Human-mediated Disturbances Research Articles

Human-mediated disturbance in multitrophic interactions results in outbreak levels of North America's most venomous caterpillar.

Anthropogenic environmental change is predicted to disrupt multitrophic interactions, which may have drastic consequences for population-level processes. Here, we investigate how a large-scale human-mediated disturbance affects the abundance of North America's most venomous caterpillar species, Megalopyge opercularis. Specifically, we used a natural experiment where netting was deployed to cover the entire canopies of a subset of mature southern live oak trees (Quercus virginiana) to exclude urban pest birds (grackles and pigeons), throughout an 8.1 km2 area encompassing a medical centre in Houston, Texas. We used this experimental exclusion to test the following hypothesis: release from avian predators increases caterpillar abundance to outbreak levels, which increases the risk to human health. Results from a multi-year survey show that caterpillar abundance increased, on average, more than 7300% on netted versus non-netted trees. Thus, increases in caterpillar abundance due to anthropogenic enemy release increase human exposure to this venomous pest, and should be considered a health threat in the area. This study emphasizes the unforeseen consequences of ecological disturbance for species interactions and highlights the importance of considering ecology in urban planning.

Non-invasive monitoring of adrenocortical activity in free-ranging Namaqua rock mice Micaelamys namaquensis from South Africa in response to anthropogenic land use and season

Stress in animals has been linked to behavioural and physiological changes in response to environmental, social and anthropogenic stimuli. Hence, stress-related responses in animals, especially in rodents, have been used as biological indicators of ecosystem health. This study aimed to establish an enzyme immunoassay (EIA) for monitoring adrenocortical activity in free-ranging Namaqua rock mice Micaelamys namaquensis (Rodentia: Muridae) using faeces as a prerequisite for assessing the effects of anthropogenic land use and season on faecal glucocorticoid metabolite (fGCM) concentration. Rodents were live-trapped seasonally across four land use types: an agricultural crop farm, an agricultural livestock farm, a human-populated site and a nature reserve; all situated in Limpopo Province, South Africa. Determined fGCM concentrations from capture and recapture events were used for biologically validating an EIA detecting steroids with a 5α-3β-11β-diol structure. Recapturing resulted in a significant overall 40% elevation of individual fGCM concentrations demonstrating the effectiveness of the chosen EIA to reliably detect glucocorticoid output in the study species. Neither land use type nor season affected fGCM concentrations in the species, suggesting that land use and season-related environmental changes do not necessarily act as stressors for M. namaquensis, presumably due to their adaptive and resilient nature. Such species can be used to identify ecosystems affected by human-mediated disturbances and allow insights into the management and restoration of these threatened ecosystems and their associated species.

A novel approach involving the use of Odonata as indicators of tropical forest degradation: When family matters

• Odonata can be effective and cost-efficient indicators of habitat status. • Coenagrionidae and Libellulidae as indicator groups. • Odonata adult-based bioassessment method is reliable. • The method may be easily applied in any tropical forest habitat worldwide. Odonata have proven to be good indicators of freshwater as well as terrestrial habitat conditions. Several studies have shown changes in odonate species richness and/or community composition in response to deforestation, suggesting their potential as bioassessment tools in the tropics. However, former approaches using Odonata as an indicator group required comparative samples from differently disturbed sites and/or knowledge of the focal species environmental specificity. Here, we tested a robust, adult-based bioassessment method assuming that the level of tropical forest degradation reflects the proportional representation of the taxa above species. Based on Web of Science, ScienceDirect, and Scopus databases, we used data from previously published studies linking odonate assemblages to human-mediated disturbances in tropical forests. We hypothesized that along a disturbance gradient (from primary forest to non-forest), (i) the proportion of the suborder Zygoptera (mostly habitat specialists sensitive to deforestation) will decrease in favor of the suborder Anisoptera (high proportion of generalists); and (ii) the proportions of largely generalist families Coenagrionidae and Libellulidae will increase at the expense of other Zygoptera and Anisoptera, respectively. Our results revealed that a ratio of Zygoptera/Anisoptera is a poor indicator of tropical forest conditions, probably because of ecological diversity within these groups. However, the proportions of Coenagrionidae/other Zygoptera and Libellulidae/other Anisoptera significantly increased along a disturbance gradient, suggesting their potential to be a good indicator of well-preserved, altered, and heavily degraded forest habitats. Therefore, our results are in line with studies presenting the usefulness of adult Odonata as versatile indicators for assessing human-mediated changes in tropical forest environments, supporting the practical use of this group in biological monitoring.

Characterizing nonnative plants in wetlands across the conterminous United States

Nonnative plants are widely recognized as stressors to wetlands and other ecosystems. They may compete with native plant species or communities and alter ecosystem properties, which can affect ecological condition, posing challenges to resource managers. As part of the United States Environmental Protection Agency’s National Wetland Condition Assessment (NWCA), we characterized the status of nonnative plants in wetlands across the conterminous United States (US). Our primary goals were to (1) document the composition of nonnative taxa at 1138 NWCA sites sampled in 2011 and (2) estimate the areal extent of wetland under stress from nonnative plants within the NWCA 2011 sampled population of ~ 25 million ha of wetland (represented by 967 sampled probability sites and the NWCA survey design). A total of 443 unique nonnative taxa were observed, encompassing a species pool adapted to diverse ecological conditions. For individual sites, the number of nonnative taxa ranged from 0 to 29, and total absolute cover of nonnatives ranged from 0 to 160%. We devised the nonnative plant indicator (NNPI) as a categorical indicator of stress (low to very high) from the collective set of nonnative plant taxa occurring at a particular location, based on a decision matrix of exceedance values for nonnative richness, relative frequency, and relative cover. Wetland area of the sampled population occurring in each NNPI category was estimated at the scale of the conterminous US and within five large ecoregions and four broad wetland types. Potential stress from nonnative plants, as indicated by the NNPI category, was low for approximately 61% (~ 15.3 million ha), moderate for about 20% (~ 5.2 million ha), high for about 10% (~ 2.48 million ha), and very high for about 9% (~ 2.2 million ha) of the wetland area in the entire sampled population. Percent of wetland area with high and very high NNPI varied by ecoregional subpopulations: greater within interior and western ecoregions (~ 29 to 87%) than within ecoregions in the eastern half of the nation (~ 11%). Among wetland type subpopulations, greater percent of wetland area with high and very high NNPI was observed for herbaceous vs. woody types and for inland vs. estuarine types. Estimates of wetland area by NNPI categories are expected to be useful to policy makers or resource managers for prioritizing management actions by identifying situations where stress from nonnative plants is most extensive. We also considered four exploratory analyses aimed at providing ecological information useful in interpreting NNPI extent results. We conducted three population-scale analyses examining ecoregional and wetland type population means for (1) the three NNPI metrics, (2) absolute cover of growth-habit groups of nonnative plants, and (3) metrics describing human-mediated disturbance. Finally, we examined ecological relationships with site-level NNPI status using a random forest (RF) analysis with NNPI as the response variable and predictor variables including ecoregion, wetland type, and a variety of characteristics describing natural vegetation structure, environment, and human-mediated disturbance.

More than just numbers

Conservation We often frame negative human impacts on animal species in terms of numbers of individuals reduced or numbers of regions from which species are absent. However, human activities are likely affecting species in more complex ways than these figures can capture. Kuhl et al. studied behavioral and cultural diversity in our closest relative, the chimpanzee. They found that human-mediated disturbance is reducing these complex traits. Human influence thus goes well beyond simple loss of populations or species, leading to behavioral change even where populations persist. Science , this issue p. [1453][1] [1]: /lookup/doi/10.1126/science.aau4532

Comparing the network structure and resilience of two benthic estuarine systems following the implementation of nutrient mitigation actions

The structure and resilience of benthic communities in coastal and estuarine ecosystems can be strongly affected by human mediated disturbances, such as nutrient enrichment, often leading to changes in a food webs function. In this study, we used the Ecopath model (EwE) to examine two case studies where deliberate management actions aimed at reducing nutrient pollution and restoring ecosystems resulted in ecological recovery. Five mass-balanced models were developed to represent pre and post-management changes in the benthic food web properties of the Tamar (1990, 1992, 2005) and Eden (1999, 2015) estuarine systems (UK). The network functions of interest were measures related to the cycling of carbon, nutrients and the productivity of the systems. Specific attention was given to the trophic structure and cycling pathways within the two ecosystems. The network attribute of ascendency was also examined as a proxy for resilience and used to define safe system-level operating boundaries. The results of the resilience metrics ascendancy (A) and its derivatives capacity (C) and overhead (O) indicate that both systems were more resilient and had higher resistance to potential stressors under low nutrient conditions. The less perturbed networks also cycled material more efficiently, according to Finns cycling index (CI), and longer cycling path lengths were indications of less stressed systems. Relative Ascendency (A/C) also proved useful for comparing estuarine systems of different sizes, suggesting the Tamar and Eden systems network structures have remained within their pre-defined “safe operating zones”. Overall, this analysis presents justification that efforts to reduce nutrient inputs into the Tamar and Eden estuaries have had a positive effect on the trophic networks of each system. Moreover, the consensuses of the network indicators in both systems suggest ecological network analysis (ENA) to be a suitable methodology to compare the recovery patterns of ecosystems of different sizes and complexity.

Multiple drivers of plant diversity in coastal dunes: A Mediterranean experience

In light of the global biodiversity loss, syntheses of the available knowledge about drivers of biodiversity are becoming increasingly important. However, despite the high number of studies analyzing patterns of plant species diversity, few attempts have been made to synthesize findings within different ecosystems. In this work, the relative role of a wide set of predictors imputable to three conceptual-methodological domains (abiotic, human-mediated disturbance and landscape domain, hereafter AD, DD and LD) was simultaneously analyzed in 644 random plots distributed along the coastal dunes of Central Italy. Native species richness and focal species cover, both field-recorded, were used as response variables. Predictors pertaining to the three domains were derived from both field surveys and high-resolution remotely sensed imagery (LiDAR and orthophotos). To test how AD, DD and LD affect native species richness and focal species cover, a GLM and a linear model were fitted respectively. The three domains were then ranked according to their relative importance.Although the role of the three domains was always significant, they turned out to unequally contribute to the explanation of native species richness and focal species cover patterns. For Mediterranean coastal dune ecosystems, AD appears to be the key biodiversity driver, followed by DD and LD. Our results suggest that as long as human disturbance is limited, plant diversity will distribute according to species abiotic tolerances, regardless of habitat loss and fragmentation per se. Representing a first effort towards a synthesis of plant diversity drivers in coastal dunes, this work points to the importance, in Mediterranean coastal dune ecosystems, of zonation dynamics, whose occurrence should be addressed as a priority issue by efficient conservations strategies.

Functional trait and community phylogenetic analyses reveal environmental filtering as the major determinant of assembly of tropical forest tree communities in the Western Ghats biodiversity hotspot in India

BackgroundImproved understanding of the processes shaping the assembly of tropical tree communities is crucial for gaining insights into the evolution of forest communities and biological diversity. The climate is thought to be the first order determinant of abundance and distribution patterns of tree species with contrasting traits such as evergreen and deciduous leaf phenology. However, the relative role of neutral, and niche-based processes in the evolution of these patterns remain poorly understood.MethodsHere, we perform an integrated analysis of the data on tree species abundance, functional traits and community phylogeny from a network of 96 forest plots, each 1 ha in size, distributed along a broad environmental gradient in the central Western Ghats, India. Then, we determine the relative importance of various process in assembly and structuring of tropical forest communities with evergreen and deciduous leaf phenology.ResultsThe deciduous leaf phenological trait has repeatedly evolved among multiple distantly related lineages. Tree communities in dry deciduous forests were phylogenetically clustered and showed a low range and variance of functional traits related to light harvesting, reproduction, and growth suggesting niche-based processes such as environmental filtering play a vital role in the assembly of tree communities in these forests. The external factors such as human-mediated disturbance also significantly, but to a lesser extent, influences the species and phylogenetic turnover.ConclusionsThese findings revealed that the environmental filtering plays a significant role in assembly of tree communities in the biologically diverse tropical forests in the Western Ghats biodiversity hotspot.

Resource depletion and mechanisms for food web robustness in a Neotropical estuary

Human activities severely threaten biological communities in Neotropical estuaries. Nevertheless, these communities have been poorly studied in comparison to low biodiversity regions, despite the fact that conservation efforts in these habitats are expected to require longer time-scales and greater efforts. In the present study we simulated resource depletion in a consumer–resource food web in a high-diversity Neotropical estuary. We first describe the feeding patters of local assemblages, split across distinct upper and lower estuary habitats. Further, because fish are opportunistic consumers of locally abundant prey, we modelled community robustness using resource availability, number of resources consumed, consumption diversity and environmental constraints. We found different feeding patterns between the upper and lower estuary habitats. Although crustaceans and detritus were preferably consumed in both habitats, thorough identification demonstrated higher dissimilarity between sites of different habitats relative to sites within the same habitat. We found that community robustness has a positive relationship with consumption diversity and that habitat type (upper or lower estuary) was a poor predictor of robustness. However, the modelling results also indicated an interaction between consumption diversity and habitat type. This suggests that promoting spatial gradients across resources, abiotic conditions and local feeding patterns within habitats can help protect against human-mediated disturbances.

The potential range of Ailanthus altissima (tree of heaven) in South Africa: the roles of climate, land use and disturbance

Invasive trees are a major problem in South Africa. Many species are well established whereas others are still in the early stages of invasion. The management of invasive species is most cost effective at the early stages of invasion; it is thus essential to target and contain naturalizing invaders before they spread across the landscape. Multi-scale species distribution models (SDMs) provide useful insights to managers; they combine species-occurrence observations with climatic variables to predict potential distributions of alien species. Applying SDMs in human-dominated ecosystems is complicated because many factors associated with human actions interact in complex ways with climatic and edaphic factors to determine the potential suitability of sites for species. The aim of this study was to determine the degree to which a worldwide invader, A. altissima (Simaroubaceae) has occupied its potential range in South Africa, to identify areas at risk of future invasion. To do this we built a set of SDMs at both global and country scales using climatic, land use and human-footprint data. Climatic data best explained the distribution of A. altissima at the global scale whereas variables reflecting human-mediated disturbances were most influential at the national scale. Our analyses show the importance of human-mediated disturbances at a global scale and human occupancy at a country scale in determining the range limits of A. altissima. Populations of this tree species are already present in most parts of South Africa that are environmentally suitable for the species, and management actions need to focus on preventing increases in density in these areas.

Cultivation may not dramatically alter rhizobial community diversity or structure associated with rooibos tea (Aspalathus linearis Burm.f.) in South Africa

Rooibos tea, Aspalathus linearis (Burm.f.), represents one of South Africa's most important indigenous crops, and monotypic plantations are rapidly replacing wild populations. Dwindling wild rooibos populations may drastically reduce possible, but hitherto overlooked, natural resources to bolster commercial productivity and long-term sustainability.Here, using next generation sequencing data, we seek to determine whether cultivation impacts on the diversity and community structure of mutualistic nitrogen fixing bacteria (rhizobia) associated with rooibos plants. We do this by generating operational taxonomic units (OTUs) from nodulation (nodC) and nitrogenase (nifH) DNA sequence data from rhizobia within root nodules of rooibos plants from cultivated and wild populations. For these rhizobial communities we found significant differences for various OTU diversity metrics due to geography (site), the interaction between site and status (cultivated vs. wild), but not for status. We also sequenced nodC soil microbiomes and found evidence for compositional differences in soil rhizobial communities due to geography, status (cultivated vs. wild), and the interaction between geography and status.Our data adds to existing evidence suggesting that tea cultivation in South Africa may have limited impacts on soil microbial community diversity and structure, and that such changes are mainly driven by larger geographic processes rather than human-mediated disturbances such as cultivation.

Decline of the Land SnailAnguispira alternata(Pulmonata: Discidae) in Pennsylvania, U.S.A

Population declines of species can be a concern, but before taking action, we need to verify whether apparent declines are real. Land snails are one of the most threatened groups of animals in the world, and anecdotes suggest that the abundance of the land snail Anguispira alternata has declined in Pennsylvania, U.S.A., over the past few decades. Might the apparent decline represent inadequate sampling by recent surveyors or could it represent a real decline? Past search effort is rarely documented, hindering direct comparisons of search effort. We used 547 museum records of A. alternata collected primarily from 1890 to 1960 and 2000 to 2015. Following two lines of reasoning, we conclude that the abundance of A. alternata has actually declined. (1) The smaller proportion of collecting events that found A. alternata after year 2000 suggests an actual decline of A. alternata in modern decades, regardless of the total number of collecting events. (2) The accumulation curve of new county records for all land snail species showed similar slopes in both past and modern decades, indicating comparable search effort in both time periods. The apparent decline of A. alternata was not explained by differential effort with respect to snail size or geographical area searched. The decline appears to have begun about 1960, although relatively little collecting effort from 1960 to 2000 decreases confidence in our ability to infer timing of abundance change in those decades. We speculate about three hypotheses regarding the decline (acid precipitation, climate warming, human mediated disturbance) and conclude that the historical increase in acid precipitation best matches the timing of the snail's decline. Population trends of other snail species and trends of A. alternata in other geographical areas should be studied to further explore these and other hypotheses. Our study highlights the importance of museum collections in understanding the current biodiversity crisis.

Disturbance is the key to plant invasions in cold environments.

Until now, nonnative plant species were rarely found at high elevations and latitudes. However, partly because of climate warming, biological invasions are now on the rise in these extremely cold environments. These plant invasions make it timely to undertake a thorough experimental assessment of what has previously been holding them back. This knowledge is key to developing efficient management of the increasing risks of cold-climate invasions. Here, we integrate human interventions (i.e., disturbance, nutrient addition, and propagule input) and climatic factors (i.e., temperature) into one seed-addition experiment across two continents: the subantarctic Andes and subarctic Scandinavian mountains (Scandes), to disentangle their roles in limiting or favoring plant invasions. Disturbance was found as the main determinant of plant invader success (i.e., establishment, growth, and flowering) along the entire cold-climate gradient, explaining 40-60% of the total variance in our models, with no indication of any facilitative effect from the native vegetation. Higher nutrient levels additionally stimulated biomass production and flowering. Establishment and flowering displayed a hump-shaped response with increasing elevation, suggesting that competition is the main limit on invader success at low elevations, as opposed to low-growing-season temperatures at high elevations. Our experiment showed, however, that nonnative plants can establish, grow, and flower well above their current elevational limits in high-latitude mountains. We thus argue that cold-climate ecosystems are likely to see rapid increases in plant invasions in the near future as a result of a synergistic interaction between increasing human-mediated disturbances and climate warming.

Endemic and Emerging Pathogens Threatening Cork Oak Trees: Management Options for Conserving a Unique Forest Ecosystem.

Cork oak (Quercus suber) forests are economically and culturally intertwined with the inhabitants of the Mediterranean basin and characterize its rural landscape. These forests cover over two million hectares in the western Mediterranean basin and sustain a rich biodiversity of endemisms as well as representing an important source of income derived from cork production. Currently cork oak forests are threatened by several factors including human-mediated disturbances such as poor or inappropriate management practices, adverse environmental conditions (irregular water regime with prolonged drought periods), and attacks of pathogens and pests. All these adverse factors can interact, causing a complex disease commonly known as "oak decline." Despite the numerous investigations carried out so far, decline continues to be the main pathological problem of cork oak forests because of its complex etiology and the resulting difficulties in defining suitable control strategies. An overview of the literature indicates that several pathogenic fungi and oomycota can play a primary role in the etiology of this syndrome. Therefore, the aim of this review is to analyze the recent advances achieved regarding the bio-ecology of the endemic and emerging pathogens that threaten cork oak trees with particular emphasis on the species more directly involved in oak decline. Moreover, the effect of climate change on the host-pathogen interactions, a task fundamental for making useful decisions and managing cork oak forests properly, is considered.

Functional diversity, succession, and human-mediated disturbances in raised bog vegetation

Raised and transitional bogs are one of the most threatened types of ecosystem, due to high specialisation of biota, associated with adaptations to severe environmental conditions. The aim of the study was to characterize the relationships between functional diversity (reflecting ecosystem-shaping processes) of raised bog plant communities and successional gradients (expressed as tree dimensions) and to show how impacts of former clear cuts may alter these relationships in two raised bogs in ‘Bory Tucholskie’ National Park (N Poland). Herbaceous layers of the plant communities were examined by floristic relevés (25m2) on systematically established transects. We also assessed patterns of tree ring widths. There were no relationships between vegetation functional diversity components and successional progress: only functional dispersion was negatively, but weakly, correlated with median DBH. Lack of these relationships may be connected with lack of prevalence of habitat filtering and low level of competition over all the successional phases. Former clear cuts, indicated by peaks of tree ring width, influenced the growth of trees in the bogs studied. In the bog with more intensive clear cuts we found more species with higher trophic requirements, which may indicate nutrient influx. However, we did not observe differences in vegetation patterns, functional traits or functional diversity indices between the two bogs studied. We also did not find an influence of clear cut intensity on relationships between functional diversity indices and successional progress. Thus, we found that alteration of the ecosystems studied by neighbourhood clear cuts did not affect the bogs strongly, as the vegetation was resilient to these impacts. Knowledge of vegetation resilience after clear cuts may be crucial for conservation planning in raised bog ecosystems.

Recreational use of urban and suburban forests affects plant diversity in a Western Siberian city

The recreational use of urban forests is a highly valued service. However, strong recreational pressure may contribute to the loss of biodiversity in forests. This study assessed the frequency of visitors and their characteristics in 14 urban and 11 suburban forests in the rapidly expanding city of Pavlodar, Kazakhstan, in Western Siberia. Furthermore, the effects of recreation disturbance (trampling, damage to ground vegetation and damage to trees and shrubs) and other human-mediated disturbances (waste deposits, soil disturbance, etc.) on both the vegetation and plant characteristics of urban and suburban forests were quantified. In Pavlodar, urban forests are poorly managed, motivating the people to spend their sparetime in the more distant suburban forests. Urban and suburban forests did not differ in visitor frequency during the summer season (July–September). However, the two forest types differed in the age structure and group size of visitors as well as in the activities of visitors. Urban forests were more frequently visited by younger people for walking, sports, sitting and talking, and playing with children, while suburban forests were often visited by older people for picnicking, fishing and gathering mushrooms. In urban forests, total plant species richness was reduced by recreation disturbance. Urban forests also harboured a large proportion of alien plant species (0.42; in suburban forests 0.24). Neither recreation disturbance nor other human-mediated disturbance affected plant species richness in suburban forests, while both disturbance types enhanced the colonization success of alien species. Alterations in plant life forms can be considered as an indicator of changes in ecosystem function. In suburban forests, recreation disturbance caused a decline of geophytes and an increase of therophytes. We recommended various management actions to improve the recreation value of degraded urban forests in this Western Siberian city.

Fine-scale spatial genetic structure analysis in two Argentine populations of Prosopis alba (Mimosoideae) with different levels of ecological disturbance

Spatial genetic structure (SGS) in plants is primarily determined by the interaction between pollen and seed dispersal, but it is strongly affected by both evolutionary and ecological processes. SGS studies in forest species also allow evaluating the consequences of human-mediated disturbance on pollen and seed movement and designing strategies of sustainable use of native forest resources. The present paper compares fine-scale SGS between two populations of Prosopis alba: Fernandez-Forres (FF) and Campo Duran (CD), based on the variation of 12 SSR markers. Populations show different history, management, and levels of disturbance. FF is highly disturbed and fragmented by agricultural activity and stock-breeding. Although no significant differences were observed in genetic variability parameters, highly significant genetic differentiation was detected with virtually no admixture between populations. SGS was positive and significant at short distances only in the non-disturbed population of CD. Accordingly, estimated neighborhood size and effective gene dispersal are higher in FF than in CD. This result might be explained by the higher incidence of livestock in seed dispersal and the patchy structure favoring longer pollen movement and artificial thinning and selection in FF. The results are relevant to conservation and breeding programs, suggesting that the distance between seed trees to be sampled should be larger than 22 m, the estimated distance of significant SGS in P. alba.

Humans and seasonal climate variability threaten large-bodied coral reef fish with small ranges.

Coral reefs are among the most species-rich and threatened ecosystems on Earth, yet the extent to which human stressors determine species occurrences, compared with biogeography or environmental conditions, remains largely unknown. With ever-increasing human-mediated disturbances on these ecosystems, an important question is not only how many species can inhabit local communities, but also which biological traits determine species that can persist (or not) above particular disturbance thresholds. Here we show that human pressure and seasonal climate variability are disproportionately and negatively associated with the occurrence of large-bodied and geographically small-ranging fishes within local coral reef communities. These species are 67% less likely to occur where human impact and temperature seasonality exceed critical thresholds, such as in the marine biodiversity hotspot: the Coral Triangle. Our results identify the most sensitive species and critical thresholds of human and climatic stressors, providing opportunity for targeted conservation intervention to prevent local extinctions.

不同类型人类活动干扰对河岸带外来植物群落的影响——以北京永定河为例

PDF HTML阅读 XML下载 导出引用 引用提醒 不同类型人类活动干扰对河岸带外来植物群落的影响——以北京永定河为例 DOI: 10.5846/stxb201501060032 作者: 作者单位: 中国科学院生态环境研究中心,中国科学院生态环境研究中心,中国科学院生态环境研究中心 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重点项目（41030744）；国家重点基础研究发展计划（973计划）项目（2006CB403402）；科技部国家重点实验室专项经费项目（SKLURE2008-1-01） Community characteristics of riparian alien plants influenced by different types of human disturbance: A case study of Yongding River, Beijing Author: Affiliation: State Key Laboratory of Urban and Regional Ecology,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences,State Key Laboratory of Urban and Regional Ecology,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences,State Key Laboratory of Urban and Regional Ecology,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences 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:强烈的人类活动对自然生境的扰动促进了外来植物侵入河岸带，但不同类型的人类活动干扰对外来植物的影响有所不同。按照不同人类活动干扰类型设置了山峡段、平原段和城市段，通过比较河段间河岸带外来植物群落特征的差异，探讨不同人类活动干扰类型对河岸带外来植物群落的影响。结果表明：（1）永定河河岸带共有维管束植物27科72属101种，外来植物13科28属29种。外来种比例高达28.7%，其中82.4%的国外外来种来自美洲和亚洲。（2）不同河段间的外来植物群落的物种构成和优势度呈现出显著性差异。外来种比例由山峡段的20.9%，上升至平原段和城市段的30.2%和25.5%；而优势度由12.1%，分别上升至13.4%和17.5%。（3）不同河段间的外来植物群落生活型结构有显著性差异。多年生草本植物在山峡段比例最高，达到66.7%，在平原段和城市段较低，分别为46.2%和30.8%；而一年生草本植物在城市段比例最高，达到69.2%，在平原段和山峡段较低，分别为53.8%和33.3%。（4）平原段属于农业干扰类型，其河岸带外来植物主要以农业类杂草为主，如禾本科的假稻（Leersia japonica）和菊科的钻叶紫菀（Aster subulatu）；城市段是城市干扰类型，外来植物中入侵种比例和优势度较高，典型入侵种为反枝苋（Amaranthus retroflexus）和牛筋草（Eleusine indica）等。北京永定河不同河段河岸带外来植物的种类构成特点，反映了河岸带外来植物受快速城市化、农业活动等不同人类活动干扰的影响呈逐渐扩大的趋势。 Abstract:Riparian zones are highly modified by frequent and intense human disturbances worldwide. Human-mediated disturbances often occur in concert with the proliferation of alien plants in the riparian zone, although their effect on alien riparian plants may differ among disturbance types (agriculture, urbanization). However, few studies in China have attempted to detect these effects on alien plants in riparian zone. The objectives of this study are (1) to compare the characteristics of alien herbal plant communities in different sections of a river (mountain section, agricultural section, and urban section) and (2) to explain the differences in alien plant communities that are caused by different types of disturbances (agriculture and urbanization).This study was conducted in 2009 in the riparian zone of the Yongding River in Beijing. The river stretches were categorized into three river sections based on the human-mediated disturbance types in that stretch of the river: mountain section (natural section without disturbance), plain section (agricultural disturbance), and urban section (urbanization disturbance). Using the transect method, 11 study sites were set up in this three river sections. The results show that the vascular herbal flora of the study area comprises 101 species from 72 genera and 27 families, including 29 alien plant species from 28 genera and 13 families. Alien species represent 28.7% of the total herbal flora, of which 82.4% originated from America and Asia. The species composition and dominance index of alien riparian plant communities change significantly among the three river sections. The percentage of alien species increases from 20.9% in the mountain section to 30.2% and 25.5% in the plain and urban river sections, respectively; the dominance index increases significantly from 12.1% to 13.4% and 17.5% in the plain and urban river sections, respectively. The composition of alien riparian plant communities inferred from the life cycle of the plants also shows significant difference among the three river sections. Perennial species are the most abundant in the mountain section (66.7%), while they are represented by 46.2% and 30.8% in the plain and urban sections, respectively. In contrast, the highest percentage of annual species is found in the urban section (69.2%) followed by the plain section (53.8%) and the mountain section (33.3%). The plain section is greatly affected by agriculture, where the alien riparian plants are mainly dominated by agricultural weeds such as Leersia japonica and Aster subulatus. The urban section is strongly influenced by the disturbance from rapid urbanization, in which the percentage and dominance index of invasive plant species are high. The typical invasive plants are Amaranthus retroflexus and Eleusine indica. These results indicate that the species composition of alien riparian plants differs among river sections and they are affected by different types of human-mediated disturbance (agriculture, urbanization). Our results also indicate that alien riparian plants may become predominant and spread further in the riparian zone due to human activities such as rapid urbanization and agriculture. 参考文献 相似文献 引证文献

A multi-scale approach to identify invasion drivers and invaders’ future dynamics

Climate, land use and disturbances are well known drivers of invasion. However, their relative influence may change across spatial scales, where climate is expected to be the main filter at broad scales; land use is expected to have more influence at intermediate scales, and disturbance, at fine ones. Understanding the underlying processes that drive invasion patterns at different spatial scales is thus crucial to be able to anticipate the future spread of invaders. Here, we quantified the relative importance of climate, land use, and disturbance on the distribution of the invasive trees Ailanthus altissima and Robinia pseudoacacia, across three nested spatial scales, namely global, country (Spain) and riverbank (three riparian riverbanks). To do so, for each species and scale, we built ensemble species distribution models. We also identified their range filling and inferred the most suitable areas in Spain for them to spread. In general, our study confirms that climate acts as an initial coarse filter of species distribution, whilst both climate and land use were important at the country scale; at the riverbank scale human-mediated disturbances gained importance. However, R. pseudoacacia and A. altissima showed differences in their degree of range filling, where A. altissima has a higher potential for range expansion in the near future. Overall, the integration of different scales into invasion studies shows a great potential to enrich our understanding of species-habitat relationships, and to help anticipate their future dynamics.