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PubMed2005

Permian tetrapods from the Sahara show climate-controlled endemism in Pangaea.

New fossils from the Upper Permian Moradi Formation of northern Niger provide an insight into the faunas that inhabited low-latitude, xeric environments near the end of the Palaeozoic era (approximately 251 million years ago). We describe here two new temnospondyl amphibians, the cochleosaurid Nigerpeton ricqlesi gen. et sp. nov. and the stem edopoid Saharastega moradiensis gen. et sp. nov., as relicts of Carboniferous lineages that diverged 40-90 million years earlier. Coupled with a scarcity of therapsids, the new finds suggest that faunas from the poorly sampled xeric belt that straddled the Equator during the Permian period differed markedly from well-sampled faunas that dominated tropical-to-temperate zones to the north and south. Our results show that long-standing theories of Late Permian faunal homogeneity are probably oversimplified as the result of uneven latitudinal sampling.

Amphibians↗
PubMed2004

Modelling the impact of climate change on woody plant population dynamics in South African savanna.

BACKGROUND: In Southern Africa savannas climate change has been proposed to alter rainfall, the most important environmental driver for woody plants. Woody plants are a major component of savanna vegetation determining rangeland condition and biodiversity. In this study we use a spatially explicit, stochastic computer model to assess the impact of climate change on the population dynamics of Grewia flava, a common, fleshy-fruited shrub species in the southern Kalahari. Understanding the population dynamics of Grewia flava is a crucial task, because it is widely involved in the shrub/bush encroachment process, a major concern for rangeland management due to its adverse effect on livestock carrying capacity and biodiversity. RESULTS: For our study we consider four climate change scenarios that have been proposed for the southern Kalahari for the coming decades: (1) an increase in annual precipitation by 30-40%, (2) a decrease by 5-15%, (3) an increase in variation of extreme rainfall years by 10-20%, (4) and increase in temporal auto-correlation, i.e. increasing length and variation of periodic rainfall oscillations related to El Nino/La Nina phenomena. We evaluate the slope z of the time-shrub density relationship to quantify the population trend. For each climate change scenario we then compared the departure of z from typical stable population dynamics under current climatic conditions. Based on the simulation experiments we observed a positive population trend for scenario (1) and a negative trend for scenario (2). In terms of the projected rates of precipitation change for scenario (3) and (4) population dynamics were found to be relatively stable. However, for a larger increase in inter-annual variation or in temporal auto-correlation of rainfall population trends were negative, because favorable rainfall years had a limited positive impact due to the limited shrub carrying capacity. CONCLUSIONS: We conclude that a possible increase in precipitation will strongly facilitate shrub encroachment threatening savanna rangeland conditions and regional biodiversity. Furthermore, the negative effects found for positive auto-correlated rainfall support current ecological theory stating that periodically fluctuating environments can reduce population viability because species suffer disproportionately from poor environmental conditions.

Biodiversity↗
PubMed1997

Identity and biodegradative abilities of yeasts isolated from plants growing in an arid climate.

Plants harvested in the Canary Islands Lanzarote and Fuerteventura were analyzed for the yeasts inhabiting their surface. Half of the isolates (22 out of 44) were identified as Debaryomyces hansenii. Black ascomycetes, viz. Hortaea werneckii and two Hormonema species were represented by 7 strains. Basidiomycetous yeasts, viz. Cryptococcus sp. (8 strains), Rhodotorula sp. (5 strains), Cerinosterus cyanescens (1 strain) and Pseudozyma sp. (1 strain) constituted a minority of 33%. Thirty strains were screened for their ability to assimilate various plant constituents including lipids of the cuticle and the cell membrane, hemicelluloses, nitrogenous compounds (protein, nucleic acids, amino acids) and benzene compounds. All strains were able to assimilate or to hydrolyze lipids, lecithin included. Many strains of D. hansenii, H. dematioides, H. werneckii, C. cyanescens, Cr. laurentii, Pseudozyma sp. and Rh. glutinis were proteolytic. Hemicelluloses like xylan and pectin were assimilated by black ascomycetous yeasts, Cryptococcus sp., Pseudozyma sp. and Rh. glutinis. Ferulic and hydroxycinnamic acids, gallic and tannic acids were assimilated by some strains of H. dematioides, C. cyanescens, Pseudozyma sp. and Rhodotorula sp.

Amino Acids↗
PubMedDate not supplied

Allergenic pollen in the subdesert areas of the Iberian peninsula.

The yearly distribution of Artemisia and Chenopodiaceae-Amaranthaceae, two of the most common types of pollen in a rural area located in the southeastern part of the Iberian peninsula, was studied over a 3-year period (1995-1997). The particular bioclimatic conditions of the area, such as its subdesert climate, extreme dryness and high mountain location (1,000 m above sea level), have led to the adaptation and abundance of these species in this area. They usually flower in the second half of the year, and are the main pollen types collected in the samples in that time period. The Artemisia pollen levels recorded are the highest in Spain, since there are several species in the area which flower at different times. Chenopodiaceae-Amaranthaceae pollen counts are also very high. The severity of both pollen types was also analyzed. The height of the sampler was taken into account because the quantities at human height can be considerably higher than those recorded at 20 m off the ground. It was concluded that both pollen types should be considered some of the main causes of allergy in this area.

Air Pollution↗
PubMed2003

Evaluation of landfill leachate in arid climate-a case study.

Generation of leachate from municipal solid waste (MSW) landfill in arid regions has long been neglected on the assumption that minimal leachate could be formed in the absence of precipitation. Therefore, a case study was conducted at two unlined MSW landfills, of different ages, in the state of Kuwait in order to determine the chemical characteristics of leachate and examine the mechanism of leachate formation. Leachate quality data were collected from both active and old (closed) landfills where co-disposal of MSW and other solid and liquid wastes is practiced. The analysis of data confirms that leachates from both landfills are severely contaminated with organics, salts and heavy metals. However, the organic strength of the leachate collected from the old landfill was reduced due to waste decomposition and continuous gas flaring. A significant degree of variability was encountered and factors which may influence leachate quality were identified and discussed. A water balance at the landfill site was assessed and a conceptual model was presented which accounts for leachate generation due to rising water table, capillary water and moisture content of the waste.

Chemical Precipitation↗
PubMed1999

Considerations for the control of equine cyathostomes in arid areas.

Internal parasites of horses are ubiquitous but that does not suppose that the level of infection does not vary with climatic conditions. Climate determines the limits of where a parasite species can survive the external environment and weather determines the transmission pattern within the climatic bounds [Levine, N.D., 1963. Adv. Vet. Sci. 8, 215-261]. Arid areas have a more limited exposure potential to important parasites but the level of exposure can nonetheless lead to disease. It must be remembered that, even in arid areas, it does rain and irrigation, overflow from water troughs, dew dripping off buildings and on the vegetation can also provide the medium to allow escape of larval cyathostomes from feces to forage. How horses earn their living is most important in determining the level of exposure to cyathostomes. Recreational grazing, which surely does more for the soul of the owner than for the nutrition of the horse, almost absolutely insures that horses will encounter larvae. To be certain, in arid areas there may be an opportunity for horses to spatially separate grazing and dunging areas but not all horses are so disposed, and even if they are they may not be able to do so.

Animals↗
PubMedDate not supplied

[Effect of climate of arid zone on adaptive and non-adaptive changes in microcirculation].

State of microcirculatory bed of the bulbar conjunctiva and nail wall skin has been studied in 134 men (18-28 years old) of native (62 men) and non-native (72 men) population. It was found out that under heat discomfort the compensation is observed in native population due to the induration of the capillary network, opening of plasmatic capillaries which did not function before, tonus of venules and arterioles being preserved while the amount of "gigantic" capillaries increased. In this case the blood flow was entire, uniform and moderately accelerated. The number of functioning capillaries does not increase in non-native population, but arterioles does not increase in non-native population, but arterioles and venules were dilated, blood flow in them became more rapid, sludge-phenomenon of the I stage being observed in some people. Consequently, the observed changes in microcirculation under heat discomfort are insignificant in the native population due to available structure-morphological potentialities, while in non-native population these changes are accompanied by certain strain at the expense of available functional reserves.

Adaptation, Physiological↗
PubMed2002

Growth and reproductive characteristics of the columnar cactus Stenocereus queretaroensis and their relationships with environmental factors and colonization by arbuscular mycorrhizae.

Three natural populations of pitayo (Stenocereus queretaroensis (Weber) Buxbaum), a columnar arborescent cactus, were studied in their subtropical environments in western Mexico. All of the sites were characterized by shallow, nutrient-poor soils. Percentage of colonization by arbuscular mycorrhizae (AM) fungi, stem growth, fruit mass, and percentage germination were greater in S. queretaroensis at Autlan, Jalisco (AJ) than at Zacoalco de Torres, Jalisco (ZTJ) or Santa Rosa, Zacatecas (SRZ). The onset of root colonization by arbuscular mycorrhizae during the middle of the summer wet period preceded increases in stem extension rate and stem phosphorus concentration. Based on previous studies of effects of environmental factors on photosynthesis, climatic conditions were more favorable for photosynthesis at AJ than at SRZ and ZTJ, as indicated by the amount of summer rainfall, the amount of light, and the moderate air temperatures that prevailed during the fall and winter seasons. There was a significant positive correlation between stem growth and percentage of total root length colonized by arbuscules of AM fungi for S. queretaroensis at SRZ and AJ, but not at ZTJ. A negative significant correlation was observed between stem growth and maximal and minimal air temperatures at the three study sites. Stem growth was positively related to rainfall only at SRZ, and light was statistically related to stem growth only at ZTJ. Among sites, S. queretaroensis at AJ had the highest carbon gain and greatest AM colonization, creating physiological conditions that led to the highest stem growth, fruit mass and percentage of seed germination.

Cactaceae↗
PubMed2004

Landfarm performance under arid conditions. 1. Conceptual framework.

The primary disposal method for oily sludge in the Kingdom of Saudi Arabia, which is a major oil-exporting country in the world, is landfarming. It is an attractive method of oily sludge disposal in hot arid climatic conditions. Although landfarming technology was introduced to Saudi Arabia in 1982, no scientific studies have been conducted within the Kingdom to support this decision. The results presented in this paper are based on a comprehensive field experiment conducted under Saudi Arabian environmental conditions. Details of experimental setup and conceptual framework of degradation process based on field observations are presented in this paper. The paper also addresses kinetics of oily sludge degradation in landfarm cells under natural and enhanced conditions in the presence of water, nutrients, and tilling. The 12-month field study showed that weathering (evaporation) and not biodegradation is the overall dominant degradation mechanism occurring in landfarms in the study area. The results of this study showed that up to 76% of the oil and grease (O&G) in the sludge has been lost from soil as a result of weathering. However, the results of this study also indicated the primary mechanism for the loss of C17 and C18 alkanes as compared to branched alkanes was due to biodegradation.

Biodegradation, Environmental↗
PubMed2006

Predicted performance of clay-barrier landfill covers in arid and semi-arid environments.

Conventional landfill cover systems for municipal solid waste include low-permeability compacted clay barriers to minimize infiltration into the landfilled waste. Such layers are vulnerable in climates where arid to semi-arid conditions prevail, whereby the clay cover tends to desiccate and crack, resulting in drastically higher infiltration, i.e., lower cover efficiency. To date, this phenomenon, which has been reported in field observations, has not been adequately assessed. In this paper, the performance of a cover system solely relying on a clay barrier was simulated using a numerical finite element formulation to capture changes in the clay layer and the corresponding modified hydraulic characteristics. The cover system was guided by USEPA Subtitle-D minimum requirements and consisted of a clay layer underlying a protective vegetated soil. The intrinsic characteristics of the clay barrier and vegetative soil cover, including their saturated hydraulic conductivities and their soil-water characteristic curves, were varied as warranted to simulate intact or "cracked" conditions as determined through the numerical analyses within the proposed methodology. The results indicate that the levels of percolation through the compromised or cracked cover were up to two times greater than those obtained for intact covers, starting with an intact clay hydraulic conductivity of 10(-5)cm/s.

Aluminum Silicates↗
PubMed2002

Agricultural sustainability in a sensitive environment--a case analysis of Loess Plateau in China.

Loess Plateau, an arid and semi-arid region in Northwest China, is well-known for its most serious soil erosion in terms of sediment yield each year. Soil erosion, which is intensified by agricultural activities, is the major factor influencing sustainable agriculture development in this region. It reduces productivity by removing nutrients and especially reducing water availability that is essential for crop production in the area. It also brings about off-site costs by demanding more efforts for maintenance of banks and dams along Yellow River through raising the riverbed with sediment. Climate is capricious and extreme weather conditions occur frequently, which impairs normal agricultural production with erosion and also decrease of water availability. Extensive way of farming still dominates on the Loess Plateau, which cannot produce satisfying economic results and needs to be improved or altered. Conventional agricultural production pattern needs to be reconsidered for husbandry has not been granted its due position. Agriculture is the backbone of economy. Poor agricultural production impedes economic development and vice versa, backward economy also influences the advancement of agriculture. Besides a large population, education status of farmers is another threshold that requires being resolved for a sustainable agriculture. Although conventional agriculture has been practiced there for more than 5000 years, now it cannot meet the demand for food and fiber by the increasing population and some of its farming practices are contributing to environmental degradation directly or indirectly and can sustain no longer. Agriculture on Loess Plateau needs to find its own way of sustainability. To work toward a sustainable agriculture, chances and challenges both indwell on Loess Plateau.

Agriculture↗
PubMed1975

Characteristics of chronic bronchitis in a warm, dry region.

Subjects residing in the warm, dry climate of Tucson, Arizona showed the same relationship of productive cough to smoking as noted elsewhere, but they less regularly reported seasonal or diurnal exacerbations of their symptoms and they less regularly reported phlegm production along with chronic cough. In this locale, even nonchronic dry cough was associated with an increased frequency of other respiratory symptoms and of ventilatory impairment. In comparing characteristics of subjects with a clinical diagnosis of chronic bronchitis with characteristics of subjects who had only questionnaire-detected chronic productive cough, it was found that smoking habits were more closely related to the presence of chronic cough than to the clinical diagnosis. The clinical diagnosis was associated with other features, such as wheezing, at least as often as with productive cough. This was especially true in children, in whom a suprisingly high prevalence of both chronic cough and clinically confirmed chronic bronchitis was noted. These observations led to questions concerning the appropriateness of using a common clinical term such as chronic bronchitis to describe subjects whose only known abnormality is an affirmative answer to a direct question concerning phlegm production.

Adolescent↗
PubMed2005

Bioremediation of oil refinery sludge by landfarming in semiarid conditions: influence on soil microbial activity.

Bioremediation of a refinery sludge containing hydrocarbons in a semi-arid climate using landfarming techniques is described. The objective of this study was to assess the ability of this technique to reduce the total hydrocarbon content added to the soil with the refinery sludge in semiarid climate (low rain and high temperature). In addition, we have evaluated the effect of this technique on the microbial activity of the soil involved. For this, biological parameters (carbon fractions, microbial biomass carbon, basal respiration and ATP) and biochemical parameters(different enzymatic activities) were determined. The results showed that 80% of the hydrocarbons were eliminated in eleven months, half of this reduction taking place during the first three months. The labile carbon fractions, MBC, basal respiration and ATP of the soils submitted to landfarming showed higher values than the control soil during the first months of the process, although these values fell down by the end of the experimental period as the hydrocarbons were degraded by mineralisation. All the enzymatic activities studied: oxidoreductases such as dehydrogenase activity, and hydrolases of C(beta-glucosidase activity) and N Cycle (urease and protease) showed higher values in the soils amended with the refinery sludge than in the control. As in the case of the previous parameters, these value fell down as the bioremediation of the hydrocarbons progressed, many of them reaching levels similar to those of the control soil after eleven months.

Biodegradation, Environmental↗
PubMed1998

Host range and the maintenance of Haemonchus spp. in an adverse arid climate.

Three Haemonchus species (Haemonchus contortus, Haemonchus placei and Haemonchus longistipes) live in sympatry in Sahelian areas such as Mauritania (West Africa). Four host species (dromedary, zebu cattle, sheep and goats) share the same pastures for several months per year. Experimental infection by H. contortus or H. placei was achieved only poorly in dromedaries, and H. contortus or H. longistipes infection failed to establish in zebu cattle. Conversely, H. placei and H. longistipes successfully infected sheep and goats. Under field conditions, mixed congeneric infections were very rare in dromedaries but frequent in zebu cattle (H. contortus represented 16% of Haemonchus spp. burden), in sheep (H. placei: 15%) and in goats (H. placei: 9% and H. longistipes: 6% of worms). The importance of the different host species was evaluated for Haemonchus spp.: small ruminants are the main hosts of H. contortus, dromedaries harboured the large majority of H. longistipes worms but 5% of them were found in goats which seemed to be additional hosts. The most striking finding was the role played by the small ruminants in the survival strategy of H. placei in Sahelian regions: 56% of the total of H. placei worms were found in sheep, 34% in goats and only 10% in zebu cattle. These results are consistent with the hypothesis that the extension of host range plays an important role in the survival strategy of H. placei, whereas H. longistipes or H. contortus might well survive utilising their usual hosts.

Animals↗
PubMed2003

[A research review on "fertile islands" of soils under shrub canopy in arid and semi-arid regions].

Due to the inclemency of climate and soil conditions and the intense disturbance of human beings, the soil resources heterogeneity in arid and semi-arid grassland ecosystems worldwide was gradually increased during the last century. The interaction between soil heterogeneity and shrubs induced the autogenic development of "fertile islands" and the increasing spread of shrubs in the grassland ecosystems. The development of "fertile islands" around individual shrubs could change the vegetation composition and structure, as well as the distribution patterns of soil resources, and thus, reinforced the changes of the ecosystem function and structure from a relative stable grassland ecosystem to a quasi-stable shrubland ecosystem. The study of "fertile islands" phenomenon would help us to understand the causes, consequences and processes of desertification in arid and semi-arid areas. In this paper, the causes of "fertile islands", its study methods and significance and its relationship with shrub spreading as well as the responses of vegetation to it were summarized. The problems which might occur in the study of this phenomenon were also pointed out. Our aim was to offer some references to the study of land desertification processes and vegetation restoration in the arid and semi-arid regions.

Desert Climate↗
PubMed2003

Evolution of subterranean diving beetles (Coleoptera: Dytiscidae: Hydroporini, Bidessini) in the arid zone of Australia.

Calcrete aquifers in arid inland Australia have recently been found to contain the world's most diverse assemblage of subterranean diving beetles (Coleoptera: Dytiscidae). In this study we test whether the adaptive shift hypothesis (ASH) or the climatic relict hypothesis (CRH) is the most likely mode of evolution for the Australian subterranean diving beetles by using a phylogeny based on two sequenced fragments of mitochondrial genes (CO1 and 16S-tRNA-ND1) and linearized using a relaxed molecular clock method. Most individual calcrete aquifers contain an assemblage of diving beetle species of distantly related lineages and/or a single pair of sister species that significantly differ in size and morphology. Evolutionary transitions from surface to subterranean life took place in a relatively small time frame between nine and four million years ago. Most of the variation in divergence times of the sympatric sister species is explained by the variation in latitude of the localities, which correlates with the onset of aridity from the north to the south and with an aridity maximum in the Early Pliocene (five mya). We conclude that individual calcrete aquifers were colonized by several distantly related diving beetle lineages. Several lines of evidence from molecular clock analyses support the CRH, indicating that all evolutionary transitions took place during the Late Miocene and Early Pliocene as a result of aridification.

Adaptation, Biological↗
PubMed2000

Genetic and environmental effects on the productivity of Holstein-Friesian cattle under the climatic conditions of central Sudan.

A herd of 370 Holstein-Friesian cows were maintained in Central Sudan, Khartoum for intensive dairy production during the period 1990-1996. The area is characterized by high temperatures during the day and cools down at night, with an average thermal-humidity index (THI) of 74.8. The average adjusted lactation milk yield, milk yield per day, milk yield per day of calving interval and lactation length of the animals in the herd were 5117 +/- 123 (SE) kg, 14.7 +/- 0.25 kg, 11.3 +/- 0.36 kg and 350 +/- 8.0 days, respectively. Heifers calved at 25.2 +/- 2.3 (SD) months of age. The variation was large, which suggested large environmental fluctuations. Sire variance contributed 1.35% and 19.6% to the total variance in cows and heifers, respectively, while cow within sire contributed 19%. The heritabilities of total lactation yield, 305-day yield, milk per day of lactation, milk per day of calving interval, and lactation length in heifers were 0.78 +/- 0.24, 0.36 +/- 0.34, 0.39 +/- 0.24, 0.23 +/- 0.23, and 0.23 +/- 0.22, respectively. In cows, the heritability estimates were 0.05 +/- 0.24, 0.06 +/- 0.24, 0.08 +/- 0.24, 0.00 and 0.00 for the same traits, respectively. The repeatabilities of total lactation yield, 305-day yield, milk per day, milk per day of calving interval and lactation length were 0.02 +/- 0.03, 0.22 +/- 0.03, 0.17 +/- 0.02, 0.05 +/- 0.02 and 0.00, respectively. Regression analysis showed that, for each unit increase in THI, milk yield decreased by 0.29 +/- 0.04 kg. The stress usually caused by the combined effects of temperature and humidity was not severe in this area.

Animal Husbandry↗
PubMed1996

Adaptation to arid environment: Haemonchus longistipes in dromedaries of Saharo-Sahelian areas of Mauritania.

The adaptations of the trichostrongylid nematode Haemonchus longistipes of dromedaries (Camelus dromedarius) to the harsh environment of Saharo-Sahelian climate were assessed by means of (i) an epidemiological survey of dromedary infection in the south-west of Mauritania, (ii) an estimate over a 3 year period of parasite distribution within the host population and of prolificacy of H. longistipes females recovered from natural populations of infected dromedaries sampled at Nouakchott's slaughterhouse, and (iii) experimental infections of young dromedaries during three different periods of the year (end of the rainy season, middle and end of the dry season). Egg excretions (estimated by faecal egg counts), infective larvae derived from eggs as well as female prolificacy showed a marked seasonal pattern: high values in the rainy season and very low values in the dry season (especially March and April). Female prolificacy differed slightly between morphotypes: the knobbed type excreting over a longer period than the linguiform and smooth types. Following experimental infections in young dromedaries, arrest of larval development took place irrespective of the period. The survival strategy of H. longistipes in the dry season was based only on arrested larval development. Patent infections occurred from July to October, i.e. during the rainy season and was facilitated by the conjunction of high prevalence and intensity of adult worm burdens associated with high female prolificacy.

Adaptation, Physiological↗