Variability between Scales: Predictors of Nomadism in Birds of an Australian Mediterranean-climate Ecosystem

Nomadism in animals is a response to resource distributions that are highly variable in time and space. Using the avian fauna of the Mediterranean-climate region of southcentral Australia, we tested a number of variables to determine if they predicted nomadism. These variables were species body mass, the distance in body mass terms to the edge of a body mass aggregation, and diet (for example, seeds, invertebrates, nectar, or plants). We utilized two different classifications of the avifauna that diverged in their definition of nomadic to build two different predictive models. Using both classifications, distance to the edge of a body mass aggregation was found to be a significant predictor of nomadism. There was also evidence that nomads tend to feed on nectar and tend to be large. The significance of the variables body mass and diet (nectar) may reflect the greater energy requirements of large birds and the inherent variability of nectar as a food source. The significance of the variable distance to the edge of a body mass aggregation provides further evidence of inherent variability in resources between domains of scale. The edges of body mass aggregations are hypothesized to be areas of increased resource variability that reflect the transition from one scale of landscape pattern to another. Received 14 November 2000; accepted 27 June 2001.     

Multimodel Inference and the Understanding of Complexity, Discontinuity, and Normadism

Nomadism has received surprisingly little attention in the ecological literature, and further work in this area is needed. The results of Woinarski’s reanalysis of our research findings are broadly similar to our own, and they support our original interpretation. However, his presentation is confusing and difficult to interpret.We used an information-theoretic approach to multimodel selection. We a priori defined plausible candidate models relating the variables described in our original paper or Woinarski’s reanalysis to the phenomenon of nomadism. We tested models that investigate nomadism as a function of nectivory, granivory, diet diversity, mixed diet, distance to body mass aggregation edge, mass, interactions between distance to edge and nectivory, distance to edge and mass, mass and nectivory, or mass and the interaction of edge and nectivory. There is consistency in our results across all sets of models, suggesting that mass, distance to body mass aggregation (scale breaks), and diet (nectivory) are all important factors in determining nomadism. In no case was nectivory or any other diet variable supported in a single-variable model. Given the same data and similar results, we and Woinarski reach fundamentally different conclusions. Woinarski views nomadism as an easily understandable result given knowledge of the proper single mechanistic variable, and he discounts interactions with structural features of the landscape and scaling. We conclude that nomadism is a fundamentally complex phenomenon without a single source of causation, and that it is the interaction of species, species attributes, and landscapes that is responsible for nomadic behavior.     

Body Mass Patterns Predict Invasions and Extinctions in Transforming Landscapes

Scale-specific patterns of resource distribution on landscapes entrain attributes of resident animal communities such that species body-mass distributions are organized into distinct aggregations. Species within each aggregation respond to resources over the same range of scale. This discontinuous pattern has predictive power: invasive species and extinct or declining species in landscapes subject to human transformation tend to be located at the edge of body-mass aggregations (P < 0.01), which may be transition zones between distinct ranges of scale. Location at scale breaks affords species great opportunity, but also potential crisis. Received 19 May 1998; accepted 24 November 1998     

Island biogeography of temporary wetland carabid beetle communities

Aim The study tests if island biogeography is applicable to invertebrate communities of habitat islands in the agricultural landscape that are not fragments of formerly larger habitats. Location Thirty temporary wetlands in the agricultural landscape of northeast Germany. Methods The composition and species richness of carabid beetle communities was analysed. Habitat area, isolation, the density of temporary wetlands in the landscape, land‐use intensity and the maximum duration of flooding were recorded as independent variables. Overall species richness and wetland species richness were studied in independent regression analyses. The community composition was analysed by means of a Canonical Correspondence Analysis (CCA). A partial CCA was used to analyse the effect of the distance to the edge of the field after removing impacts of other independent variables. Results The area of the habitats and various measures of isolation (mean distances = 81–240 m) did not influence species richness or wetland species richness. The community composition was mainly determined by the land‐use intensity, habitat area did not have significant effects, and the distance to the edge of the field was the only effective isolation parameter. Short‐winged species were more often affected by the distance to the edge of the field than full‐winged species. Main conclusion There is evidence that the distances between the wetlands do not provide an effective barrier to the species dispersal and, therefore, metapopulation structures including subpopulations of multiple temporary wetlands might counteract local area effects on subpopulations. Short‐winged species, however, might be more affected by isolation than full‐winged species. As carabid beetle community structure in most early successional habitats is similar, these results may be representative of many agricultural landscape habitats. Nature conservancy concepts that aim to increase habitat area and habitat connectivity have successfully been applied to fragmented late‐successional habitats. The present study indicates that such concepts do not necessarily result in higher diversity or larger populations in early successional habitats.     

The effects of city–suburb–exurb landscape context and distance to the edge on plant diversity of forests in Wuhan,China

Abstract

We analysed the relative role of landscape context (city, suburb and exurb) and distance to the edge (from forest edge to 45 m in interior) on plant diversity of natural forests in Wuhan city. The results indicated that landscape context had significant effects on plant diversity, and both landscape context and distance to the edge affect vegetation and disturbance characteristics. Landscape context was the main factor affecting richness of woods, herbs, indigenous species, forest generalists and insect or wind pollination species. These species tended to be higher in exurban forests while non-indigenous species were higher in the urban forests. The number of non-indigenous species, forest specialists, herbs and insect pollination species also depended on distance to the edge or on both interactions. Richness of non-indigenous species decreased with increasing distance to the edge in urban forest. Vegetation characteristics that shrub cover was lower and disturbance characteristics that disturbed cover and human activity were higher in the urban edge than in the suburb and exurb edge, which decreased from the edge to the interior. Therefore, we should prioritize the preservation of less disturbed and frequented forests (suburban and exurban) to buffer the invasion of non-indigenous species, and to reserve more indigenous species.     

Complex effects of scale on the relationships of landscape pattern versus avian species richness and community structure in a woodland savanna mosaic

Landscape pattern metrics are widely used for predicting habitat and species diversity. However, the relationship between landscape pattern and species diversity is typically measured at a single spatial scale, even though both landscape pattern, and species occurrence and community composition are scale‐dependent. While the effects of scale on landscape pattern are well documented, the effects of scale on the relationships between spatial pattern and species richness and composition are not well known. Here, our main goal was to quantify the effects of cartographic scale (spatial resolution and extent) on the relationships between spatial pattern and avian richness and community structure in a mosaic of grassland, woodland, and savanna in central Wisconsin. Our secondary goal was to evaluate the effectiveness of a newly developed tool for spatial pattern analysis, multiscale contextual spatial pattern analysis (MCSPA), compared to existing landscape metrics. Landscape metrics and avian species richness had quadratic, exponential, or logarithmic relationships, and these patterns were generally consistent across two spatial resolutions and six spatial extents. However, the magnitude of the relationships was affected by both resolution and extent. At the finer resolution (10‐m), edge density was consistently the best predictor of species richness, followed by an MCSPA metric that measures the standard deviation of woody cover across extents. At the coarser resolution (30‐m), NDVI was the best predictor of species richness by far, regardless of spatial extent. Another MCSPA metric that denotes the average woody cover across extents, together with percent of woody cover, were always the best predictors of variation in avian community structure. Spatial resolution and extent had varying effects on the relationships between spatial pattern and avian community structure. We therefore conclude that cartographic scale not only affects measures of landscape pattern per se, but also the relationships among spatial pattern, species richness, and community structure, often in complex ways, which reduces the efficacy of landscape metrics for predicting the richness and diversity of organisms.     

种间作用对物种分布模拟的影响及建模方法

物种分布模型(SDMs)通过量化物种分布和环境变量之间的关系,并将其外推到未知的景观单元,模拟、预测地理空间中生物的潜在分布,是生态学、生物地理学、保护生物学等研究领域的重要工具.然而,目前物种分布模型主要采用非生物因素作为预测变量,由于数据量化和建模表达困难,生物因素特别是种间作用在物种分布模型中常被忽略,将种间作用...     

Multi-scale turtle dove nest habitat selection in a Mediterranean agroforestry landscape: implications for the conservation of a vulnerable species

Determination of factors affecting nest habitat selection is a major topic in avian ecology, with strong implications for conservation purposes especially for the species with unfavorable status. The turtle dove (Streptopelia turtur) is a vulnerable species that has undergone a rapid and serious decline across its distribution range. I investigated the effect of different variables at two spatial scales (10-m radius, nest site; and 100-m radius, landscape) on the probability of presence of turtle dove nests in an agroforestry system of Central Morocco. Topography, habitat structure, human disturbance, and land use parameters were measured at nests (n?=?70) and random points (n?=?70) at both scales. Generalized linear model analyses showed that, at the nest site scale, tree height best explained occurrence of turtle dove nests (with nest occurring preferentially in smaller trees). At the landscape scale, nest occurrence probability decreased with elevation and distance to the nearest forest edge, and increased with forest cover and distance to the nearest habitation. Comparison of explanatory power of the single-scale models showed that the most relevant scale was the nest site level, followed by landscape scales, but the model including both nest-scale and landscape-scale variables was best. The variation partitioning analysis confirmed this pattern. In study area, the turtle dove nest habitat selection process occurs within a relatively small scale, but the joint effect of variables at the two scales is relevant. From a practical perspective, it would be interesting to reproduce the same experimental approach on other Mediterranean breeding habitats (agricultural and other forest habitats) to find out if this species would adopt the same nest habitat selection pattern.     

Role of topography and soils in grassland structuring at the landscape and community scales

The relative importance of abiotic factors in community assembly is debated and thought to be dependent on the scale. I investigated the relative role of topography and soils as structuring agents at the landscape and the community scales in 126 subalpine calcareous grasslands in the Pyrenees, in terms of species composition and abundance. I wished to know: (1) the role of abiotic factors in the organization of plant communities across the landscape; (2) how much of the variation in community distribution was accounted for by abiotic factors; and (3) how well their role applied to the distribution of dominant species at the landscape and the community scales. The hypothesis was: abiotic factors play an important role in community distribution in the landscape, but species interactions are more important within communities. Multivariate methods generated four communities, organized in two contrasting groups along the main vegetation axis, which explained 13% of the variation: mesic grasslands (Nardus stricta and Festuca nigrescens communities) and xeric grasslands (Carex humilis and Festuca gautieri communities). Mesic communities were more acidic and fertile than xeric communities. Changes in the abiotic environment, accounting for up to 80% of the variation in the vegetation, were smooth, while the transition between xeric and mesic grasslands was sharp in terms of species composition. The distribution in the landscape of the first main species from each community was closely related to abiotic factors, which modeled poorly the abundance of the main species at smaller scales. At the within-community scale, the explanatory power of biotic relationships was community dependent, producing the most significant models for plants highly dominant within their communities, such as N. stricta and F. gautieri. Contrary to current hypothesis, there was a shift from mainly positive relationships among dominant species in fertile mesic communities to mainly negative in infertile xeric ones.     

The role of landscape configuration in plant composition of floodplain forests across different physiographic areas

Questions: What is the relative importance of landscape variables compared to habitat quality variables in determining species composition in floodplain forests across different physiographic areas? How do species composition and species traits relate to effects of particular landscape variables? Do lowland and mountain areas differ in effects of landscape variables on species composition? Location: Southern Czech Republic. Methods: A total of 240 vegetation relevés of floodplain forests with measured site conditions were recorded across six physiographic areas. I tested how physiographic area, habitat quality variables and landscape variables such as current land‐cover categories, forest continuity, forest size and urbanization influenced plant species composition. I also compared how mountain and lowland areas differ in terms of the relative importance of these variables. To determine how landscape configuration affects the distribution of species traits, relationships of traits and species affinity with landscape variables were tested. Results: Among landscape variables, forest continuity, landscape forest cover and distance to nearest settlement altered the vegetation. These variables also influenced the distributions of species traits, i.e. life forms, life strategies, affinity to forest, dispersal modes, seed characteristics, flooding tolerance and Ellenberg indicator values for nitrogen, light, moisture and soil reaction. Nevertheless, physiographic area and habitat quality variables explained more variation in species composition. Landscape variables were more important in lowland areas. Forest continuity affected species composition only in lowlands. Conclusions: Although habitat quality and physiographic area explained more vegetation variability, landscape configuration was also a key factor influencing species composition and distribution of species traits. However, the results are dependent on forest geographical location, with lowland forests being more influenced by landscape variables compared to mountain forests.     

次生林不同类型森林边缘的鸟类物种丰富度及个体多度比较

边缘效应对动物的分布及行为会产生一定的影响,在鸟类生态学研究中已证实某些鸟类在森林内部和森林边缘区域存在着物种丰富度和个体多度的差异。于1999至2001年的春夏季,在吉林省左家自然保护区对阔叶林/农田边缘、阔叶林/灌丛边缘及阔叶林/针叶林边缘3种不同类型边缘地带的鸟类物种丰富度及个体多度进行了比较研究。结果表明,不同年间鸟类物种丰富度无显著变化,但个体多度存在着一定的波动。不同类型森林边缘的鸟类物种丰富度存在着一定的差异,阔叶林/灌丛边缘的鸟类物种丰富度最高,而阔叶林/针叶林边缘的鸟类物种丰富度最低。鸟类个体多度的总体趋势在3种不同类型的边缘差异不显著,但存在种间差异,灰椋鸟、灰头啄木鸟和喜鹊在阔叶林/农田边缘的个体多度最高,斑啄木鸟、黄胸、三道眉草和日本树莺在阔叶林/灌丛边缘的个体多度最高,而沼泽山雀、冕柳莺和山在阔叶林/针叶林边缘的个体多度最高。     

基于鸟类边缘种行为的景观连接度研究——空间句法的反规划应用

在城市森林及其他生态景观的研究与规划中,结合特定物种(使用者)行为的景观连接度已得到业界越来越多的重视。为了给基于物种行为的景观连接度提供新的建模和分析理念,拟将建筑及城市规划学科中一种可靠的人工智能语言通过反规划思想引入景观生态学领域,通过模拟演绎展示空间句法在研究中的优越性。鉴于鸟类边缘种的栖息地景观构型特点,将空间句法轴线图借用于基于鸟类边缘种行为的景观连接度研究。首先介绍了传统景观连接度的量化方法及物种迁移模型,通过文献综述归纳出此类研究方法的局限性;接着,由反规划启蒙提出将空间句法模型引入"边缘种-栖息地"互动研究的设想;最后,以贺州城市森林规划为例,利用空间句法轴线图探究基于鸟类边缘种行为的景观连接度。模拟实验旨在展示轴线图模型能反映物种对不同景观元素非等权重的选择行为,并可根据物种邻域感知信息预测其复合尺度的行为。     

Environmental stress alters native-nonnative relationships at the community scale

The invasion of natural habitats by nonnative species is affected by both native biodiversity and environmental conditions; however few tests of facilitation between native community members and nonnative species have been conducted along disturbance and stress gradients. There is strong evidence for an increase in facilitation between native plant species with increasing levels of natural environmental stress, however it is unknown whether these same positive interactions occur between nonnative invaders and native communities. I investigated the effects of natural stress on community interactions between native heathland species and nonnative species with two field studies conducted at the landscape and community scale. At the landscape scale of investigation, nonnative species richness was positively related to native species richness. At the community level, nonnative invaders experienced facilitation with natives in the most stressful zones, whereas they experienced competition with native plants in the less stressful zones of the heathlands. Due to the observational nature of the landscape scale data, it is unclear whether nonnative diversity levels are responding positively to extrinsic factors or to native biodiversity. The experimental component of this research suggests that native community members may ameliorate stressful environmental conditions and facilitate invasion into high stress areas. I present a conceptual model which is a modification of the Shea and Chesson diversity-invasibility model and includes both facilitation as well as competition between the native community and nonnative invaders at the community level, summing to an overall positive relationship at the landscape scale.     

Factors influencing species selection for littoral rainforest restoration: Do environmental gradients matter?

Summary Littoral rainforest in northern New South Wales, Australia, has been severely reduced in area and is now extremely limited in extent. Factors influencing the floristics, species richness and abundance, and relationship of this coastal rainforest community type to other lowland rainforests are explored. The purpose of the study was to provide ecological information to support (i) the development of management recommendations and assist habitat expansion and restoration planning for a coastal site at Lennox Head, in northern New South Wales, and (ii) the implementation of recovery actions for an endangered ecological community and an endangered tree species. Multivariate analysis techniques were used to classify and ordinate sampled sites relative to environmental variables to provide an explanation for current floristic assemblages. Eight locations at varying distances to the coast, and representing a range of soil types, were chosen to test the influence of selected environmental variables. At the broad scale, the results show that proximity to the coast and altitude were generally correlated and represented the most influential variables; soil depth, topographic position and slope were broadly correlated but markedly less influential; disturbance was a significant but independent influence on floristics; and soil type and aspect had the least influence. The study provided insight into the ecological parameters of a range of species suited to the habitat rehabilitation and restoration project, and identified finer‐scale floristic patterns at the Lennox site that appear to reflect the influence of environmental variables. In that case, areas in closer proximity to the ocean are dominated by several littoral rainforest and disturbance‐related species, and species richness increases relative to distance from the ocean. This highlights the need to be sensitive to landscape variation, and the influence of environmental variables on plant species distributions, and population dynamics and structure, to guide final selection of appropriate plant material for littoral rainforest restoration projects.     

Niches versus neutrality: uncovering the drivers of diversity in a species-rich community

Ecological models suggest that high diversity can be generated by purely niche-based, purely neutral or by a mixture of niche-based and neutral ecological processes. Here, we compare the degree to which four contrasting hypotheses for coexistence, ranging from niche-based to neutral, explain species richness along a body mass niche axis. We derive predictions from these hypotheses and confront them with species body-mass patterns in a highly sampled marine phytoplankton community. We find that these patterns are consistent only with a mechanism that combines niche and neutral processes, such as the emergent neutrality mechanism. In this work, we provide the first empirical evidence that a niche-neutral model can explain niche space occupancy pattern in a natural species-rich community. We suggest this class of model may be a useful hypothesis for the generation and maintenance of species diversity in other size-structured communities.     

Relationships between spatial configuration of tropical forest patches and woody plant diversity in northeastern Puerto Rico

The destruction and fragmentation of tropical forests are major sources of global biodiversity loss. A better understanding of anthropogenically altered landscapes and their relationships with species diversity and composition is needed in order to protect biodiversity in these environments. The spatial patterns of a landscape may control the ecological processes that shape species diversity and composition. However, there is little information about how plant diversity varies with the spatial configuration of forest patches especially in fragmented tropical habitats. The northeastern part of Puerto Rico provides the opportunity to study the relationships between species richness and composition of woody plants (shrubs and trees) and spatial variables [i.e., patch area and shape, patch isolation, connectivity, and distance to the Luquillo Experimental Forest (LEF)] in tropical forest patches that have regenerated from pasturelands. The spatial data were obtained from aerial color photographs from year 2000. Each photo interpretation was digitized into a GIS package, and 12 forest patches (24–34 years old) were selected within a study area of 28 km². The woody plant species composition of the patches was determined by a systematic floristic survey. The species diversity (Shannon index) and species richness of woody plants correlated positively with the area and the shape of the forest patch. Larger patches, and patches with more habitat edge or convolution, provided conditions for a higher diversity of woody plants. Moreover, the distance of the forest patches to the LEF, which is a source of propagules, correlated negatively with species richness. Plant species composition was also related to patch size and shape and distance to the LEF. These results indicate that there is a link between landscape structure and species diversity and composition and that patches that have similar area, shape, and distance to the LEF provide similar conditions for the existence of a particular plant community. In addition, forest patches that were closer together had more similarity in woody plant species composition than patches that were farther apart, suggesting that seed dispersal for some species is limited at the scale of 10 km.     

The effects of fire on communities,guilds and species of breeding birds in burnt and control pinewoods in central Italy

Breeding bird communities in burnt and unburnt residual pinewoods were studied over 3 years by line-transect method, following a catastrophic fire event in Castelfusano (Rome, Central Italy; July 2000). We applied bootstrap procedures to evaluate whether the observed data were true or just produced by chance, and then examined the emerging patterns at three levels: community, guild and species levels. At the community level, fire acted on breeding bird communities by altering especially the total abundance patterns: the species abundance decreased in the burnt pinewood compared to the residual one, but other parameters were not significantly affected by fire. As a consequence of fire, the destruction and structural simplification of the canopy and shrubby component, as well as the increase of edge habitat and patchiness at landscape scale, induced a turnover in species between pinewoods. Species turnover was higher at the burnt than at the residual pinewoods, during all the 3 years of study. At the guild level, the forest species decreased strongly in terms of richness and abundance in the burnt pinewoods, contrary to the edge and open habitat species which increased in terms of richness, abundance and evenness. Edge species showed the highest turnover in burnt pinewood during the whole period of study. At species level, after an a priori subdivision (based on bibliographic search) of the various species in two ecological guilds (forest versus edge species), it was found that an a posteriori statistical analysis confirmed the expected trend, i.e. that the species which decreased significantly in burnt pinewood were essentially the forest species, whereas the species which increased were essentially the edge/open habitat ones. Overall, in order to investigate the effects of fire catastrophes on birds, the guild approach seems more exhaustive than the taxonomic community approach, where intrinsic confounding trends are present.     

Reshaping our understanding of species’ roles in landscape‐scale networks

In network ecology, landscape‐scale processes are often overlooked, yet there is increasing evidence that species and interactions spill over between habitats, calling for further study of interhabitat dependencies. Here, we investigate how species connect a mosaic of habitats based on the spatial variation of their mutualistic and antagonistic interactions using two multilayer networks, combining pollination, herbivory and parasitism in the UK and New Zealand. Developing novel methods of network analysis for landscape‐scale ecological networks, we discovered that few plant and pollinator species acted as connectors or hubs, both within and among habitats, whereas herbivores and parasitoids typically have more peripheral network roles. Insect species’ roles depend on factors other than just the abundance of taxa in the lower trophic level, exemplified by larger Hymenoptera connecting networks of different habitats and insects relying on different resources across different habitats. Our findings provide a broader perspective for landscape‐scale management and ecological community conservation.