Spatial niche partitioning in dinosaurs from the latest cretaceous (Maastrichtian) of North America

We examine patterns of occurrence of associated dinosaur specimens (n = 343) from the North American Upper Cretaceous Hell Creek Formation and equivalent beds, by comparing their relative abundance in sandstone and mudstone. Ceratopsians preferentially occur in mudstone, whereas hadrosaurs and the small ornithopod Thescelosaurus show a strong association with sandstone. By contrast, the giant carnivore Tyrannosaurus rex shows no preferred association with either lithology. These lithologies are used as an indicator of environment of deposition, with sandstone generally representing river environments, and finer grained sediments typically representing floodplain environments. Given these patterns of occurrence, we argue that spatial niche partitioning helped reduce competition for resources between the herbivorous dinosaurs. Within coastal lowlands ceratopsians preferred habitats farther away from rivers, whereas hadrosaurs and Thescelosaurus preferred habitats in close proximity to rivers, and T. rex, the ecosystem's sole large carnivore, inhabited both palaeoenvironments. Spatial partitioning of the environment helps explain how several species of large herbivorous dinosaurs coexisted. This study emphasizes that different lithologies can preserve dramatically dissimilar vertebrate assemblages, even when deposited in close proximity and within a narrow window of time. The lithology in which fossils are preserved should be recorded as these data can provide unique insights into the palaeoecology of the animals they preserve.     

Changes in the water level of Lake Peipsi and their reflection in a sediment core

A comprehensive study (chronological, lithological and geochemical) of an 8.5 m postglacial sediment sequence from Lake Peipsi was conducted to elucidate the effects of lake-level changes on the sedimentary environment and biogeochemical dynamics in a large lake. Four lithological units were distinguished in the sediment sequence studied: clayey silt, slightly laminated greyish carbonaceous gyttja, brownish-grey gyttja and dark gyttja. These units indicate that large shifts in sedimentation processes occurred in the past. The sediment data show that fluctuations in water depth had a profound impact on the lake environment, recorded as changes in the lithological composition, phosphorus content of sediments and composition of diatom assemblages. The corresponding changes are best reflected in sediments accumulated during phases of regression when the lake area was also smaller. As the water depth and area of the lake increased, wave-induced erosion and resedimentation smoothed or even disturbed the initial information. The increase of phosphorus content in the unconsolidated, high-porosity surface sediments (0.5 m) is most probably connected with active diffusion and matter exchange between the water-sediment pools.     

Weather underground: Subsurface hydrologic processes mediate tree vulnerability to extreme climatic drought

Drought extent and severity have increased and are predicted to continue to increase in many parts of the world. Understanding tree vulnerability to drought at both individual and species levels is key to ongoing forest management and preparation for future transitions in community composition. The influence of subsurface hydrologic processes is particularly important in water‐limited ecosystems, and is an under‐studied aspect of tree drought vulnerability. With California's 2013–2016 extraordinary drought as a natural experiment, we studied four co‐occurring woodland tree species, blue oak (Quercus douglasii), valley oak (Quercus lobata), gray pine (Pinus sabiniana), and California juniper (Juniperus californica), examining drought vulnerability as a function of climate, lithology and hydrology using regional aerial dieback surveys and site‐scale field surveys. We found that in addition to climatic drought severity (i.e., rainfall), subsurface processes explained variation in drought vulnerability within and across species at both scales. Regionally for blue oak, severity of dieback was related to the bedrock lithology, with higher mortality on igneous and metamorphic substrates, and to regional reductions in groundwater. At the site scale, access to deep subsurface water, evidenced by stem water stable isotope composition, was related to canopy condition across all species. Along hillslope gradients, channel locations supported similar environments in terms of water stress across a wide climatic gradient, indicating that subsurface hydrology mediates species’ experience of drought, and that areas associated with persistent access to subsurface hydrologic resources may provide important refugia at species’ xeric range edges. Despite this persistent overall influence of the subsurface environment, individual species showed markedly different response patterns. We argue that hydrologic niche segregation can be a useful lens through which to interpret these differences in vulnerability to climatic drought and climate change.     

礁滩分类以及在岩芯中的识别

百余年来涉及生物礁滩的有关论著,从对具体例证的剖析到时空模式的综述,催生着各种分类方案的出台。生物礁滩纵横展布上显示生态环境的相变,礁一滩灰岩具有非均一性,其岩石学特征能指示其生态群落类型。在岩芯中能识别出与各类礁一滩在成因上密切相关的岩性段时,勾勒礁滩体生态单元序列在一定程度上还是可行的。     

Structural equation modelling detects unexpected differences between bryophyte and vascular plant richness along multiple environmental gradients

Aim The aim of this study was to develop and evaluate a structural equation model explaining the species richness of bryophytes and vascular plants along multiple environmental gradients. Our primary interests in developing this model were: (1) to evaluate the effect of tree canopy along an altitudinal gradient on bryophyte and vascular plant richness; (2) to determine to what extent lithology was able to explain richness in the two groups of plants; (3) to assess whether anthropogenic disturbances decrease richness; and (4) to explore, comparing competing models, the causal links connecting spring area, discharge and spring complexity and to assess how these variables are related to richness. Location Eighty‐six springs were sampled in the south‐eastern Alps of Italy, from the lowlands to high‐mountain regions, and on different lithologies. Methods A structural equation model (SEM) was used to test certain hypotheses about the direct and indirect effects of altitude, canopy, lithology, disturbance, spring complexity, discharge and spring area on bryophyte and vascular plant richness. Competing models were evaluated and bootstrap simulation was used to determine the stability of parameter estimates. Results SEM analysis made it possible to disentangle the different effects of canopy and lithology on bryophyte and vascular plant richness: for the former it was demonstrated that the increased richness with altitude was related primarily to lithology, whereas the latter increased because of the reduction of canopy cover. In addition, the model predicted that spring discharge determined the size of the spring area and even the complexity of the spring; these latter two variables influenced to different degrees both bryophyte and vascular plant richness. Anthropogenic disturbances affected the richness of bryophytes more than that of the vascular plants. Main conclusions Our study demonstrates that several similarities in the patterns of bryophyte and vascular plant richness are in fact induced by different environmental variables.     

不同岩性背景下土壤侵蚀与石漠化关联性分析

喀斯特地区土壤侵蚀与石漠化问题备受关注,为了定量分析不同岩性下土壤侵蚀与石漠化的关联性,为研究区优化生态环境提供决策依据,以贵州省沿河县为例,以Landsat遥感影像、1∶5000地形图、岩性和石漠化为基础数据,采用监督分类方法、表面分析和栅格计算,提取出土壤侵蚀的各项指标因子。对不同岩性背景下土壤侵蚀与石漠化关联性分析,结果显示:(1)沿河县石漠化面积为284.44 km2,占全县国土面积的11.52%。已发生石漠化等级以轻度、中度、强度较显著;土壤侵蚀面积为1838.97 km2,占全县总面积的74.48%,已经发生土壤侵蚀等级以轻度、中度、强度侵蚀为主。(2)灰岩与碎屑岩互层和连续性白云中,石漠化与土壤侵蚀发生面积较显著,分别占石漠化与土壤侵蚀面积的57.99%和50.45%。(3)非碳酸盐岩、灰岩夹碎屑岩、灰岩与白云岩混合、灰岩与碎屑岩互层、连续性白云岩和石灰岩上,石漠化等级与土壤侵蚀程度在潜在和轻度呈负相关、轻度和中度石漠化内呈正相关、中度和极重度石漠化内呈负相关,土壤侵蚀等级与石漠化在微度和轻度侵蚀内呈正相关,在轻度和剧烈侵蚀内呈负相关,其中灰岩与白云岩混合和连续性白云岩上,石漠化等级与土壤侵蚀存在单一的负相关。     

Disentangling environmental correlates of vascular plant biodiversity in a Mediterranean hotspot

We determined the environmental correlates of vascular plant biodiversity in the Baetic‐Rifan region, a plant biodiversity hotspot in the western Mediterranean. A catalog of the whole flora of Andalusia and northern Morocco, the region that includes most of the Baetic‐Rifan complex, was compiled using recent comprehensive floristic catalogs. Hierarchical cluster analysis (HCA) and detrended correspondence analysis (DCA) of the different ecoregions of Andalusia and northern Morocco were conducted to determine their floristic affinities. Diversity patterns were studied further by focusing on regional endemic taxa. Endemic and nonendemic alpha diversities were regressed to several environmental variables. Finally, semi‐partial regressions on distance matrices were conducted to extract the respective contributions of climatic, altitudinal, lithological, and geographical distance matrices to beta diversity in endemic and nonendemic taxa. We found that West Rifan plant assemblages had more similarities with Andalusian ecoregions than with other nearby northern Morocco ecoregions. The endemic alpha diversity was explained relatively well by the environmental variables related to summer drought and extreme temperature values. Of all the variables, geographical distance contributed by far the most to spatial turnover in species diversity in the Baetic‐Rifan hotspot. In the Baetic range, climate was the most significant driver of nonendemic species beta diversity, while lithology and climate were the main drivers of endemic beta diversity. Despite the fact that Andalusia and northern Morocco are presently separated by the Atlantic Ocean and the Mediterranean Sea, the Baetic and Rifan mountain ranges have many floristic similarities – especially in their western ranges – due to past migration of species across the Strait of Gibraltar. Climatic variables could be shaping the spatial distribution of endemic species richness throughout the Baetic‐Rifan hotspot. Determinants of spatial turnover in biodiversity in the Baetic‐Rifan hotspot vary in importance between endemic and nonendemic species.     

A palaeogeographic link between Australia and eastern North America: a New England connection?

Abstract. This research tests the hypothesis that Australia and eastern North America met in rotational collision during the Palaeozoic with the corollary that the New England fold belt of Australia, rather than the Reguibat promontory of Africa, collided with the Alleghanian orogen in the central Appalachians. Identical Lancefieldian-stage, zone 1 (Early Ordovician) graptolites of the Anisograptid family are found in identical environments in Newfoundland, Norway, and the Lachlan fold belt of Australia. Palaeozoic granites are consistent with a tectonic model in which the Lachlan fold belt caused mechanical deformation of the Canadian Appalachians. The Lachlan and New England fold belts of Australia and the Alleghanian orogen of North America are tectonically consistent with the east coast hypothesis. Major deformations and magmatic episodes are coeval from Silurian to Permian. The tectonic, palaeontologic, lithologic, and geometric evidence for this position is more abundant and precise than the stratigraphic evidence for a west coast location of Australia relative to North America.