Biotic Succession Research Articles

Impacts of Soil Properties on Species Diversity and Structure in Alternanthera philoxeroides-Invaded and Native Plant Communities.

Soil properties can affect plant population dynamics and the coexistence of native and invasive plants, thus potentially affecting community structure and invasion trends. However, the different impacts of soil physicochemical properties on species diversity and structure in native and invaded plant communities remain unclear. In this study, we established a total of 30 Alternanthera philoxeroides-invaded plots and 30 control plots in an area at the geographical boundary between North and South China. We compared the differences in species composition between the invaded and native plant communities, and we then used the methods of regression analysis, redundancy analysis (RDA), and canonical correspondence analysis (CCA) to examine the impacts of soil physicochemical properties on four α-diversity indices and the species distribution of these two types of communities. We found that A. philoxeroides invasion increased the difference between the importance values of dominant plant species, and the invasion coverage had a negative relationship with the soil-available potassium (R2 = 0.135; p = 0.046) and Patrick richness index (R2 = 0.322; p < 0.001). In the native communities, the species diversity was determined with soil chemical properties, the Patrick richness index, the Simpson dominance index, and the Shannon-Wiener diversity index, which all decreased with the increase in soil pH value, available potassium, organic matter, and ammonium nitrogen. However, in the invaded communities, the species diversity was determined by soil physical properties; the Pielou evenness index increased with increasing non-capillary porosity but decreased with increasing capillary porosity. The determinants of species distribution in the native communities were soil porosity and nitrate nitrogen, while the determinants in the invaded communities were soil bulk density and available potassium. In addition, compared with the native communities, the clustering degree of species distribution in the invaded communities intensified. Our study indicates that species diversity and distribution have significant heterogeneous responses to soil physicochemical properties between A. philoxeroides-invaded and native plant communities. Thus, we need to intensify the monitoring of soil properties in invaded habitats and conduct biotic replacement strategies based on the heterogeneous responses of native and invaded communities to effectively prevent the biotic homogenization that is caused by plant invasions under environmental changes.

Transgression–regression cycles drive correlations in Ediacaran–Cambrian rock and fossil records

AbstractStrata of the Ediacaran Period (635–538.8 Ma) yield the oldest known fossils of complex, macroscopic organisms in the geologic record. These “Ediacaran-type” macrofossils (known as the Ediacaran biota) first appear in mid-Ediacaran strata, experience an apparent decline through the terminal Ediacaran, and directly precede the Cambrian (538.8–485.4 Ma) radiation of animals. Existing hypotheses for the origin and demise of the Ediacaran biota include: changing oceanic redox states, biotic replacement by succeeding Cambrian-type fauna, and mass extinction driven by environmental change. Few studies frame trends in Ediacaran and Cambrian macroevolution from the perspective of the sedimentary rock record, despite well-documented Phanerozoic covariation of macroevolutionary patterns and sedimentary rock quantity. Here we present a quantitative analysis of North American Ediacaran–Cambrian rock and fossil records from Macrostrat and the Paleobiology Database. Marine sedimentary rock quantity increases nearly monotonically and by more than a factor of five from the latest Ediacaran to the late Cambrian. Ediacaran–Cambrian fossil quantities exhibit a comparable trajectory and have strong (rs &gt; 0.8) positive correlations with marine sedimentary area and volume flux at multiple temporal resolutions. Even so, Ediacaran fossil quantities are dramatically reduced in comparison to the Cambrian when normalized by the quantity of preserved marine rock. Although aspects of these results are consistent with the expectations of a simple fossil preservation–induced sampling bias, together they suggest that transgression–regression and a large expansion of marine shelf environments coincided with the diversification of animals during a dramatic transition that is starkly evident in both the sedimentary rock and fossil records.

Bayesian analyses indicate bivalves did not drive the downfall of brachiopods following the Permian-Triassic mass extinction

Certain times of major biotic replacement have often been interpreted as broadly competitive, mediated by innovation in the succeeding clades. A classic example was the switch from brachiopods to bivalves as major seabed organisms following the Permian-Triassic mass extinction (PTME), ~252 million years ago. This was attributed to competitive exclusion of brachiopods by the better adapted bivalves or simply to the fact that brachiopods had been hit especially hard by the PTME. The brachiopod-bivalve switch is emblematic of the global turnover of marine faunas from Palaeozoic-type to Modern-type triggered by the PTME. Here, using Bayesian analyses, we find that unexpectedly the two clades displayed similar large-scale trends of diversification before the Jurassic. Insight from a multivariate birth-death model shows that the extinction of major brachiopod clades during the PTME set the stage for the brachiopod-bivalve switch, with differential responses to high ocean temperatures post-extinction further facilitating their displacement by bivalves. Our study strengthens evidence that brachiopods and bivalves were not competitors over macroevolutionary time scales, with extinction events and environmental stresses shaping their divergent fates.

Nitrogen enrichment alters the resistance of a noninvasive alien plant species to Alternanthera philoxeroides invasion

Soil nitrogen can significantly affect the morphology, biomass, nutrient allocation, and photosynthesis of alien vs. native plants, thereby changing their coexistence patterns; however, the effect of soil nitrogen on the interspecific relationship between alien plants is currently unclear. We conducted a nitrogen addition experiment in a greenhouse to explore the effect of soil nitrogen on the interspecific relationship between invasive alien weed Alternanthera philoxeroides and the noninvasive alien horticultural plant Oxalis articulata. We set three experimental factors—nitrogen treatment, planting type, and species and measured the morphology, biomass, carbon (C) and nitrogen (N) content, physiological traits, and photosynthetic fluorescence of the studied plant species. We then used multi-way ANOVA and multiple comparisons to examine the differences in the above indicators among treatment combinations. We found that, in mixed cultures, nitrogen addition significantly increased the root area of O. articulata by 128.489% but decreased the root length by 56.974% compared with the control, while it significantly increased the root length of A. philoxeroides by 130.026%. Nitrogen addition did not affect the biomass accumulation of these two plant species; however, the biomass and root/shoot ratio of O. articulata were significant higher than those of A. philoxeroides. Nitrogen addition significantly increased the N content of A. philoxeroides by 278.767% and decreased the C:N ratio by 66.110% in mixed cultures. Nitrogen addition caused a significant trade-off between flavonoid and anthocyanin in O. articulata, and decreased the initial fluorescence (F0) and maximal fluorescence (Fm) of A. philoxeroides by 18.649 and 23.507%, respectively, in mixed cultures. These results indicate that nitrogen addition increased the N absorption and assimilation ability of A. philoxeroides in deep soil; furthermore, it significantly enhanced the advantages for O. articulata in terms of morphology, physiological plasticity, and photosynthetic efficiency. In addition, O. articulata had better individual and underground competitive advantages. Under intensified nitrogen deposition, the biotic replacement effect of O. articulata on A. philoxeroides in natural ecosystems could be further enhanced.

The rangeomorph Pectinifrons abyssalis: Hydrodynamic function at the dawn of animal life

Rangeomorphs are among the oldest putative eumetazoans known from the fossil record. Establishing how they fed is thus key to understanding the structure and function of the earliest animal ecosystems. Here, we use computational fluid dynamics to test hypothesized feeding modes for the fence-like rangeomorph Pectinifrons abyssalis, comparing this to the morphologically similar extant carnivorous sponge Chondrocladia lyra. Our results reveal complex patterns of flow around P.abyssalis unlike those previously reconstructed for any other Ediacaran taxon. Comparisons with C. lyra reveal substantial differences between the two organisms, suggesting they converged on a similar fence-like morphology for different functions. We argue that the flow patterns recovered for P.abyssalis do not support either a suspension feeding or osmotrophic feeding habit. Instead, our results indicate that rangeomorph fronds may represent organs adapted for gas exchange. If correct, this interpretation could require a dramatic reinterpretation of the oldest macroscopic animals.

Environmental drivers of the first major animal extinction across the Ediacaran White Sea-Nama transition

The Ediacara Biota-the oldest communities of complex, macroscopic fossils-consists ofthree temporally distinct assemblages: the Avalon (ca. 575-560 Ma), White Sea (ca.560-550 Ma), and Nama (ca. 550-539 Ma). Generic diversity varies among assemblages, with a notable decline at the transition from White Sea to Nama. Preservation and sampling biases, biotic replacement, and environmental perturbation have been proposed as potential mechanisms for this drop in diversity. Here, we compile a global database of the Ediacara Biota, specifically targeting taphonomic and paleoecological characters, to test these hypotheses. Major ecological shifts in feeding mode, life habit, and tiering level accompany an increase in genericrichness between the Avalon and White Sea assemblages. We find that ∼80% of White Sea taxa are absent from the Nama interval, comparable to loss during Phanerozoic mass extinctions. The paleolatitudes, depositional environments, and preservational modes that characterize the White Sea assemblage are well represented in the Nama, indicating that this decline is not the result of sampling bias. Counter to expectations of the biotic replacement model, there are minimalecological differences between these two assemblages. However, taxa that disappear exhibit a variety of morphological and behavioral characters consistent with an environmentally driven extinction event. The preferential survival of taxa with high surface area relative to volume may suggest that this was related to reduced global oceanic oxygen availability. Thus, our data support a link between Ediacaran biotic turnover and environmental change, similar to other major mass extinctions in the geologic record.

Hydrodynamic Simulations of Millimeter‐Scale Cambrian Sedentary Medusozoans

AbstractModern medusae are primarily macroscopic, free‐swimming marine organisms with a tetraradial symmetry. But the early Cambrian medusozoans, such as biradial Hexaconularia sichuanensis and tetraradial Quadrapyrgites quadratacris from the basal Cambrian Kuanchuanpu Formation in South China, were millimeter‐scale and sedentary forms. Although well‐documented as common components in a shelf environment, little is known about their in situ life conditions since they are easily transported by tidal flow before burial. Specifically, the interactions between their exoskeleton shapes and the hydrodynamic conditions are poorly known. Here we use fluid–structure interaction computational fluid dynamics to analyze the functional performance of the two taxa using 3D mesh models constructed from scanned fossils. The simulation experiments reveal that: (a) due to their millimeter‐scale size, most sedentary small shelly fossils (SSFs), including those of medusozoans lived within the viscous sublayer range of tidal flow; (b) the biradial symmetry of Hexaconularia was more structurally stable than the tetraradial symmetry of Quadrapyrgites; (c) different orientations of Hexaconularia, relative to the water flow, resulted in different force distributions on the surface. This research provides quantitative data of the hydrodynamic conditions of SSFs in shelf environments and critical insights into the biotic replacement of the early Cambrian benthic medusozoan community.

Are Insects Heading Toward Their First Mass Extinction? Distinguishing Turnover From Crises in Their Fossil Record

AbstractTime and again, over hundreds of millions of years, environmental disturbances have caused mass extinctions of animals ranging from reptiles to corals. The anthropogenic loss of species diversity happening now is often discussed as the ‘sixth mass extinction’ in light of the ‘Big Five’ mass extinctions in the fossil record. But insects, whose taxonomic diversity now appears to be threatened by human activity, have a unique extinction history. Prehistoric losses of insect diversity at the levels of order and family appear to have been driven by competition among insect lineages, with biotic replacement ensuring minimal net losses in taxonomic diversity. The end-Permian extinction, the ‘mother of mass extinctions’ in the seas, was more of a faunal turnover than a mass extinction for insects. Insects’ current biotic crisis has been measured in terms of the loss of abundance and biomass (rather than the loss of species, genera, or families) and these are essentially impossible to measure in the fossil record. However, should the ongoing loss of insect abundance and biomass cause the demise of many insect families, the current extinction event may well be the first sudden loss of higher-level insect diversity in our planet’s history. This is not insects’ sixth mass extinction—in fact, it may become their first.

&lt;p&gt;&lt;strong&gt;Unravelling the complexity of Mexican biogeographical patterns by naturalists in the 19th century: From Alexander von Humboldt (1769—1859) to Francis Sumichrast (1829—1882)&lt;/strong&gt;&lt;/p&gt;

Gonzalo Halffter developed the concept of a transition zone in Mexico during the mid-twentieth century, when he superimposed the distributional patterns of different groups of Coleoptera, finding that some groups share a common biogeographical history. The complexity of the Mexican biogeographical patterns had already caught the eyes of nineteenth-century naturalists, who tried to discern some kind of order within this biotic complexity. Herein, we analyse the original studies of different nineteenth-century authors on the distributional patterns of different Mexican taxa, highlighting the main explanations provided by them. The complexity of the Mexican biota was interpreted by Humboldt as the result of the interaction between northern and southern floras, as a taxonomic peculiarity by Augustin de Candolle, as a strong biotic replacement by Alphonse de Candolle and Sumichrast, and as different dispersal stages by Wallace. Before the theory of evolution was accepted, different biogeographical patterns (endemism, diversity and taxonomic replacement gradients, among others) had coexisted without contradictions. Botanical and zoological regions first acquired a connotation of independent centres of creation, and the wider distributions (mainly disjunct distributions) later became the backbone of hypotheses concerning historical relationships between biotas based on a dispersalist model. Nevertheless, during the 20th century, the explanations of 19th century naturalists such as the limits between regions and biotic transition entered the biogeographical debate again.

Increase in metazoan ecosystem engineering prior to the Ediacaran-Cambrian boundary in the Nama Group, Namibia.

The disappearance of the soft-bodied Ediacara biota at the Ediacaran–Cambrian boundary potentially represents the earliest mass extinction of complex life, although the precise driver(s) of this extinction remain unresolved. The ‘biotic replacement’ model proposes that an evolutionary radiation of metazoan ecosystem engineers in the latest Ediacaran profoundly altered marine palaeoenvironments, resulting in the extinction of Ediacara biota and setting the stage for the subsequent Cambrian Explosion. However, metazoan ecosystem engineering across the Ediacaran–Cambrian transition has yet to be quantified. Here, we test this key tenet of the biotic replacement model by characterizing the intensity of metazoan bioturbation and ecosystem engineering in trace fossil assemblages throughout the latest Ediacaran Nama Group in southern Namibia. The results illustrate a dramatic increase in both bioturbation and ecosystem engineering intensity in the latest Ediacaran, prior to the Cambrian boundary. Moreover, our analyses demonstrate that the highest-impact ecosystem engineering behaviours were present well before the onset of the Cambrian. These data provide the first support for a fundamental prediction of the biotic replacement model, and evidence for a direct link between the early evolution of ecosystem engineering and the extinction of the Ediacara biota.

Recognizing spatial patterns of biodiversity during the nineteenth century: The roots of contemporary biogeography

AbstractAimWe review the works of three pre‐Darwinian authors—Alexander von Humboldt, Augustin de Candolle and Alphonse de Candolle. Contrary to what other historiographers have claimed, we think that their works were not merely descriptive, nor did they adhere strictly to the inductivist model. Furthermore, the patterns described by these authors are still being studied extensively in biogeography.MethodWe analyse the main concepts provided by these authors on the spatial patterns of biodiversity, and discuss how they served to construct the conceptual framework of contemporary biogeography.ResultsIn the early 19th century, secular naturalists began postulating explanations supported by empirical evidence and based on physical causes. The studied authors were extremely cautious when proposing hypotheses, considering that any statement not based on empirical evidence was mere conjecture. When we analyse the way they developed explanations, it seems evident that they were rather closer to deductive thought than to the orthodox inductivist model. With the rise of Darwinian evolutionism, naturalists lost interest in the spatial patterns of life and began constructing dynamic models where dispersal of individual lineages from northern centres of origin was proposed to explain their current distribution. Paradoxically, even though the evolutionary paradigm soon proved its great explanatory power, it simultaneously promoted a large number of studies in which speculation prevailed.Main conclusionsEven though the practices and methods of current biogeography have changed substantially, the studied patterns are still the same: (1) geographical gradients of richness and biotic replacement, (2) spatial gradients of functional groups, (3) geographical variation of the phenotype, (4) geographical patterns of expansion‐differentiation of single lineages and (5) biogeographical homology. The studied authors not only described rigorously biogeographical patterns, but also proposed explanations about them and even sometimes tested them based on empirical evidence, going beyond the prevalent inductivist canon.

A mixed Ediacaran-metazoan assemblage from the Zaris Sub-basin, Namibia

It has been proposed that the terminal Neoproterozoic Ediacara biota were driven to extinction by the evolution of metazoan groups capable of engineering their environments (the ‘biotic replacement’ model). However, evidence for an overlapping ecological association between metazoans and soft-bodied Ediacaran organisms is limited. Here, we describe new fossil localities from southern Namibia that preserve soft-bodied Ediacara biota, enigmatic tubular organisms thought to represent metazoans, and vertically-oriented metazoan trace fossils. Although the precise identity of the tracemakers remains elusive, the structures bear several striking similarities with the Cambrian-Recent ichnogenus Conichnus. These new data support inference of stratigraphic and ecological overlap between two very different eukaryotic clades, and indicate the existence of unusual ecosystems comprising both Ediacara biota and metazoans immediately prior to the Cambrian explosion.

Биоремедиация морских прибрежных экосистем: использование искусственных рифов

The development of the biotic community on the artificial reefs in the coastal zone of the northeast Black Sea region has been studied. Colonization stages of the artificial reefs by hydrobionts depended on substance, time and depth of reef construction have been considered. Reef colonization by fouling organisms is a biotic primary succession of the benthic mature community. It has been found that in 2–3 years on an artificial reef species diversity and biomass of aquatic organisms rise sharply and reef biocenose becomes a powerful biofilter involved in the process of environment self-purification. The results of the functioning of the reef biocenose can serve as a basis for using artificial reefs in biological treatment of water in the coastal zone. Ключевые слова: биоремедиация, прибрежные экосистемы, искусственные рифы, рифовый биоценоз, биофильтрация, биологическая очистка, Черное море.

Biotic replacement and mass extinction of the Ediacara biota.

The latest Neoproterozoic extinction of the Ediacara biota has been variously attributed to catastrophic removal by perturbations to global geochemical cycles, 'biotic replacement' by Cambrian-type ecosystem engineers, and a taphonomic artefact. We perform the first critical test of the 'biotic replacement' hypothesis using combined palaeoecological and geochemical data collected from the youngest Ediacaran strata in southern Namibia. We find that, even after accounting for a variety of potential sampling and taphonomic biases, the Ediacaran assemblage preserved at Farm Swartpunt has significantly lower genus richness than older assemblages. Geochemical and sedimentological analyses confirm an oxygenated and non-restricted palaeoenvironment for fossil-bearing sediments, thus suggesting that oxygen stress and/or hypersalinity are unlikely to be responsible for the low diversity of communities preserved at Swartpunt. These combined analyses suggest depauperate communities characterized the latest Ediacaran and provide the first quantitative support for the biotic replacement model for the end of the Ediacara biota. Although more sites (especially those recording different palaeoenvironments) are undoubtedly needed, this study provides the first quantitative palaeoecological evidence to suggest that evolutionary innovation, ecosystem engineering and biological interactions may have ultimately caused the first mass extinction of complex life.

Geochronology of the Cambrian: a precise Middle Cambrian U–Pb zircon date from the German margin of West Gondwana

AbstractA volcanic tuff 1.0 m above the base of the Triebenreuth Formation in the Franconian Forest provides the first precise and biostratigraphically bracketed date within the traditional Middle Cambrian. The first illustration of fossils from the Triebenreuth Formation in this report and their discussion allow a more highly refined correlation within the Middle Cambrian. A weighted mean206Pb–238U date of 503.14±0.13/0.25/0.59 Ma on zircons from this subaerial pyroclastic tuff was determined by U–Pb chemical abrasion isotope dilution mass spectrometry (CA-TIMS) techniques. Atc. 6.0–7.0 Ma younger than the base of the traditional Middle Cambrian in Avalonia, the new West Gondwanan date from east-central Germany suggests that estimates of 500 Ma for the base of the traditional Upper Cambrian and 497 Ma on the base of the Furongian Series may prove to be too ‘old’. Biostratigraphically well-bracketed dates through most of the Middle Cambrian/Series 3 and below the upper Upper Cambrian/upper Furongian Series do not exist. An earlier determined 494.4±3.8 Ma date from the Southwell Group of Tasmania may actually prove to be a reasonable estimate for the age of the base of the traditional Upper Cambrian. Until high precision dates are determined on the base of the traditional Upper Cambrian and base of the Furongian Series, the rates of biotic replacements and geological developments and the durations of biotic zones in the Middle/Series 3 and Upper Cambrian/Furongian Series remain as ‘best guesses’.

Alexandre Brongniart (1770-1847) Shows that a ‘FActs First’ Scientific Approach Can Lead to Large-Scale Conclusions

The early nineteenth century has been described as a time of ‘Positive Geology’. The goal was to pursue fieldwork and build the edifice of science on ‘facts,’ thereby displacing the theorizing of previous centuries. French naturalists contributed prominently to the evolution of geoscience in that era. Georges Cuvier (1769-1832) and Alexandre Brongniart (1770-1847) were among the researchers who adhered to the ‘Facts First’ approach to understanding nature. Brongniart is an exemplar of the dedicated empiricist, careful observer, and cautious writer who was able to see ways to synthesize facts into conclusions of far-reaching consequence. The result is that collection and description of fossils, and observation of field relationships of rock units, led to an appreciation of the theoretical power of biotic succession, biostratigraphy, the geologic column, and geologic mapping.

Depth transect of an Upper Triassic (Rhaetian) reef from Gosau, Austria: Microfacies and community ecology

In the Late Triassic (~235–201.3Ma) scleractinian corals and hypercalcified sponges built large, diverse reef ecosystems, the most famous of which are the Dachstein reefs. This study presents a depth transect along an Upper Triassic (lower Rhaetian) Dachstein reef from the Gosausee margin of the Dachsteingebirge (Gosau, Austria). The Gosausee microbial-sponge-coral reef is a complete barrier reef with an almost continuous fore reef to lagoon transect preserved (a very rare occurrence for the Triassic), and thus provides a window into depth zonation of Dachstein-type reef facies and biotic succession. The Gosausee reef facies exhibit strong depth control and five classic reef facies or zones are identified: the fore reef, reef front, reef crest, back reef, and lagoon facies. Thin, rare microbial fabrics and a high abundance of fine-grained, mud-rich skeletal wackestones (transported reef debris) characterize the deepest fore reef. As the reef shallows, muddy sediments decrease in abundance and are replaced by microbial fabrics, corals, and cements. Abundant sponges, microbial crusts, and thick, marine cements typify the reef crest, whereas microbialite-coated phaceloid corals are dominant in the back reef facies. Heavily cemented oncoids or microbial-sponge bindstones are characteristic of the lagoon. Based on their compositional and biotic similarities, the Gosausee reef was likely part of the same barrier reef systems as the source reef for the Gosaukamm reef breccia (one of the classic Norian–Rhaetian Dachstein reefs). The reef zones of the Gosausee margin can be used to interpret the depth or reef zone of less well preserved reef fragments, can inform models of community ecology and niche utilization in the Late Triassic, and highlight the need for additional research into the environmental factors that controlled biotic distribution in Upper Triassic reefs.

RESPONSE OF SHALLOW MARINE BIOTAS TO SEA-LEVEL FLUCTUATIONS: A REVIEW OF FAUNAL REPLACEMENT AND THE PROCESS OF HABITAT TRACKING

Associations of fossil genera and species commonly display repeated and predictable patterns of change in stratigraphic sections. These changes exhibit some analogies with the phenomenon of ecological succession but are longer-term allogenic temporal changes, occurring over time scales of tens to hundreds of thousands of years, that should be referred to as biotic (faunal-floral) replacement. Habitat tracking is one of a suite of possible mechanisms of biotic replacement, but one that may be important in certain marine settings. Evidence of tracking includes (1) recurrence of similar replacement series of differing age; (2) mirroring of vertical replacement of faunas by lateral gradients of species associations along single time planes; (3) the occurrence of similar gradient transects at different time planes; (4) the correlatability of highs and lows of quantitative faunal curves (e.g., variations of detrended correspondence analysis scores) at different localities despite offsets of absolute scores; and (5) the high fidelity recurrence of stenotopic species in particular associations representing narrowly defined environments. The degree of ecological fidelity (e.g., similarity of species richness, guild structure) that is maintained during tracking is variable. Recurrent assemblages in different cycles, separated by as much as several million years, can be very similar in terms of species composition and trophic structure. Common species, however, may show significant differences in rank and relative abundances. This evidence indicates individualistic tracking of preferred habitat by various species. In shallow-shelf and ramp settings, sea-level fluctuations may produce approximately symmetrical patterns of biotic replacement where biofacies are arrayed typically in elongate belts parallel to depositional strike. Asymmetries, however, are common and may result from variations in sediment supply during sea-level fluctuation. Hence, the low siliciclastic input typical of transgressions predictably favors those organisms that require lower sedimentation or turbidity and perhaps firmgrounds to hardgrounds, whereas the regressive half cycle at analogous depths favors more eurytopic organisms that tolerate or prefer higher sedimentation or turbidity. The phenomenon of tracking may be of considerable importance in evolutionary paleoecology. Tracking implies that species commonly respond to long-term physical changes, not by adaptation, but primarily by migration of species to preferred habitats, if the rate or magnitude of environmental change is not too great. Provided that the same basic environment existed through time, despite lateral shifting by up to hundreds of kilometers, most species of benthic invertebrates were capable of surviving with little or no evolutionary change. Tracking may be the primary basis of patterns of morphological stasis, as well as relative stability in biofacies richness, composition, and trophic structure.

Brachiopod miniaturization and its possible causes during the Permian–Triassic crisis in deep water environments, South China

Brachiopod miniaturization is both the reduction in size of individuals of a species over time, and where one brachiopod fauna dominated by larger individuals was replaced by a brachiopod fauna dominated by smaller individuals over time. This paper investigates this phenomenon prior to and during the end-Permian crisis in a deep water setting in South China, based on precise measurements of brachiopod body size and on the abundance and diversity of brachiopod species. The process of miniaturization near the Permian–Triassic boundary in deep water environments is characterized by: (1) Larger species, including Martinia sp., Costatumulus dongpanensis, and Anidanthus mucronata, reduced in average body size and abundance over time towards the end-Permian brachiopod extinction event. (2) Small species, including Attenuatella mengi and Spinomarginifera semicircridge, showed a mixed response with either no size change, or a reduction in average body size, while these species increased in abundance over time, indicating they were less sensitive to the stressed environmental setting. (3) Both the total abundance and the diversity of this brachiopod fauna decreased over time towards the end-Permian crisis. Regression, an increased input of terrestrial material and productivity decline are considered to all have contributed to brachiopod miniaturization, based on the biotic replacement and changes in sea-water chemistry. Among these factors, the fall in sea level is perhaps the primary factor, and led to a decline in productivity and an increased input of terrestrial material into the marine setting.

Comparative bacterial diversity in recent Hawaiian volcanic deposits of different ages

Volcanic activity creates new landforms that can change dramatically over time as a consequence of biotic succession. Nonetheless, volcanic deposits present severe constraints for microbial colonization and activity. We have characterized bacterial diversity on four recent deposits at Kilauea volcano, Hawaii (KVD). Much of the diversity was either closely related to uncultured organisms or distinct from any reported 16S rRNA gene sequences. Diversity indices suggested that diversity was highest in a moderately vegetated 210-year-old ash deposit (1790-KVD), and lowest for a 79-year-old lava flow (1921-KVD). Diversity for a 41-year-old tephra deposit (1959-KVD) and a 300-year-old rainforest (1700-KVD) reached intermediate values. The 1959-KVD and 1790-KVD communities were dominated by Acidobacteria, Alpha- and Gammaproteobacteria, Actinobacteria, Cyanobacteria, and many unclassified phylotypes. The 1921-KVD, an unvegetated low pH deposit, was dominated by unclassified phylotypes. In contrast, 1700-KVD was primarily populated by Alphaproteobacteria with very few unclassified phylotypes. Similar diversity indices and levels of trace gas flux were found for 1959-KVD and 1790-KVD; however, statistical analyses indicated significantly different communities. This study not only showed that microorganisms colonize recent volcanic deposits and are able to establish diverse communities, but also that their composition is governed by variations in local deposit parameters.