Comparison of lepidopteran larval communities among tree species in a temperate deciduous forest, Japan

Abstract.  1. The enormous diversity of phytophagous insects in forest canopies is hypothesised to be supported by the number of herbivorous species per host tree species or host specificity. It is therefore necessary to examine the effect of host plant species on compositional changes in the herbivore communities.
2. The lepidopteran larval communities were examined in the canopies of 10 tree species in a temperate deciduous forest of Japan. The phylogeny and leaf flush phenology of host plant species were taken into account as factors affecting the herbivore community assembly.
3. Examination of seasonal changes in the larval community structures on each tree species showed that larval species richness, abundance, and evenness decreased significantly from spring to summer. Larval species richness and abundance were characterised by family-level phylogenetic differences among tree species, whereas evenness was determined at a higher taxonomic level.
4. Compositional changes in the larval communities among tree species showed a remarkable pattern, with a phylogenetic effect at a high taxonomic level in spring, similar to evenness, but a phenological effect in summer. This suggests that host specificity could support the lepidopteran larval diversity in spring.
5. These results suggest that the differences in host utilisation of the herbivore, which reflects the phylogenetic effect of the host plants, can be important as a factor affecting the diversity of lepidopteran larval communities in temperate forests.     

Microclimate and tree community linked to differences in lepidopteran larval communities between forest fragments and continuous forest

Aim  We aim to assess the impact of forest fragmentation on lepidopteran larval community and study the associations of microclimate and tree community with lepidopteran assemblage.
Location  Kibale National Park, Uganda.
Methods  We investigated the effects of forest fragmentation on leaf herbivory, density of lepidopteran caterpillars, species richness and diversity as well as the composition of herbivorous lepidopteran larval community. Microclimate, size of the fragment, distance to the continuous forest, and tree diversity were studied as possible explanatory factors. We sampled 10 Neoboutonia macrocalyx Pax. (Euphorbiaceae) trees in each fragment during dry and rainy season, total of four times, in a year to cover the seasonal variation.
Results  The rates of herbivory, total larval density and species richness were significantly lower in the forest fragments than in the continuous forest but species diversity expressed as Fisher's alpha did not differ. The dominance structure and community composition of the larval communities in the fragments was different from that of the continuous forest. None of the differences we observed were related to the fragment area or distance to the continuous forest. Instead, we found an indication of association between the herbivore and the tree communities. The fragments had significantly lower humidity during most of the day and higher temperature during the afternoons (14–17 h), which might partially explain the differences in lepidopteran larval communities.
Main conclusions  Decreased larval density and species richness as well as differences in the community composition and structure all highlight the importance of large continuous forest areas for maintaining larval biodiversity.     

Different seasonal feeding activity of diverse herbivores in two temperate forests

The aim of the present study was to understand the effects of abiotic conditions on seasonal feeding activity of diverse herbivores on the same oak tree species in two different forests. We tracked changes in herbivore feeding activities on an oak tree species (Quercus serrata) in two localities: a low elevation small hillock forest patch (Muan, MN) and a middle elevation mountain forest patch (Mt. Jirisan, JR). A total of five sites were selected in each of two forest localities. Data for leaf expansion, leaf chemical qualities, leaf damage ratio, and numbers of lepidopteran caterpillars were collected during spring (May) and summer (July to August), 2012. Leaf expansion rate was higher at the low hillock forest than the mid‐mountain forest from spring to summer. Nitrogen and carbon content decreased seasonally at both localities. Lepidopteran larval diversity was high in the mid‐mountain forest, and two‐way ANOVA showed that species richness of lepidopteran larvae was significantly affected by the interaction between season and locality. Leaf damage by all herbivores was higher in the low hillock forest than the mid‐mountain forest in spring, but was higher in the mid‐mountain forest in summer. Relative proportion of general herbivores increased from spring to summer in the mid‐mountain forest, but not in the low hillock forest. Canonical Correspondence Analysis (CCA) ordination showed that altitude‐ and season‐related variables were significant species and environment interaction factors. Our data indicate that locality and temperature disproportionally affected the feeding activities of diverse herbivores in two different temperate forests.     

Spatio-temporal variation in Lepidopteran larval assemblages associated with oak, Quercus crispula: the importance of leaf quality

Abstract.  1. Lepidoptera larval abundance and diversity in the canopies of oak ( Quercus crispula ) trees and saplings were surveyed in a cool-temperate, deciduous broadleaf forest in northern Japan.
2. In general, newly developed leaves were soft, rich in water and nitrogen, and low in tannin, whereas they became tough, poor in water and nitrogen, and high in tannin as the season proceeded. Leaf quality also varied among forest strata, such variations resulting in seasonal and among-strata differences in the structure of the Lepidoptera larval assemblage.
3. The greater Lepidoptera larval abundance and species richness may related to the higher leaf quality on spring foliage compared with summer foliage. On the other hand, diversity (Shannon's H' ) and evenness (Pielou's J' ) were greater on summer foliage than on spring foliage. Strengthened defences of the host plants against herbivory may cause these differences by filtering the larvae of Lepidoptera species and by constraining the super-dominance of a few species on summer foliage.
4. Canonical Correspondence Analysis (CCA) ordination also revealed a stratified structure of the Lepidoptera larval assemblage in the forest. In both spring and summer, the assemblage composition was more similar between sunlit and shaded canopies than between canopies and saplings. Such assemblage stratification was highly correlated with toughness and tannin content (in spring and summer) or water content (in summer).
5. This study emphasised the importance of spatio-temporal variations in leaf quality, even within the same host plant species, for promoting herbivore diversity in forests.     

Additive apportioning of lepidopteran and coleopteran species diversity across spatial and temporal scales in a cool–temperate deciduous forest in Japan

Abstract.  1. Forest entomofauna retain high diversity, and examining beta diversity, or species turnover, among assemblages in a forest community is vital to elucidate the source of this diversity.
2. Under the DIVERSITAS in Western Pacific and Asia–International Biodiversity Observation Year (DIWPA–IBOY) project for simultaneously documenting biodiversity throughout the Western Pacific and Asian Region, 892 lepidopteran species (51 742 specimens) and 355 coleopteran species (11 633 specimens) were collected in 2001 by light traps in a cool–temperate forest in northern Japan.
3. This study evaluated the beta diversity of lepidopteran and coleopteran communities by ecological categories (i.e. trap location, forest strata, sampling days, and months), and assessed the habitat preferences of lepidopteran and coleopteran species.
4.  anova -like additive apportioning models were used to quantify the beta diversity among the categories. The models simultaneously provide assessments of whether species distributions are biased in favour of particular habitats.
5. Significantly high beta diversity was observed among months for both Lepidoptera and Coleoptera. The category of months corresponded fairly well to the number of specialist species detected in the category, although a remarkably large number of significant specialists in Coleoptera were observed on strata.
6. The high beta diversity and number of specialist species among strata in both communities indicate that stratification between canopy and ground, and seasonal variation, played major roles in species composition and the rich entomofauna in the forest. Highly mobile adults were influenced by the vertical spatial scale, as previously suggested for larvae.     

亚热带不同树种组成森林中土壤甲螨群落结构特征: 以江西新岗山为例

在全球环境变化的大背景下, 生物多样性丧失日益加剧。土壤动物作为生物多样性重要组成之一, 受到广泛的关注。位于我国江西省新岗山的亚热带森林生物多样性与生态系统功能实验样地(BEF-China)是全世界25个森林生物多样性控制实验样地之一。本研究自2019年9月至2022年4月在BEF-China两个不同树种组成的样地(A样地和B样地)内采样, 共获得甲螨23,704头, 隶属于34科50属61种。本文分析和对比了两个样地内甲螨群落结构的差异, 及其多度、物种丰富度、Shannon多样性指数的季节性差异; 通过Pearson检验探讨了甲螨多度与环境因子的关系。结果表明: 在A、B两个不同树种组成的森林生态系统内, 土壤甲螨群落结构及其季节动态具有显著差异。具体表现在: A样地奥甲螨科、罗甲螨科、若甲螨科和尖棱甲螨科的相对多度高于B样地; B样地菌甲螨科、盖头甲螨科和礼服甲螨科的相对多度高于A样地。A样地中夏季和秋季甲螨多度、物种丰富度和Shannon多样性指数显著低于春季和冬季; 而B样地中秋季甲螨多度和物种丰富度与春季差异不显著。Pearson检验结果显示, 凋落物木质素含量与单翼甲螨科和菌甲螨科多度呈负相关关系, 而与奥甲螨科多度呈正相关关系。菌甲螨科多度与土壤和凋落物同一理化因子的相关性基本相同(碳氮比除外), 但与凋落物碳氮比呈正相关关系而与土壤碳氮比呈负相关关系。     

Microclimate Fluctuation Correlated with Beta Diversity of Epiphyllous Bryophyte Communities

Site‐to‐site variation in community composition, or beta diversity, is a major component of regional diversity. While many mechanisms, such as dispersal limitation and habitat heterogeneity, have been shown to affect beta diversity, interactions between habitat heterogeneity and environmental fluctuation have not been thoroughly investigated. This study uses leaf‐colonizing (epiphyllous) bryophyte communities as a model system to investigate the effects of microclimate fluctuation on beta diversity. I hypothesized that beta diversity would increase with increasing microclimate fluctuation, as niche breadth of species was reduced with increasing fluctuation. A total of 354 leaf‐colonizing bryophyte communities from 18 sites on the island of Moorea, French Polynesia were collected and identified. At each site, temperature and relative humidity were measured and converted to vapor pressure deficit (VPD). My analyses showed that beta diversity among communities on different host types tended to increase with the increasing daily range of VPD at a given site. It is possible that high fluctuation in microclimate conditions augments the differences in habitat quality among host types, resulting in greater dissimilarities among epiphyllous communities. However, host niche breadths of major epiphyllous species did not decrease with increasing VPD range. Overall, the results suggest that beta diversity may increase with environmental fluctuation, but it is not likely to be the results of reduced niche breadth as theoretically suspected.     

Tree diversity promotes generalist herbivore community patterns in a young subtropical forest experiment

Stand diversification is considered a promising management approach to increasing the multifunctionality and ecological stability of forests. However, how tree diversity affects higher trophic levels and their role in regulating forest functioning is not well explored particularly for (sub)tropical regions. We analyzed the effects of tree species richness, community composition, and functional diversity on the abundance, species richness, and beta diversity of important functional groups of herbivores and predators in a large-scale forest biodiversity experiment in south-east China. Tree species richness promoted the abundance, but not the species richness, of the dominant, generalist herbivores (especially, adult leaf chewers), probably through diet mixing effects. In contrast, tree richness did not affect the abundance of more specialized herbivores (larval leaf chewers, sap suckers) or predators (web and hunting spiders), and only increased the species richness of larval chewers. Leaf chemical diversity was unrelated to the arthropod data, and leaf morphological diversity only positively affected oligophagous herbivore and hunting spider abundance. However, richness and abundance of all arthropods showed relationships with community-weighted leaf trait means (CWM). The effects of trait diversity and CWMs probably reflect specific nutritional or habitat requirements. This is supported by the strong effects of tree species composition and CWMs on herbivore and spider beta diversity. Although specialized herbivores are generally assumed to determine herbivore effects in species-rich forests, our study suggests that generalist herbivores can be crucial for trophic interactions. Our results indicate that promoting pest control through stand diversification might require a stronger focus on identifying the best-performing tree species mixtures.     

Community structure of arboreal caterpillars within and among four tree species of the eastern deciduous forest

Abstract.  1. A seasonally replicated experimental design was used to address the question of how differences within and among host tree species affect arboreal caterpillar communities.
2. Seasonal variation influenced caterpillar community composition most significantly, and the similarity among caterpillar assemblages did not necessarily follow the pattern of phylogenetic relatedness among host trees.
3. Species richness and abundance of caterpillars were higher on oaks and maples than on American beech. Diversity partitioning models revealed that β diversity was only occasionally greater or less than expected by chance alone.
4. When β diversity was significant, values tended to be greater than expected by chance among replicate trees within each species and lower than expected by chance among the four tree species.
5. Differences among trees appeared important for determining patterns of species presence/absence for rare species and influencing patterns of species dominance within caterpillar assemblages. Differences among tree species had a significant effect on overall lepidopteran community composition and mean species diversity (i.e. α diversity).
6. Because β diversity of caterpillars among host trees was lower than expected by chance, host specificity within the Lepidoptera may be less prevalent than thought previously.     

长白山溪流河岸带森林木本植物多样性沿海拔梯度分布规律

采用样带网格调查方法和α、β多样性指数分析方法,研究了长白山河岸带原始林和次生林群落木本植物多样性沿海拔梯度分布规律及其对采伐干扰的响应.结果表明：不同海拔区域河岸带原始林群落均由11～13个树种组成,其在群落中的地位随海拔升高而发生变化,阔叶树种优势地位逐步被针叶树种所取代,采伐干扰不仅改变了群落树种丰富度及其在群落中的地位,而且使针叶树种取代阔叶树种的趋势有所增强;河岸带原始林群落物种多样性沿海拔梯度呈现出中、低海拔区域相对较高且比较恒定(2.454～2.544),高海拔区域(2.250)下降的分布规律,采伐干扰改变了其沿海拔梯度分布格局(波动型),加大了不同海拔区域群落间的波动性(2.174～2.692);河岸带原始林群落树种沿海拔梯度的变动速率相对较低(1.5～3.5),且群落相似性较高(0.85～0.94),采伐干扰使次生林群落树种沿海拔梯度的变动幅度增大(0.5～6.0),群落相似性下降(0.68～0.91),但次生林群落沿海拔梯度分布仍具有较高连续性.     

Summer season and long-term drought increase the richness of bacteria and fungi in the foliar phyllosphere of Quercus ilex in a mixed Mediterranean forest

We explored the changes in richness, diversity and evenness of epiphytic (on the leaf surface) and endophytic (within leaf tissues) bacteria and fungi in the foliar phyllosphere of Quercus ilex, the dominant tree species of Mediterranean forests. Bacteria and fungi were assessed during ontogenic development of the leaves, from the wet spring to the dry summer season in control plots and in plots subjected to drought conditions mimicking those projected for future decades. Our aim was to monitor succession in microbiota during the colonisation of plant leaves and its response to climate change. Ontogeny and seasonality exerted a strong influence on richness and diversity of the microbial phyllosphere community, which decreased in summer in the whole leaf and increased in summer in the epiphytic phyllosphere. Drought precluded the decrease in whole leaf phyllosphere diversity and increased the rise in the epiphytic phyllosphere. Both whole leaf bacterial and fungal richness decreased with the decrease in physiological activity and productivity of the summer season in control trees. As expected, the richness of epiphytic bacteria and fungi increased in summer after increasing time of colonisation. Under summer dry conditions, there was a positive relationship between TRF (terminal restriction fragments) richness and drought, both for whole leaf and epiphytic phyllosphere, and especially for fungal communities. These results demonstrate that changes in climate are likely to significantly alter microbial abundance and composition of the phyllosphere. Given the diverse functions and large number of phyllospheric microbes, the potential functional implications of such community shifts warrant exploration.     

哀牢山亚热带中山湿性常绿阔叶林树种beta多样性格局形成的驱动力

Beta多样性通常指群落在时间和空间上物种组成的差异, 包括物种周转组分和物种丰富度差异组分。驱动beta多样性格局形成的生态过程决定了群落的时空动态, 然而关于beta多样性及其两个组分格局形成的驱动力还存在较多争议。以往研究表明, beta多样性的格局存在取样尺度的依赖性, 驱动其形成的生态过程在不同取样尺度下的相对重要性也随之改变。本研究以哀牢山亚热带中山湿性常绿阔叶林20 ha动态监测样地为研究对象, 在不同取样尺度上, 将样方间的Bray-Curtis指数分解为物种周转组分和物种丰富度差异组分, 通过典范冗余分析和方差分解的方法揭示环境过滤和扩散限制对于beta多样性及其两个组分格局形成的相对重要性及其尺度依赖性。结果表明: (1) beta多样性、物种周转组分和物种丰富度差异组分均随取样尺度的增大而减小。在不同取样尺度下, 物种周转组分对于beta多样性的贡献始终占主导地位。(2)随着取样尺度的增大, 环境过滤驱动beta多样性格局形成的相对重要性逐渐增加, 而扩散限制的相对重要性逐渐降低。本研究进一步证实了取样尺度在beta多样性格局形成及其驱动力定量评价中的重要性, 今后的研究需要进一步解析上述尺度效应的形成机制。     

The Influence of Soil Type on Rain Forest Insect Herbivore Communities

Insect herbivores were collected from five species of dipterocarp tree seedling within a large‐scale reciprocal transplant experiment in Sabah, Malaysia, on alluvial and sandstone soils in both gap and understory plots. The aim was to determine whether the location and ecological specialization of seedlings influenced the herbivore communities found on and around them. Three major groups of folivores were collected: Coleoptera, Orthoptera, and larval Lepidoptera. Herbivory of all species was confirmed through laboratory trials. Herbivore abundance in the understory plots was extremely low relative to the gaps. Rank‐abundance curves were similar on both soil types, differing only within the Lepidoptera. Coleoptera and Orthoptera communities were numerically dominated by a small suite of species capable of feeding on all dipterocarp species tested, whereas lepidopteran communities had both greater species richness and diversity. When corrected for leaf area surveyed, the abundance of Coleoptera was similar on both soil types, while larval Lepidoptera were more abundant in sandstone plots and Orthoptera were more abundant in alluvial plots. Estimated species richness of all three taxa was greater in alluvial forest, but there were contrasting patterns in Simpson diversity and evenness between groups. Species richness of Lepidoptera was greatest on seedlings when grown in their native soil type, providing partial evidence for possible escape effects, although this was not matched by differences in folivore abundance. The link between herbivore communities and herbivory rates on rain forest tree seedlings is complex and is unlikely to be detected through simplistic measures of abundance, species richness, or diversity.     

Importance of the understory stratum to entomofaunal diversity in a temperate deciduous forest

The vertical stratification of lepidopteran and coleopteran communities in a cool-temperate deciduous forest in Japan was examined to evaluate the hypothesis of an expected uniform distribution of mobile flying insects between the canopy and understory of temperate forests. Lepidopteran and coleopteran insects were trapped using light traps at three sites in each of the canopy and understory for three consecutive nights each month from April to October 2001. For Lepidoptera, species richness, abundance, and family richness were significantly higher in the understory than in the canopy. For Coleoptera, only abundance was larger in the canopy relative to the understory; species and family richness did not differ between the strata. The beta diversity of the lepidopteran community was larger between the strata than among sites, but the coleopteran community showed an inverse pattern. These results imply the presence of vertical stratification within the lepidopteran community, but not within the coleopteran community, in the temperate forest. The understory contributes more than the canopy to lepidopteran diversity in the temperate forest, although this stratification may be relatively weak because, in contrast to the situation in tropical forests, the canopy and understory assemblages share many species.     

Genetic variation in a tropical tree species influences the associated epiphytic plant and invertebrate communities in a complex forest ecosystem

Genetic differences among tree species, their hybrids and within tree species are known to influence associated ecological communities and ecosystem processes in areas of limited species diversity. The extent to which this same phenomenon occurs based on genetic variation within a single tree species, in a diverse complex ecosystem such as a tropical forest, is unknown. The level of biodiversity and complexity of the ecosystem may reduce the impact of a single tree species on associated communities. We assessed the influence of within-species genetic variation in the tree Brosimum alicastrum (Moraceae) on associated epiphytic and invertebrate communities in a neotropical rainforest. We found a significant positive association between genetic distance of trees and community difference of the epiphytic plants growing on the tree, the invertebrates living among the leaf litter around the base of the tree, and the invertebrates found on the tree trunk. This means that the more genetically similar trees are host to more similar epiphyte and invertebrate communities. Our work has implications for whole ecosystem conservation management, since maintaining sufficient genetic diversity at the primary producer level will enhance species diversity of other plants and animals.     

Living in the litter: the influence of tree leaf litter on wetland communities

Empirical research in streams has demonstrated that terrestrial subsidies of tree leaf litter influence multiple community factors including composition, diversity and growth of individuals. However, little research has examined the importance of tree litter species on wetlands, which are ubiquitous across the landscape and serve as important habitats for a unique and diverse community of organisms. Using outdoor mesocosms, we assessed the impact of 12 litter monocultures and three litter mixtures (from both broadleaf and conifer trees) on pond communities containing gray tree frog tadpoles Hyla versicolor, periphyton, phytoplankton and zooplankton. We found that leaf litter species had substantial and differential impacts on all trophic groups in the community including effects on algal abundance, zooplankton density and amphibian growth. In many instances, patterns of responses were specific to individual litter species yet some responses, including both pH values and periphyton biomass, were generalizable to broad taxonomic groups. In addition, while most responses of litter mixtures were additive, we found evidence for antagonistic effects of litter mixing among responses of periphyton and amphibian body mass. Our results highlight the potential impact of human and naturally driven changes in forest composition on wetland communities through associated changes in leaf litter.     

Leaf water relations during summer water deficit: differential responses in turgor maintenance and variation in leaf structure among different plant communities in south-western Australia

We measured leaf water relations and leaf structural traits of 20 species from three communities growing along a topographical gradient. Our aim was to assess variation in seasonal responses in leaf water status and leaf tissue physiology between sites and among species in response to summer water deficit. Species from a ridge-top heath community showed the greatest reductions in pre-dawn leaf water potentials (Psi(leaf)) and stomatal conductance during summer; species from a valley-floor woodland and a midslope mallee community showed less reductions in these parameters. Heath species also displayed greater seasonal reduction in turgor-loss point (Psi(TLP)) than species from woodland or mallee communities. In general, species that had larger reductions in Psi(leaf) during summer showed significant shifts in either their osmotic potential at full turgor (Psi(pi 100); osmotic adjustment) or in tissue elasticity (epsilon(max)). Psi(pi 100) and epsilon(max) were negatively correlated, during both spring and summer, suggesting a trade-off between these different mechanisms to cope with water stress. Specific leaf area varied greatly among species, and was significantly correlated with seasonal changes in Psi(TLP) and pre-dawn Psi(leaf). These correlations suggest that leaf structure is a prerequisite for cellular mechanisms to be effective in adjusting to water deficit.     

Effect of Leaf Type and Pesticide Exposure on Abundance of Bacterial Taxa in Mosquito Larval Habitats

Lentic freshwater systems including those inhabited by aquatic stages of mosquitoes derive most of their carbon inputs from terrestrial organic matter mainly leaf litter. The leaf litter is colonized by microbial communities that provide the resource base for mosquito larvae. While the microbial biomass associated with different leaf species in container aquatic habitats is well documented, the taxonomic composition of these microbes and their response to common environmental stressors is poorly understood. We used indoor aquatic microcosms to determine the abundances of major taxonomic groups of bacteria in leaf litters from seven plant species and their responses to low concentrations of four pesticides with different modes of action on the target organisms; permethrin, malathion, atrazine and glyphosate. We tested the hypotheses that leaf species support different quantities of major taxonomic groups of bacteria and that exposure to pesticides at environmentally relevant concentrations alters bacterial abundance and community structure in mosquito larval habitats. We found support for both hypotheses suggesting that leaf litter identity and chemical contamination may alter the quality and quantity of mosquito food base (microbial communities) in larval habitats. The effect of pesticides on microbial communities varied significantly among leaf types, suggesting that the impact of pesticides on natural microbial communities may be highly complex and difficult to predict. Collectively, these findings demonstrate the potential for detritus composition within mosquito larval habitats and exposure to pesticides to influence the quality of mosquito larval habitats.     

神农架南坡送子园珍稀植物群落的区系及生态特征研究

研究了分布于神农架南坡的珍稀植物群落的区系及生态学特征。结果表明：珍稀植物群落中有维管束植物１２６种,隶属于１０８属６４科。其中,第一批珍稀保护植物９种,占神农架地区珍稀植物总数的２７．３％,珍稀植物群落具温带特性。群落外貌以高位芽为主,占６５．９％;叶以中型叶占优势,达６２．７％;叶质以纸质为主,占８４．１％;叶型以单型叶为主,为８３．３％;叶缘以非全缘为主,占６９．８％。群落垂直分层明显,可分     

Non-Native Plants Disrupt Dual Promotion of Native Alpha and Beta Diversity

Non-native species can alter patterns of species diversity at multiple spatial scales, but the processes that underlie multi-scale effects remain unclear. Here we show that non-native species reduce native diversity at multiple scales through simultaneous disruption of two processes of native community assembly: species immigration, which enhances alpha diversity, and community divergence, which enhances beta diversity. Community divergence refers to the process in which local communities diverge over time in species composition because the history of species immigration and, consequently, the way species affect one another within communities are variable among communities. Continuous experimental removal of species over four years of floodplain succession revealed that, when non-native species were excluded, stochastic variation in the timing of a dominant native species’ arrival allowed local communities to diverge, thereby enhancing beta diversity, without compromising promotion of alpha diversity by species immigration. In contrast, when non-native species were allowed to enter experimental plots, they not only reduced native alpha diversity by limiting immigration, but also diminished the dominant native species’ role in enhancing native beta diversity. Our results highlight the importance of community assembly and succession for understanding multi-scale effects of non-native species.