Negative Spatial Association Research Articles

Idiosyncratic soil-tree species associations and their relationships with drought in a monodominant Amazon forest

Monodominant forests are characterized by the strong influence of a single species on the structure and diversity of the community. In the tropics, monodominant forests are rare exceptions within the generally highly diverse tropical forest biome. Some studies have shown that tree monodominance may be a transient state caused by successional and demographic variation among species over time. Working in a Brosimum rubescens Taub. (Moraceae) monodominant forest at the southern edge of Amazonia, we tested the hypotheses that local-scale variation in intra- and interspecific spatial patterns of dominant tree species is affected by i) demographic rates of recruitment and mortality following severe droughts, ii) local variation in edaphic properties, and iii) occupation of species in the vertical layer of the forest. We quantified intra- and interspecific spatial patterns and edaphic associations of the five most abundant species using aggregation and association distance indices, and examined changes over time. We found some support for all hypotheses. Thus, intra- and interspecific spatial patterns of most species varied over time, principally after severe drought, emphasizing species-level variability and their interactions in sensitivity to this disturbance, even as B. rubescens monodominance was maintained. While positive and negative spatial associations with edaphic properties provide evidence of habitat specialization, the absence of negative spatial associations of B. rubescens with edaphic properties indicates that this species experiences little environmental restriction, and this may be one of the factors that explain its monodominance. Spatial repulsion and attraction between species in the same and in different vertical layers, respectively, indicates niche overlap and differentiation, while changes over time indicate that the relationships between species are dynamic and affected by drought disturbance.

Can co-occurrence networks predict plant-plant interactions in a semi-arid gypsum community?

Biotic interactions are important drivers shaping communities and their net effect can be difficult to assess when many species are involved or the study system is not well-known. Co-occurrence data are increasingly used to infer biotic interactions, but their accuracy remains poorly studied. We hypothesize that the predictions of biotic interactions based on co-occurrence networks are scale-dependent, being more accurate when co-occurrence is sampled at the spatial scale at which biotic interactions occur. We studied a plant community in a semi-arid gypsum environment, where plant-plant interactions result in a clumped distribution of the vegetation, which allows a straightforward identification of the scale at which interactions occur (i.e. vegetation patches). We used Bayesian network inferences to detect co-occurrence patterns at two spatial scales (patches of about 0.05 m2 and plots of 2.25 m2), and measured plant-plant interactions based on the effects of plant species on the establishment and recruitment of their neigbours. The co-occurrence network inferred at the patch scale did not reflect the plant-plant interactions observed, and the networks inferred at two different spatial scales showed contrasted topologies. Negative spatial associations between species predominated in the network inferred at the patch scale, partially due to a low species richness in vegetation patches. Meanwhile, positive relationships predominated at the plot scale. Relationships at the plot scale could reflect the final outcome of multi-specific biotic interactions, but without providing accurate information about pairwise interactions. Our results suggest that co-occurrence networks can be useful to generate hypothesis about the mechanisms structuring communities, but caution is needed in the interpretation of co-occurrence patterns in terms of biotic interactions, even when they are measured at apparently appropriate spatial scales.

天然次生林蒙古栎种群空间格局

PDF HTML阅读 XML下载 导出引用 引用提醒 天然次生林蒙古栎种群空间格局 DOI: 10.5846/stxb201707101243 作者: 作者单位: 中国林业科学研究院资源信息研究所,中国林业科学研究院资源信息研究所,中国林业科学研究院资源信息研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家"十三五"重点研发计划项目（2017YFC0504101） Spatial pattern of Quercus mongolica in natural secondary forest Author: Affiliation: Research Institute of Forest Resources Information Techniques,Chinese Academy of Forestry,Research Institute of Forest Resources Information Techniques,Chinese Academy of Forestry,Research Institute of Forest Resources Information Techniques,Chinese Academy of Forestry Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以蒙古栎天然次生林中的蒙古栎（Quercus mongolica）种群为研究对象，在吉林省汪清林业局塔子沟林场设置了2块1hm2群落组成和结构存在差异的样地（样地A、样地B）。采用相邻网格调查法将每块样地划分为100个10m×10m的调查单元，精确定位单元内每株林木的空间坐标（X，Y），调查所有胸径（DBH）≥1cm的林木基本信息。采用径阶替代年龄的方法，将蒙古栎划分为4个不同的生长阶段：Ⅰ龄级（1cm≤DBH < 10cm），Ⅱ龄级（10cm≤DBH < 20cm），Ⅲ龄级（20cm≤DBH < 30cm），Ⅳ龄级（DBH≥30cm）。运用单变量、双变量成对相关函数、标记相关函数、标记变异函数，分析了不同群落中蒙古栎种群在不同空间尺度上的分布格局。结果显示：（1）两块样地中蒙古栎在大尺度上均呈随机分布，聚集分布主要集中在中小尺度，这主要是由Ⅰ、Ⅱ龄级的蒙古栎在中小尺度上的强度聚集所致，两块样地均未出现均匀分布的格局；样地A中蒙古栎聚集的尺度和强度均明显大于样地B中蒙古栎的聚集；（2）样地A中Ⅰ、Ⅱ、Ⅲ龄级的蒙古栎之间在中小尺度上呈正关联，高龄级与低龄级之间则呈负关联，尤其是Ⅳ龄级与Ⅰ、Ⅱ龄级之间；而样地B中几乎未出现负关联的格局，各龄级之间以无关联为主，伴随以小尺度和低强度的正关联；（3）样地A中蒙古栎的空间自相关性较强，尤其体现在林木胸径方面；相比之下，样地B中胸径和树高的空间自相关得以减弱。上述结果表明，研究的空间尺度大小、物种的生长阶段、群落的发育程度均会给蒙古栎种群的空间分布格局造成影响。该研究有助于深入了解蒙古栎及蒙古栎次生林的现状、生长特性和发展趋势，可为东北林区大面积的蒙古栎天然次生林的可持续经营提供参考。 Abstract:Spatial signatures often reveal ecological processes, and spatial pattern analysis is an important method for studying population characteristics, interspecies relationships, and the relationships between population and the environment. Due to the distinctive characteristics and the current situation of Quercus mongolica in China, it is necessary to investigate the ecological processes in Q. mongolica stands. To realize the status and development tendency of the Q. mongolica population in the Q. mongolica natural secondary forest, its spatial patterns were studied based on two permanent sample plots(plot A and plot B) with different compositions and structures(i.e.,different coenotypes) over an area of 1hm2(100m×100m) in Tazigou Forest Farm of Wangqing Forestry Bureau, Jilin province. The essential features, which include species identity, diameter at breast height(DBH), tree height, clear bole height, crown breadth, and coordinate information of each tree(DBH ≥ 1), of the two plots were surveyed by the adjacent grid method(10m×10m). Using the method of diameter class(instead of the age), Q. mongolica was divided into four different growth stages:stage I(1cm ≤ DBH < 10cm), stage Ⅱ(10cm ≤ DBH < 20cm), stage Ⅲ(20cm ≤ DBH < 30cm), stage IV(DBH ≥ 30cm). In accordance with the spatial point pattern theory, univariate pair-correlation function g1(r), bivariate pair-correlation function g12(r), mark correlation function kmm(r), and mark variogram function γ(r) were adopted to evaluate the spatial patterns of Q. mongolica in different communities at various scales. The results showed that(1) All Q. mongolica populations in the two plots showed random spatial distribution at large scales, and the aggregated distribution was mainly concentrated at medium and small scales. The aggregated distribution at stages I and Ⅱ at medium and small scales was the primary cause for the above phenomenon. Uniform distribution was not observed in the two plots at all scales. The aggregated distribution of Q. mongolica in plot A is stronger than that in plot B.(2) The spatial associations of Q. mongolica among the stages I, Ⅱ, and Ⅲ in plot A are positive at medium and small scales. The spatial associations between older age and younger age classes were negative, especially between the stages IV, I, and Ⅱ. In plot B, however, negative spatial association was scarcely observed at all scales. The relationships between different stages were mostly uncorrelated with positive spatial association at small scale and low intensity.(3) The spatial autocorrelation of plot A is stronger than that of plot B, and the conspicuous expression mainly appears at DBH. The spatial autocorrelation of plot B for DBH and height is weakened to some extent compared to that of plot A. These results demonstrated that the spatial patterns of Q. mongolica are affected by the space scale of the sample plot, the growth stage of species, and the developmental stage of the community. This helps us to understand the current situation, growth characteristics, and developmental tendency of Q. mongolica population and its natural secondary forest, and can provide an important reference for sustainable forest management and ecosystem conservation in the Q. mongolica natural secondary forest area of northeast China. 参考文献 相似文献 引证文献

Negative spatial and coexistence patterns and species associations are uncommon for carrion beetles (Coleoptera: Silphidae) at a small scale

Biotic interactions are an important factor in determining community composition. However, spatial and coexistence patterns and species associations within a trophic group remain unclear, particularly for belowground ecosystems. We tested the hypothesis that the spatial patterns, coexistence patterns and species associations would be negative for ground carrion beetles (Coleoptera: Silphidae) at a small scale and that negative species associations would be stronger within a subfamily than between different subfamilies. To test this hypothesis, ground carrion beetles were collected from two permanent plots (each 300 × 300 m) within a mixed broad-leaved Korean pine forest in northeastern China and separated into the subfamilies Nicrophorinae and Silphinae. Geostatistical methods were used to evaluate the spatial patterns and spatial species associations. Null model analyses were performed to examine the coexistence patterns and coexisting species associations. Overall, most communities and species populations were positively spatially autocorrelated at multiple scales. Moreover, spatial patterns of all communities and most species populations were non-randomly aggregated, and most coexisting patterns of communities were also non-random. Furthermore, most spatial species associations were positive, with only a small number of nonsignificant negative spatial species associations observed between Nicrophorinae species. All coexisting species associations that were significant occurred only within the same subfamily. Notably, all significant spatial and coexisting species associations were positive. Based on this study, negative spatial and coexistence patterns and species associations are uncommon for carrion beetles at a small scale, and the only significant positive associations were within the same subfamily.

Behavioral interactions between terrestrial salamanders and spiders: competition or intraguild predation?

Several studies suggest that small terrestrial salamanders are important regulators of leaf litter arthropod communities, and likely contribute to ecosystem processes such as decomposition and nutrient cycling. Despite the recognition that salamanders have the potential to strongly affect ecosystem function through both direct and indirect pathways, little is known regarding the nature of interactions between small vertebrates and the large, predatory arthropods with which they share both microhabitat and prey. Our study was designed to explore interactions between Eastern Red-backed Salamanders, Plethodon cinereus, and spiders in the genus Wadotes in an eastern North American temperate forest ecosystem. We were particularly interested in teasing apart behaviors such as territoriality and intraguild predation in an attempt to determine specifically which interaction is most likely responsible for the observed negative relationship between salamander and spider abundance at our field site. Field data indicate that P. cinereus and large syntopic spiders exhibit negative spatial associations in the microhabitat beneath cover objects, a possible indication of interspecific territoriality. In our laboratory experiments, resident salamanders displayed agonistic postures similarly toward both intruding conspecifics and spiders, suggesting that salamanders may perceive large intruding spiders as competitors. Finally, we observed no injuries to individual P. cinereus or adult spiders even though occasional chases and bites by both were recorded during the behavioral trials. We found no evidence that adults or juveniles of P. cinereus were envenomated by adult Wadotes spp., and there were no instances of intraguild predation in this study. Multiple lines of evidence from this study, and others, suggest that the primary interaction between individuals of P. cinereus and large spiders is competitive in nature rather than predatory. We suggest that the cost associated with intraguild predation on salamanders with noxious skin secretions may preclude them from being preyed upon by spiders.

Population structure and spatial pattern of predominant tree species in a pine–oak mosaic mixed forest in the Qinling Mountains, China

ABSTRACTThis study investigated a typical pine-oak mosaic mixed forest in the Qinling Mountains, China. In the sample plot, the population structure and spatial distribution of the stems were analyzed for the predominant species, to identify the mechanisms of species coexistence and successional trends of the forest. The population structures of all species were bimodally distributed, with young trees (DBH <1 cm) more abundant than older trees. The population structures of Quercus aliena var. acuteserrata was bimodal and rather continuous. However, Pinus tabuliformis and Pinus armandii were discontinuously bimodal, with distinct size deficiencies. Q. aliena var. acuteserrata trees were clumped throughout the plot, although those of P. tabuliformis and P. armandii were clumped at small scales. Notable negative spatial associations between Q. aliena var. acuteserrata and P. tabuliformis were found at almost scales. P. armandii and Q. aliena var. acuteserrata were negatively spatially associated at small scales but positively associated at large scales. Our findings suggest that interspecific competition gradually develops among the predominant tree species. The dynamics of the pine-oak mosaic mixed forest formed a mosaic distribution of uniformly mixed types, with the slow infiltration of Q. aliena var. acuteserrata populations that would eventually establish a pure stand.

Grazing Effects on Precipitation-Driven Associations between Sagebrush and Perennial Grasses

Abstract. While many studies have addressed the effect of individual stresses on plant—plant associations, few have addressed the effects of co-occurring stresses. We therefore investigated how associations between Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and 2 native grasses (Poa secunda and Elymus elymoides) responded to different combinations of grazing and moisture stresses in the Great Basin, USA. Positive (i.e., facilitative) interactions between nurse plants and their beneficiaries are predicted to increase with increasing moisture limitation and grazing stress, but these interactions may break down at extreme levels of stress. We hypothesized that (1) competitive interactions and negative shrub-grass spatial associations would occur under the least stressful conditions (low grazing intensity / high precipitation); (2) positive shrub-grass spatial associations would dominate at intermediate levels of stress (high grazing intensity / high precipitation and low grazing intensity...

Responses of regeneration and species coexistence to single-tree selective logging for a temperate mixed forest in eastern Eurasia

The altered proportion of Korean pine to broadleaved tree species following selective logging strongly affected post-harvest regeneration and species coexistence pattern in a temperate mixed broadleaved/Korean pine forest in eastern Eurasian. Species interaction should be considered when implementing selective logging schemes. It has been documented widely that selective logging can exert varied influences on post-harvested forest structure and dynamics via different logging intensity and rotation. However, few studies have been extended to evaluate the effects of the tree species selected for removal, which is also a critical component in prescribing a selective harvest plan. To clarify the effects and underlying mechanisms of logged tree species selection on species coexistence and regeneration pattern in post-harvested mixed broadleaved/Korean pine (Pinus koraiensis Siebold & Zucc.) forest in Changbai Mountains, China. Four types of plots were established based on different selection of logged tree species. Stand structure, spatial distribution pattern and spatial association of major tree species were analyzed using spatial point pattern (SPP) analysis. The effect of soil nitrogen concentration on forest regeneration was also examined through a Pearson correlation analysis. Sapling density of both Korean pine and commercially valuable broadleaved tree species was significantly greater on plots where Korean pines were logged than on plots where only commercial broadleaved trees were removed. Soil N and density of saplings were not correlated. SPP analysis showed strong negative spatial association between mature Korean pine and saplings of most tree species in most sampling plots. The proportion of Korean pine to broadleaved tree species selected for removal can lead to different stand structure and spatial distribution patterns of tree locations. Due to species–specific competition effects, such variations in spatial association of tree locations can exert varied effects on regeneration in this pine-dominated Eurasian temperate forest. To promote post-harvest tree regeneration and species coexistence, forest managers in this region should consider controlling the density of competition-superior trees such as large-size Korean pines when implementing a selective logging scheme.

Agent-mediated spatial storage effect in heterogeneous habitat stabilizes competitive mouse lemur coexistence in Menabe Central, Western Madagascar.

BackgroundSpatio-temporal distribution patterns of species in response to natural and anthropogenic drivers provide insight into the ecological processes that determine community composition. We investigated determinants of ecological structure in a species assemblage of 4 closely related primate species of the family Cheirogaleidae (Microcebus berthae, Microcebus murinus, Cheirogaleus medius, Mirza coquereli) in western Madagascar by extensive line transect surveys across spatial and temporal heterogeneities with the specific goal of elucidating the mechanisms stabilizing competitive coexistence of the two mouse lemur species (Microcebus spp.).ResultsInterspecific competition between the mouse lemurs was indicated by negative spatial associations in degraded habitat and by habitat partitioning along anthropogenic disturbance gradients during dry seasons with resource scarcity. In non-degraded habitat, intraguild predator M. coquereli, but not C. medius, was negatively associated with M. murinus on the population level, whereas its regional distribution overlapped spatially with that of M. berthae. The species’ interspecific distribution pattern across spatial and temporal heterogeneities corresponded to predictions for agent-mediated coexistence and thus confirmed M. coquereli’s stabilizing impact on the coexistence of mouse lemurs.ConclusionsInterspecific interactions contribute to ecological structure in this cheirogaleid assemblage and determinants vary across spatio-temporal heterogeneities. Coexistence of Microcebus spp. is stabilized by an agent-mediated spatial storage effect: M. coquereli creates refuges from competition for M. berthae in intact habitat, whereas anthropogenic environments provide M. murinus with an escape from resource competition and intraguild predation. Species persistence in the assemblage therefore depends on the conservation of habitat content and context that stabilizing mechanisms rely on. Our large-scale population level approach did not allow for considering all potential functional and stochastic drivers of ecological structure, a key limitation that accounts for the large proportion of unexplained variance in our models.

Replacement of a dominant viral pathogen by a fungal pathogen does not alter the collapse of a regional forest insect outbreak.

Natural enemies and environmental factors likely both influence the population cycles of many forest-defoliating insect species. Previous work suggests precipitation influences the spatiotemporal patterns of gypsy moth outbreaks in North America, and it has been hypothesized that precipitation could act indirectly through effects on pathogens. We investigated the potential role of climatic and environmental factors in driving pathogen epizootics and parasitism at 57 sites over an area of ≈72,300 km(2) in four US mid-Atlantic states during the final year (2009) of a gypsy moth outbreak. Prior work has largely reported that the Lymantria dispar nucleopolyhedrovirus (LdNPV) was the principal mortality agent responsible for regional collapses of gypsy moth outbreaks. However, in the gypsy moth outbreak-prone US mid-Atlantic region, the fungal pathogen Entomophaga maimaiga has replaced the virus as the dominant source of mortality in dense host populations. The severity of the gypsy moth population crash, measured as the decline in egg mass densities from 2009 to 2010, tended to increase with the prevalence of E. maimaiga and larval parasitoids, but not LdNPV. A significantly negative spatial association was detected between rates of fungal mortality and parasitism, potentially indicating displacement of parasitoids by E. maimaiga. Fungal, viral, and parasitoid mortality agents differed in their associations with local abiotic and biotic conditions, but precipitation significantly influenced both fungal and viral prevalence. This study provides the first spatially robust evidence of the dominance of E. maimaiga during the collapse of a gypsy moth outbreak and highlights the important role played by microclimatic conditions.

Species-specific impact of introduced largemouth bass Micropterus salmoides in the Groot Marico Freshwater Ecosystem Priority Area, South Africa

Largemouth bass Micropterus salmoides are among the world's 100 worst invaders and negatively affect aquatic biodiversity in many regions worldwide. In South Africa there is a paucity of empirical studies describing their impacts. The impact of M. salmoides on the fish community in the Groot Marico River catchment, an otherwise near-pristine river ecosystem and a freshwater ecosystem priority area, was assessed from surveys conducted in 2012. Fish presence and abundance were enumerated using multiple survey techniques, and their association with key habitat variables and the presence or absence of M. salmoides were assessed. A total of 14 native fish species were recorded, besides introduced M. salmoides, which occupied the majority of the mainstem and several tributaries downstream of barriers to upstream movement. Canonical correspondence analysis showed that only one native species, the Marico barb Barbus motebensis, had a negative spatial association with M. salmoides. Assessment of relative distributions showed this species to be excluded from M. salmoides-invaded river reaches, whereas the other native species were not visibly affected by the invader. This species-specificity of the impact of M. salmoides indicates that their impacts in South African streams may be dependent on predator-naiveté of prey.

Spatio-temporal patterns of pre-harvest brown rot epidemics within individual peach tree canopies

Tree canopies are architecturally complex and pose several challenges for measuring and characterizing spatial patterns of disease. Recently developed methods for fine-scale canopy mapping and three-dimensional spatial pattern analysis were applied in a 3-year study to characterize spatio-temporal development of pre-harvest brown rot of peach, caused by Monilinia fructicola, in 13 trees of different maturity classes. We observed a negative correlation between an index of disease aggregation and disease incidence in the same tree (r = −0.653, P < 0.0001), showing that trees with higher brown rot incidence had lower aggregation of affected fruit in their canopies. Significant (P ≤ 0.05) within-canopy aggregation among symptomatic fruit was most pronounced for early-maturing cultivars and/or early in the epidemic. This is consistent with the notion of a greater importance of localized, within-tree sources of inoculum at the beginning of the epidemic. Four of five trees having >10 blossom blight symptoms per tree showed a significant positive spatial association of pre-harvest fruit rot to blossom blight within the same canopy. Spatial association analyses further revealed one of two outcomes for the association of new fruit rot symptoms with previous fruit rot symptoms in the same tree, whereby the relationship was either not significant or exhibited a significant negative association. In the latter scenario, the newly diseased fruit were farther apart from previously symptomatic fruit than expected by random chance. This unexpected result could have been due to uneven fruit ripening in different sectors of the canopy, which could have affected the timing of symptom development and thus led to negative spatial associations among symptoms developing over time in a tree.

Context Based Positive and Negative Spatio-Temporal Association Rule Mining

This paper proposes a new approach to mine context based positive and negative spatial association rules as they might be applied to hydrocarbon prospection. Many researchers are currently using an Apriori algorithm on spatial databases but this algorithm does not utilize the strengths of positive and negative association rules and of time series analysis, hence it misses the discovery of very interesting and useful associations present in the data. In dense spatial databases, the number of negative association rules is much higher compared to the positive rules which need exploitation. Using positive and negative association rule discovery and then pruning out the uninteresting rules consumes resources without much improvement in the overall accuracy of the knowledge discovery process. The associations among different objects and lattices are strongly dependent upon the context, particularly where context is the state of entity, environment or action. We propose an approach to spatial association rule mining from datasets projected at a temporal bar in which the contextual situation is considered while generating positive and negative frequent itemsets. An extended algorithm based on the Apriori approach is developed and compared with existing spatial association rule algorithms. The algorithm for positive and negative association rule mining is based on Apriori algorithm which is further extended to include context variable and simulate temporal series spatial inputs. The numerical evaluation shows that our algorithm is more efficient at generating specific, reliable and robust information than traditional algorithms.

Pioneer effects on exotic and native tree colonizers: Insights for Araucaria forest restoration

We integrate analyses of spatial association with empirical measures of juvenile performance to develop a strategy for Araucaria forest restoration in Brazil. Because pioneer species can differentially facilitate or inhibit target species, we measure native Araucaria angustifolia and exotic Pinus taeda responses to two common pioneer species, Baccharis uncinella and Vernonia discolor in a clear-cut pine plantation. P. taeda establishment and growth was greater than that of A. angustifolia in all treatments, showing its potential for invasiveness. B. uncinella showed significant positive spatial associations with P. taeda and negative spatial associations with A. angustifolia. V. discolor showed significant negative spatial associations with P. taeda but neutral spatial associations with A. angustifolia, it also supported a higher diversity of native species under its canopy than B. uncinella. Experimental results show that these patterns are due to differential establishment restrictions imposed by both pioneers on target species. We conclude that B. uncinella promotes pine invasion while V. discolor restrains it. We suggest strategies for Araucaria forest restoration and highlight the broad applicability of our approach to restoration programs.

Different spatial organisation strategies of woody plant species in a montane cloud forest

The coexistence of a high number of species in the forest is a central issue in tropical ecology. In this paper, we aim to characterise the spatial pattern of woody species in an Andean montane cloud forest to determine whether differences exist among the species in terms of spatial organization and if so, whether these differences are related to the life-form, primary dispersal mode, shade tolerance or the diameter distribution of the species. For this purpose, we analysed the spatial pattern of each species as well as the spatial relationships between young and adult individuals. Almost all the analysed species showed a cluster pattern, followed by a random pattern at larger distances. The cluster size is more evident for the young trees whereas adult trees tended to be more randomly distributed. The shade-tolerant species showed greater distances of aggregation than gap or medium-shade-tolerant species. Species primarily dispersed by wind and small birds showed larger distances of aggregation than species dispersed by mammals or big birds. All the under-story woody plants showed a notable cluster pattern, whereas canopy trees showed a variety of spatial patterns, with clustering at small scales being the most frequent. In the case of emergent trees, association was found between young and adult individuals on a large scale. Positive associations between young and adult individuals predominate at small scales for medium and shade tolerant species and at larger scales for bird-dispersed species whereas negative spatial associations at smaller scales were found for shade tolerant species and wind dispersed species. Our study confirms that conspecific organization varies among the woody plants in the analysed forest, and that the spatial pattern of woody plants is partially linked to shade tolerance, primary dispersal mode and life form of the species.

Point pattern analysis of several psammophyte populations in the riparian ecotone in the middle reaches of Yarlung Zangbo River of Tibet, China

Aims Artemisia wellbyi, A. younghusbandii and Sophora moorcroftiana are the major psammophyte populations on the aeolian desertified land in the riparian ecotone of the middle reaches of the Yarlung Zangbo River. Our ob-jectives were to determine how spatial scales are related to population patterns and how species spatially adapt to semi-arid conditions in the riparian ecotone, as well as to provide theoretical foundation for vegetation restoration on sand dunes in the study area. Methods We selected four representative plant communities under different habitat conditions in the riparian ecotone, measured the position, height and crown diameter of each individual in a 20 m × 30 m plot and studied the population structure, spatial distribution and association of these psammophyte populations using point pattern analysis.Important findings The population structure of A. wellbyi on semi-exposed sandy gravel land and semi-fixed sandy land is that of a growing population, while A. younghusbandii and S. moorcroftiana on fixed sandy land both have the structure of a declining population. Artemisia wellbyi and A. younghusbandii both have a clumped distri-bution at different scales, while the distribution pattern of S. moorcroftiana changed from clumped to random to clumped to random as the scale increased. Spatial distribution is mainly determined by the smaller size classes, while fluctuations or changes of population distribution are mainly determined by the larger size classes. There is a scale effect among the studied populations, and positive spatial association occurs mainly at certain scales. Spatial association is often affected by plant size and environmental heterogeneity. The spatial association of A. wellbyi and S. moorcroftiana on semi-exposed sandy gravel land or semi-fixed sandy land changes from independent to positive to independent to positive.The spatial association of A. wellbyi and Oxytropis sericopetala on semi-exposed sandy gravel land changes from positive to independent to positive to independent to negative, and that of A. younghus-bandii and S. moorcroftiana changes from positive to independent. The degree of aggregation weakens with in-creasing plant size. The smaller size class has a clumped distribution, and the larger has a random distribution or random and clumped. The positive spatial association between different size classes of the same species appears to weaken when the difference of plant size becomes greater and even changes into negative spatial association, while the spatial association of various size classes at a smaller scale often is positive or independent.

Associações espaciais entre indivíduos de diferentes espécies de Miconia spp. Ruiz &amp; Pav. (Melastomataceae)

Este estudo avaliou as associações espaciais de indivíduos pertencentes a todas as espécies arbóreas do gênero Miconia presentes no sub-bosque de um plantio experimental de espécies dos gêneros Eucalyptus e Corymbia. Como o gênero Miconia possui a maioria das espécies pioneiras, a hipótese testada foi de que os pares de espécies analisadas apresentam indivíduos com sobreposição total ou parcial de habitat. Considerando o histórico da área, é possível supor que todos os indivíduos se regeneraram a partir da chuva e do banco de sementes. Foi estabelecido um transecto cruzando a área de estudo no sentido de seu maior comprimento, a partir do qual foram determinadas as coordenadas dos indivíduos do gênero Miconia com DAS (diâmetro medido na altura do solo) maior ou igual a 1 cm. As associações espaciais entre os indivíduos das diferentes espécies foram analisadas por meio da função K de Ripley bivariada. Foram amostrados indivíduos de Miconia pepericarpa DC., Miconia sellowiana Naudin, Miconia albicans Triana, Miconia argyrophylla DC., Miconia chartacea Triana e Miconia cinnamomifolia (DC.) Naudin. De forma geral, os resultados demonstraram ausência de associação espacial negativa entre os pares das espécies, indicando que os indivíduos de Miconia spp. compartilham parcial ou totalmente o mesmo espaço no sub-bosque de um plantio de eucalipto. Os resultados obtidos, apesar de não poderem ser extrapolados para outras espécies, corroboram a ideia de que algumas espécies pioneiras tendem a coexistir, em florestas tropicais, em áreas onde há maior disponibilidade de luz.

Spatial patterns in cushion‐dominated plant communities of the high Andes of central Chile: How frequent are positive associations?

AbstractQuestion: In stressful abiotic environments positive plant interaction is expected to be a frequent and an important process driving community composition and structure. In the high Andes in central Chile, the cushion plant Azorella madreporica dominates plant communities and appears to benefit the assemblage of species that grows within it. However, there are also many other species that grow outside this nurse cushion plant, which may or may not interact with this species. What is the prevailing type of spatial associations among the plant species that are not growing inside the nurse plant? What is the type of interactions between cushion plants and those species growing outside them?Location: Molina River basin (33°20'S, 70°16’ W, 3600 m a.s.l.), in the Andes of central Chile, ca. 50 km east of Santiago.Methods: Two accurate mapping plots of individual plants of different species were located at two summits (Franciscano and Tres Puntas sites). The spatial distributions and associations between species growing outside cushions and within cushions at each site were estimated by point‐pattern analyses using the univariate and bivariate transformations of Ripley's K‐functions.Results: We found both positive and, especially, negative spatial associations (8 out of 12 species in Franciscano site) between A. madreporica cushions and plants growing outside them. However, most of the species showed positive spatial associations among them. The variation in spatial association was site‐specific and also depended on the type of plants involved. Adesmia spp., the second most abundant non‐cushion species, displayed negative associations with cushions and positive associations with other species growing outside cushions.Conclusions: Our study suggests very complex interactions among species, which ranged from positive to negative, and are also affected by abiotic environmental conditions.

Emergent spatial pattern of herpetofauna in Alabama, USA

Analyzing spatial pattern of regional biodiversity and its relationships with environmental factors is important for biodiversity conservation at large scales. The emergent spatial pattern of herpetofauna in Alabama is examined by combining thousands of historical records from 132 species of 24 families and environmental conditions. Our results indicate that species richness of herpetofauna increases with the increase of latitude, while it decreases with the increase of elevation. A negative spatial association exists between amphibians and reptiles on the scale of 10 km2, but 40% of habitats are still shared by amphibians and reptiles at this scale. The highest species richness of herpetofauna is in the Mobile and Baldwin Counties. Power-law relation exists between the county size and the average species richness. Total stream length, and road density are highly correlated with species richness at the county level. With the increase of annual precipitation, species richness decreases. Species richness is higher in the area with the annual average temperature around 17-18 °C. Herpetofaunal diversity in the Coosa/Tallapoosa River, the Alabama River, and the Tombigbee River basins is relatively higher than in the Perdido River and the Escatawpa River basins. The highest species richness exists at the Gulf Coastal Plain, but its species density is the lowest. The highest species richness of herpetofauna exists in the Longleaf-Slash Pine and Loblolly-Shortleaf Pine forests, while lower in Oak- Hickory forest. The emergent spatial pattern may provide important implications for herpetofauna conservation in the face of global climate change and large-scale habitat destruction. The spatial pattern and the possible underlying ecological processes have to be considered for the large scale land zoning and planning.

Priority effects of the early breeding fire salamander on the late breeding banded newt

Early breeding intraguild predators may have advantages over late breeding predators via priority effects; early breeding predators may reduce shared prey resources before late breeders appear and may also prey upon the late breeders. Here we show that predatory larvae of the late-breeding predatory banded newt, Triturus vittatus vittatus, occupy the same temporary pond toward the end of the developmental period of the early-breeding predatory fire salamander, Salamandra salamandra, resulting in a large size disparity between larvae of these two species while they co-occur. We conducted outdoor artificial pool experiments to assess priority effects of large larval Salamandra at the end of their larval development period, on recently hatched larval Triturus. We also assessed how artificial vegetation may influence larval Triturus performance in the presence or absence of Salamandra Salamandra, introduced into the experimental pools two weeks prior to the newt larvae, strongly reduced invertebrate prey abundance shared by these two predatory urodeles and with only a one week period of overlap, strongly reduced abundance of Triturus larvae. The artificial vegetation had only a small ameliorating effect on Triturus survival when Salamandra was present. Triturus size at metamorphosis (snout-tail length) was significantly larger in the Salamandra pools, presumably due to a combination of a strong “thinning effect” and greater vulnerability of smaller Triturus individuals to predation by Salamandra. Time to metamorphosis was not significantly affected by Salamandra. These results have conservation implications as T. v. vittatus is listed as highly endangered and may also explain the largely negative spatial association of the two species.