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In shrubland ecosystems, shrubs as ecosystem engineers play an important role in structuring ground beetle communities. However, the influence of shrub vegetation on the distribution and diversity of ground beetles remains unknown in Gobi desert, northwest China, where shrubland is a major biome type. Using Gobi shrubland dominated by shrub species Nitraria sphaerocarpa and Reaumuria soongorica as a model system, we sampled ground beetle communities using a pitfall trapping method under canopies of both shrubs and in intershrub bare areas during spring, summer and autumn corresponding to the main period of beetle activity. Simultaneously, physical environment of the three microhabitats and plant characteristics of both shrubs were measured. We determined whether shrubs and species identity influence ground beetle distribution and diversity patterns and whether the response of beetles to the presence and species of shrubs is consistent across species. At the community level, total beetle abundance and species richness were significantly greater under shrubs than in intershrub bare areas, whereas more beetles were captured under N. sphaerocarpa than under R. soongorica. At the population level, eight dominant beetle species responded differently to the presence and species of shrubs. The abundance of Anatolica sp., Carabus sp., Cyphogenia chinensis, Microdera sp. and Sternoplax setosa was consistently much greater under shrubs than in intershrub bare areas, whereas the abundance of Blaps gobiensis, Lethrus apterus and Pterocoma reitteri under shrubs was similar to that in intershrub bare areas. The shrub N. sphaerocarpa was commonly preferred by Anatolica sp., C. chinensis and S. setosa, whereas the shrub R. soongorica was commonly preferred by L. apterus, but the abundance of B. gobiensis, Carabus sp., Microdera sp. and P. reitteri was unaffected by shrub species. Differences in the abundance, species richness and composition of ground beetles among microhabitat types were largely related to among-microhabitat differences in the physical environment and resource availability. Our results suggest that shrubs and species identity play key roles in structuring ground beetle communities, but their influence differed between species. This study emphasizes the importance of protecting shrub habitats for the maintenances of beetle biodiversity in this Gobi desert ecosystem. [ABSTRACT FROM AUTHOR]

Objective: To explore the feasibility of exact logistic regression, used as a complemental method for the maximum liklihood estimation, and to analyse with data small sample, unbalanced structure and highly stratal nature under the situations of questionable results or inexistence of the maximum likelihood estimation., Methods: Data from 37 postoperative breast cancer cases were analyzed in 1997 by exact logistic regression under SAS system., Results: Data calculated by SAS software showed that Quasi-complete separation of data points was detected but the results of maximum likelihood estimation did not exist, SAS outputs conflicted the results of the last maximum likelihood iteration (likelihood Chi-square and score Chi-square have similar P, less than 0.05, but the Wald chi-square had a larger P, more than 0.05). Under conditional exact parameter estimation, it appeared that: (1) the joint effect of conditional score statistics was 21.12 with P = 0.000 3; (2) for individual parameters, the effect conditional score statistics of histological classification (grades) was 5.80 with P = 0.020 8; axillary node metastasis (diversion) was 5.74 with P = 0.019 5; tumor size (size) was 0.79, with P = 0.647 6. The effects of tumor histological classification and axillary node metastasis were statistically significant on breast cancer tumour., Conclusion: Exact logistic regression seemed to be a very useful method in analyzing data from small sample when the maximum likelihood estimation was either with no effect or did not exist.