Abundance Of Invasive Species Research Articles

Contribution of Ecological and Socioeconomic Factors to the Presence and Abundance of Invasive Tree Species in Mississippi, USA

Invasive tree species cause increasing damage to the environment and local economies. Previous studies have seldom treated the presence and abundance of invasive species as different phenomena. Using Classification and Regression Trees (CART) analysis, important driving factors affecting the presence and abundance of invasive tree species in Mississippi were identified. These selected factors were spatially analyzed using a spatial lag model at the county level. The empirical results from the spatial lag model showed that: (1) the presence of invasive tree species was more likely at lower elevations, private ownerships, and in counties with higher per capita annual income; and (2) the abundance of invasive tree species was related to stand age, and elevation. The odds ratio revealed that the presence was most affected by per capita mean annual income. This result might reflect impacts from intensified urban development and alteration of the landscape. As revealed by the coefficients, the abundance was most strongly affected by stand age. Thus, management prescriptions designed to monitor and control invasions should target young private forestlands at low elevations in counties with higher per capita mean annual income.

Ecological assessment of type, abundance and infestation status of invasive alien species (IAS) in eastern part of Ethiopia; suggestion of inventory and monitoring protocols–IAS

Background: The type and distribution of IAS in eastern part of Ethiopia become a very serious issue and infested with in a very high speed. The main aim of this assessment is in order to assess the type, current infestation rate, and to estimate the general abundance of IAS in the eastern part of Ethiopia and used to take or plan appropriate measurement methods as well as in the long run it is important for policy makers to take over an immediate action. Methods: Data collection was performed though interview, filed survey, group discussion, and from different formerly published prepares. Result: From this data we can understand that the infestation stage of IAS, its impact, majorly dominate spices and future projection of those IAS is clearly identified. Conclusion: The issues need an immediate and fast response before it becomes totally damage the whole native biodiversity resource and also the community leave on that area become both economically, socially and healthy dependence due to the effect of those IAS on the other body.

Invasive flora within urban railway areas: a case study from Lublin (Poland) and Lviv (Ukraine)

Heterogeneous and disturbed habitats within railway areas create an ideal environment for establishment of invasive plant species. In this study, we compared the invasive species composition and abundance within railway areas of two cities, Lublin, SE Poland and Lviv, W Ukraine. In total, 70 invasive species were recorded. The invasive species list was similar for the two cities, with the most invasive species occurring at both (81.4%), 8.5% occurring only in Lublin and 10% only in Lviv. The proportion of invasive species in the total flora was almost 1.5-fold higher at Lviv compared to Lublin. Invasive species have originated mainly from continental America (45.7%), followed by Asia and Eurasia. The participation of invasive plants derived from Asia and Eurasia at Lviv is higher than at Lublin. The invasive flora includes a wide range of taxonomic groups, with a predominance of Asteraceae and Poaceae. The ecological attributes of invasive species on railway areas are: mainly annual therophytes, mostly wind- and insect pollination modes, a predominance of generative reproduction, anthropochorous and anemochorous dispersal and short-term persistent, long-term persistent or transient seed banks.

The role of topography, river size and riverbed grain size on the preservation of riverine mollusk shells

The degree to which a group of fossils reflects the original community from which it was derived can be estimated by comparing living communities with locally accumulated dead remains. Such live–dead approaches (LA/DA) can provide important baseline information on the ecological structure of ancient freshwater systems. This study explored variations in composition, richness, evenness and rank-abundance in live and dead mollusk assemblages recovered from the Ibicui River Basin, southern Brazil. LA/DA was related to topography, river size, and sediment grain size, separated respectively into plain (altitude 0–100 m) versus slope (100–500 m), small versus medium-large stream orders, and gravel versus sand substrate. Positive correlation between LA and DA species composition was significant only in large rivers. Slope areas showed LA/DA species compositions that were significantly different, whereas the communities from sand and gravel substrates were quite similar. Important factors that affected live/dead similarity in the study area included (1) destruction of thin, fragile shells of dead animals by acidic waters that are common in the region, (2) downstream drift of small spherical shells from species common in slope areas, such as Potamolithus sp., and (3) high abundances of invasive species in the local death assemblage, especially in large rivers. High fidelity in large rivers is caused by the presence of favorable habitats for bivalve communities. Coarse sediments are an important driver of macro invertebrate diversity, acting as shell traps that slow the downstream drift of bivalve remains and improve the preservation of fluvial mollusks. The preservation potential of dead assemblages of the Ibicui River showed that fossil assemblages are useful tools for recognizing ancient riverscapes, such as flat areas with sandy substrates.

Trait‐based approaches for guiding the restoration of degraded agricultural landscapes in East Africa

Abstract Functional ecology provides a framework that can link vegetation characteristics of various land uses with ecosystem function. However, this application has been mostly limited to [semi‐]natural systems and small spatial scales. Here, we apply functional ecology to five agricultural landscapes in Kenya, Uganda and Ethiopia, and ask to what extent vegetation characteristics contribute to soil functions that are key to farmers’ livelihoods. We used the Land Degradation Surveillance Framework (LDSF), a multi‐scale assessment of land health. Each LDSF site is a 10 × 10 km landscape in which vegetation cover and erosion prevalence were measured, a tree inventory was carried out, and topsoil (0–20 cm) samples were collected for organic carbon (SOC) analysis in approximately 160 × 1,000 m2 plots. Land degradation is a recurring phenomenon across the five landscapes, indicated by high erosion prevalence (67%–99% of the plots were severely eroded). We used mixed models to assess if vegetation cover, above‐ground woody biomass and the functional properties of woody vegetation (weighted‐mean trait values, functional diversity [FD]) explain variation in SOC and erosion prevalence. We found that the vegetation cover and above‐ground biomass had strong positive effects on soil health by increasing SOC and reducing soil erosion. After controlling for cover and biomass, we found additional marginal effects of functional properties where FD was positively associated with SOC and the abundance of invasive species was associated with higher soil erosion. Synthesis and applications. This work illustrates how functional ecology can provide much‐needed evidence for designing strategies to restore degraded agricultural land and the ecosystem services on which farmers depend. We show that to ensure soil health, it is vital to avoid exposed soil, maintain or promote tree cover, while ensuring functional diversity of tree species, and to eradicate invasive species.

Factors responsible for the distribution of invasive plant species in the surroundings of railway areas. A case study from SE Poland

AbstractInvasive plant species are a growing concern in global biodiversity management. In this study, we tried to determine whether invasive plants could spread from railway track into the surrounding areas and focused on the factors responsible for the invasive plant species composition, richness, and abundance. We sampled invasive species along transects located outside a railway route and recorded the invasive species richness and abundance at a distance of < 5 (control), 5–10, 10–15, and > 15 m away from the railway edge in three geographical regions in SE Poland. We revealed that the mechanism allowing alien species to invade was complex. Canonical correspondence analysis (CCA) explained 30.9% of variance. On a regional scale, the invasive flora composition in the surroundings of railway habitats was determined by abiotic environment diversity (mean annual air temperature, mean annual precipitation), but not habitat-related factors (soil type, soil properties). On a spatial scale, the traffic volume, the distance from the railway area, the distance from build-up areas, and the interaction of these factors affect the invasive species composition away from railway areas. The invasive species spread from railways to the surrounding vegetation, therefore, regular monitoring of railway areas should be a framework for assessing the risk of invasive species.

Pathogen accumulation cannot undo the impact of invasive species

Pathogen accumulation can decrease, increase, or not change invasive species abundance, but their impacts may persist in all scenarios.

Ants Indicate Urbanization Pressure in Sacred Groves of Southwest India:A Pilot Study

Sacred groves may contain remnants of pristine and primary forests outside the state-owned protected area system. As they are small fragments and located in the neighbourhood of human settlements, towns, and cities, they are likely to be affected by urbanization. We studied the effect of urbanization on the ecosystem health of sacred groves of Kerala using litterdwelling ants as the indicator taxa. Ants were pitfalltrapped (10-12 traps/sacred grove) from three rural and two urban sacred groves, and identified to species. Overall, 1,119 ants of 32 species and 6 subfamilies (Aenictinae, Dolichoderinae, Ectatomminae, Formicinae, Myrmicinae and Ponerinae) were collected. This corresponds to 76.54% of the estimated species richness. Urbanization had little impact on the species diversity of ants. Abundance was remarkably high in urban sacred groves, mainly due to higher abundance of generalist and invasive species. The effect of urbanization was indicated by different ant assemblages. Rural sacred groves had nine species and three subfamilies exclusive to them as against the five exclusive species of urban sacred groves. Urban sacred groves were characterized by high abundance of Anoplolepis gracilipes , a globally important invasive species. Sacred groves were clustered based on the rural-urban gradient as hypothesized by the study.

Frequency of invasive plant occurrence is not a suitable proxy for abundance in the Northeast United States

AbstractMeasuring and predicting invasive plant abundance is critical for understanding impacts on ecosystems and economies. Although spatial abundance datasets remain rare, occurrence datasets are increasingly available across broad regional scales. We asked whether the frequency of these point occurrences can be used as a proxy for abundance of invasive plants. We compiled both occurrence and abundance data for 13 regionally important invasive plants in the northeast United States from herbarium records and several contributed distribution datasets. We integrated all available abundance information based on infested area, stem count, percent cover, or qualitative descriptions into abundance rankings ranging from 0 (absent) to 4 (highly abundant). Within equal‐area grid cells of 800 m, we counted numbers of occurrence points and used ordinal regression to test whether higher densities of occurrence points increased the odds of a higher abundance ranking. We compiled a total of 86,854 occurrence points in 34,596 grid cells, of which 26,114 points (30%) within 11,976 cells (35%) had some form of abundance information. Eleven of the 13 species had a slight but significantly positive odds ratio; that is, more occurrence points of a species increased the odds that the species was abundant within the grid cell. However, the predictive ability of the models was poor (κ < 0.2) for the majority of species. Additionally, most grid cells contained only one or two occurrence points, making it impossible to infer abundance in all but a few locations. These results suggest that currently available occurrence datasets do not effectively represent abundance, which could explain why many distribution models based on occurrence data are poor predictors of abundance. Increased efforts to consistently collect and report invasive species abundance, ideally estimating both infested area and average cover, are strongly needed for regional‐scale assessments of potential abundance and associated impact.

Comparative profiling of hepatopancreas transcriptomes in satiated and starving Pomacea canaliculata

BackgroundAlthough Pomacea canaliculata is native to South and Central America, it has become one of the most abundant invasive species worldwide and causes extensive damage to agriculture and horticulture. Conventional physical and chemical techniques have been used to eliminate P. canaliculata, but the effects are not ideal. Therefore, it is important to devise a new method based on a greater understanding of the biology of P. canaliculata. However, the molecular mechanisms underlying digestion and absorption in P. canaliculata are not well understood due to the lack of available genomic information for this species, particularly for digestive enzyme genes.ResultsIn the present study, hepatopancreas transcriptome sequencing produced over 223 million high-quality reads, and a global de novo assembly generated a total of 87,766 unique transcripts (unigenes), of which 19,942 (22.7%) had significant similarities to proteins in the UniProt database. In addition, 296,675 annotated sequences were associated with Gene Ontology (GO) terms. A Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment was performed for the unique unigenes, and 262 pathways (p-value < 10−5) in P. canaliculata were found to be predominantly related to plant consumption and coarse fiber digestion and absorption. These transcripts were classified into four large categories: hydrolase, transferase, isomerase and cytochrome P450. The Reads Per Kilobase of transcript per Million mapped reads (RPKM) analysis showed that there were 523 down-regulated unigenes and 406 up-regulated unigenes in the starving apple snails compared with the satiated apple snails. Several important genes are associated with digestion and absorption in plants: endo-beta-1, 4-glucanase, xylanase, cellulase, cellulase EGX1, cellulase EGX3 and G-type lysozyme genes were identified. The qRT-PCR results confirmed that the expression patterns of these genes (except for the longipain gene) were consistent with the RNA-Seq results.ConclusionsOur results provide a more comprehensive understanding of the molecular genes associated with hepatopancreas functioning. Differentially expressed genes corresponding to critical metabolic pathways were detected in the transcriptome of starving apple snails compared with satiated apple snails. In addition to the cellulase gene, other genes were identified that may be important factors in plant matter metabolism in P. canaliculata, and this information has the potential to expedite the study of digestive physiology in apple snails.

Floods affect the abundance of invasive Impatiens glandulifera and its spread from river corridors

AbstractAimRiparian habitats are amongst the most invaded ecosystems world‐wide. The great abundance of invasive species in river corridors is attributed to the efficient transport of alien species’ propagules and reduced competition from native plants due to regular flooding. Once an invasive species has become established, river corridors can serve as stepping stones for spread into other habitats. We have chosen the Himalayan balsam Impatiens glandulifera Royle, highly invasive annual in riparian areas, as a model for spread of invasive species from linear river corridors.LocationCentral Europe.MethodsWe mapped its distribution and recorded its abundance in over 1200 patches along four rivers in central Europe, differing in the time of balsam's introduction (1900–1995). The patches were characterized in terms of the distance from the riverbank, height above the river surface, degree of soil disturbance and flooding regime.ResultsThe patches at sites subject to flooding had twice as many individuals as those that were not subject to flooding, regardless of their distance from the riverbank and height above the river surface. There was a strong effect of the river identity, with river invaded 20 years ago being less infested than those invaded earlier. The distance from the riverbank at which the populations occurred differed and did not depend on river identity/residence time. The patches in tributaries were on average two times further from the bank of the main river than those located elsewhere.Main conclusionsFlooding is an important factor affecting the abundance of I. glandulifera, and accounts for its spread and dominance along river corridors probably due to spreading the seeds, increasing nutrient availability and disturbing native vegetation. It is likely that the number of I. glandulifera populations will increase in the future, especially along small water courses.

Biotic resistance in the tropics: patterns of seed plant invasions within an island

Charles Elton proposed that high species diversity and low levels of disturbance provide a measure of biotic resistance against invasions by alien species. While there is some evidence for this hypothesis, there are numerous other factors associated with invasive species richness, and the strength of those relationships is often scale-dependent. Among oceanic island groups, habitat diversity, human population size and economic activity have been identified as among the significant drivers of invasive species richness. However, intra-island patterns are rarely analyzed. We investigate the relationship between the number of invasive seed plant species and human, physical and biotic factors among municipalities of the tropical island of Puerto Rico using Generalized Linear Models. While elevation amplitude and, to a lesser extent, area had significant effects on the diversity of the most abundant invasive species, we found that the best models, according to Akaike Information Criterion, consistently involve a positive relationship between the number of invasive and native species. Moreover, when we examined the relationship between forest reserves and those regions without reserves, proportionately fewer invasive species occur in forest reserves where native species richness is higher, resource competition is presumably greater, and human impacts are no longer as pervasive. Because the invasive species pool consists almost entirely of ruderal species, forest reserves, while not impenetrable, are less susceptible to invasions than the heavily human-impacted landscapes. Consequently, forest reserves may play an important role in slowing the pace of biological invasions on tropical islands.

Inferring invasive species abundance using removal data from management actions.

Evaluation of the progress of management programs for invasive species is crucial for demonstrating impacts to stakeholders and strategic planning of resource allocation. Estimates of abundance before and after management activities can serve as a useful metric of population management programs. However, many methods of estimating population size are too labor intensive and costly to implement, posing restrictive levels of burden on operational programs. Removal models are a reliable method for estimating abundance before and after management using data from the removal activities exclusively, thus requiring no work in addition to management. We developed a Bayesian hierarchical model to estimate abundance from removal data accounting for varying levels of effort, and used simulations to assess the conditions under which reliable population estimates are obtained. We applied this model to estimate site-specific abundance of an invasive species, feral swine (Sus scrofa), using removal data from aerial gunning in 59 site/time-frame combinations (480-19,600 acres) throughout Oklahoma and Texas, USA. Simulations showed that abundance estimates were generally accurate when effective removal rates (removal rate accounting for total effort) were above 0.40. However, when abundances were small (<50) the effective removal rate needed to accurately estimates abundances was considerably higher (0.70). Based on our post-validation method, 78% of our site/time frame estimates were accurate. To use this modeling framework it is important to have multiple removals (more than three) within a time frame during which demographic changes are minimized (i.e., a closed population; ≤3months for feral swine). Our results show that the probability of accurately estimating abundance from this model improves with increased sampling effort (8+ flight hours across the 3-month window is best) and increased removal rate. Based on the inverse relationship between inaccurate abundances and inaccurate removal rates, we suggest auxiliary information that could be collected and included in the model as covariates (e.g., habitat effects, differences between pilots) to improve accuracy of removal rates and hence abundance estimates.

Temperature, space availability, and species assemblages impact competition in global fouling communities

Competition drives community composition in many ecosystems and can influence the spread of invasive species. Marine fouling communities are excellent study systems for competition because of space limitation and the abundance of invasive species. While many studies have examined individual or site-specific responses to changes in temperature or presence of invasive species, it is difficult to predict ecological impacts without assessing interspecific interactions over a wide geographic range. This study compared interactions between several globally distributed invasive fouling species over a broad geographic range. Weekly examination of photographs of settlement panels in marinas at 18 sites around the world allowed for the quantification of competitive outcomes. In the north Atlantic, experimental panels became covered with fouling organisms exponentially faster at warmer temperatures, while northeast and south Pacific sites did not. An invasive ascidian (Diplosoma listerianum) and bryozoan (Bugula neritina) were strong competitors, but most species displayed a negative response in high competition settings where there was little available space. Two species (Botryllus schlosseri and Botrylloides violaceus) had better competitive outcomes at cooler temperatures, possibly due to fewer strong competitors at these sites. Thus, warmer sites with little open space and multiple strong competitors are likely most resistant to future invasions, while colder sites with more open space and weaker competitors would be more susceptible to invasive species. These results suggest that the establishment and spread of invasive fouling species is likely to be influence by seawater temperature, available space, and the competitive abilities of community members.

Urbana House Ants 2.0: Revisiting M. R. Smith's 1926 Survey of House-Infesting Ants in Central Illinois After 87 Years

Quantifying the long-term ecological impacts of urbanization requires high-quality historical records and similar re-surveys over time. We replicated a survey conducted in 1924-1926 by Marion R. Smith of house-infesting ants in Urbana, Illinois, to examine how the house-infesting ant fauna and its control measures have changed over 87 years. We complemented residential sampling with pitfall, visual, and leaf litter surveys in the surrounding urban neighborhood and in three nearby forest fragments to characterize the ant fauna from which the house-infesting ants are drawn. In 1924-26, 12 ant species were collected in houses; the four most common were Tapinoma sessile (Say), Lasius alienus (Forster), Camponotus pennsylvanicus (DeGeer) and Solenopsis molesta (Say). In 2012-2013, we found eight species in houses, the four most common of which were Tapinoma sessile, Tetramorium caespitum (Linnaeus), C. pennsylvanicus , and C. nearcticus (Emery). Ant control measures have also changed dramatically, with the average amount spent per household in 2012-2013 nearly doubling (adjusted for inflation). We also found that the residential urban site had similar estimated species richness to one of the nearby forest remnants, demonstrating that the diversity of some arthropod groups can remain high in forested urban environments. Moreover, each site had a unique community of species, reinforcing the value of both small forest fragments and urban sites for supporting biodiversity. Our survey revealed changes in urban and house-infesting ant communities since the 1920s, but, in view of the global abundance of invasive ant species and the extensive changes in land use patterns in central Illinois, the relative similarity of the ant communities separated in time by 87 years was unexpected.

Monitoring Understory Composition of Blue Oak Woodlands on Conservation Easements

Conservation easements are an increasingly popular strategy for conserving biological diversity on private land. Long-term vegetation monitoring on conservation easements can provide critical information on persistence of biological diversity and abundance of invasive species. We sampled understory plant composition on five of The Nature Conservancy’s conservation easements in the Mt. Lassen foothills of Northern California. We established 73 plots of 10-meter radius, measured species composition with the point-intercept method, and compiled a full species list for each plot in 2005 and 2006. We found significant differences in the relative cover of native and non-native annual grasses and annual forbs among easement properties. Relative cover of native plants was significantly higher in herbaceous plots (50 percent) than in plots with blue oak (Quercus douglasii) canopy (21 percent). We found medusahead (Taeniatherum caput-medusae) in 64 percent of plots and yellow star thistle (Centaurea solstitialis) in 9 percent of plots. Overlap of species composition between years was correlated with difference in date sampled each year but not correlated with confidence in plot relocation. Our analysis of community diversity and relative abundance provides a baseline for future change. Finally, we make recommendations for the design of future monitoring efforts on conservation easements.

Booms, busts and population collapses in invasive ants

The abundance of many invasive species can vary substantially over time, with dramatic population declines and local extinctions frequently observed in a wide range of taxa. We highlight population crashes of invasive ants, which are some of the most widespread and damaging invasive animals. Population collapse or substantial declines have been observed in nearly all of the major invasive ant species including the yellow crazy ant (Anoplolepis gracilipes), Argentine ants (Linepithema humile), big-headed or coastal brown ant (Pheidole megacephala), the tropical fire ant (Solenopsis geminata), red imported fire ants (Solenopsis invicta), and the little fire ant or electric ant (Wasmannia auropunctata). These declines frequently attract little attention, especially compared with their initial invasion phase. Suggested mechanisms for population collapse include pathogens or parasites, changes in the food availability, or even long-term effects of the reproductive biology of invasive ants. A critical component of the collapses may be a reduction in the densities of the invasive ant species, which are often competitively weak in low abundance. We propose that mechanisms causing a reduction in invasive ant abundance may initiate a local extinction vortex. Declines in abundance likely reduce the invasive ant’s competitive ability, resource acquisition and defense capability. These reductions could further reduce the abundance of an invasive ant species, and so on. Management of invasive ants through the use of pesticides is expensive, potentially ecologically harmful, and can be ineffective. We argue that pesticide use may even have the potential to forestall natural population declines and collapses. We propose that in order to better manage these invasive ants, we need to understand and capitalize on features of their population dynamics that promote population collapse.

Flood control structures in tidal creeks associated with reduction in nursery potential for native fishes and creation of hotspots for invasive species

Habitat connectivity is important for maintaining biodiversity and ecosystem processes yet globally is highly restricted by anthropogenic actions. Anthropogenic barriers are common in aquatic ecosystems; however, the effects of small-scale barriers such as floodgates have received relatively little study. Here we assess fish communities in ten tributaries over the spring–summer season of the lower Fraser River (British Columbia, Canada), five with floodgates and five reference sites without barriers, located primarily in agricultural land use areas. While the Fraser River supports the largest salmon runs in Canada, the lower Fraser river–floodplain ecosystem has numerous dikes and floodgates to protect valuable agricultural and urban developments. Floodgate presence was associated with reduced dissolved oxygen concentrations, threefold greater abundance of invasive fish species, and decreased abundances of five native fish species, including two salmon species. These findings provide evidence that floodgates decrease suitable habitat for native fishes, and become hotspots for non-native species. Given climate change, sea-level rise, and aging flood protection infrastructure, there is an opportunity to incorporate biodiversity considerations into further development or restoration of this infrastructure.

Asynchronous changes in abundance over large scales are explained by demographic variation rather than environmental stochasticity in an invasive flagellate

Summary Environmental stochasticity is important in explaining the persistence and establishment of invasive species, but the simultaneous effects of environmental and demographic factors are difficult to separate. Understanding how demography and environmental factors affect invasive species abundance over large temporal and spatial scales is essential to anticipate populations at risk of becoming established and setting appropriate management measures. Using a hierarchical mixed modelling approach, we analysed the spatial and interannual dynamics of the invasive raphidophyte Gonyostomum semen, a noxious flagellate which is spreading in northern Europe, in response to demographic and environmental variation. We used data from 76 lakes distributed across two biogeographical regions in Sweden (Central Plains in the south and Fennoscandian region in the north) and sampled during 14 years. We found a strong asynchrony in the density dynamics of G. semen populations between the two regions. G. semen showed positive trends (i.e. increasing frequency of high density peaks) in most southern lakes, forming established populations with recurrent blooms in successive years in some of them. In contrast, G. semen populations were smaller and more stochastic in the north. G. semen previous year's abundance, a proxy for cyst production and recruitment, had a strong control on the dynamics, likely contributing to the stability of high density populations in southern lakes. Conversely, the effects of climate and habitat were weaker and their influence varied across regions. Temperature was the limiting factor in the north whereas local habitat was more important in the south. Synthesis. A full understanding of the mechanisms driving abundance changes across large scales can only be gained if endogenous and environmental factors are analysed together. For phytoplankton species, and specially, noxious microalgae, this implies that proxies for cyst production and recruitment, which are the inoculum for next year population, should be included in e.g. distribution, bloom formation and climate models, as these may modify establishment and population response to environmental variation. Asynchronous changes in abundance across regions also indicate that management plans should be developed for small regions, as inference at a large scale may obscure the mechanisms driving local population changes.

A rapid survey of the invasive plant species in western Angola

Angola is one of the most neglected African countries in terms of botanical research, in respect of both native and naturalized species. We conducted a rapid assessment of invasive plant species in western Angola during August 2014. In thirteen primary vegetation types, we recorded populations of 44 naturalized plant species, nineteen of which are conclusively invasive (spreading far from introduction sites). Dense invasive populations of Chromolaena odorata, Inga vera and Opuntia stricta pose the greatest environmental and economic threats. Some species with known taxonomic and/or biogeographic uncertainties (e.g. Chromolaena odorata and Ageratina adenophora) or which lacked key characteristics for identification such as flowers during our survey (e.g. Eucalyptus spp.) were subjected to DNA barcoding for comparisons with available genetic data from other studies. This approach allowed us to confirm the identity of taxonomically challenging taxa such as Inga vera, Opuntia stricta and Prosopis chilensis, to conclusively differentiate Chromolaena odorata from Ageratina adenophora, and identify the subspecific identity of Acacia saligna. Canonical correspondence analysis was used to assess the presence and abundance of invasive plant species with respect to the major abiotic factors and vegetation types. Three fairly distinct groups of species emerge from this analysis: (i) species of dry lowland habitats (Calotropis gigantea, Leucaena leucocephala and Opuntia stricta); (ii) species of relatively wet habitats at mid elevations (Ageratum conyzoides, Bidens pilosa, Cardiospermum grandiflorum, Chromolaena odorata, Solanum mauritianum and Tithonia diversifolia); and (iii) upland species (Ageratina adenophora, Galinsoga parviflora and Tagetes minuta). Several invasive species that are widespread in other tropical and subtropical African countries are currently either missing (e.g. many Australian Acacia species, Azolla filiculoides, Broussonetia papyrifera, Clidemia hirta, Parthenium hysterophorus, Rubus rosaefolius, Salvinia molesta), have only very localized populations in Angola (e.g. Lantana camara, Prosopis chilensis) or exist only as planted individuals (e.g. Acacia mearnsii and A. saligna subsp. saligna).