A constrained least-squares approach to combine bottom-up and top-down CO2 flux estimates

Terrestrial CO₂ flux estimates are obtained from two fundamentally different methods generally termed bottom-up and top-down approaches. Inventory methods are one type of bottom-up approach which uses various sources of information such as crop production surveys and forest monitoring data to estimate the annual CO₂ flux at locations covering a study region. Top-down approaches are various types of atmospheric inversion methods which use CO₂ concentration measurements from monitoring towers and atmospheric transport models to estimate CO₂ flux over a study region. Both methods can also quantify the uncertainty associated with their estimates. Historically, these two approaches have produced estimates that differ considerably. The goal of this work is to construct a statistical model which sensibly combines estimates from the two approaches to produce a new estimate of CO₂ flux for our study region. The two approaches have complementary strengths and weaknesses, and our results show that certain aspects of the uncertainty associated with each of the approaches are greatly reduced by combining the methods. Our model is purposefully simple and designed to take the two approaches’ estimates and measures of uncertainty at ‘face value’. Specifically, we use a constrained least-squares approach to appropriately weigh the estimates by the inverse of their variance, and the constraint imposes agreement between the two sources. Our application involves nearly 18,000 flux estimates for the upper midwest United States. The constrained dependencies result in a non-sparse covariance matrix, but computation requires only minutes due to the structure of the model.     

Experimental evidence that workers recognize reproductives through cuticular hydrocarbons in the ant Odontomachus brunneus

Eusociality is characterized by a reproductive division of labor, wherein workers respond to the presence of reproductive individuals by refraining from reproduction themselves and restricting the reproductive efforts of others. Our understanding of how eusociality is maintained therefore depends on characterizing the mechanism by which workers detect the presence of a reproductive. Variations in cuticular hydrocarbons correspond to changes in reproductive ability in ants, and experimental studies are beginning to reveal the function of hydrocarbons as signals. In this study, we compare the cuticular hydrocarbon profiles of dominant and reproductive workers and queens of the ant Odontomachus brunneus with profiles of non-reproductive workers. Using split/reunification tests we document the existence of worker policing in both queenless and queenright colonies; supernumerary reproductives were treated aggressively by nestmates. Finally, we induce aggression and replicate queen-like submissive nestmate responses by supplementing the hydrocarbon profile of workers with (Z)-9-nonacosene, a compound that was significantly more abundant on the cuticles of reproductives. In three bioassays, we compare this manipulation to various control manipulations of the hydrocarbon profile and demonstrate that workers gauge the reproductive activity of nestmates through changes in their cuticular hydrocarbon profiles.     

A test for space limitation with an application to recently settled lobsters

Space limitation in larval settlement can play an important role in the population dynamics of marine species. A novel statistical test for space limitation based on quadrat counts of individuals is described. The test is based on identifying a significant relationship between the relative dispersion of quadrat counts and overall mean density. An application to a time series of quadrat counts of recently settled American lobsters Homarus americanus covering the period 1993–2007 in Casco Bay, Maine, USA (43°45′N; 69°58′W), is presented. For this data set, the null hypothesis that space is not limiting could not be rejected (P = 0.10).     

Soil nutrient supply modulates temperature-induction cues in mast-seeding grasses

Synchronous and intermittent reproduction in long-lived plants, known as mast seeding, is induced by climatic cues, but the mechanism explaining variation in masting among neighboring but edaphically segregated species is unknown. Soil nutrients can enhance flowering, and thus, populations on nutrient-rich soils may require less-favorable growing temperatures to flower. We tested this hypothesis by predicting the probability of flowering in response to air temperature for five species of alpine Chionochloa grasses in South Island, New Zealand, over 37 years and relating our predictions to soil N supply (NH4(+) + NO3(-)). Summer air temperatures better predicted flowering than spring air temperatures, which were correlated with soil N mineralization. Species on N-rich soils required lower mean temperatures to induce flowering and/or responded more consistently across a gradient of air temperatures, contributing to the higher probability of their tillers and tussocks flowering at low summer temperatures. Our results suggest that flowering primarily occurs in response to warm summer temperatures, but species on N-rich soils require less favorable growing conditions because they invest relatively less N in seeds. Thus, predicting masting requires a consideration of the interactions among climate, the internal resources of plants, and mineral nutrient uptake.     

Unintended consequences of price controls: An application to allowance markets

Price controls established in a cap-and-trade allowance market are intended to reduce cost uncertainty by constraining allowance prices between a ceiling and floor; however, they could provide opportunities for strategic actions by firms that would lower government revenue and increase emissions. In particular, when the ceiling price is supported by introducing new allowances into the market, firms could choose to buy allowances at the ceiling price, regardless of the prevailing market price, in order to lower the equilibrium price of all allowances. Those purchases could either be transacted by firms intending to manipulate the market price or be induced through the introduction of inaccurate information about the cost of emissions abatement. Theory and simulations using allowance elasticity estimates for U.S. firms suggest that the manipulation could be profitable under the stylized setting and assumptions evaluated in the paper, although in practice many other conditions will determine its use.     

Height-growth response to climatic changes differs among populations of Douglas-fir: a novel analysis of historic data

Projected climate change will affect existing forests, as substantial changes are predicted to occur during their life spans. Species that have ample intraspecific genetic differentiation, such as Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), are expected to display population-specific growth responses to climate change. Using a mixed-effects modeling approach, we describe three-year height (HT) growth response to changes in climate of interior Douglas-fir populations. We incorporate climate information at the population level, yielding a model that is specific to both species and population. We use data from provenance tests from previous studies that comprised 236 populations from Idaho, Montana, and eastern Washington, USA. The most sensitive indicator of climate was the mean temperature of the coldest month. Population maximum HT and HT growth response to changes in climate were dependent on seed source climate. All populations had optimum HT growth when transferred to climates with warmer winters; those originating in sites with the warmest winters were taller across sites and had highest HT growth at transfer distances closest to zero; those from colder climates were shortest and had optimum HT growth when transferred the farthest. Although this differential response damped the height growth differences among populations, cold-climate populations still achieved their maximum growth at lower temperatures than warm-climate populations. The results highlight the relevance of understanding climate change impacts at the population level, particularly in a species with ample genetic variation among populations.     

Human lung injury following exposure to humic substances and humic-like substances

Among the myriad particles the human respiratory tract is exposed to, a significant number are distinctive in that they include humic substances (HS) and humic-like substances (HULIS) as organic components. HS are heterogeneous, amorphous, organic materials which are ubiquitous occurring in all terrestrial and aqueous environments. HULIS are a complex class of organic, macromolecular compounds initially extracted from atmospheric aerosol particles which share some features with HS including an aromatic, polyacidic nature. As a result of having a variety of oxygen-containing functional groups, both HS and HULIS complex metal cations, especially iron. Following particle uptake by cells resident in the lung, host iron will be sequestered by HS- and HULIS-containing particles initiating pathways of inflammation and subsequent fibrosis. It is proposed that (1) human exposures to HS and HULIS of respirable size (<10 µm diameter) are associated with inflammatory and fibrotic lung disease and (2) following retention of particles which include HS and HULIS, the mechanism of cell and tissue injury involves complexation of host iron. Human inflammatory and fibrotic lung injuries following HS and HULIS exposures may include coal workers’ pneumoconiosis, sarcoidosis, and idiopathic pulmonary fibrosis as well as diseases associated with cigarette smoking and exposures to emission and ambient air pollution particles.     

Linking predator and prey behaviour: contrasts between Antarctic fur seals and macaroni penguins at South Georgia

Antarctic fur seals Arctocephalus gazella and macaroni penguins Eudyptes chrysolophus are the two main land-based krill Euphausia superba consumers in the northern Scotia Sea. Using a combination of concurrent at-sea (predator observations, net hauls and multi-frequency acoustics), and land-based (animal tracking and diet analysis) techniques, we examined variability in the foraging ecology of these sympatric top predators during the austral summer and autumn of 2004. Krill availability derived from acoustic surveys was low during summer, increasing in autumn. During the breeding season, krill occurred in 80% of fur seal diet samples, with fish remains in 37% of samples. Penguin diets contained the highest proportion of fish in over 20 years of routine monitoring (46% by mass; particularly the myctophid Electrona antarctica), with krill (33%) and amphipods (Themisto gaudichaudii; 21%) also occurring. When constrained by the need to return and feed their offspring both predator species foraged to the northwest of South Georgia, consistent with an area of high macrozooplankton biomass, but fur seals were apparently more successful at exploiting krill. When unconstrained by chick-rearing (during March) penguins foraged close to the Shag Rocks shelf-break, probably exploiting the high daytime biomass of fish in this area. Penguins and seals are able to respond differently to periods of reduced krill abundance (in terms of variability in diet and foraging behaviour), without detriment to the breeding success of either species. This highlights the importance of myctophid fish as an alternative trophic pathway for land-based predators in the Scotia Sea ecosystem.     

Interaction between herbivore defense and microbial signaling: bacterial quorum-sensing compounds weaken JA-mediated herbivore resistance in Nicotiana attenuata

Bacteria play important roles in plant–herbivore interactions and communicate with each other with chemical signals, often N-acylhomoserine lactones (AHL). Plant responses to these signals may influence resistance to microbial attack, but the effects of these signals on herbivore defense are unstudied. To determine whether AHL influence jasmonate (JA)-mediated herbivore resistance in Nicotiana attenuata, we treated wild-type (WT) and JA-deficient genotypes (antisense expression of NaLOX3) with N-hexanoyl-dl-homoserine lactone (C6-HSL) and measured the performance of Manduca sexta larvae. Larval mass gain on C6-HSL-treated WT plants was equivalent to that on non-treated NaLOX3-silenced plants, but significantly 4.1-fold larger than on untreated WT plants. Mass gain was unaffected by C6-HSL treatment of NaLOX3-silenced plants. Microarray analysis of the plants elicited with C6-HSL and JA inducing fatty acid–amino acid conjugates revealed a down-regulation of a proteinase inhibitor in the C6-HSL-treated WT plants. The results therefore suggest that the increased performance of M. sexta was due to direct or indirect effect of C6-HSL on JA-mediated defenses.     

Semiparametric space–time survival modeling of chronic wasting disease in deer

In this paper, we propose a semiparametric survival model to investigate the pattern of spatial and temporal variation in disease prevalence of chronic wasting disease (CWD) in wild deer in Wisconsin over the years 2002 and 2006. The semiparametric survival model we suggested allows to build a more flexible model than the parametric model with fewer parametric assumptions by modeling the baseline hazard using a Gamma process prior. Based on the proposed model, we investigate the geographical distribution of CWD, and assess the effect of sex on disease prevalence. We use a Bayesian hierarchical framework where latent parameters capture temporal and spatial trends in disease incidence, incorporating sex and spatially correlated random effects. We also propose bivariate baseline hazard which change over age and time simultaneously to adopt different effects of age and time on the baseline hazard. Inference is carried out by using MCMC simulation techniques in a fully Bayesian framework. Our results suggest that disease has been spreaded mainly in the disease eradication zone and male deer show a significantly higher infection probability than female deer.