Effects of recent acidification on Cladocera in small clear-water lakes studied by means of sedimentary remains

Cladoceran populations, as revealed by sedimentary remains, were studied in six lakes which by diatom evidence have become strongly acidified during the past 30 years. The accumulation rates of cladoceran remains and in two of the most strongly acidified lakes both relative and absolute numbers ofBosmina greatly increased during this period. Species numbers were not reduced, but there were shifts in relative abundances of cladoceran species.Bosmina longispina dominated all the lakes. Low pH (4.7) seemed not to be straight-forwardly harmful toDaphnia longispina, but the relative abundances of this taxon were reduced because ofBosmina.     

The Pleistocene lake deposits of the NE Baza Basin (Spain): salinity variations and ostracod succession

The Guadix-Baza Basin in Spain covers an area of approximately 3000 km² and yields a sedimentary sequence ranging from Lower Miocene to Pleistocene. Twenty five meters of Lower Pleistocene lacustrine sediments have been located in the NE part of the Basin at about 1000 meters in altitude. This sequence which overlies dolomitic mud flat deposits consists of limestones, calcareous and dolomitic mudstones, dolostones, silty clays, sands and gravels. Salinity fluctuations and short dry episodes, related to lake level oscillations, have been recorded by textural, mineralogical and faunal changes throughout the sequence. Ostracods, which are the most commonly encountered fossils, permit to detect recurrent changes in water salinity and regime, and solute composition. The faunal changes indicate an alternation of slightly saline and bicarbonate-rich water (when ostracods and gastropods occur) with a saline NaCl-dominant water (in which ostracods, Cerastoderma bivalves and non-marine foraminifers are found).The frequent and recurrent hydrochemical changes in the Baza Basin in the Early Pleistocene point to a climate of high contrast like in the Mediterranean region today but with a greater availability of water within the system compared to the present situation in the area.     

MORPHOLOGICAL VARIABILITY IN POPULATIONS OF CHRYSOPHYCEAN RESTING CYSTS. I. GENETIC (INTERCLONAL) AND ENCYSTMENT TEMPERATURE EFFECTS ON MORPHOLOGY1

Many chrysophycean species produce resting cysts (statospores) with purportedly species-specific morphology. I investigated variation in the cyst morphology of a single species that may result from genetic differences among the vegetative clones involved and from variation in the temperature of the environment during cyst development. Populations of Dinobryon cylindricum Imhof cysts were produced under defined conditions in vitro and then sampled for morphological analysis based on SEM micrographs. Morphological data is presented and then used in a multivariate discriminant analysis to determine the utility of each morphological character in distinguishing the six populations studied. Results suggest that some features of cyst morphology (i.e. cyst diameter) are invariant among the populations, while other features show distinctive variation. The density of spines covering the cyst body as well as the morphology of those spines appear correlated to the specific clones involved, and thus may represent useful phenotypic genetic markers. The length and definition of both the spines and the cyst collar, on the other hand, are markedly influenced by encystment temperature. The implications of these findings for paleoecological studies is discussed.     

Quaternary and recent Lamprothamnium groves (Charophyta) from Argentina

Only recently have extant Lamprothamnium species been reported from the American continent. L. succinctum (A. Br. in Asch.) R. D. W. was found in Lago Titicaca, Bolivia and L. haesseliae Dont. en Laguna Luro and Laguna La Salada, Argentina.Fossil gyrogonites of L. succinctum and L. haesseliae, however, are here reported to be widely distributed in Quaternary sediments of Argentina, associated with other charophytes, ostracods and foraminiferans. Localities include Laguna del Siasgo, Laguna Salada Grande, Laguna Mar Chiquita, Laguna La Amarga and Salina del Bebedero. Lamprothamnium is a genus that prefers shallow, alkaline, hyposaline to mesosaline environments. Analysis of the characteristics of Laguna La Salada contributes information on the factors that influence the distribution of the genus.The morphology characteristics of the gyrogonites and oospores of L. haesseliae and the gyrogonites of L. succinctum are described. The use of Lamprothamnium as a biomarker and its application in the reconstruction of Quaternary saline environments are also discussed.     

Influences of sea level changes and volcanic eruptions on Holocene vegetation in Tonga

Here, we investigate Mid- to Late-Holocene vegetation changes in low-lying coastal areas in Tonga and how changing sea levels and recurrent volcanic eruptions have influenced vegetation dynamics on four islands of the Tongan archipelago (South Pacific). To investigate past vegetation and environmental change at Ngofe Marsh (‘Uta Vava’u), we examined palynomorphs (pollen and spores), charcoal (fire), and sediment characteristics (volcanic activity) from a 6.7-m-long sediment core. Radiocarbon dating indicated the sediments were deposited over the last 7700 years. We integrated the Ngofe Marsh data with similar previously published data from Avai’o’vuna Swamp on Pangaimotu Island, Lotofoa Swamp on Foa Island, and Finemui Swamp on Ha’afeva Island. Plant taxa were categorized as littoral, mangrove, rainforest, successional/ disturbance, and wetland groups, and linear models were used to examine relationships between vegetation, relative sea level change, and volcanic eruptions (tephra). We found that relative sea level change has impacted vegetation on three of the four islands investigated. Volcanic eruptions were not identified as a driver of vegetation change. Rainforest decline does not appear to be driven by sea level changes or volcanic eruptions. From all sites analyzed, vegetation at Finemui Swamp was most sensitive to changes in relative sea level. While vegetation on low-lying Pacific islands is sensitive to changing sea levels, island characteristics, such as area and elevation, are also likely to be important factors that mediate specific island responses to drivers of change.     

Hominid paleoecology: The competitive exclusion principle and determinants of niche relationships

Some paleonanthropologists invoke the competitive exclusion principle programmatically in support of a single-species (or lineage) hypothesis of hominid evolution. Others apparently accept the association between competitive exclusion and a single species view, and develop multi-species interpretations using only taxonomic concepts. This paper demonstrates that the competitive exclusion principle itself is too assumption-bound to be appropriate for analyzing questions of hominid coexistence. Especially, the principle does not establish the ecological validity of the single-species hypothesis. Contrary to its immediate appearances, the principle has developed historically and analytically to predict and explain the evolution and maintenance of diversity in communities. Used in this manner it constitutes an important basis for the study of hominid paleoecology. Niche concepts necessary to demonstrate this are introduced, and competition and other factors that may have influenced the realized niches of sympatric hominid species are discussed. Nearly all modifications of the competitive exclusion principle that make it more realistic also illuminate factors that generate stable coexistence among competing species. These factors and their organizing theory establish the relevance of a broad data base to the analysis of hominid paleoecology; they should help to guide research on the ecology of early homonid species and their interrelationships.     

Ichnofossils of the Psilonichnus Ichnofacies and Their Paleoecological and Paleoenvironmental Significance in the Scottish Middle Jurassic

In the Bathonian (Middle Jurassic) Kilmaluag Formation, Great Estuarine Group, on the Isle of Skye, northwest Scotland, are ichnofossils that can be attributed to the burrowing activity of semi-terrestrial crab-like animals. The ichnofossils are preserved within supralittoral breccia-conglomerates and littoral calcareous mudstones and micrites deposited in a closed and shallow, low-salinity to freshwater coastal-lagoon setting. The dominant ichnofossil assemblage is preserved in the supralittoral rocks and comprises variable burrow types forming an ichnocoenosis and assigned to the Psilonichnus ichnofacies. These ichnofossils potentially provide the earliest known record of crab activity and their physiological adaptation to survive in a semi-terrestrial environment. Burrow characteristics include enlarged funnel-shaped apertures, unlined walls, absence of branching or biogenic reworking, inclined to vertical, U- and L-shaped forms and possible basal dwelling chamber. The ichnofossil assemblage preserved in the littoral rocks is attributed to the activity of either semi-terrestrial crabs or shrimps. Ichnofaunal characteristics reveal unique aspects of the paleoenvironments and paleoecology of the tracemaking community, including climatic conditions, substrate characteristics, the possible influence of paleowater table levels, paleoshoreline position, spatial variation in burrow morphology and possible gregarious and territorial behavior.     

A Review of: “New Interpretations of Complex Trace Fossils”

Dinosaur Tracks and Traces, edited by David D. Gillette and Martin G. Lockley, 1989. Cambridge University Press, 110 Midland Avenue, Port Chester, New York 10573, USA. lvii + 454 pages. US$54.50.     

Evolutionary patterns of Clavatoraceae (Charophyta) in the mesogean basins analysed according to environmental change during Malm and lower cretaceous

Evolutionary patterns of Clavatoraceae during the Malm and the Lower Cretaceous can be understood by considering how palaeoecological constraints of these charophytes were affected by palaeoenvironmental change. Speciation of Clavatoraceae reached maxima in the Tithonian and especially in the Lower Barremian, coinciding with an important areal extension and environmental diversification of freshwater swamps. Extinction reached a peak in the Upper Barremian, coinciding with the marine flooding of freshwater environments in Mesogea, and continued through the Aptian and Albian due to substitution of carbonatic freshwater swamps by terrigenous deltaic environments and probably by development of highly competitive aquatic flora of angiosperms. Anagenetic change within species attained maxima during the Berriasian and Lower Barremian, when freshwater environments became extensively developed. Absence of change (stasis) was marked during the Valanginian and Hauterivian, in a geological context of environmental stability and areal reduction of the freshwater environments.     

Biostratigraphy and paleoecology of the Oligo-Miocene succession in Fars and Khuzestan areas (Zagros Basin,SW Iran)

Paleontological and biostratigraphical studies on carbonate platform succession from southwest Iran documented a great diversity of shallow-water benthic foraminifera during the Oligocene–Miocene. Larger foraminifera are the main means for the stratigraphic zonation of carbonate sediments. The distributions of larger benthic foraminifera in two outcrop sections (Abolhayat and Lali) in the Zagros Basin, Iran, are used to determine the age of the Asmari Formation. Four assemblage zones have been recognized by distribution of the larger benthic foraminifera in the study areas. Assemblage 3 (Aquitanian age) and 4 (Burdigalian age) have not been recognized in the Abolhayat section (Fars area), due to sea-level fall. The end Chattian sea-level fall restricted marine deposition in the Abolhayat section and Asmari Formation replaced laterally by the Gachsaran Formation. This suggests that the Miocene part of the formation as recognized in the Lali section (Khuzestan area) of the Zagros foreland basin is not present in the Abolhayat outcrop. The distribution of the Oligocene larger benthic foraminifera indicates that shallow marine carbonate sediments of the Asmari Formation at the study areas have been deposited in the photic zone of tropical to subtropical oceans. Based on analysis of larger benthic foraminiferal assemblages and microfacies features, three major depositional environments are identified. These include inner shelf, middle shelf and outer shelf. The inner shelf facies is characterized by wackestone–packstone, dominated by various taxa of imperforate foraminifera. The middle shelf is represented by packstone–grainstone to floatstone with a diverse assemblage of larger foraminifera with perforate wall. Basinwards is dominated by argillaceous wackestone characterized by planktonic foraminifera and large and flat nummulitidae and lepidocyclinidae. Planktonic foraminifera wackestone is the dominant facies in the outer shelf.