The impact of urbanization on taxonomic and functional similarity among bird communities

Aim To assess spatial relationships between avian community similarity and level of urbanization. We tested the following hypotheses for taxonomic similarity: Hypothesis A – the decline in taxonomic similarity with distance is stronger for the least urbanized locations compared to the most urbanized locations; Hypothesis B – the converse of Hypothesis A; and Hypothesis C – the decline in taxonomic similarity with distance is stronger for the most and least urbanized locations compared to locations with intermediate levels of urbanization. We also determined if increasing urbanization led to increased functional similarity within bird communities. Location South‐eastern Australia. Methods Bird species occurrence and density were sampled across 18 towns and 72 neighbourhoods occupying a spatial gradient of up to 882 km. We calculated pairwise values in taxonomic similarity among each town and neighbourhood using the Sørenson coefficient and a similarity measure that accounts for differences in species richness among locations. These values were plotted against pairwise distances among towns and neighbourhoods using linear regression to measure similarity–distance relationships. Neighbourhoods were categorized into four levels of urban development based on dwelling density, urban intensity, vegetation cover, or the density of native, nectar‐rich plants. Variation in bird species density across neighbourhoods and frequency of occurrence across broad habitat types (habitat specialization) was used to assess functional similarity of bird communities in each neighbourhood. Results Among the 18 towns, the decline in taxonomic similarity with distance was weak and significantly less than among regional bird communities that occurred within a 1° grid square around each town. Among the 72 neighbourhoods, similarity–distance relationships differed substantially depending on the level of urban development. Generally, the strongest decline in similarity with distance was for neighbourhoods with the highest and lowest dwelling density, urban intensity and vegetation cover, supporting Hypothesis C. The functional similarity of bird communities increased significantly with dwelling density, and decreased significantly with an increasing density of nectar plants. Main conclusions At the town level, urbanization appears to homogenize regional bird communities. Among neighbourhoods, similarity–distance relationships are substantially influenced by the level of urban development, and increasing urbanization leads to greater functional similarity within bird communities.     

Urban nectarivorous bird communities in Cape Town,South Africa,are structured by ecological generalisation and resource distribution

Biological communities are increasingly faced with novel urban habitats and their response may depend on a combination of biological and habitat traits. The response of pollinator species to urban habitats are of particular importance because all species involved in the pollination mutualism may be affected. Nectarivorous bird communities worldwide show varying tolerances to urban areas, but studies from Africa are lacking. We investigated nectarivorous bird communities in a medium‐sized South African city and asked which biological and garden traits best predict the community assembly of specialist and opportunistic nectarivorous birds. Information was collected on garden traits and the frequency of nine nectarivorous bird species for 193 gardens by means of a questionnaire. Information on biological traits of birds was obtained from published literature. Habitat generalism and tree nesting were identified as the most important biological traits influencing bird occurrence in gardens. A greater diversity of indigenous bird‐pollinated plants and the presence of sugar water feeders increased the numbers of nectar specialist birds and species richness of nectarivorous birds. While bird baths increased the species richness of nectar specialist birds, opportunistic birds’ urban adjustment was further facilitated by large vegetated areas in gardens and limited by the distance to the nearest natural habitat. In conclusion, though some biological traits and dispersal barriers seem to limit urban adjustment, a combination of natural and artificial nectar resource provisioning could facilitate this adjustment.     

Responses of nectar‐feeding birds to floral resources at multiple spatial scales

The responses of animal pollinators to the spatially heterogeneous distribution of floral resources are important for plant reproduction, especially in species‐rich plant communities. We explore how responses of pollinators to floral resources varied across multiple spatial scales and studied the responses of two nectarivorous bird species (Cape sugarbird Promerops cafer, orange‐breasted sunbird Anthobaphes violacea) to resource distributions provided by communities of co‐flowering Protea species (Proteaceae) in South African fynbos. We used highly resolved maps of about 125 000 Protea plants at 27 sites and estimated the seasonal dynamics of standing crop of nectar sugar for each plant to describe the spatiotemporal distribution of floral resources. We recorded avian population sizes and the rates of bird visits to > 1300 focal plants to assess the responses of nectarivorous birds to floral resources at different spatial scales. The population sizes of the two bird species responded positively to the amount of sugar resources at the site scale. Within sites, the effects of floral resources on pollinator visits to plants varied across scales and depended on the resources provided by individual plants. At large scales (radii > 25 m around focal plants), high sugar density decreased per‐plant visitation rates, i.e. plants competed for animal pollinators. At small scales (radii < 5 m around focal plants), we observed either competition or facilitation for pollinators between plants, depending on the sugar amount offered by individual focal plants. In plants with copious sugar, per‐plant visitation rates increased with increasing local sugar density, but visitation rates decreased in plants with little sugar. Our study underlines the importance of scale‐dependent responses of pollinators to floral resources and reveals that pollinators’ responses depend on the interplay between individual floral resources and local resource neighbourhood.     

Garden bird feeding predicts the structure of urban avian assemblages

Households across the developed world cumulatively spend many millions of dollars annually on feeding garden birds. While beneficial effects on avian assemblages are frequently claimed, the relationships between levels of garden bird feeding and local avian populations are unknown. Using data from a large UK city, we show that both avian species richness and abundance vary across different socioeconomic neighbourhood types. We examined whether patterns in bird feeding could explain this variation. The density of bird feeding stations across the urban environment was strongly positively related to avian abundance, after controlling for differences in habitat availability. This effect was almost exclusively driven by the abundance of those species known to utilize garden feeding stations frequently. In contrast, the density of feeding stations had no effect on avian species richness. We also examined variation in the proportion of households in different communities that provide food for birds, a factor that is not correlated with feeder density. The prevalence of bird feeding across different neighbourhoods declined as socioeconomic deprivation increased, and increased with avian species richness and abundance. Our results suggest that the provision of supplementary food for birds by multiple landowners across a city can impact the status of urban bird populations. The potential for harnessing these actions for conservation needs to be explored.     

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.     

The community structure of bird assemblages on urban strangler figs

Figs have been regarded as keystone plant resources that support diverse tropical vertebrate frugivore communities. Planting or conserving large fig trees, such as stranglers, have therefore been proposed for enhancing urban biodiversity. We compared the diversity and community structure of bird assemblages on strangler figs with non‐fig urban trees as well as between the fruiting and non‐fruiting fig trees in an urban setting in Singapore. The total bird abundance across all the fig trees when in fruit was 4.5‐fold higher than on non‐fig trees and 3.5‐fold higher than when the same fig trees were not fruiting, but only attracted two more species. On individual trees, after accounting for the presence of mistletoes, tree height, the area covered by buildings, road lane density, and the distance to natural vegetation, mean diversity was not different between non‐fig trees and fig trees when they were not in fruit. On the other hand, when fruiting, each fig tree on average had 1.4 more species, 3 more counts of non‐native birds, and 1.6 more counts of insectivorous birds than when not fruiting. There was significant compositional turnover between non‐fig trees and non‐fruiting fig trees, while community dispersion was significantly lower among fig trees in fruit. Our results demonstrate that fig trees provide fruit and non‐fruit resources for birds in an urban landscape but do not necessarily support more diverse total bird assemblages than non‐fig trees. Instead, bird communities on fruiting urban figs would be highly homogeneous and dominated by a few species. Abstract in Malay is available with online material.     

Habitat selection of breeding riparian birds in an urban environment: untangling the relative importance of biophysical elements and spatial scale

Aim Urbanization is a leading threat to global biodiversity, yet little is known about how the spatial arrangement and composition of biophysical elements – buildings and vegetation – within a metropolitan area influence habitat selection. Here, we ask: what is the relative importance of the structure and composition of these elements on bird species across multiple spatial scales? Location The temperate metropolitan area of Cincinnati, Ohio, USA. Methods We surveyed breeding birds on 71 plots along an urban gradient. We modelled relative density for 48 bird species in relation to local woody vegetation composition and structure and to tree cover, grass cover and building density within 50–1000 m of each plot. We used an information‐theoretic approach to compare models and variables. Results At the proximate scale, native tree and understory stem frequency were the most important vegetation variables explaining bird distributions. Species’ responses to landscape biophysical features and spatial scales varied. Most native species responded positively to vegetation measures and negatively to building density. Models combining both local vegetation and landscape information represented best or competitive models for the majority of species, while models containing only local vegetation characteristics were rarely competitive. Smaller spatial scales (≤ 500 m) were most important for 36 species, and eight species had best models at larger scales (> 500 m); however, several species had competitive models across multiple scales. Main conclusions Habitat selection by birds within the urban matrix is the result of a combination of factors operating at both proximate and broader spatial scales. Efforts to manage and design urban areas to benefit native birds require both fine‐scale (e.g., individual landowners and landscape design) and larger landscape actions (e.g., regional comprehensive planning).     

Exoskeletons and economics: indoor arthropod diversity increases in affluent neighbourhoods

In urban ecosystems, socioeconomics contribute to patterns of biodiversity. The ‘luxury effect’, in which wealthier neighbourhoods are more biologically diverse, has been observed for plants, birds, bats and lizards. Here, we used data from a survey of indoor arthropod diversity (defined throughout as family-level richness) from 50 urban houses and found that house size, surrounding vegetation, as well as mean neighbourhood income best predict the number of kinds of arthropods found indoors. Our finding, that homes in wealthier neighbourhoods host higher indoor arthropod diversity (consisting of primarily non-pest species), shows that the luxury effect can extend to the indoor environment. The effect of mean neighbourhood income on indoor arthropod diversity was particularly strong for individual houses that lacked high surrounding vegetation ground cover, suggesting that neighbourhood dynamics can compensate for local choices of homeowners. Our work suggests that the management of neighbourhoods and cities can have effects on biodiversity that can extend from trees and birds all the way to the arthropod life in bedrooms and basements.     

Bird and insect pollinators differ in specialization and potential pollination services along disturbance and resource gradients

Combined studies of the communities and interaction networks of bird and insect pollinators are rare, especially along environmental gradients. Here, we determined how disturbance by fire and variation in sugar resources shape pollinator communities and interactions between plants and their pollinating insects and birds. We recorded insect and bird visits to 21 Protea species across 21 study sites and for 2 years in Fynbos ecosystems in the Western Cape, South Africa. We recorded morphological traits of all pollinator species (41 insect and nine bird species). For each site, we obtained estimates of the time since the last fire (range: 2–25 calendar years) and the Protea nectar sugar amount per hectare (range: 74–62 000 g/ha). We tested how post-fire age and sugar amount influence the total interaction frequency, species richness and functional diversity of pollinator communities, as well as pollinator specialization (the effective number of plant partners) and potential pollination services (pollination service index) of insects and birds. We found little variation in the total interaction frequency, species richness and functional diversity of insect and bird pollinator communities, but insect species richness increased with post-fire age. Pollinator specialization and potential pollination services of insects and birds varied differently along the environmental gradients. Bird pollinators visited fewer Protea species at sites with high sugar amount, while there was no such trend for insects. Potential pollination services of insect pollinators to Protea species decreased with increasing post-fire age and resource amounts, whereas potential pollination services of birds remained constant along the environmental gradients. Despite little changes in pollinator communities, our analyses reveal that insect and bird pollinators differ in their specialization on Protea species and show distinct responses to disturbance and resource gradients. Our comparative study of bird and insect pollinators demonstrates that birds may be able to provide more stable pollination services than insects.     

Metropolitan lizards? Urbanization gradient and the density of lagartixas (Tropidurus hispidus) in a tropical city

Urbanization, with its cohort of environmental stressors, has a dramatic effect on wildlife, causing loss of biodiversity and decline in population abundance customarily associated with increasing levels of impervious surface and fragmentation of native habitats. Some studies suggest that faunal species from open habitats, and with higher abundance in natural environments, seem more likely to tolerate and live in urban environments. Here I evaluate how the level of urbanization affects lagartixas (Tropidurus hispidus) one of the most common lizards found in open vegetation ecosystems in NE Brazil. I surveyed a total of 47 transects across sites that differed in proportion of impervious surface (high, mild, peri‐urban, and rural). I also collected specific biotic (herbaceous cover, tree, and arthropod abundance) and abiotic (amount of shelters and impervious surfaces) factors that could affect lagartixas abundance. Ants were the most common arthropod both in the rural and urban environment. Lagartixas thrive in urban environments, and trees and shelter were key predictors of their abundance. Lagartixas show a clear association with use of artificial structures. The low densities of lagartixas in rural areas and higher density in urbanized areas suggest that they colonized urban areas due to the hard surfaces and they probably are not exploiting a novel habitat, but somewhat responding to conditions resembling those in which they evolved. Finally, lagartixas are extremely common in tropical cities, they have a suite of features that are associated with selective pressures in cities and they might play a key functional role in urban ecosystems making this lizard an excellent system for the study of ecology and adaptation to the urban environments.     

Does size really matter? Species–area relationships in human settlements

Aim To describe species–area relationships in human settlements and compare them with those from a non‐urban habitat. Location West‐central Mexico. Methods We surveyed breeding birds in 13 human settlements and five shrubland patches. We estimated bird species richness using an abundance‐based coverage estimator with equal sample sizes to eliminate biases related to sampling effort differences. To assess species–area relationships, we performed log–log linear regressions between the size of the studied patches and their estimated bird richness. We also used a logarithmic approach to determine how the species–area relationship asymptoted and made use of the Michaelis–Menten model to identify the size at which the studied patches reached their maximum species richness. We also investigated (1) possible relationships among the estimated bird richness and other variables known to affect urban‐dwelling birds (built cover, plant species richness, tree cover or human population density) and (2) changes in bird community composition related to the size of the studied human settlements. Results Species–area relationships exhibited different patterns among the studied habitats. The log–log regression slope was steeper in human settlements, while the intercept was higher in shrublands. The maximum number of species was more than twofold higher in shrublands. Human settlement patch size was the only variable significantly related to bird richness. Our community composition results show that two main bird groups are related to human settlement size, and that as the size of human settlements increases, bird community similarity in relation to the largest city increases. Main conclusions Human settlements act as ecological islands, with pronounced species–area relationships. Our results suggest that an important threshold for bird species richness and community composition is reached in human settlements > 10.2 km². This threshold is unlikely to be generalizable among bio‐regions, and thus should be quantified and considered when studying, managing and/or planning urban systems.     

Foraging Blue Tits Parus caeruleus may trade-off calorific value of food items and distance from cover

Capsule Flowers of an invasive plant species are more visited by native birds than flowers of ornithophilous endemic plants.

Aims To describe the bird guild and its behaviour visiting the century plant Agave americana in an insular environment and to determine which factors are affecting visitation rates.

Methods We noted number and species of birds visiting inflorescences on Tenerife, Canary Islands. We used multimodel inference of generalized linear models to analyse the factors affecting the number of visits and the visitor species richness.

Results Eighty-one per cent of inflorescences were visited by eight native bird species. All species fed on nectar and only the Atlantic Canary fed also on pollen. Foraging behaviour varied among species. Visitation rate increased with density and diversity of birds and flower characteristics and decreased through the day. The number of species visiting the inflorescences increased with diversity and density of birds in the surroundings and decreased through the day.

Conclusion The native bird community uses the invasive century plant as a feeding resource at a higher rate than it uses endemic ornithophilous plants. This could have negative effects for the pollination of endemic plants, but positive effects for birds.     

Flower visitation by birds in Europe

Most flowering plants depend on animal pollination. Several animal groups, including many birds, have specialized in exploiting floral nectar, while simultaneously pollinating the flowers they visit. These specialized pollinators are present in all continents except Europe and Antarctica, and thus, insects are often considered the only ecologically relevant pollinators in Europe. Nevertheless, generalist birds are also known to visit flowers, and several reports of flower visitation by birds in this continent prompted us to review available information in order to estimate its prevalence. We retrieved reports of flower–bird interactions from 62 publications. Forty‐six bird species visited the flowers of 95 plant species, 26 of these being exotic to Europe, yielding a total of 243 specific interactions. The ecological importance of bird–flower visitation in Europe is still unknown, particularly in terms of plant reproductive output, but effective pollination has been confirmed for several native and exotic plant species. We suggest nectar and pollen to be important food resources for several bird species, especially tits Cyanistes and Sylvia and Phylloscopus warblers during winter and spring. The prevalence of bird flower‐visitation, and thus potential bird pollination, is slightly more common in the Mediterranean basin, which is a stopover to many migrant bird species, which might actually increase their effectiveness as pollinators by promoting long‐distance pollen flow. We argue that research on bird pollination in Europe deserves further attention to explore its ecological and evolutionary relevance.     

Scale-dependent relationships between native richness, resource stability and exotic cover in dock fouling communities of Washington, USA

Aim In terrestrial plant communities, the relationship between native species diversity and exotic success is typically scale‐dependent. It is often proposed that within local neighbourhoods, high native diversity limits resources, thereby inhibiting exotic success. However, environmental variation that manifests over space or time can create positive correlations between native diversity and exotic success at larger scales. In marine habitats, there have been few multi‐scale surveys of this pattern, so it is unclear how diversity, resource limitation and the environment influence the success of exotic species in these systems. Location Washington, USA. Methods I analysed nested spatial and temporal surveys of fouling communities, which are assemblages of sessile marine invertebrates, to test whether the relationships between native richness, resource availability and exotic cover supported the diversity‐stability and diversity‐resistance theories, to test whether these relationships changed with spatio‐temporal scale, and to explore the temperature preferences of native and exotic fouling species. Results Survey data failed to support diversity‐stability theory: space availability actually increased with native richness at the local neighbourhood scale, and neither space availability nor variability decreased with native richness across larger spatio‐temporal scales. I did find support for diversity‐resistance theory, as richness negatively correlated with exotic cover in local neighbourhoods. Unexpectedly, this negative correlation disappeared at intermediate scales, but emerged again at the regional scale. This scale‐dependent pattern could be partially explained by contrasting water temperature preferences of native and exotic species. Main conclusions Within local neighbourhoods, native diversity may inhibit exotic abundance, but the mechanism is unlikely related to resource limitation. At the largest scale, correlations suggest that native richness is higher in cooler environments, whereas exotic richness is higher in warmer environments. This large‐scale pattern contrasts with the typical plant community pattern, and has important implications for coastal management in the face of global climate change.     

Bird pollination syndrome is the plant's adaptation to ornithophily,but nectarivorous birds are not so selective

Many tropical plants are pollinated by birds and several bird phylogenetical lineages have specialised to a nectar diet. The long-assumed, intimate ecological and evolutionary relationship between ornithophilous plants and phenotypically specialised nectarivorous birds has nevertheless been questioned in recent decades, where such plant–pollinator interactions have been shown to be highly generalised. In our study, we analysed two extensive interaction datasets: bird–flower and insect–flower interactions, both collected on Mt Cameroon, west-central Africa. We tested if: 1) insects and birds interact with distinct groups of plants; 2) plants with a typical set of ornithophilous floral traits (i.e. bird pollination syndrome) interact mainly with birds; 3) birds favour plants with bird pollination syndrome and; 4) if and how the individual floral traits and plant level nectar production predict bird visitation. Bird-visited plants were typically also visited by insects, while approximately half of the plants were visited by insects only. We confirmed the validity of the bird pollination syndrome hypothesis, as plants with bird-pollination syndrome traits were visited by birds at a higher rate and mostly hosted a lower frequency of visiting insects. However, these ornithophilous plants were not more attractive than the other plants for nectar-feeding birds. Nectar production per plant individual was a better predictor of bird visitation than any other floral trait traditionally related to the bird pollination syndrome. Our study thus demonstrated the highly asymmetrical relationship between ornithophilous plants and nectarivorous birds.     

Foraging height and landscape context predict the relative abundance of bird species in urban vegetation patches

In Australian urban environments, revegetation and vegetation restoration are increasingly utilized conservation actions. Simple methods that help assess the utility of urban vegetation for bird species will help direct this effort for bird conservation purposes. We therefore examine whether ecological principles can be used to predict, a priori, the relative abundance of different bird species in urban vegetation. Our model proposes that a bird species will be in greater abundance where vegetation structure better reflects its foraging height requirements, and this relationship will be moderated by the landscape context of the patch. To quantify and test this model, we created an index to rank existing and revegetated urban vegetation sites in order of greatest expected abundance for each of 30 bird species. We tested this model, alongside two simpler models which consider landscape context and foraging height preferences alone, using bird abundance data from 20 woodland remnants and 20 revegetated sites in Brisbane, Australia. From these bird abundance data, we calculated the relative abundance of each species between the top‐ranking sites and lowest‐ranking sites. The model which incorporated both foraging height requirements and landscape context made predictions that were positively correlated with the data for 77% of species in remnant vegetation and 67% in revegetation. The results varied across species groups; for example, we achieved lower predictive success for canopy foraging species in the less mature revegetation sites. Overall, this model provided a reasonable level of predictive accuracy despite the diversity of factors which can influence species occurrence in urban landscapes. The model is generic and, subject to further testing, can be used to examine the effect of manipulating vegetation structure and landscape context on the abundance of different bird species in urban vegetation. This could provide a cost‐effective tool for directing urban restoration and revegetation efforts.     

Figs (Ficus,Moraceae) in Urban Hong Kong,South China1

Hong Kong (22°N) is on the northern margins of the Asian tropics and has a native fig flora of 24 species. A total of 3.4 km² of the urban area on Hong Kong Island was surveyed for spontaneous and planted fig plants of reproductive size. The 1124 individuals included 14 species in four subgenera: seven native species (F. fistulosa, F. hirta, F. hispida, F. microcarpa, F. pumila, F. subpisocarpa, and F. variegata), four of which were sometimes planted, one probably native (F. virens), one naturalizing species (F. religiosa), and five exotic species that occurred only in cultivation, two of which (F. altissima, F. rumphii) are pollinated and produce viable seeds. The native species in the two most common subgenera form distinct ecological guilds: those in subgenus Sycomorus bear large, many‐seeded, green or yellow figs and are bat‐dispersed pioneers on exposed soil; those in subgenus Urostigma bear small, few‐seeded, dark‐purple figs and are largely bird‐dispersed and epilithic. The density of potentially fruiting fig plants in the study area (2.3/ha) was within the range reported for tropical forests and between them they were visited by the entire urban frugivore fauna. This study shows the importance of the urban fig flora to urban wildlife and also highlights the risk of cultivated Ficus species becoming invasive, despite their obligate species‐specific pollinator mutualisms.     

Experimental evidence for specialized bird pollination in the endangered South African orchid Satyrium rhodanthum and analysis of associated floral traits

The bird pollination syndrome is characterized by red, unscented flowers with dilute nectar in long nectar tubes. However, the extent to which plants with such traits actually depend on birds for seed production is seldom determined experimentally, and traits such as colour and scent production are often assessed only subjectively. We documented bird pollination and quantified floral traits in the critically endangered Satyrium rhodanthum (Orchidaceae) from mistbelt grasslands in the summer‐rainfall region of South Africa. Direct observations and motion trigger camera footage revealed amethyst sunbirds as the only pollinators, despite the presence of other potential pollinators. Experimental exclusion of sunbirds significantly reduced pollination and fruit set to near zero. Pollination success in naturally pollinated plants was close to 100% in one year, and fruit set varied from 23 to 64% in other years. Pollen transfer efficiency was 5.8%, which is lower than in related insect‐pollinated species, probably due to a tendency of birds to wipe pollinaria from their beak. Flowers of S. rhodanthum only reflect light in the red range of the spectrum, and they produce only a few aliphatic and monoterpene scent compounds at comparatively low emission rates. Nectar volume and sugar concentration varied between 2.7 and 3.7 μL and 23.7 and 25.9%, respectively. We conclude that S. rhodanthum is highly specialized for pollination by sunbirds. Colour, scent and nectar characteristics differ from insect‐pollinated Satyrium species and are consistent with those expected for bird‐pollinated flowers, and may contribute to lack of visitation by other potential long‐tongued pollinators. Habitat loss probably underlies the critically endangered conservation status of S. rhodanthum, but the specialization for pollination by a single bird species means that reproduction in this orchid is vulnerable to losses in surrounding communities of plants that subsidize the energetic requirements of sunbirds. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 177 , 141–150.     

人为干扰对武汉市城市绿地鸟类群落结构的影响

城市绿地生态系统是城市景观的重要组成部分,具有重要的生态与文化价值。鸟类是城市绿地生态系统的指示类群,研究人类活动对鸟类资源的影响能够为城市生态景观的建设与维护提供重要理论依据。本研究于2021年10月至2022年5月,采用样线法对武汉市不同干扰强度的城市绿地内林鸟群落进行调查。共记录到鸟类11目34科100种,其中国家二级重点保护鸟类9种,在物种组成上以雀形目为主(76种,占调查到总鸟种数的76%),在居留型上以留鸟为主(42种,42%),在区系上主要属于东洋界(45种,45%)。繁殖季鸟类物种数高于非繁殖季,主要是由于夏候鸟和旅鸟的增加导致。在不同干扰强度中,重度干扰斑块的平均鸟类个体数最多,轻度干扰斑块的鸟类物种丰富度、多样性指数和均匀度指数最高,而中度干扰斑块的鸟类个体数、物种丰富度、多样性指数和均匀度指数均为最低,且繁殖季和非繁殖季鸟类群落结构在不同人为干扰强度中的格局未发生变化。综上所述,武汉市城市绿地的鸟类多样性较为丰富,随着干扰强度增加,鸟类多样性出现非线性差异,揭示了人为干扰与自然干扰对生态影响的差异;在面积狭小、破碎化严重的斑块中,人为干扰可能有利于城市绿地鸟类多样性的维持。