Island Size Research Articles

Global-scale changes in the area of atoll islands during the 21st century

The long-term persistence of atoll islands is under threat due to continued sea level rise driven by anthropogenic climate change. One widely discussed potential impact of sea level rise is the widespread, chronic erosion of atoll islands. Despite concerns of erosion driven by sea level rise, no published evidence exists of pervasive erosion of atoll islands at a global scale. Existing studies of atoll island change have been based on small, temporally sparse samples of islands on a limited number of atolls. As a result, the global response of atoll islands coincident with sea level rise remains uncertain. Using rich collections of Landsat imagery, this study analyses changes in land area on 221 atolls in the Indian and Pacific Oceans. Results show that, between 2000 and 2017, the total land area on these atolls has increased by 61.74 km2 (6.1 %) from 1007.60 km2 to 1069.35 km2. Most of the change in land area resulted from island building within the Maldives and on atolls in the South China Sea. Since 2000, the Maldives have added 37.50 km2 of land area, while 16.57 km2 of new islands have appeared within the South China Seas Spratly and Paracel chains. Understanding the extent of land area change at the global scale improves insights into the variation in responses, and how the manipulation of land is shaping the potential habitability trajectory for some atoll communities. Results highlight the anthropogenic imprint on the size of atoll islands, thereby providing a better understanding of variations in the future trajectories of human settlement and adaptation within atoll settings.

Longitudinal trends of the small mammal community of the Apostle Islands archipelago

Documenting longitudinal changes in small mammal communities provides insights into ecosystem dynamics. We examined changes in small mammal communities of the Apostle Islands archipelago (Wisconsin, USA) since the establishment of the Apostle Islands National Lakeshore in 1970. We trapped small mammals from 20 of the 22 islands of the archipelago (2017–2020) and compared those results to historical (1961–2004) records. Microtus pennsylvanicus (p = 0.0076) and Sorex cinereus (p = 0.0268) exhibited significant changes in distribution. Microtus pennsylvanicus was likely extirpated from 10 of the 11 islands where it was previously detected, while S. cinereus increased in distribution. Peromyscus spp. colonized at least three islands since the establishment of the National Lakeshore, potentially through human-facilitated dispersal (i.e., boating, kayaking). Myodes gapperi remained widespread and abundant. Recent trends (2003–2004 to 2017–2020) in abundance indicated that S. cinereus may be declining locally on the islands, whereas Tamiasciurus hudsonicus may be increasing. Community diversity was driven by island size, regardless of variation over time. Long-term changes in small mammal populations across the archipelago likely reflect reduction of human extractive activities following the establishment of the National Lakeshore and the corresponding succession of vegetative communities. Our work suggests that even though small mammal communities of the archipelago have changed over time, larger islands may be able to better retain species that have been lost on others; therefore, island size remains an important predictor of community diversity.

Anisotropic zero-resistance onset in organic superconductors

We study the coexistence of superconductivity (SC) and density-wave state and reconcile various puzzling experimental data in organic superconductors (TMTSF)$_{2}$PF$_{6}$ and (TMTSF)$_{2}$ClO$_{4}$. The anisotropic resistance drop above $T_c$ is qualitatively described by nascent isolated SC islands within a bulk analytical model. However, the observed anisotropic SC onset is explained only when the finite size and flat needle shape of samples is considered. Our results pave a way to estimate the volume fraction and the typical size of SC islands in far from the sample surface, and apply to many inhomogeneous superconductors, including high-$T_c$ cuprate or Fe-based ones.

Microbiome and environment explain the absence of correlations between consumers and their diet in Bornean microsnails.

Classical ecological theory posits that species partition resources such that each species occupies a unique resource niche. In general, the availability of more resources allows more species to co‐occur. Thus, a strong relationship between communities of consumers and their resources is expected. However, correlations may be influenced by other layers in the food web, or by the environment. Here we show, by studying the relationship between communities of consumers (land snails) and individual diets (from seed plants), that there is in fact no direct, or at most a weak but negative, relationship. However, we found that the diversity of the individual microbiome positively correlates with both consumer community diversity and individual diet diversity in three target species. Moreover, these correlations were affected by various environmental variables, such as anthropogenic activity, habitat island size, and a possibly important nutrient source, guano runoff from nearby caves. Our results suggest that the microbiome and the environment explain the absence of correlations between diet and consumer community diversity. Hence, we advocate that microbiome inventories are routinely added to any community dietary analysis, which our study shows can be done with relatively little extra effort. Our approach presents the tools to quickly obtain an overview of the relationships between consumers and their resources. We anticipate our approach to be useful for ecologists and environmentalists studying different communities in a local food web.

Three-Dimensional Characterization of Morphology and Crystallography of a Gold Nanoisland Film

The morphological and crystallographic characteristics of noble metal nanoisland films play an important role in determining their properties, performance, and reliability. In this work we have applied a rapid three-dimensional orientation mapping technique in the transmission electron microscope (3D-OMiTEM) in the characterization of a gold nanoisland film. A volume of 200×1024×1024 nm3 has been analyzed, generating a 3D orientation map composed of more than 500 nanoislands and 7000 grains constituting the islands. The 3D shapes and sizes of individual islands and grains have been analyzed, revealing their true 3D morphological features and the correlation between the number of grains within individual islands and the size of the islands. The crystallographic orientations of the grains and the misorientations across the grain boundaries have been quantified, revealing a weak texture but a preferential presence of Σ3 and Σ9 grain boundaries in the gold nanoisland film.

Controlling hydrogen evolution reaction activity on Ni core-Pt island nanoparticles by tuning the size of the Pt islands.

Pt islands with different sizes were grown on amorphous Ni nanoparticles, allowing the tuning of the Pt-Ni interface without changing the hydrogen binding energy of the Pt sites. As a result, the HER activity of the electrocatalysts increases by decreasing the size of the Pt islands due to the greater surface area of the Pt-Ni interfaces.

Maintenance of long-term equilibrium in a perturbed metacommunity of sub-arctic marine fishes

The theory of island biogeography (TIB) predicts that species richness in isolated areas is determined by the processes of colonization and extinction, and, in turn, governed by island size and isolation. Metacommunity models extend the TIB, predicting that both habitat and species interactions are important drivers of community vital rates and structure, and that marine metacommunities will exhibit higher extinction/colonization rates relative to terrestrial ecosystems. Here we demonstrate that oceanic banks can be considered islands, and document how application of these theories advanced our understanding of the dynamics of these submarine islands following the fishery-induced collapse of predatory groundfish populations. We employed a 48 yr dataset of fish communities on 10 offshore banks of the Scotian Shelf, Northwest Atlantic Ocean to examine colonization and extinction rates before and after the collapse. Bank-specific colonization, extinction and turnover rates were quantified using the island R package to correct for imperfect detectability, inherent to all sampling of natural systems. Colonization and extinction events were briefly unbalanced following the predator collapse, and reflected in increases in species richness and turnover, most notably on the largest banks. However, over the longer term, a dynamic equilibrium of colonization and extinction events prevailed on 8 of the 10 banks. This resulted in a generally time-invariant species richness, and a negative relationship between species turnover and bank area, as predicted by theory. Our study provides support for the relevance of island biogeography and metacommunity theories in guiding exploration and understanding of the mechanisms governing marine community vital rates and structure.

Migratory pattern and larval duration of an amphidromous goby (

The larval period is a critical stage for many aquatic organisms, because larvae are small, fragile, and have high mortality rates. Amphidromous fish spend their larval stages in the sea, and larval durations vary, possibly reflecting their dispersal tendencies. The genus Rhinogobius (suborder Gobioidei) is widely distributed throughout Asia and exhibits a variety of migratory patterns. Despite some studies of their migratory histories, larval durations of Rhinogobius species are uncertain. This study used analyses of otolith microstructure and trace-elemental chemistry to investigate habitat use throughout the life history of R. nagoyae. Twenty-six adult gobies were collected from seven rivers on Sado Island, in northern Japan, and otolith Sr : Ca ratios were quantified using electron microprobe analysis to infer amphidromous movement. All individuals showed shifts in Sr : Ca ratio across the otolith transect, which indicated movement between freshwater and saltwater. Marine larval duration was estimated by otolith increment counting, combined with Sr : Ca ratio. Larval duration ranged from 29 to 45 days (mean, 35.3), and there were no significant differences among rivers on the island. The relatively short larval duration of R. nagoyae, compared with other amphidromous fish such as ayu and galaxids, may reflect environmental factors such as island size, cool weather or species characteristics.

О ТЕРМИНОЛОГИИ И КЛАССИФИКАЦИИ РАЗВЕТВЛЕНИЙ РУСЕЛ РАВНИННЫХ РЕК

Braided river channels are very diverse both morphologically (in terms of the number and water content of channel branches, size and shape of islands, their position, ratios, evolution, etc.), and in the mode of channel changes. Nevertheless, both in Russian and foreign literature, when describing them, there are different points of view on terms and classifications that define them, which make it difficult to analyze types of braided channels and regimes of channel changes, possible reactions of channels to changes in factors due to too much generalization. The classification of Moscow State University is considered to be an exception. It is constantly being improved as new data are obtained based on scientific research. Braided channel reaches are formed at several structural levels – point, midchannel bars, channel (island), floodplain-channel and floodplain (split channels). Each higher level of braided channels includes channel types of the previous levels. The main channel patterns that determine channel regime of braided rivers are island-braided channels, along which there are distinguished morphological homogeneous reaches or single patterns of channels or certain channel branches. In turn, in island-braided channels each of their types has several varieties depending on the number and morphology of islands, channel stability, water content of channel branches and peculiarities of water and sediment runoff dispersion along them. Braided channel types and their varieties are characterized by certain values of the flow quasi-uniformity indicator of I.F. Karasev and special coefficients in hydrological and morphological relationships linking morphological parameters of channels with characteristics of determining factors. The article provides a detailed, most complete classification of braided channels and substantiates the use of terms and concepts that characterize each type or braided channel reaches and their elements.

Influence of marsh island size on nekton communities: intermediate optima rather than Single-Large-or-Several-Small (SLOSS)

Habitat extent and configuration are critical drivers of faunal abundance, diversity, and ecosystem functioning. Evidence from terrestrial systems often suggests that large contiguous tracts of habitat generally support more species and individuals than several small patches of equal summed area. However, studies from shallow-water marine systems often suggest the opposite trend or that there are more complex interactions. Since tidal wetlands (e.g. salt marshes and mangrove forests) are at the interface between terrestrial and marine ecosystems and provide essential nursery habitat for a variety of estuarine taxa, it is important to elucidate how the size, configuration, and surrounding matrix of these wetlands influence their role in supporting faunal communities. We sampled 12 isolated marsh islands ranging in size from 300 to 55000 m2 within North Carolina, USA, to better understand the influence of marsh size and configuration on overall biodiversity and faunal abundance of estuarine nekton. Field observations indicated that nekton catch rates were directly correlated with marsh area and perimeter; however, species richness did not change with marsh size or configuration. Further analysis indicated that small and medium marsh islands support higher species turnover among islands than large marsh islands. Quantitative simulations using the ‘Single-Large-Or-Several-Small’ framework and idealized, circular islands showed that intermediate-sized islands support the highest relative abundance of nekton after standardizing for total marsh area. Our findings suggest that focused conservation or restoration efforts for marsh islands ranging in size from 1000 to 10000 m2 may help maintain and enhance estuarine nekton communities.

Solid-State Dewetting Dynamics of Amorphous Ge Thin Films on Silicon Dioxide Substrates.

We report on the dewetting process, in a high vacuum environment, of amorphous Ge thin films on SiO2/Si (001). A detailed insight of the dewetting is obtained by in situ reflection high-energy electron diffraction and ex situ scanning electron microscopy. These characterizations show that the amorphous Ge films dewet into Ge crystalline nano-islands with dynamics dominated by crystallization of the amorphous material into crystalline nano-seeds and material transport at Ge islands. Surface energy minimization determines the dewetting process of crystalline Ge and controls the final stages of the process. At very high temperatures, coarsening of the island size distribution is observed.

The island biogeography of the eBird citizen‐science programme

AbstractAimIsland biotas face an array of unique challenges under global change. Monitoring and research efforts, however, have been hindered by the large number of islands, their broad distribution and geographical isolation. Global citizen‐science initiatives have the potential to address these deficiencies. Here, we determine how the eBird citizen‐science programme is currently sampling island bird assemblages annually and how these patterns are developing over time.LocationGlobal.TaxaBirds.MethodsWe compiled occurrence information of non‐marine bird species across the world's islands (n = 21,813) over an 18‐year period (2002–2019) from eBird. We estimated annual survey completeness and species richness across islands, which we examined in relation to six geographical and four climatic features.ResultseBird contained bird occurrence information for ca. 20% of the world's islands (n = 4,205) with ca. 8% classified as well surveyed annually (n = 1,644). eBird participants tended to survey larger islands that were more distant from the mainland. These islands had lower proximity to other islands and contained a broader range of elevations. Temperature, precipitation and temperature seasonality were at intermediate levels. Precipitation seasonality was at low and intermediate levels. Islands located between 10 and 60° N latitude and 20 and 40° S latitude were overrepresented, and islands located in Southeast Asia were underrepresented. From 2002 to 2019, the number of islands surveyed annually increased by ca. 96.4 islands/year. During this period, island size decreased, distance from mainland did not change, proximity to other islands increased and elevation range decreased.Main conclusionsThe eBird programme tends to survey larger islands containing intermediate climates that are more isolated from the mainland and other islands. These findings provide a framework to support the informed application of the eBird database in avian island biogeography. Our findings emphasize citizen science as an empirical resource to support long‐term ecological research, conservation and monitoring efforts across remote regions of the globe.

Wind plays a major but not exclusive role in the prevalence of insect flight loss on remote islands.

Terrestrial species on islands often show reduced dispersal abilities. For insects, the generality of explanations for island flight loss remains contentious. Although habitat stability is considered the most plausible explanation, others are frequently highlighted. Adopting a strong inference approach, we examined the hypotheses proposed to account for the prevalence of flightlessness in island insect assemblages, for a region long suspected to be globally unusual in this regard-the Southern Ocean Islands (SOIs). Combining comprehensive faunal inventories, species' morphological information, and environmental variables from 28 SOIs, we provide the first quantitative evidence that flightlessness is exceptionally prevalent among indigenous SOI insect species (47%). Prevalence among species which have evolved elsewhere is much lower: Arctic island species (8%), species introduced to the SOIs (17%), and globally (estimated as approx. 5%). Variation in numbers of flightless species and genera across islands is best explained by variation in wind speed, although habitat stability (thermal seasonality proxy) may play a role. Variables associated with insularity, such as island size, are generally poor predictors of flightlessness. The outcomes redirect attention to Darwin's wind hypothesis. They suggest, however, that wind selects for flightlessness through an energy trade-off between flight and reproduction, instead of by displacement from suitable habitats.

Island size affects wood decomposition by changing decomposer distribution

Island biogeography theory describes the relationship between island size, isolation and biodiversity, but it does not address the effects on ecosystem processes such as wood decomposition. Wood decomposition rates can be expected to increase with decomposer diversity, which increases with island size and decreases with increasing island isolation. However, island size and isolation effects on wood decomposition may also act by impacting substrate composition, forest composition and biotic interactions among decomposers. In this study, branch‐wood decomposition rates of three locally dominant tree species deployed at 154 plots on 15 islands in Thousand Island Lake, China, were measured over one year. The results showed that decomposition rates in coarse‐mesh bags where both termites and fungi were allowed access increased with island size for the two tree species preferred by the termites. By contrast, decomposition rates in fine‐mesh bags which only fungi could access decreased with island size for the two tree species preferred by fungi. The positive effects of island size on termite feeding activity were mediated by a higher deadwood diversity, a more diverse forest composition and a higher soil moisture content, with forest composition shaping soil moisture. For fungal diversity, the negative effects of island size were attributable to a higher soil moisture content and termite feeding activity. Island isolation decreased fungal diversity but increased wood decomposition rates. Our study indicates that island size affects wood decomposition by altering the distribution of decomposers and their relative contributions to wood decomposition. Size–decomposition relationship further depends on the affinity between substrates and decomposer taxa. In general, our results show that ecosystem processes may be affected by island size and isolation, but the patterns are more complex than expected from the island biogeography theory. This discrepancy is largely due to the different responses and trade‐offs among different functional groups.

What makes an island a suitable refuge for an endemic lizard?

AbstractAimTo identify and evaluate the environmental properties of the Mediterranean islands that make them a suitable habitat for their endemic lizards. This would represent an important improvement in our knowledge and would assist the conservation of these lizards, which are threatened by both the expansion of mainland species and the increasing intensity of human disturbance on these islands.LocationMediterranean Basin.MethodsI assessed the environmental associations of 50 species of lizard (19 endemic) across 552 Mediterranean islands using outlying mean index analysis. The strength of the species responses was assessed using binomial generalized linear models.ResultsThe presence of endemic species is positively correlated with the distance of the island from the mainland. Island connectivity is also positively correlated with an increased presence of endemic lizards, but not with an increased presence of mainland species (i.e. those with exclusive or mainly continental natural distribution). In addition, island size, temperature and vegetation productivity are positively correlated with the presence of mainland species. Outlying mean index (OMI) analysis showed that the endemic species occupy niche positions that are similar to the average environmental conditions in the archipelago, but frequently without using the entire range of niches. The mainland species usually occur in more peripheral positions in the environmental space, except for some highly expansive species.ConclusionsLizards that are endemic to the Mediterranean islands were found to be present on a large number of islands within an archipelago, but they quickly disappear as the conditions change, largely because of human activity. Large islands act as population reservoirs for mainland species, facilitating secondary colonization of peripheral islets.

Inter- and intra-archipelago dynamics of population structure and gene flow in a Polynesian bird

Islands are separated by natural barriers that prevent gene flow between terrestrial populations and promote allopatric diversification. Birds in the South Pacific are an excellent model to explore the interplay between isolation and gene flow due to the region’s numerous archipelagos and well-characterized avian communities. The wattled honeyeater complex (Foulehaio spp.) comprises three allopatric species that are widespread and common across Fiji, Tonga, Samoa, and Wallis and Futuna. Here, we explored patterns of diversification within and among these lineages using genomic and morphometric data. We found support for three clades of Foulehaio corresponding to three recognized species. Within F. carunculatus, population genetic analyses identified nine major lineages, most of which were composed of sub-lineages that aligned nearly perfectly to individual island populations. Despite genetic structure and great geographic distance between populations, we found low levels of gene flow between populations in adjacent archipelagos. Additionally, body size of F. carunculatus varied randomly with respect to evolutionary history (as Ernst Mayr predicted), but correlated negatively with island size, consistent with the island rule. Our findings support a hypothesis that widespread taxa can show population structure between immediately adjacent islands, and likely represent many independent lineages loosely connected by gene flow.

Parasites in a hotspot: diversity and specificity patterns of apicomplexans infecting reptiles from the Socotra Archipelago.

Although parasites represent a major component of biodiversity, they remain poorly assessed, especially in remote regions. In this study, we screened 461 reptiles from Socotra, the largest and most biologically diverse archipelago in Arabia. Using 18S rRNA primers, we detected various apicomplexan parasites, namely haemogregarines, sarcocystids and eimeriids. Haemogregarines were the most common and genetically diverse, followed by sarcocystids (genus Sarcocystis) and eimeriids (genera Isospora and Lankesterella). All were related to parasites of other reptiles, including species from Arabia, Northern Africa and Asia. Like their 29 endemic reptile hosts, almost all Socotran parasites presented high genetic divergence and ecological differences from those found elsewhere, and probably represent undescribed endemic species. Among hosts, skinks were the most parasitized, which contrasted with similar studies from other areas, probably due to their more generalist diet and habitat use. As expected due to its high species richness, geckos harboured the highest parasite diversity in the archipelago. Parasite diversity also seemed to be correlated to island size, as the largest island harboured most haplotypes. This study emphasizes the importance of screening parasites in wild hosts from remote regions and of considering host ecology to understand disease transmission across taxa.

Molecular beam epitaxy growth and strain-induced bandgap of monolayer 1T′-WTe2 on SrTiO3(001)

A monolayer 1T′-WTe2 film is grown on SrTiO3(001) with in-plane tensile strain. A height of ∼0.7 nm, obvious charge transfer, and incommensurate charge fluctuations in 1T′-WTe2 suggest strong coupling to the STO substrate. Scanning tunneling spectroscopy on the surface reveals that a large energy gap opens at the Fermi level with nearly zero conductance. The opened energy gap decreases with the increase in the WTe2 island size. The lack of the metallic edge state on monolayer 1T′-WTe2/SrTiO3(001) indicates the absence of the quantum spin Hall (QSH) state. Our study here demonstrates that the energy gap of monolayer 1T′-WTe2 can be tuned by lattice strain and illustrates the importance of interface coupling to realize the metallic edge state and QSH in monolayer 1T′-WTe2.

Atomic Layer Epitaxy of III-Nitrides: A Microscopic Model of Homoepitaxial Growth.

We develop a microscopic theoretical model of AlN, GaN, and InN film growth by atomic layer epitaxy. To make the model realistic, we take into account the atomic hydrogen that is created by the hydrogen plasma commonly used in plasma-assisted atomic layer epitaxy. This growth technique relies on separate deposition steps for nitrogen and the group-III cation. Our model addresses the processes that occur after a complete monolayer of nitrogen has formed, that is, the deposition, adsorption, surface diffusion, island nucleation, and island growth of group-III cations. According to our model, the three nitrides grow in a standard and qualitatively similar manner: during a brief nucleation phase, a modest attractive interaction leads to stable island nuclei consisting of just a few atoms. These then grow in place at a nearly constant island density and with an island size distribution which obeys an expected universal scaling relationship that depends only on the critical island size.

Coulomb blockade effects in a topological insulator grown on a high-Tc cuprate superconductor

The evidence for proximity-induced superconductivity in heterostructures of topological insulators and high-Tc cuprates has been intensely debated. We use molecular-beam epitaxy to grow thin films of topological insulator Bi2Te3 on a cuprate Bi2Sr2CaCu2O8+x, and study the surface of Bi2Te3 using low-temperature scanning tunneling microscopy and spectroscopy. In few unit-cell thick Bi2Te3 films, we find a V-shaped gap-like feature at the Fermi energy in dI/dV spectra. By reducing the coverage of Bi2Te3 films to create nanoscale islands, we discover that this spectral feature dramatically evolves into a much larger hard gap, which can be understood as a Coulomb blockade gap. This conclusion is supported by the evolution of dI/dV spectra with the lateral size of Bi2Te3 islands, as well as by topographic measurements that show an additional barrier separating Bi2Te3 and Bi2Sr2CaCu2O8+x. We conclude that the prominent gap-like feature in dI/dV spectra in Bi2Te3 films is not a proximity-induced superconducting gap. Instead, it can be explained by Coulomb blockade effects, which take into account additional resistive and capacitive coupling at the interface. Our experiments provide a fresh insight into the tunneling measurements of complex heterostructures with buried interfaces.