Scale-dependent effects of windthrow disturbance on forest arthropod communities

The effect of disturbance on local communities may operate within the context of the spatial landscape. We examined the scale-dependent effects of windthrow disturbance caused by a large typhoon on three arthropod communities in a temperate forest of Japan. Canopy arthropods were collected by beating foliage, forest-floor arthropods were collected by sweeping the vegetation, and flying arthropods were collected in Malaise traps. To assess the “functional spatial scale” at which arthropods responded to tree-fall disturbance, the gap rate was quantified at different spatial scales by sequentially enlarging the radius of a circular landscape sector in 10-m increments from 10 to 500 m. We then analyzed the responses of order richness and abundance to the gap rate for each arthropod community. The spatial scale of the significant best-fitting model, which was selected from the models fitted to the gap rate at stepwise spatial scales, was regarded as the arthropod-specific functional spatial scale. Arthropod order richness was not dependent on the gap rate. In contrast, arthropod order abundance depended significantly on the gap rate in many orders, but varied in the response direction and functional spatial scale. These order-specific, scale-dependent responses to tree-fall gaps could complicate interactions among organisms, leading to complex community organization. An understanding of the spatial processes that link the use of space by organisms with the spatial scale at which ecological processes are experienced is required to elucidate the responses of populations, communities, and biotic interactions to disturbances in a spatial landscape context.     

Effects of windthrow disturbance on a forest bird community depend on spatial scale

Community structure is expected to be affected by spatial heterogeneity in a landscape. We examined the spatial-scale-dependent effects of windthrow caused by a large typhoon on a forest bird community. Typhoon events of this magnitude are rare in Hokkaido, Japan, occurring only once or twice a century. To assess the “functional spatial scale” at which bird groups (community, species, body-size class, and foraging guild) specifically responded to landscape heterogeneity, the canopy gap rate (CGR, gap percentage) was evaluated at different spatial scales by varying the radius of a circular landscape sector from 100 to 500 m stepwise by 10 m. We then analysed bird community responses, in terms of species richness and abundance, to CGR. Bird species richness did not significantly depend on CGR. In contrast, abundance was significantly dependent on CGR in many groups (species, body-size class, and foraging guild). The guild-level response was clearer than the species-level response, which suggests that the integration and filtration of species traits by guild can reveal a clear response of bird abundance to the extent of canopy gaps. For example, the scale dependence of responses to disturbance clearly varied among body-size classes, where larger birds had larger functional spatial scales. These results reveal that different groups of organisms have different functional spatial scales at which they respond to habitat heterogeneity. Our results also suggest that monitoring only a small number of species could be misleading for conserving biodiversity at the landscape level.     

Effects of landscape complexity and stand factors on arthropod communities in poplar forests

The arthropod communities are influenced by both local conditions and features of the surrounding landscape. Landscape complexity and stand factors may both influence arthropod communities in poplar forests, but the multiscale effects of these factors on poplar defoliators and natural enemies are still poorly understood. We collected poplar arthropods at 30 sampling sites within five forest landscapes in Xinjiang, China, and assessed whether landscape complexity and stand factors influence species abundance and diversity of poplar arthropods. Landscape complexity was quantified by several independent metrics of landscape composition, configuration, and connectivity at three spatial scales. We also determined the most powerful explanatory variables and the scale effect of each arthropod. Results found that landscape complexity and stand factors had different effects on different poplar arthropod communities. Landscape complexity promoted natural enemies at different spatial scales, but it inhibited the population of poplar defoliators at the scale of 200 m. Specifically, the abundance and diversity of all defoliators decreased with increasing proportion of nonhost plants. Landscape diversity only had a negative effect on defoliator abundance. The shape complexity of habitat patches increased the abundance of carabid beetles but reduced the abundance of green leafhoppers and migratory locusts. The abundance and diversity of predators increased with increasing structural connectivity of forest landscape. Additionally, both the abundance and diversity of all defoliators were positively correlated with the average height of herbaceous plants. Diversity of all defoliators increased with increasing size of host trees. The distance from sampling site to the nearest village positively influenced the abundance and diversity of all predators. Arthropod abundance and diversity in poplar forests were driven by stand factors and landscape complexity. Therefore, maintaining complex shape and structural connectivity of habitat patches and keeping poplar stands away from the village are crucial for management of forest landscape to enhance natural enemies. And in order to reduce the abundance of defoliators in poplar forest, the diversity of surrounding habitat types should be promoted within 200 m radii.     

A spatial scale assessment of habitat effects on arthropod communities of an oceanic island

Most habitats in the Azores have undergone substantial land-use changes and anthropogenic disturbance during the last six centuries. In this study we assessed how the richness, abundance and composition of arthropod communities change with: (1) habitat type and (2) the surrounding land-use at different spatial scales. The research was conducted in Terceira Island, Azores. In eighty-one sites of four different habitat types (natural and exotic forests, semi-natural and intensively managed pastures), epigaeic arthropods were captured with pitfall traps and classified as endemic, native or introduced. The land-use surrounding each site was characterized within a radius ranging from 100 to 5000 m. Non-parametric tests were used to identify differences in species richness, abundance and composition between habitat types at different spatial scales. Endemic and native species were more abundant in natural forests, while introduced species were more abundant in intensively managed pastures. Natural forests and intensively managed pastures influenced arthropod species richness and composition at all spatial scales. Exotic forests and semi-natural pastures, however, influenced the composition of arthropod communities at larger scales, promoting the connectivity of endemic and native species populations. Local species richness, abundance and composition of arthropod communities are mostly determined by the presence of nearby natural forests and/or intensively managed pastures. However, semi-natural pastures and exotic forests seem to play an important role as corridors between natural forests for both endemic and native species. Furthermore, exotic forests may serve as a refuge for some native species.     

农业景观动态对林地地表节肢动物多样性的影响

以黄河下游典型农区封丘县为研究区,在林地景观中进行地表节肢动物的观测。用物种丰富度和香农多样性指数代表物种多样性,选择代表景观背景的5个竞争模型:生境特性(H1,2012)、基质特性(H2,2012)、生境变化(H3,1984—2012)、基质变化(H4,1984—2012)和土壤-环境条件(H5,2012)从4个空间尺度上(100,250,350和500 m)进行分析,通过运用基于赤池信息量准则(Akaike information criterion,AIC)的多模型推理(Multi-model Inference,MMI)方法,在R软件里用广义线性模型(Generalized Linear Models,GLM)探究了研究区近30年(1984—2012年)景观背景变化对林地地表节肢动物多样性的影响。研究表明,不同景观背景模型对地表节肢动物多样性的影响具有尺度依赖性。在100 m的尺度下,生境特性(H1)最能够解释香农多样性和物种丰富度,但是随着尺度的增加,生境特性变化(H3)在较大(250、350 m和500 m)的尺度对物种丰富度和香农多样性影响最大,而基质特性和土壤-环境条件(H2和H5)的作用不显著。景观背景对地表节肢动物多样性的解释量达到40%。在研究区域,生境特性是表征香农多样性指数和物种丰富度的指标。     

Functional biotic homogenization of bird communities in disturbed landscapes

Aim  Worldwide, functional homogenization is now considered to be one of the most prominent forms of biotic impoverishment induced by current global changes. Yet this process has hardly been quantified on a large scale through simple indices, and the connection between landscape disturbance and functional homogenization has hardly been established. Here we test whether changes in land use and landscape fragmentation are associated with functional homogenization of bird communities at a national scale.
Location  France.
Methods  We estimated functional homogenization of a community as the average specialization of the species present in that community. We studied the spatial variation of this community specialization index (CSI) using 1028 replicates from the French Breeding Bird Survey along spatial gradients of landscape fragmentation and recent landscape disturbance, measured independently, and accounting for spatial autocorrelation.
Results  The CSI was very sensitive to both measures of environmental degradation: on average, 23% of the difference in the CSI values between two sample sites was attributed to the difference in fragmentation and the disturbance between sites. This negative correlation between CSI and sources of landscape degradation was consistent over various habitats and biogeographical zones.
Main conclusions  We demonstrate that the functional homogenization of bird communities is strongly positively correlated to landscape disturbance and fragmentation. We suggest that the CSI is particularly effective for measuring functional homogenization on both local and global scales for any sort of organism and with abundance or presence–absence data.     

黄河下游农业景观中不同生境类型地表节肢动物优势类群

生物多样性是连接景观异质性与生态系统服务的桥梁。在区域尺度上,以指示类群代替地表节肢动物类群,可以有效的开展生物多样性的保护工作。但是,在黄河下游农业景观中,关于地表节肢动物指示类群的研究报道较少。以黄河下游农业景观中4种生境类型(农田、林地、树篱和沟渠)为研究样地,且在农田生境中划分不同尺度(尺度1,3.6 hm2、尺度2,14 hm2和尺度3,28 hm2),通过调查不同生境中地表节肢动物分布及其多样性,结合地表节肢动物优势类群的辨识,分析了优势类群和地表节肢动物多样性的相关性,确定了研究区内地表节肢动物多样性的指示类群。结果发现:研究区内地表节肢动物优势类群为膜翅目、鞘翅目和蜘蛛目。树篱和林地生境的地表节肢动物多样性指示类群是膜翅目,农田生境中地表节肢动物多样性指示类群是鞘翅目,沟渠生境中地表节肢动物多样性指示类群是蜘蛛目。农田生境中优势类群间无相关性(P0.05);林地、沟渠和树篱生境中鞘翅目与蜘蛛目之间存在显著正相关(P0.01);林地和沟渠生境中,鞘翅目与膜翅目之间存在正相关(P0.05)。在农田生境中优势类群之间的相关性存在尺度依赖性,随着空间尺度的增大,相关性有一定的增强。在尺度2和尺度3上膜翅目和鞘翅目均存在正相关(P0.05),并且随着尺度增加而呈上升趋势。研究表明,黄河下游农业景观中不同生境类型地表节肢动物多样性的指示类群差别较大,其中树篱和林地生境具有较高的相似性,而农田生境地表节肢动物优势类群相关性存在尺度依赖性。在黄河下游农业景观中,以优势类群多样性代替地表节肢动物类群的多样性,可以在条件不足、时间紧迫的情况下更加有效的开展生物多样性的保护工作。     

Arthropods and biofuel production systems in North America

Abstract Biomass harvest may eventually be conducted on over 100 000 000 ha of US crop and forest lands to meet federally-mandated targets for renewable biofuels. Such large-scale land use changes could profoundly impact working landscapes and the arthropod communities that inhabit them. We review the literature on dedicated biofuel crops and biomass harvest from forests to look for commonalities in arthropod community responses. With expanded biofuel production, existing arthropod pests of biofuel crops will likely become more important and new pests will emerge. Beneficial arthropods will also be influenced by biofuel crop habitats, potentially altering the distribution of pollination and pest control services to the surrounding landscape. Production of biofuel crops including initial crop selection, genetic improvement, agronomic practices, and harvest regimes will also influence arthropod communities. In turn, arthropods will impact the productivity and species composition of biomass production systems. Some of these processes have the potential to cause landscape-level changes in arthropod community dynamics and insect-vectored plant diseases. Finally, changes in arthropod populations and their spatiotemporal distribution in the landscape will have impacts on consumers of insects at higher trophic levels, potentially influencing their population and community dynamics and producing feedbacks to arthropod communities. Given that dedicated biofuel crops and intensified biomass harvest from forests are still relatively uncommon in North America, as they increase, we anticipate ‘predictably unpredictable’ shifts in arthropod communities and the ecosystem services and functions they support. We suggest that research on arthropod dynamics within biofuel crops, their spillover into adjacent habitats, and implications for the sustainability of working landscapes are critical topics for both basic and applied investigations.     

Arthropod but Not Bird Predation in Ethiopian Homegardens Is Higher in Tree-Poor than in Tree-Rich Landscapes

Bird and arthropod predation is often associated with natural pest control in agricultural landscapes, but the rates of predation may vary with the amount of tree cover or other environmental factors. We examined bird and arthropod predation in three tree-rich and three tree-poor landscapes across southwestern Ethiopia. Within each landscape we selected three tree-rich and three tree-poor homegardens in which we recorded the number of tree species and tree stems within 100 × 100 m surrounding the central house. To estimate predation rates, we attached plasticine caterpillars on leaves of two coffee and two avocado shrubs in each homegarden, and recorded the number of attacked caterpillars for 7–9 consecutive weeks. The overall mean daily predation rate was 1.45% for birds and 1.60% for arthropods. The rates of arthropod predation varied among landscapes and were higher in tree-poor landscapes. There was no such difference for birds. Within landscapes, predation rates from birds and arthropods did not vary between tree-rich and tree-poor homegardens in either tree-rich or tree-poor landscapes. The most surprising result was the lack of response by birds to tree cover at either spatial scale. Our results suggest that in tree-poor landscapes there are still enough non-crop habitats to support predatory arthropods and birds to deliver strong top-down effect on crop pests.     

Aerial arthropod communities of native and invaded forests, Robinson Crusoe Island, Chile

Invasive species significantly contribute to biological change and threaten biodiversity, with a growing body of evidence that plant invasions affect higher trophic levels. We explored the relative importance of plant invasion and forest structure on aerial arthropod abundance, diversity, and composition on Robinson Crusoe Island, Chile. We used flight intercept traps to sample aerial arthropods within distinct canopy strata of native and invaded forests over 3-mo periods in 2006 and 2007. Arthropod abundance and diversity were higher in native than invaded forest, and arthropod communities were distinct between forest types. In both forest types, arthropod abundance was highest in the lower canopy, and canopy strata exhibited some differences in arthropod community composition. Several morphospecies were distinctly associated with each forest type. The strong differences in aerial arthropod communities associated with the invasion of native forest by non-native plants may affect other trophic levels, such as insectivorous birds. Steps to stop invasive plant spread and to restore native forest composition and structure are needed to safeguard the integrity of native communities, from plants to higher-level consumers.     

Bird and bat predation services in tropical forests and agroforestry landscapes

Understanding distribution patterns and multitrophic interactions is critical for managing bat‐ and bird‐mediated ecosystem services such as the suppression of pest and non‐pest arthropods. Despite the ecological and economic importance of bats and birds in tropical forests, agroforestry systems, and agricultural systems mixed with natural forest, a systematic review of their impact is still missing. A growing number of bird and bat exclosure experiments has improved our knowledge allowing new conclusions regarding their roles in food webs and associated ecosystem services. Here, we review the distribution patterns of insectivorous birds and bats, their local and landscape drivers, and their effects on trophic cascades in tropical ecosystems. We report that for birds but not bats community composition and relative importance of functional groups changes conspicuously from forests to habitats including both agricultural areas and forests, here termed ‘forest‐agri’ habitats, with reduced representation of insectivores in the latter. In contrast to previous theory regarding trophic cascade strength, we find that birds and bats reduce the density and biomass of arthropods in the tropics with effect sizes similar to those in temperate and boreal communities. The relative importance of birds versus bats in regulating pest abundances varies with season, geography and management. Birds and bats may even suppress tropical arthropod outbreaks, although positive effects on plant growth are not always reported. As both bats and birds are major agents of pest suppression, a better understanding of the local and landscape factors driving the variability of their impact is needed.     

The community structures of the coniferous and deciduous dead wood‐dwelling arthropods in Korea

We examined the structure of the arthropod community among deciduous and coniferous dead woods along the process of wood decay. We collected dead wood‐dwelling arthropods from April 2010 to October 2011 by using a vacuum aspirator and an electric chain saw in three areas (Mt. Woonak, Mt. Wolchul, Mt. Jingang) in Korea. We identified them to species levels and classified them into functional groups. We collected 8792 arthropods (5 classes, 20 orders, 58 families, and 93 species). The species richness and abundance of arthropods increased with the progress of decay in dead woods. The evenness index seemed to be shown at a lower value at late decay stage than at early‐ and mid‐decay stages. The diversity index (H′) in conifers was lower than that in deciduous dead woods at the early decay stage but this situation was reversed at the late decay stage. Arthropod communities of functional groups, except the xylophagous insects, did not differ in the variables, but the proportion of xylophagous insects increased as the decay stages progressed. The abundance of arthropods and xylophagous was statistically significantly different. The patterns generated by non‐metric multidimensional scaling in the overall arthropod community composition revealed that the species composition between study areas were significantly different. We confirmed that dead woods play very important roles as arthropods' habitats. Thus, we suggest that the role of dead woods should be emphasized in the management of forest ecosystems.     

Management intensity at field and landscape levels affects the structure of generalist predator communities

Agricultural intensification is recognised as a major driver of biodiversity loss in human-modified landscapes. Several agro-environmental measures at different spatial scales have been suggested to mitigate the negative impact of intensification on biodiversity and ecosystem services. The effect of these measures on the functional structure of service-providing communities remains, however, largely unexplored. Using two distinct landscape designs, we examined how the management options of organic farming at the field scale and crop diversification at the landscape level affect the taxonomic and functional structure of generalist predator communities and how these effects vary along a landscape complexity gradient. Organic farming as well as landscapes with longer and more diversified crop rotations enhanced the activity-density of spiders and rove beetles, but not the species richness or evenness. Our results indicate that the two management options affected the functional composition of communities, as they primarily enhanced the activity-density of functionally similar species. The two management options increased the functional similarity between spider species in regards to hunting mode and habitat preference. Organic farming enhanced the functional similarity of rove beetles. Management options at field and landscape levels were generally more important predictors of community structure when compared to landscape complexity. Our study highlights the importance of considering the functional composition of generalist predators in order to understand how agro-environmental measures at various scales shape community assemblages and ecosystem functioning in agricultural landscapes.     

Composition and diversity of bird communities in Swedish farmland–forest mosaic landscapes

CapsuleThe amount of forest (at local and landscape scales) and occurrence of residual habitats at the local scale are shown to be the major factors influencing bird community composition in farmland–forest landscapes in central Sweden.

Aims To investigate the importance of local habitat and landscape structure for breeding birds in farmland–forest landscapes in central Sweden.

Methods Breeding birds were censused at 292 points. A detailed habitat mapping was made within 300 m of the points. Within a 300–600 m radius only two major habitats (forests and arable fields) were identified.

Results Cluster analyses of bird communities identified three site types that also differed in habitat composition: (i) partially forested sites in forested landscapes; (ii) heterogeneous sites with residual habitats in mosaic landscapes; and (iii) field-dominated farmland sites in open landscapes. A total of 19 of 25 farmland bird species (restricted to farmland or using both farmland and forest) had the highest abundance in farmland sites with mosaics of forest and farmland, while only six farmland species had the highest abundance in field-dominated sites. The bird community changed from being dominated by farmland species to being dominated by forest species (common in forest landscapes without farmland) at small proportions (10–20%) of forest at the local scale. A major difference in habitat composition between heterogeneous and field-dominated sites was the occurrence of different residual habitats (e.g. shrubby areas and seminatural grasslands). These habitats seemed to influence bird community composition more than land-use, despite covering <10% of the area. Seminatural grasslands were important for bird community composition and species-richness, but grazing seemed to be less important. Among different land-use types, cereal crops were the least preferred fields. Set-asides with tall vegetation and short rotation coppices were positively associated with species-richness of farmland birds.

Conclusion In general, the composition of the landscape was important for bird community composition, although amount and distribution of forests, occurrence of residual habitats and land-use of fields at the local scale had the strongest influence on bird community composition. The possible implications of these patterns for managing farmland–forest landscapes are discussed.     

Functional diversity of phyllostomid bats in an urban–rural landscape: A scale-dependent analysis

Urbanization is one of the most pervasive processes of landscape transformation, responsible for novel selection agents promoting functional community homogenization. Bats may persist in those environments, but the mechanisms responsible for their adaptability and the spatial scales in which the landscape imposes environmental filtering remain poorly studied in the Neotropics. We tested the hypothesis that landscape composition interacts with the spatial scale to affect the functional diversity of phyllostomids in an urban–rural gradient. Based on functional traits, we calculated indices of functional richness, divergence, evenness, and community-weighted means of morphological traits, and classified species into functional groups. We evaluated the changes in those variables in response to forest, grassland, and urbanized areas at 0.5, 1.25, and 2km scales. The number of functional groups, functional richness, and functional evenness tended to be higher in areas far from cities and with higher forest cover, whereas functional divergence increased in more urbanized areas. Our results show that the mean value of wing loading in the assemblage was negatively associated with landscape transformation at several spatial scales. However, environmental filtering driven by grass cover was particularly robust at the 0.5km scale, affecting big-sized species with long-pointed wings. Retaining natural forest in cattle ranging systems at ~12 km² appears to favor the functional evenness and number of functional groups of phyllostomids. Recognizing the scale of the effect on phyllostomid functional responses appears to be a fundamental issue for elucidating the spatial extent to which phyllostomid conservation planning in urban–rural landscapes should be addressed.     

Use of Tropical Dry Forests and Agricultural Areas by Neotropical Bird Communities

Agricultural activities represent a global threat to biodiversity, yet little is known about the relative importance of different agricultural land uses in relation to their wildlife communities. We explored bird community structure, diversity, and composition in a landscape dominated by primary tropical dry forest, and in three agricultural systems (i.e., tree orchards, herbaceous cropfields, cattle pastures) to evaluate the way in which birds use different habitats within the landscape. Tropical dry forests had the highest species richness and community evenness, although the bird community in tree orchards was also relatively species rich and even. Cattle pastures had more bird species than cropfields but both habitats were comparatively species poor with low evenness. Our results are related to habitat structure and the spatial location of sites within the landscape matrix. Based on our observations, we recommend including native tree species within agricultural systems and surrounding areas to provide additional resources for birds. Finally, we suggest promoting natural recruitment of native trees and shrubs within cattle pastures to provide suitable habitat for species that use tropical dry forest plants. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Control of arthropod abundance, richness, and composition in a heterogeneous desert city

There is a demand for mechanistic studies to explore underlying drivers behind observed patterns of biodiversity in urban areas. We describe a two-year field experiment in which we manipulated bottom-up (resource availability) and top-down (bird predation) forces on arthropod communities associated with a native plant, Encelia farinosa, across three land-use types—urban, desert remnant, and outlying natural desert—in the Phoenix metropolitan area, Arizona, USA. We monitored the trophic structure, richness, and similarity of the arthropod communities on these manipulated plants over a two-year period. We predicted that (1) increased water resources increase plant productivity, (2) increased productivity increases arthropod abundances, and (3) in the urban habitat, top-down forces are greater than in other habitats and limit arthropod abundances. We also predicted that urban remnant habitats are more similar to urban habitats in terms of arthropod richness and composition. Strong interannual differences due to an unusual cold and dry winter in the first year suppressed plant growth in all but urban habitats, and arthropod abundances in all habitats were severely reduced. In the following year, arthropod abundances in desert and remnant habitats were higher than in urban habitats. Water had positive effects on plant growth and arthropod abundance, but these water effects emerged through complex interactions with habitat type and the presence/absence of cages used to reduce bird predation. Plants grew larger in urban habitats, and phenology also differed between urban and desert habitats. The results from caging suggest that bird predation may not be as important in cities as previously thought, and that arthropods may retard plant growth. As expected, desert communities are strongly bottom-up regulated, but contrary to predictions, we did not find evidence for strong top-down control in the city. Remnant habitats were intermediate between desert and urban habitats in terms of diversity, richness, evenness, arthropod composition and phenology, with urban habitats generally lowest in terms of diversity, richness, and evenness. Our study shows that control of biodiversity is strongly altered in urban areas, influenced by subtle shifts in top-down and bottom-up controls that are often superseded by climatic variations and habitat type.     

Heterogeneous Landscapes on Steep Slopes at Low Altitudes as Hotspots of Bird Diversity in a Hilly Region of Nepal in the Central Himalayas

Understanding factors determining the distribution of species is a key requirement for protecting diversity in a specific area. The aim of this study was to explore the factors affecting diversity and distribution of species of birds on different forested hills in central Nepal. The area is rich in species of birds. Because the area is characterized by steep gradients, we were also interested in the importance of altitude in determining the diversity and species composition of the bird communities. We assessed bird diversity and species composition based on point observations along a gradient of increasing altitude in two valleys (Kathmandu and Palung) in central Nepal. Data on environmental variables were also collected in order to identify the main determinants of bird diversity and species composition of the bird communities. We recorded 6522 individual birds belonging to 146 species, 77 genera and 23 families. Resident birds made up 80% (117 species) of the total dataset. The study supported the original expectation that altitude is a major determinant of species richness and composition of bird communities in the area. More diverse bird communities were found also in areas with steeper slopes. This together with the positive effect of greater heterogeneity suggests that forests on steep slopes intermixed with patches of open habitats on shallow soil at large spatial scales are more important for diverse bird communities than more disturbed habitats on shallow slopes. In addition, we demonstrated that while different habitat characteristics such as presence of forests edges and shrubs play an important role in driving species composition, but they do not affect species richness. This indicates that while habitat conditions are important determinants of the distribution of specific species, the number of niches is determined by large scale characteristics, such as landscape level habitat heterogeneity and altitude. Thus, to protect bird diversity in the mid-hills of central Nepal, we should maintain diverse local habitats (viz. forest, shrubs, open land, etc.) but also make sure the natural habitats on steeper slopes with large scale heterogeneity are maintained.     

放牧后自然恢复沙质草地土壤节肢动物群落结构与多样性

以中国科学院奈曼沙漠化研究站为依托,对不同放牧强度后自然恢复沙质草地土壤节肢动物群落进行了调查,分析了土壤节肢动物群落结构及其多样性变化,探讨了植被和土壤环境对土壤节肢动物群落的影响.结果表明: 无牧草地土壤动物种类丰富,个体数量较多,多样性最高;中牧后恢复草地土壤动物个体数量少,但主要类群较多,分布较均匀,多样性较高;重牧后恢复草地土壤动物主要类群少,但个体数量多,多样性较高;而轻牧后恢复草地土壤动物分布均匀性最差,多样性最低.植物个体数、高度及盖度和土壤酸碱度是影响不同放牧强度后恢复草地土壤动物种类和个体数量分布的主要因素.说明沙质草地经过12年的围封可以一定程度上恢复土壤动物群落,而放牧干扰对土壤动物群落的负面影响是长期的.     

Effects of Landscape Composition on Winter Survival of Northern Bobwhites

Abstract: In a manipulative experiment, we tested effects of select elements of landscape structure and composition on winter survival of northern bobwhites (Colinus virginianus) at Ames Plantation, Tennessee, USA. We hypothesized that abundance of closed canopy forested habitats (52% of the landscape) on Ames diminished usable space for bobwhite and provided usable space for a suite of important predators, thereby contributing to low winter survival. To test this hypothesis we divided a 2,217-ha portion of the property into 4 approximately equal areas. We altered landscape structure and composition by converting approximately 33% of the timber to early successional herbaceous plant communities on 2 treatment sites, which reduced percentage of landscape and edge density of closed canopy forest and increased percentage of landscape in early successional herbaceous communities, and left 2 control sites in their former composition. During one pretreatment year (1998–1999) and 3 posttreatment years (1999–2000, 2000–2001, 2001–2002), we estimated winter (15 Oct-10 Apr) survival on treatment and control sites from a radiomarked sample of 920 bobwhites. We used Cox Proportional Hazard models to test for effects of treatment (forest conversion) and covariates describing landscape structure and composition (% closed canopy forest, % early successional herbaceous, wooded edge density) on winter survival at multiple spatial scales. Winter survival on the treatment sites pooled across the 4 winter seasons was 41% compared to 32% for control sites. Additionally, for each 1 m/ha increase in closed canopy woods edge density within winter covey ranges, risk of mortality increased 0.3%. Our results suggest composition at the landscape scale and landscape structure at the local scale influence winter survival of bobwhite. Management strategies that alter composition and structure and increase usable space may be effective in mitigating winter mortality thereby altering population trajectories. Typical bobwhite management plans focus on improving quality of herbaceous vegetation structure within existing herbaceous patches, however, population processes may work at larger spatial scales influencing design and implementation of conservation programs.