Different relationships between galling and non-galling herbivore richness and plant species richness: a meta-analysis

The plant richness hypothesis (PRH) is used to explain herbivorous insect richness based on the number of plant species, predicting a positive relationship. However, the influence of plant richness on insect distribution can become stronger with greater levels of specialization of herbivores. In this meta-analysis, I tested whether there is any difference in the correlation force recorded between studies that investigated endophagous versus exophagous herbivores, and galling versus non-galling guilds, in order to determine whether more specialized groups have a stronger relationship. Furthermore, I calculated whether effect sizes were homogeneous between galling studies carried out at local and regional scales, and between tropical and temperate regions. A total of 52 correlations were analyzed between plant species richness and herbivore species richness, with 18 correlations derived from galling herbivores and 34 from non-galling herbivores. The effect sizes were significant and positive in all studies, being higher for endophages than for exophages, and for galling than for non-galling studies. These results provide evidence that groups of insects with a higher level of host specialization and specificity (e.g., endophagous and galling) exhibit a greater dependence on plant richness. There was no difference in effect sizes for galling studies between the local and regional level or between tropical and temperate groups. Despite the large variability found for galling studies, effect sizes were consistent independently of climatic region and latitudinal variation. These results suggest that the PRH for galling insects can be generalized to most ecosystem and vegetation types.     

Regional and global elevational patterns of microbial species richness and evenness

Although elevational gradients in microbial biodiversity have attracted increasing attention recently, the generality in the patterns and underlying mechanisms are still poorly resolved. Further, previous studies focused mostly on species richness, while left understudied evenness, another important aspect of biodiversity. Here, we studied the elevational patterns in species richness and evenness of stream biofilm bacteria and diatoms in six mountains in Asia and Europe. We also reviewed published results for elevational richness patterns for soil and stream microbes in a literature analysis. Our results revealed that even within the same ecosystem type (that is, stream) or geographical region, bacteria and diatoms showed contrasting patterns in diversity. Stream microbes, including present stream data, tend to show significantly increasing or decreasing elevational patterns in richness, contrasting the findings for soil microbes that typically showed nonsignificant or significantly decreasing patterns. In all six mountains for bacteria and in four mountains for diatoms, species richness and evenness were positively correlated. The variation in bacteria and diatom richness and evenness were substantially explained by anthropogenic driven factors, such as total phosphorus (TP). However, diatom richness and evenness were also related to different main drivers as richness was mostly related to pH, while evenness was most explained by TP. Our results highlight the lack of consistent elevational biodiversity patterns of microbes and further indicate that the two facets of biodiversity may respond differently to environmental gradients.     

The relationship between species richness and productivity in metazoan parasite communities

Biodiversity is not distributed homogeneously in space, and it often covaries with productivity. The shape of the relationship between diversity and productivity, however, varies from a monotonic linear increase to a hump-shaped curve with maximum diversity values corresponding to intermediate productivity. The system studied and the spatial scale of study may affect this relationship. Parasite communities are useful models to test the productivity-diversity relationship because they consist of species belonging to a restricted set of higher taxa common to all host species. Using total parasite biovolume per host individual as a surrogate for community productivity, we tested the relationship between productivity and species richness among assemblages of metazoan parasites in 131 vertebrate host species. Across all host species, we found a linear relationship between total parasite biovolume and parasite species richness, with no trace of a hump-shaped curve. This result remained after corrections for the potential confounding effect of the number of host individuals examined per host species, host body mass, and phylogenetic relationships among host species. Although weaker, the linear relationship remained when the analyses were performed within the five vertebrate groups (fish, amphibians, reptiles, mammals and birds) instead of across all host species. These findings agree with the classic isolationist-interactive continuum of parasite communities that has become widely accepted in parasite ecology. They also suggest that parasite communities are not saturated with species, and that the addition of new species will result in increased total parasite biovolume per host. If the number of parasite species exploiting a host population is not regulated by processes arising from within the parasite community, external factors such as host characteristics may be the main determinants of parasite diversity.     

Species richness vs evenness: independent relationship and different responses to edaphic factors

The main components of species diversity are richness and evenness. Species richness has been the subject of biodiversity studies more often than species evenness. Some simulated models suggest that the relationship between these two components is equal and predictable in a stable environment. This study was conducted in a human-shaped and unstable environment in arable field boundaries. A total of 30 sampling plots were laid out at random in the boundaries. Vegetation at the sites was of meadow type. The relationship between species richness and evenness, and their responses to edaphic nutrient factors in the field boundaries, were examined by correlation analysis and an ordination method. Correlation analyses demonstrated that no consistent pattern was present in the relationship between species evenness and species richness in this human-shaped ecosystem. Species richness and evenness also had different responses to edaphic factors, with species richness being negatively correlated with phosphorus, and species evenness negatively correlated with the ratio of organic carbon to total nitrogen in soil. The results indicate that different and independent ecological processes determine species richness and evenness. The relationship between these two components may be site-specific, reflecting variation in resource utilization by plant species. The pattern thus reflects the spatial heterogeneity of disturbances or 'patchiness' of resources between sites in a semi-natural ecosystem.     

The relationship between tree size and epiphyte species richness: testing four different hypotheses

Aim For epiphytic plants trees are habitat units, and tree size determines epiphyte species richness. While growing, trees generate vertical microhabitats that are exploited by epiphytes. One would expect to find four different types of relationship between tree size and epiphyte species richness: positive linear (young trees), neutral (old trees), negative (old decaying trees) and positive asymptotic (trees of mixed size class in a mature forest). We tested these relationships in plots of colonizing sweetgum trees in pastureland, isolated remnant trees in pastureland (old oaks) and sweetgum and oaks in a pristine forest. Location The study was carried out in a landscape shaped by the fragmentation of lower montane cloud forest in San Andrés Tlalnelhuayocan (19°30′56′′ N and 96°59′50′′ W; 1500–1600 m a.s.l.) in central Veracruz, Mexico. Methods We measured the d.b.h. of all oaks and sweetgum trees (d.b.h. ≥ 5 cm) present in pastureland and in three 100 m² plots of a lower montane cloud forest. All trees were climbed and species richness of the epiphytes recorded. Results As expected, colonizer trees in pastureland showed a linear positive relationship. Although we found evidence that remnant oaks in pastureland had a neutral relationship between tree size and epiphyte species richness, the low power of the test did not allow us to make conclusions about the kind of relationship. Mixed size‐class pristine forest trees showed a positive linear relationship between tree size and epiphyte species richness instead of a positive asymptotic one. Main conclusions Our results suggest that in the study area epiphyte communities are unsaturated, as the number of species increases with tree size and does not reach a ceiling. This evidence supports the idea that the species–area relationship is not asymptotic. However, the epiphyte community on remnant pastureland oaks may be saturated as epiphyte species richness did not increase with tree size, but a larger sample size is needed to confirm the neutral pattern. Neutral, asymptotic and negative patterns in the relationship between tree size and epiphyte species richness depend on the saturation of the trees by epiphytes. Other studies have suggested tree saturation, but further research is necessary in order to confirm or rule out these patterns.     

An assessment of the dependence of evenness indices on species richness

Evenness is the component of species diversity that was built to be mathematically independent from species richness. Yet, earlier work questioned the generality of this independence. However, this earlier work involved only a few relative abundance distributions (RADs), very limited gradients of species richness, or evenness indices, such as Pielou's index, that were not defined in relation to a precise, coherent set of axioms. We show that for very different theoretical RADs, a relationship between evenness indices and species richness does exist and is strong-at least for some RADs and/or when species richness is under 20. Furthermore, this relationship is mostly negative, which contradicts some previous studies. We also show that, for the very uneven RADs we tested, evenness indices depend even more on species richness than diversity indices do. Finally, we discuss the philosophy behind the analysis of evenness-richness relationships within and between RADs, as well as the interest of correcting evenness indices for species richness when species richness varies, especially with many values under 20.     

The effect of resveratrol on longevity across species: a meta-analysis

Resveratrol has shown evidence of decreasing cancer incidence, heart disease, metabolic syndrome and neural degeneration in animal studies. However, the effects on longevity are mixed. We aimed to quantify the current knowledge of life extension from resveratrol. We used meta-analytic techniques to assess the effect resveratrol has on survival, using data from 19 published papers, including six species: yeast, nematodes, mice, fruitflies, Mexican fruitflies and turquoise killifish. Overall, our results indicate that resveratrol acts as a life-extending agent. The effect is most potent in yeast and nematodes, with diminished reliability in most higher-order species. Turquoise killifish were especially sensitive to life-extending effects of resveratrol but showed much variation. Much of the considerable heterogeneity in our analysis was owing to unexplained variation between studies. In summary, we can report that few species conclusively show life extension in response to resveratrol. As such, we question the practice of the substance being marketed as a life-extending health supplement for humans.     

The relationship between species richness and standing crop in wetlands: the importance of scale

One of the few important empirical generalizations regarding herbaceous plant systems has been the demonstration that species richness is related to standing crop with maximum richness occurring at moderate levels of standing crop. This relationship is normally demonstrated by comparing among vegetation types (i.e., vegetation with different dominants). We undertook this study to test whether the species richness-standing crop relationship was evident at a finer-grained level of organization, the within vegetation type level. Fifteen wetland sites were sampled in eastern Canada and species richness and standing crop determined in each of 224 0.25 m² quadrats. Each site was relatively homogeneous in terms of the dominant species present and were therefore categorized as single vegetation types. However, as a group, the sites comprised a wide range of vegetation types.A second order polynomial regression indicated a significant bitonic relationship between species richness and standing crop at the among-vegetation types scale, that is, when all 15 sites were combined. At the within-vegetation type level, however, no significant relationships were observed (p>0.05). The results indicate that the model of species richness proposed by Grime has predictive power at a coarse-grained level of organization, among vegetation types, but does not survive the transition to a finer-grained level of organization, the within vegetation type level. Therefore, the higher level processes which structure species richness patterns among vegetation types are not the same processes which determine richness patterns within a vegetation type.     

Tree species richness decreases while species evenness increases with disturbance frequency in a natural boreal forest landscape

Understanding species diversity and disturbance relationships is important for biodiversity conservation in disturbance‐driven boreal forests. Species richness and evenness may respond differently with stand development following fire. Furthermore, few studies have simultaneously accounted for the influences of climate and local site conditions on species diversity. Using forest inventory data, we examined the relationships between species richness, Shannon''s index, evenness, and time since last stand‐replacing fire (TSF) in a large landscape of disturbance‐driven boreal forest. TSF has negative effect on species richness and Shannon''s index, and a positive effect on species evenness. Path analysis revealed that the environmental variables affect richness and Shannon''s index only through their effects on TSF while affecting evenness directly as well as through their effects on TSF. Synthesis and applications. Our results demonstrate that species richness and Shannon''s index decrease while species evenness increases with TSF in a boreal forest landscape. Furthermore, we show that disturbance frequency, local site conditions, and climate simultaneously influence tree species diversity through complex direct and indirect effects in the studied boreal forest.     

Multi-extent analysis of the relationship between pteridophyte species richness and climate

Aim To determine the relationship between the distribution of climate, climatic heterogeneity and pteridophyte species richness gradients in Australia, using an approach that does not assume potential relationships are spatially invariant and allows for scale effects (extent of analysis) to be explicitly examined. Location Australia, extending from 10° S to 43° S and 112° E to 153° E. Method Species richness within 50 × 50 km grid cells was determined using point distribution data. Climatic surfaces representing the distribution and availability of water and energy at 1 km and 5 km cell resolutions were obtained. Climate at the 50 km resolution of analysis was represented by their mean and standard deviation in that area. Relationships were assessed using geographically weighted linear regression at a range of spatial bandwidths to investigate scale effects. Results The parameters and the predictive strength of all models varied across space at all extents of analysis. Overall, climatic variables representing water availability were more highly correlated to pteridophyte richness gradients in Australia than those representing energy. Their variance in cells further increased the strength of the relationships in topographically heterogeneous regions. Relationships with water were strong across all extents of analysis, particularly in the tropical and subtropical parts of the continent. Water availability explained less of the variation in richness at higher latitudes. Main conclusions This study brings into question the ability of aspatial and single‐extent models, searching for a unified explanation of macro‐scaled patterns in gradients of diversity, to adequately represent reality. It showed that, across Australia, there is a positive relationship between pteridophyte species richness and water availability but the strength and nature of the relationship varies spatially with scale in a highly complex manner. The spatial variance, or actual complexity, in these relationships could not have been demonstrated had a traditional aspatial global regression approach been used. Regional scale variation in relationships may be at least as important as more general relationships for a true understanding of the distribution of broad‐scale diversity.     

Spatial patterns of invertebrate species richness in a river: the relationship between riffles and microhabitats

This study describes the pattern of invertebrate species richness in a river reach with large differences in habitat complexity at two, hierarchically nested, spatial scales. The aim was to determine whether the mass effect was likely to be increasing invertebrate species richness in epilithic microhabitats in this river. The mass effect is the process by which the species richness of a patch is increased when it acts as a ‘sink’ for species generated by ‘source’ patches. Microhabitat patch types in Mountain River, Tasmania, were distinguished on the basis of physical structure and orientation on the river bed. They were nested within two types of riffle with contrasting structural complexity: bedrock and boulder-cobble riffles. It was hypothesized that microhabitats with high species richness would act as source patches, contributing species to other microhabitats (sinks) and thereby increasing their species richness. Microhabitat sampling was carried out in four consecutive seasons and rarefaction was used to estimate riffle-scale species richness. Analysis of variance ( ANOVA ) was used to compare the identical microhabitats present in the contrasting riffle types, to detect evidence of the mass effect in either riffle type. The more structurally complex boulder-cobble riffles had higher species richness than did bedrock riffles. Amongst the microhabitats, the spaces beneath the cobbles had the most species. Microhabitats accounted for a higher percentage of the variation in species richness than did differences between riffles of the same type. No evidence was found for the operation of the mass effect in either riffle type. The majority of species found only in boulder-cobble riffles were unique to the beneath-cobble microhabitat and appeared to be unable to colonize other microhabitats, even as transients. In Mountain River, small-scale habitat characteristics appeared to be more important than larger-scale effects in determining microhabitat species richness.     

The relationship between species richness and productivity in four typical grasslands of northern China

The relationship between plant species richness and primary productivity has long been acentral topic in biodiversity research.In this paper,we examine the relationship between species richness and productivity in four typical grasslands of Northern China at different spatial scales.At the community scale,a positive correlation was found for six of seven communities.A unimodal pattern was found only for one community (Stipa glareosa community),while at a large scale (vegetation type or landscape/region),the relationship was also found significantly positive.Species richness ranged from 4 to 35 species,and community aboveground productiand aboveground productivity were found in alpine meadow,followed by meadow steppe,typical steppe and desert steppe.     

中国北方典型草地物种丰富度与生产力的关系

利用2002–2004年内蒙古和甘肃南部几种典型草地的实测资料,研究了不同尺度物种丰富度与生产力的关系,并初步探讨了其形成机制。结果显示,温带草地的物种丰富度随生产力的增加而增加,但受空间尺度影响。在群落尺度(同一群落),在7种样方数大于15的群落中,仅沙生针茅(Stipaglareosa)群落物种丰富度与生产力呈现单峰型关系,其余均呈现线性正相关关系;在植被类型尺度,物种丰富度–生产力之间表现为显著的正相关关系;在研究区尺度,物种丰富度随生产力的增加而显著增加。研究还表明,研究区群落生产力的变化范围为13–368g·m–2·yr–1,物种丰富度为4–35种;生产力从高到低的顺序为:高寒草甸>草甸草原>典型草原>荒漠草原。     

Effects of plant species richness and evenness on soil microbial community diversity and function

Understanding the links between plant diversity and soil communities is critical to disentangling the mechanisms by which plant communities modulate ecosystem function. Experimental plant communities varying in species richness, evenness, and density were established using a response surface design and soil community properties including bacterial and archaeal abundance, richness, and evenness were measured. The potential to perform a representative soil ecosystem function, oxidation of ammonium to nitrite, was measured via archaeal and bacterial amoA genes. Structural equation modeling was used to explore the direct and indirect effects of the plant community on soil diversity and potential function. Plant communities influenced archaea and bacteria via different pathways. Species richness and evenness had significant direct effects on soil microbial community structure, but the mechanisms driving these effects did not include either root biomass or the pools of carbon and nitrogen available to the soil microbial community. Species richness had direct positive effects on archaeal amoA prevalence, but only indirect impacts on bacterial communities through modulation of plant evenness. Increased plant evenness increased bacterial abundance which in turn increased bacterial amoA abundance. These results suggest that plant community evenness may have a strong impact on some aspects of soil ecosystem function. We show that a more even plant community increased bacterial abundance, which then increased the potential for bacterial nitrification. A more even plant community also increased total dissolved nitrogen in the soil, which decreased the potential for archaeal nitrification. The role of plant evenness in structuring the soil community suggests mechanisms including complementarity in root exudate profiles or root foraging patterns.     

The relationship between species richness and productivity in four typical grasslands of northern China

The relationship between plant species richness and primary productivity has long been a central topic in biodiversity research. In this paper, we examine the relationship between species richness and productivity in four typical grasslands of Northern China at different spatial scales. At the community scale, a positive correlation was found for six of seven communities. A unimodal pattern was found only for one community (Stipa glareosa community), while at a large scale (vegetation type or landscape/region), the relationship was also found significantly positive. Species richness ranged from 4 to 35 species, and community aboveground productivity from 13 to 368 g·m⁻²·a⁻¹. The highest species richness and aboveground productivity were found in alpine meadow, followed by meadow steppe, typical steppe and desert steppe. Translated from Biodiversity Science, 2006, 14(1): 21–28 [译自: 生物多样性]