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J. A. van Vegten 《Plant Ecology》1984,56(1):3-7
The paper describes the thornbush invasion (bush encroachment) found in the savanna at Olifants Drift in eastern Botswana. Overgrazing by cattle is responsible for the opening up of the grass sward and has enabled woody species to establish. A quantification of this process between 1950 and 1975 in an area of ca. 100 km2 is given in terms of plant density as well as aboveground biomass. The loss of herbaceous biomass which generally accompanies bush encroachment and the possibilities for pasture restoration are mentioned.Species nomenclature follows the Flora of Southern Africa and the system in use at the herbarium of the Botanical Research Institute at Pretoria, South Africa. 相似文献
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Accurate and ecologically meaningful characterisation of reference conditions is a fundamental premise of restoration ecology. Restoration practice and research commonly define reference conditions in terms of compositional and structural elements. We propose a “process-centred” framework that places central emphasis on ecological functions and ecosystem processes. A wide variety of processes is central to the functioning and dynamics of ecological systems, and can be placed at the foundation of restoration research and practice. A process-centred approach allows the definition of “reference dynamics”, where spatial and temporal variability and underlying mechanisms of change are primary. We illustrate this approach using a 303-yr reconstruction of the natural surface fire regime to guide restoration of a Pinus ponderosa forest in the Jemez Mountains of southwestern North America. Fire occurrence varied over space and time during the period of record, with ecologically significant variation in fire intervals (yr fire−1) governed by process–structure interactions. We defined a variety of reference variables for reintroduction of fire as the keystone ecological process, along with related structural variation. A process-centered approach and the reference dynamics paradigm can replace a more static concept of reference conditions in defining restoration baselines and provide an improved standard of comparison for restoration ecology. 相似文献
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1.?When an invasive species first colonizes an area, there is an interval before any host-specific natural enemies arrive at the new location. Population densities of newly invading species are low, and the spatial and temporal interactions between spreading invasive species and specific natural enemies that follow are poorly understood. 2.?We measured infection rates of two introduced host-specific pathogens, the entomophthoralean fungus Entomophaga maimaiga and the baculovirus Lymantria dispar nucleopolyhedrovirus (LdNPV), occurring in spreading populations of an invasive forest defoliator, L. dispar (gypsy moth), in central Wisconsin. 3.?Over 3 years, we found that host density was closely associated with the presence and prevalence of both pathogens. The fungal and viral pathogens differed in the sensitivity of their response as E. maimaiga was present in lower-density host population than LdNPV. 4.?We examined the relationship between weather conditions and infection prevalence and found that activity of both the fungus and virus was strongly seasonally influenced by temperature and rainfall or temperature alone, respectively. 5.?Purposeful releases of pathogens (median distances of study sites from release sites were 65·2 km for E. maimaiga and 25·6 km for LdNPV) were not associated with pathogen prevalence. 6.?A generalist fly parasitoid, Compsilura concinnata, also killed L. dispar larvae collected from the study sites, and parasitism was greater when infection by pathogens was lower. 7.?Our results demonstrated that although infection levels were low in newly established host populations, host-specific pathogens had already moved into host populations close behind advancing populations of an invasive host; thus, spreading hosts were released from these enemies for only a relatively short time. 相似文献
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Pablo González-Moreno Joan Pino Núria Gassó Montserrat Vilà 《Biological invasions》2013,15(3):547-557
Natural habitats in human-altered landscapes are especially vulnerable to biological invasions, especially in their edges. We aim to understand the influence of landscape and local characteristics on biological invasions by exploring the level of plant invasion and alien species traits in forest edges in highly urbanized landscapes. We identified all plant species in 73 paired plots in the edge and 50 m towards the interior of the forest. We explored the association between alien species richness and similarity in species composition between edge and interior plots with landscape and local variables, using generalized linear models and variance partitioning techniques. Then, we performed Fourth-corner analyses to explore the association between alien plant traits and local and landscape variables. In contrast to native species richness, alien species richness was more affected by the surrounding landscape than by the local characteristics of the edge. Road proximity was positively associated with alien species richness and proportion and was its most important correlate, whereas disturbance was negatively associated with native species richness and was its most influential factor. Alien plant traits were also primarily associated with landscape characteristics. For instance, species of Mediterranean origin and introduced for agriculture were associated with higher agriculture use in the landscape. Our findings suggest that risk analyses of habitat vulnerability to invasion must consider the landscape context in order to successfully predict highly invaded areas and identify potentially successful invaders. 相似文献
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The status and causes of alien species invasion in China 总被引:5,自引:0,他引:5
Haigen Xu Sheng Qiang Zhengmin Han Jianying Guo Zongguo Huang Hongying Sun Shunping He Hui Ding Hairong Wu Fanghao Wan 《Biodiversity and Conservation》2006,15(9):2893-2904
Data of classification, origin, pathway and environmental impacts of invasive alien micro-organisms, invertebrates, amphibians
and reptiles, fish, birds, mammals, weeds, trees, and marine organisms in terrestrial, aquatic and marine ecosystems of China,
were analyzed, based on literature retrieval, field survey and consultation. Some 283 invasive alien species were recorded
in China, including 19 invasive alien micro-organisms, 18 aquatic plants, 170 terrestrial plants, 25 aquatic invertebrates,
33 terrestrial invertebrates, 3 amphibians and reptiles, 10 fish, and 5 mammals. Of the invasive alien species, 55.1% originated
from North and South America, 21.7% from Europe, 9.9% from Asia, 8.1% from Africa and 0.6% from Oceania. Many institutions
and individuals in China lack adequate knowledge of ecological and environmental consequences caused by invasive alien species,
with some ignorance of the dangerous invasion in the introduction of alien species. For instance, 50.0% of invasive alien
plants were intentionally introduced as pasture, feedingstuff, ornamental plants, textile plants, medicinal plants, vegetables,
or lawn plants, 25% of alien invasive animals were intentionally introduced for cultivation, ornament, or biological control,
In addition, more efforts are being made in the introduction of alien species, and little attention is paid on the management
of introduced alien species, which may cause their escape into natural environment and potential threats to the environment.
There were also gaps in quarantine system in China. All microorganisms were unintentionally introduced, through timber, seedling,
flowerpot, or soil; 76.3% of alien invasive animals invaded through commodity or transportation facility because of the failure
of quarantine. Therefore, quarantine measures should be strictly implemented; and meanwhile the intentional introduction of
alien species should be strictly managed and a system of risk assessment should be implemented. 相似文献
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《Current biology : CB》2023,33(3):566-571.e3
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Temporary depression wetlands form a characteristic feature of the wet-season landscape in the south-western Cape region of South Africa, yet they remain largely unstudied. We hypothesized that the loss of sclerophyllous Sand fynbos habitat around these temporary wetlands causes in-wetland physico-chemical changes. We expected to observe a decrease in the concentration of humic substances in wetlands and a corresponding rise in surface water pH as fynbos cover decreases around wetlands, in this case owing to alien vegetation invasion. A set of 12 differentially invaded temporary depression wetlands within a Sand fynbos ecosystem in Cape Town were repeatedly sampled during the 2009 wet season. Multivariate gradient analysis techniques revealed associations between fynbos cover bordering wetlands and various physico-chemical and biotope constituents within wetlands. Univariate linear regression models reported strong and temporally consistent negative relationships between terrestrial fynbos vegetation cover and wetland pH and positive relationships with humic content. Results indicate that replacement of Sand fynbos with alien vegetation causes a reduction of humic input to wetlands, which in turn has knock-on effects on other wetland environmental constituents such as pH. These findings are expected to be applicable to any wetland where surrounding humic-rich sclerophyllous vegetation is replaced by a non-sclerophyllous agent. 相似文献
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Ana de Moura Queirós Jan Geert Hiddink Gareth Johnson Henrique Nogueira Cabral Michel Joseph Kaiser 《Biological invasions》2011,13(5):1059-1075
Introduced ecosystem engineers can severely modify the functioning on invaded systems. Species-level effects on ecosystem
functioning (EF) are context dependent, but the effects of introduced ecosystem engineers are frequently assessed through
single-location studies. The present work aimed to identify sources of context-dependence that can regulate the impacts of
invasive ecosystem engineers on ecosystem functioning. As model systems, four locations where the bivalve Ruditapes philippinarum (Adams and Reeve) has been introduced were investigated, providing variability in habitat characteristics and community composition.
As a measure of ecosystem engineering, the relative contribution of this species to community bioturbation potential was quantified
at each site. The relevance of bioturbation to the local establishment of the mixing depth of marine sediments (used as a
proxy for EF) was quantified in order to determine the potential for impact of the introduced species at each site. We found
that R. philippinarum is one of the most important bioturbators within analysed communities, but the relative importance of this contribution at
the community level depended on local species composition. The net contribution of bioturbation to the establishment of sediment
mixing depths varied across sites depending on the presence of structuring vegetation, sediment granulometry and compaction.
The effects of vegetation on sediment mixing were previously unreported. These findings indicate that the species composition
of invaded communities, and the habitat characteristics of invaded systems, are important modulators of the impacts of introduced
species on ecosystem functioning. A framework that encompasses these aspects for the prediction of the functional impacts
of invasive ecosystem engineers is suggested, supporting a multi-site approach to invasive ecology studies concerned with
ecosystem functioning. 相似文献
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Joseph R. Bennett Mark Vellend Patrick L. Lilley William K. Cornwell Peter Arcese 《Biological invasions》2013,15(3):707-716
Community assembly through species invasions is a long-term process, for which vital information regarding future trends can be contained in current patterns. Using comparative analyses of native and exotic plant assemblages from meadow patches on islands in British Columbia, Canada, we examined multiple lines of evidence for ‘invasion debt’, a latent expansion of exotic species populations. We show that: (1) short-dispersing species are underrepresented compared to their long-dispersing counterparts in exotic species only; (2) among species that are invasive elsewhere in North America, a greater proportion of long dispersers are common in the study area and a greater proportion of short dispersers are rare; and (3) time since arrival in the study region is positively related to number of occurrences in exotic species. In addition, we show that a suite of exotic species possesses the facility of rapid long-distance dispersal and ability to establish viable populations on even the most isolated and least disturbed patches. While some highly-dispersive exotic species can rapidly colonize new areas, short dispersers appear to exhibit invasion debt, with their potential distributions only being realized in the long term. Removing or even reducing populations of many rapid colonizers could be extremely difficult; however, for species exhibiting patterns most consistent with invasion debt, an opportunity exists for monitoring and removal to help reduce potential competition with native species. 相似文献
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Predicting invasion dynamics of four alien Pinus species in a highly fragmented semi-arid shrubland in South Africa 总被引:6,自引:0,他引:6
This study explored the determinants of spread of four alien Pinus species and the ability of models to predict invasion dynamics in a complex fragmented landscape. The role of environmental factors, natural and anthropogenic disturbance in relation to invasion history was assessed for different stages in the invasion process using a Geographic Information System. Pines escaped from plantations over the past 30 years and spread into the natural semi-arid shrubland (renosterveld). The pattern of spread was compared with a simulated random distribution using two different techniques, a standard logistic regression, and a new recursive modelling approach (Formal Inference-based Recursive Modelling; FIRM). FIRM analysis improved the accuracy of predictions and revealed interactive effects of variables hidden by the logistic regression analysis. More than 80% of isolated pine individuals were found in 20% of the habitat classified as suitable by the models. Soil pH was the most important predictor for the distribution of isolated trees, whereas the establishment of dense pine stands was largely determined by fire history. Differences in invasive behaviour could be explained by species attributes such as limited dispersal for P. canariensis, and better drought-tolerance for P. halepensis. Sixty-five percent of the current pine distribution was accurately predicted by the spatial distribution of the first trees to have invaded. Such models could be used to predict potential spread of invasive plants and gain a better understanding of the main factors driving the invasion process. However, the spread of invasive species in fragmented landscapes, strongly modified by human activities, is very complicated, and the spread remains difficult to predict in the long term. The dynamics of invasion are discussed in relation to changes in land use and disturbance regime. 相似文献
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Haigen Xu Hui Ding Mingyan Li Sheng Qiang Jianying Guo Zhengmin Han Zongguo Huang Hongying Sun Shunping He Hairong Wu Fanghao Wan 《Biological invasions》2006,8(7):1495-1500
Invasive alien species have become one of the most serious environmental issues in the world. Data of taxon, origin, pathway,
and environmental impacts of invasive alien microorganisms, invertebrates, amphibians and reptiles, fish, birds, mammals,
herbs, trees, and, marine organisms in terrestrial, aquatic, and marine ecosystems of China were analyzed during 2001 and
2003, based on literature retrieval and field survey. There were 283 invasive alien species in China, and the number of species
of invasive alien microorganisms, aquatic plants, terrestrial plants, aquatic invertebrates, terrestrial invertebrates, amphibians
and reptiles, fish, and mammals were 19, 18, 170, 25, 33, 3, 10, and 5, respectively. The proportion of invasive alien species
originated from America, Europe, Asia, Africa, and Oceania were 55.1, 21.7, 9.9, 8.1, and 0.6%, respectively. Methods for
estimation of direct economic losses to agriculture, forestry, stockbreeding, fishery, road and water transportation, storage,
water conservancy, environment and public facilities, and human health were established. Methods for estimation of indirect
economic losses caused by invasive alien species to service functions of forest ecosystems, agricultural ecosystems, grassland
ecosystems, and wetland ecosystems were also established. The total economic losses caused by invasive alien species to China
were to the time of USD 14.45 billion, with direct and indirect economic losses accounting for 16.59% and 83.41% of total
economic losses, respectively. 相似文献
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Plant invasion potentially alters ecosystem carbon (C) and nitrogen (N) cycles. However, the overall direction and magnitude of such alterations are poorly quantified. Here, 94 experimental studies were synthesized, using a meta-analysis approach, to quantify the changes of 20 variables associated with C and N cycles, including their pools, fluxes, and other related parameters in response to plant invasion. Pool variables showed significant changes in invaded ecosystems relative to native ecosystems, ranging from a 5% increase in root carbon stock to a 133% increase in shoot C stock. Flux variables, such as above-ground net primary production and litter decomposition, increased by 50-120% in invaded ecosystems, compared with native ones. Plant N concentration, soil NH+4 and NO-3 concentrations were 40, 30 and 17% higher in invaded than in native ecosystems, respectively. Increases in plant production and soil N availability indicate that there was positive feedback between plant invasion and C and N cycles in invaded ecosystems. Invasions by woody and N-fixing plants tended to have greater impacts on C and N cycles than those by herbaceous and nonN-fixing plants, respectively. The responses to plant invasion are not different among forests, grasslands, and wetlands. All of these changes suggest that plant invasion profoundly influences ecosystem processes. 相似文献
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Brendon M. H. Larson 《Biological invasions》2007,9(8):947-956
Several authors have recently argued that invasion biologists should adopt a more objective and dispassionate stance towards invasive species. Brown and Sax (Austral Ecol 29:530–536, 2004; Austral Ecol 30:481–483, 2005) assert that invasion biologists risk their objectivity, “commit the naturalist fallacy” or “embark on a slippery slope” with engaged concern about invasive species. Elsewhere, Colautti and MacIsaac (Divers Distrib 10:135–141, 2004) propose a neutral language for invasion biology, one that insulates scientific from popular discussion about invasive species. While there is certainly hyperbole about the effects of some invasive species, the type of objectivity promoted in these papers may often be inappropriate for invasion biology. It implies a policy of non-action that is inconsistent with the conservation values of many invasion biologists. To engage these values, invasion biologists can adopt deliberative methods for environmental problem-solving that involve stakeholders in their research design and which still promote high standards of scientific rigor. 相似文献
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Eppinga Maarten B. Haber Elizabeth A. Sweeney Luke Santos Maria J. Rietkerk Max Wassen Martin J. 《Biological invasions》2022,24(2):353-371
Biological Invasions - Invasions by non-native plant species are widely recognized as a major driver of biodiversity loss. Globally, (sub-)tropical islands form important components of biodiversity... 相似文献