摘要:

An upper evolutionary limit on species equilibrium number (S of MacArthur&Wilson) has been postulated but never demonstrated. Results of the present study indicate that an S of about 10 was attained very rapidly in a Late Ordovician benthic marine invertebrate faunal succession. This S value was then maintained for perhaps five million years within a marine environment that did not remain uniform but changed progressively from relatively deep to shallow water. Most importantly, significant taxonomic and presumed trophic changes that accompanied the gradual habitat alteration seem to have had a negligible effect on the plateau‐like limit to species equilibrium number. We conclude from these preliminary results that the maintenance of evolutionary equilibrium in an open ecosystem strongly suggests a long‐term component of biotic resiliency, at least within this one marine ecosystem, and perhaps in many others. The reasons for this resiliency remain to be explo

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1976.tb01314.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1976.tb01315.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The variability in the plicae of the central fold of eight rhynchonellid brachiopods –Lepidocyclus capax(Ordovician),Stegerhynchus whitii(Silurian),Megalopterorhynchus baldwini(Devonian),‘Camarotoechia’ purduei(Mississippian),Wellerella osagensis(Pennsylvanian),Leiorhynchus weeksi(Permian),‘Pugnoides’; Iriassicus(Triassic) andTetrarhynchiasp. (Jurassic) – is inversely related to the diversity of brachiopods within the faunal assemblage. Explanations for the phenotypic variability due to taxonomic splitting, sexual polymorphism or ontogenetic development are precluded or unsupported by the morphologic analysis, although a small percentage of the morphologic variability can be ascribed to ecophenotypic differentiation by environmental stimuli.After considerations of the abiotic influences of time, geographic location and isolation, and environmental stability and homogeneity, most of the morphologic variability in these brachiopods is attributed to the biotic influence, namely competition. Other proposed relationships, i.e. population abundance, sample size, shell size or ribbing pattern and intraspecific variability are not statistically

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1976.tb01316.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Documentation of bivalve generic and species diversity and times of first and last appearance through successive Jurassic stages in Europe, together with data on turnover and changes in taxonomic and ecological composition of the faunas, indicate an approximation to the establishment of an equilibrium fauna by early Middle Jurassic times. Subsequently faunal change was slight compared with the early Jurassic. A diversity increase through the Lower into the Middle Jurassic correlates with an increase in the area of epicontinental seas, while a major species extinction in the early Toarcian is bound up with the onset of widespread stagnation associated with a rise of sea level. An increase of the generic extinction rate at the end of the period correlates with a regional marine regression. The mean species longevity is estimated at 15×106years. The ecological factors thought to control bivalve distribution are reviewed and four ecological associations distinguished: the reefal, lagoonal and nearshore and basinal marine

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1976.tb01317.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1976.tb01318.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The Elk River Reef of Tennessee has an assemblage of incrusting bryozoans, ‘incrusting’ echinoderms, and receptaculitids (calathids) concentrated near its base. This assemblage is thought to have initially inhabited small local sites in a substrate of pelmatozoan sand containing various amounts of carbonate mud. The gregarious style of growth of these organisms and their close interrelationships stabilized the substrate and produced a biological hardground, later occupied by colonial corals and stromatoporoids to form the main reef body. The anastomosing root structures of the echinoderms helped stabilize the substrate and hindered sediment movement. In an effort to support themselves, these echinoderms achieved additional baffling effects of their incrusting and engulfing growth abilities. They particularly attached themselves to calathids. Calathids are the most noticeable taxon in the community. They differ from other calathids presently known in that they have a ‘porous' convoluted outer wall very much like a sponge in appearance. The Elk River Reef and its contained receptaculitids fall within 10–15° of the presently accepted position of the Ordovician equator.SummaryA unique assemblage of incrusting bryozoans, incrusting echinoderms, and upright branching calathids (algae?) occur in the lower parts of the Elk River Reef in south‐central Tennessee. Because of their numbers and incrusting and gregarious growth characteristics these taxa stabilized the substrate by limiting the movement of carbonate mud and skeletal debris. The incrusting bryozoans and echinoderms grew over and around each other and each incrusted calathids, eventually forming a biologic hardground. The echinoderms had the peculiar ability to ‘invade’ the living chambers of dead organisms and completely ‘engulf’ entire fragments. The calathids described herein have a thick, commonly amorphous outer layer formed by the expansion of the heads of laterals which extend outward in all directions from the central axis. The fusion of these irregularly shaped heads forms a ‘porous’ sponge‐like layer a feature which has not been previously described in calathids.The local sites stabilized by this assemblage were later occupied by stromatoporoids and colonial corals forming the main body of the reef (for a discussion of the upper parts of these reefs s

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1976.tb01319.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1976.tb01320.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Wetheredella tumulusn.sp. was an important constituent, both binder and frame builder, in reef and off‐reef sediments of the Ashgillian Ellis Bay Formation of Anticosti Island in eastern Canada. In individual small, stromatolite‐like mounds, it built a skeletal platform for attachment of associated serpulid worm tubes, bryozoans, crinoids and small brachiopods. In larger bioherms,Wetheredellawas an encruster, binding waveswept reef tops of halysitid and heliolitid corals.Wetheredellais interpreted as a blue‐green alga related to SilurianRothpletzellafrom Gotland and the genusGirva

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1976.tb01321.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1976.tb01322.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Blue‐green algae of the families Rivulariaceae, Oscillatoriaceae, Stigonemataceae and Nostochopsidaceae have been identified by scanning electron microscopy in Upper Jurassic (Malm δ) sponge reefs near Solnhofen‐Eichstätt, southern Franconia. Algal growth may account for 50–75% of the volume of the reef limestone. ‘Hollow‐sphere’ algal structures up to 500 µm predominate. Rivulariaceae are the typical form and act as main reef‐building biotic component. Pellets, intraclasts and oncolites as well as stromatolitic and cryptalgal crusts are of blue‐green algal origin. These observations introduce new aspects regarding the evolution of the siliceous‐sponge reefs of the Upper Jurassic in Southern Germany.Mit dem Rasterelektronenmikroskop wurden in der jurassischen Schwammfazies des Malm δ bei Solnhofen‐Eichstätt Blaugrün‐Algen der Familien Rivulariaceae, Oscillatoriaceae, Stigonemataceae und Nostochopsidaceae nachgewiesen. 50–75% des Riffkalkes ist direkt auf Algen zurückzuführen. Vorherrschend sind Hohlkugelkolonien bis 500 µm, die zu den Rivulariaceae gestellt werden und die wichtigste riffbildende Biogenkomponente darstellen. Pellets, Intraklasten, Onkoide, Stromatolithen und strukturlose Krusten auf den Schwämmen sind Algenprodukte. Es ergeben sich neue ökologische Aspekte für die Kieselschwamm‐Ri

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1976.tb01323.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY