Interaction between algae and seed germination in tropical dune slack species: a facilitation process

The importance of algae dune slack stabilisation has been extensively analysed, but little has been done regarding their potentially favourable role in germination and establishment of phanerogams. Dune slack is a seasonal freshwater habitat that depends on water table level fluctuation. Our hypothesis is that in these highly unpredictable systems, algae maintain a certain degree of humidity in the soil and, thus, permit phanerogam germination and establishment. The objective of this study was to compare the germination of four species characteristic of tropical dune systems: Cyperus articulatus L., Fimbristylis cymosa R. Br., Fuirena simplex Vahl and Rhynchospora colorata (L.) Pfeiffer, in different substrates and degrees of humidity. For germination trials, seeds of the four species were placed each on three substrates: in sand (control), filamentous algae on sand and cotton on sand. Two irrigation protocols were followed: continual watering (wet treatment) and weekly watering (dry treatment). Each week during a 21-week period, the number of germinated seeds from each species was recorded. The highest percentage of germination for the four species was observed during wet treatment. C. articulatus had the highest germination rate of the four species in algae (70%), and cotton (51%) on sand. Highest germination for F. simplex, F. cymosa and R. colorata took place in algae, although the percentages were very low. Differences in germination between the three substrates for these species were statistically significant (P<0.05). During dry treatment, C. articulatus was the only species that exhibited a significant germination, principally in algae and cotton. The results suggest that algae maintain substrate humidity and favour germination of the four species. This could be important in sand dune slacks where marked fluctuations in temperature and humidity occur.     

呼伦贝尔草原人为火空间分布格局

人为草原火及其影响因素的空间分布格局与相关关系研究对于草原火发生、草原火管理等研究具有重要的意义.应用Ripley's K函数对呼伦贝尔草原1976-1996年间发生的人为草原火进行了空间统计分析,确定人为草原火空间分布在年内主要发生月份和年际间均呈聚集分布;应用Kernel密度函数对人为草原火及其影响因素居民点、道路和农田的空间分布密度进行了研究,结果表明呼伦贝尔草原人为火分布广泛,热点区域主体在123.05-124.82°E、48.25-50.21°N之间;居民点、农田空间分布密度的热点区域主要分布在东部和中部地区,道路的分布密度较农田和居民点分布更加均匀.人为草原火空间分布密度与居民点、道路和农田的空间分布密度呈显著性正相关,其Pearson相关系数依次为0.448、0.236、0.602 (P＜0.001),火源因素(居民点、道路、农田)的空间分布格局是呼伦贝尔草原人为火空间分布格局的主要影响因素.     

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.     

Habitat suitability models for the conservation of thermophilic grasshoppers and bush crickets—simple or complex?

One goal of conservation biology is the assessment of effects of land use change on species distribution. One approach for identifying the factors, which determine habitat suitability for a species are statistical habitat distribution models. These models are quantitative and can be used for predictions in management scenarios. However, they often have one major shortcoming, which is their complexity. This means that they need several, often costly-to-determine parameters for predictions of species occurrence. We first used habitat suitability models to investigate and determine habitat preferences of three different Orthoptera species. Second, we compared the predictive powers of simple habitat suitability models considering only the ‘habitat type’ as predictor with more complex models taking different habitat factors into account. We found that the habitat type is the most reliable and robust factor, which determines the occurrence of the species studied. Thus, analyses of habitat suitability can easily be carried out on the basis of existing vegetation maps for the conservation of the three species under study. Our results can serve as a basis for the estimation of spatio-temporal distribution and survival probabilities of the species studied and might also be valuable for other species living in dry grasslands.     

Body size patterns in Drosophila inhabiting a mesocosm: interactive effects of spatial variation in temperature and abundance

Body size is a major component of fitness. However, the relative contributions of different factors to optimal size, and the determinants of spatial and temporal variation in size, have not been fully established empirically. Here, we use a mesocosm of a Drosophilidae assemblage inhabiting decaying nectarines to investigate the influence of spatial variation in temperature on adult body size in Drosophila simulans Sturtevant. Two treatments were established; one in the sun where developing larvae were exposed to high temperatures and the other in the shade where temperature conditions were milder. The simple developmental effects of temperature differences (i.e. larger flies are likely to emerge from cooler environments), or the simple effects of stressful temperatures (i.e. high temperatures yield wing abnormalities and smaller flies), were overridden by interactive effects between temperature and larval density. Emergences were lower in the sun than shade, probably as a result of temperature-induced mortality. However, flies attained the same final sizes in the shade and sun. In addition, abnormally winged flies were clustered in the shaded treatments. In the shade treatments, where emergences were higher than in the sun, stressful conditions as a result of high larval density likely resulted in wing abnormalities and small size. Consequently, there was little spatial variation in size across the mesocosm, but substantial spatial variation in abundance. Under natural conditions both mortality and non-lethal effects of temperature and/or crowding are likely to play a role in the evolution of body size.     

Hierarchical analysis of the relationship between spatial distribution and abundance of epiphytic lichens (Mt. Olympos-Greece)

The relationship between distribution and abundance of epiphytic lichens on five different substrates (Fagus sylvatica, Pinus nigra, Quercus coccifera, Pinus heldreichii and Quercus pubescens) has been studied. For the first three substrates the above relationship has been studied hierarchically. It was concluded that this relationship is partly represented by the core-satellite distribution. This abundance-distribution pattern could probably be explained by more than one hypothesis and it is probably related with the life strategies of lichen species.     

Development of vegetation in dune slack wetlands of Cape Cod National Seashore (Massachusetts,USA)

Interdunal seasonal wetlands, known as dune slack wetlands, were mapped and their vegetation surveyed across a large region of dunes within the Cape Cod National Seashore. Wetland sizes and ages were estimated from digitized, georeferenced aerial photographs available from 1938, 1947, 1960, 1986, 1994, and 2001, and from LIDAR elevation data. A total of 346 sites were found, covering an area of ∼45.4 ha., in which 97 species of vascular plants were identified. Vegetation structure and composition exhibited a distinct sequence of development with age, following a pattern of succession from herbaceous, graminoid-dominated communities to shrub- and tree-dominated communities. Floristic variables were not related to proximity to the coast and although wetland size appeared to have some bearing on species richness, the correlation was statistically weak. Soil organic matter determined for a subset of 60 wetlands was positively correlated with age and woody cover but showed no relationship with water depth. The results suggest that vegetation development is primarily driven by the internal mechanisms of succession. Notwithstanding, any changes in the environment that alter the process of succession will collectively influence these wetlands. In addition, stabilization of the dunes resulting in a reduction in the formation of new wetlands, may translate into permanent loss of early and mid-successional dune slack communities. Maintenance of these communities will depend on succession being periodically reset by disturbance or active management.     

鼎湖山旅游路径对针阔混交林个体数量和生物量空间分布格局的影响

以与旅游路径相邻的鼎湖山针阔混交林样地为研究对象,应用垂直路径和平行路径两种样带取样方法,探讨旅游路径影响下不同取样尺度群落个体数量和生物量的空间分布格局,以及不同优势种群空间分布格局对旅游路径干扰的响应.结果表明,群落生物量在各取样尺度上均未检测到显著变化(P>0.05),群落个体数在远离旅游路径方向各取样尺度上均呈显著的增加趋势(P<0.05).优势物种20 m取样尺度的空间分布格局反映了不同种群对旅游路径干扰的不同响应,其中荷木的生物量、豺皮樟的个体数和生物量在远离旅游路径方向上均呈显著增长趋势,其他物种的个体数和生物量变化不显著.     

Successive mapping of dune slack vegetation

Summary The succession of the dune slack vegetation around an artificial lake was studied by means of successive mapping. A succession scheme was prepared on the basis of comparison of the maps made in various years. This scheme was discussed in terms of systems theory, with reference to a kinematic graph prepared on the basis of the transformations. The succession derived from the vegetation maps was compared with that derived from the permanent plots; the results of this comparison indicated that only a small proportion of the total number of succession lines could be detected with the aid of the permanent plots. In addition, the information that could be derived from the permanent plot analysis depended on the degree of change of the vegetation in the area; more information could be derived from drier areas which showed the least degree of change. The best method for the investigation of the succession proved to be a combination of a restricted number of permanent plots and successive mapping. Nomenclature of species follows Heukels-van Ooststroom Flora van Nederland, 16 ed. 1970. R.I.N.-Comm. nr. 107.     

不同作物田烟粉虱发生的时空动态

2008～2009年连续2年系统调查了番茄、茄子、棉花、大豆、玉米等寄主植物上烟粉虱种群发生的时间与空间动态。结果表明：不同寄主植物上的烟粉虱成虫及其伪蛹数量有显著性差异,其密度大小依次为：茄子>棉花>番茄>大豆>玉米。其中,在玉米上除了发现极少量的成虫逗留外,没有发现烟粉虱的卵及若虫。在发生的时间序列上,烟粉虱成虫及伪蛹的数量呈现为先逐渐上升后又下降的变化过程,发生高峰期集中在8月5日到8月31日,9月初以后烟粉虱数量慢慢减少。在空间分布上,表现为烟粉虱成虫喜食寄主的上部叶片。统计分析显示,寄主对烟粉虱成虫和伪蛹的数量的影响极显著,而年份对其数量的影响没有显著差异。由此得出的烟粉虱发生和达到高峰的时间,可为烟粉虱预测预报和区域性综合治理提供重要理论依据。     

Vegetation,land use and management of the inner-dune zone in the North-Holland Dune Reserve,The Netherlands

The inner-dune zone between the villages of Bakkum and Egmond in the North-Holland Dune Reserve is one of the few remaining examples of the semi-natural boundary between the dunes and the polders. For several centuries this area has been used for various purposes, in particular for grazing. Large-scale excavating, especially after about 1900, has encroached upon the dunes. Vegetation and land-use history were studied and a provisional scheme on the vegetation development is presented. Management policies discussed are non-intervention, mowing in order to start natural processes such as rabbit grazing, and the continuation of traditional livestock grazing. Proposals for external management policies were made in order to maintain or enhance the original transition zone, based on comprehensive physical-geographical studies of the whole inner-dune zone.     

Environmental gradients and community attributes underlying biodiversity patterns of semi-arid Mediterranean grasslands

Protection and/or establishment of forest plantation have been used as a management strategy to conserve and stop the deterioration of semi-arid Mediterranean grasslands ecosystems, producing a mosaic of vegetation types. This study was intended to investigate the changes in grassland community in response to protection and forest tree plantation practice as well as to explore the underlying environmental gradients responsible for the observed differences or similarities among these vegetation types. Two multivariate analysis methods including discriminate analysis and non-metric multi-dimensional scaling were used to quantify changes in community composition and attributes following different management practices (free grazing, protection with open grassland, sparse and dense forest tree plantations). This was investigated using species frequency, species abundance, or habitat characteristics. The study results showed that habitat types differed significantly between each other and were significantly separated using multivariate approaches. Discrimination based on habitat characteristics and species composition indicated that protection (or grazing) and light (or shade) explained more than 90% of the observed variability in community changes in response to the protection and forest tree plantation. Also, results indicated that shade effect can be attributed to tree canopy cover and/or litter accumulation on the ground. It could be hypothesized that protection from grazing and afforestation resulted in complex environmental gradients of which shade, litter accumulation as well as protection from grazing disturbance are major constituents. A careful manipulation of protection and afforestation can be used to create a spatially different environmental gradients leading to greater habitat diversity as well as a greater species diversity, and better conservation means of grassland in semi-arid areas.     

Scale specific determinants of tree diversity in an old growth temperate forest in China

The major processes generating pattern in plant community composition depend upon the spatial scale and resolution of observation, therefore understanding the role played by spatial scale on species patterns is of major concern. In this study, we investigate how well environmental (topography and soil variables) and spatial variables explain variation in species composition in a 25-ha temperate forest in northeastern China. We used new variation partitioning approaches to discover the spatial scale (using multi-scale spatial PCNM variables) at which environmental heterogeneity and other spatially structured processes influence tree community composition. We also test the effect of changing grain of the study (i.e. quadrat size) on the variation partitioning results. Our results indicate that (1) species composition in the Changbai mixed broadleaf-conifer forest was controlled mainly by spatially structured soil variation at broad scales, while at finer scales most of the explained variation was of a spatial nature, pointing to the importance of biotic processes. (2) These results held at all sampling grains. However, reducing quadrat size progressively reduced both spatially and environmentally explained variance. This probably partly reflects increasing stochasticity in species abundances, and the smaller proportion of quadrats occupied by each species, when quadrat size is reduced. The results suggest that environmental heterogeneity (i.e. niche processes) and other biotic processes such as dispersal work together, but at different spatial scales, to build up diversity patterns.