Controls on radial growth of mountain big sagebrush and implications for climate change

Mountain big sagebrush ( Artemisia tridentata Nutt. ssp. vaseyana ) covers large areas in arid regions of western North America. Climate-change models predict a decrease in the range of sagebrush, but few studies have examined details of predicted changes on sagebrush growth and the potential impacts of these changes on the community. We analyzed effects of temperature, precipitation, and snow depth on sagebrush annual ring width for 1969 to 2007 in the Gunnison Basin of Colorado. Temperature at all times of year except winter had negative correlations with ring widths; summer temperature had the strongest negative relationship. Ring widths correlated positively with precipitation in various seasons except summer; winter precipitation had the strongest relationship with growth. Maximum snow depth also correlated positively and strongly with ring width. Multiple regressions showed that summer temperature and either winter precipitation or maximum snow depth, which recharges deeper soil horizons, are both important in controlling growth. Overall, water stress and perhaps especially maximum snow depth appear to limit growth of this species. With predicted increases in temperature and probable reduced snow depth, sagebrush growth rates are likely to decrease. If so, sagebrush populations and cover may decline, which may have substantial effects on community composition and carbon balance.     

Competitive interactions between endangered kit foxes and nonnative red foxes

We investigated interference and exploitative competition between endangered San Joaquin kit foxes ( Vulpes macrotis mutica ) and nonnative red foxes ( V. vulpes ). Seven kit foxes and 16 red foxes were radio-collared and tracked via radiotelemetry near Lost Hills, California. One kit fox was killed by a red fox. Home ranges of the 2 species did not overlap extensively. Although both species used similar habitats, they used different parcels of land. Kit foxes and red foxes primarily consumed rodents on the study site, and dietary overlap was considerable. Red foxes also may have been using dens formerly used by kit foxes. Thus, red foxes were engaging in both interference and exploitative competition with kit foxes, and red foxes constitute a potentially significant threat to kit foxes. Coyotes ( Canis latrans ) co-occur with kit foxes and may limit red fox abundance and distribution. Therefore, although they occasionally kill kit foxes, the presence of coyotes may benefit kit foxes by excluding red foxes.     

Native plant community composition and genetic diversity associated with long-term weed invasions

Many studies have assessed genetic changes in exotic plant species in their native and introduced ranges, but none have focused on genetic variation in native plant species in response to exotic invasion. We examine characteristics of native plant communities within and outside old (> 25 year) invasions of Acroptilon repens (Russian knapweed) and Cardaria draba (hoary cress). We also document genetic variability of 4 native grass populations ( Hesperostipa comata [needle and thread], Achnatherum hymenoides [Indian ricegrass], Sporobolus airoides [alkali sacaton], and Poa secunda [Sandberg bluegrass]) from 2 areas: adjacent to and within weed invasions. Native plant species richness and diversity did not differ between invaded and noninvaded areas. Inter-simple sequence repeat (ISSR) analysis of individual native perennial grasses of each of the 4 species suggests that populations exposed to long-term coexistence with exotics may differ from adjacent noninvaded populations. We suggest that future research efforts should focus on intraspecific diversity of native plant species to identify possible candidates for restoration following weed control.     

Capture rates of reptiles and amphibians on black-tailed prairie dog ( Cynomys ludovicianus ) colonies and on uncolonized prairie in Colorado

Prairie dog eradication negatively affects dependent wildlife. Assessing the effects of prairie dog activities on reptiles and amphibians may depend upon the efficacy of trapping designs. We compared capture rates of reptiles and amphibians on black-tailed prairie dog ( Cynomys ludovicianus ) colonies and on adjacent uncolonized short-grass prairie, using funnel traps and pitfall traps with drift fences, as well as ground captures. We captured 152 reptiles and amphibians representing 10 species. We captured 51.3% of all reptiles and amphibians on colonies, compared to 48.7% from uncolonized sites. Overall, captures of reptiles and amphibians were similar on colonies and uncolonized sites for all capture methods combined. We achieved higher capture rates on uncolonized sites using funnel traps and pitfall traps but higher capture rates on colonies for ground captures. For all years on all sites combined, we captured significantly more animals in funnel traps (52.6%), surpassing pitfall trap captures (23.0%) and ground captures (24.3%). We recommend using multiple Y-shaped drift fence arrays ≥7.6 m in length, funnel traps with double-ended openings, and black-colored pitfall traps with opening diameters ≥30 cm.     

Jewish theologies of space in the scientific revolution: Henry More,Joseph Raphson,Isaac Newton and their predecessors

Theological speculations on God's relation to place and space were introduced into the Jewish tradition by the early rabbis, initially in response to the previous appearance of words like māqôm (place) in Biblical literature. In the Middle Ages, Jewish philosophers modified these rabbinical ideas in the context of Aristotelian, Neoplatonic, and anti-Aristotelian currents within Jewish thought. One development in medieval Jewish thought of special interest for the development of ideas of space was the rise of Cabala, which Christian thinkers of the Renaissance and early modern periods saw as a sacred and primeval deposit of wisdom akin to prisca theologia. Both Henry More and, under More's influence, Joseph Raphson made use of Cabalist ideas in developing their own theologies of space. Isaac Newton was aware of these Jewish ideas but for the most part repudiated them, while making some use of māqôm as an expression of God's omnipresence.     

Rare independent mutations in renal salt handling genes contribute to blood pressure variation

The effects of alleles in many genes are believed to contribute to common complex diseases such as hypertension. Whether risk alleles comprise a small number of common variants or many rare independent mutations at trait loci is largely unknown. We screened members of the Framingham Heart Study (FHS) for variation in three genes-SLC12A3 (NCCT), SLC12A1 (NKCC2) and KCNJ1 (ROMK)-causing rare recessive diseases featuring large reductions in blood pressure. Using comparative genomics, genetics and biochemistry, we identified subjects with mutations proven or inferred to be functional. These mutations, all heterozygous and rare, produce clinically significant blood pressure reduction and protect from development of hypertension. Our findings implicate many rare alleles that alter renal salt handling in blood pressure variation in the general population, and identify alleles with health benefit that are nonetheless under purifying selection. These findings have implications for the genetic architecture of hypertension and other common complex traits.     

Effect of natural iron fertilization on carbon sequestration in the Southern Ocean

The availability of iron limits primary productivity and the associated uptake of carbon over large areas of the ocean. Iron thus plays an important role in the carbon cycle, and changes in its supply to the surface ocean may have had a significant effect on atmospheric carbon dioxide concentrations over glacial-interglacial cycles. To date, the role of iron in carbon cycling has largely been assessed using short-term iron-addition experiments. It is difficult, however, to reliably assess the magnitude of carbon export to the ocean interior using such methods, and the short observational periods preclude extrapolation of the results to longer timescales. Here we report observations of a phytoplankton bloom induced by natural iron fertilization--an approach that offers the opportunity to overcome some of the limitations of short-term experiments. We found that a large phytoplankton bloom over the Kerguelen plateau in the Southern Ocean was sustained by the supply of iron and major nutrients to surface waters from iron-rich deep water below. The efficiency of fertilization, defined as the ratio of the carbon export to the amount of iron supplied, was at least ten times higher than previous estimates from short-term blooms induced by iron-addition experiments. This result sheds new light on the effect of long-term fertilization by iron and macronutrients on carbon sequestration, suggesting that changes in iron supply from below--as invoked in some palaeoclimatic and future climate change scenarios--may have a more significant effect on atmospheric carbon dioxide concentrations than previously thought.     

冷轧体心立方金属中微带的形成机制

该文对冷轧体心立方金属中微带的形成机制进行了探讨,利用塑性形变理论对轧制板材中晶粒的滑移系上的切应变进行了计祘,结果表明:当晶粒的<110>或<111>方向平行于轧制横向,轧制方向平行于某一特定方向时,大部份切变聚集在某一滑移面上,这样在该滑移面上便能形成微带,而这时微带与轧制方向之间的夹角约30°。计祘结果还表明:当轧制横向平行于晶粒的<110>或<111>方向时,晶粒在轧制时可能绕横向转动,这样,2套微带就可能形成。又由于双交滑移的存在,微带便呈现由双位错壁组成的片状结构。透射电子显微镜对微带的观察证实了这一结果。