Hydrochory,seed banks,and regeneration dynamics along the landscape boundaries of a forested wetland

Following the environmental sieve concept, the setting in which the recruitment of Taxodium distichum occurs in, becomes increasingly restrictive from the seed to seedling stage in an impounded forested wetland. Although a wide elevational band of dispersing seed moves across the boundary of a swamp-field in the water sheet, the zone of germination is relegated to that portion of the forested wetland that draws down during the growing season. Seedling recruitment is further restricted to the uppermost zone of the winter water sheet. These patterns are likely applicable to other species of dominant swamp species, e.g., Cephalanthus occidentalis crossed the boundary of a forested wetland and abandonded field in winter flooding (November–December and November–March, respectively) in Buttonland Swamp. The elevation of the boundary was 101.3 m NGVD. While the seeds of at least 40 swamp species were dispersed across the boundary, few viable seeds were dispersed after the winter season. Kriged maps showed seeds of T. distichum and C. occidentalis dispersed in patches in the water depending on the position of the water sheet. Most species of both water- and gravity-dispersed species had a localized pattern of seed distribution (either spherical or exponential) and this indicated that seeds may not be dispersed for great distances in the swamp. Water-dispersed T. distichum and C. occidentalis had larger dispersal ranges (A ₀=225 and 195 m, respectively) than Bidens frondosa and B. discoidea (A ₀=14 and 16 m, respectively). Seed dispersal varied with season depending on the availability of seeds. In Buttonland Swamp, viable seeds typically were dispersed for T. distichum in November–June, and for C. occidentalis in November-July. Low water occurred in August 1993 and high in February 1994 (99.8 and 101.6 m NGVD, respectively). The seed banks along the landscape boundary varied in species composition according to elevation (r ² = 0.996). While the similarity of species richness between water-dispersed seeds and the seed bank at elevations that flooded (during June 1993 through May 1995) was high (10–17%), it was low between water-dispersed seeds and the seed bank at elevations that did not flood (5%). T. distichum seeds had a short germination window in that seeds germinated within a year following their production in zones that were flooded in the winter followed by drawdown during the next growing season. After 1 year, less than 5% of the T. distichum seeds remained viable on the surface of the soil. Germination of T. distichum was confined to specific elevations (above 99.3 but below 101.6 m NGVD) during this study with 4.1% of the seedlings surviving for more than 2 years at a mean of 101.4 m NGVD. All seedlings below this elevation died. To maximize natural regeneration along the boundaries of swamps in abandoned farm fields targeted for restoration, this study suggests a flood pulse regime consisting of high water in the winter to maximize dispersal of live seeds followed by low water in the summer to facilitate seed germination and seedling recruitment. Hydrologic restoration could assist in the natural recovery of damaged wetlands if a seed source exists nearby.     

Factors influencing the spatial distribution of forest plant species in hedgerows of North-western Germany

In North-western Germany woodland fragmentation has caused a decline in many forest plant species. Hedgerows partly offer a similar environment as forests and have been identified as potential habitats for forest plants in various studies from North America and Western Europe. The objective of this study was to examine whether this applies also to Central Europe and which variables affect the spatial distribution and abundance of forest plant species in hedgerows on a local scale. Three hedgerow networks north of the city of Bremen, Germany, were selected as study areas and divided into totally 515 hedgerow segments. In each segment we recorded all vascular plants and a large number of explanatory variables relating to structure, spatial configuration, environment and management. Averaged across species there was a predominant effect of environmental factors on the occurrence of forest species in the hedgerows, followed by spatial configuration and management. Hedgerow structure was found to be less important. In general, forest species were favored by low nutrient and light availability as well as high connectivity with other hedgerows or forest; they avoided hedgerows with a west-easterly orientation and an adjacent land use in the form of fields or grasslands. Forest species found and not found in hedgerows did not differ in their environmental preferences or life history traits. The number of threatened forest species in the hedgerows, however, was lower than expected with respect to their overall proportion to the total number of forest species in the region.     

羊草与其主要伴生种竞争与共存的格局分析

在羊草种群与其它植物种群的交错区,应用频度、格避形式,格局强度指数对羊草及其主要伴生种之间的共存格局进行了分析。结果表明,羊草及其主要伴生种的格局呈多样化,集聚格局形式是羊草抵御外来物种入侵,或者是自身扩散的一种对策,羊草与其主要伴生种之间存在竞争与共存作用,羊草与芦苇之间通过拮抗作用实现竞争与共存,羊草与鸡儿肠通过竞争而实现共存,光稃茅香,碱茅以营养繁殖策略实现与羊草竞争,指子茅的生长受羊草竞争的抑制。     

Genetic monogamy in blue-headed vireos and a comparison with a sympatric vireo with extrapair paternity

Based on the breeding synchrony hypothesis, we predicted, intwo congeners that nest in simiilar habitat but differ in nestingsynchrony, that blue-headed vireos (Vireo solitarius) wouldhave fewer extrapair fertilizations (EPFs) thaii red-eyed vireos(V. olivaceus EPFs were rare in blue-headed vireos (1/37 nestlings),but common in red-eyed vireos (11/19 nestlings). We studiedthe behavior of blue-headed vireos to determine what factorscould promote genetic monogamy. We found no evidence that malesmate guarded to prevent extrapair copulations from occurring.Males did not follow fertile mates closely when mates left thenest (14–25% of female departures) and, during the egg-layingperiod, males were often alone on the nest (22.3 mm/h). Femaleblue-headed vireos, but not red-eyed vireos, obtain direct benefitsfrom social mates such as nest building and incubation (49.1%of the total), and they assess male quality long before becomingfertile. Female blue-headed vireos spent more time incubatingwhen their mates had low incubation effort. Furthermore, maleincubation effort was positively correlated with nest survivalduring incubation. We discuss the evolution of genetic monogamyand sex role convergence in blue-headed vireos in relation toasynchronous breeding.     

Ecological niche modeling of the sympatric giant and red pandas on a mountain-range scale

Habitat use and separation between the two sympatric species, the giant panda and the red panda, have been primary causes of coexistence at the fine scale. In this paper, we addressed the question of coexistence between species in space. By Ecological Niche Factor Analysis, we calculated species-specific habitat requirements, built habitat suitability maps and examined interspecific differences in spatial niche parameters. According to the ENFA scores, suitable habitats in the giant and red panda are surrounded by high-altitude, and are rich in conifer forest. Compared with the giant panda, however, the red panda rather preferred sparse forests, and normally colonized far from village and road. Despite similar narrow niche breadth for both pandas, difference of niche overlap indices implied that the width of environmental niche of red pandas almost completely encompasses that of the giant panda. We, therefore, suggest that differences in use of ecological niche variables may contribute to coexistence of the sympatric species in space. Based on highly suitable locations of the sympatric species maps, most official reserves appear to be poorly located or are too small, and new reserves are recommended to be established in the central part of core habitats in the Liangshan Mountains.     

菱角萤叶甲种群抽样技术研究

在研究菱角萤叶甲各虫态空间分布型的基础上,利用负二项公共Kc值;Iwao回归式中的α,β;Teylor幂法则中的a,b以及Morisita的I_δ求得理论抽样模型,从而导出在不同置信度t,不同的平均虫口密度(?)和不同允许误差D下的理论抽样数．同时利用Kuno(1969),Iwao(1975)和Willson(1983)提出的序贯抽样法,得到菱角萤叶甲各虫态的序贯抽样模型,并对这些模型进行比较．最后,结合Kuno和Iwao模型获得了菱角萤叶甲各虫态的Kuno-Iwao复合序贯抽样法,从而大大减少了在某种情况下的抽样数．     

Spatial and temporal habitat use patterns for salt marsh nekton: implications for ecological functions

We synthesized information on temporal and spatial patterns of salt marsh habitat use by nekton in order to infer the importance of five main types of marsh function: reproduction, foraging, refuge from predation, refuge from stressful environmental conditions and environmental enhancement of physiology. We then extended the concept that intertidal gradients regulate habitat use patterns of nekton to a more universal concept that applies to all salt marsh habitats. We contend that all marsh habitats are linked to each other and to adjacent estuarine habitats along a depth gradient that mediates gradients in abiotic and biotic conditions. Tidal, diel and seasonal shifts in the magnitude and direction of these gradients result in gradients in tidal, diel and seasonal variation in biotic and abiotic conditions within the salt marsh. Collectively these gradients form the `marsh gradient'. We propose that patterns of marsh use and ecological function for nekton result primarily from physiological and behavioral responses to this marsh gradient. A comparison of habitat use patterns in the context of the marsh gradient is an important – and underutilized – method to study marsh function and essential fish habitat. We note that our limited insight into the function of the marsh habitat results from a significant lack of information on the occurrence and causes of tidal, diel and ontogenetic marsh use patterns by nekton; this is particularly relevant with respect to data on the variation in environmental conditions along marsh gradients over tidal, diel and seasonal cycles and on how environmental variation on these scales influences nekton behavior, growth and survival.     

Spatial synchrony of planthopper species with contrasting outbreak behaviour

1 We studied the synchrony of two sympatric delphacids species with different outbreak behaviours over a range of 250 km in Argentina. 2 The spatial synchrony in the dynamics of Delphacodes kuscheli and Toya propinqua was quantified by collecting individuals of both species simultaneously at three sampling heights: ground, 1.5 m and 6 m above the ground. Synchrony between paired sampling sites separated by increasing distances was estimated using a nonparametric covariance function. 3 A significant difference was found between the spatial synchrony of the species studied. Delphacodes kuscheli individuals collected at 6 m above the ground showed consistent spatial synchrony over long distances with correlation values declining by 40%. Population dynamics showed declining synchrony as site separation increased. Toya propinqua populations did not show this pattern. This species had a lower mean regional synchrony at at 6 m above the ground, but their ground height synchrony was greater than that observed for D. kuscheli. 4 One possible synchronizing mechanism is seasonality and the dispersal strategies of each species. The main host plants of D. kuscheli are winter cereals sown as pasture for cattle grazing and the synchrony of the crop may affect the general pattern of dispersing individuals of this species. The lack of synchrony observed in T. propinqua populations was probably due to the wider host range of this species.     

基于景观尺度过程模型的长白山地表径流量时空变化特征的模拟

运用已建立的景观尺度生态系统生产力过程模型EPPML对长白山自然保护区地表径流量的季节动态和空间分布特征进行了模拟,对其与环境因子间的相互关系进行了分析．模拟结果表明,长白山自然保护区地表径流量的季节进程表现出明显的三峰型,6月和9月出现低谷,8月达最大(2．58mm·d^-1),与土壤含水量的季节变化趋势十分相似．1995年地表径流量的模拟值平均为0．203m·年^-l,空间分布随海拔升高呈现明显增加的趋势,最高为高山流砾滩(0．619m·年^-1),最低为阔叶红松林(0．081m·年^-1)．年地表径流量与叶面积指数(LAI)呈极显著负相关指数关系(R^2＝0．857)．年地表径流量与气温和总辐射呈负相关关系(R^2分别为0．965和0．836),与降水量、相对湿度和风速呈正相关关系(R^2均大于0．950),还与土壤特性密切相关。     

Spatial structure of a subtidal macrobenthic community in the Bay of Veys (western Bay of Seine, English Channel)

The spatial distribution of the muddy fine sand community from the Bay of Veys (western English Channel) were investigated during spring and autumn 1997. A grid of 55 and 54 sites was sampled in March and October, respectively, using two replicates per site of a Hamon grab (0.25 m²) for macrofauna collection and an additional one for sediment analysis. A total of 172 species were sampled with a dominance of polychaetes, followed by crustaceans and bivalves. The species richness and abundance show low temporal changes despite higher values in October than in March. In March, the mean abundance was 165 ind. 0.5 m⁻²; in October, the mean abundance was 212 ind. 0.5 m⁻². Four assemblages from the Abra alba-Pectinaria koreni community were identified corresponding to a bathymetric and sedimentary gradient from muddy fine sands with high levels of fine particles in shallow water to fine sands in deeper water. The discussion focuses on factors prevailing on the spatial structure of sandy communities in the English Channel.