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Abstract: Aim: While the contribution of abiotic factors to species distribution is well known, the geographic structure, if any, of biotic interactions within the species range is poorly understood. Most studies neglect biotic interactions when generating Species Distribution Models (SDMs) and projecting them, using future climatic scenarios, while others argue that biotic interactions may extend species tolerances to suboptimal abiotic conditions. Elucidating the extent to which biotic interactions play a role at a macro‐scale is challenging due to its inherent complexity. In this study, we characterized the independent contribution of prey abundance distributions on the Merlin's wintering distribution (Falco columbarius). Then, to examine the hypothesis that biotic interactions may counteract other suboptimal conditions, we tested for a differential importance of physical habitat characteristics and prey abundance distributions along the species’ wintering range. Location: Peninsular Spain. Methods: We modelled the Merlin's geographic distribution with Boosted Classification Trees as a function of environmental predictors (environmental model) and prey relative abundances (prey model), either separately or jointly (combined model). We tested whether the predictive success of environmental and prey models differ spatially. Results: Partialling out the variation into independent components we found that the prey abundance distributions explained the largest part of variation. Furthermore, the first four predictors with the highest contribution in our combined models were the abundances of prey species. Finally, our model predictions revealed a north‐to‐south increase in the importance of prey abundance distributions. Interestingly, our results suggest that biotic interactions can enable species to inhabit a wider range of suboptimal habitat conditions on range margins. Main conclusions: Relevant biotic interactions may not be always fully interchangeable with environmental surrogates. Abiotic factors and biotic interactions may shape species range limits and cores of distributions differently. Neglecting biotic interactions may compromise spatiotemporal transferability of SDMs, especially on species margins, and hence their applicability. [ABSTRACT FROM AUTHOR]

Aim Quantifying species abundances is costly, especially when many species are involved. To overcome this problem, several studies have predicted local abundances (at the sample unit level) from species occurrence distribution models ( SODMs), with differences in predictive performance among studies. Surprisingly, the ability of SODM to predict regional abundances of an entire area of interest has never been tested, despite the fact that it is an essential parameter for species conservation and management. We tested whether local and regional abundances of 21 terrestrial bird species could be predicted from SODMs in an exhaustively surveyed island, and examined the variation explained by species-specific traits. Location La Palma Island, Canary Islands. Methods We firstly assessed two types of algorithms representing the two main families of SODMs. We built models using presence/absence (boosted classification trees) and presence/background ( Max Ent) data as a function of relevant environmental predictors and tested their ability to predict the observed local abundances. The predicted probabilities of occurrence ( P i) were translated into animal numbers ( n′) using the revisited equation n i ′ = − ln(1−P i ), and we obtained regional abundances (for the whole island). Results Predictive ability of presence/absence models was superior than that of MaxEnt. At the regional level, the observed average densities of all species were highly predictable from occurrence probabilities ( R2 = 93.5%), without overall overestimation or underestimation. Interspecific variation in the accuracy of predicted regional density was largely explained ( R2 = 73%), with habitat breath and variation in local abundance being the traits of greatest importance. Main conclusions Despite uncertainties associated with local predictions and the idiosyncrasies of each species, our procedures enabled us to predict regional abundances in an unbiased way. Our approach provides a cost-effective tool when a large number of species are involved. Furthermore, the influence of species-specific traits on the prediction accuracy provides insights into sampling designs for focal species. [ABSTRACT FROM AUTHOR]

Aim To explore the determinants of island occupancy of 48 terrestrial bird species in an oceanic archipelago, accounting for ecological components while controlling for phylogenetic effects. Location The seven main islands of the Canary archipelago. Methods We obtained field data on population density, habitat breadth and landscape distribution in Tenerife, Fuerteventura and La Palma, aiming to sample all available habitats and the gradient of altitudes. In total, 1715 line transects of 0.5 km were carried out during the breeding season. We also reviewed the literature for data on occupancy, the distance between the Canary Islands and the nearest distribution border on the mainland, body size and endemicity of the 48 terrestrial bird species studied. Phylogenetic eigenvector regression was used to quantify (and to control for) the amount of phylogenetic signal. Results The two measurements of occupancy (number of occupied islands or 10 × 10 km UTM squares) were tightly correlated and produced very similar results. The occupancy of the terrestrial birds of the Canary Islands during the breeding season had a very low phylogenetic effect. Species with broader habitat breadth, stronger preferences for urban environments, smaller body size, and a lower degree of endemicity had a broader geographical distribution in the archipelago, occupying a larger number of islands and 10 × 10 UTM squares. Main conclusions The habitat-generalist species with a tolerance for novel urban environments tend to be present on more islands and to occupy a greater area, whereas large-sized species that are genetically differentiated within the islands are less widespread. Therefore, some properties of the ranges of these species are explicable from basic biological features. A positive relationship of range size with local abundance, previously shown in continental studies, was not found, probably because it relies on free dispersal on continuous landmasses, which may not be applicable on oceanic islands. [ABSTRACT FROM AUTHOR]

The houbara bustard in the Canary Islands is included into the category ‘Endangered’ on the Spanish Bird Red List according to suspected declines in bird numbers, the loss of previously occupied areas and the suggested endemicity of the taxon. This paper deals with the population size and the distribution pattern of the houbara bustard in Fuerteventura (the largest island occupied by the species in the Canary archipelago, 1730 km2) and analyses its habitat use according to topography, soil, vegetation and human impact variables. We employ distance sampling on 1471 (early spring) and 602 (summer) 500-m transects and measure habitat characteristics within the transects to estimate local densities and population sizes and to test whether the features of the used habitats (as measured in transects where the species was recorded) differed from those available (measured in the whole sample). Topographic and anthropic features are the main determinants of the habitat use of the species, while other descriptors related to vegetation structure and substrate characteristics play a minor role in its habitat preferences. The slope of the terrain is the most important habitat feature constraining the occurrence of the houbara bustard... [ABSTRACT FROM AUTHOR]

We identify autoecological traits of bird species that influence the accuracy of predictive models of species distribution based on census data obtained from stratified sampling. These models would serve as a complementary approach to the development of regional bird atlases. We model the winter bird abundance of 64 terrestrial bird species in 77 census plots in Central Spain (Madrid province), using regression tree analyses. The predicted distribution of species density derived from statistical models (birds/10 ha) was compared with the published relative abundances depicted by a very accurate regional atlas of wintering birds (birds observed per 10 h). Statistical models explained an average of 41.7% of the original deviance observed in the local bird distribution (range 19.6–79.3%). Significant associations between observed relative abundances (atlas data) and predicted average densities in 1×1 km squares within 10×10 km UTMs were attained for 44 out of 64 species. Interspecific discrepancies between predicted and observed distribution maps decreased with between-year constancy in regional bird distribution and the degree of ecological specialization of species. Therefore, statistical modeling using census localities allowed us to depict geographical variations in bird abundance that were similar to those in the quantitative atlas maps. Nevertheless, bird distributions derived from statistical models are less reproducible in some species than in others, depending on their autoecological traits. [ABSTRACT FROM AUTHOR]

We analyzed the variation in island bird communities of urban environments related to habitat characteristics, using regression/classification tree analyses. Data from field censuses in cities/towns representing the urban heterogeneity of the whole island were obtained in Tenerife (Canary Islands, Spain). Urban bird abundance in Tenerife was negatively affected by altitude and the cover of dry Euphorbia shrubs and positively influenced by the height and cover of the tree layer. Species richness was negatively associated with building cover and positively related to tree height and altitude. Data from field censuses in Tenerife were compared with that of similar urban environments in the mainland (Madrid Province, central Spain). Species diversity was higher in the urban sample of Tenerife than in that of Madrid and the proportion of bird species from the regional pool ‘captured’ by urban environments was higher in the island than in the mainland. Nine native species and three alien species were more abundant in island urban environments than in the continent (densities, at least, 100% higher), the converse occurring for only five species. At a biogeographic scale, we conclude that the avifauna of Tenerife Island is more prone to occupy a new artificial environment than the mainland bird fauna of central Spain. [ABSTRACT FROM AUTHOR]