Faunal Patterns Research Articles

INVESTIGATING FAUNAL AND GEOCHEMICAL METHODS FOR TRACING SALINITY IN AN ATLANTIC COASTAL LAGOON, DELAWARE, USA

Benthic foraminifera were sampled in Rehoboth Bay, Atlantic coast of Delaware (USA), to evaluate the use of canonical correlation on foraminiferal distributions, and the applicability of stable isotope analyses to track the relative proportions of fluvial versus marine inputs to the sedimentwater interface. Canonical correlations indicate that water depth, bottom-water dissolved oxygen (D.O.) levels, temperature, and salinity are the principal environmental factors related to the distribution of foraminifera in the bay. There are five dominant species in the bay fauna; in order of decreasing abundance, they are Ammonia tepida, Elphidium poeyanum, E. excavatum, Haynesina germanica, and Ammotium salsum. The canonical analysis shows that Elphidium excavatum and Haynesina germanica have the strongest response to salinity, with the former species favoring higher values and the latter species favoring lower ones. The importance of salinity is apparent in the stable isotopic composition of Ammonia tepida and Elphidium poeyanum, which yield d 18 O values that are lowest at the sites closer to the freshwater input and increase with distance from it. The relationship between d 18 O values and salinity for both stained and unstained tests is statistically significant (P , 0.05). With respect to temperature, only the d 18 O values of unstained (non-living) specimens also correlate with temperature. These results suggest that faunal patterns and the stable isotopic composition of these foraminiferal species reflect mixing of marine and fresh waters in this bay. The faunal and geochemical approaches could provide a means to trace fresh versus seawater mixing from core samples.

Faunal assemblages and multi-scale habitat patterns in headwater tributaries of the South Fork Trinity River – an unregulated river embedded within a multiple-use landscape

Headwaters can represent 80% of stream kilometers in a watershed, and they also have unique physical and biological properties that have only recently been recognized for their importance in sustaining healthy functioning stream networks and their ecological services. We sampled 60 headwater tributaries in the South Fork Trinity River, a 2,430 km2, mostly forested, multiple-use watershed in northwestern California. Our objectives were: (1) to differentiate unique headwater types using 69 abiotic and vegetation variables measured at three spatial scales, and then to reduce these to informative subsets; (2) determine if distinct biota occupied the different tributary types; (3) determine the environmental attributes associated with the presence and abundance of these biotic assemblages; and (4) using niche modeling, determine key attribute thresholds to illustrate how these biota could be employed as metrics of system integrity and ecological services. Several taxa were sufficiently abundant and widespread to use as bio-indicators: the presence and abundance of steelhead trout (Oncorhynchus mykiss), herpetofauna (reptile and amphibian) species richness, and signal crayfish (Pacifastacus leniusculus) represented different trophic positions, value as commercial resources (steelhead), sensitivity to environmental stress (amphibians), and indicators of biodiversity (herpetofauna species richness). Herpetofauna species richness did not differ, but abundances of steelhead trout, signal crayfish, and amphibian richness all differed significantly among tributary types. Niche models indicated that distribution and abundance patterns in both riparian and aquatic environments were associated with physical and structural attributes at multiple spatial scales, both within and around reaches. The bio-indicators responded to unique sets of attributes, reflecting the high environmental heterogeneity in headwater tributaries across this large watershed. These niche attributes represented a wide range of headwater environments, indicating responses to a number of natural and anthropogenic conditions, and demonstrated the value of using a suite of bio-indicators to elucidate watershed conditions, and to examine numerous disturbances that may influence ecological integrity.

Testing taxonomic resolution levels for detecting environmental impacts using macrobenthic assemblages in tropical waters

Macrobenthic assemblages are widely used as a tool for ecological assessment studies and monitoring programs. However, studies of macrobenthic assemblages have been limited in tropical coastal and marine environments in comparison with those in temperate zones. This study characterized at different resolution of taxonomic levels the responses of macrobenthic assemblages inhabiting subtidal areas in Bahrain to sewage effluents and heavy metal contamination. Macrobenthic assemblages impacted by nutrient enrichment showed lower levels of biodiversity, richness and evenness, and higher degree of disturbance. Multivariate statistical analyses revealed that faunal patterns of species were sufficiently comparable to those of genus and family taxonomic levels and showed 98% and 95% similarity, respectively. Ammonia, phosphate, and depth were the main environmental parameters responsible for explaining 41% of the community patterns in the study areas.

Faunal patterns in tenebrionids (Coleoptera: Tenebrionidae) on the Tuscan Islands: The dominance of paleogeography over Recent geography

The tenebrionid fauna of the Tuscan Islands (Central Italy) is well known and is an ideal system for studying the role of current and historical factors in determining the biogeographical patterns in a complex archipelago. Cluster analyses, species-area relationships and Mantel tests were used to investigate the influence of current geography and Pleistocene connections with the mainland on the structure of insular communities. Current biogeographical similarity patterns fit both Pleistocene and Recent geog- raphy, but marked effects of Pleistocene geography appeared when the influence of Recent geography was removed. Thus, in con- trast to more mobile insects, such as butterflies and chrysidids, tenebrionid colonization is likely to have occurred via land-bridges when the islands were connected to the mainland in the Pleistocene. The relict distributions of organisms with poor mobility should be of great concern to conservationists, because depletion of island populations cannot be balanced by new immigrations from main- land populations. The continued influence of man on the Tuscan Islands has adversely affected the natural environment, however, man made habitats may also be colonized and exploited by tenebrionids.

Vicariance and dispersal form a ring distribution in nightsnakes around the Gulf of California

Plate tectonics can have profound effects on organismal distribution and is often the driving force in speciation. Through geologic processes, the Baja California Peninsula depicts two faunal patterns: one through southern vicariance with Cape separation, and the other through dispersal onto the northern peninsula, referred to as a ‘dual-peninsular effect.’ Here we apply a hierarchical sampling strategy that combines population-level sequence data (∼800 bp, nad4 region) with complete mt-genome data (aligned 15,549 bp) and 5 nuclear protein encoding loci (3315 bp), to test whether both patterns have occurred in one group of nightsnakes ( Hypsiglena). The geologic formation of the peninsula is thought to have occurred in three stages: (1) Cape separation from mainland Mexico; (2) the northern peninsula separated, forming the northern Gulf of California; and (3) the peninsula was united through volcanic activity, while moving northward causing collision with southern California. However, the timing of events is debated. We explore phylogenetic relationships and estimate dates of divergence for nightsnakes using our hierarchical sampling strategy. Our data support both ‘southern-vicariance’ and ‘northern-dispersal’ have occurred in nightsnakes, forming a ring distribution around the Gulf of California. Two divergent forms are sympatric on the southern half of the peninsula with no indication of hybridization. Nightsnakes represent the first group to depict the ‘dual-peninsular effect’ with extensive overlap on the Baja California Peninsula.

Effects of habitat history and extinction selectivity on species-richness patterns of an island land snail fauna

Aim Local-scale diversity patterns are not necessarily regulated by contemporary processes, but may be the result of historical events such as habitat changes and selective extinctions that occurred in the past. We test this hypothesis by examining species-richness patterns of the land snail fauna on an oceanic island where forest was once destroyed but subsequently recovered. Location Hahajima Island of the Ogasawara Islands in the western Pacific. Methods Species richness of land snails was examined in 217 0.25 × 0.25 km squares during 1990–91 and 2005–07. Associations of species richness with elevation, current habitat quality (proportion of habitat composed of indigenous trees and uncultivated areas), number of alien snail species, and proportion of forest loss before 1945 in each area were examined using a randomization test and simultaneous autoregressive (SAR) models. Extinctions in each area and on the entire island were detected by comparing 2005–07 records with 1990–91 records and previously published records from surveys in 1987–91 and 1901–07. The association of species extinction with snail ecotype and the above environmental factors was examined using a spatial generalized linear mixed model (GLMM). Results The level of habitat loss before 1945 explained the greatest proportion of variation in the geographical patterns of species richness. Current species richness was positively correlated with elevation in the arboreal species, whereas it was negatively correlated with elevation in the ground-dwelling species. However, no or a positive correlation was found between elevation and richness of the ground-dwelling species in 1987–91. The change of the association with elevation in the ground-dwelling species was caused by greater recent extinction at higher elevation, possibly as a result of predation by malacophagous flatworms. In contrast, very minor extinction levels have occurred in arboreal species since 1987–91, and their original patterns have remained unaltered, mainly because flatworms do not climb trees. Main conclusions The species-richness patterns of the land snails on Hahajima Island are mosaics shaped by extinction resulting from habitat loss more than 60 years ago, recent selective extinction, and original faunal patterns. The effects of habitat destruction have remained long after habitat recovery. Different factors have operated during different periods and at different time-scales. These findings suggest that historical processes should be taken into account when considering local-scale diversity patterns.

Impact of oil-based drill mud disposal on benthic foraminiferal assemblages on the continental margin off Angola

Abstract In order to assess the possible environmental impact of oily cuttings discharged during oil exploration activities, we studied the benthic foraminiferal faunas in a five-station, 4-km-long sampling transect around a cuttings disposal site at about 670 m depth offshore Angola (W Africa), where drilling activities started 1.5 years before sampling. Living (Rose Bengal stained) and dead foraminiferal faunas were sampled in March 2006. The faunal patterns mirror the spatial distribution of hydrocarbons, which are dispersed into a southeastern direction. Four different areas can be distinguished on the basis of the investigated faunal parameters (density, diversity and species composition of the living fauna, and comparison with subrecent dead faunas). The fauna at station S31, 300 m SE of the oil cuttings disposal site, appears to be clearly impacted: the faunal density and diversity are maximal, but evenness is minimal. Taxa sensitive to organic enrichment, such as Uvigerina peregrina, Cancris auriculus and Cribrostomoides subglobosus, have largely disappeared, whereas the low-oxygen-resistant taxon Chilostomella oolina and opportunistic buliminids and bolivinids attain relatively high densities. At station S32, 500 m SE of the disposal site, environmental impact is still perceptible. The faunal density is slightly increased, and U. peregrina, apparently the most sensitive species, is still almost absent. The faunas found at 1 and 1.8 km SE of the disposal site are apparently no longer impacted by the drill mud disposal. Faunal density and diversity are low, and the faunal composition is typical for a mesotrophic to eutrophic upper slope environment. Finally, Station S35, 2 km NW of the disposal site, contains an intermediate fauna, where both the low-oxygen-resistant C. oolina and the more sensitive taxa (U. peregrina, C. auriculus and C. subglobosus) are present. All taxa live close to the sediment–water interface here, indicating a reduced oxygen penetration into the sediment. Since the hydrocarbon concentration is low at this station, it appears that the faunal characteristics are the consequence of a slightly different environmental setting, and not due to a contamination with drill cuttings. Our data underline the large potential of benthic foraminifera as bio-indicators of anthropogenic enrichment in open marine settings, such as caused by the disposal of oily drill cuttings. The foraminiferal faunas react essentially by a density increase of a number of tolerant and/or opportunistic taxa, and a progressive disappearance of more sensitive taxa in the most impacted area. Rather surprisingly, large-sized taxa appear to be more sensitive than small-sized foraminiferal taxa.

Suprabenthic fauna from the Bellingshausen Sea and western Antarctic Peninsula: spatial distribution and community structure

During the austral summers of 2003 and 2006 suprabenthic assemblages were investigated at 35 stations located in the Bellingshausen Sea and off the western Antarctic Peninsula, at depths ranging from 45 to 3280 m. Suprabenthos was collected with a Macer-GIROQ sledge equipped with an automatic opening and closing system. This study presents data on the occurrence and relative abundance of the major suprabenthic taxa collected in the water layer immediately adjacent to the bottom (10-140 cm above bottom). Assemblages were dominated by Peracarida and the most common groups were Amphipoda, Mysida, Isopoda and Cumacea. Among the 66 taxa identified, 40 account for more than 80% of the dissimilarity levels among any of the different combinations between groups of stations. The highest dissimilarity values in the segregation of the pairwise station groups were obtained for Mysidae, Lysianassidae, Gammaridea, Cumacea and Munnopsidae. The recorded faunistic patterns showed dependences in the environmental variables depth and percentage of mud in the sediment, as single and combined variables.

Littoral biodiversity across scales in the Seychelles, Indian Ocean

The 16 Marine Protected Areas in the Seychelles Archipelago (Western Indian Ocean) are monitored by a wide range of scientific and conservation organizations, but these mainly focus on coral or fish. We have investigated variability in littoral biodiversity (with emphasis on molluscs, anomuran and brachyuran crustaceans, echinoderms and polyclad flatworms) across four spatial scales, including the largest, and previously unsurveyed, Silhouette Marine National Park. We recorded all fauna >4 mm within 1-m2 quadrats replicated at three tidal heights across transects and sites on the central granitic islands of Mahe and Silhouette and the outer Desroches coral cay. We sampled 438 quadrats and recorded 292 species of our study taxa, but accumulation curves did not reach asymptote. Most species were rare and encountered only once, although a few key species were highly abundant. Biodiversity was dominated by gastropod molluscs, which non-metric multidimensional scaling analyses showed to be a reasonable surrogate for overall faunal patterns. Non-metric multidimensional scaling showed that the fauna of each island were quite dissimilar, and after island, site explained the most variance in our generalised linear mixed models. The two least rich sites were adjacent to the only established hotel on Desroches but we cannot establish causality due to lack of a-priori data. However major enlargening of a hotel adjacent to one site on Silhouette should enable future scrutiny of tourism influences.

A TEST OF BIOGEOGRAPHICAL, ENVIRONMENTAL, AND ECOLOGICAL EFFECT ON MIDDLE AND LATE TRIASSIC BRACHIOPOD AND BIVALVE ABUNDANCE PATTERNS

Analysis of Middle Triassic data indicates that biogeography influences sample distributions, whereas depositional environment and stratigraphic position play secondary roles in governing sample patterns. During this time, taxa differed among biogeographic realms, while the general ecology remained the same: epifaunal benthos— pedunculate and epibyssate suspension feeders—dominate Middle Triassic samples much as they did in the Early Triassic. In contrast, Late Triassic data prove to be more complex in terms of ecology compared to Middle Triassic. Here, guild structure dictates the faunal patterns in addition to biogeographic realm and stratigraphic position, and an overall increase of infaunal life habits occurs—burrowing suspension and deposit feeders increase. Although diversity after mass extinction began to recover at the Early-Middle Triassic boundary, our results indicate that ecology remained stable through the Middle Triassic until the more modern life habits (e.g., infaunalization) increased in the Late Triassic. We conclude that the taxonomic and ecological differences among Late Triassic geographic regions recorded the initiation of a more mobile and infaunal life habit indicative of a modern lifestyle. Our results also indicate that this modernization did not necessarily unfold simultaneously and in coordinated fashion within regions and throughout time. Instead, details of guild expansion or stability may be region specific.

Faunal patterns in Tuscan archipelago butterflies (Lepidoptera): The dominant influence is recent geography not paleogeography

The aim of this paper is to examine whether current and/or Pleistocene geography affect the species richness and composition of Tuscan archipelago butterflies. This archipelago is located between Tuscany (Italy) and Corsica (France). Faunistic data was obtained from the literature and surveys. Our data revealed that contemporary geography is the most important factor determining the species richness and faunal composition of Tuscan archipelago butterflies. Indeed, current area and isolation of the islands are the only predictors significantly correlated with species richness. Paleogeographic features of the archipelago are not significantly correlated with species richness. Multidimensional scaling revealed patterns similar to those reported for other living groups. Specifically, Capraia and Montecristo group together with Corsica, while Elba, Giglio, Pianosa, Gorgona, Giannutri and the fossil island of Monte Argentario group with the Tuscan mainland. Recent geography seems to affect the faunal composition. Indeed Mantel test indicates that the similarity in the faunal composition of the Tuscan Archipelago islands is mainly related to present-day island characteristics and their relative distance from Tuscany and Corsica. Our results are similar to those recently obtained for Aegean archipelago butterflies.

Phytoliths in palaeoecology

With increasing interest in climate change and other issues associated with the history of the environment and anthropogenic evolution there is an ongoing requirement to investigate the Earth's natural systems. A key approach is for scientists to look back into geological time, perhaps millions of years, to see how the world has reacted to natural climatic changes in the past. Using evidence from the fossil record, fluctuations in palaeoclimate can be assessed with reference to changes in global floral and faunal patterns. Phytoliths, Greek for ‘plant stones’, is a fossil group that is being increasingly utilized in the understanding of past climates and environments.

Inference models for tidal flat elevation and sediment grain size: A Preliminary approach on tidal flat macrobenthic community

A vertical transect with 4 km length was established for the macrofaunal survey on the Chokchon macrotidal flat in Kyeonggi Bay, Incheon, Korea, 1994. Tidal elevation (m) and sediment mean grain size (φ) were inversely predicted by the transfer functions from the faunal assemblages. Three methods: weighted average using optimum value (WA), tolerance weighted version of the weighted average (WAT ) and maximum likelihood calibration (MLC) were employed. Estimates of tidal elevation and mean grain size obtained by using the three different methods showed positively corresponding trends with the observations. The estimates of MLC were found to have the minimum value of sum of squares due to errors (SSE). When applied to the previous data (1990~1992), each of three inference models exhibited high predictive power. This result implied there are visible relationships between species composition and faunas’ critical environmental factors. Although a potential significance of the two major abiotic factors was re-affirmed, a weak tendency of biological interaction was detected from faunal distribution patterns across the flat. In comparison to the spatial and temporal patterns of the estimates, it was suggested that sediment characteristics were the primary factors regulating the distribution of macrofaunal assemblages, rather than tidal elevation, and the species composition may be sensitively determined by minute changes in substratum properties on a tidal flat.

Ecological boundaries in estuaries: macrobenthic β-diversity in the Río de la Plata system (34–36°S)

In this study, we analyse spatial patterns of macrobenthic communities of the Río de la Plata system, and assess the species turnover or beta diversity and its relationship with environmental gradients. Macrobenthic samples and physico-chemical parameters were collected from 20 sampling sites along a transect of 560 km, including the freshwater (FW), estuarine (ES) and marine (MA) sectors. Three main assemblages corresponding to the above mentioned sectors were defined with multivariate analysis (cluster, MDS). In total 134 taxa were recorded, 81 in MA, 33 in FW and 38 in ES, represented mainly by polychaete, mollusc and crustacean species. Depth, salinity and %clay showed the strongest correlation with the observed faunal patterns (ρw=0.62; BIO-ENV analysis). Beta diversity varied between dominant taxonomic groups and was positively correlated with changes in salinity. The high variability in the composition of assemblages was reflected in beta diversity, reaching its highest values at the boundaries between the defined sectors. This study suggests that beta diversity represents a useful tool to define ecological boundaries for benthic communities in the Río de la Plata.

Taxonomic sufficiency for soft-bottom sublittoral mollusks assemblages in a tropical estuary, Guanabara Bay, Southeast Brazil

Guanabara Bay (GB) is considered to be one of the most polluted environments of the southern Brazilian coastline. This typical estuarine system is impacted by the heavy discharge of both industrial and domestic waste from the Rio de Janeiro metropolitan area. The mollusc community structure and distribution was investigated between 2000 and 2001, using a three month sampling design of 38 stations, according to austral seasons. Species abundance was aggregated into progressively higher taxa matrices (genus, family, order) and were analysed using multivariate techniques. Mollusc distribution in GB varied significantly in space and time and was probably ruled by the organic enrichment effects of hypoxia and altered redox conditions coupled with prevailing patterns of circulation. Within the sectors of GB an increasing gradient in mollusc diversity and occurrence was observed, ranging from the azoic and impoverished stations in the inner sector to a well-structured community in terms of species composition and abundance inhabiting the outer sector. The non-metric multidimensional scaling (nMDS) and cluster analysis showed similar results when species were aggregated into genera and families, while greater difference occurred at coarser taxonomic identification (order). The literature about taxonomic sufficiency has demonstrated that faunal patterns at different taxonomic levels tend to become similar with increased pollution. In Guanabara Bay, an analysis carried out solely at family level is perfectly adequate to describe the ecophysiological stress. Further aggregation to order level changed the perceived patterns of differences. However, a different taxonomic resolution can be chosen depending on the type of ecological patterns investigated.

Correlation of Middle Devonian Hamilton Group-equivalent strata in east-central North America: implications for eustasy, tectonics and faunal provinciality

Abstract An integrated approach, involving nearly all available biostratigraphic data, event and sequence stratigraphy, has been utilized in correlation of the Middle Devonian (latest Eifelian–Givetian) Hamilton Group and equivalent strata in north-central North America. This approach permits high-resolution correlation of strata equivalent to the Oatka Creek (upper Marcellus), Skaneateles, Ludlowville and Moscow Formations from New York into sections bordering the Michigan Basin in Ontario, Canada, as well as southern Michigan, northern Ohio and Indiana, USA. Most member and submember-scale units, herein slightly redefined and interpreted as 3rd and 4th order sequences, respectively, and their bounding condensed beds can be correlated regionally. Moreover, many faunal patterns also persist across this region, which, together with sequence stratigraphy, provides a bridge for correlation into the Michigan Basin. The detailed stratigraphy presented herein permits a more-resolved understanding of far-field tectonics, eustasy and biotic responses during the Middle Devonian. Allocyclic processes, primarily eustasy, played a key role in generating persistent sedimentary cycles. Episodes of rapid mud sedimentation occurred over large areas of the cratonic interior, distal to Acadian source terrains. The major Algonquin–Findlay Arch, which presently separates the Michigan Basin from the Appalachian foreland basin, was not present during deposition of these strata. Conversely, a roughly north–south trending region, running approximately through present-day Cleveland, Ohio, was first a local subsiding area during late Eifelian–early Givetian time and then underwent topographic inversion to form a local arch at which upper Hamilton units were condensed and then bevelled during the later Givetian; we infer that this feature may represent a migrating forebulge. Finally, fossil biotas do not show strong partitioning into Appalachian and Michigan basin faunal subprovinces during the early Givetian, as there appears to have been no physical barrier to migration at least in the study area. However, Hamilton-equivalent strata in the most proximal portion of the Appalachian Basin do show a relatively minor admixture of typical Michigan Basin taxa with normal Hamilton forms.

A QUANTITATIVE STUDY OF BENTHIC FAUNAL PATTERNS WITHIN THE PENNSYLVANIAN AND EARLY PERMIAN

Abstract Using abundance data, this study explores quantitative patterns from marine benthos, including implications for paleogeography, depositional environment, stratigraphic position, taxonomic groups (brachiopod or mollusc), substrate preferences, and ecological niches. Twenty-nine brachiopod- and bivalve-dominated fossil assemblages from the Pennsylvanian and Early Permian of North and South America, Thailand, and Australia were analyzed from carbonate-platform environments; specifically, Nevada, Kansas, Oklahoma, Texas, Utah, New Mexico, Venezuela, Kanchanaburi (Thailand), and Queensland (Australia). Samples were categorized by paleogeographic location, depositional environment, and age to help differentiate factors controlling the faunal patterns. Pooled from primary and summary literature resources, 336,321 specimens were identified to genus level and classified in terms of taxonomic membership, substrate preference, and ecological niche. Data were analyzed using detrended correspondence analysis ...

The Early Triassic ammonoid recovery: Paleoclimatic significance of diversity gradients

Ammonoids recovered much faster than other marine shelly invertebrates after the end-Permian mass extinction. Based on a refined global data set at the basin level, we investigate the paleobiogeographical global latitudinal and longitudinal diversity patterns in terms of climatic changes during the Early Triassic. Such analysis differs from already published qualitative or quantitative studies in that it estimates faunal patterns and endemicity at an ecologically meaningful level of spatial resolution, i.e. at the basin level. During the Early Triassic, the global first order trend in increasing ammonoid diversity was accompanied by a progressive change from cosmopolitan to latitudinally-restricted distributions. This led to the emergence of a clear latitudinal diversity gradient during most of the Smithian and Spathian stages, which entails increased steepness of the Sea Surface Temperature gradient during the late Early Triassic. However, two brief episodes of ammonoid cosmopolitanism combined with low global diversity interrupted the first order increasing trend at the very beginning of the Smithian and at its very end. The longitudinal analysis of Smithian distributions indicates a westward decrease of diversity within the Tethys, which faded away during the Spathian. Analysis of endemicity indicates a rapid biogeographical maturing and structuring of faunas concomitant with the edification of the latitudinal diversity gradient.

Testing the role of biological interactions in the evolution of mid-Mesozoic marine benthic ecosystems

Evaluating the relative importance of biotic versus abiotic factors in governing macroevolutionary patterns is a central question of paleobiology. Here, we analyzed patterns of changes in global relative abundances and diversity of ecological groups to infer the role of biological interactions as driving evolutionary forces in mid-Mesozoic macrobenthic marine ecosystems. Specifically, we tested the hypothesis of escalation, which states that macroevolutionary patterns were controlled by an increasing pressure exerted by enemies on their victims. Associated with evidence of increasing levels of predation and biogenic sediment reworking (bulldozing) is an increasing representation of predation- and disturbance-resistant groups in the fossil record. In particular, we observe increasing proportions of mobile organisms; a decline of vulnerable epifauna living freely on the substrate; and a trend toward infaunalization of the benthos. These trends were most pronounced in the paleotropics, i.e., the region where biological activity is thought to have been highest. The observation that these changes affected several biotic traits and occurred within independent clades argues against the overriding role of a single key adaptive innovation in causing shifts in ecological abundance. Also, changes in the abiotic environment cannot explain these faunal patterns because of lacking cross-correlations with physico-chemical parameters such as global sea level, climate, and seawater chemistry. We conclude that in marine benthic ecosystems of the mid Mesozoic, enemy-driven evolution, or escalation, was a plausible and important factor.

The Pattern and Timing of Biotic Recovery from the End-Permian Extinction on the Great Bank of Guizhou, Guizhou Province, China

Abstract Microfacies analysis and point counts of thin sections from 608 hand samples were used to track changes in the abundance and diversity of fossil grains through the extended recovery interval following end-Permian mass extinction on the Great Bank of Guizhou (GBG)—an isolated Late Permian to Late Triassic carbonate platform in south China. Exposure of a two-dimensional cross-section of the platform permits the comparison of faunal patterns along an environmental gradient from shallow to deep water. The diverse Late Permian biota was dominated by calcareous sponges, crinoids, articulate brachiopods, foraminifera, and calcareous algae. In contrast, Early Triassic communities were dominated by mollusks, with increasing abundance of crinoids beginning in the Spathian. Increase in the diversity and abundance of fossils on the GBG was confined to a brief interval near the Spathian–Anisian boundary and concentrated along the platform margin. Later Middle Triassic diversification, the return of calcareous...