Search

Two-sex populations are usually studied through frequency-dependent models that describe how sex ratio affects mating, recruitment and population growth. However, in two-sex populations, mating and recruitment should also be affected by density and by its interactions with the sex ratio. Density may have positive effects on mating (Allee effects) but negative effects on other demographic processes. In this study, we quantified how positive and negative inter-sexual interactions balance in two-sex populations. Using a dioecious grass (Poa arachnifera), we established experimental field populations that varied in density and sex ratio. We then quantified mating success (seed fertilization) and non-mating demographic performance, and integrated these responses to project population-level recruitment. Female mating success was positively density-dependent, especially at female-biased sex ratios. Other demographic processes were negatively density-dependent and, in some cases, frequency-dependent. Integrating our experimental results showed that mate-finding Allee effects dominated other types of density-dependence, giving rise to recruitment that increased with increasing density and peaked at intermediate sex ratios, reflecting tension between seed initiation (greater with more females) and seed viability (greater with more males). Our results reveal, for the first time, the balance of positive and negative inter-sexual interactions in sex-structured populations. Models that account for both density- and sex ratio dependence, particularly in mating, may be necessary for understanding and predicting two-sex population dynamics.

Pairwise comparisons of the individual studies, NMA plots and results for those outcomes not included in the main text. (DOCX 2566 kb)

Summary tables of included and excluded study characteristics [47–60]. (DOCX 87 kb)

Litigation challenging the legality of an Internal Revenue Service rule that became final on May 2012 has traveled a long, winding, and contentious path. The IRS rule authorized the distribution of federal premium assistance tax credits in all health benefits exchanges under the Patient Protection and Affordable Care Act of 2010 (the “ACA”). However, potential legal problems with reconciling various sections of the final legislation involving those tax credits were identified as early as December 6, 2010. On September 19, 2012, the first of four different legal challenges to the IRS rule was filed in federal district court in Oklahoma. In 2013, subsequent lawsuits were filed in three different federal district courts in the District of Columbia, Virginia, and Indiana. After a mixed record of wins and losses in those lower courts, King v. Burwell became the first case to reach the Supreme Court

A state space model is constructed so that a state variable representing the unobservable state of the economy is estimated from information on new orders, production, employment, supplier delivery time, and finished inventory obtained from the purchasing managers’ sur-vey for Georgia. This state variable captures the co-movements of the time series used in its construction and serves as an economic indicator for Alabama, Florida, Georgia, North Caro-lina, South Carolina, and Tennessee. Even though this economic indicator is estimated from information from the purchasing managers’ survey on manufacturing activity for just Geor-gia, it produces reasonable forecasts for the real growth rates of the gross domestic products of Alabama, Florida, Georgia, North Carolina, South Carolina, and Tennessee for 1991 through 2008.

This article presents an overview of the air to ground lasercom demonstration performed under the Free-Space Optical Communications Airborne Link (FOCAL) program. Techniques used to mitigate fading, demonstrated in 2008 and reported earlier, are reviewed as are the basic equipment approach, also reported earlier. We overview the new results for tracking, fiber coupling, channel measurements and communications performance for the air-to-ground link.

An extensive karst developed on Cretaceous limestones in Belize, Central America, was the site of a hydrochemical, hydrologic, and morphologic study. This thesis describes the results of analysis of several hundred water samples from this humid tropical environment (mean annual rainfall - 2376 mm; temperature - 24.5°C). An unusual positively correlated discharge/total hardness loading curve in a major cavern conduit is explained as due to a two-component mixing model. Hydrologic modelling, soil CO₂ sampling, and discriminant analysis were used to infer the interior structure of a karst aquifer. Minimum effective porosity was determined to be 0.7%. Mean areal hardness of 187 mg/L (as CaCO₃) was found for springs draining the aquifer, indicating a denudation rate of about 90 m³/Km²/year. Aqueous Pco₂ of these springs was 1.1%, significantly higher than the 0.7% of mean karst soil CO₂ levels. This implies open system calcite solution evolution and/or internal CO₂ production within the aquifer. Various morphologic analyses suggest the cockpit-type surfaces of numerous karsts in the tropics may be significant due to disaggregation of existing topographic lows originally formed by creation of a fluvial topography. These fluvial valleys acted as favorable sites for concentration of aggressive water and consequent cockpit formation. Over 40 km of cavern passage were explored in the Caves Branch, including one of the largest tropical cavern systems known. Cavern development appeared to have been chiefly influenced by regional fracture patterns and topographic dip. The present development was completed by at least 140,000-215,000 years B.P., according to results of speleothems dated by the uranium/thorium disequilibrium method. Doctor of Philosophy (PhD)