Individual-based chaos: Extensions of the discrete logistic model

Simple models of density-dependent population growth such as the discrete logistic map provide powerful demonstrations of complex population dynamics. Yet it is unclear whether the dynamics observed in such idealized systems would be present, under realistic conditions, in the context of demographic stochasticity, which is well known to exist in finite natural populations. Here, using a set of simple, individual-based models (IBM's) and their population-level iterative map counterparts, we computationally investigate the contribution of demographic stochasticity to density-dependent population dynamics in a simple model of seed production and recruitment. Notably, for a sufficiently large lattice, even in the presence of demographic stochasticity, many of the qualitative features of these idealized maps – including bifurcations – are still present. Demographic stochasticity and the constraints imposed by a finite lattice size appear to produce mixed dynamics that are partially stochastic, yet qualitatively similar to the deterministic models. The mechanistic assumptions and lattice sizes required to generate these dynamics cast doubt on whether they might be observable in annual plant populations. Nevertheless, we cannot rule out the theoretical possibility that such dynamics might be observable in ecological communities having similar mechanistic properties

Anthropogenic Transformation at Angel Mounds: Construction, Chronology and Context for Mounds A and F

Investigations at Angel Mounds since 2005 have tackled a series of questions related to anthropogenic transformation, the built landscape and mound construction. During the 2013 NSF-sponsored research, investigations focused on Mound A’s lower platform and the reopening of Mound F. Results from these investigations revealed a series of use-surfaces on Mound A’s lower platform with evidence for burning episodes that were followed by reconstruction. Excavations on Mound F also revealed a burning episode associated with a structure on the “inner mound,” as well as a sub-mound structure and features demonstrating use of the space prior to mound construction

Different intra- and inter-molecular hydrogen-bonding patterns in (3S,4aS,8aS)-2-[(2R,3S)-3-(2,5-X2-benzamido)-2-(2,5-X2-benzo-yloxy)-4-phenyl-butyl]-N-tert-butyldeca-hydro-iso-quinoline-3-carboxamides (X = H or Cl) : compounds with moderate aspartyl protease inhibition activity

We thank the EPSRC National Crystallography Service (University of Southampton) for the X-ray data collections.Peer reviewedPublisher PD

RISK PERCEPTIONS AND MANAGEMENT RESPONSES: PRODUCER-GENERATED HYPOTHESES FOR RISK MODELING

Farm level risk analyses have used price and yield variability almost exclusively to represent risk. Results from a survey of 149 agricultural producers in 12 states indicate that producers consider a broader range of sources of variability in their operations. Significant differences exist among categories with respect to the importance of the sources of variability in crop and livestock production. Producers also used a variety of management responses to variability. There were significant difference among categories in the importance given to particular responses and their use of them. These results have implications for research, extension, and policy programs.Risk and Uncertainty,

Fishes of the Red River in Arkansas

Fishes were collected from Red River mainstem habitats in Arkansas with seines, rotenone, hoop nets, gill nets, and trotlines from 1995 through 2001. Seventy-two species were identified distributed among 17 families, and 15 species were new records for the Red River in Arkansas. Eighty-three species are now historically known from the Arkansas segment of the Red River. Approximately 67% of the fishes known from the entire Red River have been found in the Arkansas segment, which is only 11% of the entire river length. Baseline data on the fish fauna of the Red River is critical for the analysis of potential effects to aquatic systems, and because of the potential for deleterious effects from alteration of aquatic habitats by a proposed project to extend the Red River Navigation System upstream from Shreveport, Louisiana to Index, Arkansas and by desalination projects upstream in Texas

Turf wars: experimental tests for alternative stable states in a two-phase coastal ecosystem

Alternative stable states have long been thought to exist in natural communities, but direct evidence for their presence and for the environmental switches that cause them has been scarce. Using a combination of greenhouse and field experiments, we investigated the environmental drivers associated with two distinctive herbaceous communities in coastal ecosystems in New Zealand. In a mosaic unrelated to micro-topography, a community dominated largely by native turf species (notably Leptinella dioica, Samolus repens, and Selliera radicans) alternates with vegetation comprising exotic (i.e., nonnative) pasture species (notably Agrostis stolonifera, Holcus lanatus, Lolium perenne, and Trifolium repens). The species of these two communities differ in functional characters related to leaf longevity and growth rate, and occupy soils of differing nitrogen levels. Both spatial and environmental factors influenced the species composition locally. Reciprocal transplants of soil, with and without associated vegetation, showed that a native turf community developed when sward or soil from either community was bounded by turf, and a pasture community developed when sward or soil from either community was surrounded by pasture. In artificial mixed communities in the greenhouse, turf was able to invade the pasture community where the vegetation was clipped to simulate grazing, and also where Trifolium was removed and/or salt spray was applied. The pasture community invaded the turf where Trifolium was present or nitrogen was added. These results were supported by trends in experimentally manipulated field plots, where the amount of turf cover increased when nitrogen was kept low and when salt spray was applied, whereas pasture cover increased in the absence of salt spray. Thus, persistence of the native turf community is dependent on grazing, both directly and via its effect on keeping nitrogen levels low by excluding the exotic, nitrogen-fixing Trifolium, and by exposing the vegetation to salt spray. If any of these factors change, there could be a state change to pasture dominance that might be resistant to reversion to turf. Managing such coastal herbaceous communities therefore requires an understanding of the environmental and species characteristics that maintain alternative states

Abundance of Selected Fish Species in Relation to Temperature and Salinity Patterns in the Sagavanirktok Delta, Alaska, Following Construction of the Endicott Causeway

Hydrography data from 1985 to 1993 in the vicinity of the Endicott Causeway near Prudhoe Bay, Alaska, were analyzed to determine if the trend in yearly post-causeway construction temperature and salinity was toward colder and more saline conditions. No significant (P<=0.05) relationship was found for temperature; however, salinity levels significantly decreased with time following construction. Intra-year variations in hydrographic conditions appeared to be due to coast-wide meteorological and oceanographic events rather than causeway-induced. We analyzed abundance indices, as log e, transformed catch-per-unit-effort (CPUE), of four marine species (arctic cod, Boreogadus saida; fourhorn sculpin, Myoxocephalus quadricornis; arctic flounder, Pleuronectes glacialis; saffron cod, Eleginus gracilis); two freshwater species (round whitefish, Prosopium cylindraceum; arctic grayling, Thymallus arcticus); and the anadromous rainbow smelt, Osmerus mordax, to determine whether there were increases in the abundance of marine species and declines in anadromous and freshwater species. We developed the "best-fit" regression models, based on the criterion of maximized regression F-ratio (i.e., minimized regression p-values), using year, temperature, salinity, and all possible interactions. Results suggested that all species exhibited changes in abundance levels over the period of record. In particular, arctic flounder and rainbow smelt both showed sharp increases in abundance five years after construction. For all species, the observed changes in abundance levels appears to be due to naturally occurring events in the species life history or changes in coast-wide meteorological conditions rather than to causeway-induced alterations in local hydrographic conditions.On a analysé les données hydrographiques obtenues de 1985 à 1993 dans le voisinage immédiat du pont-jetée Endicott situé près de Prudhoe Bay en Alaska, en vue de déterminer si, après la construction du pont, la température annuelle avait tendance à être plus froide et l'eau plus saline. On n'a trouvé aucun rapport significatif (p <= 0,05) pour la température. Le niveau de salinité, par contre, a considérablement baissé à mesure que le temps passait après la construction. Les variations intra-annuelles dans les conditions hydrographiques semblaient être dues à des phénomènes météorologiques et océanographiques affectant le littoral tout entier plutôt qu'au pont-jetée lui-même. On a analysé les indices d'abondance, exprimés en log\dn4 e des prises par unité d'effort (PPUE) de quatre espèces marines (morue arctique, Boreogadus saida; chaboisseau à quatre cornes, Myoxocephalus quadricornis; plie arctique, Pleuronectes glacialis; navaga jaune, Eleginus gracilis); deux espèces d'eau douce (ménomini rond, Prosopium cylindraceum, et ombre arctique, Thymallus arcticus); ainsi qu'une espèce anadrome (éperlan arc-en-ciel, Osmerus mordax), afin de déterminer s'il y avait une augmentation dans l'abondance des espèces marines et une diminution dans les espèces anadromes et d'eau douce. On a développé des modèles de régression de meilleur ajustement, fondés sur le critère de maximisation du F de régression (c.-à-d. minimum des valeurs p de régression), en utilisant l'année, la température, la salinité et toutes les interactions possibles. Les résultats suggéraient que toutes les espèces montraient des changements dans les niveaux d'abondance durant la période de relevés. La plie arctique et l'éperlan arc-en-ciel en particulier affichaient tous deux un accroissement très net dans leur abondance cinq ans après la construction. Pour toutes les espèces, les changements observés dans les niveaux d'abondance semblent être dûs à des phénomènes qui se produisent naturellement dans le cycle biologique de l'espèce ou à des changements dans les conditions météorologiques affectant le littoral tout entier plutôt qu'à des transformations causées par le pont-jetée dans les conditions hydrographiques locales

Prudhoe Bay Causeways and the Summer Coastal Movements of Arctic Cisco and Least Cisco

Catch-per-unit-effort and mark-recapture data collected by fyke net during the summers of 1985-93 near Prudhoe Bay, Alaska, were analyzed to determine whether two oil industry causeways constructed perpendicular to the Beaufort Sea coast, West Dock and the Endicott Causeway, affected the feeding and migratory patterns of least cisco (Coregonus sardinella) and arctic cisco (C. autumnalis). During two of the four years in which juvenile least cisco were abundant in the study area, catch rates were significantly lower (P<=0.0005) east of West Dock, which suggested that small fish traveling eastward along the coast failed to bypass the causeway. Hydrographic conditions were generally consistent with the hypothesis that causeway-induced upwellings of saline marine water immediately west of West Dock may affect alongshore movement. No such disparities in catch were observed at the Endicott Causeway. We studied rates of return for subadult and adult (>=250 mm) arctic cisco and least cisco tagged in the Prudhoe Bay area and recovered in a commercial fishery that operates in the Colville River, Alaska. The expected rate of return was compared with actual rates of return over five years (for least cisco) and six years (for arctic cisco). Rates of return were based upon three areas of release: east of the easternmost causeway, west of the westmost causeway, and between the two causeways. For both species, across the regions and all year, there was no significant difference (p=0.25 for least cisco; p=0.30 for arctic cisco) between the expected and actual rates of tag returns. The contrasting effects of the two causeways are discussed in terms of their design and location.Les données de prises par unité d'effort et de marquage-recapture, recueillies par des verveux au cours des étés de 1985 à 1993 près de Prudhoe Bay en Alaska, ont été analysées afin de déterminer si deux ponts-jetées construits pour l'industrie pétrolière perpendiculairement au rivage de la mer de Beaufort (le pont-jetée West Dock et le pont-jetée Endicott) affectaient les schémas de nutrition et de migration du cisco sardinelle (Coregonus sardinella) et du cisco arctique (C. autumnalis). Durant deux des quatre années au cours desquelles le cisco sardinelle juvénile était abondant dans la zone de l'étude, les taux de prises étaient sensiblement inférieurs (p <= 0,0005) à l'est du West Dock, ce qui suggérait que les poissons de petite taille se dirigeant vers l'est le long de la côte ne réussissaient pas à contourner le pont-jetée. En général, les conditions hydrographiques concordaient avec l'hypothèse que les remontées d'eau marine salée provoquées par le pont-jetée juste à l'ouest du West Dock peuvent affecter le mouvement le long du rivage. On n'a observé aucun écart de ce genre dans les prises au pont-jetée Endicott. On a étudié les taux de retour pour les jeunes adultes et les adultes (>= 250 mm) du cisco arctique et du cisco sardinelle, marqués dans la région de la baie de Prudhoe et recapturés dans une pêcherie commerciale en exploitation sur la rivière Colville en Alaska. On a comparé le taux de retour escompté aux taux de retour réels sur cinq ans (pour le cisco sardinelle) et sur six ans (pour le cisco arctique). Les taux de retour s'appuyaient sur trois zones de remise à l'eau: à l'est du pont-jetée le plus oriental, à l'ouest du plus occidental et entre les deux. En tenant compte des trois emplacements et de toutes les années, il n'y avait pas de différence marquante pour les deux espèces (p = 0,25 pour le cisco sardinelle; p = 0,30 pour le cisco arctique) entre les taux de retour prévus et les taux réels des individus marqués. On discute les effets opposés des deux ponts-jetées en considérant leur design et leur emplacement

Gamma ray monitoring of a AGN and galactic black hole candidates by the Compton Gamma Ray Observatory

The Compton Gamma-Ray Observatory's Burst and Transient Source Experiment (BATSE) has a powerful capability to provide nearly uninterrupted monitoring in the 25 keV-10 MeV range of both active galactic nuclei (AGN) and galactic black hole candidates (GBHC) such as Cygnus X-1, using the occultation of cosmic sources by the Earth. Since the Crab is detected by the BATSE Large Area Detectors with roughly 25(sigma) significance in the 15-125 keV range in a single rise or set, a variation by a factor of two of a source having one-tenth the strength of Cygnus X-1 should be detectable within a day. Methods of modeling the background are discussed which will increase the accuracy, sensitivity, and reliability of the results beyond those obtainable from a linear background fit with a single rise or set discontinuity