Experimental refuges for migratory waterfowl in Danish wetlands. I. Baseline assessment of the disturbance effects of recreational activities

1. Potential human sources of disturbance, including fishing, sailing, windsurfing and different types of waterfowl hunting, are described and their effects on autumn-staging waterbirds, including mute swan, wigeon and coot, were examined at a coastal wetland in Denmark from 1985 to 1988.
2. Bird and human distributions were superimposed on the distribution of submerged vegetation and water depths to identify the extent of spatial overlap; likewise, seasonal and diurnal temporal overlap in bird abundance, and human activities were defined. Behavioural and distributional reactions of waterbirds to different human activities, in terms of escape distances, disruption of activity patterns and redistribution, were assessed to establish their relative effects.
3. Sailing and windsurfing showed little spatial overlap, and fishing partial spatial overlap with bird distributions; these activities almost ceased before the peak in autumn bird numbers. Hunting showed a high degree of spatial and temporal overlap with bird presence.
4. Birds responded to windsurfing at greatest distances, whereas hunting (especially from mobile punts) caused the longest disruptions to activities of waterfowl. In terms of behaviour and redistribution, wigeon was more affected by shooting than was mute swan or coot. One or two mobile shooting punts reduced wigeon numbers, whereas numbers were unaffected by the presence of up to 4–6 stationary punts; fishing boats had no effect on wigeon abundance.
5. Hunting, especially shooting from mobile punts, was identified as the most disturbing human activity in relation to staging waterfowl in this area. Similar results and conclusions were reached in another comparable study area. The results have implications for refuge designs and zoning of disturbing recreational activities.     

Multivariate analysis of a fine-scale breeding bird atlas using a geographical information system and partial canonical correspondence analysis: environmental and spatial effects

Aim To assess the relative roles of environment and space in driving bird species distribution and to identify relevant drivers of bird assemblage composition, in the case of a fine‐scale bird atlas data set. Location The study was carried out in southern Belgium using grid cells of 1 × 1 km, based on the distribution maps of the Oiseaux nicheurs de Famenne: Atlas de Lesse et Lomme which contains abundance for 103 bird species. Methods Species found in < 10% or > 90% of the atlas cells were omitted from the bird data set for the analysis. Each cell was characterized by 59 landscape metrics, quantifying its composition and spatial patterns, using a Geographical Information System. Partial canonical correspondence analysis was used to partition the variance of bird species matrix into independent components: (a) ‘pure’ environmental variation, (b) spatially‐structured environmental variation, (c) ‘pure’ spatial variation and (d) unexplained, non‐spatial variation. Results The variance partitioning method shows that the selected landscape metrics explain 27.5% of the variation, whilst ‘pure’ spatial and spatially‐structured environmental variables explain only a weak percentage of the variation in the bird species matrix (2.5% and 4%, respectively). Avian community composition is primarily related to the degree of urbanization and the amount and composition of forested and open areas. These variables explain more than half of the variation for three species and over one‐third of the variation for 12 species. Main conclusions The results seem to indicate that the majority of explained variation in species assemblages is attributable to local environmental factors. At such a fine spatial resolution, however, the method does not seem to be appropriated for detecting and extracting the spatial variation of assemblages. Consequently, the large amount of unexplained variation is probably because of missing spatial structures and ‘noise’ in species abundance data. Furthermore, it is possible that other relevant environmental factors, that were not taken into account in this study and which may operate at different spatial scales, can drive bird assemblage structure. As a large proportion of ecological variation can be shared by environment and space, the applied partitioning method was found to be useful when analysing multispecific atlas data, but it needs improvement to factor out all‐scale spatial components of this variation (the source of ‘false correlation’) and to bring out the ‘pure’ environmental variation for ecological interpretation.     

Distribution of specialist and generalist species along spatial gradients of habitat disturbance and fragmentation

In this paper, we tested whether the spatial distribution of a given species in more or less fragmented and disturbed landscapes depends on the species habitat specialization. We studied 891 spatial replicates from the French Breeding Bird Survey (FBBS) monitored at least two years during 2001–2005, and two independent landscape databases measuring respectively landscape fragmentation and recent landscape disturbance on each FBBS replicate. We used a continuous habitat specialization index for the 105 most common bird species monitored by the FBBS. We further modelled the spatial variation in abundance of each species according to fragmentation and disturbance across FBBS replicates, accounting for habitat differences and spatial trends. We then tested whether more or less specialized species responded to landscape fragmentation and disturbance. We found that the more specialist a species, the more negative its spatial response to landscape fragmentation and disturbance. Although there was a very high variation around these tendencies indicating that there are many other drivers of species distribution, our results suggest that measuring specialization may be helpful in predicting which species are likely to thrive in human degraded landscapes. We also emphasize the need to consider both positive and negative species responses when assessing consequences of habitat change in communities.     

Under‐representation of avian studies in landscape genetics

Landscape genetics is a rapidly growing discipline that examines how heterogeneous landscapes and other environmental factors influence population genetic variation. We conducted a systematic review of the landscape genetic literature which demonstrates that birds are severely under‐represented relative to their species diversity and general publication prevalence. Most avian studies were on species that have relatively low dispersal ability, and we suggest that this reflects an assumed high vagility of birds that precludes spatial genetic variation relatable to landscape heterogeneity. However, spatial genetic variation exists in several bird species with very high dispersal ability, but this has not been considered in the context of landscape features. Genetic patterns may also relate to landscape due to breeding habitat selection and territorial behaviour, despite the fact that species may be able to move throughout different landscape elements with minimal movement costs. Habitat loss and fragmentation are continuing globally and are strongly related to declines in bird populations. Landscape genetic studies provide a means to understand, predict and mitigate the effects of anthropogenic landscape change on birds. This review promotes the need for landscape genetic studies of birds, such that a greater understanding of the drivers of their genetic structuring can be developed and generalizations can be made from landscape genetic studies that apply more broadly across taxa.     

What drives the positive correlation between human population density and bird species richness in Australia?

Aim To test six hypotheses that could explain or mediate the positive correlation between human population density (HPD) and bird species richness while controlling for biased sampling effort. These hypotheses were labelled as follows: productivity (net primary productivity, NPP); inherent heterogeneity (diversity of vegetation types); anthropogenic heterogeneity (diversity of land uses); conservation policy (proportion of conservation land); increased productivity (human‐induced productivity increases); and the reduced‐slope hypothesis (which predicts that humans have a negative impact on species numbers across the full range of variation in HPD). Location Australia. Methods All data were collected at a spatial resolution of 1° across mainland Australia. Bird species richness was from 2007 atlas data and random subsampling was used to account for biased sampling effort. HPD was from the 2006 census. All other data were from government produced geographic information system layers. The most important biotic or abiotic factors influencing patterns in both species richness and HPD were assessed using simultaneous autoregressive models and an information theoretic approach. Results NPP appeared to be one of the main factors driving spatial congruence between bird species richness and HPD. Inherent habitat heterogeneity was weakly related to richness and HPD, although an interaction between heterogeneity and NPP indicated that the former may be an important determinant of species richness in low‐productivity regions. There was little evidence that anthropogenic landscape heterogeneity or human‐induced changes in productivity influenced the relationship between species richness and HPD, but conservation policy appeared to act as an important mediating factor and species richness was positively related to the proportion of conservation land only in regions of high HPD. Main conclusions The spatial congruence between bird species richness and HPD occurs because both respond positively to productivity and, in certain circumstances, habitat heterogeneity. Our results suggest that conservation policy could mediate this relationship, but further research is required to determine the importance of conservation reserves in supporting species in regions densely populated by humans.     

A Tanganyikan cichlid <Emphasis Type="Italic">Neolamprologus mustax</Emphasis> selectively exploits territories of another cichlid <Emphasis Type="Italic">Variabilichromis moorii</Emphasis> due to its inter-individual variation in aggression

Wetland restoration in highly modified landscapes involves balancing target ecosystem functions and values with constraints of landscape and stakeholder context. Often, a restored wetland complex cannot meet all target conditions simultaneously, and tradeoffs must be understood, evaluated, and quantified. We examined the tradeoff between providing migratory bird sanctuary and increasing public recreational opportunities within a restored floodplain wetland complex along the Illinois River. We surveyed the distribution and behavior of waterbirds in response to a gradient of spatial and temporal disturbances from waterbird hunting activities. Using ArcMap and spatial interpolation of waterbird densities as a novel approach to quantify sanctuary area, we estimated that approximately 42% of Emiquon Preserve functioned as sanctuary across disturbance intensities, hunter distribution, and time periods during autumn migration. Waterbird abundance did not increase with short-term temporal sanctuary or decreased hunting intensity. Disturbance distance around hunting locations was 752.1 m, overall, and increased 38.4 m for each additional hunting party. Exclusion distance around hunting locations was greater in areas with greater mean disturbance frequency. We question the effectiveness of short-term temporal sanctuary for waterbirds at the expense of recreational opportunities and advocate our analytical approach to quantify sanctuary area and disturbance buffers without experimentally causing disturbances.     

不同尺度下停歇点湿地对迁徙水鸟的影响研究综述

停歇点湿地是迁徙水鸟重要的能量补给地,在水鸟每年的往返迁徙过程中具有十分重要的生态意义。近年来随着全球变化和人类活动增加,迁飞路线上的停歇点湿地正发生剧烈变化。各个停歇点湿地的生境变化及周围环境不仅是影响水鸟栖息地适宜性的重要因素,还改变了各路线上迁徙水鸟的种群大小和群落多样性。分析不同尺度下停歇点湿地影响迁徙水鸟种群变化的主要生态因子和环境因素,不仅有助于理解各停歇点景观变化的生态效应,也可为迁徙水鸟种群保护提供理论支持。首先分析了在栖息地斑块尺度上停歇点湿地内的水、食物、栖息地格局和人类干扰等生态要素对水鸟觅食和栖息活动的影响;其次,分析了景观尺度上湿地周围的气候变化、土地利用和外来生物等环境条件在各停歇点对水鸟栖息地质量的改变;最后,基于多尺度条件下湿地影响因素的耦合效应,分析了当前湿地生境与水鸟种群关系研究中存在的主要问题,并总结了对湿地和水鸟保护的启示。     

Importance of gravel pits for the conservation of waterbirds in the Garonne river floodplain (southwest France)

The loss of natural wetlands throughout the World has made created habitats such as gravel pits, reservoirs or rice fields potentially important for waterbird conservation. In southwest France, the increasing abundance of gravel pits has allowed several bird species to colonize the region. The avian community was studied from 1996 to 1998 in six gravel pits in the Garonne floodplain. A total of 39 species of waterbirds were recorded, with higher abundance during the winter and post-breeding periods. We analyzed habitat use to identify key environmental factors determining the temporal and spatial distribution of the avian community. The presence of submerged macrophytes was found to be the most important factor influencing the distribution of waterbirds. The presence of paths in the vicinity of the areas reduced both the total number of birds and species richness owing to human disturbance. Gravel pits have an increasingly important role in the conservation of bird biodiversity. By controlling disturbance and management of vegetation, managers can enhance this role.     

海南岛霸王岭热带天然林景观中木本植物功能型分布的影响因素

为了探讨在热带天然林景观中不同因素对木本植物(限于乔木和灌木)功能型分布的影响,在对海南岛霸王岭的热带天然林进行样方调查的基础上,运用数量分类方法对热带天然林的木本植物进行了功能型划分,并运用冗余度分析(Redundancy analysis, RDA)分别探讨了功能型出现与否、功能型物种丰富度和功能型木本植物多度3个矩阵与环境、空间和干扰因素之间的关系。运用偏冗余度分析对影响功能型分布变化的环境、干扰、空间及其交互作用等因素进行了定量分解。结果表明:利用木材密度和潜在最大高度两个指标划分出的9个功能型,能较好的区分功能型间对生境的适应响应差异;因子分解表明,纯环境、纯人为干扰和混合的环境-人为干扰是影响3个功能型矩阵分布变化的主要因素,纯空间和与空间位置相耦合的因素相对较低;在诸多因子中,干扰类型、地形因子、土壤类型、砂砾含量、土层厚度以及经纬度坐标是影响功能型分布变化的主导因子;RDA排序分析表明,一般来讲,硬木功能型多在生境条件好和远离人为干扰的立地高发生。软木功能型则更多地出现于生境条件恶劣和人为干扰频繁的立地。而中等硬度功能型则生态幅度较宽。但除了软木灌木功能型外,其它功能型物种丰富度和木本植物多度多在土层深厚和生境条件较好的立地较高。     

Community structure and association of waterbirds with spatial heterogeneity in the Bahia Magdalena-Almejas wetland complex, Baja California Sur, Mexico

Community structure and association of waterbirds with spatial heterogeneity in the Bahia Magdalena-Almejas wetland complex, Baja California Sur, Mexico. To test the hypothesis that spatial heterogeneity determines waterbird diversity in a coastal wetland, we compared waterbird density, diversity, and species composition among various habitats and landscapes units in Bahia Magdalena-Almejas, Baja California Sur, Mexico. Based on diversity patterns and bird distribution, we assessed the effect of coastal development on the waterbird community structure. To gather information on habitat features and waterbird populations we conducted waterbird censuses in 329 habitat segments along the internal coastline of the study area, from February 2002 to February 2003. We performed non-parametric analyses to test the null hypothesis of no diference on waterbird density, and diversity among landscape units and seasons. The species composition was evaluated using ordination techniques. Waterbird density was higher in winter and autumn in the three lagoons of the study area, particularly in the insular coast, sandy beach and dunes; it was higher in the few segments of antropic sustrate. Diversity was significantly higher in mangrove habitat along the peninsular coast, and in mangrove-dunes association on the insular coast. Although modification of coastal natural habitat and boat transit disturbance had no influence on waterbird density or diversity, the highest richness of waterbirds occurred in well preserved areas. Species composition analysis showed differences between Santo Domingo Channel and Magdalena Bay. Pelagic and mangrove habitat had a species composition difference higher than those associations in other habitats. Such differences in species assemblages by habitat and landscape units suggest that communities are structured according to the range of available natural resources in structurally complex habitats, and that dominant piscivorous waterbird species were favored in this community.     

Increased behavioural responses to human disturbance in breeding Burrowing Owls Athene cunicularia

Human disturbance may have several negative impacts on bird biology. Although some species may habituate to human presence, other species do not show any signs of habituation, and may even be sensitized or affected by human disturbance. Furthermore, anthropogenic effects on bird behaviour rarely have been explored to address the alteration of frequencies of aggressive and fear‐associated behaviours. Such behavioural approaches may provide substantial data for bird conservation and management. Therefore, we assessed whether human disturbance disrupts the normal behaviour of Burrowing Owls Athene cunicularia. Specifically, we assessed whether guarding parents exhibited aggressive and fearful behaviours differentially in areas where human contact was more common. Burrowing Owls showed increased frequencies of threat displays in sites with more people walking by the nests, but not fear behaviours. These results suggest that different domains of behaviour (aggression vs. fear) may respond differently to human disturbance. We highlight the importance of quantifying a wide range of behavioural acts as indicators of bird stress in studies of anthropogenic impact.     

Study of spatial components of forest cover using partial Mantel tests and path analysis

Abstract. Plant species distributions are generally thought to be chiefly under environmental control, although they may be affected by disturbance events or dispersion properties of the species. The relative importance of these different factors is not easy to evaluate because they often share common spatial patterns, such that an inextricable network of relationships occurs between plant distributions, environmental conditions, disturbance events and endogenous factors such as propagule dispersion. In this paper we propose a method for untangling the common spatial component from the relationship between environmental conditions and the distribution of tree species. Using partial Mantel tests and path analysis, we test models of relationships between these data sets. Results show that in our study area, spatial patterns of species associated with hydric conditions remain largely correlated with environmental conditions. However, mesic sites show more complex forest covers, in which a significant spatial component persists when environmental variation is statistically controlled for. This remaining spatial variability suggests that other factors possessing spatial structure partly explain species distributions.     

宏生态尺度上景观破碎化对物种丰富度的影响

生物多样性的地理格局及其形成机制是宏生态学与生物地理学的研究热点。大量研究表明,景观尺度上的生境破碎化对物种多样性的分布格局具有重要作用,但目前尚不清楚这种作用是否足以在宏生态尺度上对生物多样性地理格局产生显著影响。利用中国大陆鸟类和哺乳动物的物种分布数据,在100 km×100 km网格的基础上生成了这两个类群生物的物种丰富度地理格局,进一步利用普通最小二乘法模型和空间自回归模型研究了物种丰富度与气候、生境异质性、景观破碎化的相关关系。结果表明,景观破碎化因子与鸟类和哺乳动物的物种丰富度都具有显著的关联关系,其方差贡献率可达约30%—50%(非空间模型)和60%—80%(空间模型),略低于或接近于气候和生境异质性因子。方差分解结果显示,景观破碎化因子与气候和生境异质性因子的方差贡献率的重叠部分达20%—40%。相对鸟类而言,景观破碎化对哺乳动物物种丰富度的地理格局具有更高的解释率。     

Functional biotic homogenization of bird communities in disturbed landscapes

Aim  Worldwide, functional homogenization is now considered to be one of the most prominent forms of biotic impoverishment induced by current global changes. Yet this process has hardly been quantified on a large scale through simple indices, and the connection between landscape disturbance and functional homogenization has hardly been established. Here we test whether changes in land use and landscape fragmentation are associated with functional homogenization of bird communities at a national scale.
Location  France.
Methods  We estimated functional homogenization of a community as the average specialization of the species present in that community. We studied the spatial variation of this community specialization index (CSI) using 1028 replicates from the French Breeding Bird Survey along spatial gradients of landscape fragmentation and recent landscape disturbance, measured independently, and accounting for spatial autocorrelation.
Results  The CSI was very sensitive to both measures of environmental degradation: on average, 23% of the difference in the CSI values between two sample sites was attributed to the difference in fragmentation and the disturbance between sites. This negative correlation between CSI and sources of landscape degradation was consistent over various habitats and biogeographical zones.
Main conclusions  We demonstrate that the functional homogenization of bird communities is strongly positively correlated to landscape disturbance and fragmentation. We suggest that the CSI is particularly effective for measuring functional homogenization on both local and global scales for any sort of organism and with abundance or presence–absence data.     

Fragmentation, habitat composition and the dispersal/predation balance in interactions between the Mediterranean myrtle and avian frugivores

Human‐induced fragmentation and disturbance of natural habitats can shift abundance and composition of frugivore assemblages, which may alter patterns of frugivory and seed dispersal. However, despite their relevance to the functioning of ecosystems, plant‐frugivore interactions in fragmented areas have been to date poorly studied. I investigated spatial variation of avian frugivore assemblages and fruit removal by dispersers and predators from Mediterranean myrtle shrubs (Myrtus communis) in relation to the degree of fragmentation and habitat features of nine woodland patches (72 plants). The study was conducted within the chronically fragmented landscape of the Guadalquivir Valley (SW Spain), characterized by ~1% of woodland cover. Results showed that the abundance and composition of the disperser guild was not affected by fragmentation, habitat features or geographical location. However, individual species and groups of resident/migrant birds responded differently: whereas resident dispersers were more abundant in large patches, wintering dispersers were more abundant in fruit‐rich patches. Predator abundances were similar between patches, although the guild composition shifted with fragmentation. The proportion of myrtle fruits consumed by dispersers and predators varied greatly between patches, but did not depend on bird abundances. The geographical location of patches determined the presence or absence of interactions between myrtles and seed predators (six predated and three non‐predated patches), a fact that greatly influenced fruit dispersal success. Moreover, predation rates were lower (and dispersal rates higher) in large patches with fruit‐poor heterospecific environments (i.e. dominated by myrtle). Predator satiation and a higher preference for heterospecific fruits by dispersers may explain these patterns. These results show that 1) the frugivore assemblage in warm Mediterranean lowlands is mostly composed of fragmentation‐tolerant species that respond differently to landscape changes; and 2) that the feeding behaviour of both dispersers and predators influenced by local fruit availability may be of great importance for interpreting patterns of frugivory throughout the study area.     

The nest predator community of grassland birds responds to agroecosystem habitat at multiple scales

Nest predation is the leading cause of reproductive failure for grassland birds of conservation concern. Understanding variation in nest predation rates is complicated by the diverse assemblage of species known to prey on nests. As part of a long‐term study of grassland bird ecology, we monitored populations of predators known to prey on grassland bird nests. We used information theoretic approach to examine the predator community's association with habitat at multiple scales, including local vegetation structure of grassland patches, spatial attributes of grassland patches (size and shape), and landscape composition surrounding grassland patches (land cover within 400 and 1600 m). Our results confirmed that nest predators respond to habitat at multiple scales and different predator species respond to habitat in different ways. The most informative habitat models we selected included variability in local vegetation (CV in the density of forbs), local patch (area and edge‐to‐interior ratio), and landscape within a 1600 m buffer around grasslands (percent of land covered by human structures and development). As a separate question, we asked if models that incorporated information from multiple scales simultaneously might improve the ability to explain variation in the predator community. Multi‐ scale models were not consistently superior to models derived from variables focused at a single spatial scale. Our results suggest that minimizing human development on and surrounding conservation land and the management of the vegetation structure on grassland fragments both may benefit grassland birds by decreasing the risk of nest predation.     

Does energy availability influence classical patterns of spatial variation in exotic species richness?

Aim At macroecological scales, exotic species richness is frequently positively correlated with human population density. Such patterns are typically thought to arise because high human densities are associated with increased introduction effort and/or habitat modification and disturbance. Exotic and native species richness are also frequently positively correlated, although the causal mechanisms remain unclear. Energy availability frequently explains much of the variation in species richness and we test whether such species–energy relationships may influence the relationships of exotic species richness with human population density and native species richness. Location Great Britain. Methods We first investigate how spatial variation in the distributions of the 10 exotic bird species is related to energy availability. We then model exotic species richness using native avian species richness, human population density and energy availability as predictors. Species richness is modelled using two sets of models: one assumes independent errors and the other takes spatial correlation into account. Results The probability of each exotic species occurring, in a 10‐km quadrat, increases with energy availability. Exotic species richness is positively correlated with energy availability, human population density and native species richness in univariate tests. When taking energy availability into account, exotic species richness is negligibly influenced by human population density, but remains positively associated with native species richness. Main conclusions We provide one of the few demonstrations that energy availability exerts a strong positive influence on exotic species richness. Within our data, the positive relationship between exotic species richness and human population density probably arises because both variables increase with energy availability, and may be independent of the influence of human density on the probability of establishment. Positive correlations between exotic and native species richness remain when controlling for the influence of energy on species richness. The relevance of such a finding to the debate on the relationship between diversity and invasibility is discussed.     

BIODIVERSITY RESEARCH: Native and introduced fish species richness in Mediterranean streams: the role of multiple landscape influences

Aim To examine the role of multiple landscape factors on the species richness patterns of native and introduced freshwater fish. Location Mediterranean streams, south‐western Iberian Peninsula, Europe (c. 87,000 km²). Methods We used a dataset of fish occurrences from 436 stream sites. We quantified the incremental explanatory power of multiple landscape factors in native, introduced, and overall local species richness using regression analysis. First, we related variation in local species richness across river basins to regional species richness (here, the basin species pool), area and factors of climate and topography. Second, we related within‐river basin local species richness to site’s climate and topography, and spatial structure derived from Principal Coordinates of Neighbour Matrices approach, after testing for species richness spatial autocorrelation; predicted local richness was mapped. Results Patterns of local species richness across river basins were strongly associated with regional species richness for overall, native and introduced species; annual rainfall showed a significant incremental contribution to variation in introduced species richness only. Within river basins, environmental factors were associated with local richness for the three species groups, though their contributions to the total explained variation were inferior to those of spatial factors; rainfall seasonality and stream slope were the most consistent environmental correlates for all species groups, while the influence of spatial factors was most prevalent for native species. Main conclusions Landscape factors operating among and within river basins seem to play a relevant role in shaping local species richness of both native and introduced species, and may be contingent on basin‐specific contexts. Nevertheless, local factors, such as habitat characteristics and biotic interactions and human‐induced disturbances may also be at play. Multiscale approaches incorporating a multitude of factors are strongly encouraged to facilitate a deeper understanding of the biodiversity patterns of Mediterranean streams, and to promote more effective conservation and management strategies.     

Functional homogenization of bird communities along habitat gradients: accounting for niche multidimensionality

Aim To test whether functional homogenization of bird communities is promoted by anthropogenic landscape transformation, using specialization and habitat preference indices that account for the multidimensionality of niches. Location Catalonia, north‐east Iberian Peninsula. Methods We used data on bird species occurrences and landscape features in 2834 1‐km² squares. Three orthogonal landscape gradients, which were taken as niche dimensions, were defined by means of principal components analysis (PCA). Specialization and habitat preference indices were created for 103 terrestrial bird species on the basis of their frequency of occurrence variation along the landscape gradients. These indices, together with species rarity, were then averaged for bird communities. We then analysed the patterns of variation of communities’ mean specialization, mean rarity and mean habitat preference values along a gradient of agricultural–forest habitat mosaics. Results Wherever we found a significant variation in the degree of specialization along the agricultural–forest gradient, agricultural habitats held more specialized bird communities than did forest ones and bore, on average, rarer species. Thus, results contradicted our initial hypothesis that humanized areas would bear more functionally homogenized bird communities. Higher α‐diversity values tended to be associated with generalist communities and with those having rarer species. Main conclusions Estimations of bird community specialization for different niche dimensions can behave differently along certain landscape gradients, and some of these differences can be explained by the variation of mean habitat preferences. Thus, we argue that a multidimensional approach to assess average niche breadth of communities can be more informative than a unidimensional measure. Our results suggest that widespread land abandonment and current secondary forest expansion throughout the Mediterranean area are promoting functional homogenization of bird communities. It would be desirable to construct larger‐scale indicators of functional homogenization in order to monitor communities’ responses to widespread landscape changes.     

Land use changes affect distributional patterns of desert birds in the Baja California peninsula, Mexico

Reliable plans for desert bird conservation will depend on accurate prediction of habitat change effects on their distribution and abundance patterns. Predictive models can help highlight relationships between human‐related and other environmental variables and the presence of desert bird species. Presence/absence of 30 desert bird species of Baja California peninsula was modelled on the basis of explanatory variables taken from the field, maps, and digital imagery. Generalized linear models were fit to each bird species using both variables representing human activity and other environmental factors as predictors that might influence distribution. Probability of species presence was used as a habitat suitability index to evaluate the effect of human activity when the model contained a significant human activity variable. No differences were found in bird species richness between natural sites and those transformed by agriculture or urbanization. Of 59 bird species recorded in surveys, 34% were positively or negatively associated with human‐transformed habitats. Fourteen species seem to benefit from transformation of natural vegetation by agriculture or urbanization, while six were negatively affected. Sensitivity analyses of final models indicated all were robust. Results suggest that the occurrence of a large percentage of bird species inhabiting scrub habitats is sensitive to human habitat transformation. This finding has important conservation implications at regional scale as fragmentation and conversion of desert ecosystems into agricultural and urban areas affect the distribution of species that are highly selective for scrub habitat. Land use and anthropogenic activities seem to change ecological patterns at large spatial scales, but other factors could drive species richness distribution too (i.e. individual species response, species–energy relationships). The spatial modelling approach at regional scale used in this study can be useful for designing natural resource management plans in the Sonoran desert scrub.