Co-occurrence and potential for competition between wild and domestic large herbivores in a South American desert

Introduction of domestic ungulates may lead to interspecific competition with native herbivores, particularly if the species involved are of similar size and share similar foraging strategies due to a scarcity of trophic resources. This interaction has not been investigated in South American deserts in which guanaco (Lama guanicoe), the larger South American wild camelid and the most widely-distributed ungulate, co-occurs with several introduced ungulates (e.g. cattle, donkeys, sheep or red deer). We studied the occurrence and abundance patterns of guanacos, donkeys and cattle in desert areas of Argentina by dung sampling. Analyses of co-occurrence show no relationship in land use between guanaco and livestock when geographical effects are removed. Distribution and abundance models of the guanaco are strongly associated with sparse plant cover, rocky substrata and human-influence variables, guanacos appearing in areas furthest from villages. Nevertheless, while guanaco distribution is weakly related to feral livestock presence, their abundance is negatively associated with donkey presence. In contrast, livestock species appear closely associated with each other, being centred on areas of densest and most productive vegetation. These results are relevant for the management of extensive arid areas of South America, where guanacos co-occur with feral donkeys and frequently conflicts with humans activities.     

Seasonal diet of black-backed jackal in the Eastern Karoo,South Africa

The ability of small canids to consume a variety of resources in an opportunistic manner has been cited as a reason for their wide distribution across many habitats. Black-backed jackals Canis mesomelas have varied diets that reflect changes in food availability as a result of seasonal fluctuations in resources. Seasonal fluctuations can include variations in food type availability, as well as variations in the phenology of food resources (i.e. ungulate birth peaks). Additionally, the presence of apex predators can affect opportunistic predator diets through the provision of carrion. We investigated the diet of black-backed jackals on a reserve in the semi-arid Karoo, South Africa. Ungulates (>5 kg) were the dominant prey item across all seasons, reflecting either active predation or scavenging. Most seasonal comparisons in percent occurrence of prey groups revealed significant seasonal fluctuations in black-backed jackal diet. However, in terms of biomass consumed, the diet remained stable, dominated by small ungulates across all seasons with no clear seasonal change in ungulate composition. These results suggest that in this study black-backed jackals, although being opportunistic in terms of diet composition, had a seasonally stable food resource, most likely facilitated by the presence of cheetahs Acinonyx jubatus providing scavenging opportunities.     

Precipitation impacts on mule deer habitat use in the chihuahuan desert of Mexico

In arid lands, food resources and predation risk become major decision factors in mule deer habitat use. We examined variables related to these two factors that might determine mule deer (Odocoileus hemionus) habitat use in a warm desert at two spatial scales: the macro-habitat scale, which relates to home range decisions, and the micro-habitat scale, which relates to decisions made during foraging. Our prediction was that habitat use should primarily be explained by food variables and, to a lesser degree, by variables related to predation risk by pumas (Puma concolor). We mapped all deer pellet groups in 72, 1 ha quadrats in the Mapimí Biosphere Reserve and measured food and habitat variables over two years with different precipitation amounts. The area was used more intensively during the dry year. Under drier conditions, deer habitat use was explained primarily by food resource variables and secondarily by variables related with predation risk. During the wetter year, food resources became unimportant while cover and visibility explained deer habitat use. The data suggest that the tradeoffs deer are willing to make between food resources and predation risk in an arid environment are strongly affected by food resource levels, as influenced by precipitation.     

Temporal and trophic niche overlap in a guild of flower-visiting ants in a seasonal semi-arid tropical environment

Studies of assemblages of insects that have largely agonistic relationships with plants are rare compared to those that study mutualistic relationships between plants and animals. Flowers have evolved multiple defense mechanisms to protect against nectar-thieving ants, which may decrease plant reproductive success. We evaluated season-specific patterns of biodiversity as well as trophic and temporal niche overlap for flower-visiting ants in the Brazilian Caatingas (dry scrub, tropical vegetation). Ant richness and evenness did not vary with season; however, Shannon diversity and Berger–Parker dominance were greater and lower, respectively, during the green season compared to the dry season. Trophic overlap was greater during the dry season than the green season. In contrast, temporal overlap was greater during the green season than the dry season. The most common flower-visiting ant (Camponotus blandus) exhibited season specific trophic and temporal niches. Flower-visiting ants exhibited seasonal complementarity, but within seasons species exhibited both trophic and temporal overlap, suggesting that competition for floral resources is not a strong structuring force in this guild.     

Foraging sexual segregation in a Mediterranean environment: Summer drought modulates sex-specific resource selection

A large body of studies have linked sexual segregation in dimorphic ungulates with differential resource selection and nutritional requirements of the sexes. However, detailed patterns of sexual dietary preferences have rarely been assessed as keystone mechanisms of sexual segregation. We compared diet and nutritional selection by 3 sex-age classes in the Iberian red deer (Cervus elaphus hispanicus Hilzheimer) across reproductive states and according to seasonal fluctuations in resource availability in a Mediterranean environment. Foraging segregation between sexes was found during rut when female/juvenile selection of shrubs was higher than that of males. Observed foraging patterns relate to a stronger selection of nitrogen, tannins and lignin by females and juveniles, and fibres by males. Our findings are associated to the Mediterranean climate, where rut and lactation concur with a shortage period, the particularly dry summer. Foraging segregation between sexes during the rut could be shaped by a conjunction of factors such as the low quality of resources and different fitness enhancement strategies. We highlight both the importance of including the dietary component and providing a temporal framework when documenting ungulate sexual segregation, and the interest of considering regional conditions when addressing management of ungulates with a wide distribution.     

Susceptibility of lizards to predation under two levels of vegetative cover

The risk of increased predation is a potential cost for habitat specialists, when dispersing through non-habitat matrix. We hypothesized that dispersal success of lizards is limited by the loss of vegetative cover, as occurs with overgrazing, due to increased susceptibility to predation. We analyzed the movement behavior of the saxicolous lizards (Liolaemus elongatus and Phymaturus patagonicus) in the Patagonian steppe using a habitat generalist (Liolaemus bibroni) as a control species. We compared the proportion of stops on bare ground during movement in two experimental enclosures with different levels of vegetative cover. Both specialists and generalists stopped more frequently on bare ground when there was less vegetative cover, and specialists stopped more frequently than generalists on bare ground. We found no significant difference in the time it took specialists to reach the end of the enclosure in the two different levels of vegetative cover. Additionally we compared the time to capture by a human predator under the two levels of vegetative cover. All species were captured more quickly when there was less vegetative cover and we found a tendency towards shorter capture times in specialists than in generalists. Our results suggest that saxicolous lizards are more susceptible to predation with less vegetative cover.     

Home-range sizes of social groups of Mongolian gerbils Meriones unguiculatus

Spacing behavior is important to the population regulation and social organization of rodents. However, little is known regarding the factors influencing space use by rodent social groups. We tested the hypotheses that food resources in the typical steppe would be so abundant that food availability would not be a limiting factor of home-range sizes of social groups of Mongolian gerbils (Meriones unguiculatus). We also assessed the effects of social organization on the home-range size of social groups of gerbils, using capture-recapture methods. Home ranges of social groups of Mongolian gerbils did not differ in size between the breeding and non-breeding periods; however, home ranges overlapped more during the breeding period than during the non-breeding period. Overlap of home ranges might allow male gerbils to access female mates of neighboring colonies during the breeding period. Home-range sizes of social groups were positively related to number of males during the breeding period, but positively related to group size and number of females during the non-breeding period. Therefore, social organization influenced home-range sizes of social groups. Our hypothesis that food availability is not a limiting factor of space use by social groups of Mongolian gerbils from spring through autumn was supported.     

Diet of a fossorial rodent (Octodontidae), above-ground food availability,and changes related to cattle grazing in the Central Monte (Argentina)

Overgrazing by livestock has caused desertification in the Monte, where ctenomyids and livestock share grasses as main food items. The diet of Ctenomys eremophilus, above-ground food availability and changes related to cattle grazing are analyzed in the arid plain of Mendoza, Argentina. The most available categories were grasses, followed by low shrubs and tall shrubs. Tuco-tucos showed dietary generalism, ate mainly above-ground plant parts, preferred grasses and avoided shrubs at both grazed and ungrazed sites. Plant cover, grass diversity and availability decreased under livestock grazing, which was reflected in the diet by a lower percentage of grasses, a shift toward low shrubs and higher number of frequently used resources. Tuco-tucos in the grazed paddock compensated for lower consumption of vegetative plant parts by increasing the use of Prosopis flexuosa pods stored inside burrows. Moreover, greater dietary variation among individuals suggests foraging restricted to the items closest to burrow holes. These feeding tactics would allow them to reduce above-ground foraging as a response to high raptor predation risk due to increased bare soil. The plant recovery detected during the rest period, favoured by moderate stocking rate and rotational grazing system, would allow coexistence of tuco-tucos and cattle.     

Speciation in gall-inducing thrips on Acacia in arid and non-arid areas of Australia

Habitat modification mediated by abiotic processes imposes consequences for the diversification of plants and plant specialists. Host plant diversification is expected to be dependent on environmental and ecological constraints that are fundamentally connected to physiography (physical geography). A phylogenetic approach is used to reconstruct ancestral host plant affiliation of gall-inducing thrips that specialize on Australian Acacia. Diversification rate models are applied to gall-thrips clades that are affiliated with different Acacia host lineages. Gall-thrips diversification is reconciled with contemporary patterns of species diversity relating to the different host lineages. Results indicate that diversification on host lineages that are mostly distributed in non-arid areas are best explained by a rate-constant model. However, this model disguised additive effects of rate-variable lineage accumulation that indicated diversification decreases in sub-clades within this larger group. Gall-thrips affiliated with hosts distributed mostly in arid areas were best characterized by rate-variable decreasing net diversification. The work infers parent gall-thrips lineages are less species diverse compared to daughter lineages that tend to be distributed away from the arid interior of Australia. Contrasting ecological and environmental interactions unique to parent and daughter lineages are suggested to influence the mode of speciation and phenotypic diversity represented by each.     

Habitat selection and partitioning of the Black-bellied Sandgrouse (Pterocles orientalis), the Stone Curlew (Burhinus oedicnemus) and the Cream-coloured Courser (Cursorius cursor) in arid areas of North Africa

Niche theory predicts that coexisting species with similar trophic requirements should demonstrate resource partitioning, particularly where resources are scarce. Conversely, this is not expected between species that do not share primary resources. This study analyses the patterns of spatial coexistence and habitat selection, on two spatial scales, of three species of semidesert regions in Morocco: the Black-bellied Sandgrouse (Pterocles orientalis), the Stone Curlew (Burhinus oedicnemus) and the Cream-coloured Courser (Cursorius cursor). Co-occurrence analysis results point to between-species segregation on a macrohabitat scale. Hotelling's T test of the species-presence data showed a pattern of macrohabitat selection that diverged from habitat availability for the three species with differences among them. Both the classification tree and the pattern of microhabitat selection obtained by model averaging showed scant overlap between the Sandgrouse and the Courser, suggesting habitat partitioning between them on a fine scale. Our results confirm spatial segregation of the three species, especially between species with different trophic strategies: the Sandgrouse versus the Stone Curlew and the Courser. The latter two species were best segregated on a microhabitat scale, supporting the conclusions that macro- and microhabitat selection are major factors in bird community configuration in arid ecosystems and contributing to reduce potential competition.     

The effects of the identity of shrub species on the distribution and diversity of ground arthropods in a sandy desert ecosystem of northwestern China

Shrub is an important factor on structuring ground arthropod communities in desert ecosystems. In this study, in order to determine how shrubs and their species influence ground arthropod distribution patterns in a sandy desert scrubland dominated by two different shrub species, Calligonum mongolicum and Nitraria sphaerocarpa, the ground arthropods were sampled with pitfall traps during spring, summer and autumn. At the community level, total arthropod abundance was shown to be significantly higher under shrubs than in intershrub bare areas in spring; similar patterns occurred in terms of the richness of arthropod groups in the spring and over three seasons, suggesting season-specific shrub presence effects on arthropod activity. In addition, more arthropods were found under N. sphaerocarpa shrubs than under C. rnongolicum shrubs in autumn, suggesting season-specific effects of shrub species of arthropod activity, whereas more arthropods taxa were captured under C. mongoIicum than N. sphaerocarpa. At the trophic group level, the abundances of predator and herbivore arthropods were significantly greater under shrubs than in intershrub bare habitats, whereas herbivore arthropods were more abundant under N. sphaerocarpa than C. rnongolicum, and an opposite rule was detected for predator arthropods At the family level, the mean abundances of Carabidae, Curculionidae, Gnaphosidae and Lycosidae were significantly higher in the shrub microhabitats than in the intershrub bare habitat, there was no significant difference between habitats on the mean abundances of Formicidae and Tenebrionidae. The study results suggested that shrub presence and shrub species variation are important determinants of ground arthropod assemblages in this desert ecosystem, but the responses of ar- thropods differed among trophic and taxonomic groups.     

A GIS-based risk rating of forest insect outbreaks using aerial overview surveys and the local Moran's I statistic

The objective of this study is to provide an approach for assessing the short-term risk of mountain pine beetle Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae) attack over large forested areas based on the spatial-temporal behavior of beetle spread. This is accomplished by integrating GIS, aerial overview surveys, and local indicators of spatial association (LISA) in order to measure the spatial relationships of mountain pine beetle impacts from one year to the next. Specifically, we implement a LISA method called the bivariate local Moran's I_i to estimate the risk of mountain pine beetle attack across the pine distribution of British Columbia, Canada. The bivariate local Moran's I_i provides a means for classifying locations into separate qualitative risk categories that describe insect population dynamics from one year to the next, revealing where mountain pine beetle populations are most likely to increase, stay constant, or decline. The accuracy of the model's prediction of qualitative risk was higher in initial years and lower in later years of the study, ranging from 91% in 2002 to 72% in 2006. The risk rating can be continually updated by utilizing annual overview surveys, thus ensuring that risk prediction remains relatively high in the short-term. Such information can equip forest managers with the ability to allocate mitigation resources for responding to insect epidemics over very large areas.     

黄河中下游水沙变化趋势

本文论述由于黄河上游清水区水资源的优先开发,中上游地区工农业用水的增长,而黄河中游地区的水土保持和支流治理的减沙作用不甚明显,龙羊峡水库投入运用后,汛期进入河口镇的水量大幅度减少,使汛期进入黄河下游的基流减小含沙量增加,高含沙洪水出现的机会增多.面临水少沙多的不利情况,应加强宽浅河道的改造及利用窄深河道输送高含沙水流的研究.     

Does land use matter in an arid Environment? A case study from the Hoanib River catchment, north-western Namibia

The effect of intensive grazing and browsing of domestic stock and wildlife on the number of species and abundance of vegetation was investigated in the Hoanib River catchment, north-western Namibia. The seasonal abundance of ground cover, bare earth, canopy cover, annual grass, perennial grass and annual forbs were measured in each of the focus-study areas. In three of the focus areas where the ranges of both domestic stock and wildlife were restricted either by fencing or water availability, impact on the vegetation was greatest. The final focus area was a more ‘open range’ system that allowed for the free movement of wildlife. Under these conditions the species abundance and availability of browsing and grazing was greater than the other focus areas during both the wet and dry seasons. However, very little difference in abundance and availability of vegetation was observed between focus areas in both seasons regardless of landuse. There is generally a low abundance of perennial grasses and browse species affording the ecosystem little resistance and resilience to disturbance caused by grazing and drought.     

High body temperatures in an arid,winter-rainfall environment: Thermal biology of the smallest tortoise

Herbivorous tortoises in arid, winter-rainfall regions need to forage in seasons that provide relatively little heat for their ectothermic metabolism. To help understand how tortoises exploit resources in winter-rainfall areas, I recorded ambient, soil, and body temperatures for Homopus signatus in four spring seasons, and in one summer, autumn, and winter. The spring thermal environment enabled H. signatus to maintain body temperatures that were high compared to other small tortoise species. Mature females had higher spring body temperatures than males and immature individuals, probably because mature females were developing eggs. In summer, autumn, and winter, body temperatures differed between males and females, relating to sexually different activities and retreat uses. The relatively high body temperatures of H. signatus in winter and spring, along with a non-isometric relationship between body temperature and soil temperature, suggest that tortoises thermoregulated and may need considerable time to gain heat. Additional studies should compare body temperatures of H. signatus to operative temperatures, and determine the vulnerability of the taxon to human interferences that affect behavioural time budgets and body temperatures.     

Cladoceran stratigraphy in two shallow brackish lakes with special reference to changes in salinity, macrophyte abundance and fish predation

Sub-fossils of Cladocera and Foraminifera were used to reconstruct changes since 1870 in the trophic dynamics of two brackish lakes, Glombak and Han Vejle, located in the Vejlerne nature reserve, Denmark, a site of international conservation importance. After creation of the lakes in the mid-1870s following land reclamation, the two lakes have developed quite differently; today Glombak is turbid, while Han Vejle is clear. In both lakes, stratigraphic changes in the assemblages of foraminifers and cladocerans indicate an abrupt shift from marine to brackish conditions at the end of the 19th century, coinciding with land reclamation. However, the composition of the fossil invertebrate assemblages in the 20th century implies differences in the exposure to salinity, in fish predation and in habitat diversity. In Glombak, the cladoceran record suggests relatively saline conditions in the first quarter of the last century and high macrophyte abundance followed by lower salinities and subsequently a major decrease in macrophyte abundance and an increase in fish predation during the past ca. 40 years. By contrast, in Han Vejle low salinity, high abundance of macrophytes and only minor changes in fish predation seem to have prevailed throughout most of the 20th century. The results are consistent with recent contemporary data, the few historical records, as well as with trends in the records of diatoms and macrofossils. This study highlights the potential of using crustacean remains as indicators of long-term changes in the trophic dynamics of brackish lakes.     

Expansive fire in Mojave Desert shrubland reduces abundance and species diversity of small mammals

Changes in plant community structure and composition of the Mojave Desert in response to greater fire intensity and extent are likely to have strong bottom-up effects on the biological community. The objective of this study was to determine how expansive fire in Mojave Desert impacts small mammal communities across seasons. We sampled small mammals in paired burned (4–5 years post-fire) and unburned areas of Beaver Dam Wash in southwestern Utah. Fire reduced total abundance of small mammals, and species richness and species diversity of the small mammal community. Merriam’s kangaroo rat (Dipodomys merriami) responded positively to fire (15% greater in burned areas). Long-tailed pocket mouse (Chaetodipus formosus) and canyon mouse (Peromyscus crinitus) were 91% and 98% less abundant in burned versus unburned areas. The positive response of Merriam’s kangaroo rat to fire is most likely correlated with their preference for open foraging microhabitat while other species captured prefer greater and more diverse cover. Because the small mammal community has been dramatically affected by fire, it is likely that top-down control of vegetation structure will be dominated by Merriam’s kangaroo rat in burned areas, which may promote more open habitat by limiting the growth of annual and perennial grasses.     

海南省连片贫困地区农户致贫风险分析

农村贫困与减贫是世界性难题,也是中国各级政府高度重视并着力解决的重大民生问题。基于农户及致贫风险的文献梳理,从区位、社会和劳动力3个要素维度构建了农户致贫风险分析的二元Logistic回归模型。采用484户农户问卷调查数据,分析了海南省连片贫困地区农户的致贫风险,提出有效减贫和持续发展对策。研究发现:①海南连片贫困地区生态环境良好但贫困发生率较高,家庭劳动力较充裕但受教育水平较低,子女教育支出负担重,因病因残致贫比例较高,女性务工人口较多,农户自身脱贫致富的发展动力不足。②海拔高度200 m以下、男性户主、拥有残疾或患病成员、务工人口比例低、女性务工人员占比高、以及单位劳动力供养学生数高的农户具有更大的致贫风险。③研究未发现女性户主、少数民族、低受教育水平户主、大型规模家庭有更高的致贫风险,女性成员比例、抚养比等因素对农户贫困影响较小。激发农户内生动力、大力发展特色化和规模化农业、增加农户就业机会、加强针对农民工、女性务工人员和病残群体的社会保障等减贫政策制定实施是实现脱贫攻坚目标的重要途径。     

Response of Pediastrum in German floodplain lakes to Late Glacial climate changes

Subfossil remains of the Pediastrum-algae group (Fam. Hydrodictyaceae) are frequently found in lake sediments, but very few studies have used them as palaeoclimate and palaeolimnological indicators. This study explored the species composition of Pediastrum assemblages in shallow floodplain lakes in northern Germany during two transitional periods from cold to temperate climate conditions (GS-2/GI-1 and GI-1/Holocene). We identified Pediastrum taxa to subspecies level and used multivariate statistics (constrained clustering, principal component analysis and redundancy analysis) to show that shifts in taxonomic composition reflected the strong Late Glacial climate oscillations. The Pediastrum assemblages indicate that climate amelioration already begun shortly before the main GS-2/GI-1 summer-temperature transition. In contrast to previous studies that identified trophic state as the main driver of change in Pediastrum species composition, we identified climate shifts and related factors as the major drivers of community change. Water depth and trophic state probably acted as secondary factors that were responsible for differences in Pediastrum response between the first and second investigated climate transitions. During cold periods, Pediastrum algae composition was controlled mainly by environmental variables, whereas during warm periods, Pediastrum assemblages may have been influenced to a greater extent by intra- and intergeneric competition. This study contributes to knowledge about ecological niches of Pediastrum species. Size-measurements on Pediastrum coenobia reveal that one response of Pediastrum algae to climate shifts probably was size change. Coenobia of Pseudopediastrum boryanum var. boryanum were significantly smaller during cold climate periods than during temperate periods. The shifts in Pediastrum species composition and coenobium size suggest this algae group has great potential for enabling palaeoecological and palaeoclimate inferences.     

基于气象干旱综合监测指数(MCI)的陕西省干旱灾害风险评估与区划北大核心CSCD

利用陕西省94个国家气象站1961—2018年逐日气象资料,根据干旱灾害气候背景和社会经济环境,结合灾害风险评估相关理论方法,选取致灾因子危险性、孕灾环境脆弱性、承灾体暴露度、防灾减灾能力4个方面指标,建立干旱灾害风险评估指数,基于GIS平台,对陕西省不同季节进行干旱灾害风险区划。结果表明:(1)陕西各区域干旱致灾因子危险性季节差异明显,陕北北部除夏季外各季节干旱危险性较高,关中地区易发生伏旱。陕南的汉中各季节干旱危险性均较大,安康东部和商洛各季节干旱危险性则较小。(2)春季、夏季和秋季,陕南的汉中平原及安康的汉江河谷地带,关中的西安和渭南地区,陕北北部榆林地区为干旱孕灾环境高脆弱性区或较高区;冬季陕南大部、秦岭地区的高脆弱性区较其他三季范围有所减小;海拔较高的秦岭山地,关中平原和陕北北部各季节皆为低脆弱性或较低脆弱性地区。(3)承灾体暴露度的高风险区主要分布于关中地区。(4)全省抵御干旱风险能力最高地区为陕北黄河沿线、关中各地的城镇地区。(5)干旱灾害综合风险的高风险区主要在陕南巴山地区、秦岭南北两侧、陕北南部,陕南汉江平原、关中平原及陕北延安、榆林等地为干旱较低、低风险区。