![The effect of nest type on log‐transformed geographical densities (a) and ecological densities (b). For statistical results, see Table 2. The figure shows differences among closed ground (GC), ground (G), hole (H), and open arboreal nests (OA). Boxes show median, the notches give approximately 95% confidence interval for comparing medians (extend 1.58 × the inter‐quartile range/sqrt[n]). Please note that raw data were used in these plots](https://www.researchgate.net/publication/362070075/figure/fig2/AS:11431281180103171@1691498649984/The-effect-of-nest-type-on-log-transformed-geographical-densities-a-and-ecological_Q320.jpg)
July 2022
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Species' geographical distributions and abundances are a central focus of current ecological research. Although multiple studies have been conducted on their elucidation, some important information is still missing. One of them is the knowledge of ecological traits of species responsible for the population density variations across geographical (i.e., total physical area) and ecological spaces (i.e., suitable habitat area). This is crucial for understanding how ecological specialization shapes the geographical distribution of species, and provides key knowledge about the sensitivity of species to current environmental challenges. Here, we precisely describe habitat availability for individual species using fine‐scale field data collected across the entire Czech Republic. In the next step, we used this information to test the relationships between bird traits and country‐scale estimates of population densities assessed in both geographical and ecological spaces. We did not find any effect of habitat specialization on avian density in geographical space. But when we recalculated densities for ecological space available, we found a positive correlation with habitat specialization. Specialists occur at higher densities in suitable habitats. Moreover, birds with arboreal and hole‐nesting strategies showed higher densities in both geographical and ecological spaces. However, we found no significant effects of morphological (body mass and structural body size) and reproductive (position along the slow–fast life‐history continuum) traits on avian densities in either geographical or ecological space. Our findings suggest that ecological space availability is a strong determinant of avian abundance and highlight the importance of precise knowledge of species‐specific habitat requirements. Revival of this classical but challenging ecological topic of habitat‐specific densities is needed for both proper understanding of pure ecological issues and practical steps in the conservation of nature. We test the relationships between traits of birds and country scale estimates of population densities assessed in both geographical and ecological space. We did not find any effect of the habitat specialization on avian densities in geographical space, but the effect turned positive once we recalculated the densities for ecological space available. Moreover, birds with arboreal and hole nesting strategies showed higher densities in both geographical and ecological space. However, we found no significant effects of the morphological and reproductive traits on avian densities.