Estuarine foraminifera from the Rappahannock River, Virginia

Populations of benthonlc foraminifera were studied from 263 samples obtained in 5 collections from the estuary, its tributaries and borderlng marshe

Modern and Holocene formanifera in the Chesapeake Bay region

Estuaries are highly variable coastal ecosystems. Some of the variation is seasonal and some is longitudinal along the environmental gradient from the river to the sea. Foraminifera are tuned to the periodicity, and a progressive change in the composition and structure of foraminiferal faunas parallels the longitudinal ecocline, identified by the gradient in salinity. In marshes and tributary estuaries where water is fresh, thecamoebinids comprise the microfauna. Three other marsh faunas are composed chiefly of the agglutinate species: Ammoastuta salsa, Miliammina fusca, Arenoparrella mexicana, Alllmobaculites crassus and species of Haplophragmoides and Trochammina. Their distribution is influenced by salinity and exposure. In the estuaries, where fresh and salt water mix:, two faunas are characterized by: Anmlobaculites crassus, in the middle and upper reaches where salinity is less than about 15 % and the estuary is periodically freshened by river flushing, and by Elphidim clavatum in lower reaches and deeper channels where salinity is higher and mixing is moderate. Elphidium, furthermore, dominates the faunas in the lower part of Chesapeake Bay and, on the inner part of the shelf. At a depth of about 25 m the Elphidium fauna is succeeded by a larger and more diverse fauna that may be partly relict. The marsh and estuarine faunas shift headward and mouthward with changing river inflow and salinity, and their changes are recorded in cores of estuarine and marsh deposits. Short-term events and paleoclimatic episodes with durations of several hundred years are superimposed on a long-term trend of decreasing salinity during the past 6,000 years as sedimentary infilling exceeded the rise in sea level.https://scholarworks.wm.edu/vimsbooks/1187/thumbnail.jp

A New Physical Picture for AGNs Lacking Optical Emission Lines

In this work, we use ~500 low-redshift (z ~ 0.1) X-ray AGNs observed by XMM-Newton and SDSS to investigate the prevalence and nature of AGNs that apparently lack optical emission lines (``optically dull AGNs''). Although 1/4 of spectra appear absorption-line dominated in visual assessment, line extraction with robust continuum subtraction from the MPA/JHU catalog reveals usable [OIII] measurements in 98% of the sample, allowing us to study [OIII]-underluminous AGNs together with more typical AGNs in the context of the L$_{\mathrm{[OIII]}}$--L$_{X}$ relation. We find that ``optically dull AGNs'' do not constitute a distinct population of AGNs. Instead, they are the [OIII]-underluminous tail of a single, unimodal L$_{\mathrm{[OIII]}}$--L$_{X}$ relation that has substantial scatter (0.6 dex). We find the degree to which an AGN is underluminous in [OIII] correlates with the specific SFR or D$_{4000}$ index of the host, which are both linked to the molecular gas fraction. Thus the emerging physical picture for the large scatter seems to involve the gas content of the narrow-line region. We find no significant role for previously proposed scenarios for the presence of optically dull AGNs, such as host dilution or dust obscuration. Despite occasionally weak lines in SDSS spectra, >80% of X-ray AGNs are identified as such with the BPT diagram. >90% are classified as AGNs based only on [NII]/H$\alpha$, providing more complete AGN samples when [OIII] or H$\beta$ are weak. X-ray AGNs with LINER spectra obey essentially the same \lxo\ relation as Seyfert 2s, suggesting their line emission is produced by AGN activity.Comment: 21 pages, 14 figures, submitted to ApJ. Comments welcom

The merger fraction of post-starburst galaxies in UNIONS

Funding information: CB gratefully acknowledges support from the Natural Sciences and Engineering Council of Canada (NSERC) as part of their post-doctoral fellowship program (PDF-546234-2020) and VW acknowledges STFC grant ST/V000861/1.Post-starburst galaxies (PSBs) are defined as having experienced a recent burst of star formation, followed by a prompt truncation in further activity. Identifying the mechanism(s) causing a galaxy to experience a post-starburst phase therefore provides integral insight into the causes of rapid quenching. Galaxy mergers have long been proposed as a possible post-starburst trigger. Effectively testing this hypothesis requires a large spectroscopic galaxy survey to identify the rare PSBs as well as high-quality imaging and robust morphology metrics to identify mergers. We bring together these critical elements by selecting PSBs from the overlap of the Sloan Digital Sky Survey and the Canada–France Imaging Survey and applying a suite of classification methods: non-parametric morphology metrics such as asymmetry and Gini-M20, a convolutional neural network trained to identify post-merger galaxies, and visual classification. This work is therefore the largest and most comprehensive assessment of the merger fraction of PSBs to date. We find that the merger fraction of PSBs ranges from 19 per cent to 42 per cent depending on the merger identification method and details of the PSB sample selection. These merger fractions represent an excess of 3–46× relative to non-PSB control samples. Our results demonstrate that mergers play a significant role in generating PSBs, but that other mechanisms are also required. However, applying our merger identification metrics to known post-mergers in the IllustrisTNG simulation shows that 70 per cent of recent post-mergers (≲200 Myr) would not be detected. Thus, we cannot exclude the possibility that nearly all PSBs have undergone a merger in their recent past.Publisher PDFPeer reviewe

Many Roads to Synchrony: Natural Time Scales and Their Algorithms

We consider two important time scales---the Markov and cryptic orders---that monitor how an observer synchronizes to a finitary stochastic process. We show how to compute these orders exactly and that they are most efficiently calculated from the epsilon-machine, a process's minimal unifilar model. Surprisingly, though the Markov order is a basic concept from stochastic process theory, it is not a probabilistic property of a process. Rather, it is a topological property and, moreover, it is not computable from any finite-state model other than the epsilon-machine. Via an exhaustive survey, we close by demonstrating that infinite Markov and infinite cryptic orders are a dominant feature in the space of finite-memory processes. We draw out the roles played in statistical mechanical spin systems by these two complementary length scales.Comment: 17 pages, 16 figures: http://cse.ucdavis.edu/~cmg/compmech/pubs/kro.htm. Santa Fe Institute Working Paper 10-11-02

Heating up the forest: Open-top chamber warming manipulation of arthropod communities at Harvard and Duke Forests

1.Recent observations indicate that climatic change is altering biodiversity, and models suggest that the consequences of climate change will differ across latitude. However, long-term experimental field manipulations that directly test the predictions about organisms\u27 responses to climate change across latitude are lacking. Such experiments could provide a more mechanistic understanding of the consequences of climate change on ecological communities and subsequent changes in ecosystem processes, facilitating better predictions of the effects of future climate change. 2.This field experiment uses octagonal, 5-m-diameter (c.22m 3) open-top chambers to simulate warming at northern (Harvard Forest, Massachusetts) and southern (Duke Forest, North Carolina) hardwood forest sites to determine the effects of warming on ant and other arthropod populations and communities near the edges of their ranges. Each site has 12 plots containing open-top chambers that manipulate air temperature incrementally from ambient to 6°C above ambient. Because the focus of this study is on mobile, litter- and soil-dwelling arthropods, standard methods for warming chambers (e.g. soil-warming cables or infrared heaters applied to relatively small areas) were inappropriate and new technological approaches using hydronic heating and forced air movement were developed. 3.We monitor population dynamics, species composition, phenology and behaviour of ants and other arthropods occupying these experimental chambers. Microclimatic measurements in each chamber include the following: air temperature (three), soil temperatures (two each in organic and mineral soil), photosynthetically active radiation (PAR), relative humidity and soil moisture (one each). In two chambers, we are also measuring soil heat flux, associated soil temperatures at 2 and 6cm and volumetric water content. To assess the composition, phenology and abundance of arthropod communities within the experiment, we use monthly pitfall trapping and annual Winkler sampling. We also census artificial and natural ant nests to monitor changes in ant colony size and productivity across the temperature treatments. 4.This experiment is a long-term ecological study that provides opportunities for collaborations across a broad spectrum of ecologists, including those studying biogeochemical, microbial and plant responses to warming. Future studies also may include implementation of multifactorial climate manipulations, examination of interactions across trophic levels and quantification of changes in ecosystem processes. © 2011 The Authors. Methods in Ecology and Evolution © 2011 British Ecological Society

Effects of short-term warming on low and high latitude forest ant communities

Climatic change is expected to have differential effects on ecological communities in different geographic areas. However, few studies have experimentally demonstrated the effects of warming on communities simultaneously at different locales. We manipulated air temperature with in situ passive warming and cooling chambers and quantified effects of temperature on ant abundance, diversity, and foraging activities (predation, scavenging, seed dispersal, nectivory, granivory) in two deciduous forests at 35° and 43° N latitude in the eastern U.S. In the southern site, the most abundant species, Crematogaster lineolata, increased while species evenness, most ant foraging activities, and abundance of several other ant species declined with increasing temperature. In the northern site, species evenness was highest at intermediate temperatures, but no other metrics of diversity or foraging activity changed with temperature. Regardless of temperature, ant abundance and foraging activities at the northern site were several orders of magnitude lower than those in the southern site. Copyright: © 2011 Pelini et al

Common garden experiments reveal uncommon responses across temperatures, locations, and species of ants

Population changes and shifts in geographic range boundaries induced by climate change have been documented for many insect species. On the basis of such studies, ecological forecasting models predict that, in the absence of dispersal and resource barriers, many species will exhibit large shifts in abundance and geographic range in response to warming. However, species are composed of individual populations, which may be subject to different selection pressures and therefore may be differentially responsive to environmental change. Asystematic responses across populations and species to warming will alter ecological communities differently across space. Common garden experiments can provide a more mechanistic understanding of the causes of compositional and spatial variation in responses to warming. Such experiments are useful for determining if geographically separated populations and co-occurring species respond differently to warming, and they provide the opportunity to compare effects of warming on fitness (survivorship and reproduction). We exposed colonies of two common ant species in the eastern United States, Aphaenogaster rudis and Temnothorax curvispinosus, collected along a latitudinal gradient from Massachusetts to North Carolina, to growth chamber treatments that simulated current and projected temperatures in central Massachusetts and central North Carolina within the next century. Regardless of source location, colonies of A. rudis, a keystone seed disperser, experienced high mortality and low brood production in the warmest temperature treatment. Colonies of T. curvispinosus from cooler locations experienced increased mortality in the warmest rearing temperatures, but colonies from the warmest locales did not. Our results suggest that populations of some common species may exhibit uniform declines in response to warming across their geographic ranges, whereas other species will respond differently to warming in different parts of their geographic ranges. Our results suggest that differential responses of populations and species must be incorporated into projections of range shifts in a changing climate.©2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd

Rarefaction and extrapolation with Hill numbers: A framework for sampling and estimation in species diversity studies

Quantifying and assessing changes in biological diversity are central aspects of many ecological studies, yet accurate methods of estimating biological diversity from sampling data have been elusive. Hill numbers, or the effective number of species, are increasingly used to characterize the taxonomic, phylogenetic, or functional diversity of an assemblage. However, empirical estimates of Hill numbers, including species richness, tend to be an increasing function of sampling effort and, thus, tend to increase with sample completeness. Integrated curves based on sampling theory that smoothly link rarefaction (interpolation) and prediction (extrapolation) standardize samples on the basis of sample size or sample completeness and facilitate the comparison of biodiversity data. Here we extended previous rarefaction and extrapolation models for species richness (Hill number qD, where q = 0) to measures of taxon diversity incorporating relative abundance (i.e., for any Hill number qD, q \u3e 0) and present a unified approach for both individual-based (abundance) data and samplebased (incidence) data. Using this unified sampling framework, we derive both theoretical formulas and analytic estimators for seamless rarefaction and extrapolation based on Hill numbers. Detailed examples are provided for the first three Hill numbers: q = 0 (species richness), q = 1 (the exponential of Shannon\u27s entropy index), and q = 2 (the inverse of Simpson\u27s concentration index). We developed a bootstrap method for constructing confidence intervals around Hill numbers, facilitating the comparison of multiple assemblages of both rarefied and extrapolated samples. The proposed estimators are accurate for both rarefaction and short-range extrapolation. For long-range extrapolation, the performance of the estimators depends on both the value of q and on the extrapolation range. We tested our methods on simulated data generated from species abundance models and on data from large species inventories. We also illustrate the formulas and estimators using empirical data sets from biodiversity surveys of temperate forest spiders and tropical ants. © 2014 by the Ecological Society of America

Using physiology to predict the responses of ants to climatic warming

Physiological intolerance of high temperatures places limits on organismal responses to the temperature increases associated with global climatic change. Because ants are geographically widespread, ecologically diverse, and thermophilic, they are an ideal system for exploring the extent to which physiological tolerance can predict responses to environmental change. Here, we expand on simple models that use thermal tolerance to predict the responses of ants to climatic warming. We investigated the degree to which changes in the abundance of ants under warming reflect reductions in the thermal niche space for their foraging. In an eastern deciduous forest system in the United States with approximately 40 ant species, we found that for some species, the loss of thermal niche space for foraging was related to decreases in abundance with increasing experimental climatic warming. However, many ant species exhibited no loss of thermal niche space. For one well-studied species, Temnothorax curvispinosus, we examined both survival of workers and growth of colonies (a correlate of reproductive output) as functions of temperature in the laboratory, and found that the range of thermal tolerances for colony growth was much narrower than for survival of workers. We evaluated these functions in the context of experimental climatic warming and found that the difference in the responses of these two attributes to temperature generates differences in the means and especially the variances of expected fitness under warming. The expected mean growth of colonies was optimized at intermediate levels of warming (24°C above ambient); yet, the expected variance monotonically increased with warming. In contrast, the expected mean and variance of the survival of workers decreased when warming exceeded 4°C above ambient. Together, these results for T. curvispinosus emphasize the importance of measuring reproduction (colony growth) in the context of climatic change: indeed, our examination of the loss of thermal niche space with the larger species pool could be missing much of the warming impact due to these analyses being based on survival rather than reproduction. We suggest that while physiological tolerance of temperature can be a useful predictive tool for modeling responses to climatic change, future efforts should be devoted to understanding the causes and consequences of variability in models of tolerance calibrated with different metrics of performance and fitness. © The Author 2013. All rights reserved