Plant genetic determinants of arthropod community structure and diversity

To test the hypothesis that genes have extended phenotypes on the community, we quantified how genetic differences among cottonwoods affect the diversity, abundance, and composition of the dependent arthropod community. Over two years, five major patterns were observed in both field and common-garden studies that focused on two species of cottonwoods and their naturally occurring F1 and backcross hybrids (collectively referred to as four different cross types). We did not find overall significant differences in arthropod species richness or abundance among cottonwood cross types. We found significant differences in arthropod community composition among all cross types except backcross and narrowleaf cottonwoods. Thus, even though we found similar richness among cross types, the species that composed the community were significantly different. Using vector analysis, we found that the shift in arthropod community composition was correlated with percent Fremont alleles in the host plant, which suggests that the arthropod community responds to the underlying genetic differences among trees. We found 13 arthropod species representing different trophic levels that were significant indicators of the four different cross types. Even though arthropod communities changed in species composition from one year to the next, the overall patterns of community differences remained remarkably stable, suggesting that the genetic differences among cross types exert a strong organizing influence on the arthropod community. Together, these results support the extended phenotype concept. Few studies have observationally and experimentally shown that entire arthropod communities can be structured by genetic differences in their host plants. These findings contribute to the developing field of community genetics and suggest a strategy for conserving arthropod diversity by promoting genetic diversity in their host plants.     

Spatial scaling of microbial biodiversity

A central goal in ecology is to understand the spatial scaling of biodiversity. Patterns in the spatial distribution of organisms provide important clues about the underlying mechanisms that structure ecological communities and are central to setting conservation priorities. Although microorganisms comprise much of Earth's biodiversity, little is known about their biodiversity scaling relationships relative to that for plants and animals. Here, we discuss current knowledge of microbial diversity at local and global scales. We focus on three spatial patterns: the distance-decay relationship (how community composition changes with geographic distance), the taxa-area relationship, and the local:global taxa richness ratio. Recent empirical analyses of these patterns for microorganisms suggest that there are biodiversity scaling rules common to all forms of life.     

Plant diversity induces shifts in the functional structure and diversity across trophic levels

Changes to primary producer diversity can cascade up to consumers and affect ecosystem processes. Although the effect of producer diversity on higher trophic groups have been studied, these studies often quantify taxonomy‐based measures of biodiversity, like species richness, which do not necessarily reflect the functioning of these communities. In this study, we assess how plant species richness affects the functional composition and diversity of higher trophic levels and discuss how this might affect ecosystem processes, such as herbivory, predation and decomposition. Based on six different consumer traits, we examined the functional composition of arthropod communities sampled in experimental plots that differed in plant species richness. The two components we focused on were functional variation in the consumer community structure (functional structure) and functional diversity, expressed as functional richness, evenness and divergence. We found a consistent positive effect of plant species richness on the functional richness of herbivores, carnivores, and omnivores, but not decomposers, and contrasting patterns for functional evenness and divergence. Increasing plant species richness shifted the omnivore community to more predatory and less mobile species, and the herbivore community to more specialized and smaller species. This was accompanied by a shift towards more species occurring in the vegetation than in the ground layer. Our study shows that plant species richness strongly affects the functional structure and diversity of aboveground arthropod communities. The observed shifts in body size (herbivores), specialization (herbivores), and feeding mode (omnivores) together with changes in the functional diversity may underlie previously observed increases in herbivory and predation in plant communities of higher diversity.     

The contribution of evening primrose (<Emphasis Type="Italic">Oenothera biennis</Emphasis>) to a modern synthesis of evolutionary ecology

In this review, I consider the contribution that common evening primrose (Oenothera biennis) has made towards integrating the ecology, evolution and genetics of species interactions. Oenothera biennis was among the earliest plant models in genetics and cytogenetics and it played an important role in the modern synthesis of evolutionary biology. More recently, population and ecological genetics approaches have provided insight into the patterns of genetic variation within and between populations, and how a combination of abiotic and biotic factors maintain and select on heritable variation within O. biennis populations. From an ecological perspective, field experiments show that genetic variation and evolution within populations can have cascading effects throughout communities. Plant genotype affects the preference and performance of individual arthropod populations, as well as the composition, biomass, total abundance and diversity of arthropod species on plants. A combination of experiments and simulation models show that natural selection on specific plant traits can drive rapid ecological changes in these same community variables. At the patch level, increasing genotypic diversity leads to a greater abundance and diversity of omnivorous and predaceous arthropods, which is also associated with increased biomass and fecundity of plants in genetically diverse patches. Finally, in questioning whether a community genetics perspective is needed in biology, I review several multifactorial experiments which show that plant genotype often explains as much variation in community variables as other ecological factors typically identified as most important in ecology. As a whole, research in the O. biennis system has contributed to a more complete understanding of the dynamic interplay between ecology, evolution and genetics.     

Plant genetics shapes inquiline community structure across spatial scales

Recent research in community genetics has examined the effects of intraspecific genetic variation on species diversity in local communities. However, communities can be structured by a combination of both local and regional processes and to date, few community genetics studies have examined whether the effects of instraspecific genetic variation are consistent across levels of diversity. In this study, we ask whether host-plant genetic variation structures communities of arthropod inquilines within distinct habitat patches – rosette leaf galls on tall goldenrod ( Solidago altissima ). We found that genetic variation determined inquiline diversity at both local and regional spatial scales, but that trophic-level responses varied independently of one another. This result suggests that herbivores and predators likely respond to heritable plant traits at different spatial scales. Together, our results show that incorporating spatial scale is essential for predicting the effects of genetically variable traits on different trophic levels and levels of diversity within the communities that depend on host plants.     

Scaling up: examining the macroecology of ectomycorrhizal fungi

Ectomycorrhizal (ECM) fungi play major ecological roles in temperate and tropical ecosystems. Although the richness of ECM fungal communities and the factors controlling their structure have been documented at local spatial scales, how they vary at larger spatial scales remains unclear. In this issue of Molecular Ecology, Tedersoo et al. (2012) present the results of a meta‐analysis of ECM fungal community structure that sheds important new light on global‐scale patterns. Using data from 69 study systems and 6021 fungal species, the researchers found that ECM fungal richness does not fit the classic latitudinal diversity gradient in which species richness peaks at lower latitudes. Instead, richness of ECM fungal communities has a unimodal relationship with latitude that peaks in temperate zones. Intriguingly, this conclusion suggests the mechanisms driving ECM fungal community richness may differ from those of many other organisms, including their plant hosts. Future research will be key to determine the robustness of this pattern and to examine the processes that generate and maintain global‐scale gradients of ECM fungal richness.     

From richer to poorer: successful invasion by freshwater fishes depends on species richness of donor and recipient basins

Evidence for the theory of biotic resistance is equivocal, with experiments often finding a negative relationship between invasion success and native species richness, and large‐scale comparative studies finding a positive relationship. Biotic resistance derives from local species interactions, yet global and regional studies often analyze data at coarse spatial grains. In addition, differences in competitive environments across regions may confound tests of biotic resistance based solely on native species richness of the invaded community. Using global and regional data sets for fishes in river and stream reaches, we ask two questions: (1) does a negative relationship exist between native and non‐native species richness and (2) do non‐native species originate from higher diversity systems. A negative relationship between native and non‐native species richness in local assemblages was found at the global scale, while regional patterns revealed the opposite trend. At both spatial scales, however, nearly all non‐native species originated from river basins with higher native species richness than the basin of the invaded community. Together, these findings imply that coevolved ecological interactions in species‐rich systems inhibit establishment of generalist non‐native species from less diverse communities. Consideration of both the ecological and evolutionary aspects of community assembly is critical to understanding invasion patterns. Distinct evolutionary histories in different regions strongly influence invasion of intact communities that are relatively unimpacted by human actions, and may explain the conflicting relationship between native and non‐native species richness found at different spatial scales.     

Conflicts in maintaining biodiversity at multiple scales

Biodiversity consists of multiple scales, including functional diversity in ecological traits, species diversity and genetic diversity within species, and is declining across the globe, largely in response to human activities. While species extinctions are the most obvious aspect of this, there has also been a more insidious loss of genetic diversity within species. While a vast literature concerns each of these scales of biodiversity, less is known about how different scales affect one another. In particular, genetic and species diversity may influence each other in numerous ways, both positively and negatively. However, we know little about the mechanism behind these patterns. In this issue of Molecular Ecology, Nestmann et al. (2011) experimentally explore the effect of species and functional diversity and composition of grassland plant communities on the genetic structure of one of the component species. Increasing species richness led to greater changes in the genetic composition of the focal populations over 4 years, primarily because of genetic drift in smaller population sizes. However, there were also genetic changes in response to particular plant functional groups, indicating selective differences driven by plant community composition. These results suggest that different levels of biodiversity can trade-off in communities, which may prove a challenge for conservation biologists seeking to preserve all aspects of biodiversity.     

Effects of plant diversity, plant productivity and habitat parameters on arthropod abundance in montane European grasslands

Arthropod abundance has been hypothesized to be correlated with plant diversity but the results of previous studies have been equivocal. In contrast, plant productivity, vegetation structure, abiotic site conditions, and the physical disturbance of habitats, are factors that interact with plant diversity, and that have been shown to influence arthropod abundance. We studied the combined effect of plant species diversity, productivity and site characteristics on arthropod abundance in 71 managed grasslands in central Germany using multivariate statistics. For each site we determined plant species cover, plant community biomass (productivity), macro- and micronutrients in the soil, and characterized the location of sites with respect to orographic parameters as well as the current and historic management regimes. Arthropods were sampled using a suction sampler and classified a priori into functional groups (FGs). We found that arthropod abundance was not correlated with plant species richness, effective diversity or Camargo's evenness, even when influences of environmental variables were taken into account. In contrast, plant community composition was highly correlated with arthropod abundances. Plant community productivity influenced arthropod abundance but explained only a small proportion of the variance. The abundances of the different arthropod FGs were influenced differentially by agricultural management, soil characteristics, vegetation structure and by interactions between different FGs of arthropods. Herbivores, carnivores and detritivores reacted differently to variation in environmental variables in a manner consistent with their feeding mode. Our results show that in natural grassland systems arthropod abundance is not a simple function of plant species richness, and they emphasize the important role of plant community composition for the abundance patterns of the arthropod assemblages.     

A global synthesis of the effects of diversified farming systems on arthropod diversity within fields and across agricultural landscapes

Agricultural intensification is a leading cause of global biodiversity loss, which can reduce the provisioning of ecosystem services in managed ecosystems. Organic farming and plant diversification are farm management schemes that may mitigate potential ecological harm by increasing species richness and boosting related ecosystem services to agroecosystems. What remains unclear is the extent to which farm management schemes affect biodiversity components other than species richness, and whether impacts differ across spatial scales and landscape contexts. Using a global metadataset, we quantified the effects of organic farming and plant diversification on abundance, local diversity (communities within fields), and regional diversity (communities across fields) of arthropod pollinators, predators, herbivores, and detritivores. Both organic farming and higher in‐field plant diversity enhanced arthropod abundance, particularly for rare taxa. This resulted in increased richness but decreased evenness. While these responses were stronger at local relative to regional scales, richness and abundance increased at both scales, and richness on farms embedded in complex relative to simple landscapes. Overall, both organic farming and in‐field plant diversification exerted the strongest effects on pollinators and predators, suggesting these management schemes can facilitate ecosystem service providers without augmenting herbivore (pest) populations. Our results suggest that organic farming and plant diversification promote diverse arthropod metacommunities that may provide temporal and spatial stability of ecosystem service provisioning. Conserving diverse plant and arthropod communities in farming systems therefore requires sustainable practices that operate both within fields and across landscapes.     

Forward from the crossroads of ecology and evolution

Community genetics is a synthesis of community ecology and evolutionary biology. It examines how genetic variation within a species affects interactions among species to change ecological community structure and diversity. The use of community genetics approaches has greatly expanded in recent years and the evidence for ecological effects of genetic diversity is growing. The goal of current community genetics research is to determine the circumstances in which, and the mechanisms by which community genetic effects occur and is the focus of the papers in this special issue. We bring a new group of researchers into the community genetics fold. Using a mixture of empirical research, literature reviews and theoretical development, we introduce novel concepts and methods that we hope will enable us to develop community genetics into the future.     

Diversity of galling arthropods and host plants in a subtropical forest of Porto Alegre, southern Brazil

Many hypotheses have been proposed to explain diversity patterns of galling insects. However, there are contradictory evidences on the evolutionary and ecological factors responsible for the trends. Furthermore, questions such as arthropod seasonality, sampling sufficiency and sampling team experience have been almost ignored. This study records galling arthropod diversity while paying attention to these questions. Seasonal sampling of galling arthropods and host plants were conducted in a humid subtropical forest of southern Brazil. Four transects were sampled twice per season, with two persons searching the vegetation for galls during 1h30min. After 96h.persons of sampling, 130 gall morphotypes on 84 species of host plants were recorded. An analysis of the numbers of galls and gall morphotypes found per transect along time showed that sampling team experience influences galler richness results and the interpretation of galler seasonality patterns. Different species had distinct seasonal patterns. Galling arthropod richness was bound to plant richness. Our results suggest that sampling team experience is an important factor that must be explicitly considered, as well as seasonality patterns of different galling species, at least for tropical/subtropical areas. Although sampling sufficiency was not reached, fauna heterogeneity at small spatial scales seems substantial: despite the proximity of the sampled transects (500 m), they harboured significantly specific faunas. This work adds to the literature records suggesting that both plant richness and specific composition of the vegetation have a strong influence on galler richness at least for local scales.     

Bottom–up and top–down forces structuring consumer communities in an experimental grassland

Synthesis The interplay between bottom‐up and top‐down effects is certainly a general manifestation of any changes in both species abundances and diversity. Summary variables, such as species numbers, diversity indices or lumped species abundances provide too limited information about highly complex ecosystems. In contrast, species by species analyses of ecological communities comprising hundreds of species are inevitably only snapshot‐like and lack generality in explaining processes within communities. Our synthesis, based on species matrices of functional groups of all trophic levels, simplifies community complexity to a manageable degree while retaining full species‐specific information. Taking into account plant species richness, plant biomass, soil properties and relevant spatial scales, we decompose variance of abundance in consumer functional groups to determine the direction and the magnitude of community controlling processes. After decades of intensive research, the relative importance of top–down and bottom–up control for structuring ecological communities is still a particularly disputed issue among ecologists. In our study, we determine the relative role of bottom–up and top–down forces in structuring the composition of 13 arthropod functional groups (FG) comprising different trophic consumer levels. Based on species‐specific plant biomass and arthropod abundance data from 50 plots of a grassland biodiversity experiment, we quantified the proportions of bottom–up and top–down forces on consumer FG composition while taking into account direct and indirect effects of plant diversity, functional diversity, community biomass, soil properties and spatial arrangement of these plots. Variance partitioning using partial redundancy analysis explained 21–44% of total variation in arthropod functional group composition. Plant‐mediated bottom–up forces accounted for the major part of the explainable variation within the composition of all FGs. Predator‐mediated top–down forces, however, were much weaker, yet influenced the majority of consumer FGs. Plant functional group composition, notably legume composition, had the most important impact on virtually all consumer FGs. Compared to plant species richness and plant functional group richness, plant community biomass explained a much higher proportion of variation in consumer community composition.     

北京东灵山土壤动物多样性海拔格局的尺度推绎规律

识别群落内部各类群多样性格局的复杂性是生态学家面临的挑战,而尺度推绎规律是揭示复杂生态结构的有效途径之一。本研究利用多重分形的方法探索了不同海拔土壤动物多样性格局的尺度推绎规律,对比分析了凋落物层和土壤层之间多重分形谱的差异。结果表明: 与之前对植物群落的分析结果相似,土壤动物多样性尺度推绎规律同样具有幂律特征,如丰富度、Shannon多样性指数和Simpson多样性的倒数。凋落物层和土壤层中不同相对多度土壤动物的丰富度也具有幂律尺度推绎规律。凋落物层和土壤层中土壤动物多样性格局都具有多重分形特征,但凋落物层中多样性的分形结构比土壤层更均匀,且两层间优势类群与稀有类群的尺度推绎特征在多重分形谱上不同格局。幂律尺度推绎规律对于有着较高丰富度与多度的土壤动物同样存在,从而有助于揭示地下生物多样性的空间分布机制。     

Bathymetric patterns of morphological disparity in deep-sea gastropods from the western North Atlantic basin

Understanding patterns of species richness requires knowledge of the individual roles species play in community structure. Here, I use gastropod shells as a source of information about both their ecological and their evolutionary functions in generating bathymetric gradients of diversity. Specifically, morphological disparity of shell architecture in deep-sea gastropods is evaluated over a depth gradient in the western North Atlantic by constructing an empirical morphospace based on an eigenshape analysis. Morphological disparity is quantified by calculating the centroid, total range, and dispersion of the morphospace at each station along the depth gradient. The results indicate that local faunas are drawn from a regional pool with the same variance but that average dissimilarity in forms reflects the number of species in the sample. The range of the morphospace at local scales is also less than at regional scales, resulting from the variability of the morphospace centroid over depth. Although the position of the morphospace changes with depth, morphological disparity remains unaffected. Despite the lack of bathymetric patterns in variance, patterns in nearest neighbor distance persist. The findings suggest the importance of interacting ecological and evolutionary processes at varying spatiotemporal scales for both morphological disparity and species richness.     

Tree diversity drives diversity of arthropod herbivores,but successional stage mediates detritivores

The high tree diversity of subtropical forests is linked to the biodiversity of other trophic levels. Disentangling the effects of tree species richness and composition, forest age, and stand structure on higher trophic levels in a forest landscape is important for understanding the factors that promote biodiversity and ecosystem functioning. Using a plot network spanning gradients of tree diversity and secondary succession in subtropical forest, we tested the effects of tree community characteristics (species richness and composition) and forest succession (stand age) on arthropod community characteristics (morphotype diversity, abundance and composition) of four arthropod functional groups. We posit that these gradients differentially affect the arthropod functional groups, which mediates the diversity, composition, and abundance of arthropods in subtropical forests. We found that herbivore richness was positively related to tree species richness. Furthermore, the composition of herbivore communities was associated with tree species composition. In contrast, detritivore richness and composition was associated with stand age instead of tree diversity. Predator and pollinator richness and abundance were not strongly related to either gradient, although positive trends with tree species richness were found for predators. The weaker effect of tree diversity on predators suggests a cascading diversity effect from trees to herbivores to predators. Our results suggest that arthropod diversity in a subtropical forest reflects the net outcome of complex interactions among variables associated with tree diversity and stand age. Despite this complexity, there are clear linkages between the overall richness and composition of tree and arthropod communities, in particular herbivores, demonstrating that these trophic levels directly impact each other.     

Conserving plant genetic diversity for dependent animal communities

While population genetic diversity has broad application in species conservation, no studies have examined the community‐level consequences of this diversity. We show that population genetic diversity (generated by interspecific hybridization) in a dominant riparian tree affects an arthropod community composed of 207 species. In an experimental garden, plant cross type structured the arthropod community of individual trees, and among stands in the wild, plant genetic diversity accounted for nearly 60% of the variation in arthropod diversity. While previous experimental garden studies have demonstrated the effects of plant genotype on arthropod communities, our study extends these findings from individual trees in an experimental garden to natural stands of cottonwoods where plant population genetic diversity was a significant factor structuring arthropod diversity. These findings argue that the preservation of genetic diversity in a dominant species is far more important than previously realized, and may be particularly important in hybridizing systems.     

古田山中亚热带常绿阔叶林群落物种多样性的空间变异特征

古田山常绿阔叶林的群落组成、结构及其维持机制已有许多研究, 但该地区亚热带常绿阔叶林生物多样性空间变异特征还缺乏认识。本文以古田山24 ha大样地(划分为24个1 ha小样地)为基础, 具体分析了α多样性和β多样性在1 ha尺度上的空间变异特征。结果表明: (1)群落第一、二优势物种在各小样地之间变化不大, 但第三优势种变化较大; (2) α多样性变化中, 样地间木本植物个体数量变异最大, 物种丰富度其次, Pielou均匀度指数变异性最小; (3)物种丰富度与植株个体数量、Pielou均匀度指数没有显著的相关性, 与Shannon-Wiener指数呈显著正相关; Shannon-Wiener指数与Pielou均匀度指数呈显著正相关; (4)相邻样地间物种替代速率空间变异较大, 与物种丰富度的空间变化格局有明显差异。这些结果说明尺度对认识群落结构、探讨群落维持机制有重要作用; 由于森林群落是多尺度生态过程作用的结果, 大尺度样地可能有利于更好地揭示森林群落维持机制。     

Clade age and species richness are decoupled across the eukaryotic tree of life

Explaining the dramatic variation in species richness across the tree of life remains a key challenge in evolutionary biology. At the largest phylogenetic scales, the extreme heterogeneity in species richness observed among different groups of organisms is almost certainly a function of many complex and interdependent factors. However, the most fundamental expectation in macroevolutionary studies is simply that species richness in extant clades should be correlated with clade age: all things being equal, older clades will have had more time for diversity to accumulate than younger clades. Here, we test the relationship between stem clade age and species richness across 1,397 major clades of multicellular eukaryotes that collectively account for more than 1.2 million described species. We find no evidence that clade age predicts species richness at this scale. We demonstrate that this decoupling of age and richness is unlikely to result from variation in net diversification rates among clades. At the largest phylogenetic scales, contemporary patterns of species richness are inconsistent with unbounded diversity increase through time. These results imply that a fundamentally different interpretative paradigm may be needed in the study of phylogenetic diversity patterns in many groups of organisms.     

Distribution of Vascular Plant Species Richness Along an Elevational Gradient in the Dongling Mountains, Beijing, China

Quantifying spatial patterns of species richness and determining the processes that give rise to these patterns are core problems In blodlveralty theory. The aim of the present paper was to more accurately detect patterns of vascular species richness at different scales along altitudinal gradients in order to further our understanding of biodlverslty patterns and to facilitate studies on relationships between biodiversity and environmental factors. Species richness patterns of total vascular plants species, including trees, shrubs, and herbs, were measured along an altitudinal gradient on one transect on a shady slope in the Dongling Mountains, near Beijing,China. Direct gradient analysis, regression analysis, and geostatistics were applied to describe the spatial patterns of species richness. We found that total vascular species richness did not exhibit a linear pattern of change with altitude, although species groups with different ecological features showed strong elevational patterns different from total species richness. In addition to total vascular plants, analysis of trees, shrubs, and herbs demonstrated remarkable hierarchical structures of species richness with altitude (i.e. patchy structures at small scales and gradients at large scales). Species richness for trees and shrubs had similar spatial characteristics at different scales, but differed from herbs. These results indicated that species groups with similar ecological features exhibit similar biodlveraity patterns with altitude, and studies of biodiversity based on species groups with similar ecological properties or life forms would advance our understanding of variations in species diversity. Furthermore, the gradients or trends appeared to be due mainly to local variations in species richness means with altitude. We also found that the range of spatial scale dependencies of species richness for total vascular plants, trees, shrubs, and herbs was relatively large. Thus, to detect the relationships betweenspecies richness with environmental factors along altitudinal gradients, it was necessary to quantify the scale dependencies of environmental factors in the sampling design or when establishing non-linear models.