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The management of water resources in arid and semiarid areas has long been a challenge, from ancient Mesopotamia to the modern southwestern United States. As our understanding of the hydrological and climatological cycles has improved, and our ability to manipulate the hydrologic cycle has increased, so too have the challenges associated with managing a limited natural resource for a growing population. Modern civilization has made remarkable progress in water management in the past few centuries. Burgeoning cities now survive in desert regions, relying on a mix of simple and complex technologies and management systems to bring adequate water and remove wastewater. These systems have permitted agricultural production and urban concentrations to expand in regions previously thought to have inadequate moisture. However, evidence is also mounting that our current management and use of water is unsustainable. Physical, economic, and ecological limits constrain the development of new supplies and additional water withdrawals, even in regions not previously thought vulnerable to water constraints. New kinds of limits are forcing water managers and policy makers to rethink previous assumptions about population, technology, regional planning, and forms of development. In addition, new threats, especially the challenges posed by climatic changes, are now apparent. Sustainably managing and using water in arid and semiarid regions such as the southwestern United States will require new thinking about water in an interdisciplinary and integrated way. The good news is that a wide range of options suggest a roadmap for sustainable water management and use in the coming decades. climate change | soft path | freshwater | sustainability | water management doi/ 10.1073/pnas.1005473107

A key feature of anticipated 21st century droughts in Southwest North America is the concurrence of elevated temperatures and increased aridity. Instrumental records and paleoclimatic evidence for past prolonged drought in the Southwest that coincide with elevated temperatures can be assessed to provide insights on temperature-drought relations and to develop worst-case scenarios for the future. In particular, during the medieval period, ~AD 900-1300, the Northern Hemisphere experienced temperatures warmer than all but the most recent decades. Paleoclimatic and model data indicate increased temperatures in western North America of approximately 1[degrees]C over the long-term mean. This was a period of extensive and persistent aridity over western North America. Paleoclimatic evidence suggests drought in the mid-12th century far exceeded the severity, duration, and extent of subsequent droughts. The driest decade of this drought was anomalously warm, though not as warm as the late 20th and early 21st centuries. The convergence of prolonged warming and arid conditions suggests the mid-12th century may serve as a conservative analogue for severe droughts that might occur in the future. The severity, extent, and persistence of the 12th century drought that occurred under natural climate variability, have important implications for water resource management. The causes of past and future drought will not be identical but warm droughts, inferred from paleoclimatic records, demonstrate the plausibility of extensive, severe droughts, provide a long-term perspective on the ongoing drought conditions in the Southwest, and suggest the need for regional sustainability planning for the future. climate change | water resources | paleoclimatology | medieval period doi/ 10.1073/pnas.0911197107

The late Pleistocene witnessed the extinction of 35 genera of North American mammals. The last appearance dates of 16 of these genera securely fall between 12,000 and 10,000 radiocarbon years ago ([approximately equal to] 13,800-11,400 calendar years B.P.), although whether the absence of fossil occurrences for the remaining 19 genera from this time interval is the result of sampling error or temporally staggered extinctions is unclear. Analysis of the chronology of extinctions suggests that sampling error can explain the absence of terminal Pleistocene last appearance dates for the remaining 19 genera. The extinction chronology of North American Pleistocene mammals therefore can be characterized as a synchronous event that took place 12,000-10,000 radiocarbon years B.P. Results favor an extinction mechanism that is capable of wiping out up to 35 genera across a continent in a geologic instant. climate change | extraterrestrial impact | overkill | Quaternary extinctions | radiocarbon dates doi/10.1073/pnas.0908153106

Although the North American megafaunal extinctions and the formation of novel plant communities are well-known features of the last deglaciation, the causal relationships between these phenomena are unclear. Using the dung fungus Sporormiella and other paleoecological proxies from Appleman Lake, Indiana, and several New York sites, we established that the megafaunal decline closely, preceded enhanced fire regimes and the development of plant communities that have no modern analogs. The loss of keystone megaherbivores may thus have altered ecosystem structure and function by the release of palatable hardwoods from herbivory pressure and by fuel accumulation. Megafaunal populations collapsed from 14,800 to 13,700 years ago, well before the final extinctions and during the Bolling-Allerod warm period. Human impacts remain plausible, but the decline predates Younger Dryas cooling and the extraterrestrial impact event proposed to have occurred 12,900 years ago. 10.1126/science.1179504

Platycrinites is traditionally one of the more recognizable crinoids, a camerate crinoid with very few if any fixed brachials or interradials and a helically twisted column. Accordingly, many taxa have been assigned to this genus. With a better understanding of the Platycrinitidae, these characters actually unite the family Platycrinitidae rather than the genus. Further, use of different genus-diagnostic characters in Western Europe versus North America has resulted in a confused systematics for this important late Paleozoic family. Here, we objectively define genera within the Platycrinitidae and assign all species to either newly defined or newly named genera. A phylogenetic hypothesis, incorporating both parsimony-based character analysis and stratigraphic ranges, of the genera within the Platycrinitidae is presented. With consideration of the type species, Platycrinites laevis Miller, 1821, Platycrinites sensu stricto is distinguished from Platycrinites sensu lato, which is used for species that cannot be assigned with confidence to any objectively defined genus. New genera are Artaocrinus n. gen., Collicrinus n. gen., Elegantocrinus n. gen., and Laticrinus n. gen.; and Exsulacrinus Bowsher and Strimple, 1986 is designated a junior synonym of Platycrinites s.s. Collicrinus shumardi n. gen. and sp., Laticrinus oweni n. gen. and sp., and Laticrinus wachsmuthi n. gen. and sp. are described; and Platycrinitesformosus approximatus (Miller and Gurley, 1896a) is designated a junior synonym of Platycrinites formosus (Miller and Gurley, 1895a), which is reassigned here to Collicrinus n. gen. Platycrinites s.s. now includes 14 species and species-level taxa, and 76 species are assigned to Platycrinites s.l. Ten species are designated nomina dubia, as are taxa based solely on columnals or pluricolumnals. Two species are designated nomina nuda, and two are transferred to genera outside of the Platycrinitidae. In addition, twenty-seven species and four opennomenclature taxa are each reassigned to a different genus.

Early invasions of the North American shore occurred mainly via deposition of ballast rock, which effectively transported pieces of the intertidal zone across the Atlantic. From 1773-1861, >880 European ships entered Pictou Harbor, Nova Scotia, as a result of emigration and trade from Europe. The rockweed Fucus serratus (1868) and the snail Littorina littorea ([approximately equal to]1840) were found in Pictou during this same period. With shipping records (a proxy for propagule pressure) to guide sampling, we used F. serratus as a model to examine the introductions because of its relatively low genetic diversity and dispersal capability. Microsatellite markers and assignment tests revealed 2 introductions of the rockweed into Nova Scotia: 1 from Galway (Ireland) to Pictou and the other from Greenock (Scotland) to western Cape Breton Island. To examine whether a high-diversity, high-dispersing species might have similar pathways of introduction, we analyzed L. littorea, using cytochrome b haplotypes. Eight of the 9 Pictou hapiotypes were found in snails collected from Ireland and Scotland. Our results contribute to a broader understanding of marine communities, because these 2 conspicuous species are likely to be the tip of an 'invasion iceberg' to the NW Atlantic from Great Britain and Ireland in the 19th Century. Fucus serratus | Littorina littorea | propagule pressure

Although geneticists and archaeologists continue to make progress world-wide in documenting the time and place of the initial domestication of a growing number of plants and animals, far less is known regarding the critically important context of coalescence of various species into distinctive sets or complexes of domesticates in each of the world's 10 or more independent centers of agricultural origin. In this article, the initial emergence of a crop complex is described for one of the best-documented of these independent centers, eastern North America (ENA). Before 4000 B.P. there is no indication of a crop complex in ENA, only isolated evidence for single indigenous domesticate species. By 3800 B.P., however, at least 5 domesticated seed-bearing plants formed a coherent complex in the river valley corridors of ENA. Accelerator mass spectrometer radiocarbon dates and reanalysis of archaeobotanical assemblages from a short occupation of the Riverton Site in Illinois documents the contemporary cultivation at 3800 B.P. of domesticated bottle gourd (Lagenaria siceraria), marshelder (Iva annua var. macrocarpa), sunflower (Helianthus annuus var. macrocarpus), and 2 cultivated varieties of chenopod (Chenopodium berlandieri), as well as the possible cultivation of Cucurbita pepo squash and little barley (Hordeum pusillum). Rather than marking either an abrupt developmental break or a necessary response to population-packing or compressed resource catchments, the coalescence of an initial crop complex in ENA appears to reflect an integrated expansion and enhancement of preexisting hunting and gathering economies that took place within a context of stable long-term adaptation to resource-rich river valley settings. agriculture | archaeology | Chenopodium | domestication

The fossil assemblages of the Late Cretaceous of North America are dominated by large-bodied dinosaur species. Associated skeletons of small dinosaurs are exceedingly rare, and small ( Campanian | Dinosaur Park Formation | microraptorinae | theropoda

The Younger Dryas cold interval represents a time when much of the Northern Hemisphere cooled from [approximately equal to] 12.9 to 11.5 kiloyears B.P. The cause of this event, which has long been viewed as the canonical example of abrupt climate change, was initially attributed to the routing of freshwater to the St. Lawrence River with an attendant reduction in Atlantic meridional overturning circulation. However, this mechanism has recently been questioned because current proxies and dating techniques have been unable to confirm that eastward routing with an increase in freshwater flux occurred during the Younger Dryas. Here we use new geochemical proxies ([DELTA]Mg/Ca, U/Ca, and [sup.87]Sr/[sup.86]Sr) measured in planktonic foraminifera at the mouth of the St. Lawrence estuary as tracers of freshwater sources to further evaluate this question. Our proxies, combined with planktonic [[delta].sup.18][O.sub.seawater] and [[delta].sup.13]C, confirm that routing of runoff from western Canada to the St. Lawrence River occurred at the start of the Younger Dryas, with an attendant increase in freshwater flux of 0.06 [+ or -] 0.02 Sverdrup (1 Sverdrup = [10.sup.6] [m.sup.3]*[s.sup.-1]). This base discharge increase is sufficient to have reduced Atlantic meridional overturning circulation and caused the Younger Dryas cold interval. In addition, our data indicate subsequent fluctuations in the freshwater flux to the St. Lawrence River of [approximately equal to] 0.06-0.12 Sverdrup, thus explaining the variability in the overturning circulation and climate during the Younger Dryas. abrupt climate change | Atlantic meridional overturning circulation | paleoclimate

Cryptic invasions are a largely unrecognized type of biological invasion that lead to underestimation of the total numbers and impacts of invaders because of the difficulty in detecting them. The distribution and abundance of Phragmites australis in North America has increased dramatically over the past 150 years. This research tests the hypothesis that a non-native strain of Phragmites is responsible for the observed spread. Two noncoding chloroplast DNA regions were sequenced for samples collected worldwide, throughout the range of Phragmites. Modern North American populations were compared with historical ones from herbarium collections. Results indicate that an introduction has occurred, and the introduced type has displaced native types as well as expanded to regions previously not known to have Phragmites. Native types apparently have disappeared from New England and, while still present, may be threatened in other parts of North America.

The existence of strong summer thermal gradients in North America is investigated using palaeoecological methods. These gradients are believed to have been formed by the combination of high summer insolation and the presence of the Laurentide ice sheet during the period when the last glacial climate was shifting to the present interglacial climate. Reconstructions of temperature gradients for the late-glacial period in the study region are found to be much stronger than those of the modern period.

The Lagerstatte present on the Virginia-North Carolina border is composed of shales that contain many insect and plant fossils from the late Triassic era. The aquatic heteropterans and the auchenorrhyncans are the most abundant fossil insects. The shales also contain fossils of a nepomorph Heteroptera, a Psychodoidea and tetrapods, and a shark's tooth. The fossil of Crosaphis shows that the insect is a dipteran. Most of the plant fossils are of ferns, cycadeoids, and conifers.

Analysis of earthquakes in the Cascadia subduction zone, located along the Pacific coast of North America, was undertaken through two radiocarbon dating procedures and the use of several plant fossils. The magnitude of earthquakes was calculated through the study of the length of the fault rupture that occurred in prehistoric times. Results show that the region experienced its last rupture or series of ruptures, which extended around 55 km.,in the 16th century.

All species of North American marsupials from the Chadronian through Hemingfordian are reviewed. Most North American species of didelphids previously referred to Peratherium are allocated to Herpetotherium. Five species of Herpetotherium are recognized. The Chadronian Peratherium donahoei Hough is synonymized with Herpetotherium valens (Lambe). The Orellan species Herpetotherium stevensoni Cope is resurrected and referred, along with the Chadronian Peratherium titanelix Matthew, to a new genus, Copedelphys. Both Copedelphys and Herpetotherium can be derived from known Duchesnean species of Peratherium from North America. Two genera of peradectids are recognized, Nanodelphys McGrew and Didelphidectes Hough. Nanodelphys minutus is synonymized with 'Herpetotherium' hunti Cope and a second species of Nanodelphys is recognized from the Arikareean, though not named.

Colonies of the runner-like bryozoans Corynotrypa delicatula (James) and C. inflata (Hall) are common encrusters of Middle and Upper Ordovician shells and hardgrounds, especially in Cincinnatian deposits. The simplicity of their zooids contrasts with complexities in the dynamics of colonial organization. Both species have uniserial branches that bifurcate at intervals and, in addition, give rise periodically to lateral ramifications. Although angles of bifurcation and lateral ramification each average about 80 degrees, bifurcations and lateral ramifications are fundamentally different modes of branch multiplication. In C. delicatula new lateral branches have conspicuous secondary zones of astogenetic change distinguished by elongation of successively budded zooids. Unlike bifurcations, the first zooids in lateral branches in Corynotrypa are not linked to the parent branch by a narrow basal canal, and each new lateral branch can be regarded as a distinct subcolonial unit. The ancestrula, described here for the first time in an Ordovician species of Corynotrypa, has a poorly differentiated protoecium and initiates a primary zone of astogenetic change. Colony growth in Corynotrypa was more plastic than in many other bryozoan runners. The systematics of C. delicatula and C. inflata are revised, and a lectotype is chosen for the former species.

Conclusive proof of postcanine dental formula in an Early Cretaceous marsupial-like mammal, from the Early Cretaceous of the western US, is represented by a lower jaw with extraordinary wholeness. The new taxon lacks the twinning of the hypoconulid and entoconcid on lower molars, a characterstic specialization of marsupials. The unique marsupial dental formula evolved before the typical specialization of lower molars. Apomorphies are comparatively recent advances in marsupial history.

Lake salinity fluctuations indicate that intense droughts occurred frequently before AD 1200 in the Northern Great Plain (NGP) region of central North America. The intensities and frequencies of drought in the last 2300 years in the NGP is reconstructed using the Moon Lake salinity fluctuations as inferred from fossil diatom assemblages. These droughts continued for centuries and those during AD 200-370, AD 700-850 and AD 1000-1200 were the extreme ones. The low salinity after AD 1200 indicates that this period had been wetter and cooler than the preceding years.

In this study, the climatological stationary wave maintenance is examined from nonlinear perspective using the GFDL R30 GCM outputs, a fully nonlinear stationary wave model, and a linear stationary wave model. The primary focus of the study is on the nature of the stationary nonlinearity and relative contribution to the total nonlinearity by various factors, such as heating, orography, and the interaction between flows forced by heating and orography. It is found that both the nonlinear effect of the diabatic heating and the nonlinear interaction between flows forced by orography and diabatic heating are important contributors toward the total stationary nonlinearity in northern winter and summer. Some regional features, such as the anticyclone off the northwest coast of North America in winter and the southwestern U.S. summer anticyclone, are entirely due to the nonlinear interaction between flows forced by heating and orography. Consistent with the linear stationary wave maintenance, the diabatic heating is the most dominant forcing mechanism in the Tropics and the Southern Hemisphere (SH) throughout the seasonal cycle in the nonlinear framework. Over the Northern Hemisphere (NH) extratropics during northern winter, however, the role of the orographic forcing is comparable to that of diabatic heating due to its strong nonlinear interaction with flows forced by heating and transients. This contrasts significantly with the conclusion drawn from the direct nonlinear responses in which the orography is much less important than the diabatic heating. The regional feature of the ridge over northwestern North America in northern winter is found to be largely due to the presence of orography. The effect of transients in the nonlinear model, including the nonlinear interaction of transients with flows forced by heating and orography, shows a wave train over the Pacific-North American region (PNA) that resembles the atmospheric response to El Nino. This differs considerably from that in the linear view as well as that of the direct nonlinear response to transients. Furthermore, it is found that the inclusion of orography or transients in the total stationary wave forcing improves the spatial pattern simulation of the GCM stationary waves for both hemispheres in their respective winter months.

Two Amerindian demographic shifts are attributed to climate change in the northwest plains of North America: at [approximately equals] 11,000 calendar years before present (yr BP), Amerindian culture apparently split into foothills--mountains vs. plains biomes; and from 8,000-5,000 yr BP, scarce archaeological sites on the open plains suggest emigration during xeric 'Altithermal' conditions. We reconstructed paleoclimates from stable isotopes in prehistoric bison bone and relations between weather and fractions of [C.sub.4] plants in forage. Further, we developed a climate-change model that synthesized stable isotope, existing qualitative evidence (e.g., palynological, erosional), and global climate mechanisms affecting this midlatitude region. Our isotope data indicate significant warming from [approximately equals] 12,400 to 11,900 yr BP, supporting climate-driven cultural separation. However, isotope evidence of apparently wet, warm conditions at 7,300 yr BP refutes emigration to avoid xeric conditions. Scarcity of archaeological sites is best explained by rapid climate fluctuations after catastrophic draining of the Laurentide Lakes, which disrupted North Atlantic Deep Water production and subsequently altered monsoonal inputs to the open plains.

A collection of 57,877 conodont elements that includes 39 species representing 30 genera was made from the upper part of the Phragmodus undatus Zone and the lower part of the Plectodina tenuis Zone (late Turinian--early Chatfieldian). Conodont samples were collected from 30 sections in eastern North America and Baltoscandia, where the P. undatus--P, tenuis Zone boundary projects into B. alobatus Subzone based on K-bentonite bed correlation. Elements previously assigned to form-species of Oistodus are shown to be apparatus associates in coniform apparatuses of Besselodus. Pseudobelodina manitoulinensis new species is described and the apparatus-based taxonomy of Scyphiodus primus and Staufferella polonica are proposed.

Raveill, J. A. Department of Biology, Central Missouri State University. HYBRIDIZATION IN THE FLORA OF NORTH AMERICA. Hybridization in the flora of the North American continent was examined using published [...]

The high July solar-radiation levels at the time when the Laurentide ice sheet in northern North America existed resulted in uncommon climatic conditions that underwent significant changes over relatively short distances. A new study conducted by Levesque et al. that examined July temperature changes within a transect of five lakes located near a North American ice sheet revealed a remarkably sharp late-glacial climatic gradient.

The mountainous regions of western North America with a high gravitational potential energy (GPE) are extending, while those with a low GPE are contracting. The deformation, essentially a flow process, is due to stress and density distribution inside the continent. The deformation is greater in areas with a high temperature. The GPE of the mountains is similar to that in oceanic plates, but the mountains show greater deformation. The geophysical data shows that the mountains are too weak to be considered as a plate, and internal forces are an important parameter in tectonic reconstructions.

The genetic analysis of two North American species of Mimulus, monkeyflower, differing only in pollinators, shows that the floral morphology separating these species is due to comparatively few genetic changes, contrary to the common beliefs. The advantages of a large variety of DNA markers for genetic analysis, through molecular technology, should allow for further studies on the genetic foundation for adaptation and speciation on other plant species from which hybrids can be produced.