The Origin and Early Radiation of Archosauriforms: Integrating the Skeletal and Footprint Record

We present a holistic approach to the study of early archosauriform evolution by integrating body and track records. The ichnological record supports a Late Permian–Early Triassic radiation of archosauriforms not well documented by skeletal material, and new footprints from the Upper Permian of the southern Alps (Italy) provide evidence for a diversity not yet sampled by body fossils. The integrative study of body fossil and footprint data supports the hypothesis that archosauriforms had already undergone substantial taxonomic diversification by the Late Permian and that by the Early Triassic archosauromorphs attained a broad geographical distribution over most parts of Pangea. Analysis of body size, as deduced from track size, suggests that archosauriform average body size did not change significantly from the Late Permian to the Early Triassic. A survey of facies yielding both skeletal and track record indicate an ecological preference for inland fluvial (lacustrine) environments for early archosauromorphs. Finally, although more data is needed, Late Permian chirotheriid imprints suggest a shift from sprawling to erect posture in archosauriforms before the end-Permian mass extinction event. We highlight the importance of approaching palaeobiological questions by using all available sources of data, specifically through integrating the body and track fossil record.     

Assessing latitudinal gradients in speciation rates and biodiversity at the global scale

The mechanisms responsible for latitudinal biodiversity gradients have fascinated and perplexed biologists since the time of Darwin. Ecological theory has yielded two general classes of mechanisms to account for variation in biodiversity: dispersal–assembly mechanisms that invoke differences in stochastic rates of speciation, extinction and dispersal; and niche–assembly mechanisms that invoke species differences, species interactions and environmental heterogeneity. Distinguishing between these two classes of mechanisms requires explicit consideration of macroevolutionary dynamics. Here, we assess the importance of dispersal–assembly mechanisms in the origin and maintenance of biodiversity using fossil data that encompass 30 million years of macroevolution for three distinct groups of ocean plankton: foraminifera, nannoplankton and radiolaria. Applying new methods of analysis to these fossil data, we show here for the first time that latitudinal biodiversity gradients exhibit strong positive correlations with speciation rates even after explicitly controlling for variation in sampling effort and for increases in habitat area towards the equator. These findings provide compelling evidence that geographical variation in macroevolutionary dynamics is a primary determinant of contemporary biodiversity gradients, as predicted by dispersal–assembly theory.     

陆地生态系统植物多样性对矿质元素输入的响应

人类活动的加剧改变了陆地生态系统矿质元素(如氮、磷、钾等)循环的速度和方向,并且对生态系统的结构和功能也产生重要影响。如今,矿质元素输入量的改变及其产生的后续效应对陆地生态系统生物多样性的影响备受学者们的关注。从4个方面综述了全球氮沉降背景下主要矿质元素输入的改变对陆地植物多样性的影响及其机理:1)矿质营养元素限制的概念、确定方法以及与植物多样性的耦合关系;2)概述了氮、磷、钾等主要矿质元素输入对陆地植物多样性的影响:主要表现为负面效应;3)探讨了矿质元素输入影响植物多样性的可能机制,包括生态系统水平上的机制(如竞争排斥、酸化铝毒、物种入侵、同质性假说,间接诱导机制等)和植物个体水平上的机制(如元素失衡和环境敏感性增加等);4)根据目前研究现状,指出了已有研究的局限性,分析了未来可能的研究方向和重点。     

The mosasaur fossil record through the lens of fossil completeness

The quality of the fossil record affects our understanding of macroevolutionary patterns. Palaeodiversity is filtered through geological and human processes; efforts to correct for these biases are part of a debate concerning the role of sampling proxies and standardization in biodiversity models. We analyse the fossil record of mosasaurs in terms of fossil completeness as a measure of fossil quality, using three novel, correlating metrics of fossil completeness and 4083 specimens. A new qualitative measure of character completeness (QCM) correlates with the phylogenetic character completeness metric. Mean completeness by species decreases with specimen count; average completeness by substage varies significantly. Mean specimen completeness is higher for species‐named fossils than those identified to genus and family. We consider the effect of tooth‐only specimens. Importantly, we find that completeness of species does not correlate with completeness of specimens. Completeness varies by palaeogeography: North American specimens show higher completeness than those from Eurasia and Gondwana. These metrics can be used to identify exceptional preservation; specimen completeness varies significantly by both formation and lithology. The Belgian Ciply Formation displays the highest completeness; clay lithologies show higher completeness values. Neither species diversity nor sea level correlates significantly with fossil completeness. A generalized least squares (GLS) analysis using multiple variables agrees with this result, but reveals two variables with significant predictive value for modelling averaged diversity: sea level, and mosasaur and plesiosaur‐bearing formations (the latter is redundant with diversity). Mosasaur completeness is not driven by sea level, nor does completeness limit the mosasaur diversity signal.     

Ecological persistence interrupted in Caribbean coral reefs

The recent mass mortality of Caribbean reef corals dramatically altered reef community structure and begs the question of the past stability and persistence of coral assemblages before human disturbance began. We report within habitat stability in coral community composition in the Pleistocene fossil record of Barbados for at least 95 000 years despite marked variability in global sea level and climate. Results were consistent for surveys of both common and rare taxa. Comparison of Pleistocene and modern community structure shows that Recent human impacts have changed coral community structure in ways not observed in the preceding 220 000 years.     

The completeness of the fossil record of mesozoic birds: implications for early avian evolution

Many palaeobiological analyses have concluded that modern birds (Neornithes) radiated no earlier than the Maastrichtian, whereas molecular clock studies have argued for a much earlier origination. Here, we assess the quality of the fossil record of Mesozoic avian species, using a recently proposed character completeness metric which calculates the percentage of phylogenetic characters that can be scored for each taxon. Estimates of fossil record quality are plotted against geological time and compared to estimates of species level diversity, sea level, and depositional environment. Geographical controls on the avian fossil record are investigated by comparing the completeness scores of species in different continental regions and latitudinal bins. Avian fossil record quality varies greatly with peaks during the Tithonian-early Berriasian, Aptian, and Coniacian-Santonian, and troughs during the Albian-Turonian and the Maastrichtian. The completeness metric correlates more strongly with a 'sampling corrected' residual diversity curve of avian species than with the raw taxic diversity curve, suggesting that the abundance and diversity of birds might influence the probability of high quality specimens being preserved. There is no correlation between avian completeness and sea level, the number of fluviolacustrine localities or a recently constructed character completeness metric of sauropodomorph dinosaurs. Comparisons between the completeness of Mesozoic birds and sauropodomorphs suggest that small delicate vertebrate skeletons are more easily destroyed by taphonomic processes, but more easily preserved whole. Lagerst?tten deposits might therefore have a stronger impact on reconstructions of diversity of smaller organisms relative to more robust forms. The relatively poor quality of the avian fossil record in the Late Cretaceous combined with very patchy regional sampling means that it is possible neornithine lineages were present throughout this interval but have not yet been sampled or are difficult to identify because of the fragmentary nature of the specimens.     

Urban greenspace composition and landscape context influence natural enemy community composition and function

Conservation research has historically been aimed at preserving high value natural habitats, but urbanization and its associated impacts have prompted broader mandates that include the preservation and promotion of biodiversity in cities. Current efforts within urban landscapes aim to support biodiversity and diverse ecosystem services such as storm water management, sustainable food production, and toxin remediation. Arthropod natural enemies provide biocontrol services important for the ecosystem management of urban greenspaces. Establishing habitat for these and other beneficial arthropods is a growing area of urban conservation. Habitat design, resource inputs, management, and abiotic conditions shape the value of greenspace habitats for arthropods. In general, larger patches with diverse plant communities support a greater abundance and diversity of natural enemies and biocontrol services, yet opposing patterns or no effects have also been documented. The surrounding landscape is likely a contributor to this variation in natural enemy response to patch-scale habitat design and management. Looking across rural–urban landscape gradients, natural enemy communities shift toward dominance by habitat generalists and disturbance tolerant species in urban areas compared to rural or natural communities. These changes have been linked to variation in habitat fragmentation, plant productivity and management intensity. In landscape-scale studies focusing solely within cities, variables such as impervious surface area and greenspace connectivity affect the community assembly of natural enemies within a patch. Given these findings, a greater mechanistic understanding of how both the composition and spatial context of urban greenspaces influence natural enemy biodiversity–biocontrol relationships is needed to advance conservation planning and implementation.     

THE EFFECTS OF SAMPLING BIAS ON PALAEOZOIC FAUNAS AND IMPLICATIONS FOR MACROEVOLUTIONARY STUDIES

Abstract:  Trilobites, a dominant component of marine faunas during the Cambrian and Ordovician and which survived until the end of the Permian (542–251 Ma) have been used in many macroevolutionary analyses. Here, we use a discovery curve to document the sampling history of trilobites, which we consider a proxy for Palaeozoic faunas in general. At higher taxonomic ranks, orders, suborders and superfamilies, the fossil record has been completely sampled, while the family rank also shows a high level of sampling completeness, having reached an asymptote in 1970. Importantly, this levelling-off occurred even though worker effort continued to increase. However, at genus level the sampling record is incomplete, indicating that families should not be used as a proxy for genera. There is little variation among the different subsets of generic data, with the sampling history of different stratigraphic periods and among different orders being very similar. However, there is noticeable variation among geographical regions, caused by variations in worker effort, and this could cause problems when comparing speciation and diversity patterns across faunal provinces. The role of synonyms on sampling history has had little effect.     

Biodiversity changes in a shallow lake ecosystem: a multi-proxy palaeolimnological analysis

Biodiversity is a key measure of environmental quality in lake ecosystems. Lake biodiversity can be assessed using modern survey data, but typically these data only provide a ‘snap-shot’ measure and in most cases it is not possible to reconstruct temporal trends in biodiversity, so that human impacts can be detected. Palaeoecological techniques offer an alternative means of identifying changes in biodiversity over the period of historical records and far beyond, but there are problems associated with this approach. This is because only a select set of organisms leave a trace in the sediment record such that it is not usually possible to make reliable assessments of diversity changes within an entire taxonomic order (e.g. the algae). Moreover these organisms are typically from the lower levels of the trophic hierarchy (i.e. plants and insects). The problems of identifying changes in biodiversity from the palaeolimnological record are addressed with reference to Groby Pool, a shallow, eutrophic, medieval lake in the English Midlands, which has been subjected to eutrophication over the last 150 years. ²¹⁰Pb and ¹³⁷Cs-dated sediment cores have been used to estimate short-term alterations in the composition and diversity of three groups of indicators, representing different levels in the trophic cascade, namely diatoms, aquatic pollen and chironomids. By exploring relationships, both between these indicators and with archival macrophyte records, an assessment is made of eutrophication-related changes in overall habitat diversity at the ecosystem level. These data suggest that the lake has undergone considerable nutrient enrichment, resulting in the loss of a diverse, mesotrophic macrophyte flora from at least the turn of the century onwards and its replacement by a few highly competitive species tolerant of high nutrient concentrations. Reductions in macrophyte diversity seem to be reflected palaeoecologically by a decline in the diversity of fossil chironomid assemblages, related to the breakdown of particular host-plant relationships amongst the phytophagic species. However, diatom assemblages generally exhibit the opposite trend, which may be related to increases in macrophyte cover and increasing opportunities for the colonization of diverse epiphyte communities. The different fossil indicators have different limitations and merits, and for this reason a ‘multi-proxy’ approach is essential if meaningful inferences are to be made of changes in lake biodiversity using palaeoecological data.     

Did the evolution of the phytoplankton fuel the diversification of the marine biosphere?

We discuss the possible links between the fossil record of marine biodiversity, nutrient availability and primary productivity. The parallelism of the fossil records of marine phytoplankton and faunal biodiversity implicates the quantity (primary productivity) and quality (stoichiometry) of phytoplankton as being critical to the diversification of the marine biosphere through the Phanerozoic. The relatively subdued marine biodiversity of the Palaeozoic corresponds to a time of relatively low macronutrient availability and poor food quality of the phytoplankton as opposed to the diversification of the Modern Fauna through the Mesozoic–Cenozoic. Increasing nutrient runoff to the oceans through the Phanerozoic resulted from orogeny, the emplacement of Large Igneous Provinces (LIPs), the evolution of deep-rooting forests and the appearance of more easily decomposable terrestrial organic matter that enhanced weathering. Positive feedback by bioturbation of an expanding benthos played a critical role in evolving biogeochemical cycles by linking the oxidation of dead organic matter and the recycling of nutrients back to the water column where they could be re-utilized. We assess our conclusions against a recently published biogeochemical model for geological time-scales. Major peaks of marine diversity often occur near rising or peak fluxes of silica, phosphorus and dissolved reactive oceanic phosphorus; either major or minor ⁸⁷Sr/⁸⁶Sr peaks; and frequently in the vicinity of major (Circum-Atlantic Magmatic Province) and minor volcanic events, some of which are associated with Oceanic Anoxic Events. These processes appear to be scale-dependent in that they lie on a continuum between biodiversification on macroevolutionary scales of geological time and mass extinction.     

A temperate palaeodiversity peak in Mesozoic dinosaurs and evidence for Late Cretaceous geographical partitioning

Aim Modern biodiversity peaks in the tropics and declines poleward, a pattern that is potentially driven by climate. Although this latitudinal biodiversity gradient (LBG) also characterizes the marine invertebrate fossil record, distributions of ancient terrestrial faunas are poorly understood. This study utilizes data on the dinosaur fossil record to examine spatial patterns in terrestrial biodiversity throughout the Mesozoic. Location We compiled data on fossil occurrences across the globe. Methods We compiled a comprehensive dataset of Mesozoic dinosaur genera (738), including birds. Following the utilization of sampling standardization techniques to mediate for the uneven sampling of the fossil record, we constructed latitudinal patterns of biodiversity from this dataset. Results The dominant group of Mesozoic terrestrial vertebrates did not conform to the modern LBG. Instead, dinosaur diversity was highest at temperate palaeolatitudes throughout the 160 million year span of dinosaurian evolutionary history. Latitudinal diversity correlates strongly with the distribution of land area. Late Cretaceous sauropods and ornithischians exhibit disparate LBGs. Main conclusions The continuity of the palaeotemperate peak in dinosaur diversity indicates a diminished role for climate on the Mesozoic LBG; instead, dinosaur diversity may have been driven by the amount of land area among latitudinal belts. There is no evidence that the tropics acted as a cradle for dinosaur diversity. Geographical partitioning among major clades of herbivorous dinosaurs in the Late Cretaceous may result from the advanced stages of continental fragmentation and/or differing responses to increasing latitudinal climatic zonation. Our results suggest that the modern‐day LBG on land was only established 30 million years ago, following a significant post‐Eocene recalibration, potentially related to increased seasonality.     

A long-term association between global temperature and biodiversity, origination and extinction in the fossil record

The past relationship between global temperature and levels of biological diversity is of increasing concern due to anthropogenic climate warming. However, no consistent link between these variables has yet been demonstrated. We analysed the fossil record for the last 520 Myr against estimates of low latitude sea surface temperature for the same period. We found that global biodiversity (the richness of families and genera) is related to temperature and has been relatively low during warm 'greenhouse' phases, while during the same phases extinction and origination rates of taxonomic lineages have been relatively high. These findings are consistent for terrestrial and marine environments and are robust to a number of alternative assumptions and potential biases. Our results provide the first clear evidence that global climate may explain substantial variation in the fossil record in a simple and consistent manner. Our findings may have implications for extinction and biodiversity change under future climate warming.     

Dinosaurs and fluctuating sea levels during the mesozoic

The very different frequency of dinosaurs during the Mesozoic can be allied to the correlation between global sea level cyclicity and fossilization. This is based upon the sedimentary situation in the inner shelf, the area of predominant fossil record of dinosaurs, and sea level fluctuations. A rich fossil record is found in times of high sea level, and vice versa. Due to natural laws acting on sea level stands, the fossil record of dinosaurs and other terrestrial tetrapods is incomplete. This is causally explainable in the sequence stratigraphy. Among causes of global sea level fluctuations, the change from warm to cold times has been accorded greatest probability even in the Mesozoic. Consequently, the problem of dinosaur evolution and distribution should not be confused with the pattern of their fossil record. The latter, however, is so far nearly always used for all interpretations. The context presented here results in basic modifications.

During the phases of reduced to missing fossil record (low sea level, cold times), dinosaurs existed at least in circumequatorial regions in high diversity. Highly diverse faunas recorded exceptionally in the Upper Jurassic, Middle and Late Cretaceous, were each time the result of a long previous evolution and not the result of short term radiations at these times. Phases of sea level highstand and warm times caused an increased fossil record and poleward distribution. Cretaceous dinosaurs in paleolatitudes of 70° to 80° N and S are no proof for endothermy, but are only the effect of favorable climatic conditions at limited times. Any endothermy of the dinosaurs is not coincident with the supposedly uniformly warm equable climate of the Mesozoic, but with the opposite. Cold times did not hamper the existence of dinosaurs, but led in extreme cases (Aalenian and Valanginian) to the global lack of their fossil record. The situation at the Cretaceous‐Tertiary boundary is also explainable in this context. According to the sea level cyclicity, no extreme sea level fall and no globablly cold time were present in the critical time segment. The regression in the late Maastrichtian is found to belong to a sequence of third‐order cycles beginning in the Campanian. Every one of the cycle boundaries with regression and transgression produced apparent extinction effects which in reality are only gaps in the fossil record. After the late Maastrichtian regression the dinosaurs persisted with six lineages. The so far youngest dinosaur fauna in the Puercan (basal Paleocene) lies in a phase of sea level highstand of minor amplitude and duration with comparatively minor chances for a fossil record. The occurrences in the Puercan are governed by natural law, and, thus, dinosaurs are untied from the short term problems of the Cretaceous‐Tertiary boundary. Why dinosaurs are then missing at the next highstand, remains an open question. Anyhow, mechanisms which control fossil record, diversification and distribution, including global cold periods, do not belong to the direct causes of extinction, because identical occurrences happened many times during the Mesozoic without inducing extinction.     

How does habitat diversity affect the species–area relationship?

Aim   To examine the way in which 'area' and 'habitat diversity' interact in shaping species richness and to find a simple and valid way to express this interaction.
Location   The Natura 2000 network of terrestrial protected areas in Greece, covering approximately 16% of the national territory.
Methods   We used the Natura 2000 framework, which provides a classification scheme for natural habitat types, to quantify habitat heterogeneity. We analysed data for the plant species composition in 16,143 quadrats in which 5044 species and subspecies of higher plants were recorded. We built a simple mathematical model that incorporates the effect of habitat diversity on the species–area relationship (SAR).
Results   Our analysis showed that habitat diversity was correlated with area. However, keeping habitat diversity constant, species richness was related to area; while keeping area constant, species richness was related to habitat diversity. Comparing the SAR of the 237 sites we found that the slope of the species–area curve was related to habitat diversity.
Main conclusions   Discussion of the causes of the SAR has often focused on the primacy of area per se versus habitat heterogeneity, even though the two mechanisms are not mutually exclusive and should be considered jointly. We find that increasing habitat diversity affects the SAR in different ways, but the dominant effect is to increase the slope of the SAR. While a full model fit typically includes a variety of terms involving both area and habitat richness, we find that the effect of habitat diversity can be reduced to a linear perturbation of the slope of the species accumulation curve.     

Biodiversity curves for the Ordovician of Baltoscandia

Biodiversity curves for the Ordovician of Baltoscandia show a substantial increase in taxonomical diversity through the period, as seen also in global data sets. A database of 10,340 records of first and last appearances of species at different localities in the region has been analysed using simple species counts, and partly validated with resampling methods. While the biodiversity curve for all fossil groups combined is probably reasonably accurate except for an unknown scaling constant, taxonomical or geographical subsets may not be sufficiently well sampled to allow precise measurement of their species counts through time. The analysis shows a major diversification event commencing in the middle Arenig (Ibex-Whiterock boundary), and more limited diversification events in the Llanvirn, Caradoc and Ashgill. The Scandinavian (Norwegian and Swedish) biodiversity curves are broadly correlated with major changes in sea level, with low biodiversity at highstands and high biodiversity at lowstands, although this pattern is not clear for all fossil groups. In the Arenig, graptolites and trilobites appear to have higher diversities at high sea levels, while the brachiopods and ostracodes show higher diversities at low sea level. As a consequence, the Arenig diversification is delayed for the latter two groups until the upper end of the interval.     

热带珊瑚礁区海参的生境选择与生态作用

珊瑚礁生态系统是一个高生产力、高生物多样性的特殊海洋生态系统,具有为生物提供栖息地、参与生物地球化学循环、防浪护岸、指示水体污染程度等生态功能。珊瑚礁生态系统的突出特点是其生境异质性很高,各种各样的生境斑块为种类繁多、习性各异的游泳和底栖生物提供栖息场所,这些礁栖生物通过参与各项生态过程而形成各种特定的功能群,共同完成重要的生态功能。在热带珊瑚礁生态系统中,海参是大型底栖动物区系的重要一员。种类繁多的海参具有各自不同的生境选择特征,通过摄食、运动等行为活动发挥着改良底质、促进有机物矿化和营养盐再生等生态作用。近几年来,全球热带海参受人类过度捕捞和珊瑚礁退化的影响而面临资源衰退、物种多样性丧失等问题,深入认识其生态学功能、加强热带海参资源保护迫在眉睫。综述了国内外热带珊瑚礁海参的基础生态学研究进展：海参对珊瑚礁生境斑块呈现显著的偏好选择特征以及种间差异和季节变动,不同生境斑块的食物质量、底质类型和水动力条件是影响海参生境偏好的重要因素;海参通过生物扰动可以改变珊瑚礁生境沉积物的含水量、渗透性、颗粒组成、再矿化率、无机营养物质释放速率以及孔隙水的化学梯度,并增加沉积物中的溶氧浓度、促进溶解...     

Foraminiferal zonation of late Paleozoic depositional sequences

From the later part of the Devonian through the Permian, calcareous foraminifers became abundant and evolved rapidly. This rapid evolution of taxa forms the basis of a detailed zonation through the Carboniferous and Permian. Comparison of this evolutionary history of foraminifers, their biostratigraphic zonation, and the depositional sequences in which they occur suggests that sea-level events in late Paleozoic depositional history contributed significantly in subdividing a fairly continuous evolutionary record into a succession of about 75 identifiable foraminiferal zones during a 100–125 Myr time span. Although variable in terms of duration and vertical occurrences, the more completely recorded high-stand intervals give brief histories of the foraminiferal evolutionary record and are sandwiched between the poorly recorded or unrecorded low-stand intervals. Many of the individual foraminiferal zones are confined to a single depositional sequence.The late Paleozoic carbonate foraminiferal fossil record, as with the rest of the fossil record, is strongly affected by sediment deposition-nondeposition as a result of major changes in sea level. This incomplete fossil record is the result of repeated depositional breaks because of the way that depositional sequences form. It is not possible to ascribe macromutations, ‘punctuated’ evolution or ‘punctuated gradualism’ as the cause of this evolutionary pattern of the shelf-carbonate fossil record. This pattern is distinctive and we refer to it as ‘sequence evolution’ and ‘sequence extinction’. In the later part of the Middle Permian and in the Late Permian, the fossil record clearly illustrates that a series of faunal losses through ‘sequence extinctions’ progressively exceeded faunal replacements and new species through ‘sequence evolution’, but not a ‘mass extinction’ as is commonly ascribed to the end of the Permian Period. Most Permian faunas became extinct in the interval of 8 to 4 million years before the end of the Late Permian.     

Productivity, herbivory, and species traits rather than diversity influence invasibility of experimental phytoplankton communities

Biological invasions are a major threat to natural biodiversity; hence, understanding the mechanisms underlying invasibility (i.e., the susceptibility of a community to invasions by new species) is crucial. Invasibility of a resident community may be affected by a complex but hitherto hardly understood interplay of (1) productivity of the habitat, (2) diversity, (3) herbivory, and (4) the characteristics of both invasive and resident species. Using experimental phytoplankton microcosms, we investigated the effect of nutrient supply and species diversity on the invasibility of resident communities for two functionally different invaders in the presence or absence of an herbivore. With increasing nutrient supply, increased herbivore abundance indicated enhanced phytoplankton biomass production, and the invasion success of both invaders showed a unimodal pattern. At low nutrient supply (i.e., low influence of herbivory), the invasibility depended mainly on the competitive abilities of the invaders, whereas at high nutrient supply, the susceptibility to herbivory dominated. This resulted in different optimum nutrient levels for invasion success of the two species due to their individual functional traits. To test the effect of diversity on invasibility, a species richness gradient was generated by random selection from a resident species pool at an intermediate nutrient level. Invasibility was not affected by species richness; instead, it was driven by the functional traits of the resident and/or invasive species mediated by herbivore density. Overall, herbivory was the driving factor for invasibility of phytoplankton communities, which implies that other factors affecting the intensity of herbivory (e.g., productivity or edibility of primary producers) indirectly influence invasions.     

Late Pleistocene beetle faunas of Beringia: where east met west

Aim   To examine the issue of Beringian steppe-tundra from an entomological standpoint, using fossil beetle data collected from late Pleistocene sites.
Location   North-eastern Siberia (Western Beringia), the Bering Land Bridge (Central Beringia), and Alaska and the Yukon Territory (Eastern Beringia).
Methods   Analysis of habitat preferences of beetle species found in fossil assemblages, leading to classification of major habitat types characterized by the faunal assemblages.
Results   Fossil beetle assemblages indicative of steppe-tundra are found mainly in the interior regions of Eastern Beringia, whereas these assemblages dominate nearly all late Pleistocene fossil sites in Western Beringia. Eastern Beringian faunas contain a much larger proportion of mesic to hygrophilous species and very few arid-habitat species. In contrast to this, the habitat requirements of the Western Beringian faunas are more evenly spread across the moisture spectrum.
Main conclusions   The taxonomic patterns of the two sets of fossil assemblages are remarkably different. Eastern Beringian faunal assemblages contain substantial numbers of mesic tundra and riparian rove beetles (Staphylinidae); this element is almost entirely lacking in the Western Beringian fossil assemblages. Taphonomic bias tends to overemphasize moisture-loving species at the expense of dry, upland species in the fossil record. Both Western and Eastern Beringian landscapes undoubtedly contained mosaics of habitats ranging from dry uplands (steppe-tundra) through mesic tundra to bogs and riparian corridors.     

Community maturity, species saturation and the variant diversity-productivity relationships in grasslands

Detailed knowledge of the relationship between plant diversity and productivity is critical for advancing our understanding of ecosystem functioning and for achieving success in habitat restoration efforts. However, effects and interactions of diversity, succession and biotic invasions on productivity remain elusive. We studied newly established communities in relation to preexisting homogeneous vegetation invaded by exotic plants in the northern Great Plains, USA, at four study sites for 3 years. We observed variant diversity–productivity relationships for the seeded communities (generally positive monotonic at three sites and non-monotonic at the other site) but no relationships for the resident community or the seeded and resident communities combined at all sites and all years. Community richness was enhanced by seeding additional species but productivity was not. The optimal diversity (as indicated by maximum productivity) changed among sites and as the community developed. The findings shed new light on ecosystem functioning of biodiversity under different conditions and have important implications for restoration.