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Knowledge on the fine‐scale spatial aggregation is pertinent for deciphering plant community dynamics, as interactions among sessile plants mainly occur in the neighbourhood. However, the spatial assemblage mechanism and interrelationships with productivity remain poorly understood.Here, species segregation index (Mscom) was used to quantify the interspecific segregation (or intraspecific aggregation) of the neighbourhood in plant communities from three contrasting plateaus. We employed the coordinates for 125,726 individual plants (within 1 m2 plots) sampled in natural grassland communities across two temperate grasslands (Loess Plateau and Mongolian Plateau) and one alpine grassland (Tibetan Plateau) to elucidate the assembly mechanisms of Mscom and interrelationships with above‐ground net primary productivity (ANPP).We found that these grassland communities tended to assemble into intraspecific aggregations; the phenomenon was more apparent in regions with low annual precipitation. In grassland communities on Loess Plateau, the strong intraspecific aggregation was mainly due to low sexual reproduction allocation; on Mongolian Plateau, reproductive allocation was also the dominant factor for Mscom variation, followed by the interactive effect of annual precipitation and species richness, whereas on Tibetan Plateau, low species richness was the main reason for increased intraspecific aggregation, followed by the interactive effect of annual precipitation and species richness, and reproductive allocation. More importantly, on all three plateaus, the independent influence of Mscom on ANPP is stronger than that of species and phylogenetic diversity.We elucidated the potential mechanisms shaping spatial aggregation in grassland communities at large scale, and emphasize the critical role of spatial aggregation in predicting the variation of ANPP. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Abstract The role of interspecific interactions in structuring low‐diversity helminth communities is a controversial topic in parasite ecology research. Most parasitic communities of fish are species‐poor; thus, interspecific interactions are believed to be unimportant in structuring these communities. We explored the factors that might contribute to the richness and coexistence of helminth parasites of a poeciliid fish in a neotropical river. Repeatability of community structure was examined in parasitic communities among 11 populations of twospot livebearer Pseudoxiphophorus bimaculatus in the La Antigua River basin, Veracruz, Mexico. We examined the species saturation of parasitic communities and explored the patterns of species co‐occurrence. We also quantified the associations between parasitic species pairs and analyzed the correlations between helminth species abundance to look for repeated patterns among the study populations. Our results suggest that interspecific competition could occur in species‐poor communities, aggregation plays a role in determining local richness, and intraspecific aggregation allows the coexistence of species by reducing the overall intensity of interspecific competition.

Questions: Studying the spatial distribution of tree species is fundamental to understanding the ecological processes governing forest dynamics. Habitat filtering and dispersal limitation are two key processes in the emergence of intraspecific aggregation in natural forest communities. The contributions of these ecological processes vary among species, communities, ontogenetic stages (i.e. juveniles and adults) and spatial scales. In this study, we investigated the ecological processes underlying species spatial distributions in two ontogenetic stages and determined how these processes are linked to species functional traits. Location: A naturally established 2.4‐ha temperate forest located on a limestone hill in SW Belgium. Methods: Trees ≥1.3 m were exhaustively censused and mapped, and environmental variables and functional traits were collected. We applied spatial point pattern modelling to explore the processes underlying species distributions. First, point process models simulating complete spatial randomness, habitat filtering and non‐habitat clustering processes were fitted to observed species point patterns. The analyses were conducted for juveniles and adults both separately and together. The most parsimonious model for each species/ontogenetic stage was selected based on three summary statistics. Secondly, we investigated the links between functional traits and the parameters of the spatial models. Results: (a) Dispersal limitation plays a central role in the formation of intraspecific aggregation in this forest, alone or in combination with habitat filtering. (b) Distributions of juveniles are less influenced by habitat filtering than distributions of adults. (c) Dispersal differ substantially among species and interspecific differences in clustering characteristics are explained by seed mass, wood density and maximum height. Conclusions: Dispersal limitation can be of major importance in shaping temperate forests. Coupling spatial point pattern modelling and functional traits is an efficient way to understand mechanisms of species assemblages at fine spatial scales in temperate forests.We combine spatial point process modelling of trees with soil, topographic and functional traits data in a temperate forest. We show: (a) dispersal limitation determines the shape of fine‐scale spatial patterns; (b) an ontogenetic shift in the importance of habitat specialisation and dispersal limitation; and (c) a correlation between specific functional traits and key parameters of spatial structure. [ABSTRACT FROM AUTHOR]

Beta diversity is a hot topic in ecology, and the same patterns of β diversity may be determined by different ecological processes. Null model and canonical variation partitioning methods were used to determine the relative importance between environmental filter and dispersal limitation on community assembly between Pinus tabulaeformis plantation and natural Quercus wutaishanica forest. The results were as follows:(1)The understory communities of Pinus tabulaeformis plantation and natural Quercus wutaishanica forest had similar β diversities and similar β deviations with strong intraspecific aggregations of most species.(2)Environmental and spatial variables jointly explained the great variation of species composition of understory plant community in the two forest types(Herb layer: [E + S] was 33%-45%; Shrub layer: [E + S] was 21%-35%), and dominated by the environmental explanations(including pure environmental variables [E | S] and spatial environmental variables [E ∩ S]).(3)Although Pinus tabulaeformis plantation and natural Quercus wutaishanica forest on the Loess Plateau were both dominated by environmental filter, β diversities in both forests reflected dissimilar mechanisms of community assembly. It was mainly reflected in the differences of habitat heterogeneity and specific environmental factors between these two forests. Such as, altitude, litter depth and soil nutrients(available nitrogen and available potassium)were significant environmental factors that caused species differentiation between the two forest types. Therefore, it suggests that even if the same environmental filter process, it is necessary to compare the differences of regional environmental heterogeneity and further analyze the differences of the specific environmental factors that cause environmental filter. To restore species diversity effectively on the Loess Plateau, habitat heterogeneity is an important guarantee. At the same time, dispersal limitation caused by geographical distance should not be neglected, and special attention should be paid to interaction between dispersal limitation and habitat heterogeneity on β diversity. [ABSTRACT FROM AUTHOR]

The role of interspecific interactions in structuring low‐diversity helminth communities is a controversial topic in parasite ecology research. Most parasitic communities of fish are species‐poor; thus, interspecific interactions are believed to be unimportant in structuring these communities.We explored the factors that might contribute to the richness and coexistence of helminth parasites of a poeciliid fish in a neotropical river.Repeatability of community structure was examined in parasitic communities among 11 populations of twospot livebearer Pseudoxiphophorus bimaculatus in the La Antigua River basin, Veracruz, Mexico. We examined the species saturation of parasitic communities and explored the patterns of species co‐occurrence. We also quantified the associations between parasitic species pairs and analyzed the correlations between helminth species abundance to look for repeated patterns among the study populations.Our results suggest that interspecific competition could occur in species‐poor communities, aggregation plays a role in determining local richness, and intraspecific aggregation allows the coexistence of species by reducing the overall intensity of interspecific competition. [ABSTRACT FROM AUTHOR]

When more than one closely related plant species share the same pollination niche, reproductive interference via interspecific pollen transfer should limit their coexistence. However, some studies have reported the sympatric coexistence of two native close relatives pollinated by the same pollinators under reproductive interference, even without niche partitioning.We examined the frequency dependency of reproductive interference between close relatives in natural conditions and the potential roles of autonomous selfing in mitigating the negative reproductive interference effects between congeneric species. We investigated sympatrically growing Commelina communis (Cc) and C. c. f. ciliata (Ccfc) populations. These species exhibit very large overlaps in habitat preference, flowering phenology and pollination niche, but seldom produce hybrids. First, we conducted a hand‐pollination experiment to examine the negative effects of heterospecific pollen deposition on seed production and the potential of self‐pollination to mitigate the effects in both species. Then, we examined the effects of reproductive interference on reproductive success and the potential for autonomous selfing in the field.We found significant negative effects of heterospecific pollen deposition on seed production and the mitigation effects of prior and competing self‐pollination, in both Cc and Ccfc. For both species in the field, intraspecific pollinator movements and reproductive success significantly decreased with an increase in the relative floral abundance of competing species, although the negative reproductive interference effect on reproductive success was lower in Cc than in Ccfc. We also found greater potential for prior autonomous selfing in Cc than in Ccfc. Our findings suggest that Cc flowers were less affected by reproductive interference from competing species, which was likely due to a higher prior selfing ability compared to Ccfc flowers. The asymmetry in susceptibility to reproductive interference may explain the Cc‐biased distribution in the study area.The study improves our understanding of how prior autonomous selfing can reduce the negative reproductive interference effect from competing species in mixed‐mating species with frequent pollinator visits. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

Demographic events such as the birth and death of organisms are ubiquitous in nature. Disentangling the processes that underlie the demographic dynamics of species is fundamental to understanding how biodiversity is organized and will be re‐organized at multiple scales.To provide new insights on multispecies demographic dynamics, I designed the present study to focus on local and biogeographic influences on mortality and recruitment rates for tree populations in forest biomes throughout the Japanese archipelago.Most populations exhibited mortality that fell within the 95% confidence intervals of a neutral model (i.e. the expectation of demographic stochasticity). However, there were also important determinants that make population dynamics to deviate from the neutral expectation. Interspecific niche differentiation was important to reduce the mortality rate, regardless of the local rarity or ubiquity of a species. Although intraspecific aggregation that caused density‐dependent mortality was only significant for locally abundant species, the degree of isolation from a species' central or optimal range determined mortality only for locally rare species. These differences between rare and common species provide important empirical quantification of aspects of population dynamics that have been less accounted for in ecology and biogeography studies.Synthesis. Unifying different theories such as those rooted in local‐scale community ecology and macro‐scale biogeography is important. At this juncture, this study emphasizes that disentangling the interactive roles of demographic stochasticity and determinism that operate at different scales would be a clue to advance the field of ecology both in theory and practice. [ABSTRACT FROM AUTHOR]

Land‐use changes, which cause loss, degradation, and fragmentation of natural habitats, are important anthropogenic drivers of biodiversity change. However, there is an ongoing debate about how fragmentation per se affects biodiversity in a given amount of habitat. Here, we illustrate why it is important to distinguish two different aspects of fragmentation to resolve this debate: (a) geometric fragmentation effects, which exclusively arise from the spatial distributions of species and habitat fragments, and (b) demographic fragmentation effects due to reduced fragment sizes, and/or changes in fragment isolation, edge effects, or species interactions. While most empirical studies are primarily interested in quantifying demographic fragmentation effects, geometric effects are typically invoked as post hoc explanations of biodiversity responses to fragmentation per se. Here, we present an approach to quantify geometric fragmentation effects on species survival and extinction probabilities. We illustrate this approach using spatial simulations where we systematically varied the initial abundances and distribution patterns (i.e., random, aggregated, or regular) of species as well as habitat amount and fragmentation per se. As expected, we found no geometric fragmentation effects when species were randomly distributed. However, when species were aggregated, we found positive effects of fragmentation per se on survival probability for a large range of scenarios. For regular species distributions, we found weakly negative geometric effects. These findings are independent of the ecological mechanisms which generate nonrandom species distributions. Our study helps to reconcile seemingly contradictory results of previous fragmentation studies. Since intraspecific aggregation is a ubiquitous pattern in nature, our findings imply widespread positive geometric fragmentation effects. This expectation is supported by many studies that find positive effects of fragmentation per se on species occurrences and diversity after controlling for habitat amount. We outline how to disentangle geometric and demographic fragmentation effects, which is critical for predicting the response of biodiversity to landscape change. The response of species and communities to fragmentation involves geometric and demographic effects. However, so far, these two types are rarely disentangled. In this paper, we demonstrate approaches for the quantification of geometric fragmentation effects. [ABSTRACT FROM AUTHOR]

The relationship between sampled area and the number of species within that area, the species-area relationship ( SAR), is a major biodiversity pattern and one of a few law-like regularities in ecology. While the SAR for isolated units (islands or continents) is assumed to result from the dynamics of species colonization, speciation and extinction, the SAR for contiguous areas in which smaller plots are nested within larger sample areas can be attributed to spatial patterns in the distribution of individuals. The nested SAR is typically triphasic in logarithmic space, so that it increases steeply at smaller scales, decelerates at intermediate scales and increases steeply again at continental scales. I will review current theory for this pattern, showing that all three phases of the SAR can be derived from simple geometric considerations. The increase of species richness with area in logarithmic space is generally determined by overall species rarity, so that the rarer the species are on average, the higher is the local slope z. Rarity is scale-dependent: species occupy only a minor proportion of area at broad spatial scales, leading to upward accelerating shape of the SAR at continental scales. Similarly, species are represented by only a few individuals at fine spatial scales, leading to high SAR slope also at small areas. Geometric considerations reveal links of the SAR to other macroecological patterns, namely patterns of β-diversity, the species-abundance distribution, and the relationship between energy availability (or productivity) and species richness. Knowledge of the regularities concerning nested SARs may be used for standardizing unequal areas, upscaling species richness and estimating species loss due to area loss, but all these applications have their limits, which also follow from the geometric considerations. [ABSTRACT FROM AUTHOR]

Background and Aims Disturbances, dispersal and biotic interactions are three major drivers of the spatial distribution of genotypes within populations, the last of which has been less studied than the other two. This study aimed to determine the role of competition and facilitation in the degree of conspecific genetic relatedness of nearby individuals of tree populations. It was expected that competition among conspecifics will lead to low relatedness, while facilitation will lead to high relatedness (selection for high relatedness within clusters). Methods The stand structure and spatial genetic structure (SGS) of trees were examined within old-growth and second-growth forests (including multi-stemmed trees at the edge of forests) of Nothofagus pumilio following large-scale fires in Patagonia, Chile. Genetic spatial autocorrelations were computed on a spatially explicit sampling of the forests using five microsatellite loci. As biotic plant interactions occur among immediate neighbours, mean nearest neighbour distance (MNND) among trees was computed as a threshold for distinguishing the effects of disturbances and biotic interactions. Key Results All forests exhibited a significant SGS for distances greater than the MNND. The old-growth forest genetic and stand structure indicated gap recolonization from nearby trees (significantly related trees at distances between 4 and 10 m). At distances smaller than the MNND, trees of the second-growth interior forest showed significantly lower relatedness, suggesting a fading of the recolonization structure by competition, whereas the second-growth edge forest showed a positive and highly significant relatedness among trees (higher among stems of a cluster than among stems of different clusters), resulting from facilitation. Conclusions Biotic interactions are shown to influence the genetic composition of a tree population. However, facilitation can only persist if individuals are related. Thus, the genetic composition in turn influences what type of biotic interactions will take place among immediate neighbours in post-disturbance forests. [ABSTRACT FROM AUTHOR]

• Context: The abundance and distribution of tree regeneration is driven by several processes acting at both the seedling establishment and survival stages. Plant- plant interactions highly contribute to regeneration dynamics through seed dispersal and competition or facilitation processes. • Aims: The aim of the present study was to assess the relative importance of different functional groups of shrubs for the early establishment of oak seedlings in the coastal forest communities of south-western France. • Material and methods: We applied spatial and non-spatial analysis methods in eleven 315-m regeneration plots. Within each plot, oak seedlings (height <25 cm) and shrubs (height >50 cm and DBH <4 cm) were mapped to ±1 cm. The spatial distribution patterns of the oak seedlings ( Quercus robur, Quercus suber and Quercus ilex) were analysed for each species while the association patterns were detected between the seedlings of the three oaks and four functional groups of shrubs (Fagaceae, Ericaceae, Fabaceae and spiny shrubs) known to have contrasting effects on other species. • Results: Oak seedling species were very often spatially aggregated at short distances (<1 m). Oak seedlings were also positively associated with shrubs of the same species within the Fagaceae group, whereas we detected negative associations with Ericaceae and no dominant significant pattern for Fabaceae and spiny shrubs. • Conclusion: The aggregated distribution of seedlings of the three oak species was due to short-distance seed dispersal, which also explained their positive spatial associations with Fagaceae shrubs. Thus, in order to enhance oak recruitment in these ecosystems, forest managers should focus on the control of Ericaceae shrubs, while preserving Fagaceae shrubs. [ABSTRACT FROM AUTHOR]

Previous studies have concluded that spatial aggregation of conspecifics should benefit weak competitors and put stronger competitors at a disadvantage, thus promoting plant species coexistence. However, if competitive ability is viewed as a behavioural trait, it becomes evident that traits determining spatial patterns and competitive ability could co-evolve, resulting in greater dispersal in stronger competitors and reduced competitive ability in spatially aggregated species., To test this prediction, we combined spatial data from a field survey of seven temperate grassland communities with the results of a common-garden competition experiment involving 28 focal species., We found that species exhibiting strong conspecific aggregation and infrequent heterospecific encounters in the field maintained greater growth in competition with conspecifics than with heterospecifics. In contrast, species that mostly encountered heterospecific neighbours in the field achieved greater growth when surrounded by heterospecific than conspecific neighbours, indicating greater competitive ability. The observed patterns of conspecific aggregation were related to variation in clonal dispersal characteristics and there was a direct positive relationship between clonal dispersal distance and competitive ability., Synthesis. Our study demonstrates that viewing competitive ability as a behavioural trait that imposes different costs and benefits on an individual depending on the identity of its neighbours can provide new insights into the long-debated topic of mechanisms promoting plant species coexistence. [ABSTRACT FROM AUTHOR]

There is little consensus about how natural (e.g. productivity, disturbance) and anthropogenic (e.g. invasive species, habitat destruction) ecological drivers influence biodiversity. Here, we show that when sampling is standardised by area (species density) or individuals (rarefied species richness), the measured effect sizes depend critically on the spatial grain and extent of sampling, as well as the size of the species pool. This compromises comparisons of effects sizes within studies using standard statistics, as well as among studies using meta-analysis. To derive an unambiguous effect size, we advocate that comparisons need to be made on a scale-independent metric, such as Hurlbert's Probability of Interspecific Encounter. Analyses of this metric can be used to disentangle the relative influence of changes in the absolute and relative abundances of individuals, as well as their intraspecific aggregations, in driving differences in biodiversity among communities. This and related approaches are necessary to achieve generality in understanding how biodiversity responds to ecological drivers and will necessitate a change in the way many ecologists collect and analyse their data. [ABSTRACT FROM AUTHOR]

Site-to-site variation in species composition (β-diversity) generally increases from low- to high-diversity regions. Although biogeographical differences in community assembly mechanisms may explain this pattern, random sampling effects can create this pattern through differences in regional species pools. Here, we compared assembly mechanisms between spatially extensive networks of temperate and tropical forest plots with highly divergent species pools (46 vs. 607 species). After controlling for sampling effects, β-diversity of woody plants was similar and higher than expected by chance in both forests, reflecting strong intraspecific aggregation. However, different mechanisms appeared to explain aggregation in the two forests. In the temperate forest, aggregation reflected stronger environmental correlations, suggesting an important role for species-sorting (e.g. environmental filtering) processes, whereas in the tropics, aggregation reflected stronger spatial correlations, more likely reflecting dispersal limitation. We suggest that biogeographical differences in the relative importance of different community assembly mechanisms contribute to these striking gradients in global biodiversity. [ABSTRACT FROM AUTHOR]

The article offers information that both intraspecific spatial aggregation and temporal priority effects have the potential to increase long term species coexistence. It states intrasepecific aggregation can facilitate coexistence by limited dispersal or asymmetric interaction distance. Temporal priority effects may represent an underappreciated pathway by which intraspecific aggregation can increase coexistence. Restorationists can maintain diverse communities by planting monospecific patches.

1. One of the possible mechanisms to maintain a high number of species in a plant community is that intraspecific aggregation due to limited dispersal reduces the importance of interspecific competition. 2. The hypothesis has been examined both theoretically and experimentally in the simplifying case of two species in a uniform abiotic environment, and there is a solid qualitative understanding that intraspecific aggregation reduces the importance of interspecific competition; however, there is considerable uncertainty as to the magnitude of this reduction in plant communities with many species in a heterogeneous environment and its effect on the number of coexisting species. 3. Here, the hypothesis was tested by comparing observed species richness at a site with a compound estimate of the intraspecific aggregation of all the species observed at the site, while taking the expected confounding effects of environmental spatial heterogeneity into account. 4. It is difficult to draw firm conclusions from the non-significant statistical results found in this study, as a lack of significance does not necessarily rule out the presence of an effect. However, based on the observation that species richness was not correlated with the degree of intraspecific aggregation, it was concluded that there was no additional support for the hypothesis that reduced interspecific competition due to intraspecific aggregation is important for maintaining the relatively species-rich flora in North-European dune grassland. 5. Synthesis. It is important to test whether it is possible to generalize the expected effects of intraspecific aggregation from manipulated experiments using only a few plant species to natural plant communities with many species, and the approach taken in this paper is a practically manageable approach. [ABSTRACT FROM AUTHOR]

Abstract: The shredder guild plays an outstanding role in the functioning of headwater stream ecosystems by processing allochthonous leaf litter. Traditionally, the abiotic habitat template is regarded as the major determinant of its organization, and only a limited number of studies support the importance of biotic interactions. The aim of the present study was to examine whether competition plays a significant role in organizing the shredder guild of caddisflies in a riffle. Null-model based co-occurrence, co-existence and guild variation analyses were used in the study of guild organization. In addition, the traditional variance to mean ratio was applied for measuring the intraspecific aggregation of guild members. The non-significant metric values of co-occurrence and co-existence analyses predicted that competition was of limited importance in structuring the spatial organization of the shredder guild. The observed aggregated spatial distribution of species, suggests that besides stochastic events, deterministic forces should also contribute to the organization of the shredder guild of caddisflies. [Copyright &y& Elsevier]

The aggregation model of species coexistence predicts that insect species diversity within a community is maintained by intraspecific aggregation among resource patches. An untested corollary of this prediction is that diversity within resource patches should decrease with increasing intraspecific aggregation. The recently derived species-aggregation relationship provides a general formulation of this prediction: as intraspecific aggregation increases within a geographic area, the species richness within samples of the area decreases. We tested this prediction by compiling and analyzing 76 data sets of arthropod species distribution and abundance. For each data set, we determined the mean amount of intra- and interspecific aggregation and three types of within-sample or local species diversity: species richness, evenness, and dominance. Using regression, we found a negative relationship between intraspecific aggregation and all three types of local diversity. Intraspecific aggregation explained a significant percentage of the variation in species diversity, typically between 20% and 60%. By comparison, interspecific aggregation usually explained <1% of the variation in species diversity. Our study provides empirical support for the species-aggregation relationship as a general macroecological pattern that emerges from intraspecific aggregation. [ABSTRACT FROM AUTHOR]

The leaves of an apple tree are a patchy environment for leaf-inhabiting predaceous and phytophagous mites, consisting of discrete patches of leaf resources connected by relatively inhospitable petioles and branches. We investigated four species of predaceous mites (Amblyseius andersoni , Galendromus occidentalis , Typhlodromus pyri (Acari: Phytoseiidae), and Zetzellia mali (Acari: Stigmaeidae)) inhabiting ‘Red Delicious’ apple trees (Malus pumila ). These mites experience intra-guild predation (IGP), and we hypothesized that the vulnerable species would show increased aggregation when they are in plots with other predators. We also hypothesized that the increase in aggregation will be proportional to the vulnerability of the predator to IGP. We measured intraspecific aggregation with a binomial model that measures P(I), the amount of space a species occupies at a given average density, and compares this statistic among species at a common average density: samples that exhibit lower values of P(I) at a particular average density are considered to be more aggregated. We measured P(I) for the predaceous mites over four years, combining counts of all life stages. Data were segregated into groups with plots containing each predator alone, and each predator together with combinations of other predators. G. occidentalis and Z. mali showed significant increases in aggregation when other predators were present, with G. occidentalis showing the greatest change. T. pyri showed significant change only in the presence of Z. mali . A. andersoni , the largest mite studied here, showed no change in aggregation in the presence of other predators. We discuss possible causes of these changes in intraspecific aggregation and how they may promote long-term coexistence of predaceous mites. [ABSTRACT FROM AUTHOR]