贡嘎山冰川退缩区植物-土壤反馈与植物间相互作用

植物-土壤反馈是揭示陆地生物群落动态变化的关键环节,为理解植物间相互作用及植被群落变化过程奠定基础。本研究以贡嘎山冰川退缩区原生演替早(5~10年)、中(30~40年)和晚期(80~100年)3个阶段典型土壤以及各阶段优势植物为对象,采用盆栽控制试验,比较优势植物在不同土壤条件下的生物量,并量化植物间相互作用以及植物-土壤反馈的方向与强度,为探究贡嘎山冰川退缩区植被群落演替规律提供依据。结果表明:(1)植物-土壤反馈作用显著影响植物在本土中的生物量,早期沙棘(Hippophae rhamnoides)在本土中生长最差,沙棘的植物-土壤反馈系数为负值;演替中期冬瓜杨(Populus purdomii)的反馈系数趋于零;晚期峨眉冷杉(Abies fabri)在本土中生长最好,峨眉冷杉的反馈系数为正值。(2)混种时,早期沙棘与演替中、晚期植物间相互作用指数为负值;中期冬瓜杨、川滇柳(Salix rehderiana)与演替早、晚期植物的相互作用指数接近于零,晚期植物峨眉冷杉、麦吊云杉(Picea brachytyla)与演替早、中期植物相互作用指数为正值。从植物-土壤反馈的方向来看,贡嘎山植被演替从早期负反馈,中期中性反馈,过渡到晚期正反馈。此外,演替早期沙棘促进演替中晚期植物生长,演替中期冬瓜杨、川滇柳对演替早晚期植物无显著影响,晚期峨眉冷杉、麦吊云杉更利于与演替早中期植物相互竞争。结果显示,植物-土壤反馈与植物间相互作用共同驱动了贡嘎山冰川退缩区植被快速演替,直至顶极群落。     

Inferring the mode of speciation in Indo-West Pacific Conus (Gastropoda: Conidae)

Aim This study aims to initially explore the mode of speciation in Indo‐West Pacific Conus. Location The Indo‐West Pacific island arc, Indian and Pacific Oceans. Methods Relating evolutionary divergence in a molecular phylogeny [T.F. Duda & S.R. Palumbi (1999) Proceedings of the National Academy of Science USA, 96 , 10272] using node height with modern range extents as a possible measure of allopatric or sympatric speciation following that of T.G. Barraclough, A.P. Vogler & P.H. Harvey [(1999) Evolution of Biological Diversity. Oxford University Press, Oxford] models of sympatric and allopatric speciation. Results The analysis seems to indicate that the relationship of sympatry with node height is not informative. Species that have diverged quite recently show 100% sympatry with the sister species. A clearer signal of recent allopatric speciation is observed in species whose distribution is at the edge of the Indian and Pacific Ocean basins. In the widely distributed Conus ebraeus clade, the relationships of node heights and range extents of the member species support a key prediction of sympatric speciation. In highly ecologically specialized species, there is a smaller degree of sympatry than those species that are less specialized. Main conclusions The modes of speciation models presented in this study are not informative. This suggests that there had been large and possibly rapid changes in range size after speciation in the various clades. This could have been due to the fact that the wide dispersal life‐history strategy in the genus had been largely conserved in Conus evolution. There is evidence of sympatric and parapatric speciation in one Conus clade. Overall, the patterns of phylogeny and range distribution when related to the timing of speciation lend circumstantial support to a Neogene centre of origin hypothesis but not to speciation on the Pacific Plate. Speciation is likely to have been associated with the Tethys Sea closure event, with rapid speciation occurring after closure.     

AMMONOIDS AND THE TRIASSIC/JURASSIC BOUNDARY IN THE HIMALAYAS OF SOUTHERN TIBET

Abstract:  The sections of Germig in the Nyalam area, southern Tibet, provide a continuous exposure of ammonoid-bearing, uppermost Triassic and basal Jurassic strata. Eighteen species (three of them new) are described and illustrated: Choristoceras marshi Hauer , C. aff. marshi, C. cf. nobile Mojsisovics , C. nyalamense sp. nov., Eopsiloceras germigense sp. nov. , Pleuroacanthites aff. biformis (Sowerby) , Rhacophyllites sp., Nevadaphyllites cf. psilomorphus (Neumayr), Neophyllites sp. indet., Neophyllites cf. biptychus (Lange), Psiloceras tibeticum sp. nov., P. calliphyllum (Neumayr), Euphyllites cf. struckmanni (Neumayr), Discamphiceras pleuronotum (Canavari), Alsatites spp., Kammerkarites frigga , and K. sp. The ammonoid fauna shows a strong affinity to that of the Northern Calcareous Alps, although diversity in the Calliphyllum Zone is markedly lower. The ammonoid succession across the Triassic/Jurassic boundary is subdivided into four zones: the Rhaetian Marshi, the basal Hettangian Tibeticum, the lower Hettangian Calliphyllum, and the middle Hettangian Pleuronotum zones. It is the only known succession across the Triassic/Jurassic boundary in the Tethyan Realm that is not condensed. The Marshi and Calliphyllum zones are correlated with the same zones in the Northern Calcareous Alps. The Tibeticum Zone, a new local zone, is transitional between the Marshi and the Calliphyllum zones in that it yields both choristoceratids and psiloceratids. Its base is taken to mark the base of the Jurassic System in the eastern Tethys.     

Biogeographic responses to geodynamics: A key study all around the Oligo–Miocene Tethyan Seaway

Extensive terrestrial exchanges were initiated by the closure of the Tethyan Seaway during the Early Miocene. Proboscideans are among the most prominent African immigrants, which arrived in Eurasia about 19 Ma ago via the “Gomphotherium Landbridge”. Several distinct waves of continental migrations, however, document that the formation of this landbridge was a multiphase process. Until the closure, a marine faunal exchange was enabled via the Mesopotamian Trough and the Zagros Basin, as reflected by contributions of Indonesian corals in the Iranian basins and by the occurrence of “western” gastropods in Pakistan and India. Nevertheless, the emergence of the landbridge was preceded in the marine biosphere by first biogeographic divergences on both sides of the seaway already during Oligocene times (e.g. within the tridacnines and strombids). Around the closure event, the breakdown of biogeographic relations was near-complete and the Proto-Mediterranean faunas bear little in common with those of the Indo-West Pacific Region (IWPR). Some of the discussed examples suggest that the Western Tethys Region (WTR) had acted as centre of origin and diversity during Oligocene and Early Miocene times. After the closure of the seaway, this centre had shifted to the southeast, heralding the enormous biodiversity of the modern IWPR. Some originally WTR elements managed to follow this shift and formed the Miocene stock for the modern IWPR faunas. In contrast, the marine fauna in the Mediterranean cul-de-sac suffered strong impoverishment due to the Miocene cooling, the Messinian Salinity Crisis and the late Pliocene and Pleistocene glacials – a fact which might explain the receptivity of the Mediterranean Sea for Lessepsian migrants.

This synthesis tries to document the practical problem of recognising biogeographic patterns despite the heterochronous developments in different systematic groups, which, in addition, are often obscured by a stratigraphically incomplete and geographically patchy fossil record.     

Bouleiceras (Hildoceratidae,Ammonitina) from the lower Toarcian (Jurassic) of the Iberian Range (Spain): Taxonomy,stratigraphic distribution and insights on its dispersal

Bouleiceras is a very rare genus among the rich assemblages of ammonoids from the lower Toarcian of the Iberian Range. So far, only two dozen specimens have been recorded in numerous field campaigns carried out since 1965 by different authors. The interest of this taxon lies in its peculiar paleogeographical distribution in comparison with most other ammonoids of the same age. A review of these specimens is carried out, including those obtained in previous works and others recently collected in selected localities. Based mainly on the differences in the shape of the ventral section and the suture line, seven species have been identified; two of which are new: Bouleiceras ibericum nov. sp. and Bouleiceras? betetensis nov. sp. All the reviewed specimens are recorded in the Semicelatum Subzone of the Tenuicostatum Zone and the Elegantulum Subzone of the Serpentinum Zone from the Central Sector and the Levantine Sector of the Iberian Range. The global distribution of the genus is summarized from the known data, and its possible dispersal routes are analyzed, as well as the factors that could have conditioned them.     

Blue carbon gains from glacial retreat along Antarctic fjords: What should we expect?

Rising atmospheric CO₂ is intensifying climate change but it is also driving global and particularly polar greening. However, most blue carbon sinks (that held by marine organisms) are shrinking, which is important as these are hotspots of genuine carbon sequestration. Polar blue carbon increases with losses of marine ice over high latitude continental shelf areas. Marine ice (sea ice, ice shelf and glacier retreat) losses generate a valuable negative feedback on climate change. Blue carbon change with sea ice and ice shelf losses has been estimated, but not how blue carbon responds to glacier retreat along fjords. We derive a testable estimate of glacier retreat driven blue carbon gains by investigating three fjords in the West Antarctic Peninsula (WAP). We started by multiplying ~40 year mean glacier retreat rates by the number of retreating WAP fjords and their time of exposure. We multiplied this area by regional zoobenthic carbon means from existing datasets to suggest that WAP fjords generate 3,130 tonnes of new zoobenthic carbon per year (t zC/year) and sequester >780 t zC/year. We tested this by capture and analysis of 204 high resolution seabed images along emerging WAP fjords. Biota within these images were identified to density per 13 functional groups. Mean stored carbon per individual was assigned from literature values to give a stored zoobenthic Carbon per area, which was multiplied up by area of fjord exposed over time, which increased the estimate to 4,536 t zC/year. The purpose of this study was to establish a testable estimate of blue carbon change caused by glacier retreat along Antarctic fjords and thus to establish its relative importance compared to polar and other carbon sinks.     

Evolution of freshwater eels of the genus Anguilla: a probable scenario

We present a molecular phylogeny of freshwater eels from three oceans and give hypotheses to address major questions about the evolution and geographic distribution of this group. A phylogenetic tree obtained from mitochondrial cytochrome b sequences of eight species of Anguilla suggests that the African species A. mossambica and Australian species A. australis form a clade together with the two Atlantic species, the European eel, A. anguilla, and American eel, A. rostrata , whereas A. marmorata in the Indo-Pacific Ocean, A. reinhardti in northeastern Australia and the Japanese eel, A. japonica, in the northwestern Pacific are placed in another. Most speciation among the lineages is proposed to have occurred during the Eocene to Oligocene (45–30 million years ago, Ma). However, the two Atlantic species are estimated to have separated much later, approximately 10 Ma. The following evolutionary scenario for the dispersal and speciation of these species of anguillid eels is proposed based on general global paleogeography and paleo-circulation. Ancestral eels evolved during the Eocene or earlier, in the western Pacific Ocean near present-day Indonesia. A group derived from this ancestor dispersed westward, by transport of larvae in the global circum-equatorial current through the northern edge of the Tethys Sea. This group split into the ancestor of the European and American eels, which entered the Atlantic Ocean, and a second group, which dispersed southward and split into the east African species and Australian species.     

Multiphase morphospace saturation in cyrtocrinid crinoids

The study of the relationship between disparity (occupied morphospace) and diversity (number of taxa) through geological time represents a powerful tool in the macroevolutionary study of groups. In this contribution, this approach is applied for the first time to the cyrtocrinid crinoids, a major clade of mostly Mesozoic articulate crinoids also represented by rare Cenozoic forms (two extant taxa). The analysis of disparity identified two separate evolutionary radiations for cyrtocrinids with maximum morphospace exploration, one at the beginning of the evolutionary history of the group in the Pliensbachian and a second one between the Late Jurassic and Early Cretaceous. On the methodological level, the disparity measured both as total variance and as sum of ranges shows compatible results, with trends well coupled to the diversity curve indicating that, in cyrtocrinid crinoids, an increase or decrease in the number of taxa in the history of the clade corresponds a proportional increase and decrease also in the occupied morphospace. The curves obtained were interpreted in the light of the clade's phylogeny, major oceanographic events, newly available ecological niches and relative key innovations, which would be able to increase the fitness of the group. The group diversity was already in decline starting from the Aptian, and the mass extinction at the K‐PG boundary had no effect on the history of the clade. The results show once again the importance and potential of diversity/disparity studies when put into the light of palaeotectonic, palaeoecological and palaeoenvironmental factors.     

Permian bryozoans of the NW-tethys

Summary Permian bryozoan faunas from the Lower Permian sequences of the Carnic Alps (UpperPseudoschwagerina Formation and Trogkofel Formation) and from some other Permian units of the NW-Tethys (Sicily, Tunisia) include cystoporid, trepostomid, fenestellid, rhabdomesid, and timanodictyid taxa. Fenestellids and cystoporids species dominate. The Lower Permian bryozoan fauna of the Carnic Alps displays close relations to faunas of Sakmarian-Artinskian age of the Russian Platform and Pamir as well as of the Lower Permian of Australia. Bryozoans from Permian sequences of Sicily and Tunisia display relations to the Permian faunas of Indonesia and Australia.     

Tethyan uppermost Permian (Dzhulfian and Dorashamian) foraminiferal faunas and their paleogeographic and tectonic implications

The foraminiferal faunas and biostratigraphic correlation of the Tethyan uppermost Permian (Dzhulfian and Dorashamian) provide important paleogeographic and tectonic data for the interpretation of the Palaeofusulina-bearing terranes in East and Southeast Asia. These interpretations have a significant bearing on understanding Japanese pre-Cretaceous tectonostratigraphic and micropaleontologic data, as well as the geodynamic evolution of the Japanese Palaeofusulina-bearing terranes. The Tethyan foraminiferal fauna in the uppermost Permian is characterized by the occurrence of provincial and endemic schubertellid genera, and the absence of neoschwagerinids and verbeekinids which had characterized the rapidly evolving Middle Permian Tethyan marine faunas until their extinction at the end of the Midian. Difficulties in world-wide correlation of the uppermost Permian have resulted because of different geographic faunal compositions and the geographic patterns of extinction of Permian marine faunas. The Palaeofusulina fauna is one of the most reliable indicators of the uppermost Permian. Its presence or absence serves as paleogeographic constraints on East and Southeast Asian terranes. For example, the absence of Palaeofusulina fauna and the presence of late Midian Lepidolina multiseptata faunas in the Lhasa Terrane in Tibet and the Wolya Terrane in Sumatra (the third continental sliver north of Gondwana) are important, particularly, for identifying the rift–drift–collision process of the Gondwana-affinity terranes. They suggest a Late Permian separation of the two terranes from Gondwana. Tethyan Palaeofusulina occur in the latest Permian tropical to subtropical latitudinal belt and along with other geologic data assist in paleogeographic reconstructions and in interpreting the possible movement and emplacement of the Palaeofusulina-bearing terranes such as the Maizuru, South Kitakami–Kurosegawa and Chichibu terranes in Japan. They reveal that: (1) the Upper Permian Maizuru Group was deposited on the eastern continental margin of South China; (2) the occurrence of the Lower Permian Cathaysian flora and a number of geologic data in the South Kitakami–Kurosegawa suggest an arc–trench system setting and the Late Permian deposition in a shallow open-marine environment in proximity to South China; (3) foraminiferal biogeograpic data and the reconstructed oceanic plate stratigraphy in the Chichibu Terrane constrain the location of the Chichibu Seamount Chains to the western part of the Panthalassan domain, as they moved westwards against the Cathaysian Continent until their Jurassic accretion.