| Ants are one group of the most important social insects in the world. Famous for their numerous species, large individual numbers and huge distribution range, they are considered as the dominant inset group in forest ecosystem, as well as the indicator of biodiversity and vertical bands. As ants have close relationship with human beings, it has important economic significance to research them.Southeastern Tibet is located in the gather place of Himalaya and Hengduan Mountain remainder. In this area, it is significant for dense forests, appropriate temperature, abundant rain full, and rich biological resources. The superior natural conditions make this area well known as the "Jiangnan of Tibet". But in the past, the ant researches in this area are very limit due to the inconvenient traffic. During the period from 1889 to 2004, researchers from home and abroad only reported 67 valid ant species in Tibet. In order to understand the fundamental situations of the ant species, diversity, and distribution pattern in this area, ant diversity and spatial distribution were probed by sample-plot and hand collecting methods.In this study,8 subfamilies,50 genera, and 174 species of Formicidae are recognized in Southeastern Tibet. In which,25 new species are included,5 species are newly recorded in China,91 species are newly recorded in Tibet. The 25 new species are namely Myopias luoba sp. nov., M. menba sp. nov., Cryptopone zala sp. nov., Ponera zayuensis sp. nov., Ponera bomiana sp. nov., Ponera linzhiensis sp. nov., Ponera xiania sp. nov., Vombisidris tibeta sp. nov., Perissomyrmex medogensis sp. nov., Stenamma yaluzangbum sp. nov., Tetramorium dongjium sp. nov., Myrmica dela sp. nov., Myrmica sejila sp. nov., Leptothorax damus sp. nov., Leptothorax zayus sp. nov., Leptothorax gus sp. nov., Leptothorax jiangtorus sp. nov., Aphaenogaster zhala sp. nov., Prenolepis demula sp. nov., Lasius cibanus sp. nov., Lasius zayus sp. nov., Lasius pailongensis sp. nov., Camponotus linzhiensis sp. nov., Camponotus medogensis sp. nov. and Camponotus beibengensis sp. nov., The 5 newly recored species are Stenamma kashmirense, Paratrechina sakurae, Lasius himalayanus, Camponotus rufoglaucus, and Pheidole bhavanae.Biodiversity analysis shows that:(1) The composition of dominant species is different in various types of vegetation, slopes and altitudes. The dominance species have obvious tropical and subtropical character in the rainforest, monsoon evergreen broad-leaved forest. The character is also obvious on the south and east slope, and in the low altitude region. So that, vegetation type, slope direction, and altitude have important influence to the development of ant communities. (2) In different vegetation types, the richness and diversity of ant species are higher in tropical monsoon forest and subtropical evergreen broad-leaved forest which possess superior living condition. In different slopes, the conditions of south and east slope are more suitable for ants, so that the richness and diversity of ant species on the south and east slopes are the highest of all the slopes. And at the different altitudes, the richness and diversity of ant species would drop with the increasing of altitude. In the region of low altitude, all kinds of environmental factors are benefit for the development of ant communities, so the richness and diversity are the highest. In contrast, in the region of high altitude, the richness and diversity is the lowest. (3) Community similarity analysis shows that the composition and structure of vegetation and the altitude have remarkable effect to the structure of ant community.The analysis of spatial distribution character shows that:(1) The subfamilies Myrmicinae and Formicinae distribute from the low altitude to the high altitude, they are the most widely distributed subfamilies. The vertical distribution ranges of Ponerinae, Dolichoderinae, and Cerapachyinae are relatively narrower, they only distributed in the area where is below 3000m. And Leptanillinae, Dorylinae, and Pseudomyrmecinae only distribute below 2000m, which are the narrowest in vertical distribution. Furthermore, the distributions of ant species which belong to the same subfamily or genus are very different. Some species have a wide vertical distribution even crossing two or three vertical zones, such as Myrmica bactriana and Pachycondyla luteipes. And some species only distribute in a single vertical zone, such as Aphaenogaster smythiesi and Pachycondyla javana. Horizontal distribution analysis indicates that the ant species in Southeastern Tibet perform latitudinal distribution rule. And most ant species distribute in the area from Zayu to Medog where has superior environmental conditions, whereas the ant species would be less and less to the north. But the influence of the altitude to the distribution of ant species is much greater than that of the latitude. (2) The analysis of habitats and nesting & foraging sites indicate that ant species firstly ensure to gain heat when they chose habitats and nesting sites. Secondly, they would ensure stable environments and rich food recourses. In the choosing of nesting & foraging sites, ant species in the same genus differentiate toward different directions so as to avoid competition among species. But the species in different genera would choose the similar nesting & foraging sites.This study has primarily revealed the ant species, diversity, and spatial distribution in Southeastern Tibet, and provided an important base for the correct identification of ant species in this area. The discovery and descriptions of large number of new species have contributed to the Formicidae contents of China and the world. The diversity and spatial distribution analysis provided an important base for the biodiversity protection in the area. All the type specimens of the new species are deposited in the Insect Collection, Southwest Forestry University (SWFU), Kunming, Yunnan Province, China.
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