Primary productivity and species richness: relationships among functional guilds, residency groups and vagility classes at multiple spatial scales

One of the major determinants of species richness is the amount of energy available, often measured as primary productivity. Heterogeneity of environmental variables has also been found to influence species richness. Predicting species distributions across landscapes and identifying areas that have high species richness, or vulnerable groups of species, is useful for land management. Remotely sensed data may help identify such areas, with the Normalized Difference Vegetation Index (NDVI) providing an estimate of primary productivity. We examined the relationship between maximum productivity (NDVI), heterogeneity of productivity, and species richness of birds and butterflies at multiple spatial scales. We also explored relationships between productivity, functional guilds and residency groups of birds, and vagility classes of butterflies. Positive linear relationships between maximum NDVI and number of functional guilds of birds were found at two spatial scales. We also found positive linear relationships between maximum NDVI and species richness of neotropical migrant birds at two scales. Heterogeneity of NDVI, by contrast, was negatively associated with number of functional guilds of birds and species richness of resident birds. Maximum NDVI was associated with species richness of all butterflies and of the most vagile butterflies. No association was found between heterogeneity of NDVI and species richness of butterflies. In the Great Basin, where high greenness and availability of water correspond to areas of high species richness and maximum NDVI, our results suggest that NDVI can provide a reliable basis for stratifying surveys of biodiversity, by highlighting areas of potentially high biodiversity across large areas. Measures of heterogeneity of NDVI appear to be less useful in explaining species richness.     

Determinants of avian species richness at different spatial scales

ABSTRACT. Studies of factors influencing avian biodiversity yield very different results depending on the spatial scale at which species richness is calculated. Ecological studies at small spatial scales (plot size 0.0025–0.4 km²) emphasize the importance of habitat diversity, whereas biogeographical studies at large spatial scales (quadrat size 400–50,000 km²) emphasize variables related to available energy such as temperature. In order to bridge the gap between those two approaches the bird atlas data set of Lake Constance was used to study factors determining avian species diversity at the intermediate spatial scales of landscapes (quadrat size 4–36 km²). At these spatial scales bird species richness was influenced by habitat diversity and not by variables related to available energy probably because, at the landscape scale, variation in available energy is small. Changing quadrat size between 4 and 36 km², but keeping the geographical extension of the study constant resulted in profound changes in the degree to which the amount of different habitat types was correlated with species richness. This suggests that high species diversity is achieved by different management regimes depending on the spatial scale at which species richness is calculated. However, generally, avian species diversity seems to be determined by spatial heterogeneity at the corresponding spatial scale. Thus, protecting the diversity of landscapes and ecosystems appears to ensure also high levels of species diversity.     

Breeding bird species richness in Spain: assessing diversity hypothesis at various scales

The variation of passerine species richness in Spain was studied at various spatial scales. Presence-absence data was resampled to construct three species richness maps in lattices of 10×10, 30×30, and 50×50 km UTM cells. The importance of habitat, species-energy, climatic variability, disturbance, history and geometric constraints hypotheses was assessed using geographical data. Stochastic, range-based models were used to simulate neutral colonization events from Europe or from Africa. The importance of small scale processes remained after the inclusion of environmental covariates, indicating a possible role of ecological interactions that was represented in the models by a conditional spatial autoregressive term. Historical effects and energy related measures explained most of the variation in regional species richness. Local and regional habitat structure measures explained the pattern only after large scale trends were considered. The differences when species richness was analyzed at each scale reveal the importance of spatial issues in diversity studies. The possible role of post glacial migration in shaping the observed patterns, and implications for conservation are discussed.     

Contribution of rare and common species to richness patterns at local scales

Several studies have recently reported that common species are more important for species richness patterns than rare species. However, most such studies have been based on broad‐scale atlas data. We studied the contribution of different species occupancy, i.e. number of plots occupied, to species richness patterns emerging from species data in 50 by 50 m plots within six 140–200 ha forests in Norway. The study included vascular plants, lichens, bryophytes, and polypore fungi. We addressed the following questions: 1) are common species more correlated with species richness than rare species? 2) How do occupancy classes combine at various levels of species richness? 3) Which occupancy class is best in identifying the overall most species‐rich sites (hotspots) by sampling? The results showed that rare species were better correlated with species richness than common species when the information content was accounted for, that high species richness was associated with a higher proportion of less frequent species, and that the best occupancy class for local hotspot identification was species present in 10–30% of the plots within a forest. We argue that the observed correlations between overall richness and sub‐assembly richness are primarily structured by the combination of the distributions of species richness and species occupancy. Although these distributions result from general ecological processes, they may also be strongly affected by idiosyncratic elements of the individual datasets caused by the specific environmental composition of a study area. Hence, different datasets collected in different areas may lead to different results regarding the relative importance of common versus rare species, and such effects should be expected on both broad and fine spatial scales. Despite these effects, we suggest that infrequent species will tend to be more strongly correlated to species richness at local scales than at broader scales as a result of more right‐skewed species‐occupancy distributions.     

Effects of total resources, resource ratios, and species richness on algal productivity and evenness at both metacommunity and local scales

The study of the interrelationship between productivity and biodiversity is a major research field in ecology. Theory predicts that if essential resources are heterogeneously distributed across a metacommunity, single species may dominate productivity in individual metacommunity patches, but a mixture of species will maximize productivity across the whole metacommunity. It also predicts that a balanced supply of resources within local patches should favor species coexistence, whereas resource imbalance would favor the dominance of one species. We performed an experiment with five freshwater algal species to study the effects of total supply of resources, their ratios, and species richness on biovolume production and evenness at the scale of both local patches and metacommunities. Generally, algal biovolume increased, whereas algal resource use efficiency (RUE) and evenness decreased with increasing total supply of resources in mixed communities containing all five species. In contrast to predictions for biovolume production, the species mixtures did not outperform all monocultures at the scale of metacommunities. In other words, we observed no general transgressive overyielding. However, RUE was always higher in mixtures than predicted from monocultures, and analyses indicate that resource partitioning or facilitation in mixtures resulted in higher-than-expected productivity at high resource supply. Contrasting our predictions for the local scale, balanced supply of resources did not generally favor higher local evenness, however lowest evenness was confined to patches with the most imbalanced supply. Thus, our study provides mixed support for recent theoretical advancements to understand biodiversity-productivity relationships.     

Plant species richness and spatial organization at different small scales in western Mediterranean landscapes

The relationship between plant species richness and the space organization of the community at different small scales was studied. The study was based on 51 sites distributed along a belt from Central Spain to Portugal. Each site was analyzed with a transect cutting across the boundary between two neighboring patches of shrubland and grassland. Local spatial organization of vegetation was analyzed at different levels of detail and each transect was divided into successively smaller portions. The first division coincides with a physiognomic perception of the site in two patches (shrubland and grassland). The average spatial niche width of the species was used to calculate the spatial organization of the vegetation of each division in each site. The correlation between species richness and spatial organization depended on the block size under consideration. A physiognomic criterion, sectorizing the sites into patches of shrubland and grassland, determines noteworthy floristic changes but does not enable us to express satisfactorily the variability in plant richness. In order to account for this variation, other factors must be taken into account which act at a more detailed small-scale and which determine the internal variability of these patches. In the case studied, the species richness of the sites increases along with an increase in the percentage of species whose occupation of the space is relatively restricted within the site. Many of these species are, however, frequent within the whole of the territory studied. The results highlight the importance of the level of local scale at which the factors influencing occupation of the space, and consequentially, plant richness, preferentially act. This circumstance ought to be taken into consideration in strategies for the conservation of biological diversity, and based on the delimitation of protected spaces with criteria frequently linked to the physiognomy of the vegetation.Nomenclature: Follows T.G. Tutin et al. 1964-1980. Flora Europaea. Cambridge University Press, Cambridge     

Opposite relationships between invasibility and native species richness at patch versus landscape scales

Using a nested plot design in oak forests in Minnesota, USA we measured the percent cover of young individuals of an exotic invading shrub, Rhamnus cathartica (common buckthorn), to assess the relationships at two scales between invasibility, propagule and light availability, and richness and cover of native species. Comparing patches (1 m²) within 17 Quercus -dominated stands (each 1 ha, within a 100 km by 150 km area), cover of young R. cathartica was negatively related to both species richness and cover of native species. In 1 m² patches, native cover was positively associated with native richness and thus cover-related competition was a likely mechanism by which richness influenced R. cathartica . At the landscape scale (comparing the aggregate stand-scale metrics among the 17 stands), native cover and richness were still positively related, but had opposite relationships with R. cathartica cover. R. cathartica cover was positively related to species richness and negatively related to native species cover. The observed switch at different scales from a positive to a negative relationship between R. cathartica cover and native richness supported the hypothesized scale dependence of these relations. Propagule pressure, which we estimated by measuring the size of nearby mature R. cathartica shrubs, had a large positive effect on R. cathartica seedling cover at the landscape scale. These results suggest that landscape patterns of invasion may be best understood in light of the combination of many factors including native diversity, native cover, and propagule pressure.     

Spatial heterogeneity and plant species richness at different spatial scales under rabbit grazing

Herbivores influence spatial heterogeneity in soil resources and vegetation in ecosystems. Despite increasing recognition that spatial heterogeneity can drive species richness at different spatial scales, few studies have quantified the effect of grazing on spatial heterogeneity and species richness simultaneously. Here we document both these variables in a rabbit-grazed grassland. We measured mean values and spatial patterns of grazing intensity, rabbit droppings, plant height, plant biomass, soil water content, ammonia and nitrate in sites grazed by rabbits and in matched, ungrazed exclosures in a grassland in southern England. Plant species richness was recorded at spatial scales ranging between 0.0001 and 150 m(2). Grazing reduced plant height and plant biomass but increased levels of ammonia and nitrate in the soil. Spatial statistics revealed that rabbit-grazed sites consisted of a mixture of heavily grazed patches with low vegetation and nutrient-rich soils (lawns) surrounded by patches of high vegetation with nutrient-poor soils (tussocks). The mean patch size (range) in the grazed controls was 2.1 +/- 0.3 m for vegetation height, 3.8 +/- 1.8 m for soil water content and 2.8 +/- 0.9 m for ammonia. This is in line with the patch sizes of grazing (2.4 +/- 0.5 m) and dropping deposition (3.7 +/- 0.6 m) by rabbits. In contrast, patchiness in the ungrazed exclosures had a larger patch size and was not present for all variables. Rabbit grazing increased plant species richness at all spatial scales. Species richness was negatively correlated with plant height, but positively correlated to the coefficient of variation of plant height at all plot sizes. Species richness in large plots (<25 m(2)) was also correlated to patch size. This study indicates that the abundance of strong competitors and the nutrient availability in the soil, as well as the heterogeneity and spatial pattern of these factors may influence species richness, but the importance of these factors can differ across spatial scales.     

Bird species richness in vegetation fences and in strips of residual rain forest vegetation at Los Tuxtlas, Mexico

Fragmentation of the lowland tropical rain forest has resulted in loss of animal and plant species and isolation of remaining populations that puts them at risk. At Los Tuxtlas, Mexico, lowland rain forests are particularly diverse in the avian fauna they contain and while most of the forests have been fragmented by human activity, many of the fragments still harbor diverse assemblages of bird species. In these landscapes, linear strips of residual rain forest vegetation along streams as well as linear strips of vegetation fences (live fences) crossing the pastures might provide some connectivity to bird populations existed in forest fragments. We investigated bird species richness and relative abundance in one 6-km long section of live fences (LF) bordering a dirt road and in two 6-km long sections of residual forest vegetation along a river (MR) and one permanent stream (BS). We used point count procedures which resulted in the count of 2984 birds representing 133 species. At the LF site we detected 74% of the species, 72% at the BS site and 57% at the MR site. Only 38% of the species were common among sites. Neotropical migratory birds accounted for 34–41% of the species counted at all sites. While edge and open habitat birds accounted for 6–10% of the species and for 50% of the records at the three vegetation strips, about 90% of the species were forest birds. Distance to forest fragments and degree of disturbance of the vegetation seemed to negatively influence bird species presence at the BS and MR strips. Rarefaction analysis indicated that the LF strip was richer in species than the other two sites, but the occurrence of the three vegetation strips in the landscape seem to favor the presence of many more species. We discuss the value of these vegetation strips to birds as stepping stones in the fragmented landscape.     

流域径流泥沙对多尺度植被变化响应研究进展

植被变化与流域水文过程构成一个反馈调节系统,是目前生态水文学研究的重点对象.由于植被自身的生长发育以及受自然因素和人为干扰的作用,植被变化具有多尺度性;由于受流域水文环境的异质性和水文通量的变化性的影响,流域水文过程也同样具有多尺度性.因此,只有通过对不同尺度生态水文过程分析,才能揭示流域径流泥沙对植被变化的响应机理.从不同时空尺度回顾了植被生长、植被演替、植被分布格局变化、造林以及森林经营措施等对流域径流泥沙影响的主要研究成果;概括了目前研究采用的3种主要方法,即植被变化对坡面水流动力学影响的实验室模拟、坡面尺度和流域尺度野外对比观测实验以及水文生态模型模拟方法;分析了植被变化与径流泥沙响应研究要考虑的尺度问题,从小区尺度上推至流域尺度或区域尺度时应考虑不同的生物物理控制过程.研究认为,要确切理解植被与径流泥沙在不同时空尺度的相互作用,必须以等级生态系统的观点为基础,有效结合生态水文与景观生态的理论,从地质-生态-水文构成的反馈调节入手,系统地理解植被变化与径流泥沙等水分养分之间的联系及反馈机制,建立尺度转换的基础.同时,作为有效的研究工具,今后水文模型的发展应更加注重耦合植被生理生态过程以及景观生态过程,从流域径流泥沙对多尺度植被变化水文响应的过程与机制入手,为植被恢复与重建、改善流域水资源状况和流域生态环境奠定基础.     

Determinants of bird species richness: role of climate and vegetation structure at a regional scale

We examined the respective roles of climate and vegetation structure on geographical variation in bird species richness. The Province of Buenos Aires (central-eastern Argentina) was divided into 146 squares of 50 km on a side. For each square we evaluated the number of bird species, the value of thirteen climatic variables, and the value of a vegetation strata index. The climatic matrix was analyzed by Principal Component Analysis (PCA), and the first factors resulting from PCA were considered as multifactorial climatic gradients. Simple and Partial Correlation Analysis among bird species richness, vegetation strata, and the first two factors derived from PCA (65% of total variation) indicated that bird richness distribution was determined by the availability of vegetation strata, associated with different vegetation types that, at the same time, were influenced by the climatic conditions summarized in the first climatic factor (a gradient of precipitation, relative humidity, annual termical amplitude, and frost occurrence). This relationships reflect the complexity of factors that can act directly as well as indirectly on the geographical patterns in species richness. Also, we evaluated the importance of study scale comparing our results with previous studies at macrogeographic and local scales, found out that the vegetation structure was the principal determinant of bird species richness at this three geographical scales.     

Patterns of species density and productivity at different spatial scales in herbaceous plant communities

A major challenge in evaluating patterns of species richness and productivity involves acquiring data to examine these relationships empirically across a range of ecologically significant spatial scales. In this paper, we use data from herb‐dominated plant communities at six Long‐Term Ecological Research (LTER) sites to examine how the relationship between plant species density and above‐ground net primary productivity (ANPP) differs when the spatial scale of analysis is changed. We quantified this relationship at different spatial scales in which we varied the focus and extent of analysis: (1) among fields within communities, (2) among fields within biomes or biogeographic regions, and (3) among communities within biomes or biogeographic regions. We used species density (D=number of species per m²) as our measure of diversity to have a comparable index across all sites and scales. Although we expected unimodal relationships at all spatial scales, we found that spatial scale influenced the form of the relationship. At the scale of fields within different grassland communities, we detected a significant relationship at only one site (Minnesota old‐fields), and it was negative linear. When we expanded the extent of analyses to biogeographic regions (grasslands or North America), we found significant unimodal relationships in both cases. However, when we combined data to examine patterns among community types within different biogeographic regions (grassland, alpine tundra, arctic tundra, or North America), we did not detect significant relationships between species density and ANPP for any region. The results of our analyses demonstrate that the spatial scale of analysis – how data are aggregated and patterns examined – can influence the form of the relationship between species density and productivity. It also demonstrates the need for data sets from a broad spectrum of sites sampled over a range of scales for examining challenging and controversial ecological hypotheses.     

Effects of productivity and disturbance on species richness: a neutral model

Productivity and disturbance are major determinants of species diversity, and results from theoretical models predict that species richness should peak at intermediate levels of both factors. Such "unimodal" responses have been documented in many field and laboratory studies and have usually been attributed to differences among species in competitive ability and/or trade-offs between competitive ability and tolerance to disturbance. Here we show that most documented patterns of disturbance-richness and productivity-richness relationships, as well as the observed interactions between the two factors, can be explained by a simple neutral model where all species are ecologically identical and lack trade-offs in species characteristics. This finding suggests that current neutral theories can be extended to explain patterns of species responses to productivity and disturbance.     

Unifying the relationships of species richness to productivity and disturbance

Although species richness has been hypothesized to be highest at 'intermediate' levels of disturbance, empirical studies have demonstrated that the disturbance-diversity relationship can be either negative or positive depending on productivity On the other hand, hypothesized productivity diversity relationships can be positive, negative or unimodal, as confirmed by empirical studies. However, it has remained unclear under what conditions each pattern is realized, and there is little agreement about the mechanisms that generate these diverse patterns. In this study, I present a model that synthesizes these separately developed hypotheses and shows that the interactive effects of disturbance and productivity on the competitive outcome of multispecies dynamics can result in these diverse relationships of species richness to disturbance and productivity The predicted productivity diversity relationship is unimodal but the productivity level that maximizes species richness increases with increasing disturbance. Similarly, the predicted disturbance diversity relationship is unimodal but the peak moves to higher disturbance levels with increasing productivity Further, these patterns are well explained by the opposite effects of productivity and disturbance on competitive outcome that are suggested by the change in community composition along these two environmental gradients: higher productivity favours superior competitors while higher disturbance levels favour inferior competitors.     

Factors influencing epiphytic bryophyte and lichen species richness at different spatial scales in managed temperate forests

The effect of management related factors on species richness of epiphytic bryophytes and lichens was studied in managed deciduous-coniferous mixed forests in Western-Hungary. At the stand level, the potential explanatory variables were tree species composition, stand structure, microclimate and light conditions, landscape and historical variables; while at tree level host tree species, tree size and light were studied. Species richness of the two epiphyte groups was positively correlated. Both for lichen and bryophyte plot level richness, the composition and diversity of tree species and the abundance of shrub layer were the most influential positive factors. Besides, for bryophytes the presence of large trees, while for lichens amount and heterogeneity of light were important. Tree level richness was mainly determined by host tree species for both groups. For bryophytes oaks, while for lichens oaks and hornbeam turned out the most favourable hosts. Tree size generally increased tree level species richness, except on pine for bryophytes and on hornbeam for lichens. The key variables for epiphytic diversity of the region were directly influenced by recent forest management; historical and landscape variables were not influential. Forest management oriented to the conservation of epiphytes should focus on: (i) the maintenance of tree species diversity in mixed stands; (ii) increment the proportion of deciduous trees (mainly oaks); (iii) conserving large trees within the stands; (iv) providing the presence of shrub and regeneration layer; (v) creating heterogeneous light conditions. For these purposes tree selection and selective cutting management seem more appropriate than shelterwood system.     

中国陆栖哺乳动物物种丰富度的地理格局及其与环境因子的关系

物种丰富度的大尺度地理格局及其成因是宏观生态学和生物地理学的中心议题之一。本文利用中国陆栖哺乳动物分布数据, 结合高分辨率的气候、地形、植被等环境信息, 探讨了中国陆栖哺乳动物及主要类群的物种丰富度格局及其影响因素。结果显示, 中国陆栖哺乳动物物种丰富度具有显著的纬度梯度格局, 总体上呈现出由低纬度向高纬度逐渐减少的趋势, 并与宏观地形具有良好的对应关系; 其中, 亚热带、热带西部山区的物种丰富度最高, 而东部平原地区、西北干旱区和青藏高原腹地则是丰富度的低值区。各主要类群的物种丰富度格局既有相似性, 又存在差异。最优线性模型的分析结果显示, 由归一化植被指数(NDVI)、生态系统类型数和气温年较差构成的回归模型对哺乳动物物种丰富度格局的解释率最高, 其中NDVI对模型解释率的贡献最大, 这表明中国陆栖哺乳动物物种丰富度的地理分异受多种环境因素的共同影响, 其中植被生产力起主导作用。各主要类群的最优线性模型显示, 影响物种丰富度格局的主要环境因子因类群而异, 这可能反映了各类群进化历史及生理适应的差异。