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Southwestern North America (southwestern + north_america)
Selected AbstractsAllometry, growth and population regulation of the desert shrub Larrea tridentataFUNCTIONAL ECOLOGY, Issue 2 2008A. P. Allen Summary 1Quantifying the effects of individual- and population-level processes on plant-community structure is of fundamental importance for understanding how biota contribute to the flux, storage and turnover of matter and energy in ecosystems. 2Here we synthesize plant-allometry theory with empirical data to evaluate the roles of individual metabolism and competition in structuring populations of the creosote Larrea tridentata, a dominant shrub in deserts of southwestern North America. 3At the individual level, creosote data support theoretical predictions with regard to the size dependence of total leaf mass, short-term growth rates of leaves and long-term growth rates of entire plants. Data also support the prediction that root,shoot biomass allocation is independent of plant size. 4At the population level, size,abundance relationships within creosote stands deviate strongly from patterns observed for steady-state closed-canopy forests due to episodic recruitment events. This finding highlights that carbon storage and turnover in water-limited ecosystems can be inherently less predictable than in mesic environments due to pronounced environmental forcing on demographic variables. 5Nevertheless, broad-scale comparative analyses across ecosystems indicate that the relationship of total abundance to average size for creosote populations adhere to the thinning rule observed and predicted by allometry theory. This finding indicates that primary production in water-limited ecosystems can be independent of standing biomass due to competition among plants for resources. 6Our synthesis of theory with empirical data quantifies the primary roles of individual-level metabolism and competition in controlling the dynamics of matter and energy in water-limited ecosystems. [source] Remote weather associated with North Pacific subtropical sea level high propertiesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2007Richard Grotjahn Abstract Remote events influencing North Pacific (NP) subtropical high properties in monthly and daily data are identified. Variability in the NP during summer is far more strongly dominated by midlatitude events than in South Pacific (SP); low-pass filtering is required to see tropical associations. The dominant pattern in composites, correlations, and regressions is a midlatitude wave train. A stronger NP high was led by higher sea-level pressure (SLP) just east of Japan and lower SLP over central Canada and to a lesser extent over western tropical Pacific. Various mechanisms have been proposed to force the NP high: (1)Heating over southwestern North America (with cooling off the west coast). However, higher temperatures over North America follow stronger SLP over the NP high and occur much further east than postulated. Higher SLP occurs where temperatures are lower over western North America and adjacent ocean. Thermal pattern is consistent with temperature advection between NP high and Canadian low. (2)Precipitation over and near Central America. However, SLP increase on the SE side of the high is led by higher SLP (and higher outgoing longwave radiation (OLR)) along the west coast of Mexico and Central America. Normalized regressions find a very weak lower OLR in North American monsoon preceding stronger NP high, but the region is much smaller in size and magnitude than other significant areas. (3)Precipitation over Indonesia and southeast Asia. Statistics provide some support for lower SLP and OLR over Indonesia preceding higher SLP in the center, west, and northwest sides of NP high. The lower SLP and OLR appear to migrate into southeast Asia, perhaps independently, perhaps from stronger NP high. (4)The NP high has a strong connection to El Niño during winter, but no significant link during summer. Only the south side of NP high appears (weakly) linked to the Madden Julian oscillation (MJO). Copyright © 2006 Royal Meteorological Society [source] A possible case of coccidioidomycosis from the Los Muertos site, Tempe, ArizonaINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 4 2006D. H. Temple Abstract Coccidioidomycosis is a fungal disease endemic to southwestern North America and parts of Central and South America. Coccidioidomycosis frequently disseminates to the human skeleton and produces mostly lytic skeletal lesions. However, this disease is infrequently described within archaeological populations. As a result, it is important to report potential cases in order to improve current understanding of the appearance and distribution of lesions resulting from coccidioidomycosis in archaeological specimens. This study describes skeletal lesions in an adult male recovered from the Los Muertos site, Tempe, Arizona (AD 500,1450). These lesions are present on the inferior border of the left scapular spine, the medial portion of the left first metacarpal head, and the medial portion of the right first metatarsal. The lesions are predominantly lytic with sclerotic and, in some cases, healed cortical bone distributed around their margins. Evidence of skeletal healing is recorded within the destructive focus of one lesion. Geographical information on pathogen endemism, overall lesion distribution, and agricultural-era Hohokom behaviour suggest that coccidioidomycosis is the most likely diagnostic option for these lesions. Mounting evidence for possible infections in the palaeopathological literature, combined with high frequencies of nutritional stress levels in endemic regions, suggests that coccidioidomycosis contributed at least moderately to morbidity in the American Southwest. Copyright © 2006 John Wiley & Sons, Ltd. [source] Molecular phylogenetic analysis of Leibnitzia Cass. (Asteraceae: Mutisieae: Gerbera -complex), an Asian,North American disjunct genusJOURNAL OF SYSTEMATICS EVOLUTION, Issue 3 2010Kristen E. BAIRD Abstract Leibnitzia comprises six species of perennial herbs that are adapted to high elevation conditions and is one of only two Asteraceae genera known to have an exclusively disjunct distribution spanning central to eastern Asia and North America. Molecular phylogenetic analysis of Leibnitzia and other Gerbera -complex members indicates that Leibnitzia is monophyletic, which is in contrast with our expectation that the American Leibnitzia species L. lyrata and L. occimadrensis would be more closely related to another American member of the Gerbera -complex, namely Chaptalia. Ancestral area reconstructions show that the historical biogeography of the Gerbera -complex mirrors that of the entire Asteraceae, with early diverging lineages located in South America that were followed by transfers to Africa and Eurasia and, most recently, to North America. Intercontinental transfer of Leibnitzia appears to have been directed from Asia to North America. Independent calibrations of nuclear (ribosomal DNA internal transcribed spacer region) and chloroplast (trnL,rpl32 intron) DNA sequence data using relaxed clock methods and either mean rate or fossil-based priors unanimously support Miocene and younger divergence times for Gerbera -complex taxa. The ages are not consistent with most Gondwanan vicariance episodes and, thus, the global distribution of Gerbera -complex members must be explained in large part by long-distance dispersal. American species of Leibnitzia are estimated to have diverged from their Asian ancestor during the Quaternary (ca. 2 mya) and either migrated overland to North America via Beringia and retreated southwards along high elevation corridors to their present location in southwestern North America or were dispersed long distance. [source] Adjustment of the atmospheric circulation to tropical Pacific SST anomalies: Variability of transient eddy propagation in the Pacific,North America sector,THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 647 2010R. Seager Abstract El Niño,Southern Oscillation (ENSO) related precipitation anomalies in North America are related to changes in the paths of storm systems across the Pacific Ocean, with a more southern route into southwestern North America during El Niños and a more northern route into the Pacific Northwest during La Niñas. Daily reanalysis data are analyzed to confirm these changes. Seasonal mean upper tropospheric eddy statistics show, for El Niños (La Niñas), a pattern that is shifted southward (northward) compared with climatology. Paths of coherent phase propagation of transient eddies and of the propagation of wave packets are analyzed. A coherent path of propagation across the Pacific towards North America is identified that is more zonal during El Niño winters and, during La Niñas, has a dominant path heading northeastward to the Pacific Northwest. A second path heading southeastward from the central Pacific to the tropical east Pacific is more accentuated during La Niñas than El Niños. These changes in wave propagation are reproduced in an ensemble of seasonal integrations of a general circulation model forced by a tropical Pacific sea-surface temperature pattern, confirming that the changes are forced by changes in the mean atmospheric state arising from changes in tropical sea-surface temperature. A simplified model with a specified basic state is used to model the storm tracks for El Niño and La Niña winters. The results suggest that the changes in transient eddy propagation and the eddy statistics can be understood in terms of the refraction of transient eddies within different basic states. Copyright © 2010 Royal Meteorological Society [source] | |||||||||||||