Demographic variation and habitat specialization of tree species in a diverse tropical forest of Cameroon

Background： Many tree species in tropical forests have distributions tracking local ridge-slope-valley topography. Previous work in a 50-ha plot in Korup National Park, Cameroon, demonstrated that 272 species, or 63% of those tested, were significantly associated with topography. Methods： We used two censuses of 329,000 trees ≥1 cm dbh to examine demographic variation at this site that would account for those observed habitat preferences. We tested two predictions. First, within a given topographic habitat, species specializing on that habitat （＇residents＇） should outperform species that are specialists of other habitats （＇foreigners＇）. Second, across different topographic habitats, species should perform best in the habitat on which they specialize （＇home＇） compared to other habitats （＇away＇）. Species＇ performance was estimated using growth and mortality rates. Results： In hierarchical models with species identity as a random effect, we found no evidence of a demographic advantage to resident species. Indeed, growth rates were most often higher for foreign species. Similarly, comparisons of species on their home vs. away habitats revealed no sign of a performance advantage on the home habitat. Conclusions＂ We reject the hypothesis that species distributions along a ridge-valley catena at Korup are caused by species differences in trees _〉1 cm dbh. Since there must be a demographic cause for habitat specialization, we offer three alternatives. First, the demographic advantage specialists have at home occurs at the reproductive or seedling stage, in sizes smaller than we census in the forest plot. Second, species may have higher performance on their preferred habitat when density is low, but when population builds up, there are negative density-dependent feedbacks that reduce performance. Third, demographic filtering may be produced by extreme environmental conditions that we did not observe during the census interval.

Biological and extrinsic correlates of extinction risk in Chinese lizards

China is a country with one of the most species-rich reptile faunas in the world.However,nearly a quarter of Chinese lizard species assessed by the China Biodiversity Red List are threatened.Nevertheless,to date,no study has explicitly examined the pattern and processes of extinction and threat in Chinese lizards.In this study,we conducted the first comparative phylogenetic analysis of extinction risk in Chinese lizards.We addressed the following 3 questions:(1)What is the pattern of extinction and threat in Chinese lizards?(2)Which species traits and extrinsic factors are related to their extinction risk?(3)How can we protect Chinese lizards based on our results?We collected data on 10 species traits(body size[BS],clutch size,geographic range size,activity time,reproductive mode,habitat specialization[HS],habitat use,leg development,maximum elevation,and elevation range)and 7 extrinsic factors(mean annual precipitation(MAP),mean annual temperature,mean annual solar insolation,normalized difference vegetation index(NDVI),human footprint,human population density,and human exploitation).After phylogenetic correction,these variables were used separately and in combination to assess their associations with extinction risk.We found that Chinese lizards with a small geographic range,large BS,high HS,and living in high MAP areas were vulnerable to extinction.Conservation priority should thus be given to species with the above extinction-prone traits so as to effectively protect Chinese lizards.Preventing future habitat destruction should also be a primary focus of management efforts because species with small range size and high HS are particularly vulnerable to habitat loss.