Late-glacial and Holocene palaeovegetation zonal reconstruction for central and north-central North America

Aim The purpose of this study is to develop palaeovegetation zonation models for central and north‐central North America, based on late‐Quaternary and Holocene pollen stratigraphic data (n = 246 sites). A secondary purpose was to evaluate an hypothesis ( Strong & Hills, 2003 ) to explain the disjunct distribution of species in western Alberta. Location Hudson Bay‐Lake Michigan to the Rocky Mountains region, north of 36° N to the Arctic Ocean (c. 70° N). Methods Pollen profiles spanning 40 years of palaeoecological research in North America were extracted from published and unpublished archival sources. Individual profiles were subdivided into 1000‐year increments based on the assumption of a constant sedimentation rate between stratigraphic dates (e.g. surface sediments, radiocarbon ¹⁴C dates, tephra layers). The pollen composition among profiles was standardized to 54 commonly recognized taxa, with percentage composition within each stratigraphic sample prorated to 100% prior to analysis. Near‐surface sediments from these profiles were included as analogues of modern vegetation. Cluster analysis was used as a guide to the classification of 2356 temporal stratigraphic samples, which resulted in the recognition of 16 pollen groups. These groups were summarized in terms of their pollen composition, mapped, and used in combination with terrain information and an ecological knowledge of the study area to construct six physiognomically‐based palaeovegetation zonation models at 2000‐year intervals from 14,000 to 4000 yr bp (radiocarbon years before present). Results The 14,000 yr bp model placed Boreal and Cordilleran Forests proximal to the southern glacial front, whereas Arctic tundra dominated the Yukon Territory–Alaska ice‐free zone. Pollen and macrofossil evidence suggests that this Boreal Forest zone contained a mixture of coniferous and deciduous tree species. Grassland was postulated immediately south of the forest zone, with its northern extreme near 49° N latitude in the Alberta–Montana border area. Separation of the Laurentide and Cordilleran glacial fronts about 12,000 yr bp initiated the northward advance of Boreal Forests into western Canada. By the end of the Hypsithermal at about 6000 yr bp , Boreal Forests occurred near the Arctic Ocean, and Grassland and Aspen Parkland zones may have extended to 54° N and 59° N latitude in Alberta, respectively. Between 6000 and 4000 yr bp , a 5° and 1° latitudinal southward shift of the northern Boreal Forest and Grassland/Aspen Parkland boundaries occurred, respectively, near their contemporary positions with corresponding expansions of the Subarctic and Arctic zones. Modern Canadian Cordilleran Forests along the eastern slopes of the Rocky Mountains were interpreted as originating from the north‐central Montana–south‐western Alberta area. Jack pine (Pinus banksiana Lamb.), a common Boreal Forest species, appears to have entered central Canada via the north side of Lake Superior after 11,000 yr bp . Main conclusions Modern vegetation in central Canada evolved from biomes located in the northern USA during the late‐Quaternary. The Boreal Forest biome contained the same arboreal taxa as the modern vegetation, except it lacked jack pine. The proposed regional palaeovegetation models support the hypothesis of Strong & Hills (2003) , but new independent palaeoecological data will be needed for a proper evaluation.     

Blackfoot Indian utilization of the flora of the northwestern great plains

The Blackfoot Indians occupied the northwestern plains along and adjacent to the eastern base of the Rocky Mountains in present-day southern Alberta, Canada, and western Montana, V. S. A. Climate and topography and, hence, vegetation of the region are diverse. Although primarily meat-eaters, the Blackfoot consumed some vegetable foods. They had a knowledge of plant medicines, which they used in the treatment of both humans and horses. Plants were used for other purposes including the production of dyes and perfumes, the manufacture of weapons, and as construction materials. The Blackfoot Indians utilized 185 species belonging to 140 genera of plants distributed among 57 families.     

Species interactions weakly modify climate‐induced tree co‐occurrence patterns

Aims

Species distributions are hypothesized to be underlain by a complex association of processes that span multiple spatial scales including biotic interactions, dispersal limitation, fine‐scale resource gradients and climate. Species disequilibrium with climate may reflect the effects of non‐climatic processes on species distributions, yet distribution models have rarely directly considered non‐climatic processes. Here, we use a Joint Species Distribution Model (JSDM) to investigate the influence of non‐climatic factors on species co‐occurrence patterns and to directly quantify the relative influences of climate and alternative processes that may generate correlated responses in species distributions, such as species interactions, on tree co‐occurrence patterns.

Location

US Rocky Mountains.

Methods

We apply a Bayesian JSDM to simultaneously model the co‐occurrence patterns of ten dominant tree species across the Rocky Mountains, and evaluate climatic and residual correlations from the fitted model to determine the relative contribution of each component to observed co‐occurrence patterns. We also evaluate predictions generated from the fitted model relative to a single‐species modelling approach.

Results

For most species, correlation due to climate covariates exceeded residual correlation, indicating an overriding influence of broad‐scale climate on co‐occurrence patterns. Accounting for covariance among species did not significantly improve predictions relative to a single‐species approach, providing limited evidence for a strong independent influence of species interactions on distribution patterns.

Conclusions

Overall, our findings indicate that climate is an important driver of regional biodiversity patterns and that interactions between dominant tree species contribute little to explain species co‐occurrence patterns among Rocky Mountain trees.     

Phylogeographic signal variation in mitochondrial DNA among geographically isolated grassland butterflies

Aim We surveyed mitochondrial DNA (mtDNA) sequence variation among regionally isolated populations of 10 grassland‐associated butterfly species to determine: (1) the utility of phylogeographic comparisons among multiple species for assessing recent evolutionary patterns, and (2) the respective roles of isolation attributable to range disjunction versus isolation attributable solely to geographic distance in establishing divergence patterns. Location The Peace River grasslands of northern Alberta and British Columbia, Canada, which are isolated by 300+ km from similar communities to the south. Methods We sequenced mtDNA (1420 bp of cytochrome c oxidase subunit I) from five grassland‐restricted butterfly species that have geographically disjunct populations and from five ecologically broader species that have more continuous distributions across the same regions. Using analysis of molecular variance (AMOVA), Mantel and partial Mantel tests, and haplotype networks, we compared population structure within and between species in order to assess the validity of single‐species phylogeographic characterizations. We then contrasted variance components between disjunct and continuously distributed species to assess whether divergences were correlated more with disjunction or with geographic distance. Results Single‐species analyses varied substantially within both the disjunct and the continuous groups. One species in each of these groups had mtDNA with unusually deep intraspecific mitochondrial lineage divergences. On the whole, however, the five species with disjunct ranges exhibited greater divergence between geographically distant populations than did the five species with continuous distributions. Comparison of variance components between disjunct and continuous species indicated that isolation attributable only to geographic distance was responsible for up to half of the total sequence variation between disjunct populations of grassland butterflies. Main conclusions Our findings show that single‐species phylogeographic analyses of post‐Pleistocene butterfly distributions are inadequate for characterizing regional biogeographic divergence histories. However, comparison of mtDNA sequence divergences between groups of disjunct and continuously distributed species can allow isolation attributable to range interruption to be quantitatively distinguished from isolation attributable solely to gene flow attenuation over the same geographic area.     

Distribution and Broadscale Habitat Relations of the Wolverine in the Contiguous United States

ABSTRACT Conservation of the wolverine (Gulo gulo) at the southern extent of its North American range requires reliable understandings of past and present distribution patterns and broad-scale habitat relations. We compiled 820 verifiable and documented records of wolverine occurrence (specimens, DNA detections, photos, and accounts of wolverines being killed or captured) in the contiguous United States from museums, the literature, and institutional archives. We spatially referenced 729 records with areal precision ≤1 township (93.2 km²) and temporal precision ≤10 years. Historical records (1827–1960) were located primarily in the western mountains and Great Lakes region. However, our data suggest that the historical distribution of wolverines in the Cascade Range and Sierra Nevada was disjunct, contradicting previous interpretations. Our results indicate that wolverine range in the contiguous United States had contracted substantially by the mid-1900s. Current records (1995–2005) are limited to north-central Washington, northern and central Idaho, western Montana, and northwestern Wyoming. We investigated potential relations between wolverines and alpine vegetation, cold temperatures, and spring snow cover by comparing the distribution of historical wolverine records with Kuchler's potential natural vegetation types, Holdridge's climatic life zones, and EASE snow-cover maps during the latter portion of the wolverine denning period (15 Apr-14 May). In the western mountains, historical wolverine records generally occurred in or near alpine vegetation and climatic conditions, especially at the limits of their distribution in the Cascade Range, Sierra Nevada, and southern Rocky Mountains. However, the only habitat layer that fully accounted for historical distribution patterns was spring snow cover. Causal factors for the extirpation of wolverines from the southern portions of their range in the contiguous United States are unknown, but are likely related to high levels of human-caused mortality and low to nonexistent immigration rates.     

晚更新世晚期以来昆仑山垭口区的植被与环境

昆仑山垭口区小南川剖面和雪水河热水剖面的孢粉分析揭示了该区４４０００ａＢ．Ｐ．以来的植被演替和气候变化。４００００ａＢ．Ｐ．前,推测昆仑山垭口区为典型的灌木荒漠植被,气候极端干燥。４００００－３００００ａＢ．Ｐ．,气候稍有好转。３００００－２４０００ａＢ．Ｐ．为草原荒漠,降水增加。２４０００－１８０００ａＢ．Ｐ．为末次冰期极盛期,气候干冷。１８０００－１３０００ａＢ．Ｐ．气候凉偏干。１３０００－８０００ａＢ．Ｐ．气候凉干。８０００－６０００ａＢ．Ｐ．为全新世温暖期,但由于植被的滞后现象,本区仍为草原荒漠景观。６０００－５０００ａＢ．Ｐ．,本区可能也存在着中全新世的降温事件。５０００－３０００ａＢ．Ｐ．在全新世大暖期的影响下,小南川附近的植被演变成温性草原植被,并有人类的放牧活动。３０００ａＢ．Ｐ．以后,气候变凉,草原迅速地演变为灌木和小乔木荒漠植被,其中３０００－１０００ａＢ．Ｐ．为凉干时期,１０００ａＢ．Ｐ．以后,可能有过一段凉湿时期。     

Late Holocene palaeoenvironment change in central Tianshan of Xinjiang,northwest China

The northern slopes of central Tianshan Mountains in Xinjiang, northwestern China can provide an ideal database to research palaeoclimate as disturbance by human impact is relatively low and the vegetation zones reflect climatic gradients. In order to establish the correlation between modern climatic factors and surface pollen assemblages and to reconstruct palaeoclimate on the northern slope of central Tianshan Mountains, three Holocene sections in Daxigou, Huashuwozi and Sichanghu located at different elevations and vegetation zones were chosen for study. A total of 80 surface pollen samples in 86 vegetation quadrats were collected for pollen‐vegetation relationship analysis. The Warmth Index (WI) and Moisture Index (MI) were calculated based on averaged modern climate data during 1951 – 2000 at eight weather stations in the study area. Pollen percentages of Picea, Artemisia, Chenopodiaceae, Ephedra, and Tamarix, as well as A/C (Artemisia/Chenopodiaceae) and AP/NAP (arboreal/nonarboreal pollen) ratio were selected as pollen variables and WI and MI were chosen as climatic variables. The relationship between pollen percentages (Picea, Artemisia, Chenopodiaceae and Tamarix), A/C, AP/NAP ratio, WI and MI values were estimated (95% confidence interval) using stepwise multiple linear regression analysis. WI and MI values for the three sections were calculated using these regression equations, and palaeoclimate for the study area could be reconstructed. The results showed periods of both cool‐humid and warm‐dry conditions on the northern slopes of Tianshan Mountain during the late Holocene.     

Bet-hedging applications for conservation

One of the early tenets of conservation biology is that population viability is enhanced by maintaining multiple populations of a species. The strength of this tenet is justified by principles of bet-hedging. Management strategies that reduce variance in population size will also reduce risk of extinction. Asynchrony in population fluctuations in independent populations reduces variance in the aggregate of populations whereas environmental correlation among areas increases the risk that all populations will go extinct. We review the theoretical rationale of bet-hedging and suggest applications for conservation management of least terns in Nebraska and grizzly bears in the northern Rocky Mountains of the United States. The risk of extinction for least terns will be reduced if we can sustain the small central Platte River population in addition to the larger population on the lower Platte. Similarly, by restoring grizzly bears to the Bitterroot wilderness of Idaho and Montana can reduce the probability of extinction for grizzly bears in the Rocky Mountains of the United States by as much as 69–93%.     

A 40,000-year woodrat-midden record of vegetational and biogeographical dynamics in north-eastern Utah, USA

Aim A conspicuous climatic and biogeographical transition occurs at 40–45° N in western North America. This pivot point marks a north–south opposition of wet and dry conditions at interannual and decadal time‐scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat (Neotoma) middens to the south]. To overcome these limitations, we are extending the woodrat‐midden record northward into the lowlands of the central Rocky Mountains. Location Woodrat middens were collected from crevices and rock shelters on south‐facing slopes of Dutch John Mountain (2000–2200 m, 40°57′ N, 109°25′ W), situated on the eastern flanks of the Uinta Mountains in north‐eastern Utah. The site is near the regional limits for Pinus ponderosa, P. edulis, P. contorta, Cercocarpus ledifolius var. intricatus, Abies concolor, Ephedra viridis and other important western species. Methods We analysed pollen and plant macrofossils from the 40,000‐year midden sequence. The middens represent brief, depositional episodes (mostly years to decades). Four middens represent the early to full‐glacial period (40,000–18,000 cal‐yr bp ), eight middens are from the late‐glacial/early Holocene transition (13,500–9000 cal yr bp ), and 33 middens span the mid‐to‐late Holocene (last 7500 years). Temporal density of our Holocene middens (one every c. 210 years) is comparable with typical Holocene pollen sequences from lake sediments. Results Early to full‐glacial assemblages are characterized by low diversity and occurrence of montane conifers (Picea pungens, Pseudotsuga menziesii, P. flexilis, Juniperus communis) absent from the site today. Diversity increases in the late‐glacial samples with the addition of J. scopulorum, J. horizontalis, C. montanus, C. ledifolius var. intricatus and mesic understory species. The coniferous trees and J. communis declined and J. osteosperma appeared during the late‐glacial/Holocene transition. Juniperus osteosperma populations have occupied the site throughout the Holocene. Pinus ponderosa was established by 7500 cal‐yr bp , and has occurred at least locally ever since. Montane conifers and J. horizontalis persisted until c. 5500 cal‐yr bp . The signature events of the late Holocene were the invasions of P. edulis and Ephedra viridis and establishment of pinyon–juniper woodland in the last 800 years. Main conclusions The Dutch John Mountain midden record adds to an emerging picture in which mid‐elevation conifers (P. flexilis, Pseudotsuga menziesii, Picea pungens, J. scopulorum, J. communis) dominated vegetation over a wide area of the Colorado Plateau and adjacent Rocky Mountains. Rather than being fragmented, as often assumed in phylogeographical studies, these species had broader and more‐connected distributions than they do in the region today. Paradoxically, subalpine conifers (Picea engelmannii, A. lasiocarpa) occurred at higher elevations to the south, possibly representing declining precipitation from south to north owing to southward displacement of the polar jet stream. The Dutch John Mountain record displays a series of extinction and invasion events. Most of the extinctions were local in scale; nearly all constituents of fossil midden assemblages occur within a few kilometres of Dutch John Mountain, and some occur at least locally on its slopes. The sole exception is J. horizontalis, which is regionally extinct. In contrast to extinctions, Holocene invasions were regional in scale; J. osteosperma, P. ponderosa, P. edulis and Ephedra viridis immigrated from glacial‐age source populations far to the south.     

Genetic signals of demographic expansion in Downy Woodpecker (Picoides pubescens) after the last North American glacial maximum

The glacial cycles of the Pleistocene have been recognized as important, large-scale historical processes that strongly influenced the demographic patterns and genetic structure of many species. Here we present evidence of a postglacial expansion for the Downy Woodpecker (Picoides pubescens), a common member of the forest bird communities in North America with a continental distribution. DNA sequences from the mitochondrial tRNA-Lys, and ATPase 6 and 8 genes, and microsatellite data from seven variable loci were combined with a species distribution model (SDM) to infer possible historical scenarios for this species after the last glacial maximum. Analyses of Downy Woodpeckers from 23 geographic areas suggested little differentiation, shallow genealogical relationships, and limited population structure across the species' range. Microsatellites, which have higher resolution and are able to detect recent differences, revealed two geographic groups where populations along the eastern edge of the Rocky Mountains (Montana, Utah, Colorado, and southern Alberta) were genetically isolated from the rest of the sampled populations. Mitochondrial DNA, an important marker to detect historical patterns, recovered only one group. However, populations in Idaho and southeast BC contained high haplotype diversity and, in general were characterized by the absence of the most common mtDNA haplotype. The SDM suggested several areas in the southern US as containing suitable Downy Woodpecker habitat during the LGM. The lack of considerable geographic structure and the starburst haplotype network, combined with several population genetic tests, suggest a scenario of demographic expansion during the last part of Pleistocene and early Holocene.     

Testing nested phylogenetic and phylogeographic hypotheses in the Plethodon vandykei species group

Mesic forests in the North American Pacific Northwest occur in two disjunct areas: along the coastal and Cascade ranges of Oregon, Washington, and British Columbia as well as the Northern Rocky Mountains of Idaho, Montana, and British Columbia. Over 150 species or species complexes have disjunct populations in each area, and a priori hypotheses based on phytogeography and geology potentially explain the disjunction via either dispersal or vicariance. Here, we test these hypotheses in the disjunct salamander complex Plethodon vandykei and P. idahoensisby collecting genetic data (669 bp of Cyt b) from 262 individuals. Maximum likelihood analysis indicated reciprocal monophyly of these species, supporting the ancient vicariance hypothesis, whereas parametric bootstrap and Bayesian hypothesis testing allow rejection of the dispersal hypothesis. The coalescent estimate of the time since population divergence (estimated using MDIV) is 3.75 x 106 years, and the 95%credibility interval of this value overlaps with the geological estimate of vicariance, but not the hypothesized dispersal. These results are congruent with the pattern seen in other mesic forest amphibian lineages and suggest disjunction in amphibians may be a concerted response to a geological/climatological event. WithinP. idahoensis, we tested the corollary hypothesis of an inland Pleistocene refugium in the Clearwater drainage with nested clade analysis and coalescent estimates of population growth rate (g). Both analyses support post-Pleistocene expansion from the Clearwater refugium. We corroborated this result by calculating Tajima's Dand mismatch distribution within each drainage, showing strong evidence for recent population expansion within most drainages. This work demonstrates the utility of statistical phylogeography and contributes two novel analytical tools: tests of stationarity with respect to topology in the Bayesian estimation, and the use of coalescent simulations to test the significance of the population growth-rate parameter.     

Effects of foundation species above and below tree line

The facilitative effects of “foundation species” on community diversity and composition in alpine systems can be strong, but the strength of these effects often varies along gradients that occur above tree line. Here, we explore the effects of foundation species above and below tree line, a globally consistent and often abrupt climatic and ecological transition. The experiment was developed in Northern Rocky Mountains of Wyoming and Montana, USA, in vegetation with similar herbaceous physiognomies without trees, but containing dominant foundation species with “cushion” morphologies. In these systems, we compared the diversity and structure of plant communities occurring within these foundation species to that in the open at three sites below tree line and three sites above tree line. Above tree line, 69–94% of all species were significantly spatially associated with foundation species, whereas below tree line, 29–62% of the species were associated with foundation species. Similar patterns were observed in species accumulation curves with foundation species affecting the accumulation of species by +17 to +47% above tree line vs. –27 to +24% below tree line. Our results were consistent with the idea that facilitative interactions are more common with greater abiotic stress. However, our results also suggest the possibility that the climatic transition representing tree line might also represent a threshold, rather than a simple linear response, in how foundation species affect community diversity. A much larger sample size is warranted to thoroughly test such thresholds, but the fundamental ecological and physiological transition that plants experience at the climate of the tree line may also be reflected in small-scale species interactions that organize communities.     

Morphological and molecular systematics of Rocky Mountain alpine Laccaria

The alpine zone is comprised of habitats at elevations above treeline, and macromycetes play important ecological roles as decomposers and mycorrhizal symbionts here as elsewhere. Laccaria is an important group of ectomycorrhizal basidiomycetes widely used in experimental and applied research. A systematic study of alpine Laccaria species using morphological, cultural and molecular (ribosomal DNA internal transcribed spacer) data revealed five taxa in the Rocky Mountain alpine zone: L. laccata var. pallidifolia, L. nobilis (the first published report for arctic-alpine habitats), L. pumila, L. montana and L. pseudomontana (a newly described taxon similar to L. montana with more ellipsoidal, finely echinulate basidiospores). All occur in the southern Rocky Mountains of Colorado; however, only L. pumila and L. montana were found on the Beartooth Plateau in the northern Rocky Mountains of Montana and Wyoming. All are associated with dwarf and shrub Salix species, with L. laccata var. pallidifolia also associated with Dryas octopetala and Betula glandulosa. Maximum-parsimony phylogenetic analysis of rDNA-ITS sequences for 27 Laccaria accessions supports the morphological species delineations.     

Climatic and geographic barriers drive distributional patterns of bird phenotypes within peninsular India

Modern phylogenetic data provide unparalleled ability to test biogeographic paradigms, often suggested by differences in species distribution patterns. However, such approaches have been applied less at regional scales, particularly in Asia. In the absence of such data, we examine if concordance of distributional patterns for phenotypes (subspecies) suggest potential biogeographic barriers for birds in peninsular India. Specifically, we examine climatic and physical factors that might limit phenotype distributions in this region. Various physical, vegetation and climatic barriers were demarcated to identify potential biogeographic units within peninsular India. We then collated occurrence of endemic or disjunctly distributed species and subspecies within these units using published range maps. We also quantified turnover between potential units, allowing us to identify significant biogeographic barriers. Three time‐step climate data (Last Glacial Maxima, mid‐Holocene and present) enabled us to examine differences between these potential biogeographic regions through time. The Palk Straits, followed by the Goa Gap (～ 16°N) and the Godavari River emerged as the major barriers in this region. The Palk Straits and Godavari are physical barriers while Goa Gap appears to be a climate‐mediated ecological divide. Mountain barriers like the Palghat Gap are not the most significant barriers as previously thought. Climatically intermediate regions appeared unstable in the past and showed inconsistent affinities to different geographic units across families. We suggest that relative climatic stability of the wet regions of the southern western Ghats could be responsible for high subspecies endemism here. Our approach provides hypotheses that can be tested with comparative multi‐species phylogeographic data in the future.     

Revisiting the historical distribution of Seasonally Dry Tropical Forests: new insights based on palaeodistribution modelling and palynological evidencegeb

Aim To investigate the potential distribution of Seasonally Dry Tropical Forests (SDTFs) during the Quaternary climatic fluctuations; to reassess the formerly proposed ‘Pleistocenic arc hypothesis’ (PAH); and to identify historically stable and unstable areas of SDTF distributions in the light of palaeodistribution modelling. Location SDTFs in lowland cis‐Andean eastern‐central South America. Methods We first developed georeferenced maps depicting the current distributional extent of SDTFs under two distinct definitions (narrow and broad). We then generated occurrence datasets, which were used with current and past bioclimatic variables to predict SDTF occurrence by implementing the maximum entropy machine‐learning algorithm. We obtained historical stability maps by overlapping the presence/absence projections of each of three climatic scenarios [current, 6 kyr bp during the Holocene, and 21 kyr bp during the Last Glacial Maximum (LGM)]. Finally, we checked the consistencies of the model prediction with qualitative comparisons of vegetation types inferred from available fossil pollen records. Results The present‐day SDTF distribution is disjunct, but we provide evidence that it was even more disjunct during the LGM. Reconstructions support a progressive southward and eastward expansion of SDTFs on a continental scale since the LGM. No significant expansion of SDTFs into the Amazon Basin was detected. Areas of presumed long‐term stability are identified and confirmed (the three nuclear regions, Caatinga, Misiones and Piedmont, plus the Chiquitano region), and these possibly acted as current and historical refugial areas. Main conclusions The LGM climate was probably too dry and cold to support large tracts of SDTF, which were restricted to climatically favourable areas relative to the present day (in contrast with the PAH, as it was originally conceived). Expansions of SDTFs are proposed to have occupied the southern portion of Caatinga nucleus more recently during the early–middle Holocene transition. We propose an alternative scenario amenable to further testing of an earlier SDTF expansion (either at the Lower Pleistocene or the Tertiary), followed by fragmentation in the LGM and secondary expansion in the Holocene. The stability maps were used to generate specific genetic predictions at both continental and regional scales (stable areas are expected to have higher genetic diversity and endemism levels than adjacent unstable areas) that can be used to direct field sampling to cover both stable (predicted refugia) and unstable (recently colonized) areas. Lastly, we discuss the possibility that SDTFs may experience future expansion under changing climate scenarios and that both stable and unstable areas should be prioritized by conservation initiatives.     

Predicting yellow toadflax infestations in the Flat Tops Wilderness of Colorado

Understanding species–environment relationships is important to predict the spread of non-native species. Yellow toadflax (Linaria vulgaris Mill.) is an invasive perennial recently found in the Flat Tops Wilderness of the White River National Forest on the western slope of the Colorado Rocky Mountains. We hypothesized yellow toadflax occurrence could be predicted from easily measured site characteristics. We used logistic regression with stepwise selection to generate a model to predict yellow toadflax occurrence on a particular plot based on that site’s physical characteristics. The experimental design was a paired-plot study in two locations using circular 1,018-m² plots. Sixty-eight plots that did not contain yellow toadflax and 65 plots that contained yellow toadflax were sampled at the Ripple Creek site in 1999. In 2000, 54 non-toadflax plots and 55 toadflax-containing plots were sampled in the Marvine Creek site. Site characteristics sampled included: vegetation type; under-canopy light level; slope; aspect; soil properties; presence of disturbance, trails, and/or water; and total species richness. A model that correctly classified >90% of the 242 plots sampled included two vegetation type parameters, the presence of trails, and total species richness. Yellow toadflax is most often found in areas that were open-canopy sites, along trails, and with higher species diversity plots (>23 species). This approach can be used for other species in other areas to rapidly identify areas vulnerable to invasion.     

俄罗斯北部平原(VYCHEGDA河盆地)全新世植物群和植被

对Vychegda河流域靠近Baika村(61°16'N,46°44'E)洪积平原的一个剖面进行了孢粉学研究.化石点位于泰加林带中部,靠近欧洲云杉林和亚乌拉尔-西伯利亚云、冷杉-西伯利亚松林界限附近.该河流盆地森林覆盖率高达98%.根据放射性碳年代测定,沉积涵盖了全新世大约自9000 yrs B.P.以来的大部分地层.主要运用化石植物群组成来恢复这一地区全新世以来的植被和气候变化,通过某些化石植物群的全部植物种类的现代地理分布的分析,可以发现与过去植被最接近的现代对应植被类型的位置,通过确定所有植物种现代生长地区的景观和气候来推测与古环境最接近的景观和气候.整个孢粉组合序列中云杉、松和桦占统治地位,但是植物群的成分和植被有变化.暖温带树种,如椴、榆及栎等在森林中的含量有变化,在全新世最暖期,相当于中晚大西洋期(6000-4500 yrs B.P.)达到最高.这些变化通过对应的现代植物群在俄罗斯平原的"迁移"反映出来,从中、南乌拉尔向西至Sukhona河盆地然后再返回到研究区的Vychegda河下游.运用古植物群的方法定量恢复的主要气候指标表明在大西洋期7月份月均温比现代高2.5℃,1月份月均温比现在高出1℃,年降雨量和现在接近.这段时间可以认为是本地区全新世的气候最适宜期.     

Finding fishers: determining fisher occupancy in the Northern Rocky Mountains

Monitoring rare and elusive carnivores is inherently challenging because they often occur at low densities and require more resources to effectively assess status and trend. The fisher (Pekania pennanti) is an elusive mesocarnivore endemic to North America; in its western populations it is classified as a species of greatest conservation need. During winter of 2018–2019, we deployed remotely triggered cameras in randomly selected, spatially balanced 7.5-km × 7.5-km grid cells across a broad study area in western Montana, Idaho, and eastern Washington, USA. As part of this large-scale, multi-state monitoring effort, we conducted an occupancy assessment of the Northern Rocky Mountain fisher population at a range-wide scale. We used non-spatial occupancy models to determine the current extent of fisher occurrence in the Northern Rocky Mountains and to provide baseline occupancy estimates across a broad study area and a refined sampling frame for future monitoring. We used a spatial occupancy model to determine patterns in fisher occurrence across their Northern Rocky Mountain range while explicitly correcting for spatially induced overdispersion. Additionally, we assessed factors that influenced fisher occurrence through covariate occupancy modeling that considered predicted fisher habitat, site-level environmental characteristics, and the influence of available harvest records (incidental and regulated). We detected fishers in 32 out of 318 (10%) of our surveyed cells, and estimated that overall, 160 (14%; 95% CI = 115–218) of 1,143 grid cells were occupied by fishers. Fisher occupancy was positively associated with our stratum that contained cells with a greater proportion of predicted fisher habitat and with proximity to nearest 2000–2015 harvest location. Fisher occupancy was weakly and positively associated with increased canopy cover. Our spatial model identified 2 areas with higher predicted occupancy: a large area across the Idaho Nez Perce-Clearwater National Forest, and a smaller area in the Cabinet Mountain Range crossing the northern border of Idaho and Montana. We used spatial occupancy results from our original sampling frame to create a biologically derived refined sampling frame for future monitoring. Within the bounds of our refined sampling frame, we estimated that 155 (22%; 95% CI = 110–209) of 700 grid cells were occupied by fishers. By incorporating our increasing understanding of fisher habitat with contemporary analytical techniques, we defined current range-wide occupancy of the Northern Rocky Mountain fisher population, identified core areas of fisher occurrence for future conservation efforts, and used our model results to create a refined sampling frame for future fisher monitoring in the Northern Rocky Mountains.     

Habitat suitability and the constraints of migration in New World warblers

Identifying the factors that influence geographic range limits can illustrate the various ecological, physiological, and evolutionary constraints imposed on a species. The range limits of migratory birds are particularly challenging to study as they occur in disjunct regions at different times of the year, which can impose different constraints. Travel between breeding and wintering regions poses a significant energetic and navigational challenge to birds, although it is not clear how these movements influence breeding dispersal and range expansion. Here I ask whether the possible costs of migration limit the breeding ranges of wood warblers, a group of birds with an extensive history of ecological and evolutionary studies. I used occurrence records for multiple wood warbler species, breeding primarily in the boreal forest of North America, to generate environmental niche models. I tested for over‐prediction of habitat suitability into the western boreal forest, where most these species do not have occurrence records but where there is presumably suitable habitat. I found that some of these vagile taxa, primarily found east of the Rocky Mountains, also have predicted habitat suitability that extends into the north and west, where they have little to no occurrence records. I discuss several possible explanations for this discordance. In particular, the patterns are consistent with the costs of a long‐distance migration limiting the benefits of range expansion, as migration may become too onerous as the distance between breeding and wintering areas increases. These results speak to the process of niche filling more generally and call attention to an under‐appreciated explanation for why migratory species may not fully occupy their fundamental niche.     

Molecular evidence for Pleistocene glacial cycles driving diversification of a North American desert spider, Agelenopsis aperta

The influence of historical climatic vs. geological changes on species diversification patterns was investigated in a widely distributed North American desert spider, Agelenopsis aperta (Araneae: Agelenidae), with particular reference to Pleistocene glacial cycles and earlier patterns of mountain building. Levels of sequence divergence obtained from the mitochondrial gene, cytochrome oxidase I, dated to the Pleistocene, eliminating Rocky Mountain orogeny as a cause of diversification, as orogeny ended 4 million years ago. The results of phylogenetic and network analyses showed the presence of three geographically defined clades, which were consistent with the presence of at least three glacial refugia: (i) east of the Rocky Mountains; (ii) between the Rocky Mountains and Sierra Nevadas; and (iii) west of the Sierra Nevadas. In addition, populations within the Rocky Mountains exhibited significantly lower genetic diversity than populations east of the Rocky Mountains and the haplotypes found within the Rockies were a subset of eastern haplotypes. These patterns suggest that a post-Pleistocene range expansion occurred out of an eastern glacial refugium into the Rocky Mountains. Examination of phylogeographical studies of other North American desert taxa indicated that mountain building explained diversification patterns more effectively for some taxa but Pleistocene climate change was more important for others, including A. aperta.