A global review of island endemic birds

Although fewer than one-fifth of the world's bird species are restricted to islands, over 90% of bird extinctions during historic times have occurred on islands. The major identified cause has been the effects of exotic animal species introduced by man; the largest number of documented extinctions has occurred on islands of the Pacific Ocean.
Some 39% (402) of threatened bird species are restricted to islands and more than 907; of these are endemic to a single geopolitical unit. The largest numbers occurring in such units are in Indonesia (91) and the Philippines (34). As a region, the Pacific holds more threatened species (110) than any other, including almost half of those considered Endangered and over 40% of the Vulnerable species.
Most threatened island species are forest-dwelling. A high proportion of the Endangered species use seasonal/temperate forest. While habitat destruction now poses the greatest overall threat to island birds (affecting over half the species restricted to islands), the presence of introduced species threatens 30 of the 66 Endangered species.
Although immediate extinctions of island species can best be averted by mitigating the effects of introductions, the removal of native forests will be a more severe problem in the longer term. There is an urgent need for ecologists to provide detailed information on the habitats of both threatened and endemic species so that more appropriate and effective conservation programmes can be developed.     

Alien pollinator promotes invasive mutualism in an insular pollination system

The alien predatory lizard, Anolis carolinensis, has reduced the insect fauna on the two main islands of the Ogasawara archipelago in Japan. As a result of this disturbance, introduced honeybees are now the dominant visitors to flowers instead of endemic bees on these islands. On the other hand, satellite islands not invaded by alien anoles have retained the native flower visitors. The effects of pollinator change on plant reproduction were surveyed on these contrasting island groups. The total visitation rates and the number of interacting visitor groups on main islands were 63% and 30% lower than that on satellite islands, respectively. On the main islands, the honeybees preferred to visit alien flowers, whereas the dominant endemic bees on satellite islands tended to visit native flowers more frequently than alien flowers. These results suggest that alien anoles destroy the endemic pollination system and caused shift to alien mutualism. On the main islands, the natural fruit set of alien plants was significantly higher than that of native plants. In addition, the natural fruit set was positively correlated with the visitation rate of honeybees. Pollen limitation was observed in 53.3% of endemic species but only 16.7% of alien species. These data suggest that reproduction of alien plants was facilitated by the floral preference of introduced honeybees.     

Habitat Structure Affects Reproductive Success of the Rare Endemic Tree Syzygium mamillatum (Myrtaceae) in Restored and Unrestored Sites in Mauritius

Invasive alien plants affect the functioning of ecosystems by altering plant–animal interactions, such as pollination, which may impede natural regeneration of native plant species. In Mauritius, we studied the reproductive traits and pollination ecology of the rare endemic cauliflorous tree Syzygium mamillatum in a restored forest (all alien plant species removed) and an adjacent unrestored area (degraded by alien plants). Flowers of S. mamillatum were only visited by generalist bird species. Although the initial number of flower buds per tree in the restored forest tended to be higher than that of trees in the unrestored area, final fruit set and the number of seeds per fruit were lower in the restored forest. This corresponded with lower bird visitation rates in the restored area. Additionally, during budding stage, most trees were severely attacked by lepidopteran larvae, and bud loss through herbivory was higher in the restored forest. Thus, the difference in reproductive performance of S. mamillatum between the two localities was caused by contrasting herbivore attack and bird visitation behavior in restored and unrestored areas. Our findings illustrate the importance of restoration efforts in mimicking the original physical structure of habitats and interaction structure of interspecific relationships, and the difficulty of doing so given the imperfect knowledge and the reality that many native species have become locally extinct and replaced by exotic species.     

How strongly do interactions with closely‐related native species influence plant invasions? Darwin's naturalization hypothesis assessed on Mediterranean islands

Aim Recent works have found the presence of native congeners to have a small effect on the naturalization rates of introduced plants, some suggesting a negative interaction (as proposed by Charles Darwin in The Origin of Species), and others a positive association. We assessed this question for a new biogeographic region, and discuss some of the problems associated with data base analyses of this type. Location Islands of the Mediterranean basin. Methods Presence or absence of congeners was assessed for all naturalized alien plants species at regional, local and habitat scales. Using general linear models, we attempted to explain the abundance of the species (as measured by the number of islands where recorded) from their congeneric status, and assessed whether the patterns could be alternatively accounted for by a range of biological, geographical and anthropogenic factors. A simulation model was also used to investigate the impact of a simple bias on a comparable but hypothetical data set. Results Data base analyses addressing Darwin's hypothesis are prone to bias from a number of sources. Interaction between invaders and congenerics may be overestimated, as they often do not co‐occur in the same habitats. Furthermore, intercorrelations between naturalization success and associated factors such as introduction frequency, which are also not independent from relatedness with the native flora, may generate an apparent influence of congenerics without implying a biological interaction. We detected no true influence from related natives on the successful establishment of alien species of the Mediterranean. Rarely‐introduced species tended to fare better in the presence of congeners, but it appears that this effect was generated because species introduced accidentally into highly invasible agricultural and ruderal habitats have many relatives in the region, due to common evolutionary origins. Main conclusions Relatedness to the native flora has no more than a marginal influence on the invasion success of alien plants in the Mediterranean, although apparent trends can easily be generated through artefacts of the data base.     

The cobblers stick to their lasts: pollinators prefer native over alien plant species in a multi-species experiment

The majority of plant species rely, at least partly, on animals for pollination. Our knowledge on whether pollinator visitation differs between native and alien plant species, and between invasive and non-invasive alien species is still limited. Additionally, because numerous invasive plant species are escapees from horticulture, the transition from human-assisted occurrence in urbanized habitats to unassisted persistence and spread in (semi-)natural habitats requires study. To address whether pollinator visitation differs between native, invasive alien and non-invasive alien species, we did pollinator observations for a total of 17 plant species representing five plant families. To test whether pollinator visitation to the three groups of species during the initial stage of invasion depends on habitat type, we did the study in three urbanized habitats and three semi-natural grasslands, using single potted plants. Native plants had more but smaller flower units than alien plants, and invasive alien plants had more but smaller flowers than non-invasive alien plants. After accounting for these differences in floral display, pollinator visitation was higher for native than for alien plant species, but did not differ between invasive and non-invasive alien plant species. Pollinator visitation was on average higher in semi-natural than in urbanized habitats, irrespective of origin or status of the plant species. This might suggest that once an alien species has managed to escape from urbanized into more natural habitats, pollinator limitation will not be a major barrier to establishment and invasion.     

Influence of different landscape design styles on plant invasions in Central Europe

When considering the most frequent invasive exotic plants on an international scale, it is evident that the majority are ornamentals and that they were deliberately introduced in relation to landscape design. Although there are worldwide numerous lists of invasive exotic plants—which means plants that have harmful effects on native biodiversity—an assessment of the contribution of different landscape design styles on plant invasions has not been done. We used the extensive database on the history of introduction and naturalization of alien plants into natural habitats of Central Europe (Lohmeyer and Sukopp, Agriophyten in der Vegetation Mitteleuropas in: Schriftenreihe Vegetationskunde 25, 1992; Nachtrag: Braunschweiger Geobotan Arbeiten 8:179–220, 2001) to examine how many alien ornamental plants there are in the different natural habitats; and how many of them are invasive exotic plants and—in contrast—how many have not spread significantly. Also, we researched contributions by different landscape design styles to these plant invasions since medieval times. Of the estimated 12,000 alien plant species introduced into Central Europe since the Neolithic period, 279 taxa (2.3 %) are currently identified as being naturalized in natural habitats; 103 (0.86 %) of these naturalized taxa are ornamentals, and of these, 40 (0.33 %) are invasive exotic plants. Our investigation has shown a correlation between the frequency of plant invasions and changes in landscape-design styles. Evaluating the impact of plant invasions through horticulture and landscape design on native biodiversity, our study illustrates that it is significantly lower in Central Europe than in other parts of the world.     

Predicting plant invasions under climate change: are species distribution models validated by field trials?

Climate change may facilitate alien species invasion into new areas, particularly for species from warm native ranges introduced into areas currently marginal for temperature. Although conclusions from modelling approaches and experimental studies are generally similar, combining the two approaches has rarely occurred. The aim of this study was to validate species distribution models by conducting field trials in sites of differing suitability as predicted by the models, thus increasing confidence in their ability to assess invasion risk. Three recently naturalized alien plants in New Zealand were used as study species (Archontophoenix cunninghamiana, Psidium guajava and Schefflera actinophylla): they originate from warm native ranges, are woody bird‐dispersed species and of concern as potential weeds. Seedlings were grown in six sites across the country, differing both in climate and suitability (as predicted by the species distribution models). Seedling growth and survival were recorded over two summers and one or two winter seasons, and temperature and precipitation were monitored hourly at each site. Additionally, alien seedling performances were compared to those of closely related native species (Rhopalostylis sapida, Lophomyrtus bullata and Schefflera digitata). Furthermore, half of the seedlings were sprayed with pesticide, to investigate whether enemy release may influence performance. The results showed large differences in growth and survival of the alien species among the six sites. In the more suitable sites, performance was frequently higher compared to the native species. Leaf damage from invertebrate herbivory was low for both alien and native seedlings, with little evidence that the alien species should have an advantage over the native species because of enemy release. Correlations between performance in the field and predicted suitability of species distribution models were generally high. The projected increase in minimum temperature and reduced frosts with climate change may provide more suitable habitats and enable the spread of these species.     

基于功能性状的外来植物入侵预测模型框架构建

预测外来植物的潜在入侵性已成为生物多样性保护研究的重要内容,外来植物与乡土物种间的亲缘关系是预测外来植物能否成功入侵的一个重要途径。然而,达尔文归化难题却预测了两种截然不同的结果(即达尔文归化假说和预适应假说)。该研究解析了达尔文归化难题的内涵,提出了基于功能性状的外来植物与乡土群落间的相似性关系应该是进行外来植物入侵预测的重要切入点,而功能性状的种间分化与种内变异可能是外来植物成功入侵的两种不同生态策略。在此基础上,该研究还通过物种功能性状的多维超体积构建了外来植物与乡土群落间的相似性,提出了基于这种相似性的外来植物入侵预测的研究框架和基本流程。该模型框架的建立有助于理解外来植物的入侵机制,对外来植物的潜在入侵性预测提供了理论依据。当然,要实现外来植物能否成功入侵的准确预测,不仅依赖于功能性状的选择,还要考虑入侵的生境依赖性、空间尺度的重要性以及乡土群落的可入侵性等,未来的研究重点是通过控制实验对该模型进行验证和进一步完善。     

The biogeography of naturalization in alien plants

Aim  This paper reviews the main geographical determinants of naturalization in plants.
Location  Global.
Methods  Comparative studies of large data sets of alien floras are the main source of information on global patterns of naturalization.
Results  Temperate mainland regions are more invaded than tropical mainland regions but there seems to be no difference in invasibility of temperate and tropical islands. Islands are more invaded than the mainland. The number of naturalized species in temperate regions decreases with latitude and their geographical ranges increase with latitude. The number of naturalized species on islands increases with temperature. Naturalized species contribute to floristic homogenization, but the phenomenon is scale-dependent.
Main conclusions  Some robust patterns are evident from currently available data, but further research is needed on several aspects to advance our understanding of the biogeography of naturalization of alien plants. For example, measures of propagule pressure are needed to determine the invasibility of communities/ecosystems/regions. The patterns discussed in this paper are derived largely from numbers and proportions of naturalized species, and little is known about the proportion of introduced species that become naturalized. Further insights on naturalization rates, i.e. the proportion of aliens that successfully naturalize within regions, and on geographical and other determinants of its variation would provide us with better understanding of the invasion process. Comparative studies, and resulting generalizations, are almost exclusively based on numbers of species, but alien species differ in their impact on native biodiversity and ecosystem processes.     

Non-intrusive systematic study reveals mutualistic interactions between threatened island endemic species and points to more impactful conservation

Oceanic islands harbour a disproportionately large share of extinct and endangered birds worldwide and up to about 6,800 highly threatened plants, stressing the urgency for conservation efforts there. However, effective conservation action can only be as sound as the ecological understanding on which it is based. Knowledge about the ecology of threatened birds and plants can be relatively sketchy even in well-studied oceanic islands and this can potentially misdirect or erode conservation actions’ effectiveness. We used camera traps to document vertebrate flower visitors of a threatened, mono-specific endemic oceanic island plant (Roussea simplex) that produces much nectar and which was abundant until the 1930s before declining severely despite its presence mostly within protected areas. We determined proportions of native and alien flower visitors in four populations and characterised their ecological role (e.g. florivore, nectar robber, pollinator) through observations and exclusion experiments alongside experiments to determine seed sets by agamospermy, autogamy, geitonogamy and xenogamy. Five native and three alien vertebrate species visited flowers (N = 5,085 camera trap-hours), 96.6% of visits being from birds. Among endemics, 74–96% of visits were by the Mauritius Bulbul (Hypsipetes olivaceus), a threatened bird able to effect pollination contrary to the other endemic birds. Roussea simplex is primarily xenogamous, producing 2,657 ± 480 seeds, and seed set dropped markedly when the bird was excluded (861.8 ± 91.0 SE, Kruskal-Wallis χ² = 14.2, p < 0.001). Natural seed set was very low (410.0 ± 85.3 SE) where the bird was locally extinct or very rare. Invasive alien rats (Rattus rattus) and long-tailed macaques (Macaca fascicularis) were important florivores or nectar robbers. Systematic non-intrusive study using camera traps combined with manipulative experiments revealed a mutualism between two relatively well-studied threatened endemic species as well as new threats from alien vertebrates acting as nectar robbers and florivores. Roussea simplex’s major decline within protected areas and its abundant and year round flowering and nectar production point to a major hitherto unrecorded drop in floral resource previously available to at least five endemic species, and particularly to its commonest flower visitor and principal pollinator, the threatened Mauritius Bulbul. These findings exemplify how systematic non-intrusive study of threatened species may radically change conservation managers’ priorities which in the current case should focus primarily on controlling alien rats and macaques and re-instating or reinforcing Bulbul-Roussea mutualism as each would be more impactful than addressing gecko-Roussea mutualism disruption by alien ants which so far was the only recorded threat thought to drive the rapid decline of Roussea simplex. Our study underscores that current conservation efforts should also pay particular attention to medium to longer-term changes in habitat or community composition which may not be obvious from merely considering extent and composition of current habitats.     

Strong indication of an extinction‐based saturation of the flora on the Pacific Robinson Crusoe Islands

Oceanic islands are vulnerable ecosystems and their flora has been under pressure since the arrival of the first humans. Human activities and both deliberately and inadvertently introduced biota have had and continue to have a severe impact on island endemic plants. The number of alien plants has increased nearly linearly on many islands, perhaps resulting in extinction‐based saturation of island floras. Here, we provide evidence for such a scenario in Alejandro Selkirk, Robinson Crusoe Islands (Archipelago Juan Fernández, Chile). We compared species richness and species composition of historical vegetation samples from 1917 with recent ones from 2011. Changes in species’ relative occurrence frequency were related to their taxonomic affiliation, dispersal mode, distribution status, and humidity and temperature preferences. While total species richness of vascular plants remained relatively similar, species composition changed significantly. Plants endemic to the Robinson Crusoe Islands declined, exotic species increased substantially within the period of ca. 100 years. Further, the relative occurrence frequency of plants with preferences for very warm and humid climate decreased, while the opposite was found for plants preferring drier and colder environments. Potential drivers responsible for this dramatic shift in the vegetation within only one century might have been the large goat population affecting especially small populations of endemic plants and climatic changes. Taking into account a substantial extinction debt, we expect further shifts in the vegetation of this small oceanic island toward alien plants. This would have significant negative consequences on global biodiversity, considering that island floras contribute substantially to global plant species richness due to their high proportion of endemics.     

Avian translocations restore dual interaction networks in an island ecosystem

Many island bird species have been driven to extinction by introduced predators. Although poorly understood, these extinctions could have a 2-fold impact on bird–plant mutualisms, because island bird species can serve as both pollinators and seed dispersers. We investigated how avian translocations into a mammal-free reserve in New Zealand affected the structure of bird–flower and bird–fruit interactions. We observed bird–fruit and bird–flower interactions over a 9-year period to establish (1) the extent to which native birds are both nectivorous and frugivorous (i.e. “dual mutualists”) and (2) how avian translocations and conservation reestablished nectivory and frugivory networks. Results showed that all but one native bird species were dual mutualists. Pairwise species interaction frequencies were positively correlated between networks. However, overall levels of nectivory by each bird species were unrelated to levels of frugivory. Interaction specialization and species strength also did not differ between networks. The reintroduction of threatened and endangered bird species appeared to have restored both interaction networks, and the sequence of species recovery accelerated restorative changes. Overall results indicate that not only does the extinction of dual mutualists have a 2-fold, negative effect on mutualistic interactions with plants, they can also accelerate the recovery of ecosystem services following restoration efforts.     

Assessing habitat suitability for the translocation of Ochrosia tahitensis (Apocynaceae), a critically endangered endemic plant from the island of Tahiti (South Pacific)

Reintroduction or translocation of threatened plant species, as part of in situ conservation efforts, often failed because of the lack or the poor quality of remaining natural habitats due to human disturbances and invasion by alien species, especially in island ecosystems. We conducted a study on Ochrosia tahitensis (Apocynaceae), a critically endangered endemic small tree in the tropical high volcanic island of Tahiti (French Polynesia, South Pacific) to find the most suitable sites for future translocation. Distribution models were produced based on climate, topography, and plant community inventories (i.e. species composition and abundance, canopy height and openness, basal area of woody species) of the few remnant populations. Results show that this species, comprising 32 reproductive trees within 16 populations known in the wild, remains restricted to a few ecological refuges representing a very small part of its potential ecological range located on the northwest side of the island, and shares its current habitats with a set of more common native woody species found in mesic-wet forests. The use of native plant communities as a proxy for habitat suitability along with species distribution modelling can enhance translocation success in island ecosystems, but only if the major threats causing population decrease, mainly forest destruction and fragmentation and invasive alien species, are effectively managed.     

不受欢迎的生物多样性：香港的外来植物物种

香港早在19世纪中叶开始就有外来植物入侵的记录,迄今为止,已发现多达238种已归化的外来或怀疑为外来的植物,其中又以薇甘菊（Mikania micrantha)、五爪金龙（Ipomoea cairica)、假臭草（Eupatorium catarium)、大黍（Panicum maximum)等最常见,外来植物最常见于受人为干扰的生境,例如荒废农田及路旁等,而较少在天然林地生境及贫瘠的灌草丛中发现,外来植物的对本地生态系统的影响主要局限于低地生境,它们常形成单优种群,减少了生境及贫瘠的灌草丛中发现,外来植物对本地生态系统的影响主要局限于低地生境,它们常形成单优种群,减少少了生境及动植物的多样性,外来动物对香港原生植物影响最大的是于20世纪70年代入侵的松树线虫（Bur-saphelenchus xylophilus)。外来的脊椎动物也有可能对香港的植物被演替产生影响,目前香港的外来植物当中,有些在大陆较少分布或没有记录,作为华南最大的港口,香港对外来物种的引入扮演着重要的角色,因此制定控制外来种在香港及华南地区的引入及传播的政策及措施非常重要。     

Alien species richness is currently unbounded in all but the most urbanized bird communities

Urban areas suffer high pressure of introductions of alien species compared to other habitats due to intensive human activities. As trading globally continues to rise, more species will likely be introduced into urban areas. To determine whether this increase in introduction pressure will lead to increased alien species richness in urban areas, or whether other processes would act to impose an upper limit on species richness, we examined how the shape of the relationship between alien species richness and the number of introduced species over time (i.e. introduction pressure) varies along gradients of urbanization. We collected species composition data from urban bird surveys worldwide and used a global database of alien bird introductions to quantify how many species have been introduced over time at different sites. We found that urbanization gradually modified the shape of the studied relationship from linear to asymptotic. Only communities in extremely urbanized environments were associated with an asymptotic relationship, suggesting that alien bird richness has likely not reached its ecological limit in most urban areas. Our results show that urbanization can reduce the importance of introduction pressure in determining alien species richness. Additionally, the results predict that alien species richness will increase at finer spatial scales, especially if the introduced species can survive in urban areas outside of their native range.     

A global analysis of the determinants of alien geographical range size in birds

Aim Determining the causes of range size variation in the distributions of alien species is important for understanding the spread of invasive species. Factors influencing alien range size have been explored for some species at a regional level, but to date there has been no global analysis of an entire class. Here, we present such an analysis for birds, testing for the effects of introduction event, location and species‐level variables on alien range sizes. Location Global. Methods We used a novel dataset on the global distributions of alien bird species to test for relationships between alien range size and colonization pressure, residence time, extent of the global climatic niche, native range size, body mass and specialization, using a statistical approach based on phylogenetic generalized least squares models. We performed this analysis globally, and for separate biogeographical realms. Results Approximately half of the variation in alien bird range size is explained by colonization pressure in univariate analysis. We identified consistent effects of higher colonization pressure at global and realm levels, as well as support for effects of native range size and residence time. We found less support for effects of body mass, specialization or extent of the global climatic niche on alien range size. Main conclusions Alien bird range sizes are generally small relative to their native range sizes, and many are continuing to expand. Nevertheless, current variation is predictable, most strongly by the event‐level factor of colonization pressure. Whether a species is widespread is a better predictor of alien range size than whether a species could be widespread (estimated by global climatic niche extent), while we also find effects of residence time on alien range size. These relationships may help to identify those alien species that are more likely to spread and hence have greater environmental and economic impacts where they have been introduced.     

A phylogenetic approach towards understanding the drivers of plant invasiveness on Robben Island,South Africa

Invasive plant species are a considerable threat to ecosystems globally and on islands in particular where species diversity can be relatively low. In this study, we examined the phylogenetic basis of invasion success on Robben Island in South Africa. The flora of the island was sampled extensively and the phylogeny of the local community was reconstructed using the two core DNA barcode regions, rbcLa and matK. By analysing the phylogenetic patterns of native and invasive floras at two different scales, we found that invasive alien species are more distantly related to native species, a confirmation of Darwin's naturalization hypothesis. However, this pattern also holds even for randomly generated communities, therefore discounting the explanatory power of Darwin's naturalization hypothesis as the unique driver of invasion success on the island. These findings suggest that the drivers of invasion success on the island may be linked to species traits rather than their evolutionary history alone, or to the combination thereof. This result also has implications for the invasion management programmes currently being implemented to rehabilitate the native diversity on Robben Island. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 142–152.     

Integration of alien plants into a native flower-pollinator visitation web

Introduced alien species influence many ecosystem services, including pollination of plants by animals. We extend the scope of recent 'single species' studies by analysing how alien plant species integrate themselves into a native flower visitation web. Historical records for a community in central USA show that 456 plant species received visits from 1429 insect and 1 hummingbird species, yielding 15 265 unique interactions. Aliens comprised 12.3% of all plant species, whereas only a few insects were alien. On average, the flowers of alien plants were visited by significantly fewer animal species than those of native plants. Most of these visitors were generalists, visiting many other plant species. The web of interactions between flowers and visitors was less richly connected for alien plants than for natives; nonetheless, aliens were well integrated into the native web. Because most visitors appear to be pollinators, this integration implies possible competitive and facilitative interactions between native and alien plants, mediated through animal visitors to flowers.     

天然林和人工林外来入侵和本地植物对比研究: 以弄岗国家级自然保护区为例

外来植物的入侵严重威胁了自然保护区的生物多样性。为探讨自然保护区内天然林和人工林林下外来植物入侵状况及其与本地优势植物的种间关系, 本研究以弄岗国家级自然保护区为研究区域, 结合保护区内4种生境72个样方的野外调查数据, 利用生态位宽度、生态位重叠和种间联结指数比较了不同生境中外来入侵草本植物的多样性和生态位宽度以及外来入侵草本植物与本土优势草本植物的生态位重叠和种间联结。结果表明: 弄岗国家级自然保护区4种生境共记录6种外来入侵草本植物, 隶属于3科6属, 其中菊科物种数量最多。外来入侵植物多样性呈现出秋枫(Bischofia javanica)人工林 > 麻竹(Dendrocalamus latiflorus)次生林 > 人面子(Dracontomelon duperreanum)人工林 > 广西澄广花(Orophea polycarpa)次生林的特征。除广西澄广花次生林生境的外来入侵草本植物丰富度与本土草本植物丰富度呈显著正相关外, 其余生境均无显著的相关关系。三叶鬼针草(Bidens pilosa)的生态位宽度最大, 为4种生境均有分布的外来入侵植物。4种生境的外来入侵植物与本土优势植物生态位重叠和种间联结程度均较低, 种间竞争较弱。本研究明确了弄岗国家级自然保护区天然林和人工林中外来入侵草本植物的分布及其与本土草本植物的种间关系。     

Naturalization of an alien ancient fruit tree at a fine scale: Community structure and population dynamics of Cydonia oblonga in China

Naturalized plants play pivotal roles in local plant biodiversity and ecological functions; however, the drivers of naturalization remain poorly understood at a fine scale. Thus, understanding the processes of the development and dominance of alien plants in local natural habitats is of paramount importance. In the present study, we report for the first time the naturalization of Cydonia oblonga in China based on community structure and population dynamics at a fine scale. We conducted a comprehensive survey of the species through field community investigations, interviews, and a literature review. Cydonia oblonga is an ancient fruit tree with a long introduction history of over 4500 years worldwide and a cultivation history of over 2500 years in China. We analyzed C. oblonga community structure using the spatiotemporal substitution method and quantitatively analyzed population dynamics using a static life table, survivorship curve, and time series model to explore the naturalization processes. The following results were obtained. (i) The community comprised 31 coexisting vascular plant species (16 woody and 15 herbaceous species) belonging to 28 genera in 20 families. Rosaceae and Asteraceae were the two most dominant families. (ii) All individuals in the shrub layer as well as the C. oblonga population exhibited a roughly inverted J-shaped basal diameter distribution. A complete age structure was noted, and the survival curve was classified as Deevey type II. According to time series analysis, the population is estimated to increase in the future, specifically of medium and large individuals. (iii) Religious exchange, potent resource competitiveness, and similarity with the native habitat may be the major drivers of the introduction and successful naturalization of C. oblonga. These results suggest that alien species closely related to native ones are more likely to invade, naturalize, and dominate communities in local habitats.