The community assembly rules and species coexistence have always been interested by ecologists. The community phylogenetic structure is the consequence of the interaction process between the organisms and the abiotic ...The community assembly rules and species coexistence have always been interested by ecologists. The community phylogenetic structure is the consequence of the interaction process between the organisms and the abiotic environment and has been used to explain the relative impact of abiotic and biotic factors on species co-existence. In recent years, grassland degradation and biodiversity loss have become increasingly severe on the Mongolian Plateau, while the drivers for these changes are not clearly explored, especially whether climate change is a main factor is debated in academia. In this study, we examined the phylogenetic structure of grassland communities along five transects of climate aridity on the Mongolian Plateau, and analyzed their relations with environmental factors, with the aims to understand the formation mechanism of the grassland communities and the role of climatic factors. We surveyed grassland communities at 81 sites along the five transects, and calculated their net relatedness index(NRI) at two different quadrat scales(small scale of 1 m2 and large scale of 5 m2) to characterize the community phylogenetic structure and analyze its relationship with the key 11 environmental factors. We also calculated the generalized UniFrac distance(GUniFrac) among the grassland communities to quantify the influence of spatial distance and environmental distance on the phylogenetic β diversity. The results indicated that plant community survey using the large scale quadrat contained sufficient species to represent community compositions. The community phylogenetic structure of grasslands was significantly overdispersed at both the small and large scales, and the degree of overdispersion was greater at the large scale than at the small scale, suggesting that competitive exclusion instead of habitat filtering played a major role in determination of community composition. Altitude was the main factor affecting the community phylogenetic structure, whereas climatic factors, such as precipitation and temperature, had limited influence. The principal component analysis of the 11 environmental factors revealed that 94.04% of their variation was accounted by the first four principal components. Moreover only 14.29% and 23.26% of the variation in community phylogenetic structure were explained by the first four principal components at the small and large scales, respectively. Phylogenetic β diversity was slightly significantly correlated with both spatial distance and environmental distance, however, environmental distance had a less explanatory power than spatial distance, indicating a limited environmental effect on the community phylogenetic structure of grasslands on the Mongolian Plateau. In view of the limited effect of climatic factors on the community phylogenetic structure of grasslands, climate change may have a smaller impact on grassland degradation than previously thought.展开更多
目的系统评价我国大陆大学生高危性行为发生率情况,为引导大学生安全性行为、开展性与生殖健康教育提供参考依据。方法计算机检索中英文数据库CNKI、CBM、万方医学网、维普、PubMed、ScienceDirect、Web of Science、Cochrane library...目的系统评价我国大陆大学生高危性行为发生率情况,为引导大学生安全性行为、开展性与生殖健康教育提供参考依据。方法计算机检索中英文数据库CNKI、CBM、万方医学网、维普、PubMed、ScienceDirect、Web of Science、Cochrane library关于调查中国大学生高危性行为的文献,各库检索时间均为建库至2021年5月10日。通过文献筛选、资料完整提取及质量评价后,利用Stata 16.0进行Meta分析。结果最终纳入24篇文献,调查我国大学生总人数共计97327人。Meta分析结果显示,我国大学生性行为发生率为15%(95%CI:12%~17%),在有性行为的大学生中,第一次性行为无避孕套的发生率49%(95%CI:41%~57%);最近一次性行为无避孕套的发生率46%(95%CI:33%~60%);初次性行为<18岁的发生率30%(95%CI:13%~46%);多性伴侣的发生率28%(95%CI:21%~36%);临时性行为的发生率18%(95%CI:15%~21%);商业性行为的发生率9%(95%CI:7%~11%);男男性行为的发生率7%(95%CI:5%~8%)。结论近年来,我国大学生各类型高危性行为的发生率均较高,建议从家庭和学校层面重视并加强对大学生的性与生殖健康教育,从而预防性传播疾病在大学生群体中的广泛传播和意外妊娠的发生。展开更多
基金supported by the National Key Research and Development Program of China (2016YFC0500503)the Science and Technology Program of Inner Mongolia Autonomous Region of China (20140409, 201503001)
文摘The community assembly rules and species coexistence have always been interested by ecologists. The community phylogenetic structure is the consequence of the interaction process between the organisms and the abiotic environment and has been used to explain the relative impact of abiotic and biotic factors on species co-existence. In recent years, grassland degradation and biodiversity loss have become increasingly severe on the Mongolian Plateau, while the drivers for these changes are not clearly explored, especially whether climate change is a main factor is debated in academia. In this study, we examined the phylogenetic structure of grassland communities along five transects of climate aridity on the Mongolian Plateau, and analyzed their relations with environmental factors, with the aims to understand the formation mechanism of the grassland communities and the role of climatic factors. We surveyed grassland communities at 81 sites along the five transects, and calculated their net relatedness index(NRI) at two different quadrat scales(small scale of 1 m2 and large scale of 5 m2) to characterize the community phylogenetic structure and analyze its relationship with the key 11 environmental factors. We also calculated the generalized UniFrac distance(GUniFrac) among the grassland communities to quantify the influence of spatial distance and environmental distance on the phylogenetic β diversity. The results indicated that plant community survey using the large scale quadrat contained sufficient species to represent community compositions. The community phylogenetic structure of grasslands was significantly overdispersed at both the small and large scales, and the degree of overdispersion was greater at the large scale than at the small scale, suggesting that competitive exclusion instead of habitat filtering played a major role in determination of community composition. Altitude was the main factor affecting the community phylogenetic structure, whereas climatic factors, such as precipitation and temperature, had limited influence. The principal component analysis of the 11 environmental factors revealed that 94.04% of their variation was accounted by the first four principal components. Moreover only 14.29% and 23.26% of the variation in community phylogenetic structure were explained by the first four principal components at the small and large scales, respectively. Phylogenetic β diversity was slightly significantly correlated with both spatial distance and environmental distance, however, environmental distance had a less explanatory power than spatial distance, indicating a limited environmental effect on the community phylogenetic structure of grasslands on the Mongolian Plateau. In view of the limited effect of climatic factors on the community phylogenetic structure of grasslands, climate change may have a smaller impact on grassland degradation than previously thought.
文摘目的系统评价我国大陆大学生高危性行为发生率情况,为引导大学生安全性行为、开展性与生殖健康教育提供参考依据。方法计算机检索中英文数据库CNKI、CBM、万方医学网、维普、PubMed、ScienceDirect、Web of Science、Cochrane library关于调查中国大学生高危性行为的文献,各库检索时间均为建库至2021年5月10日。通过文献筛选、资料完整提取及质量评价后,利用Stata 16.0进行Meta分析。结果最终纳入24篇文献,调查我国大学生总人数共计97327人。Meta分析结果显示,我国大学生性行为发生率为15%(95%CI:12%~17%),在有性行为的大学生中,第一次性行为无避孕套的发生率49%(95%CI:41%~57%);最近一次性行为无避孕套的发生率46%(95%CI:33%~60%);初次性行为<18岁的发生率30%(95%CI:13%~46%);多性伴侣的发生率28%(95%CI:21%~36%);临时性行为的发生率18%(95%CI:15%~21%);商业性行为的发生率9%(95%CI:7%~11%);男男性行为的发生率7%(95%CI:5%~8%)。结论近年来,我国大学生各类型高危性行为的发生率均较高,建议从家庭和学校层面重视并加强对大学生的性与生殖健康教育,从而预防性传播疾病在大学生群体中的广泛传播和意外妊娠的发生。
