Disappearance Of Taxa Research Articles

Impacts of two high‐head dams on macroinvertebrate communities in the regulated river reaches of Wujiang River, China

AbstractThe impact of two high‐head dams on macroinvertebrate communities within the regulated reaches of the Wujiang River in China was explored, using longitudinal monitoring data spanning from 2006 to 2016. In this study, we set up 10 sampling sites categorized into four areas based on different stressors and defined three stages based on the timeline of dam construction. Our findings revealed significant changes in community composition before and after dam impoundment. While certain original dominant taxa, such as Rivularia globosa and Lithoglyphopsis ovatus, remained dominant throughout the stages, mayflies and caddisflies nearly vanished in the downstream reaches of the dams. This trend was accompanied by the disappearance of taxa with low adaptability and the emergence of tolerant taxa downstream of the dams. Additionally, typical limnological taxa colonized the inundated reaches. Dam impoundment affected not only macroinvertebrate community composition but also diversity. In this study, the recovery effect of communities downstream of dams was not observed due to the limited distance, but the presence of Wujiangdu Dam upstream of the two dams for over 20 years makes us believe that in a large river system, macroinvertebrate communities downstream of high‐head dams may fully recover if the distance from the dams is long enough. The original and vulnerable species R. globosa, which demonstrated remarkable adaptability and thrived downstream of dams, should be further studied in the future.

Middle Cenomanian coral fauna from the Roßsteinalmen (Northern Calcareous Alps, Bavaria, Southern Germany) – a revised and extended version

In the Northern Calcareous Alps, relics of a formerly widely distributed shallow marine facies belonging to the Branderfleck Formation (upper Albian to lower Turonian) crop out and contain locally abundant corals. The fauna described here derives from Middle Cenomanian sediments. This study complements a former revision. In total, the fauna includes 98 species in 46 genera, belonging to 16 scleractinian superfamilies and two octocorallian families. One species – Enallhelia octasepta – is described as new. The fauna that was formerly located at the northern part of the Apulian plate (Austroalpine unit), south of the Penninic Ocean, shows palaeobiogeographic relationships to Cenomanian faunas from the Basque-Cantabrian Basin, the Prebetic zone, the Pelagonium, and the Quillan Basin, indicating stronger connections to Tethyan rather than Boreal faunas. The fauna also shares species with Aptian and Albian, but also with Late Cretaceous faunas of the Gosau Basin. Eight genera experienced a range extension; five genera have their last occurrence in the Middle Cenomanian fauna, and three genera have their first occurrence. Although the fauna presents numerous genera that became widespread in the Late Cretaceous, its generic composition is more closely related to late Early Cretaceous corals than to post-Cenomanian corals. The faunal turnover at the Cenomanian/Turonian boundary was not marked by the sudden appearance of new faunal elements, but rather by the disappearance of taxa. Some faunal elements that constitute post-Cenomanian faunas already existed in the Cenomanian, but they were very rare. The increase of taxa after the Cenomanian/Turonian boundary took place during the Coniacian and Santonian.

Miocene deep-sea benthic foraminifera from the Atlantic and Indian oceans: diversity patterns and palaeoceanography

During the early to middle Miocene of the Atlantic and Indian Oceans there were variations in species diversity of the lower bathyal to abyssal plain (3-4.4 km) benthic foraminifcral assemblages allhough, overall, diversity remained high and comparable with that of the modern environment. The early Miocene was a period of palaeoceanographic change and this has previously been documented both through studies of stable isotopes and the rate of appearances or disappearances of taxa (whether evolutionary or ecological). The diversity oscillations appear to represent shorter period change. The lowest diversities are associated with the peak abundance of bolivinids. Other variations cannot be correlated from one site to another and are thought to represent local environmental changes. During the early-middle Miocene, the diversity of the Atlantic abyssal plain was lower than that of the Indian and Pacific Oceans possibly indicating significant diversity differences between ocean basins. On the basis of limited data, it is possible to speculate that the species diversity of the Miocene was perhaps higher than that of today.

Linking worldwide past and present conifer vulnerability

Inventories of species recently extinct or threatened with extinction may be found in global databases. However, despite the large number of published fossil based-studies, specific databases on the vulnerability of species in the past are not available. We compiled a worldwide database of published fossil records of plant range losses over the last 30 ka across all continents. Widespread range losses of plant taxa across all latitudes were identified, with the majority representing gymnosperms. Focusing on conifers, a group of plants with well understood distribution and conservation status, we found that past range losses often overlapped areas where species are endangered at present, suggesting that such areas have been prone to biodiversity loss through time. During phases of past rapid climate change, even areas that currently have low levels of endangered species were affected by plant range losses, in some cases with disappearance of taxa from entire continents, islands or major geographic regions. Integration of modern and palaeoecological data enhance our understanding of the complex processes underlying the modes, rates, and extent of threats to plants under changing climate and increasing human pressure, which is vital information for effective conservation actions.

Distribution of Pliocene Radiolaria at Site 745 (Sections 14H-15H), LEG 119, from the Kerguelen Plateau and Biostratigraphy

This paper presents first comprehensive record of Pliocene Radiolaria from Leg 119, Site 745 of the Antarctic region. Twenty five samples were taken from two sections, viz. 14H and 15H, from Kerguelen Plateau in the Southern Ocean region. Thirty well preserved species were determined. Diversification and distribution of radiolarians in the sections were examined. On the basis of appearance and disappearance of taxa, one zone, i.e. Upsilon, is recognized, which is equivalent to the earlier established NR5 zone.

Remarks on sequence stratigraphy and taphonomy of the Malvinokaffric shelly fauna during the KAČÁK Event in the Apucarana Sub-basin (Paraná Basin), Brazil

The Eifelian–Givetian (Middle Devonian) transition constituted an important paleoenvironmental event for the Malvinokaffric Realm in the Apucarana Sub-basin (Parana Basin). This study highlights integration between taphonomy and sequence stratigraphy, and four depositional sequences are identified during the transition. In Sequence 1, the presence of a typical normal-sized Malvinokaffric fauna is recorded. In the transgressive systems tract (TST) of Sequence 2, no benthic fossils are present, and this is interpreted as a stratigraphic marker of an event of significant paleoenvironmental change (KACAK Event). In Sequence 3, the TST has abundant bioclasts, which become rarer toward the top of the section, i.e., within the transgressive systems tract. The original habitat of this autochthonous to parautochthonous fauna was a low-energy environment between the fair weather wave base and the storm wave base of the Devonian epicontinental sea. In the highstand systems tract of this sequence, the presence of normal-sized Pennaia paulianna and lingulids demonstrates the return of more ambient conditions. Sequence 4 is of Carboniferous age. Its limit is a second-order sequence boundary recording a lowstand systems tract formed by a fluvial depositional system. The low diversity and the disappearance of taxa are not the result of a taphonomic bias, but reflect the post-KACAK Event.

Pliocene and Pleistocene dinoflagellate cyst and acritarch zonation of DSDP hole 610a, Eastern North Atlantic

A diverse and well‐preserved dinoflagellate cyst and acritarch record, comprising 35 genera and 104 species of dinoflagellate cyst and 14 acritarch taxa, is presented for the Lower Pliocene through Middle Pleistocene (4.00–0.53 Ma) of eastern North Atlantic Deep Sea Drilling Project Hole 610A. The Pliocene samples contain twice as many dinoflagellate cyst taxa than the Quaternary samples but far lower cyst concentrations. The disappearance of taxa during the latest Pliocene is likely to have been associated with global cooling. Eight biozones and four subzones are established, representing a level of detail that surpasses earlier studies. The zones are based mostly on highest occurrences, as these are most prevalent in the Pliocene and Lower Pleistocene. The subzones, based on both the acme and highest persistent occurrence of Habibacysta tectata, appear regionally useful within the Lower Pleistocene. The lowest occurrence of Impagidinium cantabrigiense is a potential marker for the uppermost Gelasian Stage (Lower Pleistocene). While this biozonation is intended primarily for use in the eastern North Atlantic, elements will be applicable across the higher‐latitude North Atlantic where calcareous microfossil zonations have reduced reliability and resolution. Most of the stratigraphically useful taxa are illustrated, and selected species are described informally.

PLIOCENE AND PLEISTOCENE DINOFLAGELLATE CYST AND ACRITARCH ZONATION OF DSDP HOLE 610A, EASTERN NORTH ATLANTIC

A diverse and well-preserved dinoflagellate cyst and acritarch record, comprising 35 genera and 104 species of dinoflagellate cyst and 14 acritarch taxa, is presented for the Lower Pliocene through Middle Pleistocene (4.00–0.53 Ma) of eastern North Atlantic Deep Sea Drilling Project Hole 610A. The Pliocene samples contain twice as many dinoflagellate cyst taxa than the Quaternary samples but far lower cyst concentrations. The disappearance of taxa during the latest Pliocene is likely to have been associated with global cooling. Eight biozones and four subzones are established, representing a level of detail that surpasses earlier studies. The zones are based mostly on highest occurrences, as these are most prevalent in the Pliocene and Lower Pleistocene. The subzones, based on both the acme and highest persistent occurrence of Habibacysta tectata, appear regionally useful within the Lower Pleistocene. The lowest occurrence of Impagidinium cantabrigiense is a potential marker for the uppermost Gelasian Stage (Lower Pleistocene). While this biozonation is intended primarily for use in the eastern North Atlantic, elements will be applicable across the higher-latitude North Atlantic where calcareous microfossil zonations have reduced reliability and resolution. Most of the stratigraphically useful taxa are illustrated, and selected species are described informally.

The relationships between Late Ordovician sea-level changes and faunal turnover in western Baltica: Geochemical evidence of oxic and dysoxic bottom-water conditions

The late Sandbian to the early Katian (Late Ordovician) in southeastern Norway is dominated by marine mudstones that contain an exceptional spectrum of macrofauna and trace element geochemistry, recording both abrupt and gradual faunal changes during major sea-level and environmental shifts. This study investigates the relationships between sea-level changes and their influence on the source of clastic material, oxygen levels in the bottom water and faunal changes, with special emphasis on the brachiopod fauna. Trace element ratios indicate that nearly stable upper dysoxic bottom-water conditions prevailed in the northwestern part of the Baltoscandian Sea. The exception is during the major shallowing in the earliest Katian, when there was an abrupt shift to oxic conditions as the sea bottom came within a normal storm wave base. Nonetheless, the pre-shallowing epibenthic fauna (though not the shelly endobenthic) in this area was rich and diverse and two major immigration phases of new brachiopod taxa are seen well before the shallowing. This indicates that the immigration of new taxa was not the result of an increase in oxygen content in the bottom water. More brachiopod genera stayed during the abrupt shallowing and increased oxic level than did during the following gradual return to deeper, dysoxic environments. The major brachiopod immigration phases took place markedly earlier in this northwestern part of the Baltoscandian Sea than in the central part (Eastern Baltic) and possibly also the comparable faunal turnover in Laurentia. The following disappearance of taxa during an early Katian transgressive event coincided with the faunal turnover in the shallow-water environments of the East Baltic. The depositional history was consistent within the investigated mudstone-dominated offshore facies of the Oslo Region, which are comparable to the Central Baltoscandian Confacies Belt of Baltoscandia. The composition of the siliciclastic material which was deposited in the basin was nearly constant through the sequence, though the land area expanded to include ophiolites, expressed by Cr enrichment, coinciding with the major sea-level drop. The Cr enrichment indicates that, by that time at least, the ophiolite complexes north of the Oslo Region became subaerially exposed. This enrichment thus forms a potential geochemical marker horizon representing the basal Katian Stage.

Confidence limits on fossil ranges that account for facies changes

A drawback to most existing methods of calculating confidence limits on fossil ranges is their assumption that the probability of collecting a taxon through a stratigraphic section is constant. Marshall (1997) described an approach that would circumvent this problem, but it requires knowing the probability of collection as a function of stratigraphic position. Multivariate paleoecological methods, such as detrended correspondence analysis (DCA), offer a means of estimating these probabilities. DCA axis 1 sample scores can be used to quantify facies change through a stratigraphic section, and to calculate the probability of collection of a taxon relative to DCA axis 1. From these two, the probability of collection of each taxon can be estimated for each horizon in the measured section. This approach is applied here to the Upper Ordovician Kope Formation of the Cincinnati, Ohio, area to distinguish between disappearances of taxa that are driven by facies change and taxon rarity and those that represent true regional extinction. This new approach to confidence limits could also be applied to test the synchroneity of extinction or origination at large-scale turnover events, such as mass extinctions and the turnover pulses that bound episodes of faunal stasis.

The influence of drought-induced low freshwater flow on an upper-estuarine macroinvertebrate community

Severe drought in the Thames catchment during 1989 and 1990 resulted in increased water abstraction from the river Thames, reducing the amount of freshwater flowing into the Thames estuary over Teddington weir. Increased salinity levels were recorded in the upper estuary, related to the decrease in flow, which in turn affected the community of freshwater invertebrates inhabiting a site below Teddington weir. A large decrease in BMWP score was recorded following increased abstraction in both 1989 and 1990. However, the disappearance of taxa was not directly related to their perceived sensitivity to organic pollution, with Asellidae, Caenidae and Unionidae being amongst the first families to be affected. Multidimensional scaling ordination indicated that the community demonstrated a cyclical pattern of disturbance and recovery related to variations in salinity and flow-dependent influx of organisms via invertebrate drift. The study indicates that reducing freshwater flow below a critical level can have detrimental effects on the diversity of macroinvertebrate communities in certain sections of tidal rivers.