Railway Embankments as New Habitat for Pollinators in an Agricultural Landscape

Pollinating insect populations, essential for maintaining wild plant diversity and agricultural productivity, rely on (semi)natural habitats. An increasing human population is encroaching upon and deteriorating pollinator habitats. Thus the population persistence of pollinating insects and their associated ecosystem services may depend upon on man-made novel habitats; however, their importance for ecosystem services is barely understood. We tested if man-made infrastructure (railway embankments) in an agricultural landscape establishes novel habitats that support large populations of pollinators (bees, butterflies, hoverflies) when compared to typical habitats for these insects, i.e., semi-natural grasslands. We also identified key environmental factors affecting the species richness and abundance of pollinators on embankments. Species richness and abundance of bees and butterflies were higher for railway embankments than for grasslands. The occurrence of bare (non-vegetated) ground on embankments positively affected bee species richness and abundance, but negatively affected butterfly populations. Species richness and abundance of butterflies positively depended on species richness of native plants on embankments, whereas bee species richness was positively affected by species richness of non-native flowering plants. The density of shrubs on embankments negatively affected the number of bee species and their abundance. Bee and hoverfly species richness were positively related to wood cover in a landscape surrounding embankments. This is the first study showing that railway embankments constitute valuable habitat for the conservation of pollinators in farmland. Specific conservation strategies involving embankments should focus on preventing habitat deterioration due to encroachment of dense shrubs and maintaining grassland vegetation with patches of bare ground.     

Floral species richness,structural diversity and conservation value of vanilla agroecosystems in Madagascar

Agricultural landscapes provide financial livelihoods for farming communities in rural areas. However, such agroenvironments can significantly impact the local floral biodiversity and introduce harmful invasive species to the ecosystem. Despite the prominence of plantations throughout the tropics, their effects on local flora are limited to only a few specific cash crops and geographical regions. Here, we compared the species richness and structural diversity of vegetation in natural forest fragments and three types of vanilla plantation within the Sava region of north-east Madagascar ranging from those within or adjacent to existing forests, to intensively cultivated plantations. We recorded data on plant species abundance, diameter at breast height and canopy cover within multiple sites of each habitat. We used abundance data to calculate species richness indices, and we compared these metrics between habitats. Forested habitats contained a significantly higher floral species richness, structural diversity and more endemic and regionally native species than nonforested, anthropogenic vanilla plantations. However, our results suggest that the high floral species richness and structural diversity of natural forests can be partially achieved in vanilla plantations, depending on the site's management regime; traditionally managed vanilla plantations located close to natural forests can support diverse floral communities. These encouraging findings for plant conservation and sustainable agroforestry in Madagascar suggest that that newly created vanilla plantations and already existing nonforested plantations should endeavour to follow the more traditional forested approach to enhance the future sustainability and promote floristic diversity.     

High Bird Species Diversity in Structurally Heterogeneous Farmland in Western Kenya

Tropical ecosystems are globally important for bird diversity. In many tropical regions, land‐use intensification has caused conversion of natural forests into human‐modified habitats, such as secondary forests and heterogeneous agricultural landscapes. Despite previous research, the distribution of bird communities in these forest‐farmland mosaics is not well understood. To achieve a comprehensive understanding of bird diversity and community turnover in a human‐modified Kenyan landscape, we recorded bird communities at 20 sites covering the complete habitat gradient from forest (near natural forest, secondary forest) to farmland (subsistence farmland, sugarcane plantation) using point counts and distance sampling. Bird density and species richness were on average higher in farmland than in forest habitats. Within forest and farmland, bird density and species richness increased with vegetation structural diversity, i.e., were higher in near natural than in secondary forest and in subsistence farmland than in sugarcane plantations. Bird communities in forest and farmland habitats were very distinct and very few forest specialists occurred in farmland habitats. Moreover, insectivorous bird species declined in farmland habitats whereas carnivores and herbivores increased. Our study confirms that tropical farmlands can hardly accommodate forest specialist species. Contrary to most previous studies, our findings show that structurally rich tropical farmlands hold a surprisingly rich and distinct bird community that is threatened by conversion of subsistence farmland into sugarcane plantations. We conclude that conservation strategies in the tropics must go beyond rain forest protection and should integrate structurally heterogeneous agroecosystems into conservation plans that aim at maintaining the diverse bird communities of tropical forest‐farmland mosaics.     

Inverted invasions: Native plants can frequently colonise urban and highly disturbed habitats

There is an enormous body of literature on plant invasions, including many investigations of the types of introduced species that are most likely to invade natural ecosystems. In this study we turn invasion biology upside down, and ask what sort of native species colonise novel anthropogenic habitats such as roadside lawns, infrequently tended road shoulders, railway embankments and fire trails. We quantified species richness and cover in roadside lawns and infrequently tended road shoulders in five regions of New South Wales, Australia. The native vegetation in these regions included sclerophyll forest, fertile and infertile Eucalypt‐dominated woodlands, rainforest, and semi‐arid woodland. We performed a complementary survey of sites spanning five disturbance levels within the region containing sclerophyll forest vegetation. Although many non‐native species were present in disturbed, novel habitats, a total of 136 native species were also found. Most of these native species were in sites with low levels of disturbance (fire trails and railway embankments), but 35 native species were found to colonise roadside lawns, our most highly‐disturbed vegetation type. There was a significant negative relationship between the disturbance level in novel habitats and the number and cover of native species. Native species that colonised novel habitats were disproportionately likely be generalist species whose natural habitat includes both high and low light and high and low disturbance conditions. The native species colonising novel habitats also tended to have traits associated with a fast life‐history, including short stature and small seeds. A surprisingly high number of native plant species are colonising novel, anthropogenic habitats. Our findings highlight the potential importance of urban ecosystems for conservation and restoration biology.     

Genetic structure of <Emphasis Type="Italic">Saxifraga tridactylites</Emphasis> (Saxifragaceae) from natural and man-made habitats

In contrast to many declining plant species Saxifraga tridactylites extended its distribution range in the man-made landscape of central Europe. The species naturally colonizes rocks and calcareous grasslands, but has also spread enormously in anthropogenic habitats such as railway constructions during the last decades. To analyze the genetic structure of the species 216 individuals from 8 populations in natural and 5 populations in man-made habitats were studied using AFLPs. The molecular analysis resulted in 250 scorable fragments. Population variability, measured as Nei’s gene diversity, Shannon’s Information Index and percentage of polymorphic bands, was slightly but not significantly higher in populations from natural habitats and was not correlated with population size. Mantel test indicated no significant correlation between pairwise genetic (Φ_PT) and geographic distances. An analysis of molecular variance revealed significant differentiation between the two habitat types. About 9% variability were observed between natural and man-made habitats, 21% among populations within these two habitats and 70% within populations. In a neighbour joining cluster analysis populations from natural and man-made habitats were clearly separated from each other. Populations of S. tridactylites from man-made habitats do, therefore, not suffer from reduced genetic diversity. The observed genetic differentiation between populations from man-made and natural habitats could be due to reduced gene flow and/or habitat specific selection. However, the results of the study clearly demonstrate human impact on the genetic structure of plant populations in man-made landscapes.     

Non flying mammals and landscape changes in the tropical rain forest region of Los Tuxtlas, Mexico

The rapid and extensive conversion of Neotropical rain forests to a landscape consisting of pasture lands and other agricultural habitats has meant the local disappearance fragmentation and isolation of vertebrate populations To avoid further losses in biodiversity in Neotropical rain forests, it is imperative to determine how the different species that constitute the different vertebrate communities have responded to the anthropogenic alterations of their natural habitats To provide data in this direction we sampled non flying mammals in 35 forest fragments, in six disturbed forest sites in 12 regenerating forests, in 20 arboreal agricultural habitats (cacao coffee, mixed, citrus and allspice), in four live fence sites and in four pasture sites at Los Tuxtlas, Veracruz Mexico Sampling indicated that area of forest fragments and isolating distance were important variables influencing species richness Disturbed forest had fewer species and individuals present and supported a lower non flying mammal biomass than undisturbed and regenerating forests Shaded plantations (cacao coffee and mixed) were richer in species and in individuals than unshaded ones (citrus, allspice) Species richness in forests and agricultural habitats were associated to horizontal plant diversity and vertical foliage diversity Pasture habitats were the poorest man-made habitats in non flying mammal species Live fences supported a higher biomass and species of non flying mammals than pastures and were similar to forest and shaded man-made habitats in species assemblages     

Responses of ground living arthropods to landscape contrast and context in a forest-grassland mosaic

Landscape context and contrast are major features of transformed landscapes. These concepts are largely described in terms of vegetation and land use, and are rarely used on how other biodiversity responds to these anthropogenic boundaries. South African grassland matrix is naturally dotted with indigenous forest patches which have recently been transformed with plantations of non-native species. We investigate how various arthropod groups (detritivores, predators, ants) respond to juxtaposition of pines, natural forests and grasslands. We assess landscape context effects between natural forests and pines by determining how species that commonly occur in the interiors of these habitats use the adjacent habitat, and how landscape contrast between natural forests and grassland affects these groups proportionately. We sampled arthropods using pitfall traps and active searches in transects running from natural forest interiors across the edge into the matrix interior (grassland or pines). Natural forests had higher predator and detritivore diversity, while grassland had greater ant diversity. Results highlighted the complementarity of natural forests and grassland for arthropod diversity. Higher beta-diversity was recorded across landscape contrast than landscape context. Pine and natural forest associated species overlapped into adjacent habitats indicating that pines are used by certain natural forest species. However, pines are not true natural forest extensions, with only some species being supported. Pines may be connecting naturally isolated arthropod populations, which could have important evolutionary consequences. Only through appreciation of a range of arthropod groups and their response to context and contrast across the whole landscape can we undertake meaningful biodiversity conservation.     

Global macroecology of bird assemblages in urbanized and semi‐natural ecosystems

Aim Despite the increasing pace of urbanization, little is known about how this process affects biodiversity globally. We investigate macroecological patterns of bird assemblages in urbanized areas relative to semi‐natural ecosystems. Location World‐wide. Methods We use a database of quantitative bird surveys to compare key assemblage structure parameters for plots in urbanized and semi‐natural ecosystems controlling for spatial autocorrelation and survey methodology. We use the term ‘urbanized’ instead of ‘urban’ ecosystems as many of the plots were not located in the centre of towns but in remnant habitat patches within conurbations. Results Some macroecological relationships were conserved in urbanized landscapes. Species–area, species–abundance and species–biomass relationships did not differ significantly between urbanized and non‐urbanized environments. However, there were differences in the relationships between productivity and assemblage structure. In forests, species richness increased with productivity; in both forests and open habitats, the evenness of species abundances declined as productivity increased. Among urbanized plots, instead, both species richness and the evenness of species abundances were independent of variation in productivity. Main conclusions Remnant habitats within urbanized areas are subject to many ecological alterations, yet key macroecological patterns differ remarkably little in urbanized versus non‐urbanized plots. Our results support the need for increased conservation activities in urbanized landscapes, particularly given the additional benefits of local experiences of biodiversity for the human population. With increasing urbanization world‐wide, broad‐scale efforts are needed to understand and manage the effects of this driver of change on biodiversity.     

Vegetation diversity, composition and structure in a cattle agro-landscape of Matiguás, Nicaragua

The diversity, composition and structure of vegetation in a cattle landscape in Matiguás, Nicaragua was characterized, and the floristic and structural differences of six types of habitats (secondary forests, riparian forests, charrales, live fences and pastures with high and low tree cover) were compared. A total of 3 949 trees of 180 species and 52 families were recorded. Forty six percent of the total trees reported for the landscape were represented by Guazuma ulmifolia (18.5%), Bursera simaruha (13.2%), Tabebuia rosea (6.3%), Enterolobium cyclocarpum (4.2%) and Albizia saman (3.4%). Many of the dominant species in the landscape were typical of open and disturbed areas. There were significant differences between the different habitats in the patterns of tree species richness, abundance, diversity, structure and floristic composition. The riparian forests had greater tree richness (p=0.0001) and diversity (p=0.0009) than other habitats. The floristic composition varied across habitats. with pairs of habitats sharing between 18.4 and 51.6% of the same tree species, and with clear differences in composition between the forested (riparian and secondary forests) and agricultural habitats. Of the habitats studied, the riparian forests and secondary forests seem to have greatest value for the conservation of the flora in the agropaisaje because they have the greatest species richness, and maintain small populations of endangered species. On the basis of the study, we recommend including agricultural landscapes in strategies to conserve tree diversity and suggest measures to ensure the maintenance of tree diversity in the Matiguas landscape.     

Biodiversity in the floodplain of Saône: a global approach

Biodiversity of European floodplains is seriously threatened mainly due to (1) modifications of river courses such as channelisation or embankments, and (2) changes in traditional agricultural practices (i.e. usually pastures), into intensive production using drainage and fertilisation. A upstream-downstream survey of the Saône floodplain (France) has been done to identify the contribution of habitats to the floodplain biodiversity. Selected taxa were aquatic and terrestrial vegetation, Odonata, Coleoptera, Amphibians, and birds. The taxa were sampled in different habitat types that were: forests, grasslands and aquatic habitats. Tributary confluences with the river and cut-off channels contributed greatly to the floodplain diversity according to their invertebrates and aquatic vegetation communities. The abundance of rare species (benefitting of a national or regional protection status) was the highest in hygrophilous grasslands. Moreover, we demonstrated that diversity of breeding bird communities was correlated with the size of these habitats. We demonstrated also that alluvial forests contributed to maintain some particular species as Middle-spotted Woodpecker (Dendrocopus medius), while new plantations were colonized by openland bird communities sensible to the edge effect. Grassland fragmentation for agriculture appeared to be a major cause in biodiversity loss. Any alteration of the floodplain dynamics must be avoided to preserve the present diversity of riverine wetlands.     

Relative contribution of agroforestry,rainforest and openland to local and regional bee diversity

Due to increasing human modification of tropical landscapes, the relative importance of natural habitats and agricultural systems has become a major conservation topic to counteract global species loss. We investigated the contribution of tropical primary forest, cacao agroforestry systems of varying management practices and openland to the temporal and spatial variation of diversity of native bee communities in the herb layer (Apidae, Hymenoptera) in Sulawesi (Indonesia). Local bee density and diversity were highest in openland, followed by agroforestry systems and were lowest in primary forests, revealing the importance of herbaceous food resources in the understorey. In contrast, highest regional bee richness was found in agroforestry systems, because of high community dissimilarity. Multidimensional scaling supported these findings with openland habitats showing more compactly clustered bee species communities than agroforestry habitats. In conclusion, the herb associated bee community profited from the opening of the landscape as a result of agricultural activities, while agroforestry systems increased bee species richness especially on a regional scale due to high management diversity.     

Can grassland plant communities be preserved on road and railway verges?

Abstract. Semi‐natural grasslands are a threatened biotope type in many countries. Typical grassland plant species are adapted to continuous grazing or mowing that keeps the environment open. With the decline in grassland area, these species are ever more reliant on alternative habitats such as road verges. To find out whether plant communities comparable to those of semi‐natural grasslands can be maintained on modern road and railway sides, the vegetation of 92 grasslands and 90 road and railway verges was studied. These biotope types were compared with each other according to their community structure, total number of species, number of grassland species and restricted‐range diversity. Further study of the vegetation of road and railway verges was carried out in order to identify the treatments and environments which are most likely to support diverse plant communities. The species number and the restricted‐range diversity proved to be higher next to roads and railways than on grasslands. Grassland species were, however, most abundant on grasslands. Furthermore, the community structure of these biotope types was totally divergent. In their present state, road and railway verges are not a substitute for semi‐natural grasslands. Nevertheless, the occurrence of grassland species in verges may be enhanced by a suitable mowing regime, by giving up the use of de‐icing salt and herbicides and by allowing natural establishment of vegetation on the verges.     

A comparison of the urban flora of different phytoclimatic regions in Italy

This study is a comparison of the spontaneous vascular flora of five Italian cities: Milan, Ancona, Rome, Cagliari and Palermo. The aims of the study are to test the hypothesis that urbanization results in uniformity of urban floras, and to evaluate the role of alien species in the flora of settlements located in different phytoclimatic regions. To obtain comparable data, ten plots of 1 ha, each representing typical urban habitats, were analysed in each city. The results indicate a low floristic similarity between the cities, while the strongest similarity appears within each city and between each city and the seminatural vegetation of the surrounding region. In the Mediterranean settlements, even the most urbanized plots reflect the characters of the surrounding landscape and are rich in native species, while aliens are relatively few. These results differ from the reported uniformity and the high proportion of aliens which generally characterize urban floras elsewhere. To explain this trend the importance of apophytes (indigenous plants expanding into man-made habitats) is highlighted; several Mediterranean species adapted to disturbance (i.e. grazing, trampling, and human activities) are pre-adapted to the urban environment. In addition, consideration is given to the minor role played by the 'urban heat island' in the Mediterranean basin, and to the structure and history of several Italian settlements, where ancient walls, ruins and archaeological sites in the periphery as well as in the historical centres act as conservative habitats and provide connection with seed-sources on the outskirts.     

Naturally Saline Boreal Communities as Models for Reclamation of Saline Oil Sand Tailings

Reclaimed landscapes after oil sands mining have saline soils; yet, they are required to have similar biodiversity and productivity as the predisturbance nonsaline landscape. Given that many species in the boreal forest are not tolerant of salinity, we studied the effects of soil salinity on plant communities in natural saline landscapes to understand potential plant responses during the reclamation process. Vegetation–soil relationships were measured along transects from flooded wetlands to upland forest vegetation in strongly saline, slightly saline, nonsaline, and reclaimed boreal landscapes. In strongly saline landscapes, surface soil salinity was high (>10 dS/m) in flooded, wet‐meadow, and dry‐meadow vegetation zones as compared to slightly saline (<5 dS/m) and nonsaline (<2 dS/m) landscapes. Plant communities in these vegetation zones were quite different from nonsaline boreal landscapes and were dominated by halophytes common to saline habitats of the Great Plains. In the shrub and forest vegetation zones, surface soil salinity was similar between saline and nonsaline landscapes, resulting in similar plant communities. In strongly saline landscapes, soils remained saline at depth through the shrub and forest vegetation zones (>10 dS/m), suggesting that forest vegetation can establish over saline soils as long as the salts are below the rooting zone. The reclaimed landscape was intermediate between slightly saline and nonsaline landscapes in terms of soil salinity but more similar to nonsaline habitats with respect to species composition. Results from this study suggest it may be unrealistic to expect that plant communities similar to those found on the predisturbance landscape can be established on all reclaimed landscapes after oil sands mining.     

THE PENNSYLVANIAN-PERMIAN VEGETATIONAL TRANSITION: A TERRESTRIAL ANALOGUE TO THE ONSHORE-OFFSHORE HYPOTHESIS

An analysis of 68 floras from the Pennsylvanian and Early Permian of Euramerica reveals distinct patterns of environmental distribution. Wetland assemblages are the most commonly encountered floras from the Early and Middle Pennsylvanian. Floras from drier habitats characterize the Permian. Both wetland and dry-site floras occur in the Late Pennsylvanian, but floristic overlap is minimal, which implies strong environmental controls on the distributions of the component species. Drier habitats appear to be the sites of first appearance of orders that become prominent during the Late Permian and Mesozoic. Higher taxa originated in physically heterogeneous, drier habitats, which were geographically marginal throughout most of the Pennsylvanian. They then moved into the lowlands during periods of climatic drying in the Permian, replacing older wetland vegetation. This pattern is analogous to the marine onshore-offshore pattern of origination and migration. The derivation of Mesozoic wetland clades from the Permian dry-lowland vegetation completes the parallel. The similarities of the marine and terrestrial patterns suggest that the combination of evolutionary opportunity, created by physical heterogeneity of the environment, and migrational opportunity, created by changing extrinsic conditions, may be underlying factors that transcend the specifics of organism and environment.     

High Plant Diversity of Grasslands in a Landscape Context: A Comparison of Contrasting Regions in Central Europe

Some regions and habitats harbour high numbers of plant species at a fine scale. A remarkable example is the grasslands of the White Carpathian Mountains (Czech Republic), which holds world records in local species richness; however, the causes are still poorly understood. To explore the landscape context of this phenomenon and its relationships to diversity patterns at larger scales, we compared diversity patterns in grasslands and other vegetation types in the White Carpathians with those in nearby regions lacking extremely species-rich grasslands, using data from vegetation plots and flora grid mapping of entire landscapes. Although small-scale species richness of grasslands and ruderal/weed vegetation of the White Carpathians was higher than in the nearby regions, the number of grassland and ruderal/weed species in the regional flora of the White Carpathians was not. Diversity of forests was not higher in this region at any scale. Thus the remarkably high local species richness of the White Carpathian grasslands does not result from a larger grassland species pool in the region, but from the fine-scale co-occurrence of many grassland species in this landscape, which results in the formation of grassland communities that are locally rich but with similar species composition when comparing different sites (i.e. high alpha but low beta diversity). This pattern can be partly attributed to the large total area of these grasslands, which reduces random extinctions of rare species, low geological diversity, which enables many species to occur at many sites across the landscape, and high land-cover diversity, which supports mixing of species from different vegetation types.     

The conservation value of cacao agroforestry for bird functional diversity in tropical agricultural landscapes

Cacao agroforestry have been considered as biodiversity‐friendly farming practices by maintaining habitats for a high diversity of species in tropical landscapes. However, little information is available to evaluate whether this agrosystem can maintain functional diversity, given that agricultural changes can affect the functional components, but not the taxonomic one (e.g., species richness). Thus, considering functional traits improve the understanding of the agricultural impacts on biodiversity. Here, we measured functional diversity (functional richness‐FD, functional evenness‐FEve, and functional divergence‐Rao) and taxonomic diversity (species richness and Simpson index) to evaluate changes of bird diversity in cacao agroforestry in comparison with nearby mature forests (old‐growth forests) in the Brazilian Atlantic Forest. We used data from two landscapes with constraining areas of mature forest (49% Una and 4.8% Ilhéus) and cacao agroforestry cover (6% and 82%, respectively). To remove any bias of species richness and to evaluate assembly processes (functional overdispersion or clustering), all functional indices were adjusted using null models. Our analyses considered the entire community, as well as separately for forest specialists, habitat generalists, and birds that contribute to seed dispersal (frugivores/granivores) or invertebrate removal (insectivores). Our findings showed that small cacao agroforestry in the forested landscape sustains functional diversity (FD and FEve) as diverse as nearby forests when considering the entire community, forest specialist, and habitat generalists. However, we observed declines for frugivores/granivores and insectivores (FD and Rao). These responses of bird communities differed from those observed by taxonomic diversity, suggesting that even species‐rich communities in agroforestry may capture lower functional diversity. Furthermore, communities in both landscapes showed either functional clustering or neutral processes as the main driver of functional assembly. Functional clustering may indicate that local conditions and resources were changed or lost, while neutral assemblies may reveal high functional redundancy at the landscape scale. In Ilhéus, the neutral assembly predominance suggests an effect of functional homogenization between habitats. Thus, the conservation value of cacao agroforestry to harbor species‐rich communities and ecosystem functions relies on smallholder production with reduced farm management in a forested landscape. Finally, we emphasize that seed dispersers and insectivores should be the priority conservation targets in cacao systems.     

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.     

农业景观生物多样性与害虫生态控制

现代农业的一个重要特征就是人类对农田生态系统的干扰强度及频率不断增加,严重影响农业景观的结构及其生物多样性.农业景观结构的变化及其生物多样性的丧失,必然引起生态系统服务功能的弱化,不利于实施以保护自然天敌为主的害虫生态控制.农业的集约化经营导致自然生境破碎化,减少了农业景观的复杂性,使得作物和非作物变成一种相对离散化的生境类型和镶嵌的景观格局;破碎化的生境不仅会减少某些物种的丰度,还会影响物种之间的相互关系及生物群落的多样性和稳定性.非作物生境类型如林地、灌木篱墙、田块边缘区、休耕地和草地等,是一种比较稳定的异质化环境.非作物生境较少受到干扰,可以为寄生性和捕食性节肢动物提供适宜的越冬或避难场所以及替代猎物、花粉和花蜜等资源,因此,非作物生境有利于自然天敌的栖息和繁衍,也有利于它们迁入邻近的作物生境中对害虫起到调节和控制作用.景观的格局-过程-尺度影响农田生物群落物种丰富度、多度、多样性以及害虫与天敌之间的相互作用.从区域农业景观系统的角度出发,运用景观生态学的理论和方法来研究作物、害虫、天敌等组分在不同斑块之间的转移过程和变化规律,揭示害虫在较大尺度和具有异质性的空间范围内的灾变机理,可为利用农业景观生物多样性来保护农田自然天敌,实施害虫的区域性生态控制提供新的研究思路和手段.     

Plant species richness in continental southern Siberia: effects of pH and climate in the context of the species pool hypothesis

Aim Many high‐latitude floras contain more calcicole than calcifuge vascular plant species. The species pool hypothesis explains this pattern through an historical abundance of high‐pH soils in the Pleistocene and an associated opportunity for the evolutionary accumulation of calcicoles. To obtain insights into the history of calcicole/calcifuge patterns, we studied species richness–pH–climate relationships across a climatic gradient, which included cool and dry landscapes resembling the Pleistocene environments of northern Eurasia. Location Western Sayan Mountains, southern Siberia. Methods Vegetation and environmental variables were sampled at steppe, forest and tundra sites varying in climate and soil pH, which ranged from 3.7 to 8.6. Species richness was related to pH and other variables using linear models and regression trees. Results Species richness is higher in areas with warmer winters and at medium altitudes that are warmer than the mountains and wetter than the lowlands. In treeless vegetation, the species richness–pH relationship is unimodal. In tundra vegetation, which occurs on low‐pH soils, richness increases with pH, but it decreases in steppes, which have high‐pH soils. In forests, where soils are more acidic than in the open landscape, the species richness–pH relationship is monotonic positive. Most species occur on soils with a pH of 6–7. Main conclusions Soil pH in continental southern Siberia is strongly negatively correlated with precipitation, and species richness is determined by the opposite effects of these two variables. Species richness increases with pH until the soil is very dry. In dry soils, pH is high but species richness decreases due to drought stress. Thus, the species richness–pH relationship is unimodal in treeless vegetation. Trees do not grow on the driest soils, which results in a positive species richness–pH relationship in forests. If modern species richness resulted mainly from the species pool effects, it would suggest that historically common habitats had moderate precipitation and slightly acidic to neutral soils.