Seasonal changes in bird species diversity at the interface between forest and reed-bed

Habitat edges are landscape structures that have a major influence on animal communities. Bird communities' response to habitat edges is influenced by the season and habitat characteristics but it is still poorly understood how communities respond to structural complex (i.e. natural) edges. Inter-seasonal changes in bird species diversity were quantified at a homogeneous, sharp interface between two habitats that host distinct and well-represented bird communities: a mature broad-leaved forest and a compact reed-bed area. Resident species diversity was found higher during winter, both in terms of species richness and evenness. The presence of the reed-bed nesting migrants during the summer season did not notably modify the seasonally reversed diversity pattern; the overall evenness was higher during the winter season while the overall species richness did not differ between the two seasons. Thus, contrary to the expected regional seasonal diversity pattern, the forest – reed-bed interface is, in winter, a local bird diversity hotspot. The possible causes and implications for conservation of this phenomenon are discussed.     

Seed production in a threatened Aloe is not affected by bird exclusion or population size

Small populations of many plant species have been shown to exhibit ecological Allee effects. These effects are expected to be pronounced in plants which are obligate outcrossers and rely on pollinators which forage preferentially in larger populations with greater nectar availability. We examined the breeding and pollination systems, level of pollen limitation and seed production in populations of a threatened “ornithophilous” species, Aloe pruinosa. Experimental hand-pollinations showed that A. pruinosa is genetically self-incompatible and thus an obligate outcrosser. Experimental exclusion of birds from inflorescences did not affect seed production, suggesting that insects are effective pollinators. Supplemental hand-pollinations in several populations showed that seed production in A. pruinosa is not pollen limited. Further, there were no significant relationships between population size and any measure of reproductive success in this Aloe species. Small populations of A. pruinosa are thus viable in terms of pollination processes and should be protected from more direct threats, such as habitat alteration.     

Influences of ecology and biogeography on shaping the distributions of cryptic species: three bat tales in Iberia

To determine what shapes the distributions of cryptic species, we aimed to unravel ecological niches and geographical distributions of three cryptic bat species complexes in Iberia, Plecotus auritus/begognae, Myotis mystacinus/alcathoe and Eptesicus serotinus/isabellinus (with 44, 69, 66, 27, 121 and 216 records, respectively), considering ecological interactions and biogeographical patterns. Species distribution models (SDMs) were built using a presence‐only technique (Maxent), incorporating genetically identified species records with environmental variables (climate, habitat, topography). The most relevant variables for each species’ distribution and respective response curves were then determined. SDMs for each species were overlapped to assess the contact zones within each complex. Niche analyses were performed using niche metrics and spatial principal component analyses to study niche overlap and breadth. The Plecotus complex showed a parapatric distribution, although having similar biogeographical affinities (Eurosiberian), possibly explained by competitive exclusion. The Myotis complex also showed Eurosiberian affinities, with high overlap between niches and distribution, suggesting resource partitioning between species. Finally, E. serotinus was associated with Eurosiberian areas, while E. isabellinus occurred in Mediterranean areas, suggesting possible competition in their restricted contact zone. This study highlights the relevance of considering potential ecological interactions between similarly ecological species when assessing species distributions. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 ,150–162.     

Influence of body size on coexistence of bird species

Theory suggests that body size is an important factor in determining interspecific competition and, ultimately, in structuring ecological communities. However, there is a lack of pragmatic studies linking body size and interspecific competition to patterns in ecological communities. The objective of the present study was to determine the effect of body size (mass) on competitive interactions between bird pairs and to investigate the influence of food guilds. Point-counts were carried out in nine sites every month from November 2002 to November 2003 in the Cuetzalan Region, Mexico, and we used presence/absence and abundance data for the analyses. To calculate the strength of competition we used the Angle Frequency Method to extract form factors from 20 pairwise interactions. A prototype competition interaction and random pairs were also constructed. We used clustering techniques (PCA) to calculate the dissimilarity scores (distances, D) of each of the pairwise interactions to the prototype competition and random pairs and one-way ANOVA to test for differences between the means of the random and competitive pairs. The ratio in body mass (lnBM) for each of the interacting pairs was calculated, and the association between the lnBM ratio and the strength of competition (D) was tested using a Pearson product-moment correlation coefficient. To test for the influence of foraging guilds we used a univariate general linear model. Our results demonstrate a significant negative relationship between bird body mass ratio and competition strength – i.e. competition strength increased when the body masses of the birds became more similar. We did not find a significant influence of foraging guild on the relationship between body mass ratio and competition strength. On the basis of these results, we suggest that high variation in body sizes amongst sympatric species promotes coexistence in communities.     

Explaining bird species composition and richness in eucalypt-dominated remnants in subhumid Tasmania

Aim To determine the factors influencing the distribution of birds in remnants in a fragmented agricultural landscape. Location Forty‐seven eucalypt remnants and six sites in continuous forest in the subhumid Midlands region of Tasmania, Australia. Methods Sites were censused over a two‐year period, and environmental data were collected for remnants. The avifauna of the sites was classified and ordinated. The abundances of bird species, and bird species composition, richness, abundance and diversity were related to environmental variables, using simple correlation and modelling. Results There were two distinct groups of sample sites, which sharply differed in species composition, richness, diversity and bird abundance, separated on the presence/absence of noisy miner (Manorina melanocephala Latham) colonies, remnant size, vegetation structural attributes and variables that reflected disturbance history. The approximate remnant size threshold for the change from one group to another was 20–30 ha. Remnant species richness and diversity were most strongly explained by remnant area and noisy miner abundance, with contributions from structural and isolation attributes in the second case. Segment richness was explained by precipitation, logging history and noisy miner abundance. Bird abundance was positively related to precipitation and negatively related to tree dieback. The 28 individual bird species models were highly individualistic, with vegetation structural variables, noisy miner abundance, climatic variables, variables related to isolation, area, variables related to floristics, disturbance variables, the nature of the matrix and remnant shape all being components in declining order of incidence. Age of the remnant did not relate to any of the dependent variables. Main conclusions Degraded and small remnants may have become more distinct in their avifaunal characteristics than might otherwise be the case, as a result of the establishment of colonies of an aggressive native bird, the noisy miner. The area, isolation and shape of remnants directly relate to the abundance of relatively few species, compared to vegetation attributes, climate and the abundance of the noisy miner. The nature of the matrix is important in the response of some species to fragmentation.     

Multimodality in the individual size distributions of bird communities

Aim Body size often plays a significant role in community assembly through its impacts on the life history and ecological attributes of species. Insight into the importance of size in structuring communities can be gained by examining the distribution of sizes of individuals [i.e. the individual size distribution (ISD) or size spectrum] in a community. ISDs have been studied extensively in aquatic and tree communities, but have received little attention in terrestrial animal communities. Here, we conduct the first macroecological analysis of ISDs in terrestrial animal communities to determine whether they show broad‐scale consistency in shape. Location North America, north of Mexico. Methods Using likelihood‐based methods and Gaussian mixture modelling, coupled with data from the Breeding Bird Survey and Christmas Bird Count, we determine whether the ISDs for thousands of breeding and wintering North American bird communities are: (1) monotonically decreasing, (2) unimodal or (3) multimodal. Results We find that avian ISDs are consistently multimodal, with most characterized by more than five modes in both breeding and wintering communities from local to continental scales. In addition, the positions of these modes along the size axis are remarkably consistent. Main conclusions The striking consistency in the ISD within bird communities, as with tree and aquatic communities, indicates that the ISD is an important and informative characterization of resource utilization within an ecological assemblage. The differences in shape of the ISD among these groups also suggest that differences in body size‐related constraints affect interactions within a group and with the environment. Our results confirm that avian assemblages do exhibit structure along the body size axis, and therefore it will be fruitful to explore this pattern in greater detail.     

The maintenance of a positive spatial correlation between South African bird species richness and human population density

Aim To investigate explanations for the maintenance of a positive spatial species richness–human population density correlation at broad scales, despite the negative impact of humans on species richness. These are (hypotheses 1–4): (1) human activities that create a habitat mosaic and (2) a more favourable climate, and (3) adequate conservation measures (e.g. sufficient natural habitat), maintain the positive species richness–human density correlation; or (4) the full range of human densities decrease the slope of the correlation without changing its form. Location South Africa. Methods Avian species richness data from atlas distribution maps and human population density data derived from 2001 census results were converted to a quarter‐degree resolution. We investigated the number of land transformation types (anthropogenic habitat heterogeneity), irrigated area (increasing productivity), and other covarying factors (e.g. primary productivity) as predictors of species richness. We compared species richness–human density relationships among regions with different amounts of natural habitat, and investigated whether the full range of human densities decrease species richness in relation to primary productivity. Results Hypotheses 1, 2 and 3 were supported. Human densities and activities that increase habitat heterogeneity and productivity are important beneficial factors to common species, but not to rare species. The species richness–human density relationship persists only at low land transformation levels, and no significant relationship exists at higher levels. For common species, the relationship becomes non‐significant at lower land transformation levels than for rare species. Main conclusions The persistence of the species richness–human density relationship depends mostly on the amount of remaining natural habitat. In addition, certain human activities benefit especially common species. Common species seem to be more flexible than rare species in response to human activity and habitat loss.     

Protected areas alleviate climate change effects on northern bird species of conservation concern

Global climate change is a major threat to biodiversity, posing increasing pressures on species to adapt in situ or shift their ranges. A protected area network is one of the main instruments to alleviate the negative impacts of climate change. Importantly, protected area networks might be expected to enhance the resilience of regional populations of species of conservation concern, resulting in slower species loss in landscapes with a significant amount of protected habitat compared to unprotected landscapes. Based on national bird atlases compiled in 1974–1989 and 2006–2010, this study examines the recent range shifts in 90 forest, mire, marshland, and Arctic mountain heath bird species of conservation concern in Finland, as well as the changes in their species richness in protected versus unprotected areas. The trends emerging from the atlas data comparisons were also related to the earlier study dealing with predictions of distributional changes for these species for the time slice of 2051–2080, developed using bioclimatic envelope models (BEMs). Our results suggest that the observed changes in bird distributions are in the same direction as the BEM‐based predictions, resulting in a decrease in species richness of mire and Arctic mountain heath species and an increase in marshland species. The patterns of changes in species richness between the two time slices are in general parallel in protected and unprotected areas. However, importantly, protected areas maintained a higher level of species richness than unprotected areas. This finding provides support for the significance and resilience provision of protected area networks in preserving species of conservation concern under climate change.     

达赉湖自然保护区冬春季鸟类生物多样性与生境的关系

2004年4月-5月,利用样带法对达赉湖自然保护区5种主要生境类型中冬春季鸟类生物多样性进行了调查,利用Shannon-Wiener指数和Smith相关性系数分析了这5种生境类型中冬春季鸟类的生物多样性、区系、鸟类的群落组成、群落间的相似性和均匀度。结果表明,古北界鸟类是组成达赉湖鸟类群落的主体(约占冬春季鸟类的86%);芦苇湿地的鸟类多样性接近于芦苇甸的2倍:芦苇湿地鸟类群落的物种多样性最高(Shannon-Wiener指数为1.3001),而芦苇甸中鸟类群落的物种多样性最低(Shannon-Wiener指数为0.6629);芦苇湿地和芦苇甸两鸟类群落组成的相关性指数仅为0.038;从具有共同物种的多少考虑,典型草原和芨芨草原鸟类群落之间的关联较大。     

喜马拉雅山东段鸟类多度-垂直分布幅关系:特有种与非特有种的对比

物种多度与分布幅之间的正相关被认为是一种普遍的规律。但近年在热带山地和岛屿的研究发现多度-分布幅关系会出现不相关或负相关的现象;该现象可能是由于当地多度高且分布幅小的特有种比例较高所导致。在喜马拉雅山东段的勒布沟沿海拔2350—4950 m开展研究：1)记录了当地鸟类多度垂直分布格局;2)验证了该区繁殖鸟总体多度-垂直分布幅关系,并对比了特有种和非特有种分组子集多度-垂直分布幅关系、平均多度和垂直分布中心的差异。研究发现勒布沟鸟类多度垂直分布格局为驼峰格局。该区繁殖鸟类与非特有种的多度-垂直分布幅关系均为正相关,但特有种的多度-垂直分布幅关系为不相关。特有种的多度及海拔分布中心位置均高于非特有种。结果表明区域的鸟类特有性对多度-垂直分布幅关系存在着重要的影响;地理隔离导致的区域物种组成差异,是造成多度-分布幅关系模式变化的重要原因之一。     

Thermophysiology,microclimates, and species distributions of lizards in the mountains of the Brazilian Atlantic Forest

Thermophysiological traits, particularly thermal tolerances and sensitivity, are key to understanding how organisms are affected by environmental conditions. In the face of ongoing climate change, determining how physiological traits structure species’ ranges is especially important in tropical montane systems. In this study, we ask whether thermal sensitivity in physiological performance restricts montane lizards to high elevations and excludes them from the warmer environments reported at low elevations. For three montane lizard species in the Brazilian Atlantic Forest, we collect thermophysiological data from lizards in the highest elevation site of each species’ distribution, and ask how well the individuals exhibiting those traits would perform across the Atlantic Forest. We use microclimatic and organism‐specific models to directly relate environmental conditions to an organism's body temperature and physiological traits, and estimate measures of thermophysiological performance. Our findings demonstrate that thermophysiological constraints do not restrict montane lizards to high elevations in this system, and thus likely do not determine the warm boundaries of these montane species’ distributions. Results also suggest that competition may be important in limiting the warm boundaries of the species’ ranges for two of the focal species. These experimental results suggest that caution should be used when claiming that physiology drives patterns of diversity and endemism within montane environments. They also highlight the importance of interdisciplinary experimental studies that bridge the fields of evolution and ecology to improve predictions of biological responses to future environmental shifts.     

Tree species diversity in small, tropical riparian forest fragments in Belize, Central America

Tree species diversity was measured in a network of very small galleryforests within the Mountain Pine Ridge savanna in Belize. Research focussed onforest patches smaller than 1 ha in size (micro-forests) and linearstrips of trees along creeks lacking interior core zones with low understoreylight levels (tree thickets). Twenty-five micro-forests and 51 tree thicketsites were sampled throughout the savanna. A total of 144 morphospecies 5cm dbh (106 in micro-forests and 117 in tree thickets) werefound, which represents 1/5 of the approximately 700 native tree species in Belize.Most (85.3%) of the species encountered are typically found in tropical rainforests and few are restricted to savanna or riparian environments. Speciesaccumulated at a much faster rate in micro-forests than in tree thickets. Onlyone species, the palm Acoelorraphe wrightii, was extremelyabundant, accounting for almost 30% of all stems. Many of the species werepresent in very low densities: 19% of all species found in micro-forests and 42%of those found in tree thickets had on average one or fewer stems per hectare. Alarge proportion of species were also found infrequently across the landscape,being present in only 36% of micro-forests and at 52% of tree thicket sites. Theresults indicate that networks of very small forest patches can contain highnumbers of species and could therefore contribute to the maintenance of regionalbiodiversity.     

Invasion of Ligustrum lucidum (Oleaceae) in the southern Yungas: Changes in habitat properties and decline in bird diversity

Ligustrum lucidum is the major exotic tree in NW Argentina montane forests (Yungas). To assess the effects of its expanding invasion on avian communities we (1) measured different habitat properties (vertical forest structure and composition, vegetation cover, light availability, air temperature, air relative humidity and soil litter depth), (2) compared bird species composition and diversity in Ligustrum-dominated and native-dominated secondary forests and (3) analyzed seasonal patterns and changes in these variables between forest types. The study was conducted during 2010–2011 wet and dry seasons, at two altitudinal zones: 500–800 and 1100–1450 masl. Compared with native forests, Ligustrum dominated forests had a more homogeneous vertical forest structure and denser canopy cover (resulting in lower understory solar radiation), significantly lower understory cover and lower litter depth. Air temperature and relative humidity did not differ between forests in either season. Solar radiation was higher in the dry season in both forest types, but litter depth showed opposite patterns between seasons depending on forest type. We recorded 59 bird species in 21 families. Bird species abundance, richness and diversity indexes were significantly lower in Ligustrum-dominated relative to native forests of similar successional age, which had almost twice as many species as the former. Avian communities differed between altitudinal zones, but the difference was stronger between Ligustrum and native-dominated forests. Avian community composition was less variable in time and space in native forests than in Ligustrum-dominated ones. Our results suggest that L. lucidum invasion generates structurally homogeneous and simpler forests that represent a less suitable habitat for a diverse avifauna. This illustrates the wide ecological changes (from habitat properties and ecosystem functioning to vertebrate community composition) that the subtropical mountain forests of Argentina are experiencing with this invasion.     

The Chilean coastal range: a vanishing center of biodiversity and endemism in South American temperate rainforests

Temperate forests of southern South America are globally important because of their high level of endemism. I argue here that within southern South America, rainforests of the Chilean Coastal Range should be the primary target for new conservation efforts. Historically, most protected areas in southern South America have been designated to preserve forests above 600 m, mainly in the Andes. However, Coastal Range forests have higher species richness and are under greater threat than Andean forests at similar latitudes. Coastal forests are characterized by the presence of numerous narrow-range endemics, among them two monotypic plant families. The higher frequency of endemic species in Coastal Range forests is attributed to its more stable biogeographic history compared to the Andes, particularly during the glacial events of the Quaternary. Due to the extent of human impact, the remaining fragments of coastal forests are quite distant from one another, and are disconnected from the larger protected areas of Andean forests. Only 439000 ha of Valdivian coastal forest still remain, including some remnants of primary forest. New private or public reserves should be created to protect the last remnants of continuous forest remaining on the Coastal Range of the Valdivian region (40–42° S). A different conservation strategy should be applied north of 40° S, where protected areas are too small and fragments are too scattered to maintain viable populations of most vertebrates. In this latter area, I recommend expanding existing reserves, restoring native forests, and interconnecting remnant forests through a corridor network.     

Effects of bird predation on canopy arthropods in wandoo Eucalyptus wandoo woodland

Abstract: As top predators, birds may have significant effects on arthropod abundances and affect the trophic structure of arthropod communities through predation of lower order predators (e.g. spiders) and by competition for prey. We investigated the effects of bird predation on canopy arthropods in south‐western Australia by using plastic bird mesh to exclude insectivorous birds from the foliage of wandoo Eucalyptus wandoo saplings. Exclosure resulted in an increase in the number of herbivorous and predatory arthropods. Total arthropods (with and without ants), spiders, adult Coleoptera, and larval Lepidoptera were significantly more abundant on meshed than unmeshed saplings. All size‐classes of arthropods, taxa grouped, were more abundant on meshed than unmeshed saplings, but with no evidence of a disproportionate increase of the largest arthropods on meshed saplings. All size‐classes of spiders increased in abundance on saplings from which birds were excluded. There were significant differences in the total abundance of arthropods (with and without ants), spiders (Araneae), sucking bugs (Homoptera), adult beetles (Coleoptera), larval moths (Lepidoptera), and wasps and ants (Hymenoptera) for both unmeshed and meshed saplings between sample periods. These seasonal patterns of abundance and differences between sample periods appeared to be determined by seasonal weather patterns, with the lowest numbers associated with drier and hotter conditions in summer and autumn than in winter and spring. The conclusion reached is that eucalypt forest birds have limited effects on temporal variation in canopy arthropod abundances, but depress abundances, and affect the size and trophic composition of the fauna. Given the cascading effects of birds as predators on arthropods, successful conservation management of eucalypt ecosystems, including plantations and revegetation, should be planned to maximize bird numbers and diversity.