Dynamics of demographically open mutualists: immigration, intraspecific competition, and predation impact goby populations

Although it is now recognized that mutualistic species are common and can have stable populations, the forces controlling their persistence are poorly understood. To better understand the mechanisms that impact the stability of obligate mutualists, I conducted several field experiments within a sandy coral reef lagoon in Moorea, French Polynesia that manipulated densities of fish (gobies) that interact mutualistically with shrimp. Obligate, mutualistic partnerships of gobies and shrimp are common on Indo-Pacific coral reefs and have been shown previously to interact as follows: shrimp construct burrows in which both species reside, and gobies warn shrimp of predators through tactile communication. Augmentation of gobies by up to 100% above ambient densities within 9 m² plots produced no change in overall density of gobies or shrimp because gobies competed intraspecifically for a limited number of shrimp burrows and smaller gobies were outcompeted by larger individuals. I used predators to assess the impact of goby removal on the stability of goby and shrimp populations. First, although surveys taken throughout the lagoon revealed no relationship between goby and predator densities, predators correlated negatively with the proportion of adult gobies and positively with the proportion of small gobies paired with large shrimp. Second, experimental augmentation of predators resulted in a dramatic reduction of adult gobies within predator-addition plots, but had no impact on overall densities as immigrants rapidly replaced the missing adult gobies. Furthermore, goby turnover resulted in an increase in the proportion of small gobies paired with large shrimp because body sizes of gobies and shrimp in a burrow were similar prior to predator introduction, and predators apparently had a greater impact on gobies than shrimp. The mechanisms that prevent expansion (intraspecific competition) and collapse (immigration) of goby-shrimp populations likely contribute to local-scale stability of mutualistic populations in other terrestrial and aquatic environments.     

Four new species of Rhodophyceae from Fiji,Polynesia and Vanuatu,South Pacific

Four new species of Rhodophyceae are described from the South Pacific, with type localities in Fiji, French Polynesia and Vanuatu. Chondria bullata from the Tuamotus (French Polynesia), Vanuatu, Palmerston Atoll (Cook Islands) and Fiji is unique owing to its non‐constricted axes with markedly protruding, bubble‐like cortical cells. Halymenia nukuhivensis, from the Marquesas Islands in French Polynesia, is distinguished from others in the genus by its dichotomous, papery blades issued from a strap‐shaped basal region, and the equal proportion of anti‐clinal, periclinal and oblique filaments in its medullary layer. Jania articulata, so far known only from the Tuamotus in French Polynesia and Manihiki in the Northern Cook Islands, superficially resembles the genus Amphiroa with its articulated branches with numerous genicula between successive dichotomies, and its large axis diameter. Meristotheca peltata from the Fiji Islands is unique among the genus by its distinctly peltate, erect habit. The recent high number of newly described species from the South Pacific region emphasizes the need for more in‐depth surveys, particularly in deeper outer reef slope habitats, which remain for the most part unexplored and could yield particularly interesting new taxa or distributional records.     

Genetic analysis of Black Tiger shrimp (Penaeus monodon) across its natural distribution range reveals more recent colonization of Fiji and other South Pacific islands

The Black Tiger shrimp (Penaeus monodon) has a natural distribution range from East Africa to the South Pacific Islands. Although previous studies of Indo-Pacific P. monodon have found populations from the Indian Ocean and Australasia to differ genetically, their relatedness to South Pacific shrimp remains unknown. To address this, polymorphisms at eight shared microsatellite loci and haplotypes in a 418-bp mtDNA-CR (control region) sequence were examined across 682 P. monodon from locations spread widely across its natural range, including the South Pacific islands of Fiji, Palau, and Papua New Guinea (PNG). Observed microsatellite heterozygosities of 0.82-0.91, allele richness of 6.85-9.69, and significant mtDNA-CR haplotype variation indicated high levels of genetic diversity among the South Pacific shrimp. Analysis of microsatellite genotypes using a Bayesian STRUCTURE method segregated Indo-Pacific P. monodon into eight distinct clades, with Palau and PNG shrimp clustering among others from Southeast Asia and eastern Australia, respectively, and Fiji shrimp clustering as a distinct group. Phylogenetic analyses of mtDNA-CR haplotypes delineated shrimp into three groupings, with shrimp from Fiji again being distinct by sharing no haplotypes with other populations. Depending on regional location, the genetic structures and substructures identified from the genotyping and mtDNA-CR haplotype phylogeny could be explained by Metapopulation and/or Member-Vagrant type evolutionary processes. Neutrality tests of mutation-drift equilibrium and estimation of the time since population expansion supported a hypothesis that South Pacific P. monodon were colonized from Southeast Asia and eastern Australia during the Pleistocene period over 60,000 years ago when land bridges were more expansive and linked these regions more closely.     

Dispersal and diversification: macroevolutionary implications of the MacArthur–Wilson model, illustrated by Simulium (Inseliellum) Rubstov (Diptera: Simuliidae)

Aim Provide an empirical test of the ‘radiation zone’ hypothesis of the MacArthur–Wilson theory of island biogeography using the taxon‐pulse hypothesis of Erwin and Brooks Parsimony Analysis (BPA) on Simulium (Inseliellum) Rubstov. Location Micronesia, Cook Islands, Austral Islands, Society Islands, Marquesas Islands, Fiji and New Caledonia. Methods Primary and secondary BPA of the phylogeny of Inseliellum. Results Primary BPA showed that 15% of the taxon area cladogram contained area reticulations. Secondary BPA (invoking the area duplication convention) generated a clear sequence of dispersal for Inseliellum. The sequence follows a Micronesia – Cook Islands – Marquesas Islands – Society Islands dispersal, with a separate dispersal from the Cook Islands to the Austral Islands less than 1 Ma. A radiation in the island of Tahiti (Society Islands) produced numerous dispersals from Tahiti to other islands within the Society Islands system. Islands close to Tahiti (source island) have been colonized from Tahiti more often than islands far from Tahiti, but a higher proportion of those species colonizing distant islands have become distinct species. Main conclusions The dispersal sequence of Inseliellum exhibits both old to young island dispersal and young to old island dispersal. This is due to habitat availability on each island. Inseliellum is a model system in exemplifying the ‘radiation zone’ hypothesis of MacArthur and Wilson. As well, islands close to the source are colonized more often that those far from the source, but colonization of islands far away from the source results in a higher proportion of speciation events than for islands close to the source. The diversification of Inseliellum corresponds to a taxon‐pulse radiation, with a centre of diversification on Tahiti resulting from its large area and abundant freshwater habitats. This study illustrates the utility of BPA in identifying complex scenarios that can be used to test theories about the complementary roles of ecology and phylogeny in historical biogeography.     

Cancer epidemiology in the small nations of Pacific Islands

BackgroundPacific island countries and territories (PICTs) comprise 20,000–30,000 islands in the Pacific Ocean. PICTs face challenges in relation to small population sizes, geographic dispersion, increasing adoption of unhealthy life-styles and the burden of both communicable and non-communicable diseases, including cancer. This study reviews data on cancer incidence and mortality in the PICTs, with special focus on indigenous populations.MethodsPICTs with populations of <1.5 million (‘small nations’) were included in this study. Information on cancer incidence and mortality was extracted from the GLOBOCAN 2012 database. Scientific and grey literature was narratively reviewed for publications published after 2000.ResultsOf the 21 PICTs, seven countries were included in the GLOBOCAN 2012 (Fiji, French Polynesia, Guam, New Caledonia, Samoa, Solomon Islands, Vanuatu). The highest cancer incidence and mortality rates were reported in New Caledonia (age-standardized incidence and mortality rates 297.9 and 127.3 per 100.000) and French Polynesia (age-standardized incidence and mortality rates 255.0 and 134.4 per 100.000), with relatively low rates in other countries. Literature indicated that cancer was among the leading causes of deaths in most PICTs; thus they now experience a double burden of cancers linked to infections and life-style and reproductive factors. Further, ethnic differences in cancer incidence and mortality have been reported in some PICTs, including Fiji, Guam, New Caledonia and Northern Mariana Islands.ConclusionCancer incidence in the PICTs was recorded to be relatively low, with New Caledonia and French Polynesia being exceptions. Low recorded incidence is likely to be explained by incomplete cancer registration as cancer had an important contribution to mortality. Further endeavors are needed to develop and strengthen cancer registration infrastructure and practices and to improve data quality and registration coverage in the PICTs.     

Systematics of the extinct reed warblers Acrocephalus of the Society Islands of eastern Polynesia

In the Society archipelago (French Polynesia), Acrocephalus reed warblers are known only from four islands: Tahiti, Mo'orea, Huahine and Raiatea. All populations are now extinct except on Tahiti. Our knowledge of these birds is based on a small number of specimens preserved in museums, collected mostly during the 19th century. We present here a review of the past and present distribution, habitat and threats to the Society Islands reed warblers, including details on the specimens in museum collections. We compare the external morphology of the different populations, and use samples from museum specimens to propose a molecular phylogeny of all taxa based on partial cytochrome b gene sequences. The genetic data do not support the monophyly of the Society Islands reed warblers, which probably derived from three different lineages, found in Tahiti, Mo'orea and in the cluster Raiatea–Huahine. We outline the taxonomic consequences of this phylogeny. Our results support the hypothesis that evolutionary pattern, not distance between islands, shaped the long-distance colonization of oceanic islands by reed warblers.     

Characterization of 16 microsatellite loci for a common coral reef fish,the fierce shrimpgoby Ctenogobiops feroculus

We developed 16 pairs of primers for microsatellite loci of the fierce shrimpgoby, Ctenogobiops feroculus. Analysis of 35–40 gobies per locus from five islands in French Polynesia indicated that allele frequency varied from two to 30 per locus, while observed heterozygosity ranged between 0.05 and 0.98. These microsatellites should provide insight into patterns of dispersal and connectivity among populations of this common coral reef fish.     

THE DISPERSAL BARRIER IN THE TROPICAL PACIFIC: IMPLICATIONS FOR MOLLUSCAN SPECIATION AND EXTINCTION

Stretches of deep ocean constitute barriers to the dispersal of many shallow-water marine species in the tropical Pacific. The purpose of this study was to assess the selectivity of these barriers with respect to the habitat characteristics, adult size, and predation-related shell architecture of gastropods, and to explore the implications of this selectivity for macroevolutionary patterns of extinction and speciation. The dispersal barrier between continental islands (represented in my collections by species from eastern Indonesia, the southern Philippines, and the north coast of New Guinea) and the nearby oceanic Palau Islands was studied by evaluating the percentage of each architectural and habitat category that is present on the continental islands but missing in Palau. The barrier is significantly more effective against sand-dwelling species than against rock-dwellers, and among rock-dwellers it is most effective against aperturally unarmored taxa. Barriers between Palau and Guam, Guam and the Hawaiian Islands, and the Line Islands and the tropical Eastern Pacific are generally unselective with respect to substratum type and architecture. The fact that narrow-apertured species are less affected by the barrier between the continental islands and Palau than are other rock-dwelling gastropods is consistent with the interpretation that this group has been unusually resistant to extinction and highly susceptible to founder speciation when oceanic circulation is altered. These patterns of susceptibility and geographical distribution may explain why armored gastropods have increased in numbers relative to unarmored ones in the tropical Pacific during the Cenozoic.     

The phytogeographical affinities of the Pitcairn Islands – a model for south‐eastern Polynesia?

Aim To identify how the Pitcairn group relates biogeographically to the south‐eastern Polynesian region and if, as a subset of the regions flora, it can then be used as a model for biogeographical analyses. Location The Pitcairn group (25°4′ S, 130°06′ W) comprises four islands: Pitcairn, a relatively young, high volcanic Island; Henderson, an uplifted atoll, the uplift caused by the eruption of Pitcairn; and two atolls, Ducie and Oeno. The remote location, young age and range of island types found in the Pitcairn Island group makes the group ideal for the study of island biogeography and evolution. Methods A detailed literature survey was carried out and several data sets were compiled. Dispersal method, propagule number and range data were collected for each of the 114 species that occurs in the Pitcairn group, and environmental data was also gathered for islands in Polynesia. Analyses were carried out using non‐metric multidimensional scaling and clustering techniques. Results The flora of the Pitcairn Islands is derived from the flora of other island groups in the south‐eastern Polynesian region, notably those of the Austral, Society and Cook Islands. Species with a Pacific‐wide distribution dominate the overall Pitcairn group flora. However, each of the islands show different patterns; Pitcairn is dominated by species with Pacific, Polynesian and endemic distributions, with anemochory as the dominant dispersal method (39.5%); Henderson is also dominated by species with Pacific, Polynesian and endemic distributions, but zoochory is the dominant dispersal method (59.4); Oeno and Ducie are dominated by Pantropic species with hydrochory as the most common dispersal method (52.9% and 100%, respectively). Main conclusions ? Habitat availability is the most significant factor determining the composition and size of the flora. ? South‐east Polynesia is a valid biogeographical unit, and should include the Cook, Austral, Society, Marquesas, Gambier, Tuamotu and Pitcairn Islands with Rapa, but should exclude Easter Island, Tonga and Samoa. ? Regionalization schemes should take island type into consideration. ? The Pitcairn Island group can serve as a useful model for Pacific biogeographical analyses.     

Conservation and restoration of plant–animal mutualisms on oceanic islands

Islands harbour much of the world's threatened biodiversity. Recent work has highlighted how it is not species diversity per se but rather the interactions between organisms that breathes life into ecosystems. Thus, the real challenge to preserving and restoring biodiversity on islands is not to only focus on species themselves, but more importantly on maintaining and restoring the integrity of interactions between the species. Here we argue that mutualistic plant–animal interactions play a pivotal role with regards to conservation and restoration on islands. Furthermore, these interactions are ideally suited for inter-island comparisons due to ecological and evolutionary similarities across geographical and taxonomical boundaries. The similarities include highly generalised mutualistic systems, the evolution and readjustment of plant reproductive traits, and a disharmony in taxonomic groups of mutualists, compared to continental ecosystems. We highlight past and present threats to island plant–animal mutualisms, as well as the challenges and opportunities inherent to these interactions. In particular, we (1) argue that mutualistic networks provide an ideal approach to collect information and advance our knowledge on the systems, (2) suggest the use of interactions as biodiversity monitoring and assessment tools, (3) highlight the differences and similarities between pollination and seed dispersal interactions in the context of restoration, and (4) briefly discuss the ambiguous role of alien invasive species in the management of mutualistic interactions. Finally, we highlight how a recently proposed but controversial restoration strategy, rewilding, can be gainfully applied to and further advanced in island settings.     

Origin and evolution of endemic plants of the Bonin (Ogasawara) Islands

The Bonin Islands are typical oceanic islands, located at the western part of the North Pacific Ocean and approximately 1,000 km south of mainland Japan. This archipelago consists of about 20 small islands. Although floristic diversity is low due to the small area and limited environmental diversity, the Bonin Islands harbor unique endemic flora as in other well-known oceanic islands. This paper presents a brief summary of the results obtained from recent studies on the endemic flora of the Bonin Islands. The results are reviewed in relation to the four stages of the evolution of endemic flora in the oceanic islands; migration, establishment, enlargement and diversification. The ancestors of the flora originated mostly from tropical and subtropical Southeast Asia or mainland Japan by rare events of long distance dispersal. The proportion of bird-dispersed species is relatively high as for other oceanic islands. Genetic data sets obtained from allozyme variation in some endemic species suggest that migration occurred several million years ago and genetic diversity is correlated with current population size. At the time of establishment, self-compatible plants are expected to have an advantage. However, the percentage of dioecious plants is relatively high. This is partly due to evolutionary changes from hermaphroditic ancestors to dioecy which occurred in two genera in the Bonin Islands. In addition, there are some examples of evolutionary changes from herbaceous ancestors to woody endemics. Adaptive radiation is found in some genera, although the number of congeneric endemic species is less than five. Studies of allozyme variation inPittosporum, Symplocos andCrepidiastrum showed that genetic identity is generally very high between congeneric species in spite of their distinct morphologies. This result suggests that divergence of these species occurred rather recently and distinct morphological differences are based on a limited number of genetic changes.     

Impacts of introduced species on the biota of an oceanic archipelago: the relative importance of competitive and trophic interactions

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.     

Competition by obligate and facultative mutualists for partners in a shrimp-goby association

Mutualist species compete intra and inter-specifically for the resources provided by their partners. Because obligate mutualists are more reliant than facultative mutualists on the resources that their partners provide, they are expected to compete more strongly for those resources. Here, I examined interference competition in two goby fishes: Nes longus (an obligate mutualist) and Ctenogobius saepepallens (a facultative mutualist). Both gobies associate with the shrimp, Alpheus floridanus. Shrimp provide gobies with refuge from predators (a burrow in the sand), and gobies provide shrimp with a warning signal when predators are near. Using an aquarium experiment, I examined the behavior of a pair of gobies with access to a single shrimp burrow. I used four different goby pairings: large N. longus and small N. longus, large N. longus and small C. saepepallens, large C. saepepallens and small N. longus, and large C. saepepallens and small C. saepepallens. When paired with large N. longus individuals, small gobies of both species were less likely to occupy the single burrow than when paired with large C. saepepallens individuals. In addition, large N. longus individuals were less likely to co-occupy the single burrow with smaller gobies than were large C. saepepallens individuals. These results seem to indicate that large N. longus individuals exclude smaller gobies from burrows, while large C. saepepallens individuals do not. This study adds evidence to the supposition that obligate mutualists in general compete more strongly for mutualist partners than do facultative mutualists.     

Partner choice in Gobiid fish Myersina macrostoma living in association with the alpheid shrimp Alpheus rapax

Partner choice is an important selective force in mutualistic partnerships. Although several aspects of mutualism have been well-studied, partner choice remains a novel aspect in the study of marine mutualists. Previous research on the goby-shrimp mutualism suggested that visual cues affect the ability of gobies to discriminate between potential shrimp partners but small sample sizes limited the generalization of that result. Here, primary partner choice in Myersina macrostoma was investigated in a series of ex situ experiments. Results indicated that shrimp-associated gobies relied on visual cues in partner choice. The goby M. macrostoma was clearly able to discern between different shelter types, demonstrating a preference for burrows compared to rocks. While they were attracted to larger burrows, they were not visually attracted to larger shrimp partners. This indicates that in wild populations, intraspecific competition for larger burrows might be the driving factor in size assortment in associated partners. Myersina macrostoma could also discern between species of shrimps in laboratory experimental set-ups, indicating a clear preference for A. rapax which they naturally occur with, but not to A. lobidens, which occurs at the same locality but with which they do not naturally associate. These findings offer fundamental building blocks towards the broader understanding of partnership formations in marine mutualists.     

The role of spatial and ontogenetic morphological variation in the expansion of the geographic range of the tropical brown alga, Turbinaria ornata

Like many reefs worldwide, reefs in French Polynesia are experiencing a shift from coral-dominated to algal-dominated systems. The macroalga Turbinaria ornata comprises the majority of the increasing algal biomass on the barrier reefs surrounding these islands, and its distribution is increasing throughout this region. Aspects of the ecomorphology of Turbinaria make it ideally suited to thrive under the physical conditions found across barrier reefs throughout French Polynesia. Spatial morphological variation allows Turbinaria to produce morphotypes that are suited either to the calm, unidirectional, slowly flowing water in the backreef or to the high-energy wave-driven flow of the forereef. Backreef plants are flexible and produce airbladders that make them buoyant, whereas forereef plants are not buoyant, but strong and stiff. Production of bladders and resulting buoyancy has been found to be a phenotypically plastic trait in response to movement of water and confers advantages to backreef plants and plays an important role in dispersal. Ontogenetic variation of buoyancy, material properties, and reproductive capacity is part of a dispersal strategy whereby fertile, buoyant fronds drift between oceanic islands and form new populations, thereby contributing to the recent expansion of range of T. ornata across French Polynesia.     

Local completion of the pelagic larval stage of coastal fishes in coral-reef lagoons of the Society and Tuamotu Islands

In four lagoons at two atolls and one high island in the Tuamotu and Society Islands, French Polynesia, plankton samples were taken weekly during 4 weeks in January/February 1989. A third atoll lagoon was sampled once. The lagoons varied in size and physical openness. We also sampled in the ocean near two atolls and the high island. All locations were sampled during the day, and three lagoons (two atolls and one high island) were also sampled at night. Pelagic fish eggs were more abundant in the ocean than in the lagoons at the atolls, but not at the high island. Larvae of coastal fishes were abundant in all lagoons. In the atoll lagoons, larvae of oceanic fishes were very rare to absent, but in the high-island lagoons and in the ocean, they were commonly encountered. In the ocean, larvae of many typical reef-fish taxa were abundant (58 taxa were represented by at least 10 individuals), but in the lagoons, most of these were rare or absent, and we conclude that these rare and absent taxa normally do not complete their larval phase in lagoons.Taxa were considered to be able to complete their pelagic phase in a lagoon (i.e., were 'completers') if they were present in the lagoon plankton samples from across a full larval size range. In the high-island barrier-reef lagoon, young, preflexion larvae were abundant, but only two taxa (of 56 captured) were present over a wide size range and were considered completers in this lagoon. In the high-island lagoonal bay, 11 taxa (of 67 captured) were considered completers. The numbers of taxa captured in the three atoll lagoons ranged from 39–44, and the number of taxa considered to be completers increased with increasing lagoon size and physical openness. The 17 completer taxa in the smallest, most enclosed atoll lagoon were, with one exception, a subset of those (18) in the second lagoon which, in turn, with one exception, were a subset of those in the largest, most open lagoon (26). Completer taxa were of the families Apogonidae, Blenniidae, Bothidae, Callionymidae, Carangidae, Gobiidae, Microdesmidae, Mullidae, Pomacentridae, Schindleriidae, and Tetraodontidae. The species that can complete their pelagic periods in coral-reef lagoons are a highly predictable group, and not simply a random selection of the potential species pool. Most of these species hatch from non-pelagic eggs. Water renewal times in the atoll lagoons, unlike the high-island barrier-reef lagoon, were much longer than expected pelagic larval durations of completer taxa. Demographically, lagoon populations of completer taxa apparently self-recruit and are probably near the closed end of the open/closed population continuum. The lagoonal bay on the high island differs from the other lagoons in containing larvae of species not found elsewhere, including some completers, and lacking some species that are abundant completers in other lagoons. In French Polynesia, lagoon size is a strong predictor of the number of lagoon completer taxa. The number of completer taxa apparently peaks at intermediate lagoon water-exchange times.     

Tahiti's native flora endangered by the invasion of Miconia calvescens DC. (Melastomataceae)

Abstract. The native flora of tropical oceanic islands is known to be particularly susceptible both to displacement and extinction, following the invasion of alien organisms. Miconia calvescens DC. (Melastomataceae), first introduced to Tahiti (French Polynesia, South Pacific Ocean) in 1937 as an ornamental plant, now covers over two-thirds of the Island. As it forms dense monotypic stands which have progressively overwhelmed the native forests, this plant pest is a direct threat to the rich Tahitian indigenous flora. Between 40 and 50 species of the 107 species endemic to Tahiti are thought to be on the verge of extinction. M. calvescens was finally declared a'noxious species in French Polynesia'in 1990. Without efficient control efforts and effective endangered plant conservation and protection legislation, M. calvescens could cause Tahiti and all the high islands of French Polynesia to become ecological deserts.     

Extinction‐driven changes in frugivore communities on oceanic islands

Global change and human expansion have resulted in many species extinctions worldwide, but the geographic variation and determinants of extinction risk in particular guilds still remain little explored. Here, we quantified insular extinctions of frugivorous vertebrates (including birds, mammals and reptiles) across 74 tropical and subtropical oceanic islands within 20 archipelagos worldwide and investigated extinction in relation to island characteristics (island area, isolation, elevation and climate) and species’ functional traits (body mass, diet and ability to fly). Out of the 74 islands, 33 islands (45%) have records of frugivore extinctions, with one third (mean: 34%, range: 2–100%) of the pre‐extinction frugivore community being lost. Geographic areas with more than 50% loss of pre‐extinction species richness include islands in the Pacific (within Hawaii, Cook Islands and Tonga Islands) and the Indian Ocean (Mascarenes, Seychelles). The proportion of species richness lost from original pre‐extinction communities is highest on small and isolated islands, increases with island elevation, but is unrelated to temperature or precipitation. Large and flightless species had higher extinction probability than small or volant species. Across islands with extinction events, a pronounced downsizing of the frugivore community is observed, with a strong extinction‐driven reduction of mean body mass (mean: 37%, range: –18–100%) and maximum body mass (mean: 51%, range: 0–100%). The results document a substantial trophic downgrading of frugivore communities on oceanic islands worldwide, with a non‐random pattern in relation to geography, island characteristics and species’ functional traits. This implies severe consequences for ecosystem processes that depend on mutualistic plant–animal interactions, including ecosystem dynamics that result from the dispersal of large‐seeded plants by large‐bodied frugivores. We suggest that targeted conservation and rewilding efforts on islands are needed to halt the defaunation of large and non‐volant seed dispersers and to restore frugivore communities and key ecological interactions.     

Wetlands of the Pacific Island region

The wetlands of 21 countries and territories of the Pacific Islands region are reviewed: American Samoa, Cook Islands, Federated States of Micronesia, Fiji, French Polynesia, Guam, Kiribati, Marshall Islands, Nauru, New Caledonia, Niue, Northern Mariana Islands, Palau, Papua New Guinea, Samoa, Solomon Islands, Tokelau, Tonga, Tuvalu, Vanuatu, and Wallis and Futuna. The regions’ wetlands are classified into seven systems: coral reefs, seagrass beds, mangrove swamps, riverine, lacustrine, freshwater swamp forests and marshes. The diversity of species in each of these groups is at near global maxima at the west of the region, with decline towards the east with increasing isolation, and decreasing island size and age. The community structure is unique in each country, and many have endemic species with the habitat isolation that epitomises this island region. There remain, however, some serious gaps in basic inventory, particularly in freshwater biodiversity. Threats to wetlands include introduced freshwater species, loss of wetlands adjacent to urban growth, downstream effects of mining and land clearance, and over-use of mangrove, seagrass and coral reef resources by predominant subsistence economies that remain in this region. Only five countries are signatories to the Ramsar convention on wetlands, and this only recently with seven sites. Wetland managers have identified the need for community education, baseline surveys and monitoring, better legislation and policy for wetland management, and improved capacity of local communities to allow the wise use of their wetlands.     

Reductions in the mitochondrial DNA diversity of coral reef fish provide evidence of population bottlenecks resulting from Holocene sea-level change

This study investigated the influence of reproductive strategy (benthic or pelagic eggs) and habitat preferences (lagoon or outer slope) on both diversity and genetic differentiation using a set of populations of seven coral reef fish species over different geographic scales within French Polynesia. We hypothesized that a Holocene sea-level decrease contributed to severe reduction of population size for species inhabiting lagoons and a subsequent decrease of genetic diversity. Conversely, we proposed that species inhabiting stable environments, such as the outer slope, should demonstrate higher genetic diversity but also more structured populations because they have potentially reached a migration-genetic drift equilibrium. Sequences of the 5' end of the mitochondrial DNA (mtDNA) control region were compared among populations sampled in five isolated islands within two archipelagos of French Polynesia. For all the species, no significant divergences among populations were found. Significant differences in mtDNA diversity between lagoonal and outer-slope species were demonstrated both for haplotype diversity and sequence divergence but none were found between species with different egg types. Pairwise mismatch distributions suggested rapid population growth for all the seven species involved in this study, but they revealed different distributions, depending on the habitat preference of the species. Although several scenarios can explain the observed patterns, the hypothesis of population size reduction events relative to Holocene sea-level regression and its consequence on French Polynesia coral reefs is the most parsimonious. Outer-slope species have undergone a probable weak and/or old bottleneck (outer reefs persisted during low sea level, leading to reef area reductions), whereas lagoonal species suffered a strong and/or recent bottleneck since Holocene sea-level regression resulted in the drying out of all the atolls that are maximum 70 meters deep. Since present sea level was reached between 5000 and 6000 years ago, different demographic events (bottlenecks or founder events) have lead to the actual populations of lagoons in French Polynesia.