Palaeodistribution Models Research Articles

The importance of C3 and C4 grasses and CAM shrubs in the Greater Cape Floristic Region under contemporary and Last Glacial Maximum climates

Southern Africa’s Greater Cape Floristic Region (GCFR) – a hotspot of biological diversity and palaeo-anthropological evidence for modern human evolution – is a climatically complex region where broad climatic gradients influence the relative importance of plant photosynthetic types in local vegetation. This mix of photosynthetic pathways imprint an isotopic signature on palaeo-records, thereby allowing for the reconstruction of historical climate and vegetation. Here, we use vegetation plot data, coupled with the photosynthetic-type affinities of plant genera, to relate their relative cover to bioclimatic drivers and use these to create spatial distribution models of C3 and C4 grasses and CAM shrubs across the contemporary GCFR. We then use palaeodistribution modelling, drawing on downscaled climate models for the Last Glacial Maximum (LGM), to hindcast the LGM distributions of photosynthetic types for the GCFR and its then-exposed offshore areas. In addition, we construct a model to account for the effect of lower atmospheric CO2 concentration ([CO2]) during the LGM on the competitive interactions between C3 and C4 grasses and use this model to hindcast relative C4-grass cover across the glacial-era GCFR. Our palaeodistribution models suggest that, even though there were some reductions in CAM cover and shifts in C3-/C4-dominated grass layers between the LGM and Holocene, these were mostly localised, with changes at the regional scale being relatively muted. For C3/C4 grasses, distributional shifts were even more subtle once sub-ambient glacial [CO2] was accounted for. Our hindcasts of glacial, [CO2]-adjusted grass cover show agreements and inconsistencies with various sedimentary and herbivore-diet records in the palaeo-archive: both lines of evidence suggest the dominance of C3 species in the strongly winter-rainfall western GCFR; in the eastern GCFR, with muted rainfall seasonality, hindcasts of relative C3:C4 cover and δ13C signals from palaeo-records vary, with greater disparities between them. The lack of significant upheavals in the distribution of photosynthetic types suggests that the GCFR presented a relatively stable and dependable resourcescape for hunter-gatherer populations through the glacial–interglacial cycle of the LGM–Holocene transition. Our maps of relative C3-/C4-grass and CAM-shrub cover provide a reasonable surrogate for relative biomass of different photosynthetic types in local vegetation at a landscape scale and depict an independent estimate of carbon isoscapes across the GCFR – under both an interglacial (Holocene) and glacial (terminal Pleistocene) climate – against which palaeo-records can be assessed.

Plant speciation in the Namib Desert: potential origin of a widespread derivative species from a narrow endemic

ABSTRACT Background Parapatric (or ‘budding’) speciation is increasingly recognised as an important phenomenon in plant evolution but its role in extreme (e.g. desert) environments is poorly documented. Aims To test this speciation model in a hypothesised sister pair, the Southwest – North African disjunct Senecio flavus and its putative progenitor, the Namibian Desert endemic S. englerianus. Methods Phylogenetic inferences were combined with niche divergence tests, morphometrics, and experimental-genetic approaches. We also evaluated the potential role of an African Dry Corridor (ADC) in promoting the hypothesised northward expansion of S. flavus (from Namibia), using palaeodistribution models. Results Belonging to an isolated (potential ‘relict’) clade, the two morphologically distinct species showed pronounced niche divergence in Namibia and signs of digenic-epistatic hybrid incompatibility (based on F2 pollen fertility). The presence of ‘connate-fluked’ pappus hairs in S. flavus, likely increasing dispersal ability, is controlled by a single-gene locus. Conclusions Our results provide evidence for a possible (and rare) example of ‘budding’ speciation in which a wider-ranged derivative (S. flavus) originated at the periphery of a smaller-ranged progenitor (S. englerianus) in the Namib Desert region. The Southwest – North African disjunction of S. flavus could have been established by dispersal across intermediate ADC areas during periods of (Late) Pleistocene aridification.

From the Strait of Gibraltar to northern Europe: Pleistocene refugia and biogeographic history of heather (Calluna vulgaris, Ericaceae)

AbstractCalluna vulgaris (Ericaceae) is the most widespread and prevalent woody species of the European dry heathland, from the African side of the Strait of Gibraltar to northern Europe. However, previous biogeographic analyses of this species have ignored the western Mediterranean region, despite its preponderant role as a major glacial refugium for European biota. Here, we explore the existence of further Pleistocene glacial refugia for C. vulgaris in the Iberian Peninsula and the Strait of Gibraltar area and provide new insights into the post-glacial colonization of Europe by this emblematic heathland species. We carried out phylogeographical analyses of C. vulgaris samples from 44 locations using four plastid markers (matK, trnH-psbA, trnL-F and rpl16). We built palaeodistribution models using MAXENT to identify possible refugia for C. vulgaris during the mid-Pliocene, Last Interglacial (LIG), Last Glacial Maximum (LGM) and mid-Holocene. Our results identified a genetic lineage exclusive to the Strait of Gibraltar area s.l. (south-western Iberian Peninsula and north-western tip of Africa) as the most probable close to the clade of origin of the species. This lineage also had more private haplotypes than more recent, Eurosiberian clades. The obtained data highlighted two main refugia for C. vulgaris during the LGM, one around the Strait of Gibraltar and another in the north-western Iberian Peninsula. The Strait of Gibraltar area is a major centre of origin or glacial refugium for the heather C. vulgaris. However, the north-western Iberian Peninsula seems to have acted as a secondary glacial refugium for the more recent, Eurosiberian lineage of this species. This study stresses the importance of the Strait of Gibraltar area in the biogeographic history and conservation of the heather and, by extension, the European heathland habitat.

Insights into the importance of areas of climatic stability in the evolution and maintenance of avian diversity in the Mesoamerican dry forests

AbstractWe analysed the phylogeographic structure of five resident bird lineages distributed in the seasonally dry tropical forests (SDTF) of Mesoamerica to test whether they show patterns of synchronous and geographically coincident genetic divergence during the Quaternary. We generated phylogenetic trees, estimated divergence times and analysed the genetic structure of populations (based on sequences of mitochondrial genes), as well as estimating historical distributions (range extension and areas of long-term climate stability) during the Late Pleistocene. We tested and selected the phylogeographic divergence scenarios that best explain the current divergence patterns of taxa using the Approximate Bayesian Computation (ABC) approach. For most species, phylogenetic trees and haplotype networks showed a clear genetic structure associated with geographical distribution. Overall, the divergence times ranged from 0.29–2.0 Mya, suggesting that diversification of populations occurred at different times during the Pleistocene. The palaeodistribution models predicted at least two areas of climatic stability within the current SDTF that probably allowed glacial-interglacial persistence of isolated bird populations along the Mexican Pacific, thus promoting their genetic divergence. The results provide information relevant to the identification of diversification hotspots for the Mesoamerican SDTF avifauna.

Phylogeographic structure and ecological niche modelling reveal signals of isolation and postglacial colonisation in the European stag beetle.

Lucanus cervus (L.), the stag beetle, is a saproxylic beetle species distributed widely across Europe. Throughout its distribution the species has exhibited pronounced declines and is widely considered threatened. Conservation efforts may be hindered by the lack of population genetic data and understanding of the spatial scale of population connectivity. To address this knowledge gap this research details the first broad scale phylogeographic study of L. cervus based on mitochondrial DNA (mtDNA) sequencing and microsatellite analysis of samples collected from 121 localities across Europe. Genetic data were complemented by palaeo-distribution models of spatial occupancy during the Last Glacial Maximum to strengthen inferences of refugial areas. A salient feature of the mtDNA was the identification of two lineages. Lineage I was widespread across Europe while lineage II was confined to Greece. Microsatellites supported the differentiation of the Greek samples and alongside palaeo-distribution models indicated this area was a glacial refuge. The genetic endemism of the Greek samples, and demographic results compatible with no signatures of spatial expansion likely reflects restricted dispersal into and out of the area. Lineage I exhibited a shallow star like phylogeny compatible with rapid population expansion across Europe. Demographic analysis indicated such expansions occurred after the Last Glacial Maximum. Nuclear diversity and hindcast species distribution models indicated a central Italian refuge for lineage I. Palaeo-distribution modelling results also suggested a western refuge in northern Iberia and south-west France. In conclusion the results provide evidence of glacial divergence in stag beetle while also suggesting high, at least on evolutionary timescales, gene flow across most of Europe. The data also provide a neutral genetic framework against which patterns of phenotypic variation may be assessed.

Tabula rasa in the Patagonian Channels II: The cushion peat bog species Astelia pumila (Asteliaceae) and Donatia fascicularis (Stylidiaceae) survived the last glacial in south‐central Chile

AbstractAimPlant phylogeographic data from the Patagonian Channels are scant and it is largely unknown how the extensive Quaternary glaciations affected the population dynamics of the region's major vegetation component, that is cushion peat bogs (Magellanic moorland). Whether ice‐age glaciers wiped out all terrestrial plant life or whether some populations persisted in situ remains unclear. We reconstructed the phylogeography of two dominant Patagonian cushion peat bog species, Astelia pumila (G.Forst.) Gaudich. (Asteliaceae) and Donatia fascicularis J.R.Forst. & G.Forst. (Stylidiaceae), to test (a) the hypothesis of a glacial refugium for moorland plants in south‐central Chile and (b) the tabula rasa scenario for the Patagonian Channels. The retrieved phylogeographic patterns were compared with those reported previously for a further cushion peat bog species (Pfanzelt et al., Molecular Ecology 26, 4027–4044), with the objective to provide a broader picture of how West Patagonian moorland plants responded to the Quaternary ice‐ages.LocationWest and Fuegian Patagonia, and the Falkland Islands (Islas Malvinas), southern South America.MethodsDNA sequence data from seven and fourteen, respectively, nuclear loci containing Simple Sequence Repeats of 371 and 328 individuals of the two study species were analysed using population genetic summary statistics, phylogenetic networks and Bayesian and multivariate methods to determine genetic structure. Ecological niche modelling was used to reconstruct the spatial distribution of suitable habitat at the Last Glacial Maximum.ResultsAll A. pumila populations belong to a single population genetic cluster. In the case of D. fascicularis, only the northernmost sampled population from Nahuelbuta (Chile) is genetically distinct, whereas the remainder forms a cluster without much further substructure. According to palaeodistribution models, south‐central Chile offered suitable habitat during the last glacial.Main conclusionBoth ecological niche modelling and the very low genetic subdifferentiation are congruent with a tabula rasa scenario for the Patagonian Channels. Populations survived the last glacial in south‐central Chile, in an area to the northwest of the ice sheet. From there, southern regions were recolonized through highly bottlenecked source populations. Other, non‐mutually exclusive factors may have further shaped the population genetic patterns, among them high gene flow mediated by the strong westerly winds.

Phylogeography of an endangered disjunct herb: long-distance dispersal, refugia and colonization routes.

Quaternary glacial cycles appear to have had a consistent role in shaping the genetic diversity and structure of plant species. Despite the unusual combination of the characteristics of the western Mediterranean–Macaronesian area, there are no studies that have specifically examined the effects of palaeoclimatic and palaeogeographic factors on the genetic composition and structure of annual herbs. Astragalus edulis is a disjunct endemic found in the easternmost Canary Islands and the semi-arid areas of north-eastern Africa and south-eastern Iberian Peninsula. This endangered species shows no evident adaptations to long-distance dispersal. Amplified fragment length polymorphism (AFLP) data and plastid DNA sequences were analysed from a total of 360 individuals distributed throughout the range of this species. The modelled potential distribution of A. edulis under current conditions was projected over the climatic conditions of the Last Interglacial (130 ka BP) and Last Glacial Maximum (21 ka BP) to analyse changes in habitat suitability and to look for associations between the modelling and genetic results. Amplified fragment length polymorphism analysis showed clear phylogeographic structure with four distinct genetic clusters. Approximate Bayesian computation (ABC) models based on plastid DNA sequences indicated a Middle Pleistocene long-distance dispersal event as the origin of the populations of the Canary Islands. The models also suggested south-western Morocco as the ancestral area for the species, as well as subsequent colonization of north-eastern Morocco and the Iberian Peninsula. The data compiled indicated the possibility of the presence of refuge areas at favourable locations around the High Atlas and Anti-Atlas mountain ranges. Moreover, palaeodistribution models strongly support the events inferred by ABC modelling and show the potential distribution of the species in the past, suggesting a putative colonization route.

Travelling to the south: Phylogeographic spatial diffusion model in Monttea aphylla (Plantaginaceae), an endemic plant of the Monte Desert.

Effects of Pleistocene climatic oscillations on plant phylogeographic patterns are relatively well studied in forest, savanna and grassland biomes, but such impacts remain less explored on desert regions of the world, especially in South America. Here, we performed a phylogeographical study of Monttea aphylla, an endemic species of the Monte Desert, to understand the evolutionary history of vegetation communities inhabiting the South American Arid Diagonal. We obtained sequences of three chloroplast (trnS–trnfM, trnH–psbA and trnQ–rps16) and one nuclear (ITS) intergenic spacers from 272 individuals of 34 localities throughout the range of the species. Population genetic and Bayesian coalescent analyses were performed to infer genealogical relationships among haplotypes, population genetic structure, and demographic history of the study species. Timing of demographic events was inferred using Bayesian Skyline Plot and the spatio-temporal patterns of lineage diversification was reconstructed using Bayesian relaxed diffusion models. Palaeo-distribution models (PDM) were performed through three different timescales to validate phylogeographical patterns. Twenty-five and 22 haplotypes were identified in the cpDNA and nDNA data, respectively. that clustered into two main genealogical lineages following a latitudinal pattern, the northern and the southern Monte (south of 35° S). The northern Monte showed two lineages of high genetic structure, and more relative stable demography than the southern Monte that retrieved three groups with little phylogenetic structure and a strong signal of demographic expansion that would have started during the Last Interglacial period (ca. 120 Ka). The PDM and diffusion models analyses agreed in the southeast direction of the range expansion. Differential effect of climatic oscillations across the Monte phytogeographic province was observed in Monttea aphylla lineages. In northern Monte, greater genetic structure and more relative stable demography resulted from a more stable climate than in the southern Monte. Pleistocene glaciations drastically decreased the species area in the southern Monte, which expanded in a southeastern direction to the new available areas during the interglacial periods.

Do 120,000 years of plant–pollinator interactions predict floral phenotype divergence in Calceolaria polyrhiza? A reconstruction using species distribution models

Quaternary climatic changes impacted species’ demography and distribution worldwide. Although response to climate change could have been modulated by mutualistic interactions with other species, studies exploring the dynamics of these interactions and their role facilitating species persistence during past climatic variations are scarce. In this work, we attempt to explore the spatial dynamic of Calceolaria polyrhiza and its oil-collecting bee pollinators during the last 120,000 years, identifying stable areas of persistence and statistically determining whether the distribution of pollinator-related floral ecotypes is associated with these shared areas of persistence. To do this, we used 395 presence records of the interacting species and constructed species palaeodistribution models. Additionally, we gathered phenotypic measures of the plant and used decision tree and multiple regression analyses to link the plant phenotypic divergence with the distribution of stable areas. Our species distribution models suggest that past climatic changes affected the interaction between C. polyrhiza and both bee species in time and space. While the interaction between the plant and C. caeruleus predominated in the Andean-Patagonian forest and was relatively stable in space and time, that was not the case for the pollinator C. cineraria in the Patagonian steppe. This, along with our analyses of spatial phenotypic divergence, indicates that current floral phenotypes are the result of two historical different pollination regimes.

Late Pleistocene divergence and postglacial expansion in the Brazilian Atlantic Forest: multilocus phylogeography of Rhopias gularis (Aves: Passeriformes)

In the last decade, phylogeographic studies have revealed a complex evolutionary history of the Brazilian Atlantic Forest (AF) biota. Here, we investigated the evolutionary history of Rhopias gularis, an endemic bird of the AF, based on sequences of two mitochondrial genes and three nuclear introns from 64 specimens from 15 localities. We addressed three main questions: (1) Does the genetic diversity of R. gularis exhibit a distribution pattern congruent with the refuge hypothesis postulated for the AF? (2) Is the population genetic structure of R. gularis congruent with those observed in other AF species? (3) What were the possible historical events responsible for the population structure of this species? Our mtDNA data revealed two phylogroups: (1) phylogroup central-south, with samples from the central and southern parts of the range; (2) and phylogroup north, which included individuals from southern Bahia. Nevertheless, nuclear loci did not reveal any evidence of population structure. Bottleneck tests indicated that the central-south lineage experienced demographic expansion, starting around 20 kya, which coincides with the end of the last glacial maximum. However, there was no evidence of population growth in phylogroup north. Isolation with migration analysis indicated that these phylogroups split c.a. 304 kya, with limited gene flow among them. Palaeodistribution models indicated that R. gularis had a reduced distribution in the south and central AF during the last glacial maximum. Our results support a diversification scenario that is in accordance with proposed Pleistocene refugia. The phylogeographic results from our study exhibited spatial and temporal concordances and discordances with previous studies of organisms from the AF. Differences in habitat requirements of these species could be behind this complex scenario. Future studies correlating variables of the niche of these species with the observed phylogeographic patterns may help understand why there are congruent and incongruent results.

Comparative palaeodistribution of eight hummingbird species reveal a link between genetic diversity and Quaternary habitat and climate stability in Mexico

Large-scale phylogeographical patterns and the underlying factors driving species divergence in Mesoamerica are poorly understood, but it is widely documented that tectonic events and Pleistocene climate changes play an important role in determining species diversification. As glaciations in Mesoamerica developed only around high mountains, one hypothesis is that the known effects of the Last Glacial Maximum on the geographical distribution and genetic diversity of bird populations, producing the contraction/ expansion latitudinal pattern observed in temperate bird species, should be largely undetected in resident bird populations inhabiting environmentally more stable habitats. To gain insight into the effects of Quaternary habitat and climate stability on the genetic diversity, we use ecological niche modelling and generalised linear modelling to determine the role of changes in habitat stability on the genetic diversity in eight widespread or range restricted hummingbird species. We found lesser changes in suitable habitat from past to present in most of the species than those predicted by palaeodistribution models at northern temperate regions. Contemporary seasonal precipitation, Quaternary habitat and climate stability had superior explanatory power, but the magnitude and directionality of their effects on genetic diversity varied between range-restricted and widely distributed species. We observed that the species studied have not responded equally to changes in climate stability in this complex region, suggesting that habitat differences and/or the altitudinal range of the hummingbird species influenced genetic diversity, and that the species-specific responses are not only linked to habitat stability in the region but also to contemporary seasonality associated with the availability of floral resources.

Phylogeographical analysis of two cold‐tolerant plants with disjunct Lusitanian distributions does not support in situ survival during the last glaciation

AbstractAimWe used a combination of modelling and genetic approaches to investigate whether Pinguicula grandiflora and Saxifraga spathularis, two species that exhibit disjunct Lusitanian distributions, may have persisted through the Last Glacial Maximum (LGM, c. 21 ka) in separate northern and southern refugia.LocationNorthern and eastern Spain and south‐western Ireland.MethodsPalaeodistribution modelling using Maxent was used to identify putative refugial areas for both species at the LGM, as well as to estimate their distributions during the Last Interglacial (LIG, c. 120 ka). Phylogeographical analysis of samples from across both species' ranges was carried out using one chloroplast and three nuclear loci for each species.ResultsThe palaeodistribution models identified very limited suitable habitat for either species during the LIG, followed by expansion during the LGM. A single, large refugium across northern Spain and southern France was postulated for P. grandiflora. Two suitable regions were identified for S. spathularis: one in northern Spain, corresponding to the eastern part of the species' present‐day distribution in Iberia, and the other on the continental shelf off the west coast of Brittany, south of the limit of the British–Irish ice sheet. Phylogeographical analyses indicated extremely reduced levels of genetic diversity in Irish populations of P. grandiflora relative to those in mainland Europe, but comparable levels of diversity between Irish and mainland European populations of S. spathularis, including the occurrence of private hapotypes in both regions.Main conclusionsModelling and phylogeographical analyses indicate that P. grandiflora persisted through the LGM in a southern refugium, and achieved its current Irish distribution via northward dispersal after the retreat of the ice sheets. Although the results for S. spathularis are more equivocal, a similar recolonization scenario also seems the most likely explanation for the species' current distribution.

Quaternary range and demographic expansion of Liolaemus darwinii (Squamata: Liolaemidae) in the Monte Desert of Central Argentina using Bayesian phylogeography and ecological niche modelling

Until recently, most phylogeographic approaches have been unable to distinguish between demographic and range expansion processes, making it difficult to test for the possibility of range expansion without population growth and vice versa. In this study, we applied a Bayesian phylogeographic approach to reconstruct both demographic and range expansion in the lizard Liolaemus darwinii of the Monte Desert in Central Argentina, during the Late Quaternary. Based on analysis of 14 anonymous nuclear loci and the cytochrome b mitochondrial DNA gene, we detected signals of demographic expansion starting at ~55ka based on Bayesian Skyline and Skyride Plots. In contrast, Bayesian relaxed models of spatial diffusion suggested that range expansion occurred only between ~95 and 55ka, and more recently, diffusion rates were very low during demographic expansion. The possibility of population growth without substantial range expansion could account for the shared patterns of demographic expansion during the Last Glacial Maxima (OIS 2 and 4) in fish, small mammals and other lizards of the Monte Desert. We found substantial variation in diffusion rates over time, and very high rates during the range expansion phase, consistent with a rapidly advancing expansion front towards the southeast shown by palaeo-distribution models. Furthermore, the estimated diffusion rates are congruent with observed dispersal rates of lizards in field conditions and therefore provide additional confidence to the temporal scale of inferred phylogeographic patterns. Our study highlights how the integration of phylogeography with palaeo-distribution models can shed light on both demographic and range expansion processes and their potential causes.

Integrating species distribution models (SDMs) and phylogeography for two species of Alpine Primula

The major intention of the present study was to investigate whether an approach combining the use of niche-based palaeodistribution modeling and phylo-geography would support or modify hypotheses about the Quaternary distributional history derived from phylogeographic methods alone. Our study system comprised two closely related species of Alpine Primula. We used species distribution models based on the extant distribution of the species and last glacial maximum (LGM) climate models to predict the distribution of the two species during the LGM. Phylogeographic data were generated using amplified fragment length polymorphisms (AFLPs). In Primula hirsuta, models of past distribution and phylogeographic data are partly congruent and support the hypothesis of widespread nunatak survival in the Central Alps. Species distribution models (SDMs) allowed us to differentiate between alpine regions that harbor potential nunatak areas and regions that have been colonized from other areas. SDMs revealed that diversity is a good indicator for nunataks, while rarity is a good indicator for peripheral relict populations that were not source for the recolonization of the inner Alps. In P. daonensis, palaeo-distribution models and phylogeographic data are incongruent. Besides the uncertainty inherent to this type of modeling approach (e.g., relatively coarse 1-km grain size), disagreement of models and data may partly be caused by shifts of ecological niche in both species. Nevertheless, we demonstrate that the combination of palaeo-distribution modeling with phylogeographical approaches provides a more differentiated picture of the distributional history of species and partly supports (P. hirsuta) and partly modifies (P. daonensis and P. hirsuta) hypotheses of Quaternary distributional history. Some of the refugial area indicated by palaeodistribution models could not have been identified with phylogeographic data.

Postglacial colonization of Europe by the barbastelle bat: agreement between molecular data and past predictive modelling

The barbastelle (Barbastella barbastellus) is a rare forest bat with a wide distribution in Europe. Here, we combine results from the analysis of two mtDNA fragments with species distribution modelling to determine glacial refugia and postglacial colonization routes. We also investigated whether niche conservatism occurs in this species. Glacial refugia were identified in the three southern European peninsulas: Iberia, Italy and the Balkans. These latter two refugia played a major role in the postglacial colonization process, with their populations expanding to England and central Europe, respectively. Palaeo-distribution models predicted that suitable climatic conditions existed in the inferred refugia during the last glacial maximum (LGM). Nevertheless, the overlap between the current and the LGM distributions was almost inexistent in Italy and in the Balkans, meaning that B. barbastellus populations were forced to shift range between glacial and interglacial periods, a process that probably caused some local extinctions. In contrast, Iberian populations showed a 'refugia within refugium' pattern, with two unconnected areas containing stable populations (populations that subsisted during both glacial and interglacial phases). Moreover, the match between LGM models and the refugial areas determined by molecular analysis supported the hypothesis of niche conservatism in B. barbastellus. We argue that geographic patterns of genetic structuring, altogether with the modelling results, indicate the existence of four management units for conservation: Morocco, Iberia, Italy and UK, and Balkans and central Europe. In addition, all countries sampled possessed unique gene pools, thus stressing the need for the conservation of local populations.

Palaeodistribution modelling does not support disjunct Pleistocene refugia in several Central American plant taxa

AbstractAim We combine evidence from palaeoniche modelling studies of several tree species to estimate the extent of Central American forest during the Last Glacial Maximum (LGM). In particular, we ask whether the distributions of these species are likely to have changed since the LGM, and whether LGM distributions coincide with previously proposed Pleistocene refugia in this area.Location Central American wet and seasonally dry forests.Methods We developed ecological niche models using two simulations of Pleistocene climate and occurrence data for 15 Neotropical plant species. We focused on palaeodistribution models of three ‘focal’ tree species that occur in wet and seasonally dry Central American forests, where recent phylogeographic data suggest Pleistocene differentiation coincident with previously proposed refugia. We added predictions from six wet‐forest and six seasonally dry‐forest obligate plant species to gauge whether Pleistocene range shifts were specific to habitat type. Correlation analyses were performed between projected LGM and present distributions, LGM distributions and previously proposed refugia. We also asked whether modelled palaeodistributions were smaller than their current extents.Results According to our models, the ranges of the study species were not reduced during the LGM, and did not correlate with refugial models, regardless of habitat type. Relative range sizes between present and LGM distributions did not indicate significant range changes since the LGM. However, relative range sizes differed overall between the two palaeoclimate models.Main conclusions Many of the modelled palaeodistributions of study species were not restricted to refugia during the LGM, regardless of forest type. While constrained from higher elevations, most species found suitable habitat at coastal margins and on newly exposed land due to lowered sea levels during the LGM. These results offer no corroboration for Pleistocene climate change as a driver of genetic differentiation in the ‘focal’ species. We offer alternative explanations for genetic differentiation found in plant species in this area.

Climate change and the origin of migratory pathways in the Swainson's thrush,Catharus ustulatus

AbstractAim To provide a spatially explicit model of how geographic distributions at the last glacial maximum (LGM) and post‐glacial colonization routes shaped current migratory pathways in the Swainson's thrush,Catharus ustulatus, a long‐distance migratory bird.Location The Swainson's thrush breeds in boreal forest regions of the United States and Canada as well as in riparian woodlands along the Pacific coast of North America.Methods Palaeodistribution modelling is combined with mtDNA phylogeography to predict the breeding range of the Swainson's thrush at the LGM. Quantitative environmental analysis and bioclimatic modelling are used to reconstruct the most likely post‐glacial colonization pathways. A maximum likelihood method for estimating growth rates is used to approximate the relative change in population size since the LGM.Main conclusions The palaeodistribution models are concordant with the Swainson's thrush mtDNA phylogeography, suggesting that the inland and coastal groups were geographically isolated in eastern (inland) and western (coastal) regions at the LGM. Estimates of change in population size based on genetic data are remarkably consistent with estimates of change in range size, suggesting that the coastal group has undergone a 2‐ to 3‐fold demographic and range expansion, while the inland group has undergone a 6‐ to 12‐fold demographic and range expansion since the LGM. Bioclimatic analyses strongly support the hypothesis that populations expanding out of the east into previously glaciated areas in the west were undergoing a natural extension of their range by tracking the changes in climatic conditions. The combination of bioclimatic and molecular analyses is consistent with the idea that coastal and inland groups expanded from separate eastern and western regions after the LGM and that the current migratory pathway of the inland group retraces its post‐glacial colonization route.