The ants of the southern Sonoran desert: community structure and the role of trees

In contrast to other North American deserts, the southern Sonoran desert is dominated by trees that provide shaded microhabitats necessary for the establishment and survival of several plant species. Near the southern limit of the Sonoran desert in Sonora, Mexico, we evaluated the role that tree microhabitats may play in structuring ant communities. We recorded 39 species and 21 genera of ants from a 9.7-ha area. Total species richness was estimated to be between 47 and 49 species, a much greater species richness than that reported for other North American arid-zone habitats. Although species richness did not differ between open ground and tree-shaded microhabitats, species composition did. Opportunistic species, Camponotus species, Pheidole sciophila and P. titanis were more common near trees, whereas Pheidole sp. A and granivorous species were more active in open areas. The imperilment of trees in the Sonoran desert due to commercial cutting and the spread of buffelgrass Pennisetum ciliare may alter the existing composition of ant communities.     

短命植物分布与沙垄表层土壤水分的关系——以古尔班通古特沙漠为例

于2002年3月至2002年8月,对古尔班通古特沙漠南部短命植物分布和沙垄表层30cm厚土壤水分间的关系进行了系统监测和研究．结果表明,早春表层土壤水分在个体沙丘表面的分异直接影响到短命植物的分布．4月下旬,垄间、两坡和垄顶土壤含水率依次为4．62％、3．98％和2．01％,相应的短命植物平均盖度于5月中上旬依次为51．8％、38．2％和4．4％．5月中旬后,短命植物的分布又改变了表层土壤水分分布,上述各地貌部位的土壤含水率依次为1．0096、1．9096和2．45％,形成垄顶最高、两坡次之、垄间最差的新的空间分布格局。     

Habitat segregation based on soil texture and body size in the seed‐harvester ants Pogonomyrmex rugosus and P. barbatus

1. The seed‐harvester ants Pogonomyrmex rugosus and P. barbatus are ecologically equivalent sister species that have broadly overlapping distributions in the south‐western U.S.A.; however the two species are only sympatric in localised contact zones. 2. Soil regimes at 25–50 cm below the surface were quantified across contact zones to assess abiotic habitat factors related to distribution pattern. Physiological parameters related to foundress survival were also measured in order to test for a correlation between these parameters and distribution pattern. 3. The two species segregated among microhabitats based on soil texture; P. barbatus occurred alone in soils with a higher clay content and/or higher moisture retention. In areas of sympatry, soil texture was similar for both species but was intermediate to that in areas where the two species occurred allopatrically. The pattern of microhabitat segregation was similar across three sites that encompassed a broad range of soil regimes. 4. The only measure of foundress survival correlated with microhabitat differences was an ≈ 8% greater dry mass for alate females of P. rugosus. This resulted in their surviving significantly longer than did alate females of P. barbatus under desiccating conditions. 5. This microdistribution pattern may be caused indirectly by soil texture affecting plant species distribution and hence the seeds available to ants. A companion laboratory experiment demonstrated, however, that soils could also cause this distribution pattern of both ant species directly via effects on foundress wet mass.     

Community organization and species richness of ants (Hymenoptera/Formicidae) in Mongolia along an ecological gradient from steppe to Gobi desert

Aim Ants (Hymenoptera/Formicidae) have strong influences on ecosystems especially in arid regions. However, little is known about ants of the vast steppe and desert regions of Central Asia. Here we provide the first comprehensive study of ant communities in Mongolia, conducted along a north‐to‐south gradient in climate. We examined ants’ distribution patterns, assessed the impact of climatic parameters on community structure and species diversity and investigated the influence of the corresponding communities of plants. Location Mongolia (Central Asia). Methods We observed 31,956 ants at seed baits at 11 study sites along a transect from steppe to Gobi desert for which we attained meteorological data (mean yearly precipitation: 197 to 84 mm). Extra sampling was conducted at sugar and protein baits and by the inspection of different microhabitats. Vegetation patterns of each plot were recorded. Statistical evaluation comprised ordination and correlation. Results We observed 15 species of ants at seed baits. Three faunal complexes of ants could be distinguished by detrended correspondence analysis (DCA): (1) in steppe baits were dominated by Formica‐ and Myrmica‐species, (2) in semi desert we found mostly species of Tetramorium, Myrmica, Proformica, Plagiolepis, and Leptothorax, and (3) in desert Cataglyphis aenescens and Messor aciculatus dominated, and Lasius was exclusively found there. Another 11 rare ant species were sampled by hand and at sugar baits. Altogether five ant species were new to the Mongolian fauna: Cardiocondyla koshewnikovi, Myrmica koreana, Myrmica pisarskii, Polyergus nigerrimus, and Proformica kaszabi. Assignment of taxa to functional groups showed that in steppe cold climate specialists dominated, in semi desert we found mainly opportunists, and in desert hot climate specialists. Several functional groups know from arid zones in other parts of the world were missing. In desert certain species were highly dominant. First DCA scores of ant‐ and plant‐communities were highly correlated with each other and with climatic parameters. While plant species diversity was positively correlated with increasing northern latitude, ant diversity and ant species richness were not correlated with latitude and responded neither to precipitation, nor to any other climatic parameter. Semi desert was a transition zone between steppe and desert, with high species richness. Ant genus composition of the ecotone overlapped with both other regions. However, beta diversity between pairs of plots within this zone was low, indicating a small‐scale mosaic pattern. Main conclusions The ant communities in the Mongolian steppe and desert zones were strongly influenced by low temperatures and differed in many aspects from the ant fauna in other arid ecosystems, especially in terms of species richness, diversity of feeding guilds, and richness of functional groups.     

Influence of temporal fluctuations in seed abundance on the diet of harvester ants (Pogonomyrmex spp.) in the central Monte desert,Argentina

Harvester ants usually go through temporal fluctuations in environmental seed abundance and composition which could influence their behaviour and ecology. The aim of this study was to evaluate how these fluctuations influence the diet of Pogonomyrmex rastratus, P. pronotalis and P. inermis (Hymenoptera, Formicidae) in the central Monte desert during three consecutive growing seasons. Although seeds were the main item in the diet, these ants turned more generalist when seed abundance of the most consumed species (grasses Aristida spp., Trichloris crinita, Pappophorum spp., Digitaria californica and Stipa ichu) was low. Accordingly, diversity of items in the diet decreased with seed abundance in a logarithmical fashion, showing higher foraging efficiency for seeds at higher seed abundance. Seed diversity, however, was not related to seed abundance as ants always included several species in their diet, with alternating prevalence. The proportion of the most consumed species increased logarithmically in the diet of P. rastratus and P. pronotalis along with their abundance in the environment probably as a consequence of diet switching (from forb and shrub seeds to grass seeds) and by an increase in foraging efficiency at higher seed densities. In contrast, foraging activity of P. inermis was very low at low seed abundance and its diet included only the five grasses. Among the most consumed species, proportion in the diet was not associated with relative abundance in the environment. Aristida spp., Pappophorum spp. and D. californica were overall highly selected. However, the flexibility in the diet of P. pronotalis and P. rastratus and the low foraging activity of P. inermis during periods of low resource abundance could attenuate potential top‐down effects in the central Monte desert. This study shows that bottom‐up effects are important in ant‐seed interactions and should be considered when predicting and evaluating ants' effects on seed resources.     

Influence of temporal fluctuations in seed abundance on the foraging behaviour of harvester ants (Pogonomyrmex spp.) in the central Monte desert,Argentina

The simultaneous study of the temporal dynamics of foraging behaviour, diet and seed abundance is essential to assess the way in which resources affect the behaviour and ecology of harvester ants. Here, we evaluate how fluctuations in grass seed abundance during three consecutive growing seasons influenced the foraging behaviour and diet of the harvester ants Pogonomyrmex rastratus, P. mendozanus and P. inermis in the central Monte desert, Argentina. Seed abundance of the most consumed grasses varied greatly through ant activity season, and ants altered their foraging behaviour in response to those changes. Foragers spent more time travelling and searching for food, and their foraging trips took longer during the low seed availability season. Foraging distance was very similar among species and, contrary to our expectations, did not vary between seasons. Foraging success of P. rastratus and P. inermis increased during the high availability season. This matched the seasonal pattern of foraging activity, suggesting that colonies may detect seed abundance and regulate their foraging effort with the rate of forager success. Although grass seeds were the main item in the diet of the three species, P. mendozanus, and to a lesser extent P. rastratus, turned more generalist when grass seeds were scarce. In contrast, P. inermis showed a very narrow diet breadth, only harvesting grass seeds in both seasons. Our results indicate the relevance of seed availability on foraging behaviour of harvester ants, which should be taken into account when predicting and evaluating the effect of ants on seed resources as well as numerical responses of harvester ant populations to the temporal and spatial variations in grass seed abundance.     

阿拉善荒漠区一年生植物层片物种多样性及其分布特征

一年生植物层片是阿拉善荒漠区荒漠与绿洲生态系统的恒有植物层片,对荒漠生态系统的稳定和当地畜牧业的生产都有重要作用．对该层片的物种多样性及其在群落中的分布特征分析表明,荒漠与绿洲生态系统中,一年生植物层片植物种有12科35属61种,可归为一年生小禾草、一年生猪毛菜、一年生蒿类和一年生杂类草4个类群,并可划分成12种区系地理成分,其中有10个阿拉善或近阿拉善特有种．一年生植物层片广泛分布于土质、沙砾质、沙质、砾质、石质、盐土荒漠及各种类型的绿洲群落中,常一种或几种组成层片,均匀或斑块状分布,或沿水线分布．此外,还分析和评价了一年生植物层片在群落中的分布差异、生态适应模式与功能．     

The influence of soil texture on the soil water dynamics and vegetation structure of a shortgrass steppe ecosystem

We analyzed soil water data from three sites with different soil textures in the shortgrass steppe of northeastern Colorado, USA. Our objective was to evaluate the relationship between the occurrence of plant functional types and the effect of soil texture on soil water availability. Soil water availability was greatest in the upper soil layers at all three sites, but the loamy sand site had significantly greater soil water availability than the sandy clay loam and sandy clay sites in wetter years at depths below 60 cm. Calculations of proportional water availability by layer using both field data and fifty-year soil water model simulations, showed that the sandy clay loam and sandy clay soils on average had greater water availability in layers 30 cm and above, but that the loamy sand had the greatest water availability in layers beneath this, particularly at 105 cm. This observation can be linked to the occurrence of a fine textured subsoil at this site. The textural pattern in the loamy sand profile effectively creates two water resources: a shallow pool accessible to all plants; and a deep pool accessible only to deep-rooted plants. This is offered as an explanation for the co-dominance of the two main plant functional types at the loamy sand site. At the other two sites, shallow-rooted shortgrass vegetation dominated, being more consistent with the general pattern for the area. Thus the patterns of vegetation structure at the three sites were consistent with the hypothesis. Aboveground net primary production data for the three sites, along with transpiration estimates from the model simulations, indicated that the additional water availability in the coarse textured soil was associated with higher overall plant productivity.Nomenclature: Taxonomic nomenclature follows R. L. McGregor & T. M. Barkley (1986) Flora of the Great Plains. Great Plains Flora Association. University Press of Kansas, Lawrence.     

Soil temperature, digging behaviour, and the adaptive value of nest depth in South American species of Acromyrmex leaf-cutting ants

In leaf-cutting ants, workers are expected to excavate the nest at a soil depth that provides suitable temperatures, since the symbiotic fungus cultivated inside nest chambers is highly dependent on temperature for proper growth. We hypothesize that the different nesting habits observed in Acromyrmex leaf-cutting ants in the South American continent, i.e. superficial and subterranean nests, depend on the occurrence, across the soil profile, of the temperature range preferred by workers for digging. To test this hypothesis, we first explored whether the nesting habits in the genus Acromyrmex are correlated with the prevailing soil temperature regimes at the reported nest locations. Second, we experimentally investigated whether Acromyrmex workers engaged in digging use soil temperature as a cue to decide where to excavate the nest. A bibliographic survey of nesting habits of 21 South American Acromyrmex species indicated that nesting habits are correlated with the soil temperature regimes: the warmer the soil at the nesting site, the higher the number of species inhabiting subterranean nests, as compared to superficial nests. For those species showing nesting plasticity, subterranean nests occurred in hot soils, and superficial nests in cold ones. Experimental results indicated that Acromyrmex lundi workers use soil temperature as an orientation cue to decide where to start digging, and respond to rising and falling soil temperatures by moving to alternative digging places, or by stopping digging, respectively. The soil temperature range preferred for digging, between 20°C and maximally 30.6°C, matched the range at which colony growth would be maximized. It is suggested that temperature-sensitive digging guides digging workers towards their preferred range of soil temperature. Workers’ thermopreferences lead to a concentration of digging activity at the soil layers where the preferred range occurs, and therefore, to the construction of superficial nests in cold soils, and subterranean ones in hot soils. The adaptive value of the temperature-related nesting habits, and the temperature-sensitive digging, is further discussed.     

围封10年对荒漠草原群落物种多样性与优势种空间分布格局的影响

围封是修复退化草原生态系统的主要措施之一,科学与优化围封方式是目前草地资源管理中急需解决的科学问题。以内蒙古围栏封育10年和未围封的荒漠草原为研究对象,分析围封和未围封对内蒙古荒漠草原群落物种多样性和优势种空间分布格局的影响,旨在为荒漠草原的恢复与重建提供科学依据。结果显示:(1)围封10年显著提高了荒漠草原的植被盖度、密度、高度和地上生物量;(2)围封10年对Margalef多样性指数、Shannon-Wiener多样性指数、Simpson丰富度指数和Pielou均匀度指数无显著影响,但围封均低于未围封样地;(3)围封10年对优势种短花针茅(Stipa breviflora)及糙隐子草(Cleistogenes squarrosa)的空间分布格局有较为显著的影响,与未围封相比围封后糙隐子草的分布格局变得单一,短花针茅分布格局变得多样。总体看来,围封10年后,荒漠草原群落物种组成、物种优势度和优势种的空间分布格局均发生一定程度变化,反映出围封后草地生态系统中植物适应其生存环境的策略,围封方式应根据立地条件,科学制定围封年限以达到较好的生态恢复效果。     

Soil salt and nutrient concentration in the rhizosphere of desert halophytes

North-West China is an arid region where halophyte plants are rich. Very little is known on the rhizospheric soil of the halophytes in this arid desert region. We conducted a rhizobag experiment on the desert Solonchak soil to investigate the salt and nutrient content in the rhizospheric soil of the desert halophytes. The total salt and the concentrations of 8 major kinds of salt ions increased in the rhizosphere of both succulent halophytes and salt secreting halophytes, but this increase was insignificant for salt-resisting halophytes. Accumulation of Cl^– and Na⁺ is the most significant among the 8 major kinds of salt ions. Accumulation of Cl^– was more significant than that of SO₄^2– in succulent halophytes and salt secreting halophytes. The Na⁺/K⁺, Na⁺/Ca²⁺ and Na⁺/Mg²⁺ ratios in the rhizosphere of all 7 kinds of halophytes were higher than those in the bulk soil. Total N increased significantly in the rhizosphere, but total P and total K decreased. However, the available N, P and K in the rhizosphere of the 7 kinds of halophytes except Phragmites communis Trin. behaved in such an opposite way that available N decreased but available P and available K increased. The ionic contents in the aboveground parts were higher than those in the underground parts of the 7 kinds of halophytes, in particular of both the succulent halophytes and the salt secreting halophytes. Accumulation of Cl^– and Na⁺ in the aboveground parts of the plants was the most significant among that of the 8 major kinds of salt ions.     

荒漠盐生植物根际土壤盐分和养分特征

中国西北地区是我国干旱、盐碱化土壤分布面积较广、土壤积盐较重的地区,这里发育着丰富的盐生植物。目前对于干旱荒漠区盐生植物根际特征的研究相对较少,而不同盐生植物的根际特征对于研究盐生植物适应盐渍环境的机制有着重要意义。本研究利采用盆栽根袋法对7种不同类型的荒漠盐生植物的根际盐分和养分特征进行了初步探索。结果表明:盐分在盐生植物根际发生富集,稀盐盐生植物和泌盐盐生植物根际土壤中总盐和8种主要盐分离子的含量都有所增加,而在拒盐盐生植物根际中增加不显著,其中Cl-和Na 的富集程度相对其它6种离子的富集程度要高。稀盐盐生植物和泌盐盐生植物根际土中的SO42-/Cl-比土体有显著的降低,表明在稀盐盐生植物和泌盐盐生植物根际土壤中Cl-的富集程度比SO42-高,拒盐盐生植物根际土盐分SO42-/Cl-比略有提高。7种盐生植物根际土中的Na /K ,Na /Ca2 ,Na /Mg2 比均较土体有显著的增加,芦苇根际土中的增加最小。在所有研究植物中,根际土壤中全N含量比土体的含量高,但全P和全K含量却比土体的含量低;根际土壤中有效态养分的变化则与全态相反,根际土壤中的有效N含量比土体中的都显著降低,除芦苇外,其他六种盐生植物根际土壤中有效P和有效K的含量都高于土体,但有效P的富集不及有效K富集的程度高。在研究的七种植物中,钠猪毛菜根际土壤的有效N亏缺量最高,有效P和速效K富集也最少。7种植物,尤其是稀盐盐生植物和泌盐盐生植物的地上部分的主要盐离子含量比地下部分高,如Cl-、Na 、Ca2 和K ,在根际富集程度最高的Cl-和Na ,在植株的地上部分也增加的最多。     

库布齐东段不同植被恢复阶段荒漠生态系统碳氮储量及分配格局

为科学评价植被恢复促进沙漠化逆转对碳氮储量的影响,以流动沙地、半固定沙地、油蒿固定沙地、柠条固定沙地、沙柳固定沙地5个阶段荒漠生态系统为研究对象,采用时空替代法分析植被恢复过程中荒漠生态系统碳氮储量及分配格局。结果表明:不同恢复阶段碳氮储量均表现为:流动沙地(3320.97 kg C/hm~2、346.69 kg N/hm~2)半固定沙地(4371.46 kg C/hm~2、435.95 kg N/hm~2)油蒿固定沙地(6096.50 kg C/hm~2、513.76 kg N/hm~2)柠条固定沙地(9556.80 kg C/hm~2、926.31 kg N/hm~2)沙柳固定沙地(19488.54 kg C/hm~2、982.11 kg N/hm~2)。植被层碳氮储量均呈现随植被恢复逐渐增加的趋势,除流动沙地外,其他阶段碳氮储量均以灌木层为主,占比分别为66.65%—91.41%和52.94%—93.39%,草本和凋落物占比较小。灌木各器官生物量及碳储量分配均为:茎根叶,氮储量分配无明显规律,草本各器官生物量及碳氮储量分配均为地上部分高于地下部分。土壤层是荒漠生态系统碳氮储量的主体,碳储量占比为68.64%—99.62%,氮储量占比为89.26%—99.89%,同样呈现随植被恢复逐渐增加的趋势。碳氮储量随土层加深逐渐降低,具有明显的表层富集特征,且随植被恢复过程富集性显著加强。这说明人工建植促进植被演替实现沙漠化逆转可以显著增强荒漠生态系统的碳氮固存能力。     

Effect of harvester ants of the genus Pogonomyrmex on the soil seed bank around their nests in the central Monte desert,Argentina

1. The abundance and composition of soil seed banks is a key determinant of plant community structure. Harvester ants can remove huge quantities of preferred seeds close to the nest affecting composition and spatial distribution of plants. 2. In the central Monte desert (Argentina) ants of the genus Pogonomyrmex have high seed removal rates, especially of the five main grasses. The aim of this study was to establish if their foraging activity affects spatial patterns of the soil seed bank around their nests. Our hypotheses were: (1) removal by ants decreases seed abundance of preferred species in the soil; and (2) the effect varies in time. 3. Soil seed abundance was assessed at different distances from Pogonomyrmex nests in the litter and in bare soil at the beginning, the middle, and the end of the season (late spring‐early autumn). 4. A lower seed abundance of preferred species was observed close to the nest in the litter at the end of the season. Non‐preferred species showed no distance gradient. 5. The lower foraging activity and seed consumption at the beginning of the season could explain the temporal variation of the spatial effect. This was only observed in the litter, probably because of the higher removal frequency in this substrate. 6. Colonies of Pogonomyrmex spp. could enhance the heterogeneity of soil seed banks in the central Monte desert from the summer to the beginning of the autumn. Implications for vegetation dynamics depend on the degree to which seed density limits perennial grasses recruitment after ant activity season.     

荒漠草原优势种群油蒿空间分布格局对封育恢复的响应

灌木对维持草原生物多样性、稳定性及生态服务功能等具有重要作用,探究封育措施对优势灌木种群的影响,可为草原恢复和抚育管理提供科学指导.本研究对荒漠草原4个封育时间(封育0、5、15、25年)的优势种群油蒿个体特征及种群空间分布格局进行研究.结果表明:油蒿种群密度随着封育时间延长先增加后降低,封育15年时最高,为未封育样地...     

不同质地土壤的水热状况及其对冬小麦产量形成的影响

对豫东平原３种质地土壤的水热状况和冬小麦籽粒生长特征进行了研究．结果表明,冬小麦籽粒生长阶段,粘壤土５ｃｍ处的日平均温度最低,为１８．３℃,砂壤土最高,为１９．５℃,中壤居中,为１９．１℃．３种土壤的含水量大小顺序为粘壤＞中壤＞砂壤,粘壤土上小麦籽粒灌浆时间最长,千粒重最高,分别为３８ｄ和４５．５ｇ,砂壤土小麦籽粒灌浆时间最短,千粒重最低,分别为３３ｄ和４２．４ｇ,中壤土小麦２项指标居中,分别为３６ｄ和４３．１ｇ．高产栽培条件下,粘壤土冬小麦产量最高,为８２５３ｋｇ·ｈｍ－２,中壤次之,为７９８０ｋｇ·ｈｍ－２,砂壤最低,为７６１７ｋｇ·ｈｍ－２     

宁夏荒漠草原针毛收获蚁对植物种子的觅食作用

针毛收获蚁Messor aciculatus (F．Smith)是西北荒漠地区典型的食种子蚂蚁种类之一。以宁夏中卫县沙坡头自然保护区红卫固定沙丘地段为主要研究基地。由田间系统调查和室内饲养得出：针毛收获蚁可取食的植物种子达30余种以上。在红卫固定沙丘草地针毛收获蚁的自然种群收获的植物种子主要有6种：狗尾草Setaria viridis、猪毛菜Salsola collina、雾冰藜Bassia dasyphylla、地锦Euphobia humifuse、刺沙蓬Salsola ruthenica、叉枝鸦葱Scorzonera divaricata。被收获的种子大小主要在1．20～2．50mm之间．或有棱角、扁平、易于衔夹的种子。在蚁巢中种子以种类和形态的不同被分类、分层保存于不同深处的巢室．总贮量随工蚁和蚁后数量的增加而增加。在自然条件下,收获的种子种类及数量与穴巢附近环境中的植物种类及分布有关。蚂蚁对种子的收集贮藏在一定程度上可影响种子的萌发力．特别是对一些1年生质量较轻的种子影响力较大。蚂蚁觅食对土壤中种子库种子密度的影响因植物种类的不同而异．其中对1年生草本植物影响较大．间接的影响到植物群落的组成和空间分布的变化。     

干旱荒漠区人工植物群落演替模式及其生态学机制研究

以我国干旱荒漠区包兰铁路沙坡头地段人工植被防护林体系作为研究对象,研究了区域植被建立与发展过程中,优势植物种的种群动态和人工植物群落的演替模式,探讨了植物群落演替的内在动因和生态学机制．结果表明,该区人工植被经过40余年的演变,其植物种组成发生了很大的变化,已由原来的灌木、半灌木人工植物群落演变为一年生草本植物占优势的人工-天然荒漠植物群落．在此演替过程中,人工栽植的灌木种如柠条、花棒等的重要值不断减少,逐渐从人工植物群落中退出;而天然繁衍的一年生草本植物如小画眉草、雾冰藜、刺蓬、虎尾草等相继侵入,并逐渐成为该区的优势植物种;油蒿由于具有天然下种自行更新能力,在群落中始终占有重要地位．这种物种替代模式与该地区降水资源严重匮乏以及沙地表面结皮的增厚,致使沙子下层含水量降低。深根系的灌木及多年生草本的繁衍受到限制密不可分．