Potential Source Populations Research Articles

Population structure of Desmophyllum pertusum found along the United States eastern continental margin

ObjectiveThe connectivity and genetic structuring of populations throughout a region influence a species’ resilience and probability of recovery from anthropogenic impacts. By gaining a comprehensive understanding of population connectivity, more effective management can be prioritized. To assess the connectivity and population genetic structure of a common cold-water coral species, Desmophyllum pertusum (Lophelia pertusa), we performed Restriction-site Associated DNA Sequencing (RADseq) on individuals from nine sites ranging from submarine canyons off New England to the southeastern coast of the United States (SEUS) and the Gulf of Mexico (GOM). Fifty-seven individuals and 3,180 single-nucleotide polymorphisms (SNPs) were used to assess genetic differentiation.ResultsHigh connectivity exists among populations along the SEUS, yet these populations were differentiated from those to the north off New England and in Norfolk Canyon along the North Atlantic coast of the United States, as well as those in the GOM. Interestingly, Norfolk Canyon, located just north of North Carolina, and GOM populations exhibited low levels of genetic differentiation, corroborating previous microsatellite analyses and signifying gene flow between these populations. Increasing sample sizes from existing populations and including additional sampling sites over a larger geographic range would help define potential source populations and reveal fine-scale connectivity patterns among D. pertusum populations.

Round gobies (Neogobius melanostomus) in the River Rhine: Population genetic support for invasion via two different routes

The round goby, Neogobius melanostomus, is a successful invasive fish species. Originating from the Caspian and Black Sea, it is now distributed widely within European fresh- and brackish waters. The River Rhine was colonized in 2008 only a few years after the opening of the Rhine-Main-Danube canal and only four years after N. melanostomus was first reported in the upper Danube River. Its invasion history of the River Rhine was unclear because the species was first detected close to the Rhine river delta which would suggest a route of invasion other than via the Rhine-Main-Danube canal. To investigate the colonization history of N. melanostomus in the Rhine, we combined abundance estimates with molecular analysis. Abundance estimates found N. melanostomus to be dominant in the Lower Rhine (> 90% of all catches). Molecular analysis was done on 286 individuals from four different sites. Using the mitochondrial control region (d-loop), we found three different haplotypes in both Rhine sites. None of the potential invasive source populations in the rivers Danube and Trave exhibited all three haplotypes. The molecular data therefore supported a scenario of two different colonization directions. Our results show that the invasion history of the River Rhine is complex and warrants further investigation.

Genetic differentiation and diversity do not explain variation in heterosis or inbreeding depression: empirical evidence from a long-lived iteroparous plant

AbstractAssisted gene flow can restore genetic diversity when genetic drift has driven deleterious alleles to high frequencies in small, isolated populations. Previous crosses among 20 populations of Gymnadenia conopsea documented the strongest heterosis and the weakest inbreeding depression in sparse and small populations, consistent with fixation of mildly deleterious alleles by genetic drift. We genotyped the populations used for crosses, and used 1200–1728 SNPs to test the following predictions: (1) heterosis increases with genetic differentiation (FST) to donor populations and decreases with genetic diversity in the recipient population, (2) inbreeding depression increases with genetic diversity, and (3) genetic diversity increases, and mean FST to other populations decreases, with population size and density. Pairwise FST ranged from very low to moderate (0.005–0.20) and genetic diversity varied moderately among populations (proportion of polymorphic loci = 0.52–0.75). However, neither FST between populations, nor genetic diversity in the recipient population, were related to the strength of heterosis. There was also no association between genetic diversity and the strength of inbreeding depression. Genetic diversity increased and mean FST decreased with population size, consistent with reduced diversity and increased differentiation of small populations by genetic drift. The results indicate that the loci conferring heterosis are not mirrored by overall population differentiation, and limited additional information on potential source populations for genetic rescue is gained by the genetic data. Instead, the use of controlled crosses can directly reveal positive effects of introducing new genetic material, and is a simple method with high potential in conservation.

Colonization of mudflat substrate by microarthropods: the role of distance, inundation frequency and body size

Salt marshes represent a unique ecosystem at the marine-terrestrial boundary of shallow protected coastlines. Microarthropods form an essential component of soil food webs, but how they colonize new intertidal habitats is little understood. By establishing two experimental systems without animals, we investigated microarthropod colonization (1) at the seashore from the pioneer zone to the lower and upper salt marsh and (2) at the same tidal height on artificial islands 500 m from the seashore. Potential source populations of microarthropods in the respective zones were also investigated. Colonization of microarthropods after 5 years was consistently faster on the seashore than on the artificial islands. Collembola and Mesostigmata colonized all the zones both on the seashore and on the artificial islands, with colonization being faster in the upper salt marsh and in the pioneer zone than in the lower salt marsh. Oribatida colonized the new habitats on the seashore, but only little on the artificial islands. Variations in species composition were more pronounced between salt marsh zones than between experimental systems, indicating that local environmental conditions (i.e., inundation frequency) are more important for the assembly of microarthropod communities than the distance from source populations (i.e., dispersal processes). Variations in community body size of Oribatida and Mesostigmata indicated environmental filtering of traits, with smaller species suffering from frequent inundations. Notably, Mesostigmata most successfully colonized the new habitats across salt marsh zones on both systems. Overall, the results document major mechanisms of colonization of intertidal habitats by microarthropods with different life histories and feeding strategies.

Genetic patterns reveal geographic drivers of divergence in silvereyes (Zosterops lateralis)

Identifying mechanisms that drive population divergence under varying geographic and ecological scenarios can inform our understanding of evolution and speciation. In particular, analysis of genetic data from island populations with known colonisation timelines allows us to identify potential source populations of diverging island subspecies and current relationships among populations. Silvereyes (Zosterops lateralis) are a small passerine that have served as a valuable study system to investigate evolutionary patterns on both large and small geographic scales. We examined genetic relatedness and diversity of two silvereye subspecies, the mainland Z. l. cornwalli and island Z. l. chlorocephalus, and used 18 077 single nucleotide polymorphisms (SNPs), to compare locations across southeast Queensland, Australia. Although silvereyes are prolific island colonisers our findings revealed population divergence over relatively small spatial scales was strongly influenced by geographic isolation mediated by water barriers. Strong genetic connectivity was displayed between mainland sites, but minimal inter-island connectivity was shown despite comparable sampling distances. Genetic diversity analysis showed little difference in heterozygosity between island and mainland populations, but lower inbreeding scores among the island populations. Our study confirmed the range of the Z. l. chlorocephalus subspecies throughout the southern Great Barrier Reef. Our results show that water barriers and not geographic distance per se are important in driving incipient divergence in island populations. This helps to explain the relatively high number of phenotypically differentiated, but often geographically proximate, island silvereye subspecies compared to a lower number of phenotypically less well-defined Australian continental subspecies.

Genetic prospective of a local invader: the strange pattern of Pontastacus leptodactylus population structure in Greece and Turkey based on microsatellite DNA.

The combination of the increasing demand of freshwater crayfish exports, the reduced population sizes due to overfishing, the crayfish plague epidemics and the habitat degradation, have led to unrecorded translocations of Pontastacus leptodactylus in Greek lakes. In the present study, the genetics of five narrow clawed crayfish (P. leptodactylus) populations were studied, namely three translocated populations inhabiting in Northern Greece, one native Greek population from Evros river and one potential progeny source population from Turkey. Nine microsatellite loci previously designed for the specific species were investigated, in order to assess the levels of genetic diversity and further to confirm the origin of these translocated populations some decades after the translocation events. Our results confirmed that the source population for the translocated Greek population is the Turkish lake Eğirdir. Further, despite the low values of the number of alleles, heterozygosity, and FST the populations were generally diverse, providing evidence for local adaptation. The low values of FIS for the translocated populations in combination with the high values of gene flow, possibly indicate the existence of re-introducing events. Apart from the translocated populations, high levels of genetic diversity and heterozygosity were observed in Evros population, suggesting it as a possible unit for future conservation purposes both as a donor population for reintroduction purposes as well as a unique gene pool protection source. To the best of our knowledge this is the first study dealing with the genetic composition of Greek P. leptodactylus populations from Nothern Greece, operating as a first step towards the development of proper management practices for restocking events and monitoring of translocated populations.

Vicariance and cryptic diversity revealed by molecular phylogenetic analyses of estuarine Gammarus species (Crustacea: Amphipoda) due to formation of the Labrador Current

The metapopulation of the estuarine species Gammarus tigrinus along the east coast of the United States has been hypothesised to represent two cryptic species divided biogeographically off the coast of North Carolina, USA. This divergence has been attributed to a strong temperature gradient created by the formation of the cold Labrador Current c. 3.0 million years ago. In addition, the northern phylogeographic clade of G. tigrinus has been demonstrated to be invasive in estuarine habitats across a large portion of northern Europe. Recent collections of G. tigrinus from Florida and Maryland, USA, allow for new approaches to test this hypothesis. Using the nuclear 18S and 28S rRNA, and mitochondrial 16S rRNA and cytochrome c oxidase subunit I genes, species delimitation models provide support that the genetic divergence of the northern and southern clades is equivalent to species level. In addition, molecular clock data demonstrate that this phylogeographic divergence coincides with the formation of the Labrador Current. Furthermore, the collections of G. daiberi from Florida, a species with biogeographical and ecological characteristics similar to those of G. tigrinus, provide independent support for the hypothesis. The potential for invasive species to be cryptic highlights the need for accurate identification of taxa to ensure that appropriate biogeographical assessment of potential source populations and mechanisms of dispersal can be made.

Extremophile hypolithic communities in the Vestfold Hills, East Antarctica

Abstract The Vestfold Hills are a 400 km2, isolated ice-free oasis in eastern Antarctica featuring large areas with translucent quartz rocks that provide habitat for hypolithic microbial communities underneath. We used high-throughput DNA sequencing of 16S and 18S ribosomal RNA amplicons to characterize bacterial and eukaryotic hypolithic communities across the Vestfold Hills. We found high-level, local heterogeneity in community structure consistent with limited dispersal between hypoliths. Hypolithic communities were dominated by heterotrophic Bacteroidetes (mean bacterial relative read abundance: 56%) as well as Cyanobacteria (35%), with the eukaryote component often dominated by Chlorophyta (43%). Small but significant proportions of the variation in microbial community composition and function were explained by soil salinity (5–7%) and water availability (8–11%), with distinct taxa associated with different salinities and water availabilities. Furthermore, many inferred bacterial metabolic pathways were enriched in hypolithic communities from either dry or high-salinity sites. Vestfold Hills hypolithic habitats are likely to be local refuges for bacterial and eukaryotic diversity. Gradients in soil salinity and water availability across the Vestfold Hills, in addition to the number and diversity of lake types and fjords as potential source populations, may contribute to the observed variation in the extremophile, hypolithic microbial community composition.

Immigration delays but does not prevent adaptation following environmental change: experimental evidence.

In today's rapidly changing world, it is critical to examine how animal populations will respond to severe environmental change. Following events such as pollution or deforestation that cause populations to decline, extinction will occur unless populations can adapt in response to natural selection, a process called evolutionary rescue. Theory predicts that immigration can delay extinction and provide novel genetic material that can prevent inbreeding depression and facilitate adaptation. However, when potential source populations have not experienced the new environment before (i.e., are naive), immigration can counteract selection and constrain adaptation. This study evaluated the effects of immigration of naive individuals on evolutionary rescue using the red flour beetle, Tribolium castaneum, as a model system. Small populations were exposed to a challenging environment, and three immigration rates (zero, one, or five migrants per generation) were implemented with migrants from a benign environment. Following an initial decline in population size across all treatments, populations receiving no immigration gained a higher growth rate one generation earlier than those with immigration, illustrating the constraining effects of immigration on adaptation. After seven generations, a reciprocal transplant experiment found evidence for adaptation regardless of immigration rate. Thus, while the immigration of naive individuals briefly delayed adaptation, it did not increase extinction risk or prevent adaptation following environmental change.

Ecological niche modelling and population genomics provide insights into the geographic and demographic ‘explosion’ of a non‐indigenous salmonid

AbstractAimEffective management of non‐indigenous species requires knowledge of their dispersal factors and founder events. We aim to identify the main environmental drivers favouring dispersal events along the invasion gradient and to characterize the spatial patterns of genetic diversity in feral populations of the non‐native pink salmon within its epicentre of invasion in Norway.LocationMainland Norway and North Atlantic Basin.MethodsWe first conducted SDM using four modelling techniques with varying levels of complexity, which encompassed both regression‐based and tree‐based machine‐learning algorithms, using climatic data from the present to 2050. Then, we used the triple‐enzyme restriction‐site associated DNA sequencing (3RADseq) approach to genotype over 30,000 high‐quality single‐nucleotide polymorphisms to elucidate the patterns of genetic diversity and gene flow within the pink salmon putative invasion hotspot.ResultsWe discovered temperature‐ and precipitation‐related variables drove pink salmon distributional shifts across its non‐native ranges and that climate‐induced favourable areas will remain stable for the next 30 years. In addition, all SDMs identified north‐eastern Norway as the epicentre of the pink salmon invasion, and genomic data revealed that there was minimal variation in genetic diversity across the sampled populations at a genome‐wide level in this region. While utilizing a specific group of ‘diagnostic’ SNPs, we observed a significant degree of genetic differentiation, ranging from moderate to substantial, and detected four hierarchical genetic clusters concordant with geography.Main ConclusionsOur findings suggest that fluctuations in climate extreme events associated with ongoing climate change will likely maintain environmental favourability for the pink salmon outside its ‘native’/introduced ranges. Locally invaded rivers are themselves potential source populations of invaders in the ongoing secondary spread of pink salmon in Northern Norway. Our study shows that SDMs and genomic data can reveal species distribution determinants and provide indicators to aid in post‐control measures and potentially inferences about their success.

Anopheles gambiae on remote islands in the Indian Ocean: origins and prospects for malaria elimination by genetic modification of extant populations

The mosquito Anopheles gambiae s.s. is a primary malaria vector throughout sub-Saharan Africa including the islands of the Comoros archipelago (Anjouan, Grande Comore, Mayotte and Mohéli). These islands are located at the northern end of the Mozambique Channel in eastern Africa. Previous studies have shown a relatively high degree of genetic isolation between the Comoros islands and mainland populations of A. gambiae, but the origin of the island populations remains unclear. Here, we analyzed phylogenetic relationships among island and mainland populations using complete mitochondrial genome sequences of individual A. gambiae specimens. This work augments earlier studies based on analysis of the nuclear genome. We investigated the source population of A. gambiae for each island, estimated the number of introductions, when they occurred and explored evidence for contemporary gene flow between island and mainland populations. These studies are relevant to understanding historical patterns in the dispersal of this important malaria vector and provide information critical to assessing their potential for the exploration of genetic-based vector control methods to eliminate this disease. Phylogenetic analysis and haplotype networks were constructed from mitogenome sequences of 258 A. gambiae from the four islands. In addition, 112 individuals from seven countries across sub-Saharan Africa and Madagascar were included to identify potential source populations. Our results suggest that introduction events of A. gambiae into the Comoros archipelago were rare and recent events and support earlier claims that gene flow between the mainland and these islands is limited. This study is concordant with earlier work suggesting the suitability of these oceanic islands as appropriate sites for conducting field trial releases of genetically engineered mosquitoes (GEMs).

Long-term biogeographical processes dominate patterns of genetic diversity in a wingless grasshopper despite substantial recent habitat fragmentation.

Low-vagility species may hold strong genetic signatures of past biogeographical processes but are also vulnerable to habitat loss. Flightless grasshoppers of the morabine group were once widespread in southeastern Australia, including Tasmania, but are becoming restricted to remnant patches of vegetation, with local ranges impacted by agriculture and development as well as management. Habitat fragmentation can generate genetically differentiated "island" populations with low genetic variation. However, following revegetation, populations could be re-established, and gene flow increased. Here we characterize single nucleotide polymorphism-based genetic variation in a widespread chromosomal race of the morabine Vandiemenella viatica (race 19) to investigate the genetic health of remnant populations and to provide guidelines for restoration efforts. We update the distribution of this race to new sites in Victoria and Tasmania, and show that V. viatica populations from northern Tasmania and eastern Victoria have reduced genetic variation compared to other mainland populations. In contrast, there was no effect of habitat fragment size on genetic variation. Tasmanian V. viatica populations fell into two groups, one connected genetically to eastern Victoria and the other connected to southwestern Victoria. Mainland populations showed isolation by distance. These patterns are consistent with expectations from past biogeographical processes rather than local recent population fragmentation and emphasize the importance of small local reserves in preserving genetic variation. The study highlights how genomic analyses can combine information on genetic variability and population structure to identify biogeographical patterns within a species, which in turn can inform decisions on potential source populations for translocations.

Out of their depth: The successful use of cultured subtidal mussels for intertidal restoration

AbstractEcosystem restoration has proliferated across the globe to combat widespread ecosystem decline. Translocations of viable individuals into degraded habitats form a core component of restoration efforts, but the selection of source populations poses challenges because phenotypic differences between source populations and depleted populations result in low post‐translocation survival. Intertidal mussel restoration is typically reliant on subtidal source populations despite their weaker shells, lighter weights, and poorer respiratory abilities compared to intertidal mussels. Intertidal mussel restoration using subtidal mussels has recorded very low survival, leading to suggestions that subtidal mussels are unfit for the intertidal zone, effectively eliminating the possibility of translocation‐based intertidal mussel restoration. In this study, small‐scale intertidal mussel restoration was tested using subtidal cultured mussels transplanted to paired plots, half in the lower intertidal and half in the upper subtidal. The results demonstrate the first scientific evidence of the successful restoration of intertidal mussel reefs using subtidal mussels at this scale. Specifically, one location recorded very high survival after 12 months (95.1 ± 0.6%; mean ± SE), comparable to the survival recorded in the subtidal zone (97.6 ± 0.3%). Translocations to the intertidal at the other two locations experienced mortality during the Austral summer (final survival: 81.3 ± 1.6% and 56.6 ± 7.4%), which directly correlated with exposure to extreme temperatures (>40°C). These results reveal that despite phenotypic differences, subtidal cultured mussels are potential sources for successful intertidal restoration. However, care should also be taken to avoid locations prone to high temperatures, particularly in light of a warming global environment. Ultimately, to achieve the massive upscaling in restoration called for by the UN Decade on Ecosystem Restoration, we encourage restoration managers to think broadly about potential source populations, avoid rejections based solely on phenotypic differences, and explore every potential avenue for restoration success.

Genomic Epidemiology Linking Nonendemic Coccidioidomycosis to Travel

Coccidioidomycosis is a fungal infection endemic to hot, arid regions of the western United States, northern Mexico, and parts of Central and South America. Sporadic cases outside these regions are likely travel-associated; alternatively, an infection could be acquired in as-yet unidentified newly endemic locales. A previous study of cases in nonendemic regions with patient self-reported travel history suggested that infections were acquired during travel to endemic regions. We sequenced 19 Coccidioides isolates from patients with known travel histories from that earlier investigation and performed phylogenetic analysis to identify the locations of potential source populations. Our results show that those isolates were phylogenetically linked to Coccidioides subpopulations naturally occurring in 1 of the reported travel locales, confirming that these cases were likely acquired during travel to endemic regions. Our findings demonstrate that genomic analysis is a useful tool for investigating travel-related coccidioidomycosis.

What can genetics tell us about the history of a human-mediated introduction of the golden-striped salamander south of its native range?

The golden-striped salamander is a streamside species endemic to the northwestern corner of the Iberian Peninsula. In the first half of the twentieth century, an undisclosed number of individuals of this species were reportedly captured in Buçaco, Central Portugal, and deliberately introduced in Sintra Mountains, 170 km south of its native distribution range. The discovery of a breeding population of this salamander in Sintra during 2015 prompted this work: we used neutral genetic markers, the mitochondrial DNA cytochrome b (cytb), and seven microsatellite loci to elucidate on the relict/human-introduced nature of Sintra population, identify the potential source population, and infer the severity of founder effect. Our results support a human-mediated introduction. First, sequencing analysis of cytb showed the presence of a unique haplotype (h31) in Sintra, which was detected only in Buçaco and in two additional populations located close to Mondego river. Second, microsatellite analysis showed that Sintra is more closely related to populations in between Douro and Mondego rivers (Central Portugal), instead of its geographically closest populations (southernmost), as would be expected if Sintra was a relict population isolated in an interglacial refuge. Third, Sintra presents both reduced levels of genetic variability and effective population size when compared to native populations, particularly to those of Central Portugal. Consistent with an isolated population funded by a small number of individuals (inferred herein to be ca. 10–11 salamanders), Sintra forms a geographically coherent genetic unit that is significantly differentiated from the extant native C. lusitanica populations. Although our data provide supporting evidence for Buçaco as a likely source population, as documented in the literature, overall, we cannot unequivocally exclude other populations close to Mondego river as a potential source of the introduced individuals in Sintra.

Landcover change and habitat quality mediate impacts of temperature and precipitation on population dynamics of a threatened aridland predator

AbstractClimate and landcover change can have synergistic impacts on wildlife populations, but the pervasiveness of these threats and factors that buffer them remain unclear despite important implications for conservation. I evaluated the additive and interactive effects of spatiotemporal variation in temperature, precipitation, and landcover change on annual territory occupancy, colonization, and extinction of a threatened top‐predator, the ferruginous pygmy‐owl (Glaucidium brasilianum), across a vast binational region of the Sonoran Desert over 16 years. I also assessed how local habitat quality and regional population size mediate impacts of these stressors. Despite significant bivariate associations between occupancy and temperature, precipitation, and landcover change, evidence for interactions was much greater than for additive effects. Occupancy of territories imbedded in increasingly disturbed landscapes declined at greater rates with warming winter temperatures, but the temperature had little effect in intact landscapes suggesting they buffer impacts of climate warming. Occupancy increased markedly with precipitation due likely to major positive impacts on prey, but again, interactive effects were stronger given territories of higher quality amplified benefits of precipitation. Impacts of landcover change and habitat quality on extinction depended markedly on regional population sizes. When populations were small and few potential colonists were present, high‐quality habitat and low landcover change failed to reduce extinction. When populations were large, however, high‐quality habitat and more intact landscapes, which best foster dispersal, reduced extinction. Hence, complex interacting processes linked to the effects of precipitation and habitat quality on carrying capacity, landcover change on habitat connectivity and vulnerability to rising temperatures, and local population sizes simultaneously drove dynamics. Efforts to identify and protect high‐quality habitat and limit landcover change can enhance conservation but will be most efficient in intact landscapes. Efforts to enhance local habitat quality and quantity, and directly augment populations should consider broader landscape contexts linked to habitat connectivity and potential source populations.

Genomic analyses point to a low evolutionary potential of prospective source populations for assisted migration in a forest herb.

Climate change is increasingly impacting temperate forest ecosystems and many forest herbs might be unable to track the changing climate due to dispersal limitation. Forest herbs with a low adaptive capacity may therefore benefit from conservation strategies that mitigate dispersal limitation and evolutionary constraints, such as assisted migration. However, assisted migration strategies rarely consider evolutionary constraints of potential source populations that may jeopardize their success. In cases where climate adaptation is overshadowed by competing evolutionary processes, assisted migration is unlikely to support adaptation to future climates. Using a combination of population and landscape genomic analyses, we disentangled local adaptation drivers and quantified the adaptability and vulnerability to climate change of the self-incompatible deciduous forest herb Primula elatior. Southern populations displayed a sharp genetic turnover and a considerable amount of local adaptation under diversifying selection was discovered. However, most of the outlier loci could not be linked to climate variables (71%) and were likely related to other local adaptation drivers, such as photoperiodism. Furthermore, specific adaptations to climate extremes, such as drought stress, could not be detected. This is in line with the typical occurrence of forest herbs in buffered climatic conditions, which can be expected to reduce selection pressures imposed by climate. Finally, populations in the south of the distribution area had increased sensitivity to climate change due to a reduced adaptive capacity and a moderate genetic offset, while central European populations were sensitive due to a high genetic offset. We conclude that assisted migration from southern source populations could bear significant risk due to nonclimatic maladaptation and a low adaptive capacity. Regional admixture and restoration of ecological connectivity to increase the adaptive capacity, and assisted range expansion to suitable habitat in the north might be more appropriate mitigation strategies.

The Genetic Diversity and Structure of the Feral Raccoon (Procyon lotor) Population in Shikoku Island, Japan

We explored the genetic diversity and population genetic structure of an invasive alien species, the raccoon Procyon lotor, which was introduced into the Shikoku Island of Japan, using sequences of the mitochondrial control region and 10 polymorphic microsatellite loci. In 80 individuals examined, we detected two genetically divergent haplotypes, indicating that two maternal lineages had been introduced into Shikoku Island. Population clustering analysis suggested the nonexistence of genetic structure in the area. The relatedness network showed that the raccoon population in Shikoku Island consisted of closely related individuals. The genetic diversity of the Shikoku raccoon population was lower than that in the native range. These results and a prior report indicate that the Shikoku raccoon population is likely to have expanded from small numbers of founders originating from an initial invasive population. Raccoon captures outside Kagawa are decreasing, although past expansions into Tokushima and Ehime suggest that there are no geographical barriers among these areas. Therefore, action should be taken to prevent any re-expansion of the raccoon population in Kagawa. Intensive monitoring and the elimination of dispersers from Kagawa, as well as effort to eradicate potential source populations for expansion in Kagawa, are needed.

Observations of dispersal in the brown recluse spider, Loxosceles reclusa (Araneae: Sicariidae)

We studied dispersal of brown recluse spiders, Loxosceles reclusa (Gertsch & Mulaik, 1940), around an infested urban garage using pitfall traps. Over a four-month period, 23 were captured from a source population that averaged 100 individuals observed in nocturnal censuses. Loxosceles reclusa were captured in far lower proportions compared to their potential source population size than were other spiders such as theridiids and agelenids that also resided in the garage, albeit in far lower numbers. Dispersal was weakly positively correlated with the source population size. We compare our findings to anecdotal reports from prior studies and the general consensus that brown recluse spiders are poor dispersers to argue for more detailed examination of the movement and specific habitat requirements of this medically important spider. Habitat specificity and high mortality during dispersal may help explain the highly clustered spatial distribution of brown recluse spiders, not only a lack of attempted emigration.

Disturbance and indirect effects of climate warming support a plant invader in mountains

Climate warming and increased disturbance (resulting from intensified land use) are expected to enhance the invasibility of plant communities and the performance of exotic species also at high elevations, and thus pose additional threats to mountain ecosystems. The invasion success of introduced genotypes will also depend on their degree of pre‐adaption to high elevation climatic conditions, which may vary intra‐specifically across source populations. For populations currently spreading in the lowlands, climate warming might reduce the climatic distance to high‐elevation sites and thus remove a barrier to upwards spread.Here, we investigated the various facets of mountain invasions in a single, integrative experimental study. We applied a community transplant approach between high‐ and low‐elevation sites in the European Alps to address effects of climate warming and disturbance through land use on community invasibility and the performance of the exotic species Senecio inaequidens, a potential future plant invader in the Alps. Additionally, the transplant sites served as common gardens to test the influence of climatic pre‐adaptation to current (high site) and future (low site) climatic conditions on the performance of S. inaequidens in the transplanted communities. The 16 invasive central and western European S. inaequidens source population locations covered a wide geographic range, and thus a wide amplitude of climatic distances and presumed pre‐adaptation to our gardens.Our results attest to a strong effect of disturbance, which increased community invasibility, and promoted the performance of the exotic species. Contrary to our expectation, experimentally induced climate warming did not increase community invasibility. However, the performance of the S. inaequidens populations was positively related to their pre‐adaptation to the climatic conditions of our common gardens. Climate warming might thus promote the invasion of exotic species by reducing the climatic distance between mountain ranges and locations of potential source populations.