A global consistent positive effect of urban green area size on bird richness

Background: Although the species-urban green area relationship (SARu) has been analyzed worldwide, the global consistency of its parameters, such as the fit and the slope of models, remains unexplored. Moreover, the SARu can be explained by 20 different models. Therefore, our objective was to evaluate which models provide a better explanation of SARus and, focusing on the power model, to evaluate the global heterogeneity in its fit and slope. Methods: We tested the performance of multiple statistical models in accounting for the way in which species richness increases with area, and examined whether variability in model form was associated with various methodological and environmental factors. Focusing on the power model, we analyzed the global heterogeneity in the fit and slope of the models through a meta-analysis. Results: Among 20 analyzed models, the linear model provided the best fit to the most datasets, was the top ranked model according to our efficiency criterion, and was the top overall ranked model. The Kobayashi and power models were the second and third overall ranked models, respectively. The number of green areas and the minimum number of species within a green area were the only significant variables explaining the variation in model form and performance, accounting for less than 10% of the variation. Based on the power model, there was a consistent overall fit (r 2 = 0.50) and positive slope of 0.20 for the species richness increase with area worldwide. Conclusions: The good fit of the linear model to our SARu datasets contrasts with the non-linear SAR frequently found in true and non-urban habitat island systems; however, this finding may be a result of the small sample size of many SARu datasets. The overall power model slope of 0.20 suggests low levels of isolation among urban green patches, or alternatively that habitat specialist and area sensitive species have already been extirpated from urban green areas.Fil: Levau, Lucas M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; ArgentinaFil: Ruggiero, Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio de Ecotono; ArgentinaFil: Matthews, Thomas J.. Universidade dos Açores; Portugal. University of Birmingham; Reino UnidoFil: Bellocq, Maria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentin

Coefficient shifts in geographical ecology: an empirical evaluation of spatial and non-spatial regression

Copyright © 2009 The Authors. Copyright © ECOGRAPHY 2009.A major focus of geographical ecology and macro ecology is to understand the causes of spatially structured ecological patterns. However, achieving this understanding can be complicated when using multiple regressions, because the relative importance of explanatory variables, as measured by regression coefficients, can shift depending on whether spatially explicit or non-spatial modelling is used. However, the extent to which coefficients may shift and why shifts occur are unclear. Here, we analyze the relationship between environmental predictors and the geographical distribution of species richness, body size, range size and abundance in 97 multi-factorial data sets. Our goal was to compare standardized partial regression coefficients of non-spatial ordinary least squares regressions (i.e. models fitted using ordinary least squares without taking autocorrelation into account; “OLS models” hereafter) and eight spatial methods to evaluate the frequency of coefficient shifts and identify characteristics of data that might predict when shifts are likely. We generated three metrics of coefficient shifts and eight characteristics of the data sets as predictors of shifts. Typical of ecological data, spatial autocorrelation in the residuals of OLS models was found in most data sets. The spatial models varied in the extent to which they minimized residual spatial autocorrelation. Patterns of coefficient shifts also varied among methods and datasets, although the magnitudes of shifts tended to be small in all cases. We were unable to identify strong predictors of shifts, including the levels of autocorrelation in either explanatory variables or model residuals. Thus, changes in coefficients between spatial and non-spatial methods depend on the method used and are largely idiosyncratic, making it difficult to predict when or why shifts occur. We conclude that the ecological importance of regression coefficients cannot be evaluated with confidence irrespective of whether spatially explicit modelling is used or not. Researchers may have little choice but to be more explicit about the uncertainty of models and more cautious in their interpretation

What land use better preserves taxonomic and functional diversity of birds in a grassland biome?

The Pampean grassland in South America has been almost completely transformed by human activities and is one of the biomes at the highest conservation risk. Although several land uses are developed in temperate grasslands, studies comparing their impact on bird taxonomic and functional diversity are still missing. We determined what habitat type resulting from human land uses better preserves the assemblage of birds and their functional traits that occur in protected grasslands. We compared taxonomic and functional diversity between protected grasslands and cattle pastures, crop fields, tree plantations, and urban settlements. We surveyed birds and environmental variables in the 5 habitat types using point counts and selected 11 traits to estimate functional diversity. We performed principal component analysis to explore environmental differences between habitat types, ANOVA to compare taxonomic and functional diversity, nonmetric multidimensional scaling to explore relationships between habitat type characteristics and species traits, and similarity percentage analysis to find the bird functional traits that contributed the most to differentiate habitat types. Bird composition and functional diversity in cattle pastures was the most similar to that of protected areas but showed no significant differences with crop fields. In cattle pastures, crop fields, and protected areas, the most frequent species traits were related to narrow ranges and high vulnerability to extinction, whereas urban settlements included traits covering wide ranges or related to impervious areas. When compared with protected areas, land conversion into cattle pastures and some types of agricultural lands resulted in a lower loss of bird species and functional diversity than conversion into tree plantations or urbanized areas. Approximately 35% of species found in protected areas were not recorded in any of the other habitat types. Therefore, we emphasize the need to protect the native habitat. Our findings help with land use planning in the Pampas and other temperate grasslands

Effects of single-tree selection harvesting on hymenopteran and saproxylic insect assemblages in the canopy and understory of northern temperate forests

Insects respond to changes in microhabitat caused by canopy disturbance, and thus can be used to examine the ecological impacts of harvesting. Single-tree selection harvesting is the most common silvicultural system used to emulate local small-scale natural disturbance and maintain uneven-aged forest structure in temperate forests. Here, we test for differences in richness, abundance, and composition of hymenopteran and saproxylic insect assemblages at four different taxon levels (selected insect orders; and all hymenopteran families, and braconid subfamilies and morphospecies) between the canopy and understory of unharvested and single-tree selection harvested sites in a northern temperate forest from central Canada. Harvesting had no effect on insect assemblage richness, composition or abundance at the three highest taxon levels (order, family and subfamily). Similarly, richness and abundance at the lowest-taxon level (braconid morphospecies) were similar, although composition differed slightly between unharvested and harvested stands. Insect assemblages were vertically stratified, with generally higher abundance (for Diptera, Hymenoptera, some hymenopteran families and braconid subfamilies) and richness (for braconid morphospecies) in the understory than the canopy. In particular, composition of the braconid morphospecies assemblage showed relatively low similarity between the understory and canopy. Single-tree selection harvesting appears to influence wood-associated insect taxa only subtly through small changes in community composition at the lowest taxon level, and thus is recommended as a conservative approach for managing these northern temperate forests.Fil: Smith, Sandy M.. University of Toronto; CanadáFil: Islam, Nurul. University of Toronto; CanadáFil: Bellocq, Maria Isabel. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin