The invariant distribution of wealth and employment status in a small open economy with precautionary savings

We study optimal savings in continuous time with exogenous transitions between employment and unemployment as the only source of uncertainty in a small open economy. We prove the existence of an optimal consumption path. We exploit that the dynamics of consumption and wealth between jumps can be expressed as a Fuchsian system. We derive conditions under which an invariant joint distribution for the state variables , i.e., wealth and labour market status, exists and is unique. We also provide conditions under which the distribution of these variables converges to the invariant distribution. Our analysis relies on the notion of T-processes and applies results on the stability of Markovian processes from Meyn and Tweedie (1993a, b,c)

Biomass Dynamics of Tipula (Insecta: Diptera) in Forested Streams of the Interior Highlands, Arkansas

Abundance patterns of aquatic macroinvertebrates that utilize coarse particulate organic matter as a food source are important indicators of non--point source pollution associated with silviculture activities. This group, referred to as shredders, typically decreases in abundance as its food source—primarily leaves—is removed from the ecosystem. We tested whether larval biomass of the crane fly Tipula, a common member of the group, was an effective estimator of shredder abundance. Additionally, we used regression analysis to test whether the length to dry mass relationship of Tipula differed among geographic regions, between seasons, and between years. Results did not indicate significant differences in the relationship among these variables. Thus, we concluded that a general length to dry mass relationship was appropriate for Tipula in streams of the Interior Highlands. Our results were similar to those reported from North Carolina and Virginia. Tipula biomass was positively correlated with the total richness of the macroinvertebrate assemblage, a common measurement of stream quality, but was not correlated with the numerical abundance of the shredder functional feeding group. Thus, we concluded that Tipula biomass would not be an effective surrogate for whole assemblage metrics in biological assessments

Vertical Migration, Orientation, Aggregation, and Fecundity of the Freshwater Mussel Lampsilis Siliquoidea

Author Institution: Department of Zoology, Miami UniversityThe decline in freshwater mussels makes it imperative that more information be gathered on their population status, behavior, and habitat requirements. We examined vertical migration, aggregation, and reproductive potential of captive and field populations of Lampsilis siliquoidea. Both captive populations and a field population exhibited vertical migration. This movement was strongly correlated with day length, and somewhat less strongly correlated with water temperature. While captive mussels tended to orient their siphons into the current, no pattern of orientation was detected in the field population. The field population was significantly aggregated in the fall and winter. The spatial patterning of captive mussels was random in the fall and winter, but this result may have been an artifact of the small size of the artificial streams. Weather conditions prevented data collection in the spring and, therefore, no conclusions could be drawn about the relationship between aggregation and glochidia release. The average number of glochidia (parasitic larvae) produced by individuals across a limited size range was not correlated with any maternal or marsupial properties. These results are useful for implementing qualitative sampling methods under optimum conditions and for information on the reproductive potential of Lampsilis siliquoidea

Qualitative Freshwater Mussel Survey of the South Fork Spring River, Missouri and Arkansas

A qualitative freshwater mussel survey was performed in the South Fork Spring River, Arkansas between May 13 and June 20, 2006 to assess community composition, density, and the presence of endangered mussel species (Family Unionidae). Twenty-one species from 460 individuals of mussels were collected using qualitative methods. Of those 21 species, 11 were ranked as S1, S2, or S3 using rankings established by the Arkansas Natural Heritage Commission Heritage Program. Three species, Amblema plicata (Say 1817), Lampsilis reeveiana (Call 1887), and Ptychobranchus occidentalis (Conrad 1836), comprised 48% of all mussels collected with 12%, 15%, and 21%, respectively. Mussel abundance within beds ranged between 2 to 33 individuals/site with an overall mean of 13 individuals/site. Selecting mussel beds for long-term monitoring in streams is necessary to assess population status and recruitment and to document success of future stream restoration projects

CMB Constraints on Primordial non-Gaussianity from the Bispectrum (f_{NL}) and Trispectrum (g_{NL} and \tau_{NL}) and a New Consistency Test of Single-Field Inflation

We outline the expected constraints on non-Gaussianity from the cosmic microwave background (CMB) with current and future experiments, focusing on both the third (f_{NL}) and fourth-order (g_{NL} and \tau_{NL}) amplitudes of the local configuration or non-Gaussianity. The experimental focus is the skewness (two-to-one) and kurtosis (two-to-two and three-to-one) power spectra from weighted maps. In adition to a measurement of \tau_{NL} and g_{NL} with WMAP 5-year data, our study provides the first forecasts for future constraints on g_{NL}. We describe how these statistics can be corrected for the mask and cut-sky through a window function, bypassing the need to compute linear terms that were introduced for the previous-generation non-Gaussianity statistics, such as the skewness estimator. We discus the ratio A_{NL} = \tau_{NL}/(6f_{NL}/5)^2 as an additional test of single-field inflationary models and discuss the physical significance of each statistic. Using these estimators with WMAP 5-Year V+W-band data out to l_{max}=600 we constrain the cubic order non-Gaussianity parameters \tau_{NL}, and g_{NL} and find -7.4 < g_{NL}/10^5 < 8.2 and -0.6 < \tau_{NL}/10^4 < 3.3 improving the previous COBE-based limit on \tau_{NL} < 10^8 nearly four orders of magnitude with WMAP.Comment: 15 pages. 14 figure

Mussel Inventory and Population Status of the Federally Endangered Potamilus capax (Green 1832) in the Tyronza River, Arkansas

Currently, few data exist for the mussel assemblages of the Tyronza River, Arkansas. The goal of this project was to inventory the freshwater mussel assemblages of the Tyronza River and determine the status of the federally endangered Potamilus capax. We qualitatively and quantitatively sampled mussel assemblages and documented the occurrence of S1 (extremely rare), S2 (very rare), and S3 (rare to uncommon) species. A total of 70.4 river kilometers were sampled in 2006 and 2007 resulting in 363 sampling sites, 4030 live individuals, and 25 species. We observed a total of 1 S1, 2 S2, and 9 S3 species. Mean catch-per-unit-of-effort was 0.9 (1.2 SD) individuals / min. and mean species richness and individual abundance were 3.4 (2.7 SD) species / site and 11.1 (15.1 SD) individuals / site, respectively. Thirteen Potamilus capax were collected during this survey, with only 1 gravid female and 2 juveniles. Quantitative survey mean densities per site ranged from 1.0 to 1.9 mussels / m2 with an overall mean of 1.4 individuals / m2 (0.3 SD). A total of 7 Potamilus capax were observed during quantitative sampling. Community Numerical Standing Crop estimates ranged from 70 ± 30 to 22,986 ± 7,905 individuals. The data collected from this survey provide a valuable baseline on the mussel assemblages of an altered-alluvial river and the location and status of all S1, S2 and S3 species. This information is essential to the management of this imperiled fauna in the Tyronza River

Species Richness, Distribution, and Relative Abundance of Freshwater Mussels (Bivalvia: Unionidae) of the Buffalo National River, Arkansas

The Buffalo River in north-central Arkansas is approximately 246 km long and flows through the Boston Mountains and Springfield and Salem Plateaus to the White River near Buffalo City. The Buffalo River is America’s first National River with the National Park Service owning 11% of land in the watershed. The objectives of this project were to survey the entire perennially wet length of river, search for mussels of conservation concern, and document the freshwater mussel assemblages. During 2004 and 2005, 235 km of the river were qualitatively and quantitatively surveyed. We documented 64 mussel assemblages. Time constrained qualitatively sampled assemblages (n=41) resulted in a mean richness of 7.8 with a range of 2 to 12 species. Quantitatively sampled mussel assemblages (n=23) had a mean richness of 9.5, ranging from 4 to 16 species and a mean density of 6.9 individuals/m2 , ranging from 1.3 to 25.6 individuals/m2 . Detrended correspondence analysis revealed 4 distinct community types dominated by: 1) Ptychobranchus occidentalis (Conrad 1836), 2) Villosa iris (Lea 1829), 3) Cyclonaias tuberculata (Rafinesque 1820), and 4) Actinonaias ligamentina (Lamarck 1819) that represented approximate species gradients along the river’s length. Previous surveys collectively recorded a total of 26 species for the river, however; only 23 species were identified in this survey with no federally listed threatened or endangered species found. The Buffalo National River has a moderately diverse and abundant native freshwater mussel fauna. Seventy-eight percent of the current species are considered to be of conservation concern (S1-S3). Consequently, the Buffalo National River may prove to be an important refuge for a declining mussel resource