The article presents the biology of flowering and the daily dynamics of flowering of two species from the Lamiaceae family: ph. anisochila va ph. sogdiana of the distribution out in the Nuratau Mountains range.
<span style="font-family:Verdana;">The White-breasted Thrasher (</span><i><i><span style="font-family:Verdana;">Ramphocinclus</span></i><span> <i&...<span style="font-family:Verdana;">The White-breasted Thrasher (</span><i><i><span style="font-family:Verdana;">Ramphocinclus</span></i><span> <i><span style="font-family:Verdana;">brachyurus</span></i><span></span></span></i><span style="font-family:Verdana;">) is the smallest passerine bird in the Mimids family.</span><span style="font-family:Verdana;"> Ranked as “endangered” in the IUCN list, the demographic distribution of this species is spread unevenly across two islands in the Lesser Antilles. The Saint-Lucian subspecies, <i></i></span><i><i><span style="font-family:Verdana;">Ramphocinclus</span></i><span> <i><span style="font-family:Verdana;">brachyurus</span></i> <i><span style="font-family:Verdana;">sanctaeluciae</span></i><span style="font-family:Verdana;"></span></span></i><span style="font-family:Verdana;">, was estimated to number between 1200 and 1700 individuals, whereas the Martinique subspecies, <i></i></span><i><i><span style="font-family:Verdana;">Ramphocinclus</span></i><span> <i><span style="font-family:Verdana;">brachyurus</span></i> <i><span style="font-family:Verdana;">brachyurus</span></i><span style="font-family:Verdana;"></span></span></i><span style="font-family:Verdana;">, was estimated at between 200 and 400 individuals. As an endemic rare species with a high risk of extinction, the Martinique subspecies should be regarded as a conservation priority. The small size of the Martinique subspecies population, its restricted geographical range, and its narrow habitat tolerance make it quite difficult to study. The variability of morphological traits in this subspecies has not been biostatistically analyzed recently. In</span><span style="font-family:Verdana;"> order to update knowledge and fill in any gaps, we have used the morphometric approach to study the morphological variability of the Martinique subspecies. The study site is a small peninsula located in the northeast of t</span><span style="font-family:Verdana;">he island of Martinique (French West Indies) known as “la Caravelle”. We captured 63 White-breasted Thrashers which were marked, measured, and sexed before being released. We did not observe any significant differences betwe</span><span style="font-family:Verdana;">en the sexes, signifying an absence of sexual dimorphism. However, we were able to observe a significant variation in morphological traits between individuals measured inside and outside the national protected area of Ca</span><span style="font-family:Verdana;">ravelle. The body mass-tarsus ratio was equal at both sampled sites, something which could potentially be a clue to the bird’s adaptation to different habitats.</span>展开更多
Aims West Ordos Desert(WOD)in Inner Mongolia of China is charac-terized by unique geographical and ecological features to avoid the direct invasion of Quaternary Continental Glaciation,so it hosts many endangered reli...Aims West Ordos Desert(WOD)in Inner Mongolia of China is charac-terized by unique geographical and ecological features to avoid the direct invasion of Quaternary Continental Glaciation,so it hosts many endangered relic species such as Tetraena mongol-ica,Ammopiptanthus mongolicus and Potaninia mongolica from Tertiary.However,how these plants utilize available water sources remains unknown.The objective of this study was to investigate the water utilization strategies of selected rare and endangered plant species in WOD by comparing hydrogen isotope ratios between their xylem water and possible water sources following four rainfall events of varying-intensities.Methods We measured the hydrogen isotope ratios of xylem water from T.mongolica,A.mongolicus and P.mongolica and an accom-panying species Sarcozygium xanthoxylum and potential water sources(including precipitation and soil water in different soil layers from 0 to 150 cm)over 9 days following each of four varying-intensity rainfall events during the summer of 2012.And then calculated the percentage utilization of potential water sources by each species after each rainfall events using the linear mixing model.We also made the measurements of soil moisture and root biomass in favor of interpretation of plant water use strategies.Important Findings Tetraena mongolica,A.mongolicus and S.xanthoxylum primarily relied on deep soil water,whereas P.mongolica depended predomi-nantly on rainwater.These rare and endangered desert plants had differential utilizations of available water sources,so some com-petition for limited water existed among some species.Tetraena mongolica had a competitive relationship in absorption of soil moisture with the same family species S.xanthoxylum,suggesting that T.mongolica and S.xanthoxylum should be restored separately at different areas in the WOD.Overall,this study provides a better understanding of water use strategies of these four plants and scien-tific evidence for protecting rare and endangered plants,maintain-ing regional species diversity,and developing effective vegetation restoration plans in the WOD.展开更多
Aims One major goal of modern community ecology is to understand how deterministic and stochastic processes combine to drive community assembly.However,little empirical knowledge is known about how their relative impo...Aims One major goal of modern community ecology is to understand how deterministic and stochastic processes combine to drive community assembly.However,little empirical knowledge is known about how their relative importance varies between common and rare species.Methods We exploited two 30-year data sets of plant communities in a temperate steppe using two different methods.One is a null model method,and the other is a recently developed direct-calculation method.Important Findings We found that stochastic processes tended to be more important in influencing rare than common species.This finding suggests that stochastic forces may play a more important role in structuring communities with more rare species,providing a possible solution to the debate on the varied importance of deterministic and stochastic processes among different communities.展开更多
Our Earth is facing the challenge of accelerating climate change,which imposes a great threat to biodiversity.Many published studies suggest that climate warming may cause a dramatic decline in biodiversity,especially...Our Earth is facing the challenge of accelerating climate change,which imposes a great threat to biodiversity.Many published studies suggest that climate warming may cause a dramatic decline in biodiversity,especially in colder and drier regions.In this study,we investigated the effects of temperature,precipitation and a normalized difference vegetation index on biodiversity indices of rodent communities in the current or previous year for both detrended and nondetrended data in semi-arid grassland of Inner Mongolia during 1982-2006.Our results demonstrate that temperature showed predominantly positive effects on the biodiversity of small rodents;precipitation showed both positive and negative effects;a normalized difference vegetation index showed positive effects;and cross-correlation function values between rodent abundance and temperature were negatively correlated with rodent abundance.Our results suggest that recent climate warming increased the biodiversity of small rodents by providing more benefits to population growth of rare or less abundant species than that of more abundant species in Inner Mongolia grassland,which does not support the popular view that global warming would decrease biodiversity in colder and drier regions.We hypothesized that higher temperatures might benefit rare or less abundant species(with smaller populations and more folivorous diets)by reducing the probability of local extinction and/or by increasing herbaceous food resources.展开更多
Euptelea pleiosperma is a characteristic species of East Asian flora with both ornamental and scientific values.Based on the reduced-representation sequencing(RRS)technology of RAD-Seq,this study conducted high-throug...Euptelea pleiosperma is a characteristic species of East Asian flora with both ornamental and scientific values.Based on the reduced-representation sequencing(RRS)technology of RAD-Seq,this study conducted high-throughput Illumina paired-end sequencing to find SSR marker information in the genome of E.pleiosperma,and to screen and verify polymorphism of SSR markers.We obtained 5.5G of high-quality data using RAD-Seq.The total number of contigs of the RAD tags was 299,376,with the maximum contig length of 2,062 bp and the average length of 445 bp.From these sequences,we identified 20,718 SSR loci,with a distribution density of one SSR per 6.45 kb(1/6.45 kb).Among all SSRs,dinucleotides(52.00%)were the most detected SSRs,followed by mononucleotides(21.63%).AG/CT was the dominant motif in the SSR loci,accounting for 34.8%.Primers were successfully designed for 14,593 loci,and 100 pairs of these primers were randomly selected for chemical synthesis and validated by SSR-PCR amplification in 20 individuals of E.pleiosperma.Seventy-nine primers were able to amplify the target bands.Cervus 3.0 software was used to analyze the selected 20 SSR loci with good polymorphism.For the 20 SSR markers,the number of alleles ranged from 4 to 9,and the observed heterozygosity and expected heterozygosity were from 0.35 to 0.75 and 0.541 to 0.875,respectively.The information content of polymorphic loci ranged from 0.463 to 0.848,with an average value of 0.638.Among them,there were 18 highly polymorphic loci,and 20 SSR loci did not deviate from the Hardy-Weinberg equilibrium.Furthermore,the 20 pairs of SSR primers were used to conduct PCoA analysis based on Nei’s genetic distance of 51 individuals from three populations.The results showed that these SSR markers could distinguish genetic differences based on different geographical locations.展开更多
Background:Understanding the mechanisms underlying community assembly is helpful for conservation and restoration of communities, particularly those that contain rare and endangered species like Taxus fuana, which are...Background:Understanding the mechanisms underlying community assembly is helpful for conservation and restoration of communities, particularly those that contain rare and endangered species like Taxus fuana, which are endemic to the Western Himalayas. The niche (limiting similarity) vs. neutral (randomness) assembly of the T.fuana forest community in Gyirong County, Tibet, China, was investigated. The net relatedness index (NRI) was calculated using a phylogenetic tree. The phylogenetic characteristics of the community and its relationships with environment were analyzed.Results:The value of the mean NRI at the community level was less than-1.96, indicating that the phylogenetic structure was overdispersed;whereas majority of the NRIs at the tree, shrub, and herb layers were within-1.96 to1.96, indicating random dispersion. Environmental factors accounted for 44.38%, 46.52%, 24.04%, and 14.07%of the variation at the community level, tree, shrub, and herb layer, respectively. The phylogenetic structure at the community level and tree layer were significantly influenced by both topographic and soil factors, while shrub and herb layers tended to be affected by a single environmental factor.Conclusions:Community assembly of the T. fuana forest was simultaneously affected by niche and neutral processes, and their variations were closely related to the environment. Neutral process dominated community assembly in the shrub and herb layers. However, the interaction of limiting similarity and randomness played a dominant role at the community level and tree layer;and contributed to maintenance of biodiversity stability. The synergy of multiple environmental factors had a more obvious influence on community assembly than individual environmental factors, especially at the community level. These findings would help to understand the conservation of rare and endangered tree species, such as T. fuana, in the native community;and highlight the importance of random and non-random processes in assembly and biodiversity maintenance of alpine plant communities.展开更多
Background: The accurate estimation of soil nutrient content is particularly important in view of its impact on plant growth and forest regeneration. In order to investigate soil nutrient content and quality for the n...Background: The accurate estimation of soil nutrient content is particularly important in view of its impact on plant growth and forest regeneration. In order to investigate soil nutrient content and quality for the natural regeneration of Dacrydium pectinatum communities in China, designing advanced and accurate estimation methods is necessary.Methods: This study uses machine learning techniques created a series of comprehensive and novel models from which to evaluate soil nutrient content. Soil nutrient evaluation methods were built by using six support vector machines and four artificial neural networks.Results: The generalized regression neural network model was the best artificial neural network evaluation model with the smallest root mean square error(5.1), mean error(-0.85), and mean square prediction error(29). The accuracy rate of the combined k-nearest neighbors(k-NN) local support vector machines model(i.e. k-nearest neighbors-support vector machine(KNNSVM)) for soil nutrient evaluation was high, comparing to the other five partial support vector machines models investigated. The area under curve value of generalized regression neural network(0.6572) was the highest, and the cross-validation result showed that the generalized regression neural network reached 92.5%.Conclusions: Both the KNNSVM and generalized regression neural network models can be effectively used to evaluate soil nutrient content and quality grades in conjunction with appropriate model variables. Developing a new feasible evaluation method to assess soil nutrient quality for Dacrydium pectinatum, results from this study can be used as a reference for the adaptive management of rare and endangered tree species. This study, however, found some uncertainties in data acquisition and model simulations, which will be investigated in upcoming studies.展开更多
Aims Topography has long been recognized as an important factor in shaping species distributions.Many studies revealed that species may show species-habitat associations.However,few studies inves-tigate how species as...Aims Topography has long been recognized as an important factor in shaping species distributions.Many studies revealed that species may show species-habitat associations.However,few studies inves-tigate how species assemblages are associated with local habitats,and it still remains unclear how the community-habitat associa-tions vary with species abundance class and life stage.In this study,we analyzed the community-habitat associations in a subtropical montane forest.Methods The fully mapped 25-ha(500×500 m)forest plot is located in Badagongshan Nature Reserve in Hunan Province,Central China.It was divided into 625(20×20 m)quadrats.Habitat types were classified by multivariate regression tree analyses that cluster areas with similar species composition according to the topographic characteristics.Indicator species analysis was used to identify the most important species for structuring species assemblages.We also compared the community-habitat associations for two levels of species abundances(i.e.abundant and rare)and three different life stages(i.e.saplings,juveniles and adults),while accounting for sample size effects.Important Findings The Badagongshan plot was divided into five distinct habitat types,which explained 34.7%of the variance in tree species composi-tion.Even with sample size taken into account,community-habi-tat associations for rare species were much weaker than those for abundant species.Also when accounting for sample size,very small differences were found in the variance explained by topography for the three life stages.Indicator species of habitat types were mainly abundant species,and nearly all adult stage indicator species were also indicators in juvenile and sapling stages.Our study manifested that topographical habitat filtering was important in shaping over-all local species compositions.However,habitat filtering was not important in shaping rare species’distributions in this forest.The community-habitat association patterns in this forest were mainly shaped by abundant species.In addition,during the transitions from saplings to juveniles,and from juveniles to adults,the relative importance of habitat filtering was very weak.展开更多
Aims This study aimed to examine the changes in plant species richness,frequency and density along a habitat fragmentation gradient(with varied degrees of habitat fragmentation[DHFs])in a desertified grass-land of Hor...Aims This study aimed to examine the changes in plant species richness,frequency and density along a habitat fragmentation gradient(with varied degrees of habitat fragmentation[DHFs])in a desertified grass-land of Horqin Sandy Land,northeastern Inner Mongolia,China.Methods In this study,six landscape plots(500×500 m each)along a habi-tat fragmentation gradient were established.A new fragmentation index was formulated to study the effects of habitat fragmentation on biodiversity indices(species richness,frequency and density).Regression analyses(linear-or non-linear regression)were con-ducted to assess the changes in species richness,frequency and density along the habitat fragmentation gradient at plant commu-nity,functional group and species scales,respectively.Important Findings There was a non-linear relationship(following a quadratic function)between total species richness and the DHF.Total species richness reached its peak when the DHF was 0.2,beyond which species richness decreased along the fragmentation gradient.Plant func-tional groups showed their specific responses to habitat fragmenta-tion,and some non-linear relationships and thresholds existed.The relative richness of rare species also showed a non-linear response to habitat fragmentation,with the threshold being DHF=0.6.Species became rarer(both some common species and rare spe-cies)with the intensifying habitat fragmentation.Our study dem-onstrates the importance of the non-linear relationships and plant functional groups in exploring the effects of habitat fragmentation on biodiversity and implementing effective biological conservation in sand dunes.展开更多
文摘The article presents the biology of flowering and the daily dynamics of flowering of two species from the Lamiaceae family: ph. anisochila va ph. sogdiana of the distribution out in the Nuratau Mountains range.
文摘<span style="font-family:Verdana;">The White-breasted Thrasher (</span><i><i><span style="font-family:Verdana;">Ramphocinclus</span></i><span> <i><span style="font-family:Verdana;">brachyurus</span></i><span></span></span></i><span style="font-family:Verdana;">) is the smallest passerine bird in the Mimids family.</span><span style="font-family:Verdana;"> Ranked as “endangered” in the IUCN list, the demographic distribution of this species is spread unevenly across two islands in the Lesser Antilles. The Saint-Lucian subspecies, <i></i></span><i><i><span style="font-family:Verdana;">Ramphocinclus</span></i><span> <i><span style="font-family:Verdana;">brachyurus</span></i> <i><span style="font-family:Verdana;">sanctaeluciae</span></i><span style="font-family:Verdana;"></span></span></i><span style="font-family:Verdana;">, was estimated to number between 1200 and 1700 individuals, whereas the Martinique subspecies, <i></i></span><i><i><span style="font-family:Verdana;">Ramphocinclus</span></i><span> <i><span style="font-family:Verdana;">brachyurus</span></i> <i><span style="font-family:Verdana;">brachyurus</span></i><span style="font-family:Verdana;"></span></span></i><span style="font-family:Verdana;">, was estimated at between 200 and 400 individuals. As an endemic rare species with a high risk of extinction, the Martinique subspecies should be regarded as a conservation priority. The small size of the Martinique subspecies population, its restricted geographical range, and its narrow habitat tolerance make it quite difficult to study. The variability of morphological traits in this subspecies has not been biostatistically analyzed recently. In</span><span style="font-family:Verdana;"> order to update knowledge and fill in any gaps, we have used the morphometric approach to study the morphological variability of the Martinique subspecies. The study site is a small peninsula located in the northeast of t</span><span style="font-family:Verdana;">he island of Martinique (French West Indies) known as “la Caravelle”. We captured 63 White-breasted Thrashers which were marked, measured, and sexed before being released. We did not observe any significant differences betwe</span><span style="font-family:Verdana;">en the sexes, signifying an absence of sexual dimorphism. However, we were able to observe a significant variation in morphological traits between individuals measured inside and outside the national protected area of Ca</span><span style="font-family:Verdana;">ravelle. The body mass-tarsus ratio was equal at both sampled sites, something which could potentially be a clue to the bird’s adaptation to different habitats.</span>
基金National Natural Science Foundation of China(31170661,31290223)Special Research Program for Public-Welfare Forestry(201504423)Agriculture Science Technology Achievement Transformation Fund(2013GB24320620).
文摘Aims West Ordos Desert(WOD)in Inner Mongolia of China is charac-terized by unique geographical and ecological features to avoid the direct invasion of Quaternary Continental Glaciation,so it hosts many endangered relic species such as Tetraena mongol-ica,Ammopiptanthus mongolicus and Potaninia mongolica from Tertiary.However,how these plants utilize available water sources remains unknown.The objective of this study was to investigate the water utilization strategies of selected rare and endangered plant species in WOD by comparing hydrogen isotope ratios between their xylem water and possible water sources following four rainfall events of varying-intensities.Methods We measured the hydrogen isotope ratios of xylem water from T.mongolica,A.mongolicus and P.mongolica and an accom-panying species Sarcozygium xanthoxylum and potential water sources(including precipitation and soil water in different soil layers from 0 to 150 cm)over 9 days following each of four varying-intensity rainfall events during the summer of 2012.And then calculated the percentage utilization of potential water sources by each species after each rainfall events using the linear mixing model.We also made the measurements of soil moisture and root biomass in favor of interpretation of plant water use strategies.Important Findings Tetraena mongolica,A.mongolicus and S.xanthoxylum primarily relied on deep soil water,whereas P.mongolica depended predomi-nantly on rainwater.These rare and endangered desert plants had differential utilizations of available water sources,so some com-petition for limited water existed among some species.Tetraena mongolica had a competitive relationship in absorption of soil moisture with the same family species S.xanthoxylum,suggesting that T.mongolica and S.xanthoxylum should be restored separately at different areas in the WOD.Overall,this study provides a better understanding of water use strategies of these four plants and scien-tific evidence for protecting rare and endangered plants,maintain-ing regional species diversity,and developing effective vegetation restoration plans in the WOD.
基金National Natural Science Foundation(31300431)State Key Laboratory of Forest and Soil Ecology(LFSE2013-15)of ChinaChina Scholarship Council(CSC NO.201404910179).
文摘Aims One major goal of modern community ecology is to understand how deterministic and stochastic processes combine to drive community assembly.However,little empirical knowledge is known about how their relative importance varies between common and rare species.Methods We exploited two 30-year data sets of plant communities in a temperate steppe using two different methods.One is a null model method,and the other is a recently developed direct-calculation method.Important Findings We found that stochastic processes tended to be more important in influencing rare than common species.This finding suggests that stochastic forces may play a more important role in structuring communities with more rare species,providing a possible solution to the debate on the varied importance of deterministic and stochastic processes among different communities.
文摘Our Earth is facing the challenge of accelerating climate change,which imposes a great threat to biodiversity.Many published studies suggest that climate warming may cause a dramatic decline in biodiversity,especially in colder and drier regions.In this study,we investigated the effects of temperature,precipitation and a normalized difference vegetation index on biodiversity indices of rodent communities in the current or previous year for both detrended and nondetrended data in semi-arid grassland of Inner Mongolia during 1982-2006.Our results demonstrate that temperature showed predominantly positive effects on the biodiversity of small rodents;precipitation showed both positive and negative effects;a normalized difference vegetation index showed positive effects;and cross-correlation function values between rodent abundance and temperature were negatively correlated with rodent abundance.Our results suggest that recent climate warming increased the biodiversity of small rodents by providing more benefits to population growth of rare or less abundant species than that of more abundant species in Inner Mongolia grassland,which does not support the popular view that global warming would decrease biodiversity in colder and drier regions.We hypothesized that higher temperatures might benefit rare or less abundant species(with smaller populations and more folivorous diets)by reducing the probability of local extinction and/or by increasing herbaceous food resources.
基金This work was supported by the National Natural Science Foundation of China(31870697).
文摘Euptelea pleiosperma is a characteristic species of East Asian flora with both ornamental and scientific values.Based on the reduced-representation sequencing(RRS)technology of RAD-Seq,this study conducted high-throughput Illumina paired-end sequencing to find SSR marker information in the genome of E.pleiosperma,and to screen and verify polymorphism of SSR markers.We obtained 5.5G of high-quality data using RAD-Seq.The total number of contigs of the RAD tags was 299,376,with the maximum contig length of 2,062 bp and the average length of 445 bp.From these sequences,we identified 20,718 SSR loci,with a distribution density of one SSR per 6.45 kb(1/6.45 kb).Among all SSRs,dinucleotides(52.00%)were the most detected SSRs,followed by mononucleotides(21.63%).AG/CT was the dominant motif in the SSR loci,accounting for 34.8%.Primers were successfully designed for 14,593 loci,and 100 pairs of these primers were randomly selected for chemical synthesis and validated by SSR-PCR amplification in 20 individuals of E.pleiosperma.Seventy-nine primers were able to amplify the target bands.Cervus 3.0 software was used to analyze the selected 20 SSR loci with good polymorphism.For the 20 SSR markers,the number of alleles ranged from 4 to 9,and the observed heterozygosity and expected heterozygosity were from 0.35 to 0.75 and 0.541 to 0.875,respectively.The information content of polymorphic loci ranged from 0.463 to 0.848,with an average value of 0.638.Among them,there were 18 highly polymorphic loci,and 20 SSR loci did not deviate from the Hardy-Weinberg equilibrium.Furthermore,the 20 pairs of SSR primers were used to conduct PCoA analysis based on Nei’s genetic distance of 51 individuals from three populations.The results showed that these SSR markers could distinguish genetic differences based on different geographical locations.
基金funded by the National Key Research and Development Program of China(Grant No.2016YFC0503100)the National Natural Science Foundation of China(Grant Nos.31670429 and 31400346).
文摘Background:Understanding the mechanisms underlying community assembly is helpful for conservation and restoration of communities, particularly those that contain rare and endangered species like Taxus fuana, which are endemic to the Western Himalayas. The niche (limiting similarity) vs. neutral (randomness) assembly of the T.fuana forest community in Gyirong County, Tibet, China, was investigated. The net relatedness index (NRI) was calculated using a phylogenetic tree. The phylogenetic characteristics of the community and its relationships with environment were analyzed.Results:The value of the mean NRI at the community level was less than-1.96, indicating that the phylogenetic structure was overdispersed;whereas majority of the NRIs at the tree, shrub, and herb layers were within-1.96 to1.96, indicating random dispersion. Environmental factors accounted for 44.38%, 46.52%, 24.04%, and 14.07%of the variation at the community level, tree, shrub, and herb layer, respectively. The phylogenetic structure at the community level and tree layer were significantly influenced by both topographic and soil factors, while shrub and herb layers tended to be affected by a single environmental factor.Conclusions:Community assembly of the T. fuana forest was simultaneously affected by niche and neutral processes, and their variations were closely related to the environment. Neutral process dominated community assembly in the shrub and herb layers. However, the interaction of limiting similarity and randomness played a dominant role at the community level and tree layer;and contributed to maintenance of biodiversity stability. The synergy of multiple environmental factors had a more obvious influence on community assembly than individual environmental factors, especially at the community level. These findings would help to understand the conservation of rare and endangered tree species, such as T. fuana, in the native community;and highlight the importance of random and non-random processes in assembly and biodiversity maintenance of alpine plant communities.
基金financially supported by the Fundamental Research Funds for the Central Non-profit Research Institution of CAF (CAFBB2017ZB004)。
文摘Background: The accurate estimation of soil nutrient content is particularly important in view of its impact on plant growth and forest regeneration. In order to investigate soil nutrient content and quality for the natural regeneration of Dacrydium pectinatum communities in China, designing advanced and accurate estimation methods is necessary.Methods: This study uses machine learning techniques created a series of comprehensive and novel models from which to evaluate soil nutrient content. Soil nutrient evaluation methods were built by using six support vector machines and four artificial neural networks.Results: The generalized regression neural network model was the best artificial neural network evaluation model with the smallest root mean square error(5.1), mean error(-0.85), and mean square prediction error(29). The accuracy rate of the combined k-nearest neighbors(k-NN) local support vector machines model(i.e. k-nearest neighbors-support vector machine(KNNSVM)) for soil nutrient evaluation was high, comparing to the other five partial support vector machines models investigated. The area under curve value of generalized regression neural network(0.6572) was the highest, and the cross-validation result showed that the generalized regression neural network reached 92.5%.Conclusions: Both the KNNSVM and generalized regression neural network models can be effectively used to evaluate soil nutrient content and quality grades in conjunction with appropriate model variables. Developing a new feasible evaluation method to assess soil nutrient quality for Dacrydium pectinatum, results from this study can be used as a reference for the adaptive management of rare and endangered tree species. This study, however, found some uncertainties in data acquisition and model simulations, which will be investigated in upcoming studies.
基金National Natural Science Foundation of China(31270562,30900178,31200329 and 31500337)Key Laboratory of Aquatic Botany and Watershed Ecology,CAS(Y455432J02)the Chinese Forest Biodiversity Monitoring Network(29200931131101919).
文摘Aims Topography has long been recognized as an important factor in shaping species distributions.Many studies revealed that species may show species-habitat associations.However,few studies inves-tigate how species assemblages are associated with local habitats,and it still remains unclear how the community-habitat associa-tions vary with species abundance class and life stage.In this study,we analyzed the community-habitat associations in a subtropical montane forest.Methods The fully mapped 25-ha(500×500 m)forest plot is located in Badagongshan Nature Reserve in Hunan Province,Central China.It was divided into 625(20×20 m)quadrats.Habitat types were classified by multivariate regression tree analyses that cluster areas with similar species composition according to the topographic characteristics.Indicator species analysis was used to identify the most important species for structuring species assemblages.We also compared the community-habitat associations for two levels of species abundances(i.e.abundant and rare)and three different life stages(i.e.saplings,juveniles and adults),while accounting for sample size effects.Important Findings The Badagongshan plot was divided into five distinct habitat types,which explained 34.7%of the variance in tree species composi-tion.Even with sample size taken into account,community-habi-tat associations for rare species were much weaker than those for abundant species.Also when accounting for sample size,very small differences were found in the variance explained by topography for the three life stages.Indicator species of habitat types were mainly abundant species,and nearly all adult stage indicator species were also indicators in juvenile and sapling stages.Our study manifested that topographical habitat filtering was important in shaping over-all local species compositions.However,habitat filtering was not important in shaping rare species’distributions in this forest.The community-habitat association patterns in this forest were mainly shaped by abundant species.In addition,during the transitions from saplings to juveniles,and from juveniles to adults,the relative importance of habitat filtering was very weak.
基金This study was financially supported by National Natural Science Foundation of China(31600443,41501573)。
文摘Aims This study aimed to examine the changes in plant species richness,frequency and density along a habitat fragmentation gradient(with varied degrees of habitat fragmentation[DHFs])in a desertified grass-land of Horqin Sandy Land,northeastern Inner Mongolia,China.Methods In this study,six landscape plots(500×500 m each)along a habi-tat fragmentation gradient were established.A new fragmentation index was formulated to study the effects of habitat fragmentation on biodiversity indices(species richness,frequency and density).Regression analyses(linear-or non-linear regression)were con-ducted to assess the changes in species richness,frequency and density along the habitat fragmentation gradient at plant commu-nity,functional group and species scales,respectively.Important Findings There was a non-linear relationship(following a quadratic function)between total species richness and the DHF.Total species richness reached its peak when the DHF was 0.2,beyond which species richness decreased along the fragmentation gradient.Plant func-tional groups showed their specific responses to habitat fragmenta-tion,and some non-linear relationships and thresholds existed.The relative richness of rare species also showed a non-linear response to habitat fragmentation,with the threshold being DHF=0.6.Species became rarer(both some common species and rare spe-cies)with the intensifying habitat fragmentation.Our study dem-onstrates the importance of the non-linear relationships and plant functional groups in exploring the effects of habitat fragmentation on biodiversity and implementing effective biological conservation in sand dunes.
