Different Mechanisms Explain Decoupled Co‐Occurrence Patterns of Native and Non‐Native Macroinvertebrates

Rapid climate warming has boosted biological invasions and the distribution or expansion polewards of many species: this can cause serious impacts on local ecosystems within the invaded areas. Subsequently, native species may be exposed to threats of both interspecific competition with invaders and temperature rises. However, effects of warming on interspecific interactions, especially competition between invader and native species remains unclear. To better understand the combined threats of biological invasions and warming, the effect of temperature on competitive interactions between two dragonfly species, the expanding Trithemis aurora from Southeast Asia and the Japanese native Orthetrum albistylum speciosum were assessed based on their foraging capacity. Although the stand-alone effect of temperature on foraging intake of the native dragonfly was not apparent, its intake significantly decreased with increasing temperatures when the invader T. aurora was present. Such reductions in foraging might lead to displacement of the native species through competition for food resources. This suggests that impacts of invader species against native species are expected to be more severe when interspecific competition is exacerbated by temperature rises.

Biological invasions are one the most important drivers of the current environmental changes generating important biodiversity losses. Although several hypotheses have been proposed to understand the mechanisms underpinning biological invasions, most of them relate to negative interactions among native and invasive species, where the capacity for many invasive species to reduce diversity is often attributed to a greater competitiveness. However, neighbouring species can also show facilitative interactions, where the presence of one species can facilitate another directly by improving environmental conditions or indirectly through negative effects on a third party species. This chapter reviews the scientific literature on plant invasion, seeking examples of where facilitative interactions either among native and non-native plant species or among non-native species were demonstrated. There are several examples of native species that directly facilitate a non-native species, while examples of native species having a negative effect either on a native or a non-native species that compete with a target non-native, generating a net indirect facilitative effect of the native on the target non-native, are less numerous. Direct facilitation among non-native species has been reported as part of the 'invasional meltdown' phenomenon (Chapter 8, this volume). There are cases where non-native species can have a negative effect on a native species that competes with a target non-native, generating a net indirect facilitative effect among the non-natives. Finally, a non-native species can have a direct facilitative effect on native species, which might have important implications in restoration.

The limiting similarity theory predicts that divergence in the functional traits of native and introduced species is an essential component in species establishment, as introduced species must occupy a niche that is unoccupied by resident species. On the other hand, the environmental filtering hypothesis predicts convergence between introduced and native species, as both possess traits that make them adapted to the local abiotic environment. Morphology, spatial co-occurrence, diet, feeding selectivity, and niche breadth and overlap of Erythrinidae were evaluated to detect possible mechanisms acting in the coexistence between non-native and native species. Native (Hoplias sp. B and Hoplias cf. malabaricus) and non-native (Hoplerythrinus unitaeniatus and Hoplias mbigua) species presented differences in morphological traits, spatial co-occurrence, diet, selectivity, and niche breadth and overlap. The mechanisms mediating species coexistence seem to vary according to species. The absence of spatial and feeding overlap suggests that non-native species H. unitaeniatus occupy a different niche than native species, supporting its successful establishment without eliminating the native species. However, low feeding overlap and similar morphologies between non-native and native species of Hoplias point to environmental filters; in this case, the non-native H. mbigua is able to establish due to similarities in functional traits.

Invasive species have been identified as a major threat to native biodiversity and ecosystem functioning worldwide due to their superiority in spread and growth. Such superiority is explained by the invasional meltdown phenomena, which suggests that invasive species facilitate the establishment of more invasive species rather than native species by modifying the plant-soil feedback (PSF). We conducted a two-phase plant-soil feedback experiment using the native Prosopis cineraria and the invasive Prosopis juliflora in Oman. Firstly, we conditioned the soil by planting seedlings of native species, invasive species, native and invasive species "mixed", and unconditioned soil served as a control. Secondly, we tested the feedback of these four conditioned soil on the two species separately by measuring the productivity (total biomass) and the performance in the form of plant functional traits (plant height, specific leaf area (SLA), leaf nitrogen content (Nmass), leaf carbon content (Cmass) and specific root length (SRL) of native and invasive species as well as the nutrient availability in soil (soil organic carbon (SOC) and soil total nitrogen (STN)). We found that the native species produced more biomass, best performance, and higher SOC and STN when grown in soil conditioned by native species, additionally, it gave lower biomass, reduced performance, and lower SOC and STN when grown in the soil conditioned by invasive and mixed species. These results suggest negative PSF for native species and positive PSF for invasive species in the soil conditioned by invasive species, which can be considered as red flag concerning the restoration of P. cineraria as an important native species in Oman, as such positive PSF of the invasive species P. juliflora will inhibit the regeneration of P. cineraria.

Environmental filtering has been defined as the effect of environmental gradients on species in a plant community and can be the dominant driver of community assembly. Here, we evaluate the relationship between plant communities and the environment in the Restinga vegetation. For this, we measured 11 functional traits of plant species present along transects covering a marked edaphic environmental gradient. This gradient was characterized through Principal Component Analysis of soil characteristics. The relationships between the edaphic gradient and functional traits were evaluated using linear models. Finally, we compared the contributions of species turnover and intraspecific variation to among-site variation in functional traits. The gradients associated with soil nutrients (PCA axis 1) and soil acidity and organic matter (PCA axis 2) were then used to test the observed changes in community composition and were significant predictors of the distribution of water potential, leaf dry matter content and K content, height and chlorophyll index. Decomposing the total variation in the distribution of functional traits between species turnover and intraspecific variation revealed that species turnover explains a greater proportion of the observed variation. We conclude that community assembly is strongly limited by environmental filters and mediated by functional traits at the species level.

Summary 1 Two main views have been put forward to explain whether coexisting alien and resident plant species should show converging or diverging functional attributes. According to the ‘try‐harder’ hypothesis, successful aliens should differ from resident species with traits that allow them to deal better with the local conditions than resident species. On the other hand, the ‘join‐the‐locals’ hypothesis stresses the importance of filtering by environmental factors and predicts strong functional trait similarities between alien and native species, especially among the dominants. 2 On the basis of a functional trait comparison between native and alien species of central‐western Argentina across five contrasting ecosystems and four land‐use regimes, we tested these hypotheses over a broad range of habitats. We built a data set with common measurement methods and biogeographical factors but strongly varying environmental conditions, ranging from mesic to extremely dry, and from nearly pristine to heavily disturbed. 3 When considering all species together, the main trend of variation in trait syndromes was between acquisitive (tender, large leaves, with high specific area) and conservative (tough, small leaves, with low specific area and low nutrient content). Although both native and alien species appeared to be well spread across the whole range of trait variation, woody alien species showed a significantly more acquisitive set of attributes (higher specific leaf area, larger and thinner leaves, lower wood density) than native species. No significant difference was detected between herbaceous alien and native species. These general trends were maintained under contrasting climatic and land‐use conditions. 4 Synthesis. The patterns detected for herbaceous species were in line with the ‘join‐the‐locals’ hypothesis. In contrast, those found for woody species, with woody alien species showing more acquisitive attributes than native species in more resource‐rich habitats, provide partial support for the ‘try‐harder’ hypothesis. Overall, our findings reinforce the idea that a universal suit of attributes is unlikely to explain alien plant distribution. They also stress the need for caution when mixing major life‐forms in comparative plant trait analysis.

Background and aims - Under the assumption that ecologically similar species have similar functional traits, numerous studies have tried to use a trait-based approach to infer the abiotic and biotic factors that drive the variation in community composition. We used trait-based analyses to predict the responses in herb community composition to elevational change. We demonstrated the trait-environment relationships more precisely, and quantified the relative contribution of intraspecific variation and species replacement to shifts in community-level trait values across elevation. Methods - We measured herb community, leaf functional traits, and environmental variables along an elevational gradient at Donglingshan Mountain, China. We examined the relationships between environmental variables and functional traits and analysed the variation of functional traits along the elevational gradient. Key results - Minimum temperature (MinT) and light availability were the most important factors that shaped the herb community across elevation. Leaf hardiness and thickness were correlated strongly with MinT, while leaf mass per area, hair density, and leaf area were correlated with light availability. The trends in traits across an elevational gradient were due both to species replacement and intraspecific variation; however, the proportion of the species replacement depended on the functional traits evaluated. Conclusions - These results allowed us to identify the major functional traits and environmental factors involved in the herb community composition along the elevational gradient and demonstrate that environmental filtering (in this case MinT and light availability) is the process that shapes both herb community composition and functional traits. Moreover, we highlighted the need for greater consideration of the role that intraspecific variation plays in changes in functional traits, which can assist us in understanding herb community composition across elevations, and also in predicting its responses to climate change.

Inter-specific interactions around resources, such as nesting sites, are an important factor by which invasive species impact native communities. As resource availability varies across different environments, competition for resources and invasive species impacts around those resources change. In urban environments, changes in habitat structure and the addition of introduced species has led to significant changes in species composition and abundance, but the extent to which such changes have altered competition over resources is not well understood. Australia’s cities are relatively recent, many of them located in coastal and biodiversity-rich areas, where conservation efforts have the opportunity to benefit many species. Australia hosts a very large diversity of cavity-nesting species, across multiple families of birds and mammals. Of particular interest are cavity-breeding species that have been significantly impacted by the loss of available nesting resources in large, old, hollow-bearing trees. Cavity-breeding species have also been impacted by the addition of cavity-breeding invasive species, increasing the competition for the remaining nesting sites. The results of this additional competition have not been quantified in most cavity breeding communities in Australia. Our understanding of the importance of inter-specific interactions in shaping the outcomes of urbanization and invasion remains very limited across Australian communities. This has led to significant gaps in the understanding of the drivers of interspecific interactions and how such interactions shape resource use in highly modified environments. This knowledge deficit limits the effectiveness of conservation and management efforts to mitigate the loss of nest sites for native species and the effectiveness of ongoing management actions, such as the addition of artificial nesting boxes.To address these gaps, I examined the changes in native and invasive alien species use of resources across urban gradients and examined the factors shaping inter-specific interactions to provide a mechanistic framework for understanding competition at the community scale and invasive species impact on native cavity-nesting species. The research presented here provides the first community-level description of competitive interactions, describes a mechanism driving interaction intensity, and provides a method to predict where and when invasive species impacts on nesting are likely to occur. Additionally, I show that both habitat structure and predation are important processes for urban cavity-nesting birds. My work highlights that many birds make some use of urban habitats. While there remains much to learn about how urban environments can be improved to support long term persistence of individual species, conservation and management efforts can enhance the opportunity to help a large number of birds in Australian cities.This study established a large-scale field project that included eight field sites across southeast QLD and NSW. The study was designed along both regional-scale invasion gradients, with focus on the Common (Indian) myna (Acridotheres tristis), and local-scale urbanization gradients. I discovered that interaction webs around tree hollows in urban environments are dominated by a small number of highly aggressive species, including the invasive common myna and that interaction frequency between species was positively correlated with the overlap in preferred breeding sites (breeding niche; Chapter 2). To investigate how breeding niche overlap can be applied to a community with many unstudied invasive species, I examined the extent of niche overlap between species in the cavity-breeding birds of Tasmania detailing the potential interaction network for the island (Chapter 3). I discovered that niche overlap predicted important inters-specific interactions and that most native cavity-nesting species potentially face increased competition for nesting sites as a result of the addition of multiple invasive species.In Chapter 4, I examined how birds use supplementary nesting sites (i.e, nest boxes) varied across urban environments in different landscape contexts across New South Wales and Queensland), and across cities which have been invaded for different lengths of time. This was aimed at understanding the importance of artificial nest boxes as supplementary resources in areas with limited breeding cavities due to human impacts. There was high variation in the rates of nest box use both by invasive and native species such that the importance of nest boxes as supplemental nesting sites will differ across cities. I found that many nesting attempts in the nest boxes failed, highlighting the need to account for both competition and predation when designing and deploying nest boxes.Finally, in Chapter 5, I explored patterns in the community composition of urban bird communities. This allowed me to test the impacts of regional invasion dynamics and local variation in habitat on avian community richness and abundance. I discovered that increasing habitat structure and decreasing abundance of despotic species (i.e., species which influence community composition through aggressive interactions such as the noisy miner) predicted greater native species richness. More broadly the work presented in this thesis highlights that urban conservation efforts will be improved by a better including into management actions and future work the factors influencing breeding dynamics and resource use.

Climate change and biological invasions are affecting natural ecosystems globally. The effects of these stressors on native species' biogeography have been studied separately, but their combined effects remain overlooked. Here, we develop a framework to assess how climate change influences both the range and niche overlap of native and non-native species using ecological niche models. We hypothesize that species with similar niches will experience both range reductions and increased niche overlap under future climates. We evaluate this using the ongoing invasion of smallmouth bass (Micropterus dolomieu) and northern pike (Esox lucius) on the native habitats of redband trout (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus) in western North America. Future climate conditions will reduce habitat suitability for native and non-native species, but an increased niche overlap might exacerbate negative effects on native fishes. Our framework offers a tool to predict potential species distribution and interactions under climate change, informing adaptive management globally.

Subfossil remains of various groups of organisms preserved in peat and sediment archives are commonly used to infer past environmental changes using transfer functions based on species composition. However, the changes in community structure can also be explored using the functional trait approach. Investigation of functional traits in palaeoecological records can inform about the mechanisms through which abiotic variables such as temperature or moisture impact communities. Moreover, changes in functional traits provide information about changes in ecosystem functioning and can potentially lead to the reconstruction of past processes at the ecosystem scale. Here, we use five key functional traits of arcellinid testate amoebae (TAs), a group of protozoa that are key actors in the microbial foodwebs in peatlands. We apply this approach to the subfossil TA Holocene record of four geographically independent peatlands from Alaska, Switzerland, Poland and Russia. We found that species with larger shells were frequently eliminated from the communities most likely as a result of a switch towards drier conditions. However, when conditions were wetter, species with large shells and species with small shells could coexist because they differed in their trophic niche (i.e. preys). Our results show direct but site-specific links between TA trait data and the depth to water table and pH data inferred from TA species composition. This suggests that past environmental changes influenced both species composition and community function in these ecosystems. Overall, this study demonstrates that species- and trait-based approaches yield complementary information on past environmental changes. For instance, while taxonomic approaches reveal the changes in community composition over time, investigation of traits informs both on the causes and the consequences of these changes on ecosystem functioning.

The degree to which changes in community composition mediate the probability of colonization and spread of non-native species is not well understood, especially in animal communities. High species richness may hinder the establishment of non-native species. Distinguishing between this scenario and cases in which non-native species become established in intact (lacking extensive anthropogenic soil disturbance) communities and subsequently diminish the abundance and richness of native species is challenging on the basis of observation alone. The red imported fire ant (Solenopsis invicta), an invasive species that occurs throughout much of the southeastern United States, is such an example. Rather than competitively displacing native species, fire ants may become established only in disturbed areas in which native species richness and abundance are already reduced. We used insecticide to reduce the abundance of native ants and fire ants in four experimental plots. We then observed the reassembly and reestablishment of the ants in these plots for 1 year after treatment. The abundance of fire ants in treated plots did not differ from abundance in control plots 1 year after treatment. Likewise, the abundance of native ants increased to levels comparable to those in control plots after 1 year. Our findings suggest that factors other than large reductions in ant abundance and species density (number of species per unit area) may affect the establishment of fire ants and that the response of native ants and fire ants to disturbance can be comparable.

PDF HTML阅读 XML下载 导出引用 引用提醒 施氮对空心莲子草(Alternanthera philoxeroides)和莲子草(Alternanthera sessilis)种间关系的影响 DOI: 10.5846/stxb201405281098 作者: 作者单位: 北京林业大学自然保护区学院,北京林业大学自然保护区学院,北京林业大学自然保护区学院,北京林业大学自然保护区学院,北京林业大学自然保护区学院 作者简介: 通讯作者: 中图分类号: 基金项目: 中央高校基本科研业务费专项资金资助(TD-JC-2013-1);高等学校博士学科点专项科研基金新教师类资助课题(20120014120001);国家自然科学基金项目(31200313,31200314) Effects of nitrogen addition on interspecific competition between Alternanthera philoxeroides and Alternanthera sessilis Author: Affiliation: School of Nature Conservation, Beijing Forestry University,,School of Nature Conservation, Beijing Forestry University,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:自然界的氮素释放总是呈现出空间和时间上的异质性,但关于异质性氮释放对于入侵植物和本地植物种间关系影响的研究相对较少。将入侵植物空心莲子草(Alternanthera philoxeroides)和同属本地植物莲子草(Alternanthera sessilis)分别进行单种种植(12株,无种间竞争)和混种种植(每种6株,有种间竞争),模拟大气氮湿沉降设置由两种不同施氮总量(15g N m-2 a-1和30g N m-2 a-1)和两种不同施氮频率(每5天1次和每15天1次)交叉组成的4种施氮处理,并以不施氮为对照。施氮总量的增加显著促进了两种植物的生长,但对两种植物的种间竞争关系没有显著影响。施氮频率对两种植物的生长以及种间竞争关系都没有显著影响。两种植物在面对竞争时表现出不同的生物量分配策略,空心莲子草将更多的生物量分配到茎,而莲子草将更多的生物量分配到根。在全球变化的背景下,大气氮湿沉降可能会改变两种植物的种群结构和动态,但可能对这两种植物的种间关系影响较小。 Abstract:Nitrogen (N) is one of the most important soil nutrients for plants, and the amount and frequency of N release in soils is heterogeneous. Many studies have focused on the effects of heterogeneous N addition on a single plant species, but little is known about the effects of N amount and short-term N pulse on interspecific competition between invasive and native plant species. A replacement series experiment was conducted under greenhouse conditions to examine the effects of N amount and frequency release on the growth and interspecific competition between an invasive wetland clonal plant, Alternanthera philoxeroides (alligator weed), which is native in South America but highly invasive in China, and its native congener Alternanthera sessilis (sessile joyweed). Plant materials of A. philoxeroides and A. sessilis were collected from five locations in Xixi Wetland Park in Hangzhou, Zhejiang Province, China. Stem fragments of similar length (20 cm), with a stem tip for each species, were grown in monoculture (12 ramets in one container, no interspecific competition) and in mixture (six invasive plants with six native plants, with interspecific competition) in five different N treatments: control (no N added), low amount and high frequency (a total of 15 g N m-2 a-1 added every 5 days), low amount and low frequency (a total of 15 g N m-2 a-1 added every 15 days), high amount and high frequency (a total of 30 g N m-2 a-1 added every 5 days), and high amount and low frequency (a total of 30 g N m-2 a-1 added every 15 days). The results showed that N addition significantly increased the growth of both A. philoxeroides and A. sessilis. No significant difference was observed between the control and treatments for the relative yield (yield of each species in mixture divided by yield in its monoculture) for both species, indicating that N addition did not significantly affect the interspecific competition between the two species. The probable reason is that both species are from the same functional group and may have comparable capacities to compete and utilize the soil nutrients. The N pulse did not significantly modify growth or interspecific competition for either species. The sufficient soil water content and availability of nutrients other than N may explain why there were no effects of a N pulse on competition between the two species. Alternatively, high tolerance of both species to low soil nutrients and water content may lead to weaker responsiveness to a N pulse. With interspecific competition, the invasive species, A. philoxeroides, invested more biomass to stems, i.e., the stem biomass increased by 60%, which significantly decreased the root to shoot ratio. The native species, A. sessilis, allocated more biomass to roots, i.e., the root biomass increased by 250%, which significantly increased the root to shoot ratio. The results indicate that increasing atmospheric N deposition in the context of climate change may change population structure and dynamics of both species, but may not affect the interspecific competition of these plants. 参考文献 相似文献 引证文献

Functional trait divergence underpins many biological invasions, yet its role in native- invasive fish interactions remains poorly understood. Invasive species significantly threaten the native biodiversity by disrupting the functional structure of aquatic communities. The widespread expansion of the invasive gibel carp ( Carassius gibelio ) throughout the European freshwater systems has potentially led to notable decline of the native crucian carp ( Carassius carassius ), yet the specific functional trait mechanisms driving this shift remains unclear. To address this unexplored aspect, we aimed to study the detailed morphometric measurements with a standardized functional trait approach to in order to understand whether divergence in the key morpho- functional ecological traits gives the invasive gibel carp a competitive edge. Samples for both native crucian carp and invasive gibel carp were collected across five sympatric pond systems in Czech Republic, wherein we quantified fourteen morpho-functional traits related to feeding and locomotion in both the species. Our analysis revealed that gibel carp consistently exhibited higher gut length ratios and larger oral gape surfaces than crucian carp, reflecting broader digestive capabilities and an increased ability to exploit diverse food resources, particularly plant and detrital material. Gibel carp also displayed significantly hightened values for the fin morphological traits, including pectoral fin aspect ratio and fin surface to body size ratio, suggesting enhanced maneuverability and habitat access. On the other hand, certain traits such as eye position and body shape showed substantial overlap between the two Carassius species, indicating convergence in certain ecological functions. The observed divergence in feeding and locomotory traits under sympatric conditions indicates that the invasion success of gibel carp is closely associated with increased trophic flexibility and resource acquisition. These functional trait advantages likely underpin rapid population growth and heightened competitive pressure on the native crucian carp population, which continues to decline in the invaded habitats. Our findings therefore, underscore the importance of trait-based analysis for elucidating the ecological processes underlying invasion and highlight the urgent need for targeted conservation actions to protect the critically endangered native crucian carp population.

Cases in which introduced species facilitate one another's establishment, spread, and impacts are increasingly noted, and several experimental studies have provided strong evidence of a population-level impact. However, a full 'invasional meltdown', in which interspecific facilitation leads to an accelerating increase in the number of introduced species and their impact, has yet to be conclusively demonstrated. The great majority of suggested instances of 'invasional meltdown' remain simply plausible scenarios of long-term consequences based on short-term observations of facilitatory interactions between individuals of two species. There is a particular dearth of proven instances in which two invasive species each enhance the impact and/or probability of establishment and spread of the other. By contrast, in many authenticated cases, at least one partner is aided. The metaphor of meltdown focused attention on facilitation in invasion and has probably helped inspire recent studies. As have other metaphors from invasion biology and other sciences, 'meltdown' has struck a responsive chord with writers for the lay public; some have stretched it well beyond its meaning as understood by invasion biologists. There is no evidence that this hyperbole has impeded scientific understanding or caused loss of scientific credibility.

This study examines the impact of the exotic nitrogen-fixing legume Melilotus officinalis (L.) Lam. on native and exotic species cover in two Great Plains ecosystems in Badlands National Park, South Dakota. Melilotus is still widely planted and its effects on native ecosystems are not well studied. Melilotus could have direct effects on native plants, such as through competition or facilitation. Alternatively, Melilotus may have indirect effects on natives, e.g., by favoring exotic species which in turn have a negative effect on native species. This study examined these interactions across a 4-year period in two contrasting vegetation types: Badlands sparse vegetation and western wheatgrass (Pascopyrum smithii) mixed-grass prairie. Structural equation models were used to analyze the pathways through which Melilotus, native species, and other exotic species interact over a series of 2-year time steps. Melilotus can affect native and exotic species both in the current year and in the years after its death (a lag effect). A lag effect is possible because the death of a Melilotus plant can leave an open, potentially nitrogen-enriched site on the landscape. The results showed that the relationship between Melilotus and native and exotic species varied depending on the habitat and the year. In Badlands sparse vegetation, there was a consistent, strong, and positive relationship between Melilotus cover and native and exotic species cover suggesting that Melilotus is acting as a nurse plant and facilitating the growth of other species. In contrast, in western wheatgrass prairie, Melilotus was acting as a weak competitor and had no consistent effect on other species. In both habitats, there was little evidence for a direct lag effect of Melilotus on other species. Together, these results suggest both facilitative and competitive roles for Melilotus, depending on the vegetation type it invades.