A Behavioural Ecology Approach to Assessing the Effect of Alien Vegetation on a Threatened Giant Millipede

The importance of taking into account behavioural ecology when assessing the impacts of habitat deterioration on threatened species is evaluated. The Seychelles giant millipede (SGM), Sechelleptus seychellarum, is IUCN Red-Listed as “Vulnerable”. Here, we studied the effect of alien bamboo and coconut on the behavioural ecology of this species on Cousine Island, Seychelles. Coconut did not affect SGM density, but negatively affected its foraging behaviour, whereas bamboo negatively affected both its density and foraging behaviour. The SGM showed feeding preferences for Pisonia grandis and Ficus sp. leaf litter types. Alien bamboo and coconut pose a varied threat to the SGM, and their removal and replacement by indigenous forest species (e.g. P. grandis and Ficus sp.) should form part of an island’s restoration programme.     

Leaf litter arthropod responses to tropical forest restoration

Soil and litter arthropods represent a large proportion of tropical biodiversity and perform important ecosystem functions, but little is known about the efficacy of different tropical forest restoration strategies in facilitating their recovery in degraded habitats. We sampled arthropods in four 7‐ to 8‐year‐old restoration treatments and in nearby reference forests. Sampling was conducted during the wet and dry seasons using extractions from litter and pitfall samples. Restoration treatments were replicated in 50 × 50‐m plots in four former pasture sites in southern Costa Rica: plantation – trees planted throughout the plot; applied nucleation/islands – trees planted in patches of different sizes; and natural regeneration – no tree planting. Arthropod abundance, measures of richness and diversity, and a number of functional groups were greater in the island treatment than in natural regeneration or plantation treatments and, in many cases, were similar to reference forest. Litter and pitfall morphospecies and functional group composition in all three restoration treatments were significantly different than reference sites, but island and plantation treatments showed more recovery than natural regeneration. Abundance and functional group diversity showed a much greater degree of recovery than community composition. Synthesis and applications: The less resource‐intensive restoration strategy of planting tree islands was more effective than tree plantations in restoring arthropod abundance, richness, and functional diversity. None of the restoration strategies, however, resulted in similar community composition as reference forest after 8 years of recovery, highlighting the slow rate of recovery of arthropod communities after disturbance, and underscoring the importance of conservation of remnant forests in fragmented landscapes.     

Arthropod Diversity in Lama Forest Reserve (South Benin), a Mosaic of Natural, Degraded and Plantation Forests

Arthropod assemblages were examined in Lama forest reserve, a protected area situated in the Dahomey gap, southern Benin, composed of plantations, degraded forest and remnants of natural forest. The objectives were to compare assemblages in relation to forest type and use, to elucidate the value of forest plantations for biodiversity conservation and to identify indicator species for specific forest habitats. Arthropods were collected over an 11-month period, using standardized sets of traps (pitfall, emergence, Malaise and flight intercept traps). Nine different habitats were studied, including natural and degraded forest, forest plantations (Tectona grandis and Senna siamea) of different age, and isolated forest fragments. Our analysis focused on detritivorous and xylophagous arthropods but also included ground beetles and heteropterans, totalling 393 species. We found no differences in species richness among natural and degraded forest habitats in the centre of the reserve (Noyau central). Outside of the Noyau central, species richness was highest in old teak plantations and isolated forest fragments and lowest in young teak and fuelwood plantations. Detrended correspondence analysis (DCA) separated three main groups: (1) natural forest, (2) degraded forest and young plantations, and (3) old plantations and isolated forest fragments. Multiple regression of DCA scores of the first two axes on environmental variables identified one natural and three disturbance-related predictors of arthropod assemblages in Lama forest: soil type (texture), canopy height, naturalness (proportion of Guineo-Congolian plant species) and understorey vegetation cover. We identified 15 indicator species for six different forest habitats. The highest numbers were found in abandoned settlements and old teak plantations. β-diversity was similar among the three DCA ordination groups (degraded forest excluded). Values for β-diversity were relatively high, suggesting that all major forest habitats contribute significantly to regional species pools and should therefore be protected. To enhance arthropod diversity, we propose that management practices in Lama forest should aim to encourage the development of species-rich understorey vegetation of the Guineo-Congolian phytogeographical region.     

Restoration of a tropical island: Cousine Island,Seychelles

Tropical island species and ecosystems are threatened worldwide as a result of increasing human pressure. Yet some of these islands also lend themselves to restoration, as they are physically defined units that can be given focused attention, as long as resources are available and clear conservation targets are set. Cousine Island, Seychelles, is a tropical island that has received such intensive restoration. From a highly degraded island in the 1960s, the island has now been restored to what is believed to be a semblance of the natural state. All alien vertebrates have been eradicated, as have 25 invasive alien plants. Cultivated plants are now confined to one small section of the island. Poaching of nesting marine turtles has been stopped, leading to an increase in turtle breeding numbers. The shearwater population has increased in size with poaching activities under control. The Sooty tern has also returned to the island to breed. The coastal plain has been restored with over 2,500 indigenous shrubs and trees, which have now grown into a forest carpet. There are strict quarantine procedures on the island, keeping it free of rats, mice, various alien invertebrates and potentially invasive alien plants. Three threatened Seychelles endemic land birds (Seychelles warbler, Seychelles magpie robin and Seychelles white-eye) have been introduced and are thriving, with these introductions contributing to both the magpie robin and the white-eye being downgraded from CR to EN (the warbler remains at VU). Ecotourism, and nature conservation for the local inhabitants, have been introduced in a way that does not reduce the improved compositional, structural and functional biodiversity of the island. The result of the restoration effort appears to be sustainable in the long term, although challenges still remain, especially with regards to adequate clean water and a non-polluting power supply on the island. Cousine is thus paving the way in the art and science of tropical island restoration as a legacy for future generations.     

Response of a threatened giant millipede to forest restoration

Understanding the response of threatened and functionally important island invertebrate species to plant community restoration is essential for the successful conservation of these invertebrate species. The Seychelles giant millipede (SGM), Sechelleptus seychellarum, is a threatened and functionally important macro-detritivore endemic to the Seychelles granitic islands. Here, we studied the response of this species to the ongoing forest restoration programme on Cousine Island, Seychelles. This study was conducted over an 11 year period, representing the floral succession of a formerly degraded open scrubland area, dominated by alien plants, to a closed canopy forest, dominated by planted indigenous trees. While the time span of this study was insufficient for vegetation height in the restored area to equal that in the reference natural forest, canopy closure was nevertheless comparable. We found SGM density to be an order of magnitude lower in the restored site compared to the natural forest. In contrast, SGM physical condition improved significantly in the restored site, as vegetation structure increased. Furthermore, SGM behaviour in the restored site switched from a predominantly walking to a dominantly feeding behaviour over the study period, resulting in the forest restoration programme on Cousine increasing the foraging area of the SGM by 43 %. Competition for key resources, e.g. food and day-time refuges, are suggested as possible factors limiting SGM numbers in the restored forest.     

The importance of substrate type, shading and scorching for the attractiveness of dead wood to saproxylic beetles

Modern forestry management has reduced the amount of dead wood in forest ecosystems and this has become a serious threat to flora and fauna. Efforts are therefore being made to reverse this trend but one problem is that we still lack detailed knowledge regarding the substrate requirements of many saproxylic species. In a field experiment, conducted in three forest types (forest reserve, mature managed forest and clear-cut), we evaluated the value, from a conservation perspective, of different substrate types (logs, snags and tops) of Norway Spruce, Picea abies, and if the quality of spruce logs as saproxylic habitats can be improved by simple log treatments (scorching and shading). We collected 9982 individuals representing 262 saproxylic beetle species in window traps. Both substrate type and, to a lesser extent, log treatment had a significant effect on the abundance and species richness of saproxylic beetles attracted to the different dead wood substrates. However, more importantly, the composition of the beetle assemblages differed significantly between both substrates and log treatments. Snags, logs and tops all attracted significantly different beetle assemblages and scorched logs differed from untreated control logs. Sixteen red listed species were trapped, with the highest number (11 species) being found on scorched logs. We found strong evidence that some species preferred a specific substrate type, mainly logs, in some cases treated logs (scorched or shaded), but not snags, the substrate commonly provided for conservation purposes on e.g. clear-cuts. This stresses the importance of conducting forestry in such a way that a multitude of both forest habitats and dead wood substrates are available continuously in the forest landscape to maintain biodiversity.     

Impact of a mutualism between an invasive ant and honeydew-producing insects on a functionally important tree on a tropical island

Mutualisms between invasive ants and honeydew-producing Hemiptera have the potential to result in unusually high population levels of both partners, with subsequent major changes to ecosystem composition and dynamics. We assessed the relationship between the invasive ant, Pheidole megacephala, and its hemipteran mutualists, Dysmicoccus sp. and Pulvinaria urbicola, on Cousine Island, Seychelles. We also assessed the impacts of the mutualism on the condition of the hemipteran host plant, Pisonia grandis, a native and functionally important tree species. There was a strong positive relationship between Ph. megacephala activity and hemipteran abundance, and the exclusion of ants from Pi. grandis resulted in a significant decline in Pu. urbicola abundance. High abundance of the mutualists was strongly associated with damage to the Pi. grandis forest. This indicates that the mutualism is contributing to the massive increase in the population levels of the mutualist species, and is intensifying their impacts on the island. The widespread trophobiosis and its associated high densities of mutualists pose serious threats to the ecosystem, highlighting the need to control the ant and associated hemipteran populations.     

The effects of land-use change on arthropod richness and abundance on Santa Maria Island (Azores): unmanaged plantations favour endemic beetles

We study how endemic, native and introduced arthropod species richness, abundance, diversity and community composition vary between four different habitat types (native forest, exotic forest of Cryptomeria japonica, semi-natural pasture and intensive pasture) and how arthropod richness and abundance change with increasing distance from the native forest in adjacent habitat types in Santa Maria Island, the Azores. Arthropods were sampled in four 150 m long transects in each habitat type. Arthropods were identified to species level and classified as Azorean endemic, single-island endemic (SIE), native, or introduced. The native forest had the highest values for species richness of Azorean endemics, SIEs and natives; and also had highest values of Azorean endemic diversity (Fisher’s alpha). In contrast, the intensive pasture had the lowest values for endemic and native species richness and diversity, but the highest values of total arthropod abundance and introduced species richness and diversity. Arthropod community composition was significantly different between the four habitat types. In the semi-natural pasture, the number of SIE species decreased with increasing distance from the native forest, and in the exotic forest the abundance of both Azorean endemics and SIEs decreased with increasing distance from the native forest. There is a gradient of decreasing arthropod richness and abundance from the native forest to the intensive pasture. Although this study demonstrates the important role of the native forest in arthropod conservation in the Azores, it also shows that unmanaged exotic forests have provided alternative habitat suitable for some native species of forest specialist arthropods, particularly saproxylic beetles.     

Arthropod Distribution in a Tropical Rainforest: Tackling a Four Dimensional Puzzle

Quantifying the spatio-temporal distribution of arthropods in tropical rainforests represents a first step towards scrutinizing the global distribution of biodiversity on Earth. To date most studies have focused on narrow taxonomic groups or lack a design that allows partitioning of the components of diversity. Here, we consider an exceptionally large dataset (113,952 individuals representing 5,858 species), obtained from the San Lorenzo forest in Panama, where the phylogenetic breadth of arthropod taxa was surveyed using 14 protocols targeting the soil, litter, understory, lower and upper canopy habitats, replicated across seasons in 2003 and 2004. This dataset is used to explore the relative influence of horizontal, vertical and seasonal drivers of arthropod distribution in this forest. We considered arthropod abundance, observed and estimated species richness, additive decomposition of species richness, multiplicative partitioning of species diversity, variation in species composition, species turnover and guild structure as components of diversity. At the scale of our study (2km of distance, 40m in height and 400 days), the effects related to the vertical and seasonal dimensions were most important. Most adult arthropods were collected from the soil/litter or the upper canopy and species richness was highest in the canopy. We compared the distribution of arthropods and trees within our study system. Effects related to the seasonal dimension were stronger for arthropods than for trees. We conclude that: (1) models of beta diversity developed for tropical trees are unlikely to be applicable to tropical arthropods; (2) it is imperative that estimates of global biodiversity derived from mass collecting of arthropods in tropical rainforests embrace the strong vertical and seasonal partitioning observed here; and (3) given the high species turnover observed between seasons, global climate change may have severe consequences for rainforest arthropods.     

Strategic Management of an Invasive Ant‐scale Mutualism Enables Recovery of a Threatened Tropical Tree Species

Mutualisms between invasive ants and honeydew‐producing insects can have widespread negative effects on natural ecosystems. This is becoming an increasingly serious problem worldwide, causing certain ecosystems to change radically. Management of these abundant and influential mutualistic species is essential if the host ecosystem is to recover to its former non‐invaded status. This negative effect is particularly prevalent on some tropical islands, including Cousine Island, Seychelles. On this island, the invasive ant Pheidole megacephala has caused serious indirect damage to the threatened native Pisonia grandis trees via a mutualism with an invasive scale insect, Pulvinaria urbicola. We aimed to suppress the ant, thereby decoupling the mutualism and enabling recovery of the Pisonia trees. We treated all areas where ant pressure was high with a selective formicidal bait, which was deployed in custom‐made bait stations designed to avoid risk of treatment to endemic fauna. In the treated area, ant foraging activity was reduced by 93 percent and was followed by a 100 percent reduction in scale insect density. Abundance of endemic herbivorous insects and herbivorous activity increased significantly, however, after the decline in mutualistic species densities. Despite the native herbivore increase, there was considerable overall improvement in Pisonia shoot condition and an observed increase in foliage density. Our results demonstrate the benefit of strategic management of highly mutualistic alien species to the native Pisonia trees. It also supports the idea that area‐wide suppression is a feasible alternative to eradication for achieving positive conservation management at the level of the forest ecosystem.     

Invertebrate survey of coastal habitats and podocarp forest on Ulva Island,Rakiura National Park,New Zealand

Abstract

Inventory of the invertebrate fauna is important to establish taxonomic diversity, abundance and distribution, and hence the conservation of indigenous biodiversity. Invertebrate assemblages have been documented in some broadleaf‐podocarp forests and grassland habitats in New Zealand, but not in dense stands of coastal forest or in mature podocarp forest. This survey aimed to provide a taxonomic inventory of terrestrial invertebrates and their habitat associations on Ulva Island (Rakiura National Park, Stewart Island), an off‐shore sanctuary of significant conservation value in New Zealand. We systematically documented the invertebrate assemblages collected in ground litter and on tree trunks on the island. The invertebrate specimens identified represented 4 phyla, 6 classes, 25 orders and 62 species. The invertebrate fauna reported in this survey was distinct from those of lowland shrubland and broadleaved‐Nothofagus forests on the mainland, but shared species with that reported from another similar off‐shore island, Codfish Island (Whenua Hou).     

On the Relationships between Ground-dwelling Spider (Araneae) Assemblages and Dead Wood in a Northern Sugar Maple Forest

Downed woody material (fallen logs) offers ground-dwelling spiders (Araneae) ideal sites for nesting and foraging, but little is known about what characteristics of dead wood influence spider assemblages. In a maple forest of Forillon National Park, in eastern Québec (Canada), spider assemblages on, adjacent to, and away from fallen logs were compared. We also tested how log type (coniferous vs. deciduous) and decomposition stage influenced spider assemblages. Sampling was done for an intensive four-week period using both litter samples and pitfall traps. A total of 5613 spiders representing 83 species from 16 families was collected. Spiders were affected by the presence of logs, as both species diversity and total number of individuals collected were significantly higher on the log surface compared to the forest floor. Ordination analysis revealed a distinct compositional difference between the spider fauna found on the wood surface compared to the forest floor. Wood type and decomposition stage had few significant effects on spider assemblages, except that less decayed logs supported higher spider diversity than logs in advanced stages of decay. Dead wood is clearly important for generalist predators such as spiders, further supporting the conservation importance of fallen logs in northern forest ecosystems.     

Plant diversity accurately predicts insect diversity in two tropical landscapes

Plant diversity surely determines arthropod diversity, but only moderate correlations between arthropod and plant species richness had been observed until Basset et al. (Science, 338, 2012 and 1481) finally undertook an unprecedentedly comprehensive sampling of a tropical forest and demonstrated that plant species richness could indeed accurately predict arthropod species richness. We now require a high‐throughput pipeline to operationalize this result so that we can (i) test competing explanations for tropical arthropod megadiversity, (ii) improve estimates of global eukaryotic species diversity, and (iii) use plant and arthropod communities as efficient proxies for each other, thus improving the efficiency of conservation planning and of detecting forest degradation and recovery. We therefore applied metabarcoding to Malaise‐trap samples across two tropical landscapes in China. We demonstrate that plant species richness can accurately predict arthropod (mostly insect) species richness and that plant and insect community compositions are highly correlated, even in landscapes that are large, heterogeneous and anthropogenically modified. Finally, we review how metabarcoding makes feasible highly replicated tests of the major competing explanations for tropical megadiversity.     

Decomposing logs increase oribatid mite assemblage diversity in mixedwood boreal forest

The removal of timber during harvesting substantially reduces important invertebrate habitat, most noticeably microhabitats associated with fallen trees. Oribatid mite diversity in downed woody material (DWM) using species-level data has not been well studied. We investigated the influence of decaying logs on the spatial distribution of oribatid mites on the forest floor at the sylviculture et aménagement forestiers écosystémique (SAFE) research station in the Abitibi region in NW Québec. In June 2006, six aspen logs were selected for study, and samples were taken at three distances for each log: directly on top of the log (ON), directly beside the log (ADJ) and at least one metre away from the log and any other fallen wood (AWAY). Samples ON logs consisted of a litter layer sample, an upper wood sample and an inner wood sample. Samples at the ADJ and AWAY distances consisted of litter samples and soil cores. The highest species richness was collected ON logs, and logs harboured a distinct oribatid species composition compared to nearby forest floor. There were species-specific changes in abundance with increasing distance away from DWM, which indicates an influence of DWM in structuring oribatid assemblages on the forest floor. Additionally, each layer (litter, wood and soil) exhibited a unique species composition and hosted a different diversity of oribatid mites. This study further highlights the importance of DWM to forest biodiversity by creating habitat for unique assemblages of oribatid mites.     

Effect of prey availability on the abundance of White‐breasted Wood‐Wrens,insectivorous birds of tropical lowland forests

Some understory insectivorous birds manage to persist in tropical forest fragments despite significant habitat loss and forest fragmentation. Their persistence has been related to arthropod biomass. In addition, forest structure has been used as a proxy to estimate prey availability for understory birds and for calculating prey abundance. We used arthropod biomass and forest structural variables (leaf area index [LAI] and aerial leaf litter biomass) to explain the abundance of White‐breasted Wood‐Wrens (Henicorhina leucosticta), tropical understory insectivorous birds, in six forests in the Caribbean lowlands of Costa Rica. To estimate bird abundance, we performed point counts (100‐m radius) in two old‐growth forests, two second‐growth forests, and two selectively logged forests. Arthropod abundance was the best predictor of wood‐wren abundance (wi = 0.75). Wood‐wren abundance increased as the number of arthropods increased, and the estimated range of bird abundance obtained from the model varied from 0.51 (0.28 – 0.93 [95%CI]) to 3.70 (1.68 – 5.20 [95%CI]) within sites. LAI was positively correlated to prey abundance (P = 0.01), and explained part of the variation in wood‐wren abundance. In forests with high LAI, arthropods have more aerial leaf litter as potential habitat so more potential prey are available for wood‐wrens. Forests with a greater abundance of aerial leaf litter arthropods were more likely to sustain higher densities of wood‐wrens in a fragmented tropical landscape.     

Leaf-Litter Arthropods in Restored Forests in the Colombian Andes: A Comparison Between Secondary Forest and Tree Plantations

Tree monocultures of native and exotic species are frequently used as tools to catalyze forest recovery throughout the tropics. Although plantations may rapidly develop a canopy cover, they need to be evaluated as habitat for other organisms. We compared samples of leaf‐litter arthropods from two elevations in restored forest in the Colombian Andes. At the upper elevation (2,430 m), we compared native Andean alder (Alnus acuminata) plantation and secondary forest, and at the lower elevation (1,900 m) exotic Chinese ash (Fraxinus chinensis) plantation and secondary forest. Samples were obtained in two periods, March–April and September 1995. Species richness and abundance of arthropods were highest in secondary forest at the lower elevation. There were no differences in richness between both plantations and high‐elevation forest. Arthropod richness and abundance increased in the second sampling period in both secondary forest types and the ash plantation but not in the alder plantation, reflecting population recovery after the dry season. Alder leaf litter apparently buffered seasonal variations in arthropod richness and abundance. Composition of morphospecies was different among forest types. Although arthropod richness was lower in ash plantations compared to secondary forest, plantations still provided habitat for these organisms. On the other hand, the alder plantation was not different from secondary forest at the same elevation. At our site, plantations are embedded in a forested landscape. Whether our results apply to different landscape configurations and at different spatial scales needs to be established. The use of plantations as a restoration tool depends on the objectives of the project and on local conditions of forest cover and soils.     

Comparative patterns in taxonomic and functional spider diversities between tropical vs. temperate forests

High diversity in tropical compared to temperate regions has long intrigued ecologists, especially for highly speciose taxa like terrestrial arthropods in tropical rainforests. Previous studies showed that arthropod herbivores account for much tropical diversity, yet differences in the diversity of predatory arthropods between tropical and temperate systems have not been properly quantified. Here, we present the first standardized tropical–temperate forest quantification of spider diversities, a dominant and mega‐diverse taxon of generalist predators. Spider assemblages were collected using a spatially replicated protocol including two standardized sampling methods (vegetation sweep netting and beating). Fieldwork took place between 2010 and 2015 in metropolitan (Brittany) and overseas (French Guiana) French territories. We found no significant difference in functional diversity based on hunting guilds between temperate and tropical forests, while species richness was 13–82 times higher in tropical versus temperate forests. Evenness was also higher, with tropical assemblages up to 55 times more even than assemblages in temperate forests. These differences in diversity far surpass previous estimates and exceed tropical–temperate ratios for herbivorous taxa.     

Longevity and survival of the Endangered Seychelles Magpie Robin Copsychus sechellarum

The Seychelles Magpie Robin Copsychus sechellarum was once one of the most threatened birds in the world, but was downgraded from Critically Endangered to Endangered after a long-term recovery programme was success- fully implemented. Comprehensive long-term monitoring of this species was conducted on the islands of Cousin and Cousine over an 18-year period. We report here on the species longevity and annual survival at these two sites. The oldest recorded individual was a male who died on Cousine Island on 28 September 2000 at just under 16 years old. This individual was recorded to have hatched on Frégate Island on 3 January 1985, before being translocated to Cousine Island in 1995. Mean annual survival rates over an 18-year period were 81.6% on Cousin and 77.9% on Cousine islands. A decrease in annual survival was noted with increasing population size on both islands (Cousin: t = ?3.09, p < 0.05; Cousine: t = ?2.71, p < 0.05), which is a likely consequence of increased territory disputes and competition for food.     

Trees as templates for tropical litter arthropod diversity

Increased tree species diversity in the tropics is associated with even greater herbivore diversity, but few tests of tree effects on litter arthropod diversity exist. We studied whether tree species influence patchiness in diversity and abundance of three common soil arthropod taxa (ants, gamasid mites, and oribatid mites) in a Panama forest. The tree specialization hypothesis proposes that tree-driven habitat heterogeneity maintains litter arthropod diversity. We tested whether tree species differed in resource quality and quantity of their leaf litter and whether more heterogeneous litter supports more arthropod species. Alternatively, the abundance–extinction hypothesis states that arthropod diversity increases with arthropod abundance, which in turn tracks resource quantity (e.g., litter depth). We found little support for the hypothesis that tropical trees are templates for litter arthropod diversity. Ten tree species differed in litter depth, chemistry, and structural variability. However, the extent of specialization of invertebrates on particular tree taxa was low and the more heterogeneous litter between trees failed to support higher arthropod diversity. Furthermore, arthropod diversity did not track abundance or litter depth. The lack of association between tree species and litter arthropods suggests that factors other than tree species diversity may better explain the high arthropod diversity in tropical forests.     

系统发育多样性与系统发育结构在岛屿植物群落保护中的意义——以蜈支洲岛为例

为探讨系统发育多样性和系统发育结构在岛屿植物群落保护决策制定中的作用,以海南三亚蜈支洲岛被子植物群系为例,分析物种丰富度和系统发育多样性的相关性。结果表明,蜈支洲岛植被可分为10种群系类型,22个样方的物种丰富度与系统发育多样性呈显著正相关,但系统发育多样性与物种丰富度对植物多样性保护优先顺序的指示有差异。森林群系的物种丰富度和系统发育多样性普遍高于灌木和草本群系,4个森林群系样方表现为系统发育结构发散,3个森林群系样方表现为系统发育结构聚集。灌木群系中露兜树(Pandanus tectorius)灌丛和草海桐(Scaevola sericea)灌丛系统发育多样性较高,草本群系中厚藤(Vitex trifolia)灌草丛系统发育多样性较高,灌木和草本群系大多倾向于系统发育结构聚集。距海或人类活动区较近的群系可能受环境过滤的作用,而远离海和人类活动区的群系主要受竞争排斥作用影响。因此,在岛屿植物多样性保护策略制定中应当综合考虑物种和系统发育维度,以及环境、演替阶段及用岛方式等因素的影响。