Niche and interspecific association of dominant tree species in karst forest of Junzi Mountain, Eastern Yunnan, China

To understand the interspecific relationships of tree species in the karst forest of Junzi Mountain in Eas-tern Yunnan, we evaluated the niche and interspecific association of dominant tree species based on field survey plot data with the combining approaches of niche determination, χ2 test, association coefficient (AC), and Spearman rank correlation test. The results showed that the niche breadth of Quercus glaucoides was the largest and that of Juglans mandshurica was the smallest. The ranking of niche breadth was more consistent with the ranking of frequency than with that of importance values. The degree of niche overlap was generally low, with a mean value of 0.21, suggesting a low similarity in resource utilization among tree species. The overall association of dominant tree species was significantly positive, and the ratio of positive and negative association was 1.07, indicating that the communities were at a relatively stable and the late succession stage. The χ2 test and Spearman rank correlation test for tree dominant species showed that 65.3% species pairs were not significantly associated with each other, indicating a weak interspecific association. Both association coefficient (AC) and Spearman rank correlation coefficient showed significantly positive correlations with the corresponding niche overlap index. The species pairs of Q. glaucoides-Rhamnella martini, Viburnum propinquum-Zanthoxylum myriacanthum, Cladrastis delavayi-Carrierea calycina, Z. myriacanthum-C. delavayi had strong interspecific associations and wide ecological niches, thus may have potential application value in ecological restoration of karst region in eastern Yunnan and the vicinity areas.

[Effects of tree mortality on the spatial patterns and interspecific associations of individuals in karst evergreen deciduous broad-leaved mixed forests]

Tree mortality is an important ecological process in forests. It is crucial to understand how tree mortality affects spatial patterns and interspecific associations for revealing the mechanisms of tree mortality and community dynamics. We employed the correlation method of spatial point pattern analysis to analyse the variations in spatial patterns and interspecific relations before and after mortality using data obtained from two surveys of a 25 hm² plot in the Mulun National Natural Reserve, China. The results showed that most species had an aggregated distribution both pre- and post-mortality. The proportion of species with aggregated distribution reduced slightly post-mortality compared with that for pre-mortality. Increases in the number of species with random distribution at small scale indicated that tree death was not random. At the species level, there were significant positive associations between dead and live trees of the 13 common species at different levels of 0-30 m range, suggesting weak intraspecific and interspecific competition among dominant species. Pre- and post-mortality interspecific associations were mostly positive, which remained stable during the period of two surveys for most species, indicating that the community had reached a rather stable stage. Following tree mortality, the number of species with positive associations increased at 1-30 m scales, whereas the number of species with negative and no associations decreased at most scales. These results indicated that the pressure of interspecific competition was relieved to some extent after individual death.

[Niche and interspecific association of dominant tree species in Michelia odora community]

In order to understand the interspecific and ecological relationships of Michelia odora (extremely small population) community and strengthen the protection of wild M. odora resources in Junzifeng Nature Reserve, we studied the niche characteristics and interspecific associations of dominant tree species. The results showed that M. odora, Machilus chekiangensis, Schima superba, and Alniphyllum fortunei had obvious niche breadth advantages, which were the constructive species of the community. Among the 190 groups of species pairs among the 20 dominant tree species, 50.5% of species pairs had niche overlap value greater than 0.5. The degree of ecological niche differentiation among species was general. M. odora had large niche overlap with other 19 species, indicating a competitive risk when resources were insufficient. The overall associations of dominant tree species were significantly positive, indicating the community was at the late stage of relatively stable succession. The results ofχ² test, asso-ciation coefficient, and Pearson correlation coefficient showed that all the significance ratios of interspecific association were lower, and that the independence among species was relatively strong. There was a positive correlation between interspecific association and niche overlap. The M. odora community was relatively mature, with full utilization of resources and stable interspecific relationship. To promote the rejuvenation and create a good habitat of M. odora population, the population size with large overlap with M. odora niche and significant negative association could be appropriately limited, while that with positive interaction could be increased.

[Spatial distribution and correlation of dominant species of karst secondary forest in central Guizhou, China]

We analyzed the spatial distribution pattern and correlation of the top four dominant tree species in a 2 hm² karst secondary forest plot of Tianlong Mountain in central Guizhou, using pairwise correlation function g(r) combined with a completely random model (CSR). The results showed that the diameter structure of trees followed an inverted J-shape, and that more trees belonged to diameter class Ⅴ (≥10 cm) driven by the dominant trees of Lithocarpus confinis and Platycarya longipes. L. confinis presented an inverted J-shaped distribution, and the population could renew very well and was in the primary growth stage. The abundance of P. longipes and Itea yunnanensis increased gradually with increasing diameter class. The density of grown and large trees was far more than the young and small individuals, which indicated poor population regeneration, and the population was in the middle and late growth stages. The top dominant tree species, except L. confinis, showed clustering distribution at large scale, which was decreased gradually with scale and trended to distribute randomly. The pattern was particularly prominent in the diameter class for young trees. Different diameter classes of different tree species presented diffe-rent spatial distribution patterns which influenced by many factors. In terms of interspecific associations, the four dominant tree species showed negative or no associations. The higher importance value of tree species, the lower the degree of association with other dominant species. The two negative correlation tree species had the lowest degree of correlation at small scale. With the increase of spatial scale, the degree of negative correlation decreased gradually, and tended to be no correlation.

The Plant Interspecific Association in the Revegetated Alpine Grasslands Determines the Productivity Stability of Plant Community Across Restoration Time on Qinghai-Tibetan Plateau

Grassland cultivation is the key measure for restoring "Black Beach," the extremely degraded alpine meadow in the Three River Headwater Area of the Qinghai-Tibetan Plateau. In this study, we examined the inter-specific relationship in the vegetation community of cultivated grasslands with different restoration times through the network analysis method. The results showed that with the extension of restoration time, the development of cultivated grassland would lead to increasing neutral interactions among the plant species. The proportion of species with positive and negative associations in the community decreased, while the number of species-independent pairs increased significantly. The complexity of plant interspecific association (species network density) had more influence on community stability with the extension of recovery time, which can be used to quantify the characteristics of community structure.

Niches and interspecific association of major shrimp and crab species in Pishan waters of Zhejiang Province, China

Based on the fishery resource investigation data in Pishan waters of Zhejiang coastal area in November of 2015 (autumn), February (winter), May (spring) and August (summer) of 2016, we analyzed the spatio-temporal niche characteristics and interspecific association of the domi-nant shrimp and crab species using the methods of niche test, variance ratio, chi-square test, Spearman test and redundancy analysis. A total of 34 shrimp and crab species belonging to 14 families and 20 genera were identified. Among them, 10 species were collected in all the four seasons. Dominant species were Parapenaeopsis hardwickii, Exopalaemon carinicauda and Portunus trituberculatus. The temporal, spatial and spatio-temporal niche breadths of the major shrimp and crab species ranged from 0.03-1.34, 2.07-3.63 and 0.08-4.64, respectively. The cluster analysis of niche breadths suggested that all the species could be divided into narrow, medium and wide niche breadth groups under the 90% similarity level. In addition, the spatio-temporal niche overlap values of the major species in Pishan Sea were mainly at low level (68.9% of the species's Q_ik<0.3), implying little interspecific competition for resource utilization. The analysis of variance ratio showed that the major shrimp and crab species were mainly positively correlated, with 11.1% of the species showing significantly positive association. The JI index, OI index and Spearman test all showed the relationship between major shrimp and crab species tended to be positive correlation as a whole. Redundancy analysis showed that surface temperature, bottom temperature, and surface salinity were the main environmental factors affecting the distribution of shrimp and crab species in Pishan waters.

[Spatial pattern and interspecific association of tree species in coniferous and deciduous broad-leaved mixed forest under different disturbance intensities]

We explored the effects of disturbance densities on the spatial pattern and the association of tree species in the coniferous broadleaved mixed forest in Pangquangou Nature Reserve of Guandi Mountain. Using three factors including canopy density, stand density and number of stumps, we classified the disturbance intensities of different forest stands into three levels, non-disturbance, moderate disturbance, and severe disturbance. The spatial distribution pattern and the association of different tree species were analyzed by spatial point pattern K2 function. The results showed that the diameter distribution of trees in undisturbed plots was inverted 'J' type, while that of moderate disturbance and serious disturbance plots was under bimodal curve distribution. The stand distribution pattern showed a small-scale aggregated distribution under undisturbed and moderately distur-bance, and a random distribution under heavy disturbance. At the small scale, the coniferous and broadleaved species showed no correlation in undisturbed stands, were positively correlated in moderately disturbed stands, and negatively correlated in seriously disturbed stands. At large scale, they were no correlated in both moderately and seriously disturbed stands. The results suggested that abundance of trees with small diameter in the forests was negatively with disturbance intensity, which led to the lower degree of intraspecific aggregation at small scale. Meanwhile, appropriate levels of disturbance would benefit the collaborative use of environmental resources for trees. Our results revealed the impacts of disturbance density on forest community structure and could provide theoretical basis for forest management.

No Evidence of Competition Between the Blacklegged Tick (Acari: Ixodidae) and American Dog Tick on the Rodent Host White-Footed Deermouse (Rodentia: Cricetidae) in Southwestern Tennessee

Investigations that analyze interspecific associations of vectors on their hosts are important for understanding community structure and implementing ways to comprehend mechanisms of pathogen transmission. We assessed the interspecific association of two tick species (Ixodes scapularis Say (Ixodida: Ixodidae) and Dermacentor variabilis Say (Ixodida: Ixodidae)) on the rodent host Peromyscus leucopus Rafinesque (Rodentia: Cricetidae) at the Hobart Ames Research and Education Center in southwestern Tennessee. Of the rodents captured, 95 (63%) had neither species of tick, 6 (4%) had both tick species, 25 (16%) had I. scapularis only, and 26 (17%) had D. variabilis only. A coefficient of association (C7 = -0.08) was calculated, which suggested there was competition between the two species of ectoparasites, but this value was not significant, indicating that there was a neutral relationship between the tick species on P. leucopus. The co-occurrence of both tick species on their host at the same time suggested that the two tick species can occupy the same host and use the same resources without competing.

[Spatial distribution and interspecific associations of regenerating saplings in karst secondary forests.]

A 140 m×120 m plot was set in a secondary forest with more than 30 years natural reco-very after abandonment in Ziyun Miao and Buyi Autonomous County, a typical karst area in Guizhou Province. We investigated the spatial distribution and interspecific associations of regenerating sapling population using spatial point pattern analytical method. There were 1291 saplings with 39 tree species. Betula luminifera, Platycarya strobilacea, Liquidambar formosana, Pinus massoniana and Populus davidiana were the dominant populations of regenerating saplings, accounting for 83.7% of the saplings and 77.8% of the total importance value. The spatial distributions of B. luminifera, P. strobilacea and L. formosana were strongly aggregated at a spatial scale of 0-60 m, while the spatial distributions of P. massoniana and P. davidiana were aggregated at small scale and randomly distributed at large scale. The spatial associations among those dominant populations were mostly positively correlated, with positive correlations of P. massoniana with L. formosana and P. davidiana at small scale but no associations at large scale. In conclusion, the spatial distributions and interspecific associations differed among the dominant sapling populations, due to the different biological characteristics of different tree species, habitats and uses of spatial resources. Most of the stands investigated were dominated by pioneering species, with poor stand quality and unstable community structure. A mixed forest dominated by P. massoniana and B. luminifera would be the next stage of succession. We recommended that measures of forest management should be adopted to accelerate vegetation restoration.

An uneasy alliance: a nesting association between aggressive ants and equally fierce social wasps

Although the Neotropical territorially dominant arboreal ant Azteca chartifex Forel is very aggressive towards any intruder, its populous colonies tolerate the close presence of the fierce polistine wasp Polybia rejecta (F.). In French Guiana, 83.33% of the 48 P. rejecta nests recorded were found side by side with those of A. chartifex. This nesting association results in mutual protection from predators (i.e., the wasps protected from army ants; the ants protected from birds). We conducted field studies, laboratory-based behavioral experiments and chemical analyses to elucidate the mechanisms allowing the persistence of this association. Due to differences in the cuticular profiles of the two species, we eliminated the possibility of chemical mimicry. Also, analyses of the carton nests did not reveal traces of marking on the envelopes. Because ant forager flows were not perturbed by extracts from the wasps' Dufour's and venom glands, we rejected any hypothetical action of repulsive chemicals. Nevertheless, we noted that the wasps "scraped" the surface of the upper part of their nest envelope using their mandibles, likely removing the ants' scent trails, and an experiment showed that ant foragers were perturbed by the removal of their scent trails. This leads us to use the term "erasure hypothesis." Thus, this nesting association persists thanks to a relative tolerance by the ants towards wasp presence and the behavior of the wasps that allows them to "contain" their associated ants through the elimination of their scent trails, direct attacks, "wing-buzzing" behavior and ejecting the ants.

[Interspecific association of main fish species in the Haizhou Bay and its adjacent waters]

It is important to reveal the interspecific association and correlation of main species for deep understanding of fish community structure and function. Based on data collected from the bottom trawl surveys from 2013 to 2017 in the Haizhou Bay and the adjacent waters, we analyzed interspecific association of main species using Chi-square test, Jaccard index, and Spearman rank correlation coefficient. There were consistent results from χ²-test, Jaccard index, and Spearman's rank correlation analysis. The proportion of positively correlated species pairs was high in different years, whereas the number of significant or extremely significant species pairs was low. There were 9, 6, 7, 1, 0 significant or extremely significant species pairs over different years based on Jaccard index. There were 12, 20, 13, 5, 6 significant or extremely significant species pairs over different years based on Spearman's rank correlation coefficient. While there were inter-annual changes in related species pairs, the relationship between significant species pairs was relatively stable, indicating a relatively stable interspecific association in the main fish communities. The species within the same ecological type could replace each other in the niche, which have adapted to environmental changes in Haizhou Bay and its adjacent waters.

[Niches and interspecific association of dominant shrimp species in the offshore waters of southern Zhejiang Province, China]

Based on data from November of 2015 (autumn), February (winter), May (spring), and August (summer) of 2016 in the offshore waters of southern Zhejiang Province, the relationships between major shrimps species were examined by niche breadth, niche overlap, variance ratio, chi-square test, association coefficient and species pair co-occurrence percentage. The results showed that temporal niche breadth of Atypopenaeus stenodactylu was the largest, spatial niche breadth of Solenocera crassicornis was the largest, and A. stenodactylu had the largest spatio-temporal niche breadth. The temporal niche overlap between Parapenaeus fissuroides and Parapenaeopsis tenella was the highest. The spatial niche overlap between Solenocera koelbeli and Penaeus chinensis, P. fissuroides and Heterocarpoides laevicarina were the highest. The spatio-temporal niche overlap between S. koelbeli and P. chinensis was the highest. The analysis of variance ratio showed that the main shrimp species were significantly positively correlated. Positive correlation existed in 13 pairs (χ²≥3.841). Results from the association coefficient (AC) and co-occurrence percentage (PC) indicated that the interspecific association tended to be positive. Our results provide supports for exploring niche breadth and niche overlap of major shrimp species and improving niche differentiation.

[Niche and interspecific association of major nekton in the sea area to the east of the Nanji Islands]

According to the fishery resources investigation data in the east of the Nanji Islands during autumn in 2017 and spring in 2018, the inter-specific relationships and ecological relationships between major nekton were analyzed via the index of relative importance, niche breadth, cluster analysis, niche overlap, χ²-test, variance ratio test, association coefficient, percentage of co-occurrence, and point correlation coefficients. The results showed that there were 30 major nekton species in this area. The dominant species were Harpadon nehereus, Portunus trituberculatus, and Oratosquilla oratoria. The niche width of these dominant species was relatively wide. Based on the cluster analysis of niche breadth, the 30 major nekton species could be divided into three categories, wide niche breadth species, moderate niche breath species, and narrow niche breath species. The distribution range of niche overlap value was [0, 0.98], indicating that there were differences in the similarity of species to resource utilization and that the niche was differentiated and accompanied by inter-specific competition. The values of VR and W showed that there was a significant positive correlation among the major nekton species. The χ²-test results indicated significantly interspecific association for 76 species pair (χ²≥3.841), which was related to community stability and species coexistence. Results of association coefficient, percentage of co-occurrence and point correlation coefficients test suggested that the interspecific association was strong and tended to be positive.

Spatial patterns and interspecific associations among trees at different stand development stages in the natural secondary forests on the Loess Plateau, China

Quercus wutaishansea populations on the Loess Plateau are currently becoming more dominant in natural secondary forests, whereas Pinus tabulaeformis is declining. In the present paper, the diameter class (instead of age) was used to classify the different growth stages as juvenile, subadult, or adult, and the univariate function g(r) was used to analyze the dynamic changes in spatial patterns and interspecific associations in three 1-ha tree permanent plots on the Loess Plateau, NW China. Our results suggested that the niche breadth changed with the development stage. The diameter distribution curve was consistent with the inverted "J" type, indicating that natural regeneration was common in all three plots. There was a close relationship between the spatial pattern and scale, which showed significant aggregation at small distances, and became more random as distance increased, but in the Pinus + Quercus mixed forests, the whole species were aggregated at distances up to 50 m. The degree of spatial clumping decreased from juvenile to subadult and from subadult to adult. The spatial pattern also differed at different growth stages, likely due to strong intraspecific competition. Associations among different growth stages were positively correlated at small scales. Our study is important to the understanding of the development of the Q. wutaishansea forests; thus, the spatial dynamic change features should be received greater attention when planning forest management and developing restoration strategies on the Loess Plateau.

[Interspecific associations of the main tree populations of the Cyclobalanopsis glauca community in Karst hills of Guilin, Southwest China]

Analyzing the interspecific association of major tree populations of Cyclobalanopsis glauca community and revealing the coexistence among the populations would provide theoretical basis for the restoration and reconstruction, management and biodiversity conservation of Karst hills in Gui-lin. Based on field survey, the &chi;² test, association coefficient (AC), co-occurrence percentage (PC), Ochiai index (OI), Dice index (DI), and principal component analysis (PCA) were used to investigate the interspecific association and eco-taxonomic classification of the top 22 tree species in Cyclobalanopsis glauca community in Guilin Karst Rocky Mountains. The results showed that there was a significant positive correlation between the interspecific associations of the 22 main tree populations, indicating that this community was in a stable climax stage. The results of &chi;² test showed that 108 pairs of 231 species pairs had positive associations, 115 species pairs had negative associations, 8 species pairs were unrelated, with the positive and negative linkage ratio being 93.9%. The vast majority of species pairs showed no significant association. The strong indepen-dence between species might be mainly caused by the higher habitat heterogeneity of the Karst hills in Guilin which led to the differentiation of niches between species. The results of AC, PC, OI and DI were basically consistent with that of &chi;² test, indicating that the analysis of interspecific association should be based on the &chi;² test and supplemented by AC, PC, OI and DI indices. According to the PCA and evaluation of interspecific relationships, the 22 main tree species were divided into three ecological groups. The species within each group had the same adaptability to habitat but different ecological requirements.

[Niche and interspecific associations of major nekton in northern coastal waters in Yuhuan, Taizhou, China]

Base on the data from fishery resources survey carried out in northern coastal waters in Yuhuan in November 2016 (autumn) and April 2017 (spring), we examined the niche and interspecific associations of major nekton by the methods of index of relative importance (IRI), niche breadth, niche overlap, the variance ratio (VR), X²-test, association coefficient (AC), Jaccard index (JI), point correlation coefficient (Φ) and Spearman rank correlation index. The ecological niche breadth of Portunus trituberculatus was the largest, with the absolute competitive advantage. The niche breadths of the important economic species Coilia nasus and Octopus variabilis were the smallest, which was at a weak competitive position. The niche overlap of the major nekton species in this area was uneven, possibly caused by the diversity of local environments. Overall interspecific associations indicated that insignificant negative correlation existed among major nekton species. All results of the X²-test, association coefficient (AC) and Jaccard index (JI) were consistent with that of overall interspecific associations, which indicated the independent trend among species. The correlation coefficients (Φ) and the Spearman rank correlation index revealed that the positive coupling pairs were more than the negative ones. It was due to the positive association among the other 14 species, caused by the spatial exclusion from large captured individuals of Muraenesox cinereus. According to the Spearman rank correlation and cluster analysis, 15 species could be divided into five ecological groups. The species within one ecological group had similar ecologically adaptable requirements of habitat, while the species from different ecological groups had different living habits and different ecological requirements.

[Interspecific association and functional group classification of the dominant populations in shrub layer in secondary forest of Pinus tabuliformis in Qinling Mountain, China.]

We analyzed the interspecific association among 20 dominant populations in shrub layer in secondary natural forest of Pinus tabuliformis in Qinling Mountain, China, with X²-test, the association coefficients and the percentage of common occurrence. The results showed that the species pairs with significant positive associations accounted for only 7.4% of the total 190 species pairs. The species pairs such as Lespedeza bicolor and Elaeagnus pungens, Toxicodendron vernicifluum and Pinus tabuliformis, Euonymus alatus and Cerasus tomentosa had extremely significant positive correlations, whereas most of the species pairs showed weak interspecific association. The ratio of positive and negative correlations was less than 1. The results suggested that the interspecific association was relatively weak. Species were with certain independence among dominant populations. Community structure was at an unstable mid-stage with dynamic succession. According to the interspecific association and cluster analysis, combined with biological and ecological characters, the 20 dominant populations in shrub layer were classified into four functional groups. The ecological requirement and resource use pattern of species within the same functional groups were similar, exhibiting a close connection between the shrub species. The connection between different functional groups was relatively loose.

Tree hole mosquito species composition and relative abundances differ between urban and adjacent forest habitats in northwestern Argentina

Water-holding tree holes are main larval habitats for many pathogen vectors, especially mosquitoes (Diptera: Culicidae). Along 3 years, the diversity and composition of mosquito species in tree holes of two neighbouring but completely different environments, a city and its adjacent forest, were compared using generalized linear mixed models, PERMANOVA, SIMPER and species association indexes. The city area (Northwest Argentina) is highly relevant epidemiologically due to the presence of Aedes aegypti L. (main dengue vector) and occurrence of dengue outbreaks; the Yungas rainforests are highly biologically diverse. In total seven mosquito species were recorded, in descending order of abundance: Ae. aegypti, Haemagogus spegazzinii Brèthes, Sabethes purpureus (Theobald), Toxorhynchites guadeloupensis Dyar and Knab, Aedes terrens Walker, Haemagogus leucocelaenus Dyar & Shannon and Sabethes petrocchiae (Shannon and Del Ponte). The seven mosquito species were recorded in both city sites and forested areas; however, their mosquito communities significantly diverged because of marked differences in the frequency and relative abundance of some species: Tx. guadeloupensis and Ae. aegypti were significantly more abundant in forest and urban areas, respectively. Positive significant associations were detected between Ae. aegypti, Hg. spegazzinii and Hg. leucocelaenus. The combined presence of Ae. aegypti, Haemagogus and Sabethes in the area also highlight a potential risk of yellow fever epidemics. Overall results show an impoverished tree hole mosquito fauna in urban environments, reflecting negative effects of urbanization on mosquito diversity.

How do similarities in spatial distributions and interspecific associations affect the coexistence of Quercus species in the Baotianman National Nature Reserve, Henan, China

Congeneric species often have similar ecological characteristics and use similar resources. These similarities may make it easier for them to co-occur in a similar habitat but may also lead to strong competitions that limit their coexistence. Hence, how do similarities in congeneric species affect their coexistence exactly? This study mainly used spatial point pattern analysis in two 1 hm2 plots in the Baotianman National Nature Reserve, Henan, China, to compare the similarities in spatial distributions and interspecific associations of Quercus species. Results revealed that Quercus species were all aggregated under the complete spatial randomness null model, and aggregations were weaker under the heterogeneous Poisson process null model in each plot. The interspecific associations of Quercus species to non-Quercus species were very similar in Plot 1. However, they can be either positive or negative in different plots between the co-occurring Quercus species. The spatial distributions of congeneric species, interspecific associations with non-Quercus species, neighborhood richness around species, and species diversity were all different between the two plots. We found that congeneric species did have some similarities, and the closely related congeneric species can positive or negative associate with each other in different plots. The co-occurring congeneric species may have different survival strategies in different habitats. On the one hand, competition among congenerics may lead to differentiation in resource utilization. On the other hand, their similar interspecific associations can strengthen their competitive ability and promote local exclusion to noncongeneric species to obtain more living space. Our results provide new knowledge for us to better understand the coexistence mechanisms of species.

[Spatial point pattern analysis of main trees and flowering Fargesia qinlingensis in Abies fargesii forests in Mt Taibai of the Qinling Mountains, China]

In Abies fargesii forests of the giant panda's habitats in Mt. Taibai, the spatial distribution patterns and interspecific associations of main tree species and their spatial associations with the understory flowering Fargesia qinlingensis were analyzed at multiple scales by univariate and bivaria-te O-ring function in point pattern analysis. The results showed that in the A. fargesii forest, the number of A. fargesii was largest but its population structure was in decline. The population of Betula platyphylla was relatively young, with a stable population structure, while the population of B. albo-sinensis declined. The three populations showed aggregated distributions at small scales and gradually showed random distributions with increasing spatial scales. Spatial associations among tree species were mainly showed at small scales and gradually became not spatially associated with increasing scale. A. fargesii and B. platyphylla were positively associated with flowering F. qinlingensis at large and medium scales, whereas B. albo-sinensis showed negatively associated with flowering F. qinlingensis at large and medium scales. The interaction between trees and F. qinlingensis in the habitats of giant panda promoted the dynamic succession and development of forests, which changed the environment of giant panda's habitats in Qinling.

[Niche and interspecific association of the dominant fish in the south coastal waters of Wenzhou, China]

The studies about the niche and interspecific association in China were mainly focused on the plants, birds and marine animals, and seldom on fish. Based on the fishery resources survey in spring (May) and autumn (September) in 2015, the associations among major fish species in south coastal waters of Wenzhou were investigated. The methods including niche breadth, niche overlap, variance ratio (VR), Χ²-test, association coefficient (AC), percentage of co-occurrence (PC) and point correlation coefficients (Ф) were used. The results showed that 47 fish species were identified, including 9 orders, 27 families and 41 genera. Four species were dominant species and 9 were important species, which together accounted for 17%. The niche breadth cluster analysis demonstrated two clearly identifiable ecological niches. The first one referred to wide niche that included Harpodon nehereus, Collichthys lucidus, Engraulis japonicas, Pampus echinogaster, Argyrosomus argentatus, Polynemus sextarius, Decapterus maruadsi and Trichiurus haumela, and the second one was narrow niche that included Muraenesox cinereus, Amblychaeturichthys hexanema, Cunoglossus robustus, Pseudosciaena polyactis and Ilisha elongate. The niche overlap value of the main fish was 0-0.90, indicating that there was difference in the resource utilization among the species. The ecological niche widths of C. robustus and M. cinereus were narrow, and the overlap values were high. This indicated that there was competition between these two species. The VR analysis revealed significant positive correlation among the main fish species. In view of the advantages of Ф value, which could reduce the impact of the analysis results of Χ²-test, AC and PC to the interspecific association, the Ф value method was selected in this study, and the association of 63 couples were positive. Both the interspecific association and ecological niche had different degrees of correlation with the stability of community structure and community succession.

Grazer exclusion alters plant spatial organization at multiple scales, increasing diversity

Grazing is one of the most important factors influencing community structure and productivity in natural grasslands. Understanding why and how grazing pressure changes species diversity is essential for the preservation and restoration of biodiversity in grasslands. We use heavily grazed subalpine meadows in the Qinghai-Tibetan Plateau to test the hypothesis that grazer exclusion alters plant diversity by changing inter- and intraspecific species distributions. Using recently developed spatial analyses combined with detailed ramet mapping of entire plant communities (91 species), we show striking differences between grazed and fenced areas that emerged at scales of just one meter. Species richness was similar at very small scales (0.0625 m²), but at larger scales diversity in grazed areas fell below 75% of corresponding fenced areas. These differences were explained by differences in spatial distributions; intra- and interspecific associations changed from aggregated at small scales to overdispersed in the fenced plots, but were consistently aggregated in the grazed ones. We conclude that grazing enhanced inter- and intraspecific aggregations and maintained high diversity at small scales, but caused decreased turnover in species at larger scales, resulting in lower species richness. Our study provides strong support to the theoretical prediction that inter- and intraspecific aggregation produces local spatial patterns that scale-up to affect species diversity in a community. It also demonstrates that the impacts of grazing can manifest through this mechanism, lowering diversity by reducing spatial turnover in species. Finally, it highlights the ecological and physiological plant processes that are likely responding to grazing and thereby altering aggregation patterns, providing new insights for monitoring, and mediating the impacts of grazing.