) based on the literature and obtained species life-history traits (area requirement, wingspan and body weight) in the laboratory.The recently developed metric WNODF was used to examine the nestedness.Partial Spearman rank correlation was used to evaluate the associations of nestedness and island geographical factors as well as life-history traits related to species extinction and immigration tendencies.We found that the community composition of butterflies in the Zhoushan Archipelago was significantly nested.Island area and species' area requirements were significantly correlated with nestedness after synthesis for all independent variables.In contrast, according to the null-model random test, nestedness of butterflies might not result from passive sampling or selective colonization.Our results indicate that selective extinction is the main driver of nestedness of butterflies in our system.From a conservation perspective, we suggest that large islands and species with large area requirements should be paid more attention in order to maximize the total number of species preserved.

Is the sword moss (Bryoxiphium) a preglacial Tertiary relict?

The Southern Ocean archipelago, the South Orkney Islands (SOI), became the world's first entirely high seas marine protected area (MPA) in 2010. The SOI continental shelf (~44000km(2) ), was less than half covered by grounded ice sheet during glaciations, is biologically rich and a key area of both sea surface warming and sea-ice losses. Little was known of the carbon cycle there, but recent work showed it was a very important site of carbon immobilization (net annual carbon accumulation) by benthos, one of the few demonstrable negative feedbacks to climate change. Carbon immobilization by SOI bryozoans was higher, per species, unit area and ice-free day, than anywhere-else polar. Here, we investigate why carbon immobilization has been so high at SOI, and whether this is due to high density, longevity or high annual production in six study species of bryozoans (benthic suspension feeders). We compared benthic carbon immobilization across major regions around West Antarctica with sea-ice and primary production, from remotely sensed and directly sampled sources. Lowest carbon immobilization was at the northernmost study regions (South Georgia) and southernmost Amundsen Sea. However, data standardized for age and density showed that only SOI was anomalous (high). High immobilization at SOI was due to very high annual production of bryozoans (rather than high densities or longevity), which were 2x, 3x and 5x higher than on the Bellingshausen, South Georgia and Amundsen shelves, respectively. We found that carbon immobilization correlated to the duration (but not peak or integrated biomass) of phytoplankton blooms, both in directly sampled, local scale data and across regions using remote-sensed data. The long bloom at SOI seems to drive considerable carbon immobilization, but sea-ice losses across West Antarctica mean that significant carbon sinks and negative feedbacks to climate change could also develop in the Bellingshausen and Amundsen seas.

Invasive species cause extensive damage to their introduced ranges. Ocean archipelagos are particularly vulnerable to invasive taxa. In this study, we used polymorphic microsatellite markers to investigate the genetic structure of the social wasp Vespula pensylvanica in its native range of North America and its introduced range in the archipelago of Hawaii. Our goal was to gain a better understanding of the invasion dynamics of social species and the processes affecting biological invasions. We found that V. pensylvanica showed no significant genetic isolation by distance and little genetic structure over a span of 2000 km in its native range. This result suggests that V. pensylvanica can successfully disperse across large distances either through natural‐ or human‐mediated mechanisms. In contrast to the genetic patterns observed in the native range, we found substantial genetic structure in the invasive V. pensylvanica range in Hawaii. The strong patterns of genetic differentiation within and between the Hawaiian Islands may reflect the effects of geographic barriers and invasion history on gene flow. We also found some evidence for gene flow between the different islands of Hawaii which was likely mediated through human activity. Overall, this study provides insight on how geographic barriers, invasion history, and human activity can shape population genetic structure of invasive species.

BackgroundFor a remote oceanic archipelago of up to 8 Myr age, the Azores have a comparatively low level of endemism. We present an analysis of phylogeographic patterns of endemic Azorean island arthropods aimed at testing patterns of diversification in relation to the ontogeny of the archipelago, in order to distinguish between alternative models of evolutionary dynamics on islands. We collected individuals of six species (representing Araneae, Hemiptera and Coleoptera) from 16 forest fragments from 7 islands. Using three mtDNA markers, we analysed the distribution of genetic diversity within and between islands, inferred the differentiation time-frames and investigated the inter-island migration routes and colonization patterns.ResultsEach species exhibited very low levels of mtDNA divergence, both within and between islands. The two oldest islands were not strongly involved in the diffusion of genetic diversity within the archipelago. The most haplotype-rich islands varied according to species but the younger, central islands contributed the most to haplotype diversity. Colonization events both in concordance with and in contradiction to an inter-island progression rule were inferred, while a non-intuitive pattern of colonization from western to eastern islands was also inferred.ConclusionsThe geological development of the Azores has followed a less tidy progression compared to classic hotspot archipelagos, and this is reflected in our findings. The study species appear to have been differentiating within the Azores for <2 Myr, a fraction of the apparent life span of the archipelago, which may indicate that extinction events linked to active volcanism have played an important role. Assuming that after each extinction event, colonization was initiated from a nearby island hosting derived haplotypes, the apparent age of species diversification in the archipelago would be moved closer to the present after each extinction–recolonization cycle. Exploiting these ideas, we propose a general model for future testing.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0523-x) contains supplementary material, which is available to authorized users.

A key challenge in island biogeography is to quantity the role of dispersal in shaping biodiversity patterns among the islands of a given archipelago. Here, we propose such a framework. Dispersal within oceanic archipelagos may be conceptualized as a spatio-temporal process dependent on: (1) the spatial distribution of islands, because the probability of successful dispersal is inversely related to the spatial distance between islands and (2) the chronological sequence of island formation that determines the directional asymmetry of dispersal (hypothesized to be predominantly from older to younger islands). From these premises, directional network models may be constructed, representing putative connections among islands. These models may be translated to eigenfunctions in order to be incorporated into statistical analysis. The framework was tested with 12 datasets from the Hawaii, Azores, and Canaries. The explanatory power of directional network models for explaining species composition patterns, assessed by the Jaccard dissimilarity index, was compared with simpler time-isolation models. The amount of variation explained by the network models ranged from 5.5% (for Coleoptera in Hawaii) to 60.2% (for Pteridophytes in Canary Islands). In relation to the four studied taxa, the variation explained by network models was higher for Pteridophytes in the three archipelagos. By the contrary, small fractions of explained variation were observed for Coleoptera (5.5%) and Araneae (8.6%) in Hawaii. Time-isolation models were, in general, not statistical significant and explained less variation than the equivalent directional network models for all the datasets. Directional network models provide a way for evaluating the spatio-temporal signature of species dispersal. The method allows building scenarios against which hypotheses about dispersal within archipelagos may be tested. The new framework may help to uncover the pathways via which species have colonized the islands of a given archipelago and to understand the origins of insular biodiversity.

The Crassulacean genus Aeonium is a well-known example for plant species radiation on oceanic archipelagos. However, while allopatric speciation among islands is documented for this genus, the role of intra-island speciation due to population divergence by topographical isolation or ecological heterogeneity has not yet been addressed. The aim of this study was to investigate intraspecific genetic structures and to identify spatial and ecological drivers of genetic population differentiation on the island scale. We analyzed inter simple sequence repeat variation within two island-endemic Aeonium species of La Palma: one widespread generalist that covers a large variety of different habitat types (Ae.davidbramwellii) and one narrow ecological specialist (Ae.nobile), in order to assess evolutionary potentials on this island. Gene pool differentiation and genetic diversity patterns were associated with major landscape structures in both species, with phylogeographic implications. However, overall levels of genetic differentiation were low. For the generalist species, outlier loci detection and loci-environment correlation approaches indicated moderate signatures of divergent selection pressures linked to temperature and precipitation variables, while the specialist species missed such patterns. Our data point to incipient differentiation among populations, emphasizing that ecological heterogeneity and topographical structuring within the small scales of an island can foster evolutionary processes. Very likely, such processes have contributed to the radiation of Aeonium on the Canary Islands. There is also support for different evolutionary mechanisms between generalist and specialist species.

Eleven satellite tags were deployed on 9 killer whales at the Prince Edwards Islands in the Southern Ocean. State-space switching models were used to generate position estimates from Argos location data, while two behavioural modes were estimated from the data.Individuals were tracked for 5.6–53.2days, during which time they moved 416–4470km (mean 82.7kmday−1) but 69% of position estimates were within the 1000m depth contour around the islands (<35km from the tagging site). Killer whales showed restricted behaviour close to the islands, particularly inshore where they can effectively hunt seals and penguins, and at seamounts to the north of the islands.Generalised linear mixed effect models were used to explore the relationship between environmental variables and behavioural mode. The best model included depth, sea surface temperature, latitude, sea surface height anomaly and bottom slope, but killer whales did not clearly target features such as fronts and apparent mesoscale eddies. Killer whales showed restricted behaviour in shallow water, at high latitudes and low sea surface temperature — the conditions characterising the archipelago.Dive data from two individuals largely revealed shallow dives (7.5–50m deep), but deeper dive bouts to around 368m were also recorded. Dives were significantly deeper during the day and maximum dive depths were 767.5 and 499.5m, respectively. This suggests that killer whales might also prey on vertically migrating cephalopods and perhaps Patagonian toothfish.Three individuals made rapid and directed long-distance movements northwards of the islands, the reasons for which are speculative.

Public awareness of the economic potential and threats to sharks of a tropical oceanic archipelago in the western South Atlantic

The Hawaiian islands are an extremely isolated oceanic archipelago, and their fauna has long served as models of dispersal in island biogeography. While molecular data have recently been applied to investigate the timing and origin of dispersal events for several animal groups including birds, insects, and snails, these questions have been largely unaddressed in Hawai'i’s only native terrestrial mammal, the Hawaiian hoary bat, Lasiurus cinereus semotus. Here, we use molecular data to test the hypotheses that (1) Hawaiian L. c. semotus originated via dispersal from North American populations of L. c. cinereus rather than from South American L. c. villosissimus, and (2) modern Hawaiian populations were founded from a single dispersal event. Contrary to the latter hypothesis, our mitochondrial data support a biogeographic history of multiple, relatively recent dispersals of hoary bats from North America to the Hawaiian islands. Coalescent demographic analyses of multilocus data suggest that modern populations of Hawaiian hoary bats were founded no more than 10 kya. Our finding of multiple evolutionarily significant units in Hawai'i highlights information that should be useful for re-evaluation of the conservation status of hoary bats in Hawai'i.

Due to their high controllability and flexibility, DC power grids have broad application prospects in the fields of networking of renewable energy and the power supply for oceanic archipelagos and future cities. This paper describes the system topology, control strategy, DC breaker configuration, and research, development and testing of converter valves and DC breaker equipment of the Zhoushan multi-terminal DC transmission system. Zhejiang Zhoushan has unique geographical and developmental features to demonstrate the irreplaceable technical advantages of a DC power grid for providing reliable power supply. The experience gained from the Zhoushan DC power grid project can offer valuable insights into the development and utilization of this technology worldwide.

Phylogenetic relationships in recent, rapid radiations can be difficult to resolve due to incomplete lineage sorting and reliance on genetic markers that evolve slowly relative to the rate of speciation. By incorporating hundreds to thousands of unlinked loci, phylogenomic analyses have the potential to mitigate these difficulties. Here, we attempt to resolve phylogenetic relationships among eight shrew species (genus Crocidura) from the Philippines, a phylogenetic problem that has proven intractable with small (< 10 loci) data sets. We sequenced hundreds of ultraconserved elements and whole mitochondrial genomes in these species and estimated phylogenies using concatenation, summary coalescent, and hierarchical coalescent methods. The concatenated approach recovered a maximally supported and fully resolved tree. In contrast, the coalescent-based approaches produced similar topologies, but each had several poorly supported nodes. Using simulations, we demonstrate that the concatenated tree could be positively misleading. Our simulations also show that the tree shape we tend to infer, which involves a series of short internal branches, is difficult to resolve, even if substitution models are known and multiple individuals per species are sampled. As such, the low support we obtained for backbone relationships in our coalescent-based inferences reflects a real and appropriate lack of certainty. Our results illuminate the challenges of estimating a bifurcating tree in a rapid and recent radiation, providing a rare empirical example of a nearly simultaneous series of speciation events in a terrestrial animal lineage as it spreads across an oceanic archipelago.