Variation in structure and diversity in Mediterranean grasslands related to trophic status and grazing intensity

Abstract. The spatial organization of Mediterranean grassland in Spain is described, based on samples from 71 sites covering the existing variation in slope exposition and inclination.The whole set can be regarded as representing a trophic gradient, along which gradual variation in soil, species composition, biomass, and coverage were quantified. Corresponding to other studies from varying habitats, maximal species richness, diversity, and heterogeneity were observed on moderately infertile sites. Maximum species richness, over 60 species, occurred on sites with biomass values from 150–350 g / m². Species richness values are much higher and biomass values are much lower than those found in temperate grasslands. The decrease in diversity towards the mosteutrophic communities is stronger than expected, but can be easily explained by the high grazing pressure here. The variation in diversity observed runs parallel with that in heterogeneity. Zones with a high species richness also have a high heterogeneity, meaning a low amount of dominance. Grazing is understood as abiotic form of disturbance. Differences in grazing pressure may modify the relation between richness and fertility. While the greatest grazing pressure coincides with the most eutrophic communities, decreasing progressively towards the oligotrophic ones, the trend predicted by the resource availability theory is maintained; species diversity will be maximal at intermediate levels of disturbance. Absence of grazing in the eutrophic communities would lead to an investment in the soil of the unconsumed organic matter.     

Are conservation units in the Caatinga biome,Brazil, efficient in the protection of biodiversity? An analysis based on the drosophilid fauna

Biodiversity is believed to be low in regions with vegetation that has adapted to water stress. Additionally, there is little interest by authorities in establishing and expanding conservation units in these areas. In Brazil, the Caatinga and the Cerrado biomes comprise this xerophilous vegetation. In both, climate is tropical and the dry season is long and well-defined. The Caatinga is the Brazilian biome with the smallest area protected by conservation units. This study evaluates the efficacy of conservation units in the Caatinga biome based on abundance and richness of drosophilids. Flies were collected inside and outside these areas. In total, approximately 23,000 flies of 32 species were collected in six conservation and six non-conservation sites. Two non-described species occurred exclusively inside protected areas, underlining the importance of conservation efforts in the maintenance of biodiversity. Other species were recorded exclusively outside conservation areas, which emphasizes the importance of establishing and expanding conservation units in the Caatinga. Native species were significantly more abundant inside conservation units, though the richness was similar in protected and non-protected areas. Abundance of exotic species outside conservation areas was statistically different in comparison with that of native ones.     

泸沽湖及其附近竹地海湿地越冬水鸟群落组成及历史变化分析

泸沽湖是中国西南重要的水鸟越冬地和旅游风景区,开展泸沽湖越冬水鸟群落组成现状调查并进行历史变化分析,对指导泸沽湖水鸟及其栖息地保护和管理具有重要意义。2013年10月至2014年2月(12月除外),逐月对泸沽湖全湖及其西北方向的竹地海湿地(距离泸沽湖约500 m,面积约0.4 km2)越冬水鸟进行调查。泸沽湖共记录到水鸟27种,观察的最大个体总数约为22 600只,符合国际重要湿地标准。泸沽湖越冬水鸟群落的主要优势物种为骨顶鸡(Fulica atra),其最大观察数约为10 300只。竹地海湿地共记录到水鸟16种,观察到的最大个体总数约为3 600只,其中赤麻鸭(Tadorna ferruginea)约为2 700只;鉴于竹地海湿地亦为水鸟聚集的栖息地,建议将其划入泸沽湖自然保护区加以保护。对比1992年的调查数据,发现泸沽湖及其附近竹地海湿地越冬水鸟的物种丰富度(species richness)可能有所下降,由原来的33种下降到现在的30种,但个体总数量相对稳定。多种涉禽和喜浅水活动的钻水鸭类(dabbling ducks)消失,可能与湖岸区旅游活动的持续进行有关;泸沽湖曾经的主要优势物种赤嘴潜鸭(Netta rufina)种群数量大幅下降,暗示泸沽湖生态系统可能已发生变化。泸沽湖旅游业进一步发展的同时,保护好现存的浅水栖息地将是泸沽湖水鸟多样性不再继续下降的关键。     

Environmental factors affecting the distribution of aquatic invertebrates in temporary ponds in Mammoth Cave National Park,Kentucky, USA

Despite a recent surge of interest in temporary lentic systems, a strong theory linking the biota to its environment has not emerged. Using data from 10 temporary ponds at Mammoth Cave National Park, Kentucky, USA, we investigated how invertebrate communities were structured along environmental gradients, both between and within ponds. Samples were collected with a benthic corer in winter and spring, and a sweep net in spring. Six between-pond and two within-pond datasets were created. Between-pond analyses yielded significant CCA’s with only one of the six data sets. The ranges of environmental variables (EV’s) within ponds were often similar to the ranges of EV’s when averaged and compared between ponds. Some taxa were aggregated in a single pond, and richness increased with pond area. The theory that richness increases with hydroperiod did not apply to these systems. Within-pond analyses yielded more consistent relationships, with both CCA’s being significant. Sample depth was the best predictor of invertebrate richness and abundance, with most taxa preferring shallow habitats. Richness and abundance were higher in both shallow ponds and shallow areas of deep ponds than in deep areas of deep ponds. Standardizing sample depth may be an effective way to remove this gradient as a confounding variable in future research. The presence of within-pond gradients, possibly coupled with the limited dispersal and random colonization of tolerant taxa, makes between-pond comparisons difficult. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorised users. Handling editor: S. Declerck     

Assessment of large-vertebrate species richness and relative abundance in Neotropical forest using line-transect censuses: what is the minimal effort required?

Line-transect sampling is a strategy commonly used to assess richness and abundance of large diurnal vertebrates in tropical forests, but the relationships between the sampling effort (measured as transect length in km) and the accuracy of the estimates based on the field data have rarely been investigated. Using data from 17 distinct surveys in French Guiana, we demonstrated that 85 km of transect are sufficient to extrapolate species richness whatever the forest type and the disturbance level of the habitat. Concerning species abundances, reliable estimations were obtained after 40–90 km of transects for large birds, howlers, tamarins, and agoutis. In contrast, relative abundances of capucins, sakis, and ungulates, were still not stabilized after 100 km but can still be reliably assessed with this effort. These species have larger home range than the former, and the accuracy of abundance assessment may be related to use of space. Since species with small area requirements regularly use their entire home range, abundance prediction with a moderate sampling effort may be facilitated. On the contrary, species with large home ranges may exhibit strong seasonal habitat partitioning, therefore decreasing the accuracy of abundance estimation on a low-effort survey. This analysis provides the first evidence of the minimal efforts required to assess large vertebrate richness and relative abundance of some species in a neotropical rainforest. We encourage similar works on other sites, to collect additional information on the influence of forest productivity and species assemblage composition on the minimal required sampling effort. This would permit confident extrapolations of species richness and abundance in other Neotropical forests and may provide efficient guidelines to integrate the predictive analytical tool developed in this work in future biodiversity management plans.     

Does climate influence assemblages of anurans and lizards in a coastal area of north-eastern Brazil?

Environmental factors influence diverse assemblage features such as species abundances, richness, and nestedness. Amphibians and reptiles play important roles in terrestrial ecosystems, but there is still a lack of information about the assemblages of these animals in many regions. In this study, we aimed to understand how environmental factors influence the anurans and lizards assemblages from São Gonçalo do Amarante, Ceará, Brazil. Herpetofauna samplings were performed monthly in São Gonçalo do Amarante from January 2008 to May 2009, excluding April 2008. We sampled animals (anurans and lizards) using pitfall traps and active searches. The abundance and richness of lizards were positively related to temperature and negatively related to precipitation. Anuran assemblage was not influenced by precipitation, but its abundance was negatively influenced by temperature. Temperature generated a nested pattern in the lizard assemblage, but precipitation did not produce this pattern in anurans. Finally, our results reinforce the importance of environmental factors, mainly temperature, in structuring assemblages of anurans and lizards.     

中国种子植物特有属的生物多样性和特征

生物多样性是当今世界生物环境研究中的重要课题,植物区系研究可为之做出贡献。本文根据文献和调查资料,运用统计和比较分析法,以属的丰富度和相似性系数为指标,研究全国及各省区中国种子植物特有属的多样性,得出６点结论,找到８个分布多度中心。中国种子植物特有属计有２６９属,含５５１种６０变种,占全国同类属数８．９％。归７８科,以热带科居多,中国特有８科。云南省的丰富度最大,有１３０属１９０多种,朝各方向递减,至秦岭─江下游以北显著降低。陕－甘和浙－赣的相似性系数最高,达８０％─９０％,南方各省间一般较高至极高（３０％－８０％）,北方各省间一般较低至很低（３０％─１％）,新疆、海南等与若干省无联系。还说明它们的区系特征及多样性变化的地理原因。为进一步研究中国植物区系和保护物种资源提供了依据。     

深层海洋浮游植物研究综述

对深层海洋(200 m)浮游生物的研究是我国海洋浮游生物研究的前沿,已有的深层海洋浮游生物知识是我国相关研究的基础。浮游植物需要阳光进行光合作用,大多数浮游植物沉降到深海中会死亡,但有些浮游植物却能在深海中生存。综述深层海洋中存活的浮游植物的研究进展,为我国的研究提供参考。在深层海洋发现的浮游植物(2\"m)种类不多,共有18种,最深分布在4000 m,颗石藻的丰度大于硅藻和甲藻,最大丰度为2220个/L,出现在500 m。在1911—1985年期间,曾经发现橄榄绿细胞,由于研究手段有限,一直没有对其进行分类学研究。1985年以后的研究怀疑这些橄榄绿细胞就是聚球藻蓝细菌,聚球藻蓝细菌在太平洋、大西洋和地中海的几个站位能分布到2750 m,在深层海洋的最大丰度为3.5×105个/mL,出现在800 m。在许多海区200—700 m发现有浮游植物色素荧光的高值,但对引起高值的原因尚不清楚。浮游植物生物量在深层海洋的垂直剖面研究不多,已有的研究表明浮游植物生物量在300 m以深为0.001—0.1\"g C/L,且其随深度增加而降低。     

Acceptability of plant species along grazing gradients around watering points in Tunisian arid zone

Water points provide excellent sites for studying overgrazing effects on plant communities in dry areas. Distance from water can be considered like a surrogate of grazing pressure being high near the water and low away from it. The main aim of this study is to investigate overgrazing effects on acceptability of fodder plants along a grazing gradient around three natural watering points. To achieve this goal, we classified spontaneous plants according to their acceptability degree and we followed their cover, richness and density as well as the grazing value along a grazing gradient around these wells, using phyto-ecological studies during the spring 2004 and 2006. Main results show that very palatable plants (mainly constituted by annuals) are more dominant in both the closed and the more disturbed transect areas around wells. The unpalatable plants dominate sites with moderate disturbance around wells. Ligneous palatable species obviously have a lower degree of disturbance. During the studied seasons the grazing gradient around wells 1 and 2, the oldest ones, seemed to exert a feedback upon the grazing intensity.     

Community structure and species composition along a disturbance gradient in a communally managed South African savanna

The woody and herbaceous vegetation was investigated around four rural settlements in the savanna area of the eastern Transvaal Lowveld, South Africa. At each settlement three transects radiating out from the settlement, representing a gradient from high to low disturbance, were sampled for community structure and species composition. In general, attributes of woody community structure (density, height, biomass, basal area and diversity) were negatively related to increasing disturbance. Herbaceous cover responded positively. Although individual woody species exhibited a range of responses to disturbance, overall species compositional changes were not related directly to the intensity of disturbance. Individual woody species were classified into behavioural species response groups according to their response along the disturbance gradient. Local wood harvesters demonstrated marked selection for particular species and size classes, which should have disproportional impacts on community structure. However, proportional size class distributions were little altered along the gradient.     

Effects of large herbivore browsing on the functional groups of woody plants in a southern African savanna

This study examined the effect of different large herbivore species and stocking rates in savanna ecosystems of Zimbabwe on the richness and abundances of woody plant functional groups and woody plant functional attributes. Seven fence-lines with different herbivore species and stocking rates on either side of the fence were sampled. Plots were placed on both sides of each fence at each of 18 randomly selected positions. The size and species of each woody plant was recorded for each plot. It was found that the number of species with different functional attributes of spinescence, leaf longevity, fruit type and dispersal mechanism and in the functional groups of palatability were not different on the different sides of the fence. However, there were differences in plant abundances for 26 out of the 35 tests carried out on plant abundances with different functional attributes and functional groups. It was hypothesised that the time needed to change woody plant species richness is hundreds of years in these systems, whereas the time needed to change woody plant abundances is decades.     

Experimental study of the effect of hydrology and mechanical soil disturbance on plant communities in Mediterranean temporary pools in Western Morocco

Physical soil disturbance and the hydrology of temporary pools affect the biomass, species composition and richness of plant communities. Disturbance liberates sites for the random recruitment of new individuals. The addition of seeds modifies the structure of the communities. In order to verify these hypotheses concerning the vegetation of temporary pools, an experiment was carried out using 72 soil samples collected from a pool in Western Morocco and placed in containers. Three types of laboratory treatments were applied, each combined with control treatments: soil disturbance (control/disturbed), hydrology (flooded, saturated and dry) and seed addition (sowing/no sowing). The total biomass, the annual and perennial species richness were calculated for each sample to test the effects of disturbance, hydrology and seed addition on the biomass and species richness of the various plant communities. The results show that disturbance reduces the total biomass, especially of perennials, but without significantly increasing the richness of annuals. Seed addition does not affect the total biomass and reduces total richness only in saturated soil, where biomass production is high. The most extreme stress conditions (drought and flooding) limit the abundance of species and therefore competition. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

Mesozooplankton biomass and indices of grazing and metabolic activity in Antarctic waters

Mesozooplankton abundance, body area spectrum, biomass, gut fluorescence and electron transfer system (ETS) activity were studied in the Antarctic Peninsula during the post-bloom scenario in these waters. Values of abundance and biomass were rather low and decreased sharply from the slope waters to the coastal area. In contrast, specific gut fluorescence and ETS activity were high in the coastal area and decreased through the shelf-break. Large copepods were very scarce, similarly to the post-bloom conditions in phytoplankton where large cells are not abundant and small cells such as flagellates dominate the water column. The vertical distribution showed two well defined layers by day, one at the surface which corresponded to krill organisms and a second at depth (>300 m) formed mainly by the large copepod Metridia gerlachei. During the short night, this layer ascended at the time that krill at the surface migrated to deeper waters as observed from acoustics and net sampling. This observation and the absence of large copepods over the shelf suggest that krill consumption on large phytoplankton cells during the bloom is followed by an increase in predation upon mesozooplankton. It also suggests that krill decrease the abundance and biomass of mesozooplankton over the shelf and continues their predation upon mesopelagic copepods during the post-bloom in Antarctic waters. This behaviour could explain the long ago described impoverishment in mesozooplankton south of the Antarctic Circumpolar Current.     

Habitat complexity as a determinate of benthic macroinvertebrate community structure in cypress tree reservoirs

We analyzed benthic samples (n = 128) collected from four cypress-tree population areas within a large, shallow Arkansas reservoir over a 2-year period to investigate macroinvertebrate community distribution patterns and their relation to physical and chemical parameters. The calculated biomass, abundance and diversity of the benthic macroinvertebrate community varied significantly both temporally and spatially. Variations of these variables are most likely explained by significant differences in the concentration of carbon and nitrogen in sediments across lake sites, and on a smaller scale, the presence or absence of cypress trees. Benthic macroinvertebrate abundance, biomass, and diversity significantly decreased with distance from tree.