The importance of spatial scale in habitat selection by European beaver

We evaluated habitat selection by European beaver Castor fiber L. across a spatial gradient from local (within the family territory) to a broad, ecoregional scale. Based on aerial photography, we assessed the habitat composition of 150 beaver territories along the main water bodies of the Vistula River delta (northern Poland) and compared these data with 183 randomly selected sites not occupied by the species. The beavers preferred habitats with high availability of woody plants, including shrubs, and avoided anthropogenically modified habitats, such as arable lands. Within a single family territory, we observed decreasing woody plant cover with increasing distance from a colony centre, which suggests that beaver habitat preferences depend on the assessment of both the abundance and spatial distribution of preferred habitat elements. We tested the importance of spatial scale in beaver habitat selection with principal coordinates of neighbour matrices analysis, which showed that the geographical scale explained 46.7% of the variation in habitat composition, while the local beaver density explained only 10.3% of this variability. We found two main spatial gradients that were related to the broad spatial scale: first, the most important gradient was related to the largest distances between beaver sites and was independent of woody plant cover and the local beaver site density. The second most important gradient appeared more locally and was associated with these variables. Our results indicate that European beaver habitat selection was affected by different scale‐related phenomena related 1) to central place foraging behaviour, which resulted in the clumped distribution of woody plants within the territory, and 2) local population density and woody plant cover. Finally, 3) habitat selection occurs independently across the largest spatial scale studied (e.g. between watersheds), which was probably due to the limited natal dispersal range of the animals.     

蓝冠噪鹛繁殖期生境选择特征分析

2013年至2015年每年4—7月,在江西婺源境内对蓝冠噪鹛繁殖小群进行调查。观察并测量其繁殖地斑块海拔,距山地、水源及干扰源的距离,计算斑块面积、周长及形状指数,并在每个繁殖斑块的4个方向5km以外选取同样植被类型的对照斑块,比较繁殖斑块与对照斑块在以上7个因子的差异。结果表明繁殖斑块海拔,距山地距离和距干扰距离显著小于对照斑块。说明在斑块尺度上,蓝冠噪鹛繁殖期倾向于选择低海拔阔叶林,且在离山地更近的村庄附近繁殖,这可能与食物丰富和天敌较少有关。在微生境尺度,选择繁殖点B在巢区及同一片阔叶林中无噪鹛筑巢的对照区进行10个生态因子的测量,并用资源选择函数以及Vanderploeg和Scavia选择系数进行分析。资源选择函数结果表明草本密度、草本高度在微生境尺度对蓝冠噪鹛生境选择贡献最大;而Vanderploeg和Scavia选择系数结果表明蓝冠噪鹛喜在胸径较粗(40—80cm)的朴树、枫杨和枫香3种树上筑巢,筑巢偏好树高20m以上及草本盖度较高(60%—90%)的生境。综合两种分析结果,在微生境尺度蓝冠噪鹛对筑巢树种及高度具有选择性,对巢区隐蔽性有所要求,巢下草本情况可以反映昆虫等食物资源状况,说明蓝冠噪鹛繁殖期偏好在食物相对丰富的区域筑巢。     

Habitat fragmentation: A long and tangled tale

In this essay: I provide a brief history of habitat fragmentation research; I describe why its “non‐questions” (‘Is habitat fragmentation a big problem for wildlife species?” and, “Are the effects of habitat fragmentation generally negative or positive?”) are important to conservation; I outline my role in tackling these questions; I discuss reasons why the culture of habitat fragmentation research is largely incapable of accepting the answers; and I speculate on the future of habitat fragmentation research.     

Habitat availability for bottomland hardwood forest birds: the importance of considering elevation

ABSTRACT Estimating habitat availability at large spatial scales is critical for identifying conservation and management priorities for birds. Given the effects of patch size on habitat selection and productivity of many bird species, large‐scale approaches often focus on identifying and enumerating patches large enough to support sustainable populations. Declines in the availability of bottomland hardwood forests have made this approach imperative for species that depend on these forests. However, most remaining bottomland forests are relatively low‐elevation sites that were difficult to convert to agriculture. For species that require densely vegetated understories or well‐developed litter layers, such as Swainson's Warblers (Limnothlypis swainsonii), these relatively flood‐prone forests may not provide suitable habitat and, consequently, current prioritization methods may overestimate habitat availability. We examined the effect of elevation on estimates of habitat availability for Swainson's Warblers in a 65,000‐ha bottomland hardwood forest (White River National Wildlife Refuge) in eastern Arkansas. We detected Swainson's Warblers at 88 of 2222 sampled points, and Swainson's Warblers only used relatively high elevations in the refuge. Based on our estimates, about 25% of the refuge is at a suitable elevation for Swainson's Warblers. Without considering elevation, this refuge would support an estimated 7000 to 7600 pairs, but, when elevation is considered, the estimated number of pairs drops to 1500–2000 pairs. In reality, because of a lack of suitable seral stages at high elevations in the refuge, this area likely supports only 75–100 pairs. For Swainson's Warblers and other understory‐dependent bottomland species, elevation should be incorporated into conservation planning to obtain accurate estimates of habitat availability. In addition, management should be focused on these high‐elevation areas to maximize habitat availability for these species of concern.     

Habitat selection in a large orb‐weaving spider: vegetational complexity determines site selection and distribution

1. The distribution of the large orb‐weaving spider Argiope trifasciata in old field habitats of North America and the habitat selection process this species used was studied for 2 years. 2. Because web spiders have limited dispersal abilities and an energetically costly prey capture device, they do not have the ability to sample potential foraging sites. Structural complexity of the vegetation to which the web must be attached is relatively easy to assess. The hypothesis that the structural complexity is a primary factor in determining initial web site selection was tested both by relating the natural distribution of the spiders across habitats to vegetational complexity and by manipulating the complexity of the habitats in a series of experiments. 3. Argiope trifasciata was not distributed evenly among three old field vegetation types. Habitat complexity was related to spider density in both years although no measure of insect activity, prey capture, or prey consumption was correlated with spider distribution. 4. Three experimental manipulations were conducted to test the impact of habitat structure on spider establishment: (1) the amount of natural vegetation was reduced, (2) structures were added to a simple habitat, and (3) the complexity of the structures added was varied. In each case, spiders were introduced and establishment of webs was monitored. In all manipulations, spider establishment was related to the complexity of the substrate available. 5. These results are important for understanding the cues that influence foraging site selection and therefore provide insight into the distribution of species with limited dispersal abilities and high site investment requirements.     

Measures of giant panda habitat selection across multiple spatial scales for species conservation

Examining ecological processes across spatial scales is crucial as animals select and use resources at different scales. We carried out field surveys in September 2005, March–September 2006, and April 2007, and used ecological niche factor analysis to determine habitat preferences for the giant panda (Ailuropoda melanoleuca) across 4 spatial scales: daily movement, core range, home range, and seasonal elevational migration. We found that giant pandas prefer conifer forest and mixed forest at higher than average elevation (2,157 m) of study area in the 4 scale models. However, we also observed significant scale differences in habitat selection. The strength of habitat preference increased with scale for the 2 disturbed forests (sparse forest and fragmented forest), and decreased with scale for 0–30° gentle slope and south- and north-facing aspect. Furthermore, habitat suitability patterns were scale-dependent. These findings highlight the need to determine species–environment associations across multiple scales for habitat management and species conservation. © 2012 The Wildlife Society.     

Nestedness as a conservation tool: plants and birds of oak-hazel woodland in Sweden

Nestedness was examined for vascular plants and birds in the centres and edges of 26 sites of ancient oak-hazel woodland in Sweden. Both taxa exhibited significant nestedness in site centres and for whole sites, but not at the edges for birds. Woodland ranks of nestedness differed between plants and birds. Rank of nestedness of birds, but not of plants, depended on area. Horizontal habitat structure affected nestedness of both plants and birds. Mobility appears decisive for creating rank differences between sites for various taxa. High mobility may also explain a greater edge effect in birds from allochtonous, more or less transient individuals. Nestedness in relation to mobility, particularly at edges, should be of theoretical interest. The possible use of nestedness patterns in conservation makes further analyses urgent for less mobile taxa.     

Scales and costs of habitat selection in heterogeneous landscapes

Summary Two scales of habitat selection are likely to influence patterns of animal density in heterogeneous landscapes. At one scale, habitat selection is determined by the differential use of foraging locations within a home range. At a larger scale, habitat selection is determined by dispersal and the ability to relocate the home range. The limits of both scales must be known for accurate assessments of habitat selection and its role in effecting spatial patterns in abundance. Isodars, which specify the relationships between population density in two habitats such that the expected reproductive success of an individual is the same in both, allow us to distinguish the two scales of habitat selection because each scale has different costs. In a two-habitat environment, the cost of rejecting one of the habitats within a home range can be expressed as a devaluation of the other, because, for example, fine-grained foragers must travel through both. At the dispersal scale, the cost of accepting a new home range in a different habitat has the opposite effect of inflating the value of the original habitat to compensate for lost evolutionary potential associated with relocating the home range. These costs produce isodars at the foraging scale with a lower intercept and slope than those at the dispersal scale.Empirical data on deer mice occupying prairie and badland habitats in southern Alberta confirm the ability of isodar analysis to differentiate between foraging and dispersal scales. The data suggest a foraging range of approximately 60 m, and an effective dispersal distance near 140 m. The relatively short dispersal distance implies that recent theories may have over-emphasized the role of habitat selection on local population dynamics. But the exchange of individuals between habitats sharing irregular borders may be substantial. Dispersal distance may thus give a false impression of the inability of habitat selection to help regulate population density.     

Landscape effects on birds in urban woodlands: an analysis of 34 Swedish cities

Aim To compare bird abundances in woodlands along gradients from the city centre to the peri‐urban area. To evaluate the importance of the proportion of woodland within the city and in the peri‐urban landscape to forest bird communities breeding in urban woodlands. To test whether fragmentation effects on birds were linked to the type of peri‐urban matrix. Location A total of 34 Swedish cities with > 10,000 inhabitants in south‐central Sweden. The study area covered 105,000 km², in which 84% of the Swedish population of 9.1 million lives. Methods Repeated point count surveys were conducted in 2004 in a total of 474 woodlands. General linear models were used to test for possible differences in abundance along urban to peri‐urban gradients, and to regress bird abundances in local urban woodlands on: (1) total woodland cover in the city, (2) total woodland cover in the peri‐urban landscape, (3) the interaction between woodland cover in the city and in the peri‐urban area, (4) region, and (5) human density. Results More than 12,000 individuals of 100 forest bird species were recorded. Of the 34 most common species detected, 13 bird species had higher abundances in urban than in peri‐urban woodlands, and seven species showed the opposite trend. The bird community of urban woodlands was characterized by species associated with deciduous forests and tree nesters, whereas the bird community of peri‐urban woodlands was characterized by species associated with coniferous woodland and ground nesters. Twelve species were significantly linearly associated with the proportion of urban woodland and/or the proportion of peri‐urban woodland, and a further eight species were associated with the interaction between these two factors. Local breeding bird abundances of four species were significantly positively associated with the proportion of urban woodland only in farmland‐dominated landscapes. Main conclusions Fragmentation effects on some urban birds are linked to the type of peri‐urban matrix. In farmland landscapes, peri‐urban woodlands may have been too scarce to act as a source of bird immigrants to fragmented urban woodlands. To maintain populations of specialized forest birds within cities in landscapes dominated by agriculture, it is of paramount importance to conserve any remaining urban woodlands.     

Effects of seasonality on the species–area relationship: a case study with birds in urban parks

Aim To examine how parameters of the species–area curve and factors determining bird species richness are affected by seasonality. Location One hundred and thirty urban parks of the city of Valencia (Spain) ranging between 0.03 and 18.6 ha. Methods Bird censuses were conducted monthly during 1998 and 2004. For each park, 27 variables were recorded as measures of size, structure and isolation. Linear regression was used to test for patterns in species richness relative to independent variables. The results of each season were compared. Results Curves corresponding to the breeding period (spring–summer) had significantly higher intercepts, but slopes did not change across seasons. Turnover rates of resident species were dependent on patch size and isolation considering spring, but not autumn, from different years. Additionally, turnover rates in spring were lower in parks in close proximity to others than in isolated ones. In all seasons, the number of bird species showed a strong relationship with park area, which explained c. 60% of the variation in species numbers. Habitat variables and park isolation explained a small amount of the variation in species numbers. The data did not give support to the random placement hypothesis. Main conclusions The overall conclusions of this study give little support to the possible influence of seasonality on species–area relationship or on the three main hypotheses explaining it. This lack of influence of seasonality could be explained by the seasonal stability of the bird populations of the parks within the study area as a consequence of different factors, mainly the characteristics of the species pool, similarity in the features of the parks irrespective of their size, and stability of resources and conditions across seasons. The question of whether this lack of influence of seasonality on the species–area relationship occurs in those ecological systems that have a larger seasonal variation than the urban parks of the study area remains unresolved. Closer examination of the seasonal patterns reported in this study is likely to be useful in increasing our understanding of the species–area relationship.     

Multi‐scale effects of habitat structure and landscape context on a vertebrate with limited dispersal ability (the brown‐throated sloth,Bradypus variegatus)

As human population, food consumption, and demand for forest products continue to rise over the next century, the pressures of land‐use change on biodiversity are projected to intensify. In tropical regions, countryside habitats that retain abundant tree cover and structurally complex canopies may complement protected areas by providing suitable habitats and landscape connectivity for a significant portion of the native biota. Species with low dispersal capabilities are among the most at risk of extinction as a consequence of land‐use change. We assessed how the spatial distribution of the brown‐throated sloth (Bradypus variegatus), a model species for a vertebrate with limited dispersal ability, is shaped by differences in habitat structure and landscape patterns of countryside habitats in north‐central Costa Rica using a multi‐scale framework. We quantified the influence of local habitat characteristics and landscape context on sloth occurrence using mixed‐effects logistic regression models. We recorded 27 sloths within countryside habitats and found that both local and landscape factors significantly influenced their spatial distribution. Locally, sloths favored structurally complex habitats, with greater canopy cover and variation in tree height and basal area. At the landscape scale, sloths demonstrated a preference for habitats with high proportions of forest and nearby large tracts of forest. Although mixed‐use areas and tree plantations are not substitutes for protected forests, our results suggest they provide important supplemental habitats for sloths. To promote the conservation and long‐term viability of sloth populations in the tropical countryside, we recommend that land managers retain structurally complex vegetation and large patches of native habitat.     

A habitat island approach to conserving birds in urban landscapes: case studies from southern and northern Europe

Wildlife conservation in urban habitats is increasingly important due to current urbanization trends. We review the different approaches to studying birds in urban landscapes, and point out the importance of the habitat island ecological theory as a research framework for the management and conservation of urban birds. Based on two comprehensive research projects conducted at urban parks in Spain (Madrid) and Finland (Oulu and Rovaniemi), several different issues related to bird conservation in cities are discussed, main findings of these projects are presented, and future research needs are suggested. Urban parks are important biodiversity hotspots in cities. Fragmentation conditions have the same deleterious effects to urban birds as in other fragmented landscapes. Park size accounts for species accumulation in urban parks; this pattern being highly nested. Urban parks of 10–35 ha would contain most of the species recorded in cities, but other indicators related to the probabilities of persistence of the target species should be obtained. Wooded streets can increase urban landscape connectivity by providing alternative habitat for feeding and nesting during the breeding season. Because increasing the size of parks is difficult in cities, enhancement of habitat diversity and resource availability for birds within parks (e.g. nest boxes, winter feeding tables, etc.) appears to be a straightforward way of increasing urban bird diversity. However, human disturbance (pedestrians) should be controlled since it can negatively influence many urban birds. We present a conceptual model for urban bird conservation, which includes three aspects (management, environmental education and research) and new alternatives to promote the involvement of different sectors of the society.