The worldwide airline network and the dispersal of exotic species: 2007–2010

International air travel has played a significant role in driving recent increases in the rates of biological invasion and spread of infectious diseases. By providing high speed, busy transport links between spatially distant, but climatically similar regions of the world, the worldwide airline network (WAN) increases the risks of deliberate or accidental movements and establishment of climatically sensitive exotic organisms. With traffic levels continuing to rise and climates changing regionally, these risks will vary, both seasonally and year-by-year. Here, detailed estimates of air traffic trends and climate changes for the period 2007-2010 are used to examine the likely directions and magnitudes of changes in climatically sensitive organism invasion risk across the WAN. Analysis of over 144 million flights from 2007-2010 shows that by 2010, the WAN is likely to change little overall in terms of connecting regions with similar climates, but anticipated increases in traffic and local variations in climatic changes should increase the risks of exotic species movement on the WAN and establishment in new areas. These overall shifts mask spatially and temporally heterogenous changes across the WAN, where, for example, traffic increases and climatic convergence by July 2010 between parts of China and northern Europe and North America raise the likelihood of exotic species invasions, whereas anticipated climatic shifts may actually reduce invasion risks into much of eastern Europe.     

Multi-scale assessment of macroinvertebrate richness and composition in Mediterranean-climate rivers

1. Similar constraints in distant, but climatically comparable, regions may be expected to yield biotic assemblages with similar attributes. Environmental factors that constrain communities at smaller scales, however, may be different between climatically similar regions. Thus, patterns observed at large scales may differ from those detected at small scales, and international comparisons should be focussed at multiple scales. 2. Mediterranean‐climate regions (MCRs) are characterized by remarkable seasonal variability in precipitation and temperature. Accordingly, rivers in these regions have seasonal and predictable floods and droughts, and temporary reaches are frequent. Present in six geographical regions of the world, MCRs have similar environmental constraints and are ideal for testing intercontinental similarities between macroinvertebrate communities. 3. We examined aquatic macroinvertebrate taxon richness and composition in MCRs at three scales: regional, reach and macrohabitat. At the regional scale, the Mediterranean Basin had the highest taxon richness at family level, and southwestern Australia the lowest. Taxonomic composition showed c. 85% similarity between the northern hemisphere MCRs of California and the Mediterranean Basin, which were followed in similarity by South Africa. The two Australian MCRs (South west and South) showed a similarity to each other of about 70% whereas the Chilean fauna was the most distinct. 4. At the reach scale, taxon richness was not significantly different between permanent and temporary reaches in any MCR, whereas taxonomic composition was significantly different among northern hemisphere MCRs. At the macrohabitat scale, taxon richness was not significantly different between lotic and lentic macrohabitats within any of the MCRs, but differences in macroinvertebrate communities were found between macrohabitats when considering regions. 5. Our results show that the strength of similarity between distant but climatically similar regions is scale‐dependent, being highest at the macrohabitat scale. Although the similarities in richness and composition at the macrohabitat scale are presumed to be universal, the seasonal predictability of drought in MCRs is expected to result in characteristic macroinvertebrate responses at the reach scale. We suggest, however, that regional evolutionary history and environmental characteristics may override this general pattern of a similar response of MCRs at different scales. The Mediterranean Basin and California, having similar historical and environmental condition, thus appeared as the most similar MCRs at all scales.     

Is phylogeography helpful for invasive species risk assessment? The case study of the bark beetle genus Dendroctonus

Despite evidence that conspecific lineages may display different climatic tolerances, most invasion risk assessment tools are calibrated without considering phylogeographic information. This study aims to investigate the existence of intraspecific niche divergence within a group of insect pests and to explore how the inclusion of phylogeographic information into species distribution models may alter the estimation of the potential distribution of a species. We studied North American bark beetles belonging to the genus Dendroctonus, a group of pests of conifers that are listed as quarantine species in numerous countries. Most Dendroctonus species exhibit strong genetic divergence that appears to be geographically structured and shaped by historical events and biotic factors. We modeled all lineage distributions within five species, using MaxEnt and Boosted Regression Trees, and compared the results with the models fitted at the species scale. Multivariate analysis and niche similarity and equivalency tests were additionally performed to investigate the existence and magnitude of climatic niche divergence between conspecific lineages. We also tested the ability of lineage‐based models to predict the region invaded by D. valens in China. Conspecific lineages showed a climatic niche more similar than expected by chance, but displayed different climatic envelopes in their native range and, consequently, different estimates of potential distributions. We also observed that classical models calibrated using the entire range of the species could potentially under‐ or overestimate the potential range of the species when compared to a global prediction built by aggregating lineage‐based projections. This study showed that the invasive phylogeographic lineage of D. valens has invaded regions characterized by climatic conditions highly similar to those encountered in its native range suggesting that preadaptations to environment might have played a role in this invasion. This study highlights how our perception of the invasion risk of pests may be altered when integrating phylogeographic information.     

Climate change effects on turtles of the genus Kinosternon (Testudines: Kinosternidae): an assessment of habitat suitability and climate niche conservatism

The Chelonian lineage has been exposed to several climate change events along its evolutionary history, but the rapid contemporary change in climate patterns has the potential to erode turtle populations. This study focuses on (1) evaluating the climatically suitable area available for 15 species of mud turtles of the genus Kinosternon, and on (2) assessing whether or not these species retain their ancestral climate niche. Occurrence data was collected for these species and, using the Maxent algorithm and WorldClim bioclimatic variables, suitable present and future climatic niche areas were modeled. In addition, we also carried out climatic niche similarity analyses between pairs of species to evaluate whether these conserve their climatic niche. Our models suggest that most species of Kinosternon will lose a high proportion of their suitable habitat in the future. Most mud turtle species seem to conserve their climatic niche, suggesting the prevalence of niche conservatism in the group. Our results indicate that several mud turtle species could be at severe risk of disappearing over the next few decades due to the loss of climatically suitable areas and of the conservation of their climatic niches.

     

Home away from home — objective mapping of high-risk source areas for plant introductions

Prevention is the best way to slow the escalation of problems associated with biological invasions. Screening of potential introductions is widely applied for assessing the risk of species becoming invasive. Despite advances in the understanding of the determinants of invasiveness, screening still relies heavily on assessments of the potential of species to ‘fit in’ to the broad environmental conditions of a target region. Most screening systems ask whether species are native to, or are known to be naturalized or invasive in, regions with ‘similar’ climatic/environmental conditions to the target region. The level of similarity required to make the species a high‐risk introduction is generally not specified. This paper describes a protocol for making such assessments more objective, using South Africa as a test case. Using nonparametric niche‐based modelling (generalized additive model; GAM) calibrated on the current distribution of each South African biome, we mapped regions of the world that are climatically similar to South African biomes. Lists were produced of countries with the largest areas climatically similar to South Africa overall, and to each biome separately. Validation of the usefulness of the approach was sought by evaluating whether the main invasive plant species in South African biomes occur naturally, or have adventive ranges, in regions mapped as analogous to South African biomes. A very large part of the world is climatically similar to South Africa, with eight countries having larger areas of land classified as climatically similar to South African biomes than the total area of South Africa. Almost all the most prominent invasive species in South African biomes occur naturally or are invasive outside their natural range in areas with similar climates to those that occur in parts of South Africa. This confirms the value of objective climate matching in screening protocols. We examined climatic conditions for a representative sample of major invasive plants from other parts of the world. The analysis identified several species that are already invasive in regions that have matched climates in South Africa but that are not yet introduced or, if already present, have not yet invaded large areas. For example, the following known invasive species should be considered high‐risk species in South African grasslands: Alliaria petiolata, Cytisus scoparius, Gleditsia triacanthos, Heracleum mantegazzianum, Hieracium pilosella, Juniperus communis, Pinus contorta, P. monticola, P. ponderosa, P. sylvestris, Prunus laurcerasus, and P. serotina. Objectively matched climatic regions are also useful as a first‐cut assessment when evaluating species with no invasive history.     

Climate change increases risk of plant invasion in the Eastern United States

Invasive plant species threaten native ecosystems, natural resources, and managed lands worldwide. Climate change may increase risk from invasive plant species as favorable climate conditions allow invaders to expand into new ranges. Here, we use bioclimatic envelope modeling to assess current climatic habitat, or lands climatically suitable for invasion, for three of the most dominant and aggressive invasive plants in the southeast United States: kudzu (Pueraria lobata), privet (Ligustrum sinense; L. vulgare), and cogongrass (Imperata cylindrica). We define climatic habitat using both the Maxent and Mahalanobis distance methodologies, and we define the best climatic predictors based on variables that best ‘constrain’ species distributions and variables that ‘release’ the most land area if excluded. We then use an ensemble of 12 atmosphere-ocean general circulation models to project changes in climatic habitat for the three invasive species by 2100. The combined methodologies, predictors, and models produce a robust assessment of invasion risk inclusive of many of the approaches typically used individually to assess climate change impacts. Current invasion risk is widespread in southeastern states for all three species, although cogongrass invasion risk is more restricted to the Gulf Coast. Climate change is likely to enable all three species to greatly expand their ranges. Risk from privet and kudzu expands north into Ohio, Pennsylvania, New York, and New England states by 2100. Risk from cogongrass expands as far north as Kentucky and Virginia. Heightened surveillance and prompt eradication of small pockets of invasion in northern states should be a management priority.     

An intercontinental comparison of dung beetle diversity between two mediterranean-climatic regions: local versus regional and historical influences

The species richness of biological communities is influenced by both local ecological, regional ecological, and historical factors. The relative importance of these factors may be deduced by comparison between communities in climatically and ecologically equivalent, but geographically and historically separate regions of the world. This claim is based on the hypothesis that community processes driven by similar local ecological factors lead to convergence in species richness whereas those driven by differing regional or historical factors lead to divergence. An intercontinental comparison between the winter rainfall regions of South Africa and the Iberian Peninsula showed that overall species richness of dung beetles was dissimilar at local, subregional and regional scales in Scarabaeidae s. str. but similar at all scales in Aphodiinae. Removal of species widespread in the summer rainfall region of Africa or the temperate region of Europe (regional component) resulted in dissimilarity in species richness of mediterranean endemics at all scales in both dung beetle taxa. However, the lines joining each set of species richness values were parallel which may indicate similarities in processes between different mediterranean climatic regions despite slight differences in latitudinal range. The dominant pattern of dissimilarity or non-convergence may be related primarily to intercontinental differences in regional biogeographical and evolutionary history (faunal dispersal, glaciation effects in relation to geographical barriers to dispersal, speciation history, long-term disturbance history). The limited pattern of similarity or convergence in overall species richness of Aphodiinae may be a chance result or primarily related to intercontinental similarities in local ecological factors.     

Potential impact of climatic change on the distribution of forest herbs in Europe

The aim of this study is to evaluate the possible consequences of climate change on a representative sample of forest herbs in Europe. A fuzzy climatic envelope was used to predict the location of suitable climatic conditions under two climatic change scenarios. Expected consequences in terms of lost and gained range size and shift in distribution for 26 forest herbs were estimated. These results were combined in an Index of Predicted Range Change for each species. Finally, the effects of habitat fragmentation for potential dispersal routes were evaluated and options for management on a European scale are discussed. Generally, a good agreement of the estimated suitability under the present climate and the observed current distribution was observed. However, species vary a lot in the degree to which they occupy the presently climatically suitable areas in Europe. Many species are absent from large areas with suitable climate and thus could be said to have poor range‐filling capacity. A general change in location (range centroid) of the total suitable area was observed: The total suitable area will on average move strongly northwards and moderately eastwards under the relatively mild B1 scenario and more strongly so under the A2 scenario. The required average minimum migration rate per year to track the potential range shift is 2.1 km under the B1 scenario and 3.9 km under the A2 scenario. Moderate losses in the total suitable area in Europe are predicted for most species under both scenarios. However, the predicted changes are very variable, with one species (Actaea erythrocarpa) experiencing total range elimination in Europe (A2 scenario) while the total suitable area is predicted to show large increases for other species. The species that are predicted to experience the greatest proportional losses in their climatically suitable area within their presently realised range tend to have northern or eastern range centroids. The Index of Predicted Range Change roughly divides the species studied in four groups: One species face a high risk of extinction; eight species are expected to experience moderate to severe threat of extinction; 11 species are not considered at risk and, finally, six species may actually benefit from global warming. An analysis of potential migration routes shows the importance of maintaining and, if possible, improving the network of forest throughout Europe to make migration possible. It is also suggested to closely monitor the status of boreal and subalpine species that are most threatened by global warming. Finally it is recommended that special concern should be given to increased protection and restoration of forest habitats in southern montane areas for their crucial long‐term importance for the maintenance of European plant diversity.     

Evidence of climatic niche shift during biological invasion

Niche-based models calibrated in the native range by relating species observations to climatic variables are commonly used to predict the potential spatial extent of species' invasion. This climate matching approach relies on the assumption that invasive species conserve their climatic niche in the invaded ranges. We test this assumption by analysing the climatic niche spaces of Spotted Knapweed in western North America and Europe. We show with robust cross-continental data that a shift of the observed climatic niche occurred between native and non-native ranges, providing the first empirical evidence that an invasive species can occupy climatically distinct niche spaces following its introduction into a new area. The models fail to predict the current invaded distribution, but correctly predict areas of introduction. Climate matching is thus a useful approach to identify areas at risk of introduction and establishment of newly or not-yet-introduced neophytes, but may not predict the full extent of invasions.     

Genetic Diversity of Algal Viruses Which Lyse the Photosynthetic Picoflagellate Micromonas pusilla (Prasinophyceae)

The genetic similarity among eight clones of Micromonas pusilla virus (MpV) isolated from five geographic locations was measured by DNA hybridization. Our objective was to explore the existence of genetically distinct populations of MpV by comparing the similarity among MpVs isolated from a single water sample to the similarity among viruses isolated from geographically distant locations. The highest and lowest similarities we observed were 70% (plusmn) 1.1% (mean (plusmn) standard error [SE], n = 3) for virus strains SP1 and SP2 isolated from a California coastal water sample and 13% (plusmn) 1.9% for strains SP2 and PB6; the latter was isolated from New York estuarine water. However, the similarity between MpV isolated from a single water sample was not always greater than the similarity between viruses isolated from different locations. Viruses PB7 and PB8 were isolated from a single New York estuarine sample but were only 16% (plusmn) 0.5% similar, whereas PB7 was quite similar (43% (plusmn) 2.9%) to PL1, a virus from Texas coastal water. Overall, the similarity among MpVs isolated from a single geographic location, 34% (plusmn) 12.6% (mean (plusmn) SE, n = 4), was not significantly different from the similarity among MpVs isolated from geographically distant locations, 26.6% (plusmn) 2.7% (mean (plusmn) SE, n = 24) (P = 0.92, Mann-Whitney U test). Clones of MpV were more similar to each other than they were to the related algal virus PBCV-1, and three groups of MpVs consisting of (i) PL1, SG1, PB6, and PB7, (ii) PB8, and (iii) GM1, SP1, and SP2 were resolved. The genetic variation among MpVs isolated from a single water sample was as large as the variation between viruses isolated from different oceans. If MpVs within a geographic location share genetic characteristics not shared with MpVs from geographically distant locations, this was not reflected in the overall similarity of their genomes.     

Rapid climate‐driven loss of breeding habitat for Arctic migratory birds

Millions of birds migrate to and from the Arctic each year, but rapid climate change in the High North could strongly affect where species are able to breed, disrupting migratory connections globally. We modelled the climatically suitable breeding conditions of 24 Arctic specialist shorebirds and projected them to 2070 and to the mid‐Holocene climatic optimum, the world's last major warming event ~6000 years ago. We show that climatically suitable breeding conditions could shift, contract and decline over the next 70 years, with 66–83% of species losing the majority of currently suitable area. This exceeds, in rate and magnitude, the impact of the mid‐Holocene climatic optimum. Suitable climatic conditions are predicted to decline acutely in the most species rich region, Beringia (western Alaska and eastern Russia), and become concentrated in the Eurasian and Canadian Arctic islands. These predicted spatial shifts of breeding grounds could affect the species composition of the world's major flyways. Encouragingly, protected area coverage of current and future climatically suitable breeding conditions generally meets target levels; however, there is a lack of protected areas within the Canadian Arctic where resource exploitation is a growing threat. Given that already there are rapid declines of many populations of Arctic migratory birds, our results emphasize the urgency of mitigating climate change and protecting Arctic biodiversity.     

Utility of the CLIMEX ‘match climates regional’ algorithm for pest risk analysis: an evaluation with non-native ants in New Zealand

Pest risk analysts frequently ask if the climate of a pest risk analysis area could be suitable for the establishment of an organism of concern. Species distribution models can help to answer this question, but constructing them is technically complex, time consuming, and uninformative for additional non-modelled species. A quicker more broadly applicable approach involves using environmental distance metrics, including climate matching algorithms such as the ‘match climates regional’ function of CLIMEX (CLIMEX-MCR), to generate indices of climatic similarity between different locations without reference to particular species. Several studies have shown that various environmental distance metrics can provide biologically meaningful results. However, the veracity of the CLIMEX-MCR algorithm remains unevaluated, despite its application in numerous published studies. We used CLIMEX-MCR and high resolution New Zealand climate data to measure climatic similarities between New Zealand and the rest of the world. We then tested the veracity of the climatic match estimates by evaluating if their predictions regarding the suitability of New Zealand’s climate for 43 non-native ant species corresponded with empirical observations of those species in New Zealand. Non-native ants that are, or were once, established outdoors in New Zealand had overseas distributions that were climatically well matched with New Zealand. In contrast, species that either are established only indoors in New Zealand, or were observed to temporarily nest outdoors then die in New Zealand, had overseas distributions that were poorly matched. Species that are frequently intercepted at New Zealand’s border, but are not established there, generally also had overseas distributions with low climatic similarities to New Zealand. We also measured climatic similarities between New Zealand’s 13 national parks and the rest of the world. The overseas distributions of the non-native ants showed poor climatic matches with New Zealand’s national parks, which was consistent with the absence of persistent outdoor non-native ant populations in those parks. Our results support the utility of CLIMEX-MCR algorithm for pest risk analysis.     

The non-native chironomid Eretmoptera murphyi in Antarctica: erosion of the barriers to invasion

Antarctica is the continent least affected by invasive species, but climate change and increasing human activity are increasing this threat. Antarctic terrestrial ecosystems generally have low biodiversity with simple community structures and little competition for resources. Consequently, species with pre-adaptations or capabilities that allow them to tolerate polar conditions may have disproportionately large ecosystem impacts when introduced to Antarctica compared with other regions of the Earth. Here we investigate the invasion risk associated with the flightless chironomid midge, Eretmoptera murphyi, which was accidentally introduced from South Georgia (54°S) to Signy Island, South Orkney Islands (61°S), probably during plant transplantation experiments in the 1960s. Larval size class distribution analysis indicated that E. murphyi has a 2 year life cycle on Signy Island, supporting previous suggestions. Estimates of litter turnover show that recent large increases in E. murphyi population density and extent are likely to increase nutrient cycling rates on Signy Island substantially. Existing physiological adaptations may allow E. murphyi to colonise higher latitude locations. Growth rate and microhabitat climatic modelling show that temperature constraints on larval development on Anchorage Island (68°S) are theoretically similar to those on Signy Island even though it is ~750 km further south. Establishment of this non-native midge at climatically similar intervening locations along the western Antarctic Peninsula is therefore plausible. Currently, lack of effective natural dispersal mechanisms is probably limiting the spread of the midge. However, dispersal to other areas of the Antarctic Peninsula may occur via human-assisted transportation, highlighting the importance of appropriate biosecurity measures.     

Leaf anatomy of Carex humilis does not correlate with orographic,geological and bioclimatic habitat conditions in C&SE Europe

This paper presents the results of a multivariate morphometric study of leaf anatomical characters in different, geographically very distant populations of taxon Carex humilis from Hungary, Romania, Serbia, Bosnia & Herzegovina, Montenegro and Albania with the aim to reveal the trends of population differentiation. Analyses were performed on the cross-section of 173 leaves collected from 12 populations. In order to establish the overall morphological variation and relationships between individuals from all populations, principal component analyses (PCA) and canonical discriminant analysis (CDA) have been done. The UPGMA clustering analyses based on leaf anatomical characters and habitat climatic characteristics were carried out to explore whether the observed anatomical differences are a result of adaptive responses. Regression analysis (linear regression) was performed to identify the level of correlation between leaf anatomical characters and basic orographic, geological, and bioclimatic habitat characteristics. Quite unexpectedly, most of observed groups are formed of geographically very distant populations which are living in extremely different climatic and geological conditions, indicating that general anatomical differentiation in Carex humilis in C&SE Europe cannot be explained by the environmental impacts, and basically do not represent an adaptive response to different climatic or geological condition.     

Predicting current and future biological invasions: both native and invaded ranges matter

The classical approach to predicting the geographical extent of species invasions consists of training models in the native range and projecting them in distinct, potentially invasible areas. However, recent studies have demonstrated that this approach could be hampered by a change of the realized climatic niche, allowing invasive species to spread into habitats in the invaded ranges that are climatically distinct from those occupied in the native range. We propose an alternative approach that involves fitting models with pooled data from all ranges. We show that this pooled approach improves prediction of the extent of invasion of spotted knapweed (Centaurea maculosa) in North America on models based solely on the European native range. Furthermore, it performs equally well on models based on the invaded range, while ensuring the inclusion of areas with similar climate to the European niche, where the species is likely to spread further. We then compare projections from these models for 2080 under a severe climate warming scenario. Projections from the pooled models show fewer areas of intermediate climatic suitability than projections from the native or invaded range models, suggesting a better consensus among modelling techniques and reduced uncertainty.     

A Global Airport-Based Risk Model for the Spread of Dengue Infection via the Air Transport Network

The number of travel-acquired dengue infections has seen a consistent global rise over the past decade. An increased volume of international passenger air traffic originating from regions with endemic dengue has contributed to a rise in the number of dengue cases in both areas of endemicity and elsewhere. This paper reports results from a network-based risk assessment model which uses international passenger travel volumes, travel routes, travel distances, regional populations, and predictive species distribution models (for the two vector species, Aedes aegypti and Aedes albopictus) to quantify the relative risk posed by each airport in importing passengers with travel-acquired dengue infections. Two risk attributes are evaluated: (i) the risk posed by through traffic at each stopover airport and (ii) the risk posed by incoming travelers to each destination airport. The model results prioritize optimal locations (i.e., airports) for targeted dengue surveillance. The model is easily extendible to other vector-borne diseases.     

The grass may not always be greener: projected reductions in climatic suitability for exotic grasses under future climates in Australia

Climate change presents a new challenge for the management of invasive exotic species that threaten both biodiversity and agricultural productivity. The invasion of exotic perennial grasses throughout the globe is particularly problematic given their impacts on a broad range of native plant communities and livelihoods. As the climate continues to change, pre-emptive long-term management strategies for exotic grasses will become increasingly important. Using species distribution modelling we investigated potential changes to the location of climatically suitable habitat for some exotic perennial grass species currently in Australia, under a range of future climate scenarios for the decade centred around 2050. We focus on eleven species shortlisted or declared as the Weeds of National Significance or Alert List species in Australia, which have also become successful invaders in other parts of the world. Our results indicate that the extent of climatically suitable habitat available for all of the exotic grasses modelled is projected to decrease under climate scenarios for 2050. This reduction is most severe for the three species of Needle Grass (genus Nassella) that currently have infestations in the south-east of the continent. Combined with information on other aspects of establishment risk (e.g. demographic rates, human-use, propagule pressure), predictions of reduced climatic suitability provide justification for re-assessing which weeds are prioritised for intensive management as the climate changes.     

中华稻蝗三种群遗传结构分析

应用淀粉凝胶电泳对山西省太原黄陵村、临猗县赵村及永济县伍姓湖3个中华稻稻（Oxya chinensis）种群的4个等位酶位点（MDH-1、MDH-2、LDH、ME）进行了分析。结果表明3个种群的中华稻蝗在遗传结构上具有差异;黄陵种群的MDH-1、MDH-2以及伍姓湖种群的MDH-1均为单态位点;赵村种群的杂合性最低（H=0.112）,伍姓湖种群最高（H=0.229）;赵村种群与伍姓湖种群间的Nei‘s遗传距离为0.068,可视为1个大的种群,而黄陵种群与赵村种群和伍姓湖种群的Nei‘s遗传距离分别为0.247和0.218。考虑到赵村和伍姓湖之间的地理距离（41km）比太原黄陵（357km）要近得多,结果提示3个种群地理距离与遗传结构差异之间存在相关关系。     

Eyjafjallaj?kull and 9/11: The Impact of Large-Scale Disasters on Worldwide Mobility

Large-scale disasters that interfere with globalized socio-technical infrastructure, such as mobility and transportation networks, trigger high socio-economic costs. Although the origin of such events is often geographically confined, their impact reverberates through entire networks in ways that are poorly understood, difficult to assess, and even more difficult to predict. We investigate how the eruption of volcano Eyjafjallajökull, the September 11th terrorist attacks, and geographical disruptions in general interfere with worldwide mobility. To do this we track changes in effective distance in the worldwide air transportation network from the perspective of individual airports. We find that universal features exist across these events: airport susceptibilities to regional disruptions follow similar, strongly heterogeneous distributions that lack a scale. On the other hand, airports are more uniformly susceptible to attacks that target the most important hubs in the network, exhibiting a well-defined scale. The statistical behavior of susceptibility can be characterized by a single scaling exponent. Using scaling arguments that capture the interplay between individual airport characteristics and the structural properties of routes we can recover the exponent for all types of disruption. We find that the same mechanisms responsible for efficient passenger flow may also keep the system in a vulnerable state. Our approach can be applied to understand the impact of large, correlated disruptions in financial systems, ecosystems and other systems with a complex interaction structure between heterogeneous components.     

Climatic Niche Conservatism and Biogeographical Non-Equilibrium in Eschscholzia californica (Papaveraceae), an Invasive Plant in the Chilean Mediterranean Region

Species climate requirements are useful for predicting their geographic distribution. It is often assumed that the niche requirements for invasive plants are conserved during invasion, especially when the invaded regions share similar climate conditions. California and central Chile have a remarkable degree of convergence in their vegetation structure, and a similar Mediterranean climate. Such similarities make these geographic areas an interesting natural experiment for testing climatic niche dynamics and the equilibrium of invasive species in a new environment. We tested to see if the climatic niche of Eschscholzia californica is conserved in the invaded range (central Chile), and we assessed whether the invasion process has reached a biogeographical equilibrium, i.e., occupy all the suitable geographic locations that have suitable conditions under native niche requirements. We compared the climatic niche in the native and invaded ranges as well as the projected potential geographic distribution in the invaded range. In order to compare climatic niches, we conducted a Principal Component Analysis (PCA) and Species Distribution Models (SDMs), to estimate E. californica''s potential geographic distribution. We also used SDMs to predict altitudinal distribution limits in central Chile. Our results indicated that the climatic niche occupied by E. californica in the invaded range is firmly conserved, occupying a subset of the native climatic niche but leaving a substantial fraction of it unfilled. Comparisons of projected SDMs for central Chile indicate a similarity, yet the projection from native range predicted a larger geographic distribution in central Chile compared to the prediction of the model constructed for central Chile. The projected niche occupancy profile from California predicted a higher mean elevation than that projected from central Chile. We concluded that the invasion process of E. californica in central Chile is consistent with climatic niche conservatism but there is potential for further expansion in Chile.