Nested bird and micro-habitat assemblages in a peatland archipelago

Biotic assemblages of insular habitats are nested when poor assemblages are subsets of richer ones. Nestedness of species assemblages is frequent and may result from selective extinction or frequent colonization in insular habitats. It may also be created by a nested distribution of habitats among islands or by sampling bias. We sampled 67 isolated peatlands (7–843 ha) in southern Quebec, Canada, to measure nestedness of bird species assemblages among peatlands and assess the habitat nestedness hypothesis. Species and microhabitat assemblages were both strongly nested among peatlands. Whether sites were ranked by species richness, microhabitat richness or peatland area had no effect on nestedness. However, microhabitat nestedness was significantly reduced when sites were sorted by area rather than by microhabitat richness. As expected, if bird-microhabitat associations are responsible for the nested pattern of distribution, we found a positive correlation between the contributions of bird species and microhabitats to individual site nestedness. Nevertheless, microhabitat assemblages were significantly less nested than bird species assemblages, possibly because of frequent recolonization by birds or uneven sampling among sites. Received: 12 June 1998 / Accepted: 20 September 1998     

Seasonality of peak metabolic rate in non‐migrant tropical birds

Birds that are year‐round residents of temperate and tropical regions have divergent life histories. Tropical birds have a slower ‘pace of life’, one characteristic of which includes lower peak metabolic rate and daily activity levels. Temperate resident birds are faced with seasonal variation in thermogenic demand. This challenge is met with seasonally increased peak metabolic rate during winter. These thermogenic demands are much lower in birds that are year‐round tropical residents. By measuring peak (summit) metabolic rate in tropical and temperate resident bird species during summer and winter, we asked whether tropical birds exhibit seasonality in peak metabolic rate, and if the direction of seasonality differs between tropical and temperate species. We measured summit metabolism in seven tropical and one temperate species during the winter and during the summer breeding season to test the hypothesis that summit metabolism of tropical residents would change seasonally. We consider whether metabolic seasonality is associated with breeding season for tropical species. We found that summit metabolism was significantly greater during the summer for most tropical residents, while the temperate resident matched several previous reports with higher summit metabolism in winter. We conclude that metabolic seasonality occurs in tropical residents and differs from temperate residents, suggesting that breeding during the summer may be driving relatively higher metabolism as compared to winter thermogenesis in temperate birds.     

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.     

Distributions of forest birds and butterflies in the Andaman islands, Bay of Bengal: nested patterns and processes

The distributional patterns of forest birds and butterflies in the Andaman islands, an oceanic chain located off SE Asia, were tested for nestedness. Both taxa were highly nested. Nestedness could be due to colonization or extinction processes, area or distance effects or nestedness of habitats. Nestedness in forest bird distributions were strongly influenced by area and habitat related factors. Habitats were significantly nested in all three island groups, however most strongly for the North Andamans. However forest bird distributions in the North Andamans, as indicated by row order in the packed matrix, was not correlated with habitat diversity, suggesting that habitat related factors alone cannot account for these patterns. Other causal influences could be passive sampling, where common and abundant species and habitats are more likely to have a widespread distribution than rare species and habitats. The nested subset pattern seen in two unrelated taxa suggests that the Andamans are extinction dominated and that the protection of forests on large islands is critical for the conservation of its biodiversity.     

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.     

Fine-scale structure and cross-taxon congruence of bird and beetle assemblages in an old-growth boreal forest mosaic

Aim Nestedness occurs when species present in depauperate sites are subsets of those found in species‐rich sites. The degree of congruence of site nestedness among different assemblages can inform commonalities of mechanisms structuring the assemblages. Well‐nested assemblages may still contain idiosyncratic species and sites that notably depart from the typical assemblage pattern. Idiosyncrasy can arise from multiple processes, including interspecific interactions and habitat preferences, which entail different consequences for species co‐occurrences. We investigate the influence of fine‐scale habitat variation on nestedness and idiosyncrasy patterns of beetle and bird assemblages. We examine community‐level and pairwise species co‐occurrence patterns, and highlight the potential influence of interspecific interactions for assemblage structure. Location Côte‐Nord region of Québec, Canada. Methods We sampled occurrences of ground‐dwelling beetles, flying beetles and birds at sites within old‐growth boreal forest. We examined the nestedness and idiosyncrasy of sites and sought relationships to habitat attributes. We analysed non‐random species co‐occurrence patterns at pairwise and community levels, using null model analysis and five ‘association’ indices. Results All three assemblages were significantly nested. There was limited congruence only between birds and flying beetles whose nestedness was related to canopy openness. For ground‐dwelling beetles, nestedness was related to high stand heterogeneity and sapling density, whereas site idiosyncrasy was inversely related to structural heterogeneity. For birds, site idiosyncrasy increased with canopy cover, and most idiosyncratic species were closed‐canopy specialists. In all assemblages, species idiosyncrasy was positively correlated with the frequency of negative pairwise associations. Species co‐occurrence patterns were non‐random, and for flying beetles and birds positive species pairwise associations dominated. Community‐level co‐occurrence summaries may not, however, always reflect these patterns. Main conclusions Nestedness patterns of different assemblages may not correlate, even when sampled at common locations, because of different responses to local habitat attributes. We found idiosyncrasy patterns indicating opposing habitat preferences, consistent with antagonistic interactions among species within assemblages. Analysis of such patterns can thus suggest the mechanisms generating assemblage structures, with implications for biodiversity conservation.     

Geographical variation in reproductive investment across avian assemblages in Europe: effects of environmental drivers differ between altricial and precocial species

Reproductive traits provide information about the ways by which available resources are allocated during breeding. We tested for environmental drivers of large scale geographical patterns in assemblage mean clutch size, number of broods and overall reproductive investment per breeding season in European birds. We combined data about geographical distribution with published information about reproductive traits, and calculated mean trait values for avian assemblages occurring in 50 × 50 km grid cells. In total, we employed data from 499 species and 2059 assemblages. As the time available for breeding and the amount of food limit the reproductive effort, we related the geographical variation in reproductive traits to the length of breeding season, normalized difference vegetation index (NDVI) as a surrogate of resource availability, and its seasonality. Geographical patterns in traits may differ between reproductive modes, thus we performed the analyses separately for altricial Passerines (n = 203) and precocial non‐passerine species (n = 164) and controlled for the effect of taxonomy. Large clutches dominated in areas with high NDVI and, in precocial birds, also in areas with high annual seasonality and a long breeding season. High number of broods and high overall reproductive investment dominated in areas with a long breeding season, and high number of broods was found also in areas with low annual seasonality, but only in precocial species. High overall reproductive investment dominated in highly productive areas and also in areas with low annual seasonality in both groups. The increase in reproductive investment is caused mostly by an increase in the number of broods related to the length of season and partly by increase in clutch size related to NDVI. We found a negative correlation between clutch size and the number of broods in Passerines, which might suggest a trade‐off between these traits. Processes behind trait patterns differ between altricial and precocial species.     

Nestedness and migratory status of avian assemblages in North America and Europe

We examine patterns of nestedness and species incidence for the resident and migrant components of avifaunas in North America and Europe. While all assemblages were significantly nested, there were no significant differences between North American and European avifaunas overall in nestedness or incidence. Residents did not differ from migrants in their adherence to a nested distribution, but did exhibit significantly higher incidences when continental affiliation was ignored.¶We develop a new nestedness index that examines each species' relative contribution to an assemblage's overall pattern of nestedness. The relative nestedness index exhibits a quadratic relationship with incidence such that species with low incidences and species with high incidences generally increase the overall level of nestedness, while species with intermediate incidence tend to decrease nestedness.     

海口和三亚两城市破碎化林地中鸟类群落多样性与嵌套分布格局

城市化是生物多样性快速丧失的主要原因之一。鸟类作为城市生态系统的重要组成部分, 其生物多样性格局和物种保护已成为城市生态学研究的热点。为揭示城市化过程中城区和郊区破碎化林地中鸟类群落的多样性差异和嵌套格局, 本研究于2021年春、夏季鸟类繁殖期采用样线法对海口和三亚市的城区、郊区共13个林地斑块中的鸟类群落进行调查。使用NODF (nestedness metric based on overlap and decreasing fill)和WNODF (weighted nestedness metric based on overlap and decreasing fill)方法进行嵌套格局分析。研究发现: (1)共记录到林鸟100种, 隶属于11目39科, 其中三亚郊区的鸟类丰富度最高, 共8目29科68种。记录到国家重点保护鸟类共18种, 其中两城市郊区的国家重点保护鸟类物种数均多于城区, 海口郊区还记录到国家I级重点保护鸟类黄胸鹀(Emberiza aureola)。(2)鸟类群落多度、物种丰富度、Pielou均匀度指数和Shannon-Wiener多样性指数在不同区域中均存在差异。海口城区的鸟类群落多度显著高于海口郊区(P < 0.05), 三亚郊区的鸟类群落物种丰富度、Pielou均匀度指数和Shannon-Wiener多样性指数均显著高于三亚城区和海口郊区(P < 0.05)。(3)嵌套分析结果表明, 海口和三亚市的城区、郊区林地鸟类群落均呈现反嵌套分布格局。线性回归分析显示, 三亚市城区和郊区的斑块面积与鸟类物种丰富度呈显著正相关, 而物种丰富度与斑块距最近大面积林地的距离之间无显著相关性。研究表明, 两城市鸟类群落多样性都表现出郊区高于城区的特点, 少数优势种(如白头鹎 Pycnonotus sinensis)占据了城市中的主要生态位。受城市化的影响, 海口郊区与城区鸟类群落有同质化的趋势。鸟类在城区和郊区斑块间的高流动性、种间竞争和斑块中资源的可利用性等因素可能导致斑块间鸟类群落的反嵌套分布格局。我们建议应加强城区和郊区鸟类的保护, 减少对林地的破坏, 提高城市鸟类多样性。     

Invasive species and land bird diversity on remote South Atlantic islands

Invasive species pose significant threats to biodiversity, especially on islands. They cause extinctions and population declines, yet little is known about their consequences on the emergent, metacommunity-level patterns of native species in island assemblages. We investigated differences in species–area relationships, nestedness, and occupancy of 9 species of native land birds between island assemblages with and without invasive Norway rats (Rattus norvegicus) in the Falkland Archipelago. We found that species–area curves, nestedness, and individual species’ occurrences differed between island assemblages with and without rats. Rat-free islands had, on average, 2.1 more land bird species than rat-infested islands of similar size. Passerine bird communities on islands with and without rats were significantly nested, but nestedness was significantly higher on rat-free islands than on rat-infested islands. The presence of rats was associated with differences in the incidence of many, but not all bird species. On rat free islands the occurrence of all species increased with island area. The occurrence of most, albeit not all, bird species was lower on islands with than on islands without rats. Two species of conservation concern, Troglodytes aedon cobbi and Cinclodes antarcticus, were abundant on rat-free islands, but absent or found at very low frequencies on islands with rats. The occurrence of three species was not associated with the presence of rats. The patterns presented here can be used to evaluate the consequences of ongoing rat eradications for passerine diversity, distribution, and abundance.     

Variations in bird abundance in tropical arid and semi-arid habitats

Temporal variation in bird abundance was studied during a complete annual cycle in a thorn scrub, a thorn woodland and a deciduous forest in northeastern Venezuela. Abundance of site-attached and transient birds from different feeding guilds was determined by mist-netting at 2-week intervals. Diets were investigated by regurgitated samples. The overall avifauna was characterized by a low number of species but they were present all year despite showing strong seasonal fluctuations in abundance. The number of bird species and individuals peaked before and after the reproductive period. These high values probably were associated with movement of species feeding on plant food during the late dry season and the post-breeding dispersion of juveniles. Bird richness and abundance were lowest during the breeding season and in the early dry season when food abundance was low. Birds from different feeding guilds showed distinct patterns of seasonal abundance which tended to be similar at all three sites. Transient birds represented a large portion of the avifauna, particularly in nectarivores, frugivores and granivores during the dry season. We used a canonical correspondence analysis to demonstrate that bird abundance was correlated with breeding activity, rainfall seasonality and food abundance, with the influence of each parameter varying according to feeding guilds, spatial behaviour of individuals and habitats. Despite a great turnover in the occurrence of the diverse food types available, species composition remained strikingly constant during the year, with birds responding to seasonal changes primarily through a generalist feeding habit and a highly variable rate of transience.     

Can human disturbance promote nestedness? A case study with breeding birds in urban habitat fragments

Several factors, singly or in combination, have proven relevant in promoting nestedness in animal communities (area, isolation, habitat structure, etc.); however, little empirical evidence exists about the role of human disturbance. The goal of this paper was to assess whether human disturbance (pedestrians) may affect bird species composition in such a way as to generate a nested distributional pattern. The study was conducted in an urban fragmented landscape, the city of Madrid, where wooded parks were suitable fragments for many bird species, and had different levels of human visitation. At the community level, the distribution of species was significantly nested in two consecutive breeding seasons. Using two different procedures ("temperature" and "departures" methods) to analyse causality in nestedness, I found that pedestrian rate, fragment size and the diversity of stems were significantly correlated to the nested pattern. When analysed simultaneously, and controlling for their independent effects, these factors still accounted for nestedness. Pedestrian rate was the only factor significantly associated with changes in species composition between years. At the individual species level, 74 and 41% of species were significantly nested in relation to pedestrian rate in 1997 and 1998, respectively; however, these percentages were independent of foraging substrate and body size. Besides the classic area and habitat diversity effects, human disturbance can also promote nestedness: locally, by restraining the time and space of foraging and breeding opportunities, thus reducing fragment suitability, and regionally, by increasing extinction and decreasing colonization probabilities in highly disturbed fragments.     

上海闵行区园林鸟类群落嵌套结构

城市中的园林绿地呈现斑块状分布,其栖息地特征与岛屿栖息地相似。2008年11月至2009年10月,对上海市闵行区内的7块城市绿地进行调查,记录雀形目鸟类的分布情况,并运用Nestedness temperature calculator软件,检验其群落结构是否符合嵌套结构。运用Arc GIS软件分析该地区的卫星图片,收集7块样地的面积、绿地盖度、水源距离和人为干扰程度等数据,结合实地调查所得到的数据,分析这一嵌套结构的形成原因和影响因素。结果显示：上海市闵行区城市绿地中的雀形目鸟类分布是显著的嵌套结构,园林面积、绿地面积和水源情况都对其嵌套结构有显著影响。但是与真正岛屿上存在的群落分布嵌套结构不同,人为干扰程度对这一结构也有非常明显的影响。基于上述结果可以看出,影响上海市园林鸟类的群落嵌套结构的主要原因是栖息地的结构和人为干扰程度。因此,建议在规划和建设城市公园和绿地时,应该偏重于面积较大,植被盖度和丰富度高,结构合理的园林,并且尽量减少人为干扰。     

BIODIVERSITY RESEARCH: Nestedness for different reasons: the distributions of birds,lizards and small mammals on islands of an inundated lake

Aim We examined whether the community compositions of birds, lizards and small mammals were nested in a fragmented landscape in the Thousand Island Lake, China. We also assessed whether the mechanisms influencing nestedness differed among these taxonomic groups. Location Thousand Island Lake, China. Methods Presence/absence matrices were compiled for birds (42 islands) and lizards (42 islands) using line‐transect methods, and for small mammals (14 islands) using live‐trapping methods from 2006 to 2009. Nestedness was analysed using BINMATNEST, and statistical significance was assessed using the conservative null model 3. We used Spearman rank correlations and partial Spearman rank correlations to examine associations of nestedness and habitat variables (area, isolation, habitat diversity and plant richness) as well as life‐history traits (body size, habitat specificity, geographical range size and area requirement) related to species extinction and immigration tendencies. Results The community compositions of birds, lizards and small mammals were all significantly nested, but the causal factors underlying nestedness differed among taxonomic groups. For birds, island area, habitat specificity and area requirement were significantly correlated with nestedness after controlling for other independent variables. For lizards, habitat heterogeneity was the single best correlate of nestedness. For small mammals, island area, habitat heterogeneity and habitat specificity were significantly correlated with nestedness. The nested patterns of birds, lizards and small mammals were not attributable to passive sampling or selective colonization. Main conclusions The processes influencing nested patterns differed among taxonomic groups. Nestedness of bird assemblages was driven by selective extinction, and lizard assemblage was caused by habitat nestedness, while nestedness of small mammals resulted from both selective extinction and habitat nestedness. Therefore, we should take taxonomic differences into account when analysing nestedness to develop conservation guidelines and refrain from using single taxa as surrogates for others.     

Revealing Beta-Diversity Patterns of Breeding Bird and Lizard Communities on Inundated Land-Bridge Islands by Separating the Turnover and Nestedness Components

Beta diversity describes changes in species composition among sites in a region and has particular relevance for explaining ecological patterns in fragmented habitats. However, it is difficult to reveal the mechanisms if broad sense beta-diversity indices (i.e. yielding identical values under nestedness and species replacement) are used. Partitioning beta diversity into turnover (caused by species replacement from site to site) and nestedness-resultant components (caused by nested species losses) could provide a unique way to understand the variation of species composition in fragmented habitats. Here, we collected occupancy data of breeding birds and lizards on land-bridge islands in an inundated lake in eastern China. We decomposed beta diversity of breeding bird and lizard communities into spatial turnover and nestedness-resultant components to assess their relative contributions and respective relationships to differences in island area, isolation, and habitat richness. Our results showed that spatial turnover contributed more to beta diversity than the nestedness-resultant component. The degree of isolation had no significant effect on overall beta diversity or its components, neither for breeding birds nor for lizards. In turn, in both groups the nestedness-resultant component increased with larger differences in island area and habitat richness, respectively, while turnover component decreased with them. The major difference among birds and lizards was a higher relevance of nestedness-resultant dissimilarity in lizards, suggesting that they are more prone to local extinctions derived from habitat fragmentation. The dominance of the spatial turnover component of beta diversity suggests that all islands have potential conservation value for breeding bird and lizard communities.     

黄淮平原农业景观不同生境鸟类多样性特征及年际动态

鸟类是地球生物多样性中的重要组成部分,在生态系统功能和服务中发挥着重要作用,是生态环境变化的重要指示物种。农业景观中的食虫鸟类提供了重要的虫害控制服务。当前,农业景观中鸟类多样性丧失加剧,为探讨鸟类多样性在各生境以及年际间的变化,以黄淮平原为研究区,在河流、湖泊、农田、村庄等生境中共设置20个样点。于2016-2019年连续4年在繁殖期采用样线法对鸟类进行多样性调查。调查结果显示：（1）共发现22922只个体,分属14目,38科,53属。从区系分布来看,各生境各年间均以广布种为主;从生态类群来看,鸣禽占绝对优势;从居留型来看,留鸟所占比例最高。（2）在食性组成上,从物种丰富度看,食虫鸟类有57种,约占总物种数的77%;从个体数来看,杂食性鸟类占比超52%。（3）物种丰富度、多样性和均匀度指数最高值均出现在湖泊或河流生境中。（4）鸟类群落相似性分析显示,各生境间鸟类群落均为中等相似程度;鸟类物种丰富度波动幅度在农田和村庄中呈逐年上升趋势。（5）物种多样性加性拆分分析显示,在生境尺度上,局地的α多样性是生物多样性的最重要组成,而从整个研究区来看,生境间的差异则更为重要。造成鸟类多样性时空差异的原因复杂多样,而生境异质性的增加和水域的存在对提高鸟类多样性是具有积极作用的。调查中超过77%的物种和40%的个体均为食虫鸟类,应当充分重视鸟类为区域农业景观提供的虫害控制服务。本研究可为区域鸟类多样性保护及鸟类提供的生态系统服务的提升管理提供理论基础和科学依据。     

Changes in timing, duration, and symmetry of molt of Hawaiian forest birds

Food limitation greatly affects bird breeding performance, but the effect of nutritive stress on molt has barely been investigated outside of laboratory settings. Here we show changes in molting patterns for an entire native Hawaiian bird community at 1650-1900 m elevation on the Island of Hawaii between 1989-1999 and 2000-2006, associated with severe food limitation throughout the year beginning in 2000. Young birds and adults of all species took longer to complete their molt, including months never or rarely used during the 1989-1999 decade. These included the cold winter months and even the early months of the following breeding season. In addition, more adults of most species initiated their molt one to two months earlier, during the breeding season. Suspended molt, indicated by birds temporarily not molting primary flight feathers during the months of peak primary molt, increased in prevalence. Food limitation reached the point where individuals of all species had asymmetric molt, with different primary flight feathers molted on each wing. These multiple changes in molt, unprecedented in birds, had survival consequences. Adult birds captured during January to March, 2000-2004, had lower survival in four of five species with little effect of extended molt. Extended molt may be adaptive for a nutrient stressed bird to survive warm temperatures but not cool winter temperatures that may obliterate the energy savings. The changing molt of Hawaiian birds has many implications for conservation and for understanding life history aspects of molt of tropical birds.     

Testing multiple assembly rule models in avian communities on islands of an inundated lake,Zhejiang Province,China

Aim A fundamental question in community ecology is whether general assembly rules determine the structure of natural communities. Although many types of assembly rules have been described, including Diamond’s assembly rules, constant body‐size ratios, favoured states, and nestedness, few studies have tested multiple assembly rule models simultaneously. Therefore, little is known about the relative importance of potential underlying factors such as interspecific competition, inter‐guild competition, selective extinction and habitat nestedness in structuring community composition. Here, we test the above four assembly rule models and examine the causal basis for the observed patterns using bird data collected on islands of an inundated lake. Location Thousand Island Lake, China. Methods  We collected data on presence–absence matrices, body size and functional groups for bird assemblages on 42 islands from 2007 to 2009. To test the above four assembly rule models, we used null model analyses to compare observed species co‐occurrence patterns, body‐size distributions and functional group distributions with randomly generated assemblages. To ensure that the results were not biased by the inclusion of species with extremely different ecologies, we conducted separate analyses for the entire assemblage and for various subset matrices classified according to foraging guilds. Results The bird assemblages did not support predictions by several competitively structured assembly rule models, including Diamond’s assembly rules, constant body‐size ratios, and favoured states. In contrast, bird assemblages were highly significantly nested and were apparently shaped by extinction processes mediated through area effects and habitat nestedness. The nestedness of bird assemblages was not a result of passive sampling or selective colonization. These results were very consistent, regardless of whether the entire assemblage or the subset matrices were analysed. Main conclusions Our results suggest that bird assemblages were shaped by extinction processes mediated through area effects and habitat nestedness, rather than by interspecific or inter‐guild competition. From a conservation point of view, our results indicate that we should protect both the largest islands with the most species‐rich communities and habitat‐rich islands in order to maximize the number of species preserved.     

千岛湖陆桥岛屿鸟类集团对栖息地片段化的敏感性及其季节变化

为探究千岛湖陆桥岛屿不同鸟类集团对栖息地片段化敏感性的差异和季节变化,于2009年4月—2012年1月鸟类繁殖季(4、5、6月)和冬季(11、12、1月)对千岛湖41个陆桥岛屿鸟类集团进行了研究。结果表明,冬季杂食鸟对片段化敏感性高于食虫鸟,繁殖季时二者无显著差异,繁殖季和冬季时下层鸟对片段化敏感性均高于林冠鸟,冬季留鸟对片段化敏感性高于候鸟,繁殖季则无显著差异。杂食鸟和留鸟对片段化敏感性存在季节差异,而食虫鸟、林冠鸟、下层鸟和候鸟对片段化敏感性均无季节差异。不同鸟类集团对栖息地片段化敏感性的差异和季节变化规律,有助于人们在栖息地管理和保护区设计时采取更有针对性的鸟类保护措施。     

SOME ASPECTS OF THE BEHAVIOUR OF THE WATTLED PLOVER AFRIBYX SENEGALLUS (LINNAEUS)

The question of how aridity might influence avian clutch size, through the influences of rainfall seasonality and environmental stochasticity (unpredictability), has received little attention. A marked east-west gradient in aridity across South Africa provides a unique opportunity to test for such influences. Using an extensive collection of nest records for 106 terrestrial bird species from the South African Nest Record Card Scheme, we tested three predictions related to rainfall seasonality and stochasticity. Analyses were conducted at two levels, the first examining each species independently, and the second grouping species into five dietary guilds. The first prediction, that clutch size should generally increase with higher rainfall seasonality (i.e. higher seasonal fluctuation of food availability), was supported, particularly in the most arid environments where food abundance is more closely linked to rainfall. Controlling for rainfall seasonality, the second prediction, that clutch size should generally decrease as a bet-hedging strategy in arid, stochastic environments, was also supported. Although the timing of the rainy season differs among regions in South Africa (winter, early summer, later summer, year-round), birds primarily nest during spring. The relative timing of rainfall and breeding is expected to have different consequences for seasonal variation in clutch size among rainfall regions. The third prediction, of different patterns of seasonal variation in clutch size between rainfall regions, was also supported. In the winter and early-summer rainfall regions, early-nesting birds (breeding with or soon after the rains) generally had a larger clutch size than late-nesting birds. In the late-summer rainfall region, early-nesting birds (breeding well before the rains) had a smaller clutch size than late-nesting birds.