Methanogenesis in Eocene Arctic soils inferred from δC of tree fossil carbonates

We report on the carbon and oxygen stable isotope composition of fossil tree material collected at the White Mountain locality of the Buchanan Lake Formation on Axel Heiberg Island in the High Arctic of Canada. The fossils are Middle Eocene in age and have been permineralized with carbonate. Microscopic examination of fossils revealed them to be the remains of Metasequoia stems, composed of secondary carbonate (calcite) and original wood intermingled at the cellular level. Because the specimens show little compression, crushing, or tissue degradation, we believe that carbonate permineralization occurred soon after burial, and therefore provides insight into Eocene carbon cycling at the locality. The carbon isotope signature of the carbonate suggests that methanogenesis resulted in a ¹³C-enriched CO₂ pool that equilibrated with soil water and gave rise to unusually ¹³C-enriched CaCO₃. Tree fossil carbonate exhibited strikingly high δ¹³C values (+4.0 to +7.4‰) compared to published Phanerozoic pedogenic carbonate δ¹³C values. These δ¹³C values, in conjunction with fractionation factors (α) previously determined for carbonate precipitation and methanogenic pathways, indicate an Eocene soil CO₂ pool containing 80-95% CO₂ produced as a by-product of acetate-fermentation methanogenesis. Because methane in the atmosphere is a powerful greenhouse gas, we suggest that methane emissions from Axel Heiberg soils contributed to the relatively warm Arctic climate during the Middle Eocene.     

The impact of Cenozoic cooling on assemblage diversity in planktonic foraminifera

The Cenozoic planktonic foraminifera (PF) (calcareous zooplankton) have arguably the most detailed fossil record of any group. The quality of this record allows models of environmental controls on macroecology, developed for Recent assemblages, to be tested on intervals with profoundly different climatic conditions. These analyses shed light on the role of long-term global cooling in establishing the modern latitudinal diversity gradient (LDG)—one of the most powerful generalizations in biogeography and macroecology. Here, we test the transferability of environment-diversity models developed for modern PF assemblages to the Eocene epoch (approx. 56–34 Ma), a time of pronounced global warmth. Environmental variables from global climate models are combined with Recent environment–diversity models to predict Eocene richness gradients, which are then compared with observed patterns. The results indicate the modern LDG—lower richness towards the poles—developed through the Eocene. Three possible causes are suggested for the mismatch between statistical model predictions and data in the Early Eocene: the environmental estimates are inaccurate, the statistical model misses a relevant variable, or the intercorrelations among facets of diversity—e.g. richness, evenness, functional diversity—have changed over geological time. By the Late Eocene, environment–diversity relationships were much more similar to those found today.     

Wasatchian (Early Eocene) pollen floras from the Red Hot Truck Stop, Mississippi, USA

Sediments at the Red Hot Truck Stop (RHTS), Mississippi, USA are important because they contain the lowest latitude record of both the earliest known Eocene plant and mammal fossils in North America. The RHTS contains the uppermost Tuscahoma Formation and the lowermost part of the basal Bashi and Hatchetigbee formations. The Tuscahoma Formation is composed of glauconitic sands and silts that represent estuarine to shallow marine sediments. Faunal remains indicate that the RHTS section belongs to the Wasatchian North American land mammal age and specifically to the lower Graybullian subdivision. Pollen and spore floras from the RHTS are moderately diverse (113 taxa) and contain families that today are associated with warm‐adapted vegetation types such as Annonaceae, Bombacaceae, Burseraceae and palms. Eocene first occurrences are represented by Brosipollis sp., Celtispollenites sp., Interpollis microsupplingensis, cf. Nuxpollenites psilatus, Platycarya spp., Retistephanocolporites sp. and Symplocos? contracta and by one genus of pteridophyte spore (Granulatisporites sp.). The overall composition and within‐sample diversity of the sporomorph flora is more similar to the Hatchetigbee Formation (early Eocene) than to the middle Tuscahoma Formation (late Palaeocene) but among‐sample diversity remains unchanged across the Palaeocene/Eocene boundary. The distinct composition of the RHTS demonstrates that floral change across the Palaeocene/Eocene boundary is complex and composed of several phases of floral change.     

Patterns and controlling factors of species diversity in the Arctic Ocean

Aim The Arctic Ocean is one of the last near‐pristine regions on Earth, and, although human activities are expected to impact on Arctic ecosystems, we know very little about baseline patterns of Arctic Ocean biodiversity. This paper aims to describe Arctic Ocean‐wide patterns of benthic biodiversity and to explore factors related to the large‐scale species diversity patterns. Location Arctic Ocean. Methods We used large ostracode and foraminiferal datasets to describe the biodiversity patterns and applied comprehensive ecological modelling to test the degree to which these patterns are potentially governed by environmental factors, such as temperature, productivity, seasonality, ice cover and others. To test environmental control of the observed diversity patterns, subsets of samples for which all environmental parameters were available were analysed with multiple regression and model averaging. Results Well‐known negative latitudinal species diversity gradients (LSDGs) were found in metazoan Ostracoda, but the LSDGs were unimodal with an intermediate maximum with respect to latitude in protozoan foraminifera. Depth species diversity gradients were unimodal, with peaks in diversity shallower than those in other oceans. Our modelling results showed that several factors are significant predictors of diversity, but the significant predictors were different among shallow marine ostracodes, deep‐sea ostracodes and deep‐sea foraminifera. Main conclusions On the basis of these Arctic Ocean‐wide comprehensive datasets, we document large‐scale diversity patterns with respect to latitude and depth. Our modelling results suggest that the underlying mechanisms causing these species diversity patterns are unexpectedly complex. The environmental parameters of temperature, surface productivity, seasonality of productivity, salinity and ice cover can all play a role in shaping large‐scale diversity patterns, but their relative importance may depend on the ecological preferences of taxa and the oceanographic context of regions. These results suggest that a multiplicity of variables appear to be related to community structure in this system.     

Phytogeographical analysis of seed plant genera in China

BACKGROUND AND AIMS: A central goal of biogeography and ecology is to uncover and understand distributional patterns of organisms. China has long been a focus of attention because of its rich biota, especially with respect to plants. Using 290 floras from across China, this paper quantitatively characterizes the composition of floristic elements at multiple scales (i.e. national, provincial and local), and explores the extent to which climatic and geographical factors associated with each flora can jointly and independently explain the variation in floristic elements in local floras. METHODS: A study was made of 261 local floras, 28 province-level floras and one national-level flora across China. Genera of seed plants in each flora were assigned to 14 floristic elements according to their worldwide geographical distributions. The composition of floristic elements was related to climatic and geographical factors. KEY RESULTS AND CONCLUSIONS: Variations in percentages of cosmopolitan, tropical and temperate genera among local floras tend to be greater at higher latitudes than at lower latitudes. Latitude is strongly correlated with the proportions of 13 of the 14 floristic elements. Correlations of the proportions of floristic elements with longitude are much weaker than those with latitude. Climate represented by the first principal component of a principal component analysis was strongly correlated with the proportions of floristic elements in local floras (|r| = 0.75 +/- 0.18). Geographical coordinates independently explained about four times as much variation in floristic elements as did climate. Further research is necessary to examine the roles of water-energy dynamics, geology, soils, biotic interactions, and historical factors such as land connections between continents in the past and at present in creating observed floristic patterns.     

Patterns and regulation of mycorrhizal plant and fungal diversity

The diversity of mycorrhizal fungi does not follow patterns of plant diversity, and the type of mycorrhiza may regulate plant species diversity. For instance, coniferous forests of northern latitudes may have more than 1000 species of ectomycorrhizal (EM) fungi where only a few ectomycorrhizal plant species dominate, but there are fewer than 25 species of arbuscular mycorrhizal (AM) fungi in tropical deciduous forest in Mexico with 1000 plant species. AM and EM fungi are distributed according to biome, with AM fungi predominant in arid and semiarid biomes, and EM fungi predominant in mesic biomes. In addition, AM fungi tend to be more abundant in soils of low organic matter, perhaps explaining their predominance in moist tropical forest, and EM fungi generally occur in soils with higher surface organic matter.EM fungi are relatively selective of host plant species, while AM tend to be generalists. Similar morphotypes of AM fungi collected from different sites confer different physiological benefits to the same plant species. While the EM fungi have taxonomic diversity, the AM fungi must have physiological diversity for individual species to be so widespread, as supported by existing studies. The environmental adaptations of mycorrhizal fungi are often thought to be determined by their host plant, but we suggest that the physiology and genetics of the fungi themselves, along with their responses to the plant and the environment, regulates their diversity. We observed that one AM plant species,Artemisia tridentata, was associated with different fungal species across its range, indicating that the fungi can respond to the environment directly and must not do so indirectly via the host. Different species of fungi were also active during different times of the growing season on the same host, again suggesting a direct response to the environment.These patterns suggest that even within a single functional group of microorganisms, mycorrhizal fungi, considerable diversity exists. A number of researchers have expressed the concept of functional redundancy within functional groups of microorganisms, implying that the loss of a few species would not be detectable in ecosystem functioning. However, there may be high functional diversity of AM fungi within and across habitats, and high species diversity as well for EM fungi. If one species of mycorrhizal fungus becomes extinct in a habitat, field experimental data on AM fungi suggest there may be significant shifts in how plants acquire resources and grown in that habitat.     

Global patterns of plant diversity

Summary Using 94 data sets from across the globe, we explored patterns of mean community species richness, landscape species richness, mean similarity among communities and mosaic diversity. Climate affected community species richness primarily through productivity while other climatic factors were secondary. Climatic equability affected species richness only in temperate regions where richness was greatest at high levels of temperature variability and low levels of precipitation variability. Landscape species richness correlated positively with community species richness. A global gradient in mean similarity existed but was uncorrelated with community species richness. Mean similarity was least and mosaic diversity was greatest between 25 and 30° latitude. The most diverse landscapes (low mean similarity) correlated with warm temperatures, high elevations, large areas and large seasonal temperature fluctuations. The most complex landscapes (high mosaic diversity) correlated with large areas, high productivity and warm winters. We compared diversity measures among continents and found only one significant difference: Australian landscapes have greater mosaic diversity than African landscapes. Based on our analyses we propose two hypotheses: (1) for plants, biotic interactions are more important in structuring landscapes in warmer climates and (2) longer isolated landscapes have more clearly differentiated ecological subunits.     

Global associations between terrestrial producer and vertebrate consumer diversity

In both ecology and conservation, often a strong positive association is assumed between the diversity of plants as primary producers and that of animals, specifically primary consumers. Such a relationship has been observed at small spatial scales, and a begetting of diversity by diversity is expected under various scenarios of co-evolution and co-adaptation. But positive producer-consumer richness relationships may also arise from similar associations with past opportunities for diversification or contemporary environmental conditions, or from emerging properties of plant diversity such as vegetation complexity or productivity. Here we assess whether the producer-consumer richness relationship generalizes from plot to regional scale and provide a first global test of its strength for vascular plants and endothermic vertebrates. We find strong positive richness associations, but only limited congruence of the most diverse regions. The richness of both primary and higher-level consumers increases with plant richness at similar strength and rate. Environmental conditions emerge as much stronger predictors of consumer richness, and after accounting for environmental differences little variation is explained by plant diversity. We conclude that biotic interactions and strong local associations between plants and consumers only relatively weakly scale up to broad geographical scales and to functionally diverse taxa, for which environmental constraints on richness dominate.     

Paleocene and Eocene floras of Russia and adjacent regions: Climatic conditions of their development

Climatic changes in the western and central regions of Russian Eurasia in the Paleocene and in the first half of the Eocene were caused by the dynamics and rearrangement of the systems of marine seaways: the longitudinal one, which connected the Arctic Basin with marginal seas of the Northern Peri-Tethys, and the latitudinal one, which connected the latter seas with the Atlantic. As these systems were progressively reduced, the climate in the middle latitudes changed from paratropical to a subtropical monsoon climate with a moist summer, and later to a climate with a moist winter, and, in the Late Eocene, to a humid climate without any marked seasonal variation in precipitation. The type of flora changed in agreement with these changes. In the Paleogene, cold currents constantly influenced the climate of the Northwestern Pacific rim and facilitated the development of a warm-temperate mesophilic flora.     

The biogeography and filtering of woody plant functional diversity in North and South America

Aim In recent years evidence has accumulated that plant species are differentially sorted from regional assemblages into local assemblages along local‐scale environmental gradients on the basis of their function and abiotic filtering. The favourability hypothesis in biogeography proposes that in climatically difficult regions abiotic filtering should produce a regional assemblage that is less functionally diverse than that expected given the species richness and the global pool of traits. Thus it seems likely that differential filtering of plant traits along local‐scale gradients may scale up to explain the distribution, diversity and filtering of plant traits in regional‐scale assemblages across continents. The present work aims to address this prediction. Location North and South America. Methods We combine a dataset comprising over 5.5 million georeferenced plant occurrence records with several large plant functional trait databases in order to: (1) quantify how several critical traits associated with plant performance and ecology vary across environmental gradients; and (2) provide the first test of whether the woody plants found within 1° and 5° map grid cells are more or less functionally diverse than expected, given their species richness, across broad gradients. Results The results show that, for many of the traits studied, the overall distribution of functional traits in tropical regions often exceeds the expectations of random sampling given the species richness. Conversely, temperate regions often had narrower functional trait distributions than their smaller species pools would suggest. Main conclusion The results show that the overall distribution of function does increase towards the equator, but the functional diversity within regional‐scale tropical assemblages is higher than that expected given their species richness. These results are consistent with the hypothesis that abiotic filtering constrains the overall distribution of function in temperate assemblages, but tropical assemblages are not as tightly constrained.     

Climatic drivers of hemispheric asymmetry in global patterns of ant species richness

Although many taxa show a latitudinal gradient in richness, the relationship between latitude and species richness is often asymmetrical between the northern and southern hemispheres. Here we examine the latitudinal pattern of species richness across 1003 local ant assemblages. We find latitudinal asymmetry, with southern hemisphere sites being more diverse than northern hemisphere sites. Most of this asymmetry could be explained statistically by differences in contemporary climate. Local ant species richness was positively associated with temperature, but negatively (although weakly) associated with temperature range and precipitation. After contemporary climate was accounted for, a modest difference in diversity between hemispheres persisted, suggesting that factors other than contemporary climate contributed to the hemispherical asymmetry. The most parsimonious explanation for this remaining asymmetry is that greater climate change since the Eocene in the northern than in the southern hemisphere has led to more extinctions in the northern hemisphere with consequent effects on local ant species richness.     

Early Eocene Primates from Gujarat, India

The oldest euprimates known from India come from the Early Eocene Cambay Formation at Vastan Mine in Gujarat. An Ypresian (early Cuisian) age of ∼53 Ma (based on foraminifera) indicates that these primates were roughly contemporary with, or perhaps predated, the India-Asia collision. Here we present new euprimate fossils from Vastan Mine, including teeth, jaws, and referred postcrania of the adapoids Marcgodinotius indicus and Asiadapis cambayensis. They are placed in the new subfamily Asiadapinae (family Notharctidae), which is most similar to primitive European Cercamoniinae such as Donrussellia and Protoadapis. Asiadapines were small primates in the size range of extant smaller bushbabies. Despite their generally very plesiomorphic morphology, asiadapines also share a few derived dental traits with sivaladapids, suggesting a possible relationship to these endemic Asian adapoids. In addition to the adapoids, a new species of the omomyid Vastanomys is described. Euprimate postcrania described include humeri, radii, femora, calcanei, and tali, most of which show typical notharctid features and are probably attributable to asiadapines. Anatomical features of the limb elements indicate that they represent active arboreal quadrupedal primates. At least one calcaneus is proximally shorter and distally longer than the others, resembling eosimiids in this regard, a relationship that, if confirmed, would also suggest an Asian or southeast Asian faunal connection. Isolated teeth from Vastan Mine recently attributed to a new eosimiid, Anthrasimias gujaratensis, appear to provide that confirmation. However, their attribution to Eosimiidae is equivocal. They are similar to teeth here tentatively referred to Marcgodinotius, hence A. gujaratensis may be a junior synonym of M. indicus. Corroboration of eosimiids at Vastan requires more compelling evidence. Although definitive conclusions are premature, available evidence suggests that the Vastan adapoids, at least, were derived from western European stock that reached India near the Paleocene-Eocene boundary.     

A resource-based conceptual model of plant diversity that reassesses causality in the productivity–diversity relationship

Biogeographical studies frequently reveal positive correlations between species richness and estimates of environmental water and/or energy. A popular interpretation of this relationship relates the supply of water and energy to productivity, and then, in turn, to richness. Productivity–diversity theories are now legion, yet none has proved sufficiently intuitive to gain broad acceptance. Like productivity, heterogeneity is known to influence diversity at fine spatial scales, yet the possibility that richness might relate to water–energy dynamics at coarse spatial scales via a heterogeneity‐generating mechanism has received little attention. In this paper we outline such a conceptual model for plants that is internally consistent and testable. We believe it may help to explain the capacity of environments receiving different inputs of water and energy to support variable numbers of species at a range of spatial scales, the pervasive correlation between productivity and richness, some exceptions to the productivity–diversity relationship, the form of productivity–diversity curves and the link between richness and environmental ‘harshness’. The model may also provide an answer to one of the most venerable puzzles in the field of diversity studies: why high inputs of water and energy correspond to more species rather than simply more individuals.     

A new ‘tapir’ from Ellesmere Island, Arctic Canada — Implications for northern high latitude palaeobiogeography and tapir palaeobiology

The oldest and northernmost record of the tapir lineage, Thuliadanta mayri gen. et sp. nov. from Ellesmere Island, Arctic Canada (78°50′N) implies that tapiroid evolution was well underway by early Eocene (Wasatchian) time in northern high latitudes, and raises the possibility of a North American origin for the group. Phylogenetic analyses place the new Arctic tapir as the sister group to the later more advanced Desmatotherium, Colodon, and Irdinolophus. A phylogenetically-derived biogeographic reconstruction posed here suggests the tapir lineage may represent a rare instance of counterflow wherein an exotic North American taxon invaded Asia during the early Eocene. Moreover, Thuliadanta seems a plausible ancestor to Desmatotherium from both continents, suggesting that this branch of the tapir lineage may have originated at high latitudes and subsequently dispersed from there to mid-latitudes. Thuliadanta's occurrence on Ellesmere Island indicates that northern high latitudes should also be evaluated as a potential source area for some of the exotic taxa appearing in mid-latitudes during Eocene time. Using today's tapirs, and specifically the mountain tapir, as analogs, Thuliadanta seems a plausible year-round inhabitant in the mild temperate lowland forests of the Eocene High Arctic.     

Climate adaptation is not enough: warming does not facilitate success of southern tundra plant populations in the high Arctic

Rapidly rising temperatures are expected to cause latitudinal and elevational range shifts as species track their optimal climate north and upward. However, a lack of adaptation to environmental conditions other than climate – for example photoperiod, biotic interactions, or edaphic conditions – might limit the success of immigrants in a new location despite hospitable climatic conditions. Here, we present one of the first direct experimental tests of the hypothesis that warmer temperatures at northern latitudes will confer a fitness advantage to southern immigrants relative to native populations. As rates of warming in the Arctic are more than double the global average, understanding the impacts of warming in Arctic ecosystems is especially urgent. We established experimentally warmed and nonwarmed common garden plots at Alexandra Fiord, Ellesmere Island in the Canadian High Arctic with seeds of two forb species (Oxyria digyna and Papaver radicatum) originating from three to five populations at different latitudes across the Arctic. We found that plants from the local populations generally had higher survival and obtained a greater maximum size than foreign individuals, regardless of warming treatment. Phenological traits varied with latitude of the source population, such that southern populations demonstrated substantially delayed leaf‐out and senescence relative to northern populations. Our results suggest that environmental conditions other than temperature may influence the ability of foreign populations and species to establish at more northerly latitudes as the climate warms, potentially leading to lags in northward range shifts for some species.     

北极太平洋扇区海洋沉积物细菌多样性的系统发育分析

对北极太平洋扇区3个不同深度的海洋沉积物样品,采用PCR结合变性梯度凝胶电泳(DGGE)技术进行细菌16S rRNA基因V3区序列的系统发育分析。结果表明,同一个沉积物样品不同层次的DGGE电泳图谱不完全相同。从3个沉积物样品中共获得50条序列,大部分序列与从海洋环境尤其海洋沉积物获得的细菌16S rDNA序列相似性较高(88%~100%),归属于变形细菌(Proteobacteria)的gamma亚群、alpha亚群、beta亚群、epsilon亚群、delta亚群,Cytophaga_Flavobacterium_Bacteroides(CFB)群细菌和高G C含量的革兰氏阳性细菌等系统分类群,其中变形细菌(Proteobacteria)的gamma亚群为沉积物中的优势细菌类群。     

Sex after all: high levels of diversity detected in the arctic clonal plant Saxifraga cernua using RAPD markers

Arctic plants in general and arctic clonal plants in particular have often been assumed to contain low levels of genetic diversity. We used RAPDs (random amplified polymorphic DNAs) to investigate genetic diversity in the arctic-alpine Saxifraga cernua , which mainly reproduces clonally via bulbils, at three spatial scales in Svalbard: (i) 'macroscale', between two sites 11 km apart; (ii) 'mesoscale', along two crossing transects at each site; and (iii) 'microscale', within a 3 × 3 m square at each site. Thirteen putative clones (RAPD phenotypes) were distinguished among 93 ramets based on 38 RAPD markers. The genetic diversity ( D ; mean 0.52, range 0.10–0.81) and evenness ( E ; mean 0.42, range 0.00–0.82) were at the same level as in clonal plants in general. However, the diversity strongly depended on site and spatial scale. Several clones were highly divergent and clustered independently of site in UPGMA and PCO analyses. In an analysis of molecular variance ( AMOVA ), most of the variation (59%) was found within sites. Mantel tests revealed no correlation between spatial and genetic distance within sites. Our results suggest that occasional sexual reproduction as well as clonal migration via bulbil dispersal play a significant role in the treeless arctic environment, where S. cernua is widespread and locally very abundant. In contrast, Bauert et al. ( Molecular Ecology 7, 1519–1527) found no genetic variation within populations or regions of the Alps, where the species has highly isolated occurrences.     

Bacterial diversity in surface sediments from the Pacific Arctic Ocean

In order to assess bacterial diversity within four surface sediment samples (0–5 cm) collected from the Pacific Arctic Ocean, 16S ribosomal DNA clone library analysis was performed. Near full length 16S rDNA sequences were obtained for 463 clones from four libraries and 13 distinct major lineages of Bacteria were identified (α, β, γ, δ and ε-Proteobacteria, Acidobacteria, Bacteroidetes, Chloroflexi, Actinobacteria, Firmicutes, Planctomycetes, Spirochetes, and Verrucomicrobia). α, γ, and δ-Proteobacteria, Acidobacteria, Bacteroidetes, Actinobacteria were common phylogenetic groups from all the sediments. The γ-Proteobacteria were the dominant bacterial lineage, representing near or over 50% of the clones. Over 35% of γ-Proteobacteria clones of four clone library were closely related to cultured bacterial isolates with similarity values ranging from 94 to 100%. The community composition was different among sampling sites, which potentially was related to geochemical differences.