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Spatial Distribution Patterns of Invasive Plants in an Ecologically Heterogeneous Landscape: A Modelling Approach
Abstract and Figures
Invasive plants have become one of the menaces in the twenty first century, due mainly to globalised trades and trafficking of plants, compounded by climate change. Various empirical researches state that the invasion has caused so many negative impacts on human and animal health, heavy costs in managing the invasion, biodiversity loss and disruption of ecosystem services. However, no quantitative and scientific assessments were available in Bhutan, such as ecological niche modelling, using biogeographic information, that provides both the past and predicted geographical distributions of invasive plants. Officially, out of 46 invasive plants, 11 were recognised as alien invasive plants in the country. Six globally noxious alien invasive plants (Ageratina adenophora, Ageratum conyzoides, Chromolaena odorata, Lantana camara, Mikania micrantha and Parthenium hysterophorus) were selected as target species for the study.
The objectives of this study were to i) map the distribution of the species with the past climate scenario using the ensemble models of Desktop GARP, Openmodeller GARP and Maxent in order to enhance the accuracy of predictions; ii) assess the impact of climate change on the distributions of invasive plants; and iii) characterise and compare the ecological niches of the invasive plants that may provide better understanding of coexistence or divergence of the species.
In the first modelling, three algorithms (Desktop GARP, Openmodeller GARP and Maxent) of ecological niches were combined to generate an ensembled ecological niche model for every species. The results indicated that A. adenophora and A. conyzoides with highest ecological amplitude, ranging their potential suitable habitat of invasion from the Tropical, Subtropical, Warm temperate, Cool temperate to Cold temperate ecoregions and P. hysterophorus with the most restricted ecological range. The results also suggested the higher confidence of invasion by all the target species along the southern lowlands and valleys of agricultural lands in the country.
The assessment of distributional changes in invasion was conducted using two time series of bio-climatic variables i) past scenario being the average of 1960-1990 and ii) future scenario being the average of 2041-2060 projection. Although, there was no statistical significance in the overall distributional changes due to climate change, by proportion most species tended to increase. On the contrary and intriguingly, P. hysterophorus decreased in its area and shifted latitudinally northward.
The niche characterisation modelling was conducted using the ENMTools that is capable of comparing species niche breadth, niche overlap and niche similarity. A. adenophora, A. conyzoides and C. odorata had the wider niche breadths compared to the rest. While all the species overlapped in their ecological niches, they would not be considered equivalent in their ecological niche identity, since more than half of the species pairs diverged significantly.
Overall, the study points out that the invasion successes among the invasive species differ both in static or dynamic climatic scenarios, due to differences in their niche characteristics. Therefore, this study provides the basis for prioritising management strategies as well as leaves some questions on what physiological or the genetic traits drive the differences in invasion capabilities of the target species. The incorporation of physiological and genetic traits in ecological niche modelling still remains a challenge although recognised as essential parameters to enhance the model prediction confidence.
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... However, L. camara's distribution is limited by its inability to sustain under thick shades of taller local timber species (IUCN). Lantana camara cannot sustain itself in frigid temperatures (Corlett 1992;Thinley 2020) and saline soils. It cannot survive in water-logged or marshy lands. ...
... We found a strong influence of a few variables (Precipitation of warmest quarter, Mean temperature of wettest quarter, precipitation of driest quarter, flow accumulation, slope, soil carbon content) in determining the suitable habitat for L. camara (Table S1). Findings of other studies in different geographical locations also identified the contribution of temperature and precipitation as the most important environmental variables for L. camara distribution (Thinley 2020). Another study in a similar landscape showed that the distribution of L. camara depends on land use, NDVI in October, mean diurnal range, soil texture, NDVI in July, and annual precipitation. ...
... The study estimated that 40% of the Indian forest is at a high risk of biodiversity loss by the L. camara invasion. Considering the amount of research to identify the best method for controlling invasive occurrence or spread worldwide, a single successful and accepted way is unknown yet (Bhagwat et al. 2012;Thapa et al. 2018;Thinley 2020). ...
Spatial modelling has been an essential tool for predicting and mapping the suitable areas of a species' habitat. Ecological modelling was performed using 744 sampling locations to predict the potential habitat for the invasive plant Lantana camara in the lower Shivalik region of the Western Himalaya, India. The modelling engaged nine bioclimatic, four topographic, one land-cover, and two soil parameters that are known to be ecologically important for the species. Precipitation of the warmest quarter, mean temperature of the wettest quarter, precipitation of the driest quarter, and river flow accumulation contributed to the model. The predicted area for the invasion was classified into high, medium, and low potential areas. We identified nine potential hot spots based on species occurrence over a 2300 km2 area to determine where immediate intervention is necessary to prevent the spread of Lantana camara. The study's findings can assist policymakers and stakeholders in developing an effective and strategic weed management approach at the landscape level.
... However, L. camara's distribution is limited by its inability to sustain under thick shades of taller local timber species (IUCN). Lantana camara cannot sustain itself in frigid temperatures (Corlett 1992;Thinley 2020) and saline soils. It cannot survive in water-logged or marshy lands. ...
... We found a strong influence of a few variables (Precipitation of warmest quarter, Mean temperature of wettest quarter, precipitation of driest quarter, flow accumulation, slope, soil carbon content) in determining the suitable habitat for L. camara (Table S1). Findings of other studies in different geographical locations also identified the contribution of temperature and precipitation as the most important environmental variables for L. camara distribution (Thinley 2020). Another study in a similar landscape showed that the distribution of L. camara depends on land use, NDVI in October, mean diurnal range, soil texture, NDVI in July, and annual precipitation. ...
... The study estimated that 40% of the Indian forest is at a high risk of biodiversity loss by the L. camara invasion. Considering the amount of research to identify the best method for controlling invasive occurrence or spread worldwide, a single successful and accepted way is unknown yet (Bhagwat et al. 2012;Thapa et al. 2018;Thinley 2020). ...
Invasive alien species are one of the most significant threats to biodiversity of the earth ecosystem. Spatial modeling has played a vital role in predicting and mapping the suitable areas of the species habitat for management implementation. Lantana camara is one of the ten worst invasive weed enlisted by IUCN., and has its distribution in more than 154000 sq. km area in India. We predicted the distribution of Lantana camara using Ecological Niche Modeling (ENM) in MaxEnt software for Rajaji- Corbett landscape in the lower Shivalik region of the state of Uttarakhand, India. The predicted area for the invasion was classified into four categories high, good, medium, and low potential areas. The distribution hotspots were identified using Getis Ord G* method in ArcGIS 10.5 by calculating plot-wise species occurrence. Major hotspot areas under threat of high infestation are Dholkhand, Gohri, Ramgarh, Motichur, and Chilla from Rajaji Tiger Reserve, Palain, Mandal and Maidavan from Kalagarh Tiger Reserve and Bijrani, Dheela, Dhikala, Jhirna and Kalagarh from Corbett Tiger Reserve. This study provides a current status of the invasive species in the landscape with identified areas that need immediate actions to control the spread of the species. The study results can help the policymakers and stakeholders build an efficient and strategically weed management plan. Keywords: plant invasion, Lantana camara, habitat modeling, hotspot analysis, landscape management
... Other anthropogenic factors like grazing (0.82), lopping (1.00), logging (0.99), and human presence (0.95) showed a significant contribution to the invasion. According to several research works, topographic characteristics play an essential role in the distribution of L. camara (Priyanka and Joshi, 2013;Thinley 2020;Rai 2013). The secondary topographic factors like soil pH concentration at 0 cm, river flow accumulation, and land use characteristics negatively affected the invasion of L. camara in RTR. ...
... Suitable climatic conditions are crucial elements for any invader to establish and reproduce in an introduced range (Priyanka and Joshi 2013;Thinley 2020;Rai 2013). However, in the case of L. camara, its plasticity helps this species evolve and adjust to changing climate scenarios (Mungi et al. 2020). ...
Biological invasion is regarded as one of the most important disturbance parameters and threats for sustaining biodiversity. Global warming, industrialization, and open niche created due to the expansion of development initiatives contribute to the successful spread of invasive species around the world. The contributions of various biotic and abiotic factors in different spatial scales are crucial for an invasive to establish in its invaded area. We assessed the spatial distribution of invasion by Lantana camara in the Corbett Tiger Reserve and Rajaji Tiger Reserve within the Terai Arc Landscape Complex. The presence locations of Lantana were assessed within 10 m × 10 m plots (n = 666), and information on habitat variables such as tree density, canopy cover, shrub density, shrub cover, and anthropogenic pressures were collected. We also synthesized information on climate and topography data of the region from global databases. Confirmatory factor analysis was done using the presence of Lantana as response variable and habitat, anthropogenic, climatic, and topographic variables as predictor variables. We found that for Rajaji Tiger Reserve, habitat and anthropogenic variables were the major influencing factors for Lantana invasion, whereas, for Corbett Tiger Reserve, climate and topography were the major determining factors. Mean diurnal temperature, precipitation of warmest quarter, lopping, and logging were the factors determining the Lantana invasion in the landscape. The influence of different factors affecting the invasion of Lantana differs between Rajaji Tiger reserve and Corbett Tiger Reserve. The result of the study will be helpful for formulating effective policy intervention to reduce the invasion of Lantana in these ecologically important tiger reserves.
... The slope direction did not have an influence on higher or lower suitability of the species since all the directions were almost equally suitable as shown in Fig. 5p. This was supported by the report of Thinley (2019) which stated that A. adenophora is not sensitive to slope direction. ...
Climate change and invasive alien plant species (IAPs) are having a significant impact on mountain ecosystems. The combination of climate change and socio-economic development is exacerbating the invasion of IAPs, which are a major threat to biodiversity loss and ecosystem functioning. Species distribution modelling has become an important tool in predicting the invasion or suitability probability under climate change based on occurrence data and environmental variables. MaxEnt modelling was applied to predict the current suitable distribution of most noxious weed A. adenophora (Spreng) R. King and H. Robinson and analysed the changes in distribution with the use of current (year 2000) environmental variables and future (year 2050) climatic scenarios consisting of 3 representative concentration pathways (RCP 2.6, RCP 4.5 and RCP 8.5) in Bhutan. Species occurrence data was collected from the region of interest along the road side using GPS handset. The model performance of both current and future climatic scenario was moderate in performance with mean temperature of wettest quarter being the most important variable that contributed in model fit. The study shows that current climatic condition favours the A. adenophora for its invasion and RCP 2.6 climatic scenario would promote aggression of invasion as compared to RCP 4.5 and RCP 8.5 climatic scenarios. This can lead to characterization of the species as preferring moderate change in climatic conditions to be invasive, while extreme conditions can inhibit its invasiveness. This study can serve as reference point for the conservation and management strategies in control of this species and further research.
... The slope direction did not have an influence on higher or lower suitability of the species since all the directions were almost equally suitable as shown in Fig. 5p. This was supported by the report of Thinley (2019) which stated that A. adenophora is not sensitive to slope direction. ...
This article is an attempt to assess the invasion risk from the most noxious alien plant species using the GPS recorded locations and environmental variables. The invasion risk was modelled by combining the three ecological niche modelling algorithms- DesktopGARP, Openmodeller DesktopGARP and Maxent after validating their accuracies. The accuracies ranged from moderate to good in all the algorithms, for all six species. The result showed Ageratina adenophora and Ageratum conyzoides as highly invasive species both in terms of area coverage and the ecological tolerance range of the study site. It was also indicative that, irrespective of the species, agricultural lands are most susceptible to invasion among all other types of land uses in the study area.
... Moreover, it is very common in barren land, grassland, and cultivated land, but limited to natural environment of the forested areas [16]. Especially, it is being predicted that the southern belt and agricultural lands of Bhutan poses the highest risk due to A.adenophora [7,17], but the unsustainable management and climate change can drive this species much towards the higher altitude. ...
Ageratina adenophora (Sprengel) King and Robison, commonly known as Mexican devil, is considered as one of the aggressive species, which invades almost all parts of an ecosystem. Particularly, people who rear livestock and depend on naturally available fodders have a great concern over the invasion of this species. Therefore, this study was conducted to generate knowledge on current status of A. adenophora invasion and its potential impact on livestock and fodder species of Radhi Gewog (Village block) under Trashigang district of Bhutan. The study recorded the total of 14 fodder species distributed in both open and undisturbed forest, and Artemisia sp. was the most abundant fodder in the sampled site. We learnt that the livestock mainly used the open areas for grazing and browsing, but 87.5% of sampled plots in this area was invaded by the A. adenophora, affecting the growth of fodder species. Due to this reason, a strategic management plan needs to consider the eradicating or controlling the invasion of A. adenophora across the country, particularly at grazing sites and places where people depend on livestock for their livelihood.
... The slope direction did not have an influence on higher or lower suitability of the species since all the directions were almost equally suitable as shown in Fig. 5p. This was supported by the report of Thinley (2019) which stated that A. adenophora is not sensitive to slope direction. ...
This article is an attempt to assess the invasion risk from the most noxious alien plant species using the GPS recorded locations and environmental variables. The invasion risk was modelled by combining the three ecological niche modelling algorithms- DesktopGARP, Openmodeller DesktopGARP and Maxent after validating their accuracies. The accuracies ranged from moderate to good in all the algorithms, for all six species. The result showed Ageratina adenophora and Ageratum conyzoides as highly invasive species both in terms of area coverage and the ecological tolerance range of the study site. It was also indicative that, irrespective of the species, agricultural lands are most susceptible to invasion among all other types of land uses in the study area.
Climate change is viewed as a cause in accelerating the rate of invasion by alien species in addition to the globalization of anthropogenic activities. Ecological niche modeling has become an instrument in predicting invasion from natural or invaded ranges to uninvaded ranges based on the presence records of organisms and environmental parameters. This study explored the changes in the distributions of globally noxious alien species (Aegratina adenophora, Ageratum conyzoides, Chromolaena odorata, Lantana camara, Mikania micrantha, and Parthenium hysterophorus) in Bhutan, to provide evidence that even a mountain environment is under the threat of invasion given the change in climatic conditions. With fairly high accuracy, the model results suggest that there will be a potential increase in the areas of invasion among most of the species, except Parthenium hysterophorus, which will experience a northerly shift and decline in distribution. The results also indicate changes in patterns of invasion, some becoming more concentrated toward a given direction, while others become more dispersed over time. This study provides a framework that can be used in the strategic control of the species, future detection surveys, and further research.
Aim
Ecological inferences drawn from studies on niche dynamics of invasive species are often limited due to difficulties in disentangling evolutionary adaptations of the fundamental niche from demographic and interspecific processes shaping the realized niche. We used Ageratina adenophora, an invasive plant with restricted evolutionary potential to investigate shifts in the realized climatic niche independent of potential evolutionary adaptations.
Location
Native Mexican range; exotic ranges in Asia, the USA, the Canary Islands and Australia.
Taxon
Invasive Asteraceae A. adenophora (Spreng.) R.M.King & H.Rob. Commonly known as Crofton weed.
Methods
We compiled a robust occurrence dataset of A. adenophora for its native Mexican range and four exotic ranges (Asia, USA, Canary Islands, and Australia) and quantified pairwise niche overlap (Schoener's D) and niche dynamic (stable, unfilling and expansion) indices between the native and exotic ranges in reduced climatic space using smoothed occurrence densities. Niche shift was statistically tested using niche equivalency tests.
Results
The value of niche overlap (Schoener's D) differed considerably, ranging from relatively high between Mexico and Asia to low between Mexico and Australia. The niche dynamic indices indicated highest level of niche stability in Asia while highest degree of unstable niche was detected in Australia due to both niche expansion and unfilling. The niche similarity tests indicated that the native niche is more similar to the exotic niche than any randomly sampled niche from the exotic range. However, the niche equivalency tests showed evidence of niche differentiation as the observed niche overlap was lower than expected by chance for all pairwise comparisons. Jointly these tests indicate that despite the similarity, the native niche is not perfectly identical to any of the exotic niches.
Main conclusions
The current study has direct implications for understanding range expansion of invasive species even in the absence of evolutionary adaptation. Our study indicates that invasive species can occupy different, non‐consistent realized climatic niches in different parts of the world, thus limiting the transferability of species distribution models and corresponding risk assessments or future projections.
The eastern Himalayan climate is strongly determined by a rugged mountainous terrain and the impact of the Indian summer monsoon. Climate change increases the vulnerability of key economic sectors (e.g., agriculture, forestry and hydro-power generation) of Bhutan and threatens the countries rich biodiversity, its fragile community livelihoods and increases the probability of hazardous events (e.g., glacier lake outburst floods, flash floods, droughts and forest fires). A comprehensive knowledge of Bhutan’s climatic conditions and their variability is therefore essential to enhance the efficiency and applicability of adaptation efforts. Very few studies on the climatology of the Bhutanese Himalaya have been published so far. The scanty literature has primarily focused on the reduction of threats related to the formation of glacier lakes. In contrast, this study (1) analyses the average spatial and inner-annual variability of air temperature and precipitation regimes of Bhutan, based on local meteorological observations and climate projections, and (2) relates the effects of climatic changes on water resources, ecosystem services, agriculture and the economy of Bhutan.
Full- text available through the IPCC website:
https://www.ipcc.ch/sr15/
The global threat posed by invasive alien plants has prompted inventory compilations and screening exercises that aim to understand invasiveness in various taxa. Various traits influence the invasiveness of a species but do not apply to all plant taxa. Ferns are rare or absent from such inventories, but notable fern invasions do exist. We developed a global inventory of terrestrial alien true ferns (Polypodiophyta) comprising 157 species, using published literature and online inventories. We aimed to determine which traits influence the probability that a terrestrial alien fern will become naturalised or invasive. Generalised linear models with transition stages as response variables, were used to assess the effects of various anthropogenic, biological and distributional traits on invasiveness. Our model explained 30–40% of the variance associated with invasiveness and showed that a ground-dwelling life form, reproductive plasticity, tolerance for disturbance and varied light conditions, and a broad introduced range (interpreted as high environmental tolerance and popularity in horticulture) were important determinants of invasiveness in alien ferns. We highlighted which geographic regions and fern families had the highest incidences of alien ferns and identified particular species of concern. This study aids in the understanding of the mechanisms underlying invasiveness in alien ferns and the findings can inform future research on this understudied taxon as invasive species.
Mikania micrantha a gregarious perennial fast growing herbaceous creeping vine possess a serious threat to tea production. Negative impacts of the weed include labour cost, reduction in yield of crop, loss of native biodiversity etc. An ecological survey to study the seasonal distribution and economic impact in terms of cost and profitability of tea cultivation was carried out during 2004-2005 in two sites viz., Cinnamora Tea Estate (CTE), Division: Hatigarh and Experimental Garden for plantation crop (EGPC), Assam Agricultural University, Jorhat (Assam). The results of the present investigation showed highest population build-up 2600 and 1000 numbers of Mikania stalks/ha during the month of September and August respectively in CTE and AAU. Study on economic impact of Mikania showed an adverse effect of it on tea cultivation in the surveyed area causing a loss of 41.8% and 18.90 % respectively in CTE and EGPC.
Ageratina adenophora (Sprengel) R. King & H. Robinson (= Eupatorium adenophorum Sprengel) is one of the worst invasive alien species in China. Since A. adenophora was first noticed in Yunnan Province of China in the 1940s, its rapid spread has caused an ecological problem in southwestern China. Understanding its historical invasion pattern and its potential for further spread is needed to plan the management of the species. We reconstructed the historical process of its invasion and analysed its ecological preferences in the invaded region. After a lag phase of 20 years (1940-60), A. adenophora spread rapidly throughout the south and middle subtropical zones in Yunnan, Guizhou, Sichuan, and Guangxi, China, with an average expansion rate of 20 km per year. It spread relatively slowly in north subtropical areas, with an average expansion rate of 6.8 km per year. It has not established in warm temperate areas within the invaded regions. Although range expansion in Yunnan stopped after 1990, the expansion of its range into neighbouring provinces indicates that A. adenophora has not reached the full potential of its distribution and its range is still rapidly expanding within China. We applied ecological niche modelling (GARP-Genetic Algorithm for Rule-set Prediction) to predict potential invasion areas in mainland China on the basis of occurrence points within colonized areas where A. adenophora has reached equilibrium. The predictions, confirmed by the range of values of four key environmental parameters, generally match the parameters of the geography and ecology in the invaded region. Southern and south-central China have climatic conditions suggestive of a high potential for invasion by A. adenophora. Climatic conditions in northern and western China appear unsuitable for A. adenophora. Urgent measures should be taken to prevent this species from further spreading into the vast areas of potential habitat in southern and south-central China.