Israel Journal of Ecology & Evolution最新文献_第2页

Scale-independence in beetle species diversity-productivity relationship: The importance of heterogeneity arrangement in space 甲虫物种多样性-生产力关系的尺度独立性:空间异质性排列的重要性

IF 1.2 4区环境科学与生态学

Israel Journal of Ecology & Evolution Pub Date : 2021-05-13 DOI: 10.1163/22244662-bja10023

Gillie Pragai, Y. Ziv

{"title":"Scale-independence in beetle species diversity-productivity relationship: The importance of heterogeneity arrangement in space","authors":"Gillie Pragai, Y. Ziv","doi":"10.1163/22244662-bja10023","DOIUrl":"https://doi.org/10.1163/22244662-bja10023","url":null,"abstract":"Species diversity-productivity relationship is often, but not always, scale dependent. We hypothesize that the arrangement of environmental heterogeneity along a rainfall gradient, as a surrogate for productivity, determines whether scale dependence of beetle diversity at our sandy sites exists. We chose seven geographically distant landscapes (360 kms from south to north) within a mean annual rainfall range of 30–585 mm, each having six clusters of five uniformly distributed pitfall traps (within a range of 0.24 km2). Vegetation and physical variables were measured within each landscape and its clusters to characterize both spatial and temporal heterogeneity. We used species diversity of each cluster and the accumulative species diversity in a landscape as local and regional diversity, respectively. Between-clusters dissimilarity in diversity reflected the turnover of species within a landscape. We used environmental measures in each cluster and at the entire landscape to indicate local and regional heterogeneity, respectively, and changes between transects to characterize the within-landscape dissimilarity in heterogeneity. Beetle diversity and productivity showed a unimodal pattern at both spatial scales, with a peak at intermediate productivity of ca. 300 mm. Environmental heterogeneity increased with productivity both at the local and at the landscape scales, but within-landscape dissimilarity in heterogeneity did not change with productivity. Between-clusters dissimilarity in diversity was higher at intermediate productivity, explaining the unimodal pattern at the landscape scale. We suggest that the scale independence in our study results from the equal distribution of environmental heterogeneity within a landscape. We propose that the exploration of the diversity-productivity relationship across scales should consider the way heterogeneity is distributed along the productivity gradient.","PeriodicalId":50267,"journal":{"name":"Israel Journal of Ecology & Evolution","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47673210","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Does a bacterial infection lead to a nutritional deficiency in foraging Allenby’s gerbils? 细菌感染会导致觅食的艾伦比沙鼠营养不足吗?

IF 1.2 4区环境科学与生态学

Israel Journal of Ecology & Evolution Pub Date : 2021-04-27 DOI: 10.1163/22244662-BJA10024

Douglas F. Makin, Burt P. Kotler, Franklin Sargunaraj

{"title":"Does a bacterial infection lead to a nutritional deficiency in foraging Allenby’s gerbils?","authors":"Douglas F. Makin, Burt P. Kotler, Franklin Sargunaraj","doi":"10.1163/22244662-BJA10024","DOIUrl":"https://doi.org/10.1163/22244662-BJA10024","url":null,"abstract":"\u0000Bacterial infections can have both direct (physiological) and indirect (ecological) costs for their hosts. The direct costs of infection may include nutritional deficiencies, which reduce body condition over time, and result in the hosts modifying their foraging behaviour to compensate for any losses. Allenby’s gerbils are commonly infected with the Mycoplasma haemomuris-like bacteria, which may induce choline (essential vitamin) and arginine (amino acid) deficiencies. Gerbils should therefore alter their behaviour to make up for any shortfalls in nutrient production and retention. We tested two predictions. 1) infected gerbils would compensate for nutrient losses by spending more time foraging in patches, including, during riskier periods of owl presence, and in riskier open microhabitats. Furthermore, infected gerbils would preferentially forage from patches supplemented with choline and arginine enriched food over control food. 2) Alternatively, if infection did not create a nutrient deficiency, then infected individuals would display a similar pattern of patch use to uninfected individuals, and harvest similar amounts of food from supplemented and control patches. Our findings supported the second prediction. There was no observed difference in foraging behaviour between infected and uninfected individuals. Moreover, infected gerbils did not selectively forage more intensively from food patches enriched with either choline or arginine seed over the control patches. These results suggest that this bacteria-gerbil interaction does not result in a nutrient deficiency as observed for other Mycoplasma-rodent systems.","PeriodicalId":50267,"journal":{"name":"Israel Journal of Ecology & Evolution","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48390013","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Positive association between experimental cortisol increases and cage-measures of feeding behavior in wild-caught gerbils 实验皮质醇增加与笼中野生沙鼠摄食行为的正相关

IF 1.2 4区环境科学与生态学

Israel Journal of Ecology & Evolution Pub Date : 2021-03-05 DOI: 10.1163/22244662-BJA10014

Franklin Sargunaraj, Justin R. St. Juliana, C. Downs, I. Khokhlova, L. Koren, Devorah Matas, K. Wynne-Edwards, Burt P. Kotler

{"title":"Positive association between experimental cortisol increases and cage-measures of feeding behavior in wild-caught gerbils","authors":"Franklin Sargunaraj, Justin R. St. Juliana, C. Downs, I. Khokhlova, L. Koren, Devorah Matas, K. Wynne-Edwards, Burt P. Kotler","doi":"10.1163/22244662-BJA10014","DOIUrl":"https://doi.org/10.1163/22244662-BJA10014","url":null,"abstract":"\u0000Glucocorticoid hormone levels vary within a forager based upon environmental stressors such as illumination and riskier habitats, and a forager’s response to environmental variables depends upon its glucocorticoid levels. Here, we report on a laboratory experiment in which we manipulated cortisol in Allenbyi’s gerbils (Gerbillus andersoni allenbyi) to test the relationship between cortisol and behavior. We then quantified the resulting blood cortisol levels and feeding behavior in gerbils. Thirty gerbils were injected with 21-day slow-release cortisol pellets drawn from 5 different dosages. We quantified the physiological response to pellet implantation in gerbils by measuring cortisol level in blood serum using ELISA (Enzyme Linked Immunosorbent Assay). We fed gerbils daily by mixing millet seeds into the sand inside rodent cages and measured the remaining seeds the following day to quantify feeding efforts. Some evidence supports that subcutaneous supplementation of glucocorticoids (GCs) in the gerbils led to higher blood serum levels. Cortisol levels varied according to time period of measurement. Gerbils that received lower dosages consumed most of the food presented to them when compared to those receiving the highest doses. In this manner, we delineate a pattern on cortisol hormone level variation over time following dosing and consequences in feeding behavior.","PeriodicalId":50267,"journal":{"name":"Israel Journal of Ecology & Evolution","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47826780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Water source and transmission in Haloxylon ammodendron in the desert margin of the Manas River Basin, China 马那斯河流域沙漠边缘梭梭的水源与传播

IF 1.2 4区环境科学与生态学

Israel Journal of Ecology & Evolution Pub Date : 2021-03-03 DOI: 10.1163/22244662-BJA10022

Wanjing Li, Li Zhao, Guang Yang, Ke Yan, Xinlin He, Yongli Gao, Lianqing Xue, Fadong Li, Wu Yage

{"title":"Water source and transmission in Haloxylon ammodendron in the desert margin of the Manas River Basin, China","authors":"Wanjing Li, Li Zhao, Guang Yang, Ke Yan, Xinlin He, Yongli Gao, Lianqing Xue, Fadong Li, Wu Yage","doi":"10.1163/22244662-BJA10022","DOIUrl":"https://doi.org/10.1163/22244662-BJA10022","url":null,"abstract":"\u0000Analysis of water source and moisture transfer characteristics of desert plants is of great significance for ecological restoration in arid areas. In this study, the water source utilized by the desert plant, Haloxylon ammodendron, was analysed using the stable isotope technique, and the water transportation characteristics were obtained based on the proportional heat balance method under different weather conditions. The results showed that (1) before raining, the moisture of H. ammodendron mainly relied on groundwater (the average contribution rate was 34.14%) and on soil water located at a depth of 120–180 cm (the average contribution rate was 29.87%). After the rain, H. ammodendron mainly absorbed soil water from a depth of 60–120 cm (the average contribution rate was 33.19%) and groundwater (the average contribution rate was 30.67%); (2) the stem flow of H. ammodendron showed an obvious diurnal variation, showing a “midday rest” phenomenon. The stem flow showed a peak value, and in sunny days, it was ~2 fold higher than that in cloudy days. (3) The stem flow rate of H. ammodendron varied regularly overtime as follows: August > July > September > June > May, and the meteorological factors affecting its stem flow were solar radiation (0.826) > atmospheric temperature (0.598) > humidity (-0.573). The results provide basic support for the ecological conservation of the desert plant H. ammodendron, while also having important implications for ecological restoration in arid regions.","PeriodicalId":50267,"journal":{"name":"Israel Journal of Ecology & Evolution","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44885008","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

Absence of strict monogamy in the Eurasian jackdaw, Coloeus monedula 欧亚寒鸦没有严格的一夫一妻制

IF 1.2 4区环境科学与生态学

Israel Journal of Ecology & Evolution Pub Date : 2021-02-15 DOI: 10.1163/22244662-BJA10012

S. Turjeman, Ron-Sheng Chen, Ran Nathan

引用次数: 0

Spatial proximity and prey vibratory cues influence collective hunting in social spiders. 空间接近和猎物振动线索影响社交蜘蛛的集体狩猎。

IF 1.2 4区环境科学与生态学

Israel Journal of Ecology & Evolution Pub Date : 2020-12-01 Epub Date: 2020-12-19 DOI: 10.1163/22244662-20191062

Colin M Wright, James L L Lichtenstein, Lauren P Luscuskie, Graham A Montgomery, Sara Geary, Jonathan N Pruitt, Noa Pinter-Wollman, Carl N Keiser

{"title":"Spatial proximity and prey vibratory cues influence collective hunting in social spiders.","authors":"Colin M Wright, James L L Lichtenstein, Lauren P Luscuskie, Graham A Montgomery, Sara Geary, Jonathan N Pruitt, Noa Pinter-Wollman, Carl N Keiser","doi":"10.1163/22244662-20191062","DOIUrl":"10.1163/22244662-20191062","url":null,"abstract":"Social spiders are thought to predominantly receive information about their environment through vibrational cues. Thus, group living introduces the challenge of distinguishing useful vibrational information from the background noise of nestmates. Here we investigate whether spatial proximity between colony-mates may allow social spiders (Stegodyphus dumicola) to reduce background noise that might obstruct vibrational information from prey. To do so, we constructed experimental colonies and measured whether the number of spiders in proximity to one another whilst resting could predict the number of spiders that participated in prey capture. Additionally, we exposed spider colonies to five different simulated vibrational cues mimicking prey to determine which cue types spiders were most responsive to. We found that the number of spiders huddled together prior to foraging trials was positively correlated with the number of spiders participating in collective foraging. Furthermore, colonies responded more quickly to pulsed vibrational cues over other types of vibrational patterns. Together these data reveal that both social interactions and prey cues shape how social sit-and-wait predators experience and respond to their environment.","PeriodicalId":50267,"journal":{"name":"Israel Journal of Ecology & Evolution","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1163/22244662-20191062","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39079847","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 6

Comparative mitochondrial phylogeography of two legless lizards (Pygopodidae) from Queensland’s fragmented woodlands 昆士兰零散林地中两种无腿蜥蜴（Pygopodidae）的线粒体系统学比较

IF 1.2 4区环境科学与生态学

Israel Journal of Ecology & Evolution Pub Date : 2020-11-06 DOI: 10.1163/22244662-20191081

J. W. Wilmer, A. Amey, C. McDougall, M. Venz, Stephen Peck, P. Oliver

{"title":"Comparative mitochondrial phylogeography of two legless lizards (Pygopodidae) from Queensland’s fragmented woodlands","authors":"J. W. Wilmer, A. Amey, C. McDougall, M. Venz, Stephen Peck, P. Oliver","doi":"10.1163/22244662-20191081","DOIUrl":"https://doi.org/10.1163/22244662-20191081","url":null,"abstract":"Sclerophyll woodlands and open forests once covered vast areas of eastern Australia, but have been greatly fragmented and reduced in extent since European settlement. The biogeographic and evolutionary history of the biota of eastern Australia’s woodlands also remains poorly known, especially when compared to rainforests to the east, or the arid biome to the west. Here we present an analysis of patterns of mitochondrial genetic diversity in two species of Pygopodid geckos with distributions centred on the Brigalow Belt Bioregion of eastern Queensland. One moderately large and semi-arboreal species, Paradelma orientalis, shows low genetic diversity and no clear geographic structuring across its wide range. In contrast a small and semi-fossorial species, Delma torquata, consists of two moderately divergent clades, one from the ranges and upland of coastal areas of south-east Queensland, and other centred in upland areas further inland. These data point to varying histories of geneflow and refugial persistance in eastern Australia’s vast but now fragmented open woodlands. The Carnarvon Ranges of central Queensland are also highlighted as a zone of persistence for cool and/or wet-adapted taxa, however the evolutionary history and divergence of most outlying populations in these mountains remains unstudied.","PeriodicalId":50267,"journal":{"name":"Israel Journal of Ecology & Evolution","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1163/22244662-20191081","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41601656","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 2

Gecko diversity: a history of global discovery 壁虎多样性：全球发现史

IF 1.2 4区环境科学与生态学

Israel Journal of Ecology & Evolution Pub Date : 2020-11-06 DOI: 10.1163/22244662-bja10003

P. Uetz, Alex Slavenko, Shai Meiri, M. Heinicke

{"title":"Gecko diversity: a history of global discovery","authors":"P. Uetz, Alex Slavenko, Shai Meiri, M. Heinicke","doi":"10.1163/22244662-bja10003","DOIUrl":"https://doi.org/10.1163/22244662-bja10003","url":null,"abstract":"1935 gecko species (and 224 subspecies) were known in December 2019 in seven families and 124 genera. These nearly 2000 species were described by ~950 individuals of whom more than 100 described more than 10 gecko species each. Most gecko species were discovered during the past 40 years. The primary type specimens of all currently recognized geckos (including subspecies) are distributed over 161 collections worldwide, with 20 collections having about two thirds of all primary types. The primary type specimens of about 40 gecko taxa have been lost or unknown. The phylogeny of geckos is well studied, with DNA sequences being available for ~76% of all geckos (compared to ~63% in other reptiles) and morphological characters now being collected in databases. Geographically, geckos occur on five continents and many islands but are most species-rich in Australasia (which also houses the greatest diversity of family-level taxa), Southeast Asia, Africa, Madagascar, and the West Indies. Among countries, Australia has the highest number of geckos (241 species), with India, Madagascar, and Malaysia being the only other countries with more than 100 described species each. As expected, when correcting for land area, countries outside the tropics have fewer geckos.","PeriodicalId":50267,"journal":{"name":"Israel Journal of Ecology & Evolution","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1163/22244662-bja10003","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46984823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 14

Origin, diversity, and conservation of karst-associated Bent-toed Geckos (Genus Cyrtodactylus) in Myanmar (Burma) 缅甸喀斯特弯趾壁虎（Cyrtodactylus属）的起源、多样性和保护

IF 1.2 4区环境科学与生态学

Israel Journal of Ecology & Evolution Pub Date : 2020-11-06 DOI: 10.1163/22244662-20191094

L. Grismer, L. Perry, E. Quah, Myint Kyaw Thura

{"title":"Origin, diversity, and conservation of karst-associated Bent-toed Geckos (Genus Cyrtodactylus) in Myanmar (Burma)","authors":"L. Grismer, L. Perry, E. Quah, Myint Kyaw Thura","doi":"10.1163/22244662-20191094","DOIUrl":"https://doi.org/10.1163/22244662-20191094","url":null,"abstract":"Fifty-eight percent of the 43 known species of the Bent-toed Geckos (Cyrtodactylus) from Myanmar are found only in karstic habitats in the Shan Plateau and Salween and Ayeyarwady basins. A stochastic character mapping analysis indicated that the occupation of karstic habitats evolved at least four times independently in Burmese lineages with both Sundaic and Indian origins. Karstic habitats not only serve as foci for speciation but are refugia for species extirpated from the surrounding forested habitats due to agricultural development. Despite the high levels of biodiversity and site-specific endemism in karstic habitats in Myanmar, they are some of the least protected ecosystems. The immense financial returns from unsustainable resource extraction (cement manufacturing) makes the challenge of legal karst conservation extremely difficult. Sadly, their continued exploitation for limestone shows no signs of abating. Until karst habitats in Myanmar are thoroughly investigated, a significant portion of this country’s herpetological diversity will remain underestimated and unprotected.","PeriodicalId":50267,"journal":{"name":"Israel Journal of Ecology & Evolution","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1163/22244662-20191094","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47251446","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 6

Spatial and species-level metrics reveal global patterns of irreplaceable and imperiled gecko phylogenetic diversity 空间和物种水平的指标揭示了不可替代和濒危的壁虎系统发育多样性的全球格局

IF 1.2 4区环境科学与生态学

Israel Journal of Ecology & Evolution Pub Date : 2020-11-06 DOI: 10.1163/22244662-bja10020

R. Gumbs, Rachel C. Williams, A. Lowney, Darrell Smith

{"title":"Spatial and species-level metrics reveal global patterns of irreplaceable and imperiled gecko phylogenetic diversity","authors":"R. Gumbs, Rachel C. Williams, A. Lowney, Darrell Smith","doi":"10.1163/22244662-bja10020","DOIUrl":"https://doi.org/10.1163/22244662-bja10020","url":null,"abstract":"\u0000Phylogenetic Diversity (PD) is increasingly recognised as a useful tool for prioritising species and regions for conservation effort. Increased availability of spatial and phylogenetic data for reptiles now facilitates their inclusion in phylogenetically-informed conservation prioritisation efforts. Geckos are a highly divergent and diverse clade that comprises almost 20% of global reptile diversity. Their global distribution is coincident with numerous anthropogenic threats, making them worthy of conservation prioritisation. Here, we combine phylogenetic, spatial distribution and extinction risk data for geckos with global human encroachment data to identify both regions and species representing irreplaceable gecko diversity at risk from human pressure. We show that high levels of irreplaceable gecko diversity are restricted to regions under intense human pressure, such as India, Sri Lanka and the Caribbean. There is a lack of extinction risk data for the western regions of Angola and Namibia, and yet these regions harbour high levels of irreplaceable diversity. At the species level, geckos display more unique PD than other lizards and snakes and are of greater conservation concern under our metric. The PD represented by Data Deficient geckos is at comparable risk to that of Endangered species. Finally, estimates of potential gecko diversity loss increase by up to 300% when species lacking extinction risk data are included. Our analyses show that many evolutionarily unique gecko species are poorly known and are at an increased risk of extinction. Targeted research is needed to elucidate the conservation status of these species and identify conservation priorities.","PeriodicalId":50267,"journal":{"name":"Israel Journal of Ecology & Evolution","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2020-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"64589717","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 6