Effects of predatory risk and resource renewal on the timing of foraging activity in a gerbil community

The foraging decisions of animals are often influenced by risk of predation and by the renewal of resources. For example, seed-eating gerbils on sand dunes in the Negev Desert of Israel prefer to forage in the bush microhabitat and during darker hours due to risk of predation. Also, daily renewal of seed resource patches and timing of nightly foraging activity in a depleting environment play important roles in species coexistence. We examined how these factors influence the timing of gerbil foraging by quantifying foraging activity in seed resource patches that we experimentally renewed hourly during the night. As in previous work, gerbils showed strong preference for the safe bush microhabitat and foraged less in response to high levels of illumination from natural moon light and from artificial sources. We demonstrate here for the first time that gerbils also responded to temporal and spatial heterogeneity in predatory risk through their timing of activity over the course of each night. Typically, gerbils concentrated their activity early in the night, but this changed with moon phase and in response to added illumination. These results can be understood in terms of the nature of patch exploitation by gerbils and the role played by the marginal value of energy in determining the cost of predation. They further show the dynamic nature of gerbil foraging decisions, with animals altering foraging efforts in response to time, microhabital, moon phase, illumination, and resource availability.     

Effects of kangaroo rat exclusion on vegetation structure and plant species diversity in the Chihuahuan Desert

Long-term (1977–90) experimental exclusion of three species of kangaroo rats from study plots in the Chihuahuan Desert resulted in significant increases in abundance of a tall annual grass (Aristida adscensionis) and a perennial bunch grass (Eragrostis lehmanniana). This change in the vegetative cover affected use of these plots by several other rodent species and by foraging birds. The mechanism producing this change probably involves a combination of decreased soil disturbance and reduced predation on large-sized seeds when kangaroo rats are absent. Species diversity of summer annual dicots was greater on plots where kangaroo rats were present, as predicted by keystone predator models. However, it is not clear whether this was caused directly by activities of the kangaroo rats or indirectly as a consequence of the increase in grass cover. No experimental effect on species diversity of winter annual dicots was detected. Our study site was located in a natural transition between desert scrub and grassland, where abiotic conditions and the effects of organisms may be particularly influential in determining the structure and composition of vegetation. Under these conditions kangaroo rats have a dramatic effect on plant cover and species composition.     

The enhanced infectivity of Metarhizium flavoviride in oil formulations to desert locusts at low humidities

Formulation in non-evaporative diluents such as oils is required to exploit the advantages of controlled droplet application methods for biopesticides based on conidial suspensions of entomopathogenic fungi. In laboratory assays on desert locusts (Schistocerca gregaria), formulations of Metarhizium flauoviride conidia in cotton seed oil showed superior performance to water-based suspensions and this was especially pronounced at low humidities (35% r.h.). The LD₅₀s for oil and water suspensions at 5 days were 8900 and > 10⁶ conidia/insect respectively. The dose-mortality regression line for oil was more than four times steeper and median lethal times were typically 76% of those for aqueous suspensions. Formulation in oil improves the efficacy of this fungus and may extend the application of species with lipophilic conidia into less humid agricultural environments.     

As above,not so below: Long-term dynamics of net primary production across a dryland transition zone

Drylands are key contributors to interannual variation in the terrestrial carbon sink, which has been attributed primarily to broad-scale climatic anomalies that disproportionately affect net primary production (NPP) in these ecosystems. Current knowledge around the patterns and controls of NPP is based largely on measurements of aboveground net primary production (ANPP), particularly in the context of altered precipitation regimes. Limited evidence suggests belowground net primary production (BNPP), a major input to the terrestrial carbon pool, may respond differently than ANPP to precipitation, as well as other drivers of environmental change, such as nitrogen deposition and fire. Yet long-term measurements of BNPP are rare, contributing to uncertainty in carbon cycle assessments. Here, we used 16 years of annual NPP measurements to investigate responses of ANPP and BNPP to several environmental change drivers across a grassland–shrubland transition zone in the northern Chihuahuan Desert. ANPP was positively correlated with annual precipitation across this landscape; however, this relationship was weaker within sites. BNPP, on the other hand, was weakly correlated with precipitation only in Chihuahuan Desert shrubland. Although NPP generally exhibited similar trends among sites, temporal correlations between ANPP and BNPP within sites were weak. We found chronic nitrogen enrichment stimulated ANPP, whereas a one-time prescribed burn reduced ANPP for nearly a decade. Surprisingly, BNPP was largely unaffected by these factors. Together, our results suggest that BNPP is driven by a different set of controls than ANPP. Furthermore, our findings imply belowground production cannot be inferred from aboveground measurements in dryland ecosystems. Improving understanding around the patterns and controls of dryland NPP at interannual to decadal scales is fundamentally important because of their measurable impact on the global carbon cycle. This study underscores the need for more long-term measurements of BNPP to improve assessments of the terrestrial carbon sink, particularly in the context of ongoing environmental change.     

库木塔格沙漠土壤细菌多样性及具有群体感应抑制活性放线菌筛选

【背景】群体感应抑制剂(quorum sensing inhibitor,QSI)作为抗生素潜在替代品,可有效降低致病菌传染性和毒性。沙漠土壤蕴藏着丰富的放线菌资源,是挖掘群体感应抑制剂的重要来源。【目的】解析库木塔格沙漠土壤细菌群落多样性,筛选并挖掘群体感应抑制活性放线菌资源。【方法】采用Illumina Nova Seq高通量测序技术揭示库木塔格沙漠土壤细菌群落组成,利用可培养方法进行土壤放线菌分离和鉴定;选用紫色杆菌CV026模型筛选群体感应抑制活性放线菌,并对其功能特性进行初步评价。【结果】Illumina Nova Seq高通量测序结果显示,样品土壤细菌涉及23门96目150属,优势菌门为变形菌门(Proteobacteria,61%)、放线菌门(Actinobacteria,28%),其中分枝杆菌属(Mycobacterium)为放线菌门最优势菌属(87.3%),其次为红球菌属(Rhodococcus,6.8%)和丙酸杆菌属(Cutibacterium,0.9%)。可培养方法共分离到108株放线菌,归属9科10属,其中优势菌属为链霉菌属(Streptomyces),占65....     

Reproductive patterns in annual legume species on an aridity gradient

Reproductive patterns are analysed in annual legumes of west Asia, and their relationships to increasing aridity determined by multivariate analysis. Dormancy, seed size, dispersal and fecundity are shown to be partially substitutable in terms of their effect on survival and population growth.The range of patterns show greatest diversity under mesic conditions in coastal, mediterranean areas with high winter rainfall, low incidence of frost and long growing season. Increasing aridity leads to increasing reproductive homogeneity, in which a subset of patterns-those composed of high levels of seed dormancy, high seed to pod ratios, restricted dispersal capabilities and early flowering-become predominant. These findings corroborate earlier theoretical and empirical evidence concerning desert annuals.The majority of widespread species are shown to possess arid-type patterns. This exerts considerable influence on both the type and degree of ecotypic differentiation within species. The only feature that responds consistently to climatic change is flowering time, particularly among species characterized by high seed dormancy. In the few widespread species that do not display arid-type characteristics, ecotypic differentiation appears more frequently in a larger suite of traits.The unequal environmental demands made on species showing different levels of dormancy (e.g. variation in length of growing season from year to year and place to place) leads to strong asymmetries governing the relationships between reproduction and ecological amplitude. In this respect arid-type strategists with high seed dormancy appear to have greater chances of expansion than others. This has implications when choosing pasture legumes to improve mediterranean grasslands.     

Plant species diversity and ecological districts of the Sinai desert

Summary Lists of vascular plant species for each of the 12 ecological districts of Sinai were prepared. In all 78,000 observations on altogether 812 species were analyzed. The number of districts where each species occurred was also counted. Linear regressions were calculated for the log-transformed values of species/area, species/altitude and multiple regression of species on both area and altitude.The regression of species on area for the 12 ecological districts of Sinai gave the equation: log S = 1.0309+0.3 log A The value of z=0.3 is higher than 0.222—the measured overall value for the continents and higher than the values for the Sahara, California mainland, the British Isles, and the Netherlands. However, it is lower than the values for the Galápagos Archipelago and the California Islands.The number of species supported in districts characterized by fissured limestone, gravel plains, chalk, marl, sandstones, sands or fissured magmatic and metamorphic rocks is close to the regression of species on area, whereas large outcrops of smooth-faced rocks are relatively richer in total number of species as well as in stenotople species.It is suggested that the high gamma diversity of Sinai as compared with other parts of the world is primarily due to its environmental heterogeneity. Sinai being a meeting place of three phytogeographical regions and to past climatic changes. The effect of smooth-faced rock outcrops as conducive to providing refugia must also be taken into account.This work is based on a comprehensive study of the vegetation of Sinai directed by Prof. G. Orshan, with the collaboration of Dr. A. Shmida, the present author and the late Prof. N.H. Tadmor and Dr. G. Halevy.     

塔里木沙拐枣果实刺毛对果实扩散及萌发的影响

塔里木沙拐枣（Calligonum roborowskii A.Los.）是仅分布于我国西北地区荒漠环境的特有种,其果实为不开裂而周围有椭圆形刺毛的瘦果,以果实为单元进行扩散和萌发。本文采用野外观察与室内控制实验相结合的方法,对塔里木沙拐枣刺毛在果实扩散、吸水、脱水及萌发中的作用进行研究。结果显示：不同贮藏时间的果实颜色、大小、重量及刺毛长度存在显著差异。完整果实在水面漂浮时间及水媒扩散能力比去除刺毛的果实更强。完整果实在1 m/s和4 m/s风速下的扩散距离比无刺毛果实的扩散距离长。10 mmol/L赤霉素（AG₃）及不同干藏时间处理的完整果实与无刺毛果实在20℃/30℃光照和黑暗条件下的萌发率间存在显著差异,其中无刺毛果实的萌发率要高于完整果实的萌发率。室外盆栽实验显示,无刺毛果实的萌发率比完整果实高,说明果实刺毛对果实萌发有抑制作用。研究结果表明果实刺毛对塔里木沙拐枣在塔克拉玛干沙漠边缘荒漠环境中的扩散、萌发及种群更新具有重要的辅助作用。     

Edaphic factors and plant species distribution in a protected area in the desert of Bahrain Island

Effects of edaphic factors (salinity, pH, Na⁺, K⁺, Ca⁺⁺, CaCO₃, water holding capacity, and grain size) on the spatial distribution of plants were investigated. Soil was sampled at 22 stands. Sixteen plant species were recorded from these stands. Relation between edaphic factors and plant distribution was investigated using correlation statistical analysis. Distribution of some plants was found to be highly correlated with edaphic factor(s).     

Adaptive phenology of desert and Mediterranean populations of annual plants grown with and without water stress

Summary The dynamics of vegetative and reproductive growth were compared in matched pairs of Mediteranean and desert populations of three unrelated annual species, Erucaria hispanica (L.) Druce, Brachypodium distachyon (L.) Beauv. and Bromus fasciculatus C. Presl., under high and low levels of water availability in a common-environment experiment. Plants of all desert populations showed earlier switches to reproductive development and to subsequent phenophases, and the transition to flowering occurred at smaller plant sizes. Water stress had no effect (E. hispanica) or slightly accelerated the transition to flowering in B. fasciculatus (by 1–2 days) and in B. distachyon (by 4–6 days). Plant senescence was strongly enhanced by water stress, and this enhancement was greater in desert populations than in corresponding Mediterranean ones. Duration of life cycle was greatly shortened by water stress in all three species. Desert and Mediterranean populations of the three species exhibited small differences in their relative response, i.e. phenotypic plasticity, to water stress for phenological and plant size parameters. In E. hispanica and B. fasciculatus the population x water regime interaction amounted to less than 3% of total variance. By contrast, the Mediterranean population of B. distachyon was much more plastic in its response to water stress than the desert population in its transition to plant senescence. Plants from the desert populations appeared to be adapted to shorter, more compact growth cycles, culminating in earlier dates of seed maturation and plant senescence. In addition, they showed larger phenotypic plasticity in the transition to plant senescence, which trait was enhanced or magnified by sustained or repeated lack of water. By contrast, plants from Mediterranean populations delayed switchover from one phenophase to the next, seeming thus to bet on more water being forthcoming.