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1.
Anurans and birds rely on sound for a number of social behaviors. Species that use roadside habitats are exposed to traffic
noise that can mask important social signals and directly affect the community diversity and composition. We evaluate the
impact of traffic noise on anuran and bird species richness, species occurrence, and composition in Puerto Rico, where there
is a high density of highways and cars that generate high levels of noise pollution. We compared paired forest sites near
(100 m, n = 20, dB > 60) and far (>300 m, n = 20, dB < 60) from highways, with similar vegetation structure, but different levels of noise. We found that the anuran
community was not affected by traffic noise. In contrast, bird species richness and occurrence were significantly lower in
sites near the highway, and bird species composition also varied significantly. Bird species with low-frequency songs were
only detected in sites far from highways. The differences in the ecology and communication behavior between anurans and birds
could explain these results. Anurans mainly call at night, when traffic activity was low. In contrast, bird singing activity
occurs during the day and overlaps with the high levels of traffic noise. In addition, in natural habitats, Puerto Rican anurans
occur at high densities and form noisy choruses (>80 dB), which may allow them to tolerate high levels of anthropogenic noise. 相似文献
2.
Thrushes ( Turdus spp., Turdidae) are among the most common frugivorous birds in urban areas around the world, where they disperse the seeds
of a variety of plant species. We studied the abundance, habitat use, foraging behavior and diet of four thrush species ( Turdus rufiventris, T. amaurochalinus, T. leucomelas, and T. albicollis) in a suburban area in south Brazil. Abundance, habitat use and foraging behavior were based on birds surveyed along a 3,240 m
transect crossing open (formed by lawns, streets, and buildings) and forested areas. Diet was based on fecal samples collected
from mist-netted birds. Turdus rufiventris was the most abundant species, followed by T. amaurochalinus, T. leucomelas, and T. albicollis. All species used forest fragments more frequently than expected by chance. A total of 91.8% ( n = 147) of the fecal samples contained fruit remains, while 42.2% contained only animal matter. Most of the foraging records
were on the ground, where birds got mainly invertebrates. Fruits and invertebrates were eaten more frequently in open than
in forested areas. A total of 25 seed morfospecies were found in the droppings, including five exotic plant species. Thrushes
overlapped widely in the fruit composition of their diets. The high abundance and degree of frugivory, coupled with the frequent
use of forest patches, indicate that thrushes are among the great bird contributors to the seed dispersal occurring in urban
forest patches, potentially influencing the vegetation dynamics of such habitats so important for the maintenance of the biodiversity
in urban areas. 相似文献
3.
Residential development in urban and suburban settings is a major cause of habitat change affecting avian communities. The
effects from land-clearing prior to initiation of construction followed by landscaping focused on traditional aesthetics has
reduced habitat diversity at multiple levels. These residential developments generally emphasize the use of ornamental, nonindigenous
vegetation with little to no concern for native species and natural vegetation parameters. As a result, avian community composition
and diversity is changed. We compared avian communities at three sites in Bexar County, Texas; two residential neighborhoods
in the city of San Antonio and an unincorporated undeveloped site, Government Canyon State Natural Area. The residential neighborhoods
were a Texas Parks and Wildlife Department certified wildscapes development and a traditionally developed neighborhood. Bird
abundance and species richness in the neighborhoods were greater than at Government Canyon State Natural Area ( P < 0.01), but no differences existed between the neighborhoods. Bird diversity was greatest at the wildscapes neighborhood
( P < 0.01). Further, bird diversity did not differ between the traditional neighborhood and the natural area. Evenness differed
among sites ( P = 0.006) with the natural area having the greatest value. Bird diversity measures correlated with woody plant density and
vertical cover ( r = 0.358 to 0.673, P < 0.05) at residential sites. Residential areas incorporating natural landscapes into their design attracted a greater variety
of birds than traditionally landscaped residential areas. 相似文献
4.
Urban greenspaces harbouring many species in cities are vital planning objects for enhancing biodiversity. Seeking to optimise ecological values of urban greenspaces, this paper explores 1. Bird composition by feeding and foraging characteristics in urban greenspaces located in densely developed central districts of Taipei City; and 2. Important features of greenspaces and underlying built environments that influence bird abundance, species richness, and diversity. Results show that the majority of birds found in the study sites are omnivorous and ground foragers; whereas birds relying on water/wetland habitats for feeding and foraging are relatively small in population and species richness. This suggests water/wetland associated environments and birds might be negatively impacted by urbanisation. Secondly, bird richness and diversity increase in accordance with greenspace size, water area, and habitat heterogeneity, but little relationship is found with greenspace structure, such as greenspace shape, distance to nearest greenspaces, and proximity to source patches of mountains and rivers. Also, no significant influence is observed from development intensity, which is measured by NDBI, and building height at greenspace surroundings. According to this result, this study suggests conservation of large greenspaces as a priority strategy for enhancing urban biodiversity. The development of land should take its potential ecological value into account while assessing environmental impact. For enhancing habitat quality of existing urban greenspaces, creating water bodies and increasing habitat types can be effective methods. Yet current planning strategies to increase street greenery and to connect urban greenspaces with surrounding mountains and rivers might only benefit specific urban exploiters or adaptors and result in little overall effect on richness and diversity. 相似文献
5.
Cities are highly modified environments in which the only areas that resemble natural landscapes are urban parks with low
human population density. Attempts are frequently made to maintain high bird diversity in cities for aesthetic or educational
reasons. However, it remains unclear whether local site characteristics are important in determining bird assemblage composition
or whether simplification of the assemblage is an inevitable consequence of the changes associated with human population density.
From May 1998 to December 1999, we undertook bird counts at 521 points in Porto Alegre, Rio Grande do Sul, southern Brazil.
Our main goal was to understand the pattern of distribution of the bird species richness and density within the city and determine
which variables most affect species assemblages. We recorded 132 species belonging to 43 families that are common in Rio Grande
do Sul and obtained quantitative data on 121 species in survey sites. The two most abundant species (House Sparrow, Passer domesticus and Rock dove, Columba livia) were exotics. Analysis based on a reduced subset of 134 points surveyed in spring/early summer suggested that there was
a North–south gradient in assemblage structure. Variation in assemblage structure was also affected by the number of trees,
urban noise and human population density. However, human population density had a much smaller effect on richness and assemblage
structure than variables subject to management, such as tree density and noise levels. These results suggest that complex
communities may be maintained in densely populated urban areas of sub-tropical South-America given adequate urban planning. 相似文献
6.
Urbanization alters ecosystems worldwide, but little is known about its effects in the Neotropical region. In the present
research we examined the relative influence of different levels of urbanization and of some urban development measures on
bird species richness, abundance and composition. We surveyed 104 observation stations at which we collected data on the relative
abundance of bird species, and also data on seven environmental variables as measures of urban development and human activity.
We registered 57 native bird species. Bird species richness and bird abundance increased with lower urbanization levels. Both
variables were positively related to vegetation cover and native vegetation, and negatively to built-up cover, abundance of
Rock Pigeon ( Columa livia), pedestrian rate and car rate. A canonical correspondence analysis produced a significant model that explained 37% of the
total variation in species data. This analysis segregated bird species along two important gradients: urbanization and elevation.
The most urbanized areas were dominated by a few synanthropic species tolerant to human disturbance, such as Rufous-Collared
Sparrow ( Zonotrichia capensis), Eared Dove ( Zenaida auriculata) or Chiguanco Thrush ( Turdus chiguanco). Areas with lower urbanization levels had more species typically associated with native vegetation, such as Plain-Mantled
Tit-Spinetail ( Leptasthenura aegitaloides) or D’Orbigny’s Chat-Tyrant ( Ochthoeca oenanthoides), among others. Elevation had a significant influence in structuring bird communities, with some species restricted to higher
elevations and some to lower elevations. Although changes in elevation had an important influence, urbanization had a stronger
effect on structuring bird communities. This study provides valuable information and an important baseline for future studies. 相似文献
7.
There have been few studies investigating the relationship between the built environment and the status of bird distributions in small island tropical urban areas. We present a study investigating the relationship between bird species richness, abundance and assemblage to the built environment in Suva, Fiji. Field surveys were taken at 54 randomly selected sites throughout the city, stratified by three building density classes and the central business district (CBD). At each site bird counts were recorded, along with environmental data such as average building height, within a 150 m radius. Land-use information was obtained from screen digitized high-resolution satellite imagery within the same radius. Distance to undeveloped patches of land within the urban area was calculated using a GIS. Analysis of the effects of the built environment was carried out for all species, and for exotic and native species separately. Abundance of exotics was significantly higher in the central business district (CBD) than all other urban density classes, and significantly higher than natives in all other density classes. We found a negative relationship between native species richness and distance to undeveloped patches, but no relationship for exotics. Species assemblage was not related to urban density class. We conclude that the status of native and exotic bird species in Suva is similar to what has been found in urban areas in temperate climates, and conservation efforts should focus on minimizing the amount of heavily urbanized “core areas” and protecting undeveloped areas of forested vegetation to improve bird biodiversity in small tropical islands cities. 相似文献
8.
It is widely recognized that urbanization can affect ecological conditions in aquatic systems; numerous studies have identified
impervious surface cover as an indicator of urban intensity and as an index of development at the watershed, regional, and
national scale. Watershed percent imperviousness, a commonly understood urban metric was used as the basis for a generalized
watershed disturbance metric that, when applied in conjunction with weighted percent agriculture and percent grassland, predicted
stream biotic conditions based on Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness across a wide range of environmental
settings. Data were collected in streams that encompassed a wide range of watershed area (4.4–1,714 km 2), precipitation (38–204 cm/yr), and elevation (31–2,024 m) conditions. Nevertheless the simple 3-landcover disturbance metric
accounted for 58% of the variability in EPT richness based on the 261 nationwide sites. On the metropolitan area scale, relationship
r
2 ranged from 0.04 to 0.74. At disturbance values <15 the EPT rate of decrease was ∼10 times greater than at disturbance values
>15. Future work may incorporate watershed management practices within the disturbance metric, further increasing the management
applicability of the relation. Such relations developed on a regional or metropolitan area scale are likely to be stronger
than geographically generalized models; as found in these EPT richness relations. However, broad spatial models are able to
provide much needed understanding in unmonitored areas and provide initial guidance for stream potential. 相似文献
9.
Increased density, increased intraspecific aggression, and a reduced fear of humans have been suggested as the more observable
and frequently described characteristics of wildlife species undergoing synurbization, the process of becoming urbanized.
The relationship among these variables and how they may be related to environmental variables that change with urbanization
is poorly understood. In this paper we explore the relationship between density, intraspecific aggression, and reduced fear
of humans in urban populations of gray squirrel. In the summer and fall of 2003 and 2004, we studied a park with a documented
high density of gray squirrels, Lafayette Park, Washington, DC, and six urban parks in Baltimore, MD with unknown squirrel
densities. We used linear regression (SAS Institute, SAS/STAT user’s guide. SAS Institute, Cary, NC, 2005) to determine if there was a relationship ( P < 0.05) between squirrel density and intraspecific aggression, squirrel density and reduced fear of humans (wariness), and
squirrel density and habitat suitability. We found a positive association between density and intraspecific aggression ( R
2 = 0.81, P < 0.00). A negative relationship between density and wariness (, P < 0.00). However, no relationship was evident between habitat suitability and squirrel density (, P = 0.437). 相似文献
10.
The Neotropical region has been subjected to massive urbanization, which poses high risks for some global biodiversity hotspots and losses of ecosystem functions and services. In this study, we investigate how distance from large patches of native forests (source areas) and vegetation (green)/and infrastructure (gray) characteristics affect bird species richness and functional diversity in São Paulo megacity, southeastern Brazil. We analyzed the effects of source areas and green/gray characteristics on species richness and functional diversity (richness, evenness, and divergence) indices. We detected 231 bird species, and our data confirmed our predictions: (1) bird species richness in urbanized habitats was found to be (~?50–85%) lower than in source habitats; (2) species richness and trait composition significantly decreased as the distance from the source area increased, while functional richness was not affected by this metric; and (3) shrub and herbaceous covers and maximum height of trees were positively correlated with species richness and unique functional traits regarding habitat, diet, foraging and nesting strata and dispersal ability of birds in the forest-urban matrix. The number of buildings was negatively correlated with bird species richness and functional richness. Maximum height of buildings caused dramatic declines in functional evenness. Functional divergence was notably lower in sites with high shrub cover. Our study stresses the complexity of vegetation embedded in large Neotropical urban settlements and the need to maintain large protected areas surrounding megacities to mitigate the impacts of urbanization on birds. 相似文献
11.
At present, urban areas cover almost 3% of the Earth’s terrestrial area, and this proportion is constantly increasing. Although urbanization leads to a decline in biodiversity, at the same time it creates extensive habitats that are exploited by an assemblage of organisms, including birds. The species composition and density of birds nesting in towns and cities are determined by the types of buildings, the structure and maturity of urban greenery, and habitat diversity. In contrast, the habitat traits shaping the community of birds wintering in urban areas are not known. The aim of this work was to assess the influence of habitat structure, food resources and the urban effects (pollution, noise, artificial light) on an assemblage of birds overwintering in an urban area. It was carried out in 2014 and 2015 in the city of Kraków (southern Poland), on 56 randomly chosen sample plots, in which the composition, density and interseasonal similarity of bird assemblage were assessed with line transect method. A total of 64 bird species (mean = 17.7 ± 4.9 SD species/plot) was recorded. The mean density was 89.6 ind./km ±63.3 SD. The most numerous species were Great Tit Parus major, Magpie Pica pica, Blackbird Turdus merula, Blue Tit Cyanistes caeruleus, Rook Corvus frugilegus, Fieldfare Turdus pilaris and House Sparrow Passer domesticus. Noise adversely affected species numbers and density, but artificial light acted positively on the density of birds and their interseasonal stability. The species richness and density of birds were also determined by the number of food sources available (e.g. bird-feeders). In addition, the greater the proportion of open areas, the fewer species were recorded. In contrast, the more urban greenery there was, the greater the density of the entire bird assemblage. Urban infrastructure (buildings, roads, refuse tips) had a positive effect on the interseasonal stabilization of the species composition of wintering birds. The results of this work indicate that the urban effect, i.e. noise and light pollution, apart from purely habitat factors, provide a good explanation for the species richness, density and stability of bird assemblage wintering in urban areas. 相似文献
12.
Using a spatially extensive urban database constructed from the Maryland Biological Stream Survey (MBSS), we describe the
relationships of nutrients in small-order streams to eight defined categories of percent catchment urbanization, correlations
between chloride and conductivity in urban streams, and relationships between nutrients and chloride with two Maryland-specific
indices of biotic integrity for benthic macroinvertebrates and fish assemblages. Stream nutrients become elevated with increasing
percent catchment urbanization, followed by increases in all four measured nitrogen species and total phosphorus at catchment
urbanization levels greater than 10%. There was a strong collinear relationship ( r
2 = 0.90) between chloride and conductivity (trimeans) across all eight urbanization classes, where Cl (mg/L) = −0.397 + 0.188*conductivity
(μS/cm). Critical values for all water quality parameters with the two Maryland biological indices were derived using quantile
regression, with significant regressions developed for 11 of 16 water quality parameters and the two biotic indices. For nitrate
(NO 3-N), the critical thresholds between fair and poor stream quality for the two Maryland biological indices were 0.83 mg/L (benthic
macroinvertebrate assemblages) and 0.86 mg/L (fish assemblages). Increasing stream nutrient and chloride levels, associated
with widespread catchment urbanization intensity, now affect many small streams in Maryland, with implications for decreasing
water quality in major tributaries and the Chesapeake Bay. 相似文献
13.
With the continuing spread of urban areas, gaining a greater understanding of the effect of human presence on wildlife species
is essential for wildlife managers. We determined the influence of anthropogenic resources on home range size and habitat
selection of raccoons ( Procyon lotor) during summer (June–August) 1996–2000 for 120 raccoons at three sites exposed to varying levels of urbanization and anthropogenic
resources, specifically food. Home range estimates were larger ( P < 0.05) at the rural site than the suburban and urban sites for both genders. We used compositional analysis to examine raccoon
habitat selection at the second-order home range, second-order core area, and third-order home range scales. Woodland was
consistently a highly-selected habitat type for both sexes at every spatial scale. Relative to other habitat types, habitat
associated with human-related food (human use areas) was selected most often at the urban site, intermediately at the suburban
site, and not selected at the rural site. Spatial scale also affected habitat selection. Human use areas were preferentially
selected at the second- and third-order level at the urban site, third-order level only at the suburban site, and at neither
level at the rural site. Additionally, intersexual differences in habitat selection were reduced at the urban site, with both
sexes preferentially selecting for human use areas as well as woodland habitat. Smaller home ranges in urbanized environments
are often attributed to the abundant and concentrated anthropogenic resources associated with human activity, but with little
empirical support. Our habitat selection analyses followed our predictions that raccoon foraging is strongly influenced by
the artificial distribution and abundance of human-related food. Male and female raccoons in urban areas reduce their foraging
patterns and focus their foraging activity on anthropogenic foods. 相似文献
14.
Studies on bird fauna of urban environments have had a long history, but the potential of studies mapping the distribution
of birds in cities probably has not fully developed. The bird fauna of the municipality of Valencia (Spain) was studied to
determine the influence of urbanization on bird species richness and abundance. Birds were censused during winter and the
breeding season of years 1997–1998 in 197 squares measuring 49 ha each from a rural and an urbanized area. Across seasons
the number of species decreased around 40% in the city compared with the rural landscape surrounding it. Such pattern could
be attributed to the low number of farmland species capable to use the habitats inside the city, and the limited ability of
urban parks in attracting woodland species. In the urban landscape, the influence of the dimensions and spatial arrangement
of habitat patches was outweighed by the amount of each habitat per square. Bird richness and the abundance of most species
were negatively related with the amount of built-up habitat per square and positively with the amount of urban parks, and
of habitat diversity. Conversely, bird fauna was largely independent of mean park size per square especially during winter,
indicating that at the landscape scale even small patches of habitat could play an ecological role. Conservation of urban
bird diversity could benefit of two complementary strategies: (i) the protection of the surrounding rural landscape from urban
development; (ii) habitat enhancement within the city. Particularly, a proper design and habitat management of urban parks
could improve their suitability for urban bird fauna. 相似文献
15.
The purpose of this paper is to find out whether serum oxidizability potential measured before an exercise test (EXT) correlates
with age and ischemic heart disease severity. Oxidizability potential was determined in 3 age groups, in gr. I patients < 45 years,
in gr. II age range = 45 - 70years {\hbox{range}} = {45} - {7}0{\hbox{years}} , and in gr. III patients > 70 years. Included subjects had chronic ischemic heart disease (IHD) and underwent a symptom-limited
EXT upon initiation of a cardiac rehabilitation program. The thermo-chemiluminescence (TCL) assay was used to assess serum
oxidizability potential. This assay is based on heat-induced oxidation of serum, leading to the formation of electronically
excited species in the form of unstable carbonyls, which further decompose into stable carbonyls and light energy (low chemiluminescence).
Measured photons emission is represented by a kinetic curve which is described by its amplitude and slope (=ratio). We assessed
the correlations of TCL ratio with age, exercise duration, metabolic equivalents (METS), maximal heart rate (mHR), maximal
systolic BP, >1 mm S-T depression, diabetes, hypertension, smoking, left ventricular ejection fraction (LVEF)> or <40%, previous
myocardial infarction, and aorto-coronary bypass surgery. A high TCL ratio (%) correlated well with METS ( r = 0.82), mHR ( r = 0.77) and with exercise-induced S-T segment shift ( r = 0.86, p < 0.05). A lower serum oxidizability potential, expressed as a low TCL ratio, thus suggestive of a previous high oxidative
stress, was found in the two older age groups compared to gr. I (<45 years), p = 0.041, and in particular, in gr. III patients with low LVEF%. The TCL ratio (%) in gr. III was 188.7 ± 14.5, 192 ± 17 in
gr. II, and 214 ± 13 in gr. I ( p < 0.05), and was 166 ± 13.1 in gr. III with LVEF < 45% as compared to 271 ± 15.7 in gr. I patients with LVEF > 45% ( p < 0.01). A trend for lower TCL ratio (%) was found in diabetic, hypertensive, and post-coronary bypass surgery patients.
A paradoxically low TCL ratio (low oxidizability potential) was observed in patients without S-T depression compared to patients
with S-T depression (189 ± 22 vs. 201 ± 15, p = NS), due to the fact these patients had a much lower LVEF% and a lower exercise capacity. Serum oxidizability potential
is associated with age, EXT parameters, results, and IHD severity. TCL ratio is an “easy-to-measure marker” that might be
incorporated into risk assessment and prediction in aged IHD patients. 相似文献
16.
Considerable attention has been devoted to the effects of people and their vehicles on birds and mammals, but possible effects
on reptiles in populated areas have received less attention. Moreover, the effects of human activities on reptile reproductive
success itself has been harder to demonstrate. This paper examines the effect of management of off-road vehicles in New Jersey’s
pinelands on the reproductive success of pine snakes (Pituophus melanoleucus) from 1986 to 2005. We used the percentage of snakes in each hibernaculum that were young of the year (hatchlings) as an indicator
of reproductive success, and compared this percent for five hibernacula that were in an area with varying degrees of off-road
vehicle (ORV) disturbance, with 12 hibernacula in areas with no ORV disturbances (reference sites). This percent took into
account differences in absolute numbers from one location to another, and over time due to hibernacula destruction (by people
or predators) and natural variations (food supply). The ORV pressure in the pinelands is intense because it lies within the
most densely populated urban area in the United States. Although the number of snakes in the reference hibernacula varied
over the years from 46 to 63, the percent of young in these hibernacula did not vary significantly over the 20 year period
(21–29%). In contrast, the percent-young in the disturbed sites differed significantly in years without ORV disturbance (28%)
compared to those with ORV disturbance (15 and 16%, P < 0.01). Further, there were no differences between the percent of young in the reference sites and those in the disturbed
site in years without ORV disturbance. ORV disturbance ceased only with the creation of large dirt berms coupled with fences
that could not be easily broken. These data indicate the importance of having detailed population data on pine snakes in hibernacula,
on ORV use (or indications of such use), and of managing ORV use to protect sensitive populations. Maintenance of healthy
pine snake populations in urban areas may require continued adaptive management. 相似文献
17.
Urban marine habitats are often utilized by wildlife for foraging and other activities despite surrounding anthropogenic impact or disturbance. However little is known of the ecological factors that determine habitat value of these and other remnant natural habitats. We examined the preferential use of urban marine habitats in a northeast US estuary to try to elucidate the factors driving enhanced foraging activity at these sites. Using a bioenergetic model, we compared energy intake to energy expenditure and examined differences in behavior and foraging success of great egrets Ardea alba at three urban and three rural salt marshes in Narragansett Bay, Rhode Island USA. Mean per site available nekton energy averaged 4.44?±?0.97 GJ site ?1 and was significantly higher at urban than at rural sites. While energy expenditure by birds was similar across all sites, mean strike and prey capture rate were significantly greater at urban sites, and 70.1?±?12.2 % of strikes by egrets at urban sites were successful. Egrets foraging at urban sites consumed significantly more energy (23.2?±?6.62 W bird ?1) than those at rural sites. Model results indicated a net energy gain by egrets foraging at urban sites, versus a net energy loss at rural sites. Our results may help explain previously observed increases in the numbers of egrets foraging at urban marine habitats, and help provide input into decisions about the extent to which these areas should be considered for restoration or protection. 相似文献
18.
Urbanization and development are predicted to increase considerably in the United States over the next several decades, and
this is expected to result in large-scale habitat loss, fragmentation and loss of wildlife species. Thus, natural parks and
preserves are becomingly increasingly important in the conservation of regional biodiversity. We used mist-nets and AnabatII
acoustic detectors to survey bats in 10 national parks in the southeastern U.S. and examined the relationship between bat
community structure and development in the surrounding 5 km. We predicted that species richness would increase with park size
and that species richness and evenness would decrease with development. Species richness was not related to development or
any other landscape characteristics including park size. In contrast, species evenness declined with increasing development.
Percent Developed land in the surrounding 5 km area was the only variable that entered into the stepwise regression model.
The decrease in species evenness in the urban parks was due to the dominance of big brown bats ( Eptesicus fuscus) in these parks. The percentage of big brown bats in our captures was positively related to percent Developed land in the
surrounding area. Our data suggest that urban parks may be important for conserving regional bat biodiversity. However, the
low species evenness in these parks suggests that some bat species may be susceptible to the effects of urbanization and may
be extirpated over time. Thus, management of urban as well as rural parks should strive to conserve as much bat roosting and
foraging habitat as possible. 相似文献
19.
Biological invasions are the second most important cause of species extinction. Aided by processes such as transportation and urbanization, exotic species can establish and spread to new locations, causing changes in the function and structure of ecosystems. The House Sparrow is a widespread and highly abundant landbird associated to human presence. Previous studies performed in urban landscapes have suggested that this species could be acting, in synergy with urbanization, as a potential threat to native urban avian assemblages. In this study we assessed the relationship between House Sparrow density and native bird species richness in a region where the sparrows are scarce and sparsely distributed. We surveyed bird assemblages in and around four small-sized human settlements, considering three conditions in relation to House Sparrow presence: urban invaded, urban non-invaded, and non-urban non-invaded. To assess the potential detrimental role of House Sparrows on native bird species richness, we measured, additionally to sparrow densities, 20 predictor variables that describe vegetation structure and complexity, as well as urban infrastructure and human activities across four seasons of 1 year. Our results show that maximum shrub height was positively related to bird species richness, built cover was negatively associated with it, and House Sparrow invaded sites were related to a significant decrease of bird species richness, with increasing richness loss when more sparrows were present. Thus, we here provide evidence that urban areas can act in synergy with the presence of House Sparrows (even in low densities) in the urban-related species richness decline pattern. 相似文献
20.
Urbanization reduces the quantity of native vegetation and alters its local structure and regional spatial pattern. These
changes cause local extirpations of bird species associated with native vegetation and increases in the abundance and number
of bird species associated with human activity. We used 54–1 km 2 landscapes in the Seattle, Washington, USA metropolitan area to determine (1) the relative importance of habitat quantity,
structure, and pattern to bird diversity and abundance and (2) whether housing developments can be managed to mitigate the
negative impacts of urbanization on forest bird diversity. In general, bird species richness was high and many native forest
species were retained where urban landcover comprised less than 52% of the landscape, tree density (especially that of evergreens)
remained at least 9.8 trees/ha in developments, and forest was at least 64% aggregated across the landscape. These results
suggest that the quantity, structure, and pattern of forested habitat affected breeding bird diversity in urbanizing landscapes.
However, habitat pattern appeared less influential than other habitat attributes when results from all community- and population-level
analyses were considered. Conservation of native birds in reserves can be supplemented by managing the amount, composition,
structural complexity, and—to a lesser extent—arrangement of vegetation in neighborhoods. 相似文献
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