Global realized niche divergence in the African clawed frog Xenopus laevis

Although of crucial importance for invasion biology and impact assessments of climate change, it remains widely unknown how species cope with and adapt to environmental conditions beyond their currently realized climatic niches (i.e., those climatic conditions existing populations are exposed to). The African clawed frog Xenopus laevis, native to southern Africa, has established numerous invasive populations on multiple continents making it a pertinent model organism to study environmental niche dynamics. In this study, we assess whether the realized niches of the invasive populations in Europe, South, and North America represent subsets of the species’ realized niche in its native distributional range or if niche shifts are traceable. If shifts are traceable, we ask whether the realized niches of invasive populations still contain signatures of the niche of source populations what could indicate local adaptations. Univariate comparisons among bioclimatic conditions at native and invaded ranges revealed the invasive populations to be nested within the variable range of the native population. However, at the same time, invasive populations are well differentiated in multidimensional niche space as quantified via n‐dimensional hypervolumes. The most deviant invasive population are those from Europe. Our results suggest varying degrees of realized niche shifts, which are mainly driven by temperature related variables. The crosswise projection of the hypervolumes that were trained in invaded ranges revealed the south‐western Cape region as likely area of origin for all invasive populations, which is largely congruent with DNA sequence data and suggests a gradual exploration of novel climate space in invasive populations.     

Genetic Differentiation,Niche Divergence,and the Origin and Maintenance of the Disjunct Distribution in the Blossomcrown Anthocephala floriceps (Trochilidae)

Studies of the origin and maintenance of disjunct distributions are of special interest in biogeography. Disjunct distributions can arise following extinction of intermediate populations of a formerly continuous range and later maintained by climatic specialization. We tested hypotheses about how the currently disjunct distribution of the Blossomcrown (Anthocephala floriceps), a hummingbird species endemic to Colombia, arose and how is it maintained. By combining molecular data and models of potential historical distributions we evaluated: (1) the timing of separation between the two populations of the species, (2) whether the disjunct distribution could have arisen as a result of fragmentation of a formerly widespread range due to climatic changes, and (3) if the disjunct distribution might be currently maintained by specialization of each population to different climatic conditions. We found that the two populations are reciprocally monophyletic for mitochondrial and nuclear loci, and that their divergence occurred ca. 1.4 million years before present (95% credibility interval 0.7–2.1 mybp). Distribution models based on environmental data show that climate has likely not been suitable for a fully continuous range over the past 130,000 years, but the potential distribution 6,000 ybp was considerably larger than at present. Tests of climatic divergence suggest that significant niche divergence between populations is a likely explanation for the maintenance of their disjunct ranges. However, based on climate the current range of A. floriceps could potentially be much larger than it currently is, suggesting other ecological or historical factors have influenced it. Our results showing that the distribution of A. floriceps has been discontinous for a long period of time and that populations exhibit different climatic niches have taxonomic and conservation implications.     

Modeled global invasive potential of Asian gypsy moths, Lymantria dispar

Asian populations of gypsy moths, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), remain poorly characterized – indeed, they are not presently accorded any formal taxonomic status within the broader species. Their ecology is similarly largely uncharacterized in the literature, except by assumption that it will resemble that of European populations. We developed ecological niche models specific to Asian populations of the species, which can in turn be used to identify a potential geographic distributional area for the species. We demonstrated statistically significant predictivity of distributional patterns within the East Asian range of these populations; projecting the Asian ecological niche model to Europe, correspondence with European distributions was generally good, although some differences may exist; projecting the ecological niche model globally, we characterized a likely potential invasive distribution of this set of populations across the temperate zone of both Northern and Southern Hemisphere.     

Species delimitation and hybridization history of a hazel species complex

Background and AimsHybridization increases species adaptation and biodiversity but also obscures species boundaries. In this study, species delimitation and hybridization history were examined within one Chinese hazel species complex (Corylus chinensis–Corylus fargesii). Two species including four varieties have already been described for this complex, with overlapping distributions.MethodsA total of 322 trees from 44 populations of these four varieties across their ranges were sampled for morphological and molecular analyses. Climatic datasets based on 108 geographical locations were used to evaluate their niche differentiations. Flowering phenology was also observed for two co-occurring species or varieties.Key ResultsFour statistically different phenotypic clusters were revealed, but these clusters were highly inconsistent with the traditional taxonomic groups. All the clusters showed statistically distinct niches, with complete or partial geographical isolation. Only two clusters displayed a distributional overlap, but they had distinct flowering phenologies at the site where they co-occurred. Population-level evidence based on the genotypes of ten simple sequence repeat loci supported four phenotypic clusters. In addition, one cluster was shown to have an admixed genetic composition derived from the other three clusters through repeated historical hybridizations.ConclusionsBased on our new evidence, it is better to treat the four clusters identified here as four independent species. One of them was shown to have an admixed genetic composition derived from the other three through repeated historical hybridizations. This study highlights the importance of applying integrative and statistical methods to infer species delimitations and hybridization history. Such a protocol should be adopted widely for future taxonomic studies.     

Geographical distributions of spiny pocket mice in South America: insights from predictive models

Aim Predictive models of species’ distributions use occurrence records and environmental data to produce a model of the species’ requirements and a map of its potential distribution. To determine regions of suitable environmental conditions and assess biogeographical questions regarding their ranges, we modelled the potential geographical distributions of two spiny pocket mice (Rodentia: Heteromyidae) in north‐western South America. Location North‐western South America. Methods We used the Genetic Algorithm for Rule‐Set Prediction (GARP), environmental data from GIS maps and georeferenced collection localities from a recent systematic review of Heteromys australis and H. anomalus to produce the models. Results GARP models indicate the potential presence of H. australis throughout mesic montane regions of north‐western South America, as well as in some lowland regions of moderately high precipitation. In contrast, H. anomalus is predicted to occur primarily in drier areas of the Caribbean coast and rain‐shadowed valleys of the Andes. Conclusions The models support the disjunct status of the population of H. australis in the Cordillera de Mérida, but predict a continuous distribution between known populations of H. anomalus in the upper Magdalena Valley and the Caribbean coast. Regions of suitable environmental conditions exist disjunct from known distributional areas for both species, suggesting possible historical restrictions to their ranges. This technique holds wide application to other study systems.     

Phylogeography and genetic structure of disjunct Salix arbutifolia populations in Japan

Disjunct geographic distributions of boreal plant species at the southern edges of their ranges are expected to result in low genetic diversity and high genetic differentiation in the disjunct populations. This prediction was tested in a riparian willow, Salix arbutifolia, distributed in the northeastern Eurasian continent and the Sakhalin, Hokkaido, and Honshu Islands, using chloroplast DNA haplotypes and nuclear microsatellite genotypes. Hokkaido and Honshu populations shared a chloroplast haplotype identical to a closely related species, S. cardiophylla. This haplotype was divergent from haplotypes in the Eurasian continent (Primorsky) and the Sakhalin Island. In the nuclear microsatellites, most Hokkaido populations were genetically closer to Primorsky populations than to Sakhalin populations in spite of the geographical vicinity between Sakhalin and Hokkaido. The unexpected genetic divergence between Sakhalin and Hokkaido implies a complicated history of migration and colonization. The most peripheral populations in Honshu had the lowest genetic diversity and were most differentiated from the others. Thus, low genetic diversity and high genetic differentiation at the range periphery suggest substantial effects of genetic drift on genetic structure in the disjunct populations of Salix arbutifolia at the southern edge of its range.     

Warming off southwestern Japan linked to distributional shifts of subtidal canopy‐forming seaweeds

To assess distributional shifts of species in response to recent warming, historical distribution records are the most requisite information. The surface seawater temperature (SST) of Kochi Prefecture, southwestern Japan on the western North Pacific, has significantly risen, being warmed by the Kuroshio Current. Past distributional records of subtidal canopy‐forming seaweeds (Laminariales and Fucales) exist at about 10‐year intervals from the 1970s, along with detailed SST datasets at several sites along Kochi's >700 km coastline. In order to provide a clear picture of distributional shifts of coastal marine organisms in response to warming SST, we observed the present distribution of seaweeds and analyzed the SST datasets to estimate spatiotemporal SST trends in this coastal region. We present a large increase of 0.3°C/decade in the annual mean SST of this area over the past 40 years. Furthermore, a comparison of the previous and present distributions clearly showed the contraction of temperate species' distributional ranges and expansion of tropical species' distributional ranges in the seaweeds. Although the main temperate kelp Ecklonia (Laminariales) had expanded their distribution during periods of cooler SST, they subsequently declined as the SST warmed. Notably, the warmest SST of the 1997–98 El Niño Southern Oscillation event was the most likely cause of a widespread destruction of the kelp populations; no recovery was found even in the present survey at the formerly habitable sites where warm SSTs have been maintained. Temperate Sargassum spp. (Fucales) that dominated widely in the 1970s also declined in accordance with recent warming SSTs. In contrast, the tropical species, S. ilicifolium, has gradually expanded its distribution to become the most conspicuously dominant among the present observations. Thermal gradients, mainly driven by the warming Kuroshio Current, are presented as an explanation for the successive changes in both temperate and tropical species' distributions.     

Species distribution models for Peruvian plantcutter improve with consideration of biotic interactions

Biotic interactions have been controversial in distributional ecology, mainly in regards to whether they have effects over broad extents, with the negative view known as the Eltonian noise hypothesis (ENH). In this study, we evaluated the ENH for Phytotoma raimondii, a restricted‐range Peruvian endemic bird species: we developed models based on 1) only abiotic conditions, 2) only host plant distributions, and 3) both abiotic conditions and host plant distributions; models were evaluated with partial receiver operating characteristic test and Akaike information criteria metrics. We rejected the ENH for this case: biotic interactions improved the model. The frequency with which exceptions to the ENH are detected has important implications for distributional ecology and methods for estimating distributions of species.     

Past and future climate-driven shifts in the distribution of a warm-adapted bird species,the European Roller Coracias garrulus

ABSTRACT

Capsule: The distribution range of the European Roller Coracias garrulus has undergone large changes over geological times, but although the species is warm-adapted, the human induced climate change is predicted to affect negatively the range of the currently large populations.

Aim: Information on species-specific vulnerability to climate change is crucial not only for designing interventions and setting conservation goals, but also to inform conservation decision-making. Our goal was to map climate suitability for the European Roller in the Western Palaearctic under current climate, and for past (last glacial maximum and mid-Holocene) and future (2050 and 2070) climate scenarios.

Methods: We used MaxEnt for species distribution modelling based on the reconstructed distribution map of the species.

Results: Our results suggest that during glacial periods Rollers persisted in small southern refugia, and then spread and colonized northern latitudes during the mid-Holocene. In the future, our models forecast a shift in climatically suitable range towards northern latitudes and an overall small range contraction (4.5–5.5%). Warmer temperatures will increase climate suitability in northern countries where the species is currently declining or became locally extinct. On the other hand, wide suitable areas under current climatic conditions are predicted to become unsuitable in the future (35–38% by 2050 and 2070, respectively), significantly impacting large populations such as those in Romania, Spain, Bulgaria and Hungary. French and Italian populations are identified to be future key populations for Roller conservation.

Conclusions: Our findings suggest that future climate changes will likely amplify the impacts of existing threats on the majority of large European Roller populations in Europe.     

Restricted plant species on sub-Antarctic Macquarie and Heard Islands

The recent distributional history of two Macquarie Island vascular plant species, Carex trifida, Poa litorosa, and the Heard Island vascular plant, Ranunculus crassipes is examined. C. trifida is known from only one small population on the north west coast of Macquarie Island. Four populations of P. litorosa were first recorded in the 1980s; we believe however, that it was first observed, but misidentified in the 1950s. R. crassipes was first discovered on Heard Island in the late 1980s. We argue that all three species are indigenous and arrived on their respective islands within the last 200 years by natural processes, most likely from warmer neighbouring islands, where these species have more extensive distributions. There have been small-scale changes in distribution of all species, mainly expansion. Further expansion of all three species is expected as a response to warming climate. Feral rabbit grazing is having a confounding negative influence on populations of P. litorosa.     

Climate-Induced Range Shifts and Possible Hybridisation Consequences in Insects

Many ectotherms have altered their geographic ranges in response to rising global temperatures. Current range shifts will likely increase the sympatry and hybridisation between recently diverged species. Here we predict future sympatric distributions and risk of hybridisation in seven Mediterranean ischnurid damselfly species (I. elegans, I. fountaineae, I. genei, I. graellsii, I. pumilio, I. saharensis and I. senegalensis). We used a maximum entropy modelling technique to predict future potential distribution under four different Global Circulation Models and a realistic emissions scenario of climate change. We carried out a comprehensive data compilation of reproductive isolation (habitat, temporal, sexual, mechanical and gametic) between the seven studied species. Combining the potential distribution and data of reproductive isolation at different instances (habitat, temporal, sexual, mechanical and gametic), we infer the risk of hybridisation in these insects. Our findings showed that all but I. graellsii will decrease in distributional extent and all species except I. senegalensis are predicted to have northern range shifts. Models of potential distribution predicted an increase of the likely overlapping ranges for 12 species combinations, out of a total of 42 combinations, 10 of which currently overlap. Moreover, the lack of complete reproductive isolation and the patterns of hybridisation detected between closely related ischnurids, could lead to local extinctions of native species if the hybrids or the introgressed colonising species become more successful.     

Modeling distributions of disjunct populations of the Sierra Madre Sparrow

ABSTRACT Sierra Madre Sparrows (Xenospiza baileyi) are among the least known of all bird species in Mexico. Recent surveys have discovered previously unknown populations and the current known distribution of Sierra Madre Sparrows consists of two populations separated by >800 km. We used available distributional information to develop ecological niche models that (1) predict much of the distribution potential of the species, (2) establish that the broad disjunction separating the two populations has ecological correlates that appear to be important to the distributional of these sparrows, and (3) illustrate the extremely restricted ecological distribution of the species. We used two sets of climatic and topographic variables, with one including all 22 variables available and the second with only six variables that were positively related to quality of distributional models. Although indications of differences between the two sets of populations were found based on the full 22‐dimensional environmental dataset, such a highly dimensional analysis is vulnerable to over‐fitting; models based on the reduced dataset indicated that the two populations occur in areas with similar ecological conditions. Our models also suggest that southern population of Sierra Madre Sparrows covers most of their potential range in that region. The potential range of the northern population, however, extends beyond known points of occurrence. To clarify the distribution of Sierra Madre Sparrows and evaluate their status and conservation opportunities, detailed searches for additional populations in areas identified by the model are needed.     

Evolution and phylogenetic relationships in subterranean rodents of the Ctenomys mendocinus species complex: Effects of Late Quaternary landscape changes of Central Argentina

We conducted a thorough survey of populations of Ctenomys within the distributional ranges of all species that currently represent the Ctenomys mendocinus species complex in Central Argentina. From the Atlantic Southeastern coast to the heights of the Los Andes mountain range we sampled individuals for all the previously recognized species within this species complex (C. australis, C. azarae, C. porteousi, C. “chasiquensis” and C. mendocinus). Sequences of different fragments of mitochondrial DNA were used to assess the phylogenetic relationships between individuals and to understand the processes responsible for the observed geographic distribution of genetic variation. The genetic differentiation among most of the sequences was moderated, although highly divergent haplotypes were recorded in some localities in the West of our study area, suggestive of the occurrence of a new so far undescribed species. The phylogenetic reconstructions suggested the presence of three major clades into C. mendocinus complex species that do not agree with the currently proposed taxonomy. Phylogeographic and demographic estimates indicated that the C. mendocinus species complex experienced a strong and recent process of population expansion. We propose that the pattern of distribution of haplotype diversity in the C. mendocinus species complex corresponds to a scenario of mild local differentiation with subsequent expansion to the current distribution ranges. Demographic changes through time suggest that glacial-interglacial cycles of Late Quaternary, and the consequent variation in the aridity of Central plains in Argentina, had strong effects on the evolution and cladogenesis of the C. mendocinus species complex.     

Different climatic envelopes among invasive populations may lead to underestimations of current and future biological invasions

Aim We explore the impact of calibrating ecological niche models (ENMs) using (1) native range (NR) data versus (2) entire range (ER) data (native and invasive) on projections of current and future distributions of three Hieracium species. Location H. aurantiacum, H. murorum and H. pilosella are native to Europe and invasive in Australia, New Zealand and North America. Methods Differences among the native and invasive realized climatic niches of each species were quantified. Eight ENMs in BIOMOD were calibrated with (1) NR and (2) ER data. Current European, North American and Australian distributions were projected. Future Australian distributions were modelled using four climate change scenarios for 2030. Results The invasive climatic niche of H. murorum is primarily a subset of that expressed in its native range. Invasive populations of H. aurantiacum and H. pilosella occupy different climatic niches to those realized in their native ranges. Furthermore, geographically separate invasive populations of these two species have distinct climatic niches. ENMs calibrated on the realized niche of native regions projected smaller distributions than models incorporating data from species’ entire ranges, and failed to correctly predict many known invasive populations. Under future climate scenarios, projected distributions decreased by similar percentages, regardless of the data used to calibrate ENMs; however, the overall sizes of projected distributions varied substantially. Main conclusions This study provides quantitative evidence that invasive populations of Hieracium species can occur in areas with different climatic conditions than experienced in their native ranges. For these, and similar species, calibration of ENMs based on NR data only will misrepresent their potential invasive distribution. These errors will propagate when estimating climate change impacts. Thus, incorporating data from species’ entire distributions may result in a more thorough assessment of current and future ranges, and provides a closer approximation of the elusive fundamental niche.     

Large-scale spatial patterns in the distribution of Collembola (Hexapoda) species in Antarctic terrestrial ecosystems

Aim  We tested whether the distribution of three common springtail species ( Gressittacantha terranova , Gomphiocephalus hodgsoni and Friesea grisea ) in Victoria Land (Antarctica) could be modelled as a function of latitude, longitude, altitude and distance from the sea.
Location  Victoria Land, Ross Dependency, Antarctica.
Methods  Generalized linear models were constructed using species presence/absence data relative to geographical features (latitude, longitude, altitude, distance from sea) across the species' entire ranges. Model results were then integrated with the known phylogeography of each species and hypotheses were generated on the role of climate as a major driver of Antarctic springtail distribution.
Results  Based on model selection using Akaike's information criterion, the species' distributions were: hump-shaped relative to longitude and monotonic with altitude for Gressittacantha terranova ; hump-shaped relative to latitude and monotonic with altitude for Gomphiocephalus hodgsoni ; and hump-shaped relative to longitude and monotonic with latitude, altitude and distance from the sea for Friesea grisea .
Main conclusions  No single distributional pattern was shared by the three species. While distributions were partially a response to climatic spatial clines, the patterns observed strongly suggest that past geological events have influenced the observed distributions. Accordingly, present-day spatial patterns are likely to have arisen from the interaction of historical and environmental drivers. Future studies will need to integrate a range of spatial and temporal scales to further quantify their respective roles.     

Pselaphotumulus,a new genus of pselaphine endemic to New Zealand (Coleoptera: Staphylinidae: Pselaphinae: Pselaphitae)

ABSTRACT

Pselaphotumulus Owens and Carlton, gen. nov., is described as the sixth genus in the tribe Pselaphini known from New Zealand. Three new species are described: Pselaphotumulus aorerei, sp. nov., Pselaphotumulus dubius, sp. nov. and Pselaphotumulus unus, sp. nov.. Three species, Pselaphus cavelli (Broun 1893), Pselaphus oviceps (Broun 1917) and Pselaphus urquharti (Broun 1917) are transferred to Pselaphotumulus, nov. combs. Lectotypes from type series in the New Zealand Broun Collection (Natural History Museum, London) are designated for these three species. Habitus photographs, distributional maps and line drawings of diagnostic characters are provided for each species. A key to species is provided. Searches of museum collections have not yielded representatives outside of New Zealand, suggesting that this is the first endemic genus in the tribe Pselaphini described from the New Zealand’s main islands, specifically, the South Island. Pselaphotumulus species exhibit restricted distribution patterns that approximately coincide with the Pacific/Indo Australian Plate boundary.     

Are peripheral populations special? Congruent patterns in two butterfly species

Populations at range margins may be genetically different from more central ones for a number of mutually non‐exclusive reasons. Specific selection pressures may operate in environments that are more marginal for the species. Genetic drift may also have a strong effect in these populations if they are small, isolated and/or have experienced significant bottlenecks during the colonisation phase. The question if peripheral populations are special, and if yes then how and why, is of obvious relevance for speciation theory, as well as for conservation biology. To evaluate the uniqueness of populations at range margins and the influence of gene flow and selection, we performed a morphometric study of two grassland butterfly species: Coenonympha arcania and C. hero (Lepidoptera: Nymphalidae). The samples were collected from Swedish populations that are peripheral and isolated from the main area of the species distributions and from populations in the Baltic states that are peripheral but connected to the main area of the species distributions. These samples were compared to those from central parts of the species distributions. The isolated populations in both species differed consistently from both peripheral and central populations in their wing size and shape. We interpret this as a result of selection caused by differences in population structure in these isolated locations, presumably favoring different dispersal propensity of these butterflies. Alternative explanations based on colonisation history, latitudinal effects, inbreeding or phenotypic plasticity appear less plausible. As a contrast, the much weaker and seemingly random among‐region differences in wing patterns are more likely to be ascribed to weaker selection pressures allowing genetic drift to be influential. In conclusion, both morphological data and results from neutral genetic markers in earlier studies of the same system provide congruent evidence of both adaptation and genetic drift in the isolated Swedish populations of both species.     

Structure of genetic diversity in marginal populations of black poplar (Populus nigra L.)

It has been hypothesized that populations at the margins of the distributional range of a species show reduced genetic diversity and increased inter-population differentiation compared to central populations. Here, we test this hypothesis by examining the structure of genetic diversity in marginal populations of black poplar, Populus nigra L. (Salicaceae). This species occurs mainly in Europe but its range extends to central Asia. We collected 117 individuals from 10 populations at the edge of the distributional range of the species in central Asia to examine the structure of genetic diversity based on genetic polymorphisms at 20 microsatellite markers. As expected, the genetic diversity within these marginal populations is relatively low, with an average observed heterozygosity H_o of 0.337 and an average expected heterozygosity H_e of 0.466, compared to the genetic diversity of populations from central distributions. However, we recovered very low genetic differentiation between populations, with an average F_st of 0.0745, a value similar to those reported for central populations. AMOVA analyses confirmed this result, showing that only 9.2% of the total variation could be attributed to between-population variance (P < 0.001). Our findings do not fully support hypotheses about the structure of genetic diversity in marginal populations formed from observations on other species. We suggest that a high rate of outcrossing and possible postglacial colonization at the edge of the distributional range of this long-lived poplar may explain the observed structure of the genetic diversity.     

The influence of coarse‐scale environmental features on current and predicted future distributions of narrow‐range endemic crayfish populations

1. A major limitation to effective management of narrow‐range crayfish populations is the paucity of information on the spatial distribution of crayfish species and a general understanding of the interacting environmental variables that drive current and future potential distributional patterns. 2. Maximum Entropy Species Distribution Modeling Software (MaxEnt) was used to predict the current and future potential distributions of four endemic crayfish species in the Ouachita Mountains. Current distributions were modelled using climate, geology, soils, land use, landform and flow variables thought to be important to lotic crayfish. Potential changes in the distribution were forecast by using models trained on current conditions and projecting onto the landscape predicted under climate‐change scenarios. 3. The modelled distribution of the four species closely resembled the perceived distribution of each species but also predicted populations in streams and catchments where they had not previously been collected. Soils, elevation and winter precipitation and temperature most strongly related to current distributions and represented 65–87% of the predictive power of the models. Model accuracy was high for all models, and model predictions of new populations were verified through additional field sampling. 4. Current models created using two spatial resolutions (1 and 4.5 km²) showed that fine‐resolution data more accurately represented current distributions. For three of the four species, the 1‐km² resolution models resulted in more conservative predictions. However, the modelled distributional extent of Orconectes leptogonopodus was similar regardless of data resolution. Field validations indicated 1‐km² resolution models were more accurate than 4.5‐km² resolution models. 5. Future projected (4.5‐km² resolution models) model distributions indicated three of the four endemic species would have truncated ranges with low occurrence probabilities under the low‐emission scenario, whereas two of four species would be severely restricted in range under moderate–high emissions. Discrepancies in the two emission scenarios probably relate to the exclusion of behavioural adaptations from species‐distribution models. 6. These model predictions illustrate possible impacts of climate change on narrow‐range endemic crayfish populations. The predictions do not account for biotic interactions, migration, local habitat conditions or species adaptation. However, we identified the constraining landscape features acting on these populations that provide a framework for addressing habitat needs at a fine scale and developing targeted and systematic monitoring programmes.     

The limits to biogeographical distributions: insights from the northward range extension of the marine snail, Kelletia kelletii (Forbes, 1852)

Aim The development of accurate models predicting species range shifts in response to climate change requires studies on the population biology of species whose distributional limits are in the process of shifting. We examine the population biology of an example system using the recent northward range expansion of the marine neogastropod Kelletia kelletii (Forbes, 1852). Location This is a marine coastal shelf neogastropod species whose range extends from Isla Asuncion (Baja California, Mexico) to Monterey (CA, USA). Research sites spanned the extent of the range. Methods We examine abundance distributions and size frequency distributions of K. kelletii for evidence of factors determining historic and contemporary distributional patterns. Population studies were supplemented by historic and contemporary hydrographic data, including seawater temperature data from California Cooperative Oceanic Fisheries Investigations (CalCOFI ) and National Data Buoy Center (NDBC), and seawater circulation data. Results The structure of recently established populations varied dramatically from that of historic populations. Markedly low densities and irregular size frequency distributions characterized recently established populations and suggested only occasionally successful recruitment. The point of transition between historic and recently established populations also corresponded to the location of a gradient in seawater temperature and the confluence of two major oceanic currents. The accumulated data suggest that temperature and/or barriers to dispersal could have set both contemporary patterns in population structure as well as the former northern range limit. Main conclusions Early life stages play a critical role in determining distributional patterns of K. kelletii. Dispersal barriers and temperature limitation are two plausible mechanisms that could determine both contemporary and historic distributional patterns. Future studies on this species should attempt to tease apart the relative importance of these factors in maintaining the populations at the northern edge of the range.