Effects of microtopography and hydrology on phenology of an invasive herb

Phenological traits may influence invasion success via effects on invasiveness of the colonizing species and invasibility of the receiving ecosystems. Many species exhibit substantial fine-scaled spatial variation in phenology and interannual differences in phenological timing in response to environmental variation. Yet describing and understanding this variation is limited by the availability of appropriate spatial and temporal datasets. Remote sensing provides such datasets, but has primarily been used to monitor broad-scale phenological patterns at coarse resolutions, necessarily missing fine spatial detail and intraspecies variation. We used hyperspectral remote sensing to characterize the spatial and temporal phenological variation of the invasive species Lepidium latifolium (perennial pepperweed) at two sites in California's San Francisco Bay/Sacramento–San Joaquin River Delta. Considerable phenological variation was detected: L. latifolium was simultaneously present in vegetative, early flowering, peak flowering, fruiting, and senescent stages in late June; the relative dominance and distribution of these stages varied interannually. Environmental determinants of phenology were investigated with variables derived from the hyperspectral image data, from a high resolution LiDAR (light detection and ranging) digital elevation model (DEM), and from local precipitation and streamflow data. Lepidium latifolium phenology was found to track water availability, and may also be influenced by intraspecific competition and edaphic stress. Lepidium latifolium has a unique phenology (summer flowering) relative to the communities it invades, which may allow invasion of an empty niche. Furthermore, many habitats are invaded by L. latifolium, which occurs in locally appropriate phenologies under the different environmental conditions. The environmental responsiveness of L. latifolium phenology may mediate the wide breadth of invasible habitats.     

Benefits of hyperspectral remote sensing for tracking plant invasions

Aim We aim to report what hyperspectral remote sensing can offer for invasion ecologists and review recent progress made in plant invasion research using hyperspectral remote sensing. Location United States. Methods We review the utility of hyperspectral remote sensing for detecting, mapping and predicting the spatial spread of invasive species. We cover a range of topics including the trade‐off between spatial and spectral resolutions and classification accuracy, the benefits of using time series to incorporate phenology in mapping species distribution, the potential of biochemical and physiological properties in hyperspectral spectral reflectance for tracking ecosystem changes caused by invasions, and the capacity of hyperspectral data as a valuable input for quantitative models developed for assessing the future spread of invasive species. Results Hyperspectral remote sensing holds great promise for invasion research. Spectral information provided by hyperspectral sensors can detect invaders at the species level across a range of community and ecosystem types. Furthermore, hyperspectral data can be used to assess habitat suitability and model the future spread of invasive species, thus providing timely information for invasion risk analysis. Main conclusions Our review suggests that hyperspectral remote sensing can effectively provide a baseline of invasive species distributions for future monitoring and control efforts. Furthermore, information on the spatial distribution of invasive species can help land managers to make long‐term constructive conservation plans for protecting and maintaining natural ecosystems.     

Polymorphic microsatellite markers in polyploid Lepidium draba L. ssp. draba (Brassicaceae) and cross‐species amplification in closely related taxa

Heart‐podded hoary cress, Lepidium draba L. ssp. draba (Brassicaceae) is a noxious invasive weed in the USA. At present, efficient biological control of this Eurasian native weed in the USA is hampered by lack of knowledge of its population genetic structure and colonization process. Here, we describe the development of 11 polymorphic microsatellite markers that also reveal the polyploidy of this weed. Successful cross‐species amplification highlights the possibility of using these markers for genetic studies in other closely related species.     

Assessing current and projected suitable habitats for tree-of-heaven along the Appalachian Trail

The invasion of ecosystems by non-native species is a major driver of biodiversity loss worldwide. A critical component of effective land management to control invasion is the identification and active protection of areas at high risk of future invasion. The Appalachian Trail Decision Support System (A.T.-DSS) was developed to inform regional natural resource management by integrating remote sensing data, ground-based measurements and predictive modelling products. By incorporating NASA''s remote sensing data and modelling capacities from the Terrestrial Observation and Prediction System (TOPS), this study examined the current habitat suitability and projected suitable habitat for the invasive species tree-of-heaven (Ailanthus altissima) as a prototype application of the A.T.-DSS. Species observations from forest surveys, geospatial data, climatic projections and maximum entropy modelling were used to identify regions potentially susceptible to tree-of-heaven invasion. The modelling result predicted a 48% increase in suitable area over the study area, with significant expansion along the northern extremes of the Appalachian Trail.     

Relative importance of hydrological variables in predicting the habitat suitability of Euryale ferox Salisb.

Aims Aquatic ecosystems are a priority for conservation as they have become rapidly degraded with land-use changes. Predicting the habitat range of an endangered species provides crucial information for biodiversity conservation in such rapidly changing environments. However, the complex network structure of aquatic ecosystems restricts spatial prediction variables and has hitherto limited the use of habitat models to predict species occurrence in aquatic ecosystems. We used the maximum entropy model to evaluate the potential distribution of an endangered aquatic species, Euryale ferox Salisb. We tested the relative influence of (i) climatic variables, (ii) topographic variables, and (iii) hydrological variables derived from remote sensing data to improve the prediction of occurrence of aquatic plant species.Methods We considered the southern part of the Korean Peninsula as the modeling extent for the potential distribution of E. ferox. Occurrence records for E. ferox were collected from the literature and field surveys. We applied maximum entropy modeling using remotely sensed environmental variables and evaluated their relative importance as prediction variables with variation partitioning.Important findings The species distribution model predicted potential habitats of E. ferox that matched the actual distribution well. Floodplain wetlands and shallow reservoirs were the favored habitats of E. ferox. Quantitative loss and fragmentation of wetland habitats appeared to be a major reason for the decrease of E. ferox populations. Our results also imply that hydrological variables (i.e. normalized difference water index) derived from remote sensing data greatly increased model prediction (relative contribution: 10.5–37.0%) in the aquatic ecosystem. However, interspecific competition within a similar niche environment should be considered to increase the accuracy of the distribution model.     

Use of aerial imagery to assess habitat suitability and predict site occupancy for a declining wetland-dependent bird

Remote sensing is a valuable tool for wetland habitat quantification, monitoring and assessment. Here we show that habitat assessment via aerial image inspection is useful in predicting wetland site occupancy by black terns (Chlidonias niger), an imperiled and declining species throughout much of North America. We used Google Earth^® images and National Wetlands Inventory maps to rank 390 candidate wetlands throughout Wisconsin (USA) according to their apparent suitability as nesting habitat for black terns and quantified habitat features associated with the suitability rankings. We then conducted ground-based suitability assessments and point counts of terns at most wetlands from May to July 2010. Pre-survey assessment resulted in 123 wetlands classified as suitable, 81 as marginal, and 186 as unsuitable. Wetlands ranked as suitable were more likely to be in the hemi-marsh stage, part of a wetland complex and relatively undisturbed. Black terns were present at 47 % of the wetlands considered suitable but only 11 % of the sites considered marginal or unsuitable. Of the 42 sites where nesting was confirmed, 79 % were at wetlands classified as suitable; no nesting was recorded in any wetlands deemed unsuitable. We found strong concordance in wetland suitability rankings between the two assessment methods (remote sensing, site surveys). We propose that remote sensing is an efficient and inexpensive way to predict site occupancy by wetland birds, such as black terns, that prefer a specific kind of habitat discernible from aerial imagery. This method may be particularly useful in areas, such as the Prairie Pothole region of North America, where ground surveys of all wetlands are not feasible.     

Integrating species distribution models and interacting particle systems to predict the spread of an invasive alien plant

Aim We demonstrate how to integrate two widely used tools for modelling the spread of invasive plants, and compare the performance of the combined model with that of its individual components using the recent range dynamics of the invasive annual weed Ambrosia artemisiifolia L. Location Austria. Methods Species distribution models, which deliver habitat‐based information on potential distributions, and interacting particle systems, which simulate spatio‐temporal range dynamics as dependent on neighbourhood configurations, were combined into a common framework. We then used the combined model to simulate the invasion of A. artemisiifolia in Austria between 1990 and 2005. For comparison, simulations were also performed with models that accounted only for habitat suitability or neighbourhood configurations. The fit of the three models to the data was assessed by likelihood ratio tests, and simulated invasion patterns were evaluated against observed ones in terms of predictive discrimination ability (area under the receiver operating characteristic curve, AUC) and spatial autocorrelation (Moran’s I). Results The combined model fitted the data significantly better than the single‐component alternatives. Simulations relying solely on parameterized spread kernels performed worst in terms of both AUC and spatial pattern formation. Simulations based only on habitat information correctly predicted infestation of susceptible areas but reproduced the autocorrelated patterns of A. artemisiifolia expansion less adequately than did the integrated model. Main conclusions Our integrated modelling approach offers a flexible tool for forecasts of spatio‐temporal invasion patterns from landscape to regional scales. As a further advantage, scenarios of environmental change can be incorporated consistently by appropriately updating habitat suitability layers. Given the susceptibility of many alien plants, including A. artemisiifolia, to both land use and climate changes, taking such scenarios into account will increasingly become relevant for the design of proactive management strategies.     

物种分布模型理论研究进展

利用物种分布模型估计物种的真实和潜在分布区,已成为区域生态学与生物地理学中非常活跃的研究领域。然而,到目前为止,这项技术的理论基础仍然存在不足之处,一些关键的生态过程未能被有效纳入到物种分布模型的理论框架中,从而为解释物种分布模型预测的结果带来了诸多困惑。鉴于此,总结了物种分布模型的理论基础;系统探讨了物种分布模型与物种分布区的关系;特别指出了物种分布模型研究中存在的理论问题;重点阐述了物种分布模型未来的发展方向。研究认为,物种分布模型与生态位理论、源-库理论、种群动态理论、集合种群理论、进化理论等具有重要的联系;正确理解物种分布模型的预测结果与物种分布区的关系,有赖于对影响物种分布的3个主要因素(环境条件、物种相互作用与物种迁移能力)做出定量的分离;目前物种分布模型主要存在的问题是未能将物种的相互作用和物种的迁移能力有效纳入到模型的构建过程中;未来物种分布模型的发展应该加强模型背后理论框架的研究,并进一步加强整合物种相互作用过程、种群动态过程、迁移过程和物种进化过程等内容。研究还认为,从更高的理论层次模拟功能群和群落结构将是未来物种分布模型的重要发展方向。     

江苏省主要农田杂草种子库物种组成和多样性及其与环境因子的相关性分析

采用水洗镜检法对江苏省31个农田样点(包括旱田和水田)0～15 cm土层土壤杂草种子库的种类组成和物种多样性进行了调查研究;采用典范对应法分析了杂草种子库种类与环境因子(包括淹水天数、土壤有机质含量、土壤pH、年降水量、年均温、样点经度和样点纬度)的相关性并绘制了样点和种类与环境因子的二维排序散点图.调查结果表明:在31个样点的土壤杂草种子库中共检测到杂草种子15科54种,旱田和水田各有41和45种,二者共有种类占多数但优势种有差异,通泉草[ Mazus japonicus (Thunb.) Kuntze]、异型莎草(Cyperus difformis L.)、水苋菜(Ammannia baccifera L.)、千金子[Leptochloa chinensis (L.) Nees]、棒头革(Polypogon fugax Nees ex Steud.)和牛繁缕[ Malachium aquaticum (L.) Fries]等种类为二者的共有优势种;杂草种类最多的为禾本科(Gramineae)和莎草科(Cyperaceae),分别占种类总数的22.6％和20.8％.旱田不同样点杂草种子库的优势种类变化较大,而水田杂草种子库优势种较稳定;二者优势种频度差异较大,旱田中频度高于0.30的杂草有19种,水田中频度高于0.50的杂草有20种;旱田和水田中平均重要值大于0.03的杂草各有11和9种,这些频度高的种类重要值也较大.旱田和水田土壤种子库种子密度分别为21 015和37 847 m-2,平均为31 008 m-2;旱田3层土壤中种子密度差异不显著,而水田上、中层土壤的种子密度显著高于下层.旱田以夏熟和秋熟杂草为主,而水田则以水田和夏熟杂草为主.按形态类型划分,水田及旱田中杂草种类数和密度从大到小均依次排序为阔叶草类、禾草类、莎草类,且水田中这3类杂草的种类数和种子密度均高于旱田.与旱田相比,水田杂草种子库的物种丰富度指数(S)、Shannon-Wiener 指数(H')和Simpson指数(D)较高,但Pielou均匀度指数(E)较低;旱田杂草种子库的S、H'和D指数随土层深度增加而降低、E指数逐渐升高,水田各土层的物种多样性指数则无明显变化趋势.第1种类排序轴与淹水天数负相关性最高(R=-0.8143),第2种类排序轴与年降水量和经度也有较高的负相关性;相关性分析和CCA分析结果均表明淹水天数是影响杂草种子库群落构成的最大因素.通过二维排序可将31个样点分为旱田和水田2大类,旱田可划分为长期旱连作和水旱轮作2个亚类;水田可划分为淮河以北地区和淮河以南长江流域地区2个亚类.研究结果说明:杂草种子库潜群落优势种与地上部农田杂草显群落优势种具有一致性,通过土壤杂草种子库的研究可以预测地上杂草的发生和危害情况.     

Determining the factors affecting the distribution of Muscari latifolium,an endemic plant of Turkey,and a mapping species distribution model

Species distribution modeling was used to determine factors among the large predictor candidate data set that affect the distribution of Muscari latifolium , an endemic bulbous plant species of Turkey, to quantify the relative importance of each factor and make a potential spatial distribution map of M. latifolium . Models were built using the Boosted Regression Trees method based on 35 presence and 70 absence records obtained through field sampling in the Gönen Dam watershed area of the Kazda?? Mountains in West Anatolia. Large candidate variables of monthly and seasonal climate, fine‐scale land surface, and geologic and biotic variables were simplified using a BRT simplifying procedure. Analyses performed on these resources, direct and indirect variables showed that there were 14 main factors that influence the species’ distribution. Five of the 14 most important variables influencing the distribution of the species are bedrock type, Quercus cerris density, precipitation during the wettest month, Pinus nigra density, and northness. These variables account for approximately 60% of the relative importance for determining the distribution of the species. Prediction performance was assessed by 10 random subsample data sets and gave a maximum the area under a receiver operating characteristic curve (AUC) value of 0.93 and an average AUC value of 0.8. This study provides a significant contribution to the knowledge of the habitat requirements and ecological characteristics of this species. The distribution of this species is explained by a combination of biotic and abiotic factors. Hence, using biotic interaction and fine‐scale land surface variables in species distribution models improved the accuracy and precision of the model. The knowledge of the relationships between distribution patterns and environmental factors and biotic interaction of M. latifolium can help develop a management and conservation strategy for this species.     

Sex-specific differences and long-term trends in habitat selection of American woodcock

Effective wildlife management requires an understanding of how individuals select environmental factors, although few studies assess how habitat selection may differ over time or between sexes. During the post-breeding period (15 May to 1 Sep), we tracked 146 male American woodcock (Scolopax minor) in Rhode Island, USA, from 2010–2021 to assess how habitat selection varied over time, and 17 females and 51 males during the final 2 years of the study to document sex-specific differences in habitat selection. Males generally had smaller home ranges (35.0 ± 10.7 [margin of error] ha) and preferred habitat mosaics that consisted of forested wetlands, young forest patches, areas of deciduous forest, moist soils with gentle slopes, and riparian corridors. We detected subtle differences between sexes in selection for wetland young forest, upland young forest, percent slope, distance to upland young forest, distance to streams, and distance to moist soils. During 2020–2021, females tended to have larger home ranges (78.7 ± 46.4 ha) than males (35.0 ± 10.7 ha) and more strongly selected sites closer to riparian corridors, while males selected areas that were closer to upland young forest with flatter slopes than the available surrounding landscape. Such sex-specific differences in habitat selection may be related to males and females prospecting for potential breeding sites during this post-breeding period for the following spring. We used the top-ranked habitat selection models for males and females to produce a spatially explicit state-wide map that identifies low-to-high likelihood of use areas that can be used to guide forest management decisions in southern New England to maximize benefits for American woodcock.     

Linking biotic homogenization to habitat type, invasiveness and growth form of naturalized alien plants in North America

Aim Biotic homogenization is a growing phenomenon and has recently attracted much attention. Here, we analyse a large dataset of native and alien plants in North America to examine whether biotic homogenization is related to several ecological and biological attributes. Location North America (north of Mexico). Methods We assembled species lists of native and alien vascular plants for each of the 64 state‐ and province‐level geographical units in North America. Each alien species was characterized with respect to habitat (wetland versus upland), invasiveness (invasive versus non‐invasive), life cycle (annual/biennial versus perennial) and habit (herbaceous versus woody). We calculated a Jaccard similarity index separately for native, for alien, and for native and alien species. We used the average of Jaccard dissimilarity index (1 ? Jaccard index) of all paired localities as a measure of the mean beta diversity of alien species for each set of localities examined in an analysis. We used a homogenization index to quantify the effect of homogenization or differentiation. Results We found that (1) wetland, invasive, annual/biennial and herbaceous alien plants markedly homogenized the state‐level floras whereas non‐invasive and woody alien plants tended to differentiate the floras; (2) beta diversity was significantly lower for wetland, invasive, annual/biennial and herbaceous alien plants than their counterparts (i.e. upland, non‐invasive, perennial and woody alien plants, respectively); and (3) upland and perennial alien plants each played an equal role in homogenizing and differentiating the state‐level floras. Main conclusions Our study shows that biotic homogenization is clearly related to habitat type (e.g. wetland versus uplands), species invasiveness and life‐history traits such as life cycle (e.g. annual/biennial and herbaceous versus woody species) at the spatial scale examined. These observations help to understand the process of biotic homogenization resulting from alien vascular plants in North America.     

Evaluating strategies for facilitating native plant establishment in northern Nevada crested wheatgrass seedings

Non‐native crested wheatgrasses (Agropyron cristatum and A. desertorum) were used historically within the Great Basin for the purpose of competing with weed species and increasing livestock forage. These species continue to be used in some areas, especially after wildfires occurring in low elevation/precipitation, formerly Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis)/herbaceous communities. Seeding native species in these sites is often unsuccessful, and lack of establishment results in invasion and site dominance by exotic annuals. However, crested wheatgrass often forms dense monocultures that interfere competitively with the establishment of desirable native vegetation and do not provide the plant structure and habitat diversity for wildlife species equivalent to native‐dominated sagebrush plant communities. During a 5‐year study, we conducted trials to evaluate chemical and mechanical methods for reducing crested wheatgrass and the effectiveness of seeding native species into these sites after crested wheatgrass suppression. We determined that discing treatments were ineffective in reducing crested wheatgrass cover and even increased crested wheatgrass density in some cases. Glyphosate treatments initially reduced crested wheatgrass cover, but weeds increased in many treated plots and seeded species diminished over time as crested wheatgrass recovered. We concluded that, although increases in native species could possibly be obtained by repeating crested wheatgrass control treatments, reducing crested wheatgrass opens a window for invasion by exotic weed species.     

Biogeographical comparison of the arthropod herbivore communities associated with Lepidium draba in its native, expanded and introduced ranges

Aim To examine the composition and structure of the arthropod community on the invasive weed Lepidium draba in its native, expanded and introduced ranges, in order to elucidate the lack of a biotic constraint that may facilitate invasion. Location Europe and western North America. Methods Identical sampling protocols were used to collect data from a total of 35 populations of L. draba in its native (Eastern European), expanded (Western European) and introduced (western US) ranges. A bootstrapping analysis was used to compare herbivore richness, diversity and evenness among the regions. Core species groups (monophages, oligophages and polyphages) on the plant were defined and their abundances and host utilization patterns described. Results Species richness was greatest in the native range, while species diversity and evenness were similar in the native and expanded range, but significantly greater than in the introduced range of L. draba. Specialist herbivore abundance was greater in the native and expanded compared with the introduced range. Oligophagous Brassicaceae‐feeders were equally abundant in all three ranges, and polyphagous herbivore abundance was significantly greater in the introduced range. Overall herbivore abundance was greater in the introduced range. Host utilization was more complete in the two European ranges due to monophagous herbivores that do not exist in the introduced range. Root feeders and gall formers were completely absent from the introduced range, which was dominated by generalist sap‐sucking herbivores. However, one indigenous stem‐mining weevil, Ceutorhynchus americanus, occurred on L. draba in the introduced range. Main conclusions This is, to our knowledge, the first study documenting greater herbivore abundance on an invasive weed in its introduced, compared with its native, range. However, greater abundance does not necessarily translate to greater impact. We argue that, despite the greater total herbivore abundance in the introduced range, differences in the herbivore community structure (specialist vs. generalist herbivory) may contribute to the invasion success of L. draba in the western USA.     

Sea‐level rise,habitat loss,and potential extirpation of a salt marsh specialist bird in urbanized landscapes

Sea‐level rise (SLR) impacts on intertidal habitat depend on coastal topology, accretion, and constraints from surrounding development. Such habitat changes might affect species like Belding's savannah sparrows (Passerculus sandwichensis beldingi; BSSP), which live in high‐elevation salt marsh in the Southern California Bight. To predict how BSSP habitat might change under various SLR scenarios, we first constructed a suitability model by matching bird observations with elevation. We then mapped current BSSP breeding and foraging habitat at six estuarine sites by applying the elevation‐suitability model to digital elevation models. To estimate changes in digital elevation models under different SLR scenarios, we used a site‐specific, one‐dimensional elevation model (wetland accretion rate model of ecosystem resilience). We then applied our elevation‐suitability model to the projected digital elevation models. The resulting maps suggest that suitable breeding and foraging habitat could decline as increased inundation converts middle‐ and high‐elevation suitable habitat to mudflat and subtidal zones. As a result, the highest SLR scenario predicted that no suitable breeding or foraging habitat would remain at any site by 2100 and 2110. Removing development constraints to facilitate landward migration of high salt marsh, or redistributing dredge spoils to replace submerged habitat, might create future high salt marsh habitat, thereby reducing extirpation risk for BSSP in southern California.     

Shorebird Abundance Estimates in Interior Alaska

Interior Alaska, USA, is the least-studied region in Alaska for breeding shorebirds because of challenging accessibility and expectations of low densities and abundances. We estimated lowland and upland shorebird population sizes on 370,420 ha of military lands in interior Alaska boreal forest from May–July 2016 and 2017. We modified the Program for Regional and International Shorebird Monitoring (PRISM) protocol used elsewhere in Alaska and incorporated a probability-based sampling design and dependent double-observer methods. We pooled all lowland shorebird and all upland shorebird observations and estimated abundance using Huggins closed captures models in Program MARK. Estimated abundances of all lowland and upland shorebirds were 42,239 ± 13,431 (SE) and 3,523 ± 494, respectively. The survey area is important for shorebirds in Alaska. We estimate that military lands in interior Alaska support 45,762 ± 13,925 shorebirds, including 7 species of conservation concern. Higher abundance of lowland shorebirds was best explained by lower elevation, lower percent scrub canopy, and higher percent water on plots. Higher abundance of upland shorebirds was best explained by higher elevation and increased distance to wetland. Our modified Arctic PRISM protocol was effective for surveys in the boreal forest and we recommend continued use of method modifications for future shorebird surveys in boreal forests. Identifying baseline abundances of shorebirds using interior Alaska is an important step in monitoring distributional shifts and potential future population declines. © 2020 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.     

Exploring invasibility with species distribution modeling: How does fire promote cheatgrass (Bromus tectorum) invasion within lower montane forests?

Aim

Cheatgrass (Bromus tectorum) is notorious for creating positive feedbacks that facilitate vegetation type conversion within sagebrush steppe ecosystems in the western United States. Similar dynamics may exist in adjacent lower montane forest. However, fire‐forest‐cheatgrass dynamics have not been examined. We used species distribution modeling to answer three questions about fire and invasibility in lower montane forests: (Q1) Does fire create more suitable habitat for cheatgrass? (Q2) If so, which site attributes are altered to increase site suitability? (Q3) Does fire increase connectivity among suitable habitat and enhance spread?

Location

Shoshone National Forest, Wyoming, USA.

Methods

We measured cheatgrass presence–absence in 93 plots within Interior Douglas‐fir (Pseudotsuga menziesii var. glauca) forests. Random Forests predicted cheatgrass distribution with and without fire using nine site attributes: elevation, slope, aspect, solar radiation, annual precipitation, maximum temperature in July, minimum temperature in January, forest canopy cover and distance to nearest trail or road. Additionally, invasion pathways and spread were mapped using Circuitscape.

Results

Cheatgrass distribution was controlled by topographic and climate variables in the absence of fire. In particular, cheatgrass was most likely to occur at low elevation along dry, south‐ and east‐facing slopes. High‐severity fire increased potential cheatgrass distribution when forest canopy cover was reduced to below 30%. This process created new invasion pathways, which enhanced cheatgrass spread when modelled in Circuitscape.

Main conclusions

Our study showed that in the absence of fire, drier south‐ and east‐facing slopes at low elevation are most susceptible to cheatgrass invasion. However, high‐severity fire increased the total area susceptible to invasion—allowing cheatgrass to expand into previously unsuitable sites within lower montane forests in the western United States. These results are important for present day management and reflect that integrating responses to disturbance in species distribution models can be critical for making predictions about dynamically changing systems.

     

The vulnerability of habitats to plant invasion: disentangling the roles of propagule pressure,time and sampling effort

Aim To quantify the vulnerability of habitats to invasion by alien plants having accounted for the effects of propagule pressure, time and sampling effort. Location New Zealand. Methods We used spatial, temporal and habitat information taken from 9297 herbarium records of 301 alien plant species to examine the vulnerability of 11 terrestrial habitats to plant invasions. A null model that randomized species records across habitats was used to account for variation in sampling effort and to derive a relative measure of invasion based either on all records for a species or only its first record. The relative level of invasion was related to the average distance of each habitat from the nearest conurbation, which was used as a proxy for propagule pressure. The habitat in which a species was first recorded was compared to the habitats encountered for all records of that species to determine whether the initial habitat could predict subsequent habitat occupancy. Results Variation in sampling effort in space and time significantly masked the underlying vulnerability of habitats to plant invasions. Distance from the nearest conurbation had little effect on the relative level of invasion in each habitat, but the number of first records of each species significantly declined with increasing distance. While Urban, Streamside and Coastal habitats were over‐represented as sites of initial invasion, there was no evidence of major invasion hotspots from which alien plants might subsequently spread. Rather, the data suggest that certain habitats (especially Roadsides) readily accumulate alien plants from other habitats. Main conclusions Herbarium records combined with a suitable null model provide a powerful tool for assessing the relative vulnerability of habitats to plant invasion. The first records of alien plants tend to be found near conurbations, but this pattern disappears with subsequent spread. Regardless of the habitat where a species was first recorded, ultimately most alien plants spread to Roadside and Sparse habitats. This information suggests that such habitats may be useful targets for weed surveillance and monitoring.     

Potential distribution of the critically endangered dragonfly Libellula angelina (Odonata: Libellulidae) under shared socio-economic pathways

Libellula angelina is an endangered dragonfly species that is native to East Asia. Recently, their population has become severely reduced through habitat loss. To protect L. angelina populations, we need to understand which factors determine their distribution and how their potential habitats will change in the future. In this study, the habitat preference of L. angelina was identified through field surveys, and the potential distribution of L. angelina and the impact of integrated climate–land cover changes were simulated using the MaxEnt model. Furthermore, the wetland loss scenario was applied to areas where the current trend in wetland loss will continue in the future. The field survey identified that L. angelina prefers small inland wetlands: permanent freshwater, ponds; permanent rivers, ponds; irrigated land; and estuarine waters. From the MaxEnt results, altitude was the variable with the greatest contribution and distance from wetlands was the most unique variable. MaxEnt described the geographic pattern of occurrences under the current climate well, with few areas requiring any further survey. In the future projection, the potential habitat area was increased by up to 48.8% and 30.6% in the 2050s and 2080s, respectively. However, potential habitat loss was expected if wetlands continue to decline as they have done in the last 20 years. The wetland loss scenario resulted in potential habitat losses of 1.9%–2.3% and 4.5%–6.1% in the 2050s and 2080s, respectively. Therefore, to protect L. angelina populations we must minimize the loss of current populations, secure wetlands and strengthen the connectivity between wetlands.     

Modelling species distribution in complex environments: an evaluation of predictive ability and reliability in five shorebird species

Aim  Many wader populations around the world are declining as a consequence of habitat degradation or loss. It is therefore important to identify species-specific habitat demands accurately and to define the important factors explaining species distribution, in order to develop tools that can be used in conservation planning. The aim of this study is to create reliable, functional and ecologically interpretable predictive distribution models for five breeding wader species.
Location  The archipelago of SW Finland in the Baltic Sea.
Methods  We used multivariate adaptive regression splines (MARS) to create single-species and multiresponse distribution models based on 525 study islands and 12 abiotic and biotic environmental variables. Model evaluation was carried out on independent data not used in model building (100 + 116 islands). The models were tested for discrimination with receiver-operating characteristic statistics and for calibration with Millers calibration statistics (MCS).
Results  The single-species models for the turnstone ( Arenaria interpres ), redshank ( Tringa totanus ) and oystercatcher ( Haematopus ostralegus ) showed good predictive abilities, regarding both discrimination and calibration, when evaluated on independent data. The multiresponse models for the less prevalent species, common sandpiper ( Actitis hypoleucos ) and the common ringed plover ( Charadrius hiaticula ) had better discriminative abilities than the single-species models. The most influential predictor overall was occurrence of small larids. Exposure, area of forest and low and flat areas were also important, as well as shore habitats.
Main conclusions  We found that the ability of MARS to fit non-linear and multiresponse models makes it a useful method to quantitatively relate species occurrence to environmental characteristics of a complex environment.