The nested subset pattern (nestedness) has been widely used to explain species distributions in island and fragmented systems. Mountain sky islands serve as critical natural laboratories for understanding the evolutionary consequences of geographic isolation and climate change, but their species distribution patterns remain poorly understood. Compared to lowland fragmented habitat islands, biodiversity patterns in mountainous regions are more complex, and traditional drivers may not adequately explain the nestedness of sky islands. To uncover the underlying mechanisms of mountain biodiversity, this study sampled amphibians across 30 sky islands in the Dabie Mountains, China, aiming to explore the nestedness of amphibian assemblages and its formative mechanisms from taxonomic, functional and phylogenetic perspectives. Taxonomic nestedness was quantified by constructing species incidence matrices and calculating nestedness metrics, while functional and phylogenetic nestedness were assessed by integrating species similarities in ecological traits and phylogenetic relationships. Seven sky island characteristics and eight amphibian species traits were then selected as predictors of nestedness. Results showed that amphibian assemblages in the Dabie Mountains exhibited significant nestedness across taxonomic, functional and phylogenetic dimensions. The habitat-by-site matrix was also significantly nested. Spearman rank correlations between the selected predictors and nestedness ranks revealed that sky island area, climate stability and species traits associated with extinction vulnerability (minimum area requirement, larval stage duration, elevation range, and habitat specificity) were strongly correlated with taxonomic nestedness. Additionally, sky island area and climate stability significantly influenced functional and phylogenetic nestedness. These findings support the 'selective extinction' and 'habitat nestedness' hypotheses. To explain these results, we propose a climate stability hypothesis specific to sky islands: stable climatic conditions sustain greater species diversity, whereas climatic instability exacerbates the extinction of lineages lacking adaptive traits. This study presents the first empirical evidence of nestedness in sky island systems, extending classical hypotheses beyond lowland ecosystems and offering new insights into climate-driven assembly mechanisms affecting vulnerable taxa (e.g. amphibians). Our results indicate that conservation efforts should prioritize sky island regions with high-climate stability, large areas and diverse habitats as core areas for biodiversity protection. Moreover, species with narrow elevation ranges, large area requirements, high-habitat specificity and long larval stage durations should also be preserved to prevent local extinction.Read the free for this article on the Journal blog. 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Amidst the global biodiversity crisis, trait-based approaches for assessing species extinction risk and quantifying their ecological roles have attracted increasing interdisciplinary interest. As pivotal agents in plant seed dispersal, avian frugivores possess functional traits that strongly influence dispersal effectiveness, thus shaping plant community regeneration and ecosystem resilience. However, existing datasets are constrained by limited geographical coverage and narrow trait dimensions, lacking a comprehensive global resource for frugivorous bird traits. To address this gap, we compiled AviFrugivores, a comprehensive global trait database of avian frugivores with frugivory proportion (≥ 50%) and dietary breadth (≤ 3). The database comprises 110,635 trait records for 1,670 species, encompassing 34 morphological, 13 life-history, 17 ecological, and 4 biogeographical traits, as well as 4 variables related to conservation information. AviFrugivores represents the most up-to-date and comprehensive global trait database specifically developed for avian frugivores, featuring standardized data compilation workflows, transparent and traceable data provenance, and broad coverage across diverse trait categories and geographic regions. It provides a robust data foundation for investigating the macroecological patterns of avian frugivores at the global scale, elucidating their functional biogeography mechanisms, identifying hotspots of seed dispersal functional vulnerability, and guiding conservation priorities.

Island endemic terrestrial vertebrates, shaped by long-term isolation and ecological specialization, are particularly vulnerable to extinction pressure in the Anthropocene. However, cross-taxon extinction patterns and their drivers remain poorly understood. Here, we compiled a global dataset of 31,865 terrestrial vertebrates, including more than 7500 island endemic species, to evaluate the patterns and drivers of extinction risk in island endemics, in comparison with continent endemics and dual-range species. We found that island endemics face significantly higher extinction risk than non-island endemics, with 3.1% extinct and 34% currently threatened since 1500 CE. Extinction risk among island endemics is unevenly distributed and taxonomically structured, tightly linked to invasive species, overexploitation, and climate change. Compared with continent endemics and dual-range species, their elevated risk is closely associated with small range size and habitat specialization, while biological traits, climate, and anthropogenic pressures also exert taxon-specific effects. These findings explain the unique vulnerability of island endemic vertebrates and inform conservation priorities across island ecosystems.

Understanding public conservation willingness is crucial for mitigating the global decline in avian diversity. Secondary school students, as key future actors and stakeholders in biodiversity conservation, represent a critical demographic, but their conservation willingness toward avian species remains largely underexplored. To address this gap, we conducted a questionnaire survey in 64 secondary schools across eight riparian cities along the Yellow River in Henan Province, China. Using the Great Bustard (Otis tarda)—a national first-class protected species and local conservation flagship—as the focal species, we constructed piecewise structural equation models (SEMs) to identify the key factors influencing students' conservation willingness. The questionnaire results revealed that although nearly 90% of students supported the Great Bustard conservation, only about 30% understood both its protection class and habitat characteristics, and less than half had relevant nature experience or had participated in local forestry departments' science communication activities. The piecewise SEM results demonstrated that students' interest in birds, knowledge level of the Great Bustard, and participation in science communication activities all exerted direct and significant positive influences on their conservation willingness. In addition to its direct effect, science communication engagement also indirectly enhanced conservation willingness by strengthening interest and knowledge, while the effects of grade level and nature experience were exclusively indirect, operating through the same pathways. To improve the effective conservation of the Great Bustard, we recommend that secondary schools strengthen collaborations with universities and nature reserves to enrich students' nature experience, and that local forestry departments further expand the coverage and depth of science communication activities targeting adolescent groups.

Urbanization is one of the most extreme forms of land-use alteration that is reshaping bird community structure, yet the multidimensional patterns of bird beta diversity and their underlying drivers in urban parks remain poorly understood. In this study, we investigated bird beta diversity from taxonomic, phylogenetic, and functional dimensions and its influencing factors across 37 urban parks in Nanjing, China. Distance-based redundancy analysis combined with variance partitioning was employed to evaluate the independent and joint effects of spatial and environmental variables (area, isolation, noise, building index, and habitat diversity) on beta diversity patterns. The results showed that: (1) taxonomic and phylogenetic beta diversity were both dominated by the turnover component, whereas functional beta diversity was primarily driven by the nestedness component; (2) for total beta diversity, the taxonomic dimension was the highest, while for the nestedness component, the phylogenetic dimension was the lowest. The turnover component exhibited a declining gradient across taxonomic, phylogenetic, and functional dimensions; (3) total beta diversity was significantly affected by both spatial and environmental variables, with only spatial variables significantly influencing the turnover component and environmental variables influencing the nestedness component; (4) building index and habitat diversity emerged as the core drivers shaping beta diversity patterns, whereas the marginal effects of area, isolation, and noise were not significant. In highly urbanized landscapes, park management should give priority to maintaining functionally specialized species in a targeted manner. Enhancing park habitat heterogeneity and reducing surrounding building density are crucial strategies for sustaining and promoting bird beta diversity in urban parks.

Understanding why some insular bird species are especially vulnerable to local extinction under prolonged isolation is important for clarifying extinction processes and setting conservation priorities. However, the species traits linked to such vulnerability remain poorly understood in long-isolated island systems. Here, we examined how species traits influence local extinction vulnerability of terrestrial birds in the Zhoushan Archipelago, China, a land-bridge island system isolated from the mainland for approximately 7000–9000 years following Holocene sea-level rise. We surveyed birds on 40 islands and at 16 sites on the adjacent mainland. Using data on 10 ecological and life-history traits for 110 species, we applied phylogenetic generalized least squares models to test their associations with two vulnerability metrics: species restrictedness and species nestedness ranking. We further assessed island-level correlates of species occurrence using AICc-ranked generalized linear mixed models that included island area, isolation, habitat richness and human population density. Natural abundance on the adjacent mainland was the strongest predictor of both vulnerability metrics across breeding birds, wintering birds, resident birds and migratory birds. Species with lower natural abundance had more restricted island distributions, while other traits showed weaker and less consistent associations. Species occurrence probability increased with island area and habitat richness but showed no clear association with isolation or human population density. Conservation in this system should therefore prioritize species with low natural abundance and restricted island distributions, together with large, habitat-rich islands.

Caudata (salamanders) is a highly threatened taxonomic group with over 60% of species estimated to be threatened. However, the species traits and extrinsic factors underlying their population decline and high extinction risk remain unclear. We conducted the first global comparative analysis to investigate which factors are associated with an increased risk of decline and extinction in salamanders. We addressed the following questions: Is extinction risk randomly distributed among salamander families, and if not, which families contain more threatened species than would be expected by chance; which species traits and extrinsic factors are important in determining the extinction risk in salamanders; and are the key factors for population decline consistent with those for extinction risk in salamanders? To determine which ecological characteristics and extrinsic factors best predict extinction risk and population decline in salamanders, we employed phylogenetic generalized least squares (PGLS) models and phylogenetic logistic regression (PGLM) models, respectively. Threatened salamanders were nonrandomly distributed across nine families, among which Cryptobranchidae and Hynobiidae contained significantly more threatened species than expected. Key predictors of salamander extinction risk were breeding strategy, geographic range size, minimum elevation, human threat index, and protected area coverage. Although geographic range size, climate change, and human threats were the most important predictors of salamander extinction risk and population decline, the effect of geographic range size was the opposite between the PGLS and PGLM models. Our results suggest that priority management should focus on extinction-prone families, particularly Cryptobranchidae and Hynobiidae, and salamanders with small range sizes and sensitivity to human disturbance or climate instability.

The species-area relationship (SAR) has long been used to predict extirpation rates from habitat loss, but these rates depend not only on habitat area but also on the surrounding landscape and species' habitat specialization. We collated global data from forest islands created by river damming and forest fragments resulting from clear-cut deforestation to examine the effects of matrix type (aquatic or terrestrial) and tree cover on avian SARs. Unlike oceanic islands, which are often millions of years old, anthropogenic forest islands provide a contemporary analog to forest fragments to understand matrix effects on SARs and serve as a baseline for worst-case scenarios of forest fragmentation. Our database comprises 50 datasets from 45 studies conducted in tropical and subtropical regions, totaling 1,954 bird species detected through 39,197 incidence records from 336 forest islands and 669 forest fragments. We found that bird extirpation rates were lower in fragments than on islands, especially for forest-dependent species compared to all species. Species losses were further reduced by increasing tree cover around forest remnants at local landscape scales of 300 m, highlighting the importance of small-scale conservation strategies. Moreover, even small forest fragments with greater nearby tree cover held high conservation value, emphasizing the crucial role of the surrounding landscape in mitigating avian extirpations from forest remnants. Beyond protecting forest remnants themselves, area-based conservation efforts would therefore be greatly enhanced by improving matrix quality and expanding tree cover in otherwise hostile landscapes.

ABSTRACT Aim Nestedness possesses the capacity to unravel the ecological mechanisms underpinning biodiversity distribution and directly inform evidence‐based conservation strategies. However, previous studies have typically been confined to individual archipelagos and have predominantly focused on taxonomic nestedness alone, neglecting its cross‐assemblage generality and overlooking the role of species traits and phylogeny in driving nested patterns. Here, we systematically identify the key variables driving the occurrences of and inconsistencies between taxonomic, phylogenetic and functional nestedness in amphibians. Location Global. Methods We collated data on species occurrences, traits and island characteristics for 46 amphibian assemblages worldwide. We tested for significant patterns of taxonomic, phylogenetic and functional nestedness for each assemblage. We then used a machine learning method to assess the influence of 14 extrinsic (island characteristics, environment and anthropogenic influence) and intrinsic (species traits) variables on the occurrences of and inconsistencies between three facets of nestedness. Finally, we explored how the driving variables of nestedness influence the support rates of four hypotheses. Results Taxonomic nestedness exhibited low prevalence among amphibians and was less widespread than functional and phylogenetic nestedness. The variables influencing the occurrences of and inconsistencies between these three facets of nestedness encompassed both extrinsic and intrinsic variables. Certain key variables contributing to taxonomic nestedness showed stronger tendencies to support specific hypotheses. Main Conclusion Our synthesis presents the first global assessment of how extrinsic and intrinsic variables shape three dimensions of nestedness in insular amphibians. Conservation biogeographers can implement targeted conservation measures for each of the 46 archipelagos based on the findings of amphibian nested patterns. Moreover, our global synthesis can provide a reference for predicting amphibian nested patterns in unstudied archipelagos, thereby facilitating the rapid development of conservation plans.

Questions Understanding the composition and structure of island floras is crucial for making informed conservation decisions. Island floras are often nested, i.e. lower species richness assemblages are frequently subsets of those higher in richness. However, the circumstances under which this occurs on islands are often unclear. Moreover, research in island biogeography rarely integrates phylogeny and functional traits in nestedness studies. Here, we integrated phylogenetic and functional traits in the investigation of relationships between taxonomic nestedness and island characteristics to gain insight into the processes that shape the composition and structure of island floras. We asked whether (i) native plant species assemblages are nested according to their phylogeny and functional traits and (ii) whether nested patterns are related to island characteristics. Location 264 islands offshore from northern Aotearoa New Zealand. Methods We combined field surveys and published data for 775 native plant species across the islands. We compiled information about their phylogeny at the fine (species) and coarse level (i.e. ferns and allies, conifers, monocots, and dicots). Then, for each species, we determined three plant functional traits (growth forms, dispersal modes, and species maximum height). We quantified nestedness by organizing species incidence matrices using the NODF (i.e. nestedness metric based on overlap and decreasing fill) and fixed-fixed null models. Finally, we correlated island nestedness ranks with three island characteristics (area, isolation, and exposure to ocean-borne disturbances). Results All plant categories were nested, except for ferns and water-dispersed species. Nestedness ranks were consistently related to island area, strongly supporting the selective extinction hypothesis. Relationships with isolation and exposure to ocean-borne disturbances were less strong and varied by phylogeny and functional traits, suggesting weaker support for selective immigration and habitat nestedness. Conclusions These findings highlight the importance of nestedness studies and the integration of phylogeny and functional traits for identifying conservation priority areas. The overarching effect of island area in shaping insular plant composition underscores the key role of large islands for conserving plant diversity.

Life-history traits represent evolutionary adaptations that mediate responses to external environments. Analyzing variation in these traits provides valuable insights into macroecological processes and supports the development of effective conservation and restoration strategies. However, large-scale biogeographic patterns in life-history trait diversity among terrestrial vertebrates remain insufficiently characterized, and the processes shaping these patterns are not well understood. This study integrated life-history and spatial distribution data for 2 334 terrestrial vertebrate species in China, including 398 amphibians, 211 reptiles, 541 mammals, and 1 184 birds, to evaluate spatial patterns of trait diversity and identify underlying drivers. Assemblages in South and Southwest China exhibited high species richness, substantial assemblage-level evolutionary distinctiveness, expanded trait volumes, and elevated trait densities compared to null expectations, indicating roles as both evolutionary museums and cradles. In contrast, assemblages on the Tibetan Plateau showed expanded trait volumes but low trait densities, reflecting niche expansion among limited taxa. These findings emphasize the importance of niche packing before assemblages reach environmental carrying limits. Assemblages with high evolutionary distinctiveness tended to display high trait volumes and low trait densities, suggesting a consistent relationship between phylogenetic structure and functional diversification. Among the four groups, amphibians showed the highest sensitivity to environmental variation, highlighting the need for focused conservation efforts. Overall, this study revealed pronounced spatial heterogeneity in trait diversity across China, shaped by species richness, evolutionary distinctiveness, and environmental variation, providing valuable insights for refining conservation priorities for terrestrial vertebrate taxa.

Wildlife trade poses a major threat to biodiversity, yet the drivers determining which species are traded are not fully understood. Through a comprehensive collection of official and online trade data, we applied a binomial test to identify families that contain an unexpectedly large or small number of traded species. We also analyzed which factors predispose reptile species to be traded and explored whether traded species were more likely to be threatened with extinction. Of the 10,919 reptile species in our dataset, 3889 species (35.6%) were traded. There was strong evidence for taxonomic biases in trade risk. In particular, all turtle and crocodilian families had higher trade risk than other reptiles. Species with large body sizes, habitat generalists, insular endemics, and those found in regions with high gross domestic product were traded in greater quantities and more frequently. Species with small and large ranges were more frequently involved in trade, suggesting a demand for rare and common species in wildlife trade. When connecting trade risk to extinction risk, data-deficient and not-evaluated species had fewer traded species and were less likely to be traded than threatened or nonthreatened ones. Nonetheless, these species warrant special conservation attention considering their rarity, limited range size, and insufficient legal protection. Given the increased attention given to wildlife trade, we suggest implementing stronger regulatory measures to monitor and control the trade of reptile species, particularly those belonging to families with a high risk of being traded. Efforts should also prioritize the protection of species exhibiting traits that make them highly susceptible to exploitation. Finally, promoting international collaboration for stricter enforcement of wildlife trade regulations and support of sustainable trade practices can help mitigate the negative impacts on biodiversity.

The acceleration of global urbanization has caused habitat loss, fragmentation, and decrease of habitat quality, often leading to a decline in biodiversity. However, most previous urbanization studies focused on taxonomic diversity, with relatively less research on functional and phylogenetic diversity. In this study, we examined the phylogenetic and functional diversity and underlying influencing factors of bird communities in 37 urban parks in Nanjing, China. We conducted a systematic survey of bird communities in Nanjing urban parks and selected six park characteristics that are generally considered to affect bird diversity. Model selection based on corrected Akaike Information Criterion (AICc) and model averaging showed that park area, habitat diversity and building index (a proxy for the degree of urbanization) were significant factors affecting avian phylogenetic and functional diversity in Nanjing urban parks. Specifically, habitat diversity and park area were positively correlated with bird diversity, while the building index was negatively correlated with bird diversity. Moreover, the phylogenetic and functional structures of urban bird communities exhibited a clustered pattern, indicating that environmental filtering might play a role in shaping community composition. In addition, building index had certain impact on the construction of bird phylogenetic communities in urban parks. Our results suggest that expanding park areas, increasing habitat diversity and reducing building indexes may be effective measures to increase the avian phylogenetic and functional diversity in our system.

Body size shifts of insular organisms have been widely observed, but few studies have simultaneously tested the combined and cascading effects of biotic and abiotic factors on morphological shifts. Here, we used two body size metrics (body length and body mass) of a small rodent (Rattus losea) to investigate its morphological shifts and the cascading mechanisms in the Zhoushan Archipelago, China. We used the live-trapping method to capture rodents and compared body size metrics between insular and mainland populations. We then constructed linear regression models to examine the relationships between the body size of rodents and three island attributes (island area, island isolation, and land use). Finally, we used structural equation modeling (SEM) to determine the cascading influences of three island attributes and four biotic factors (predator species richness, net primary productivity (NPP), capture rate, and rodent species richness) on body size. Island rodent populations had significantly larger body length and body mass than mainland counterparts. Both body length and body mass of insular rodents were negatively correlated with island area. SEMs showed that predator species richness had positive impacts on body length and body mass of insular rodents, while NPP had a negative effect on body mass. Moreover, SEMs revealed that island area positively influenced predator species richness, whereas land use negatively affected NPP. Body size shifts of the small rodent follow the prediction of the island rule (insular gigantism of small-sized species), but the determinants were strongly affected by which body size metrics were used. Therefore, both body length and body mass should be included in future studies to obtain a comprehensive understanding of the mechanisms underlying the body size shifts.

Urban wetlands are considered as “habitat islands” within the urban matrix that contribute to species conservation. Waterbirds are sensitive pollution indicators in terrestrial and aquatic ecosystems, and their diversity in urban wetlands reflects the response of wildlife to urbanization. However, very few studies have investigated seasonal differences in the multidimensional diversity of waterbirds in urbanized landscapes. In this study, we analyzed various wetland parameters that could potentially affect the seasonal variations in multidimensional diversity of waterbirds in Nanjing, China. We surveyed waterbirds in 29 urban wetlands using the point count method during breeding and non-breeding seasons from November 2022 to June 2023. We then employed multiple linear regressions and information-theoretic approaches to investigate the impact of wetland characteristics on waterbird diversity. We found that water body area and buffer zone connectivity consistently emerged as positive factors affecting waterbird taxonomic and phylogenetic diversity across seasons. Conversely, the urbanization synthetic index was negatively correlated with waterbird diversity only during the breeding season. Regarding functional diversity, we found that the positive correlation between buffer zone connectivity and waterbird diversity was specific to the breeding season. Therefore, for effective conservation of waterbird diversity in our system, wetland planning should prioritize expanding wetland water body areas, enhancing wetland connectivity, minimizing human disturbance during the breeding season, and implementing ecological restoration measures in urbanized wetlands to mitigate adverse effects of urbanization.

Turtles and tortoises (chelonians) are among the most threatened vertebrates worldwide, yet the factors determining their high extinction risk and their resilience to further challenges are not fully understood. Here, we compile a dataset comprising intrinsic and extrinsic variables for chelonians to reveal their current risk patterns and extinction vulnerability to future climatic and anthropogenic threats. The results show that at-risk species are predominantly characterized by large body size, small ranges, high functional distinctness, and intense human threat levels, with high representation in the Indomalayan region. Notably, 18.6% of currently unevaluated species are projected to be threatened with extinction. Furthermore, the projected rates of climatic and environmental changes across species' distributions are significantly higher than the rates of evolution for traits linked to resilience to climate change and altered environments. Overall, this study provides insights for prioritizing conservation actions and underscores the urgent need to prevent future extinctions of chelonians.

The small-island effect (SIE) is a widely accepted pattern in island biogeography where species richness varies independently of island area below an area threshold. Three main ecological mechanisms (the disturbance hypothesis, habitat hypothesis, and subsidized island biogeography hypothesis) have been proposed to explain the SIE resulting from natural drivers. However, extensive human disturbances have led to considerable changes in insular species richness worldwide. Here, we incorporated human disturbances into the disturbance hypothesis and explored the mechanism to explain the SIE of large and medium-sized mammals in the Zhoushan Archipelago, China. We used the camera trapping method to survey large and medium-sized mammals on 50 islands from May 2020 to April 2024. We used piecewise regression, path analysis, and null models to determine the existence of the SIE. We then applied iterative partial regressions to assess the relative importance of island area and other island characteristics (human disturbances, variability of normalized difference vegetation index (VNDVI), habitat diversity, rocky shoreline proportion, and isolation) in determining species richness. We found strong evidence for the existence of SIE when using the island area, but we did not detect it when using the available habitat area (excluding uninhabited island area). Additionally, the fraction of variance in species richness explained exclusively by human disturbances (human population density and land use intensity) was high on small islands and decreased as island size increased, while that explained by island area was low and increased as island size increased. Overall, our findings supported the human-driven disturbance hypothesis, which provides a new explanation for the SIE. For effective conservation of large and medium-sized mammals in this region, we should protect large islands beyond the larger area threshold of the SIE, and conservation priorities for small islands should focus on those islands where human disturbances are weak.

Questions Understanding the composition and structure of island floras is crucial for making informed conservation decisions, especially in the context of biological invasions. Island floras are often nested, that is, species-poor assemblages are frequently subsets of species-rich ones. However, the circumstances under which this occurs on islands are often unclear. To gain insight into the processes that shape the composition and structure of island floras, we incorporated taxonomic and trait categories to investigate the relationships between the degree of nestedness of native and non-native plant species and island characteristics. We hypothesise that the degree of nestedness (1) declines with island area (non-random local extinctions), increases with isolation (non-random colonisation), declines with exposure to ocean-borne disturbances (non-random local extinction of specialists with their habitat) and is higher on volcanic compared to sedimentary islands (assembly rules). We also hypothesise that (2) plant invasions will reduce overall nestedness and (3) plant assemblages will be more nested if smaller in size (e.g., grasses, forbs) and not adapted to long-distance dispersal (e.g., wind-dispersed, ferns).Location Two hundred and sixty-four islands offshore from northern Aotearoa New Zealand.Methods We combined field surveys and published data for 1543 native and non-native plant species across 264 islands. We compiled information about taxonomy at the fine (species) and coarse level (i.e., ferns and allies, conifers, monocots and dicots) and categorised each species by its growth form (i.e., graminoids, forbs, woody species, climbers and lianas and epiphytes) and dispersal mode (i.e., water-dispersed, unspecialised, short-distance, animal-dispersed and wind-dispersed). We quantified nestedness by organising species incidence matrices using the NODF (i.e., nestedness metric based on overlap and decreasing fill) and fixed-fixed null models. Finally, we related island nestedness ranks with four island characteristics (area, isolation, exposure to ocean-borne disturbances and geological origin).Results Nearly all plant categories were nested, with a few exceptions. However, non-native species reduced the overall degree of nestedness. Nestedness ranks were consistently related to island area and largely to exposure to ocean-borne disturbances, but rarely to isolation and geological origin. These results strongly support the selective extinction (i.e., small, species-poor islands are subsets of larger, species-rich islands due to non-random local extinctions) and habitat nestedness (i.e., nested patterns generated by the non-random local extinction of specialists with their habitat) hypotheses.Conclusions Non-native plant species reduce the overall degree of nestedness, modifying the species composition of island floras. The overarching effect of island area in shaping insular plant composition underscores the key role of large islands for conserving plant diversity. Nestedness studies can suggest probable processes that determine insular community composition and aid in identifying high-priority islands for conservation.