Feather mites are arthropods that live on or in the feathers of birds, and are among the commonest avian ectosymbionts. However, the nature of the ecological interaction between feather mites and birds remains unclear, some studies reporting negative eff ects of feather mites on their hosts and others reporting positive or no eff ects. Here we use a large dataset comprising 20 189 measurements taken from 83 species of birds collected during 22 yr in 151 localities from seven countries in Europe and North Africa to explore the correlation between feather mite abundance and body condition of their hosts. We predicted that, if wing-dwelling feather mites are parasites, a negative correlation with host body condition should be found, while a mutualistic interaction should yield positive correlation. Although negative relationships between feather mite abundance and host body condition were found in a few species of birds, the sign of the correlation was positive in most bird species (69%). Th e overall eff ect size was only slightly positive (r ϭ 0.066). Th e eff ect of feather mite abundance explained Ͻ 10% of variance in body condition in most species (87%). Results suggest that feather mites are not parasites of birds, but rather that they hold a commensalistic relationship where feather mites may benefi t from feeding on uropygial gland secretions of their hosts and birds do not seem to obtain a great benefi t from the presence of feather mites.

Understanding why host species differ so much in symbiont loads and how this depends on ecological host and symbiont traits is a major issue in the ecology of symbiosis. A first step in this inquiry is to know whether observed differences among host species are species-specific traits or more related with host-symbiont environmental conditions. Here we analysed the repeatability (R) of the intensity and the prevalence of feather mites to partition within- and among-host species variance components. We compiled the largest dataset so far available: 119 Paleartic passerine bird species, 75,944 individual birds, ca. 1.8 million mites, seven countries, 23 study years. Several analyses and approaches were made to estimate R and adjusted repeatability (Radj) after controlling for potential confounding factors (breeding period, weather, habitat, spatial autocorrelation and researcher identity). The prevalence of feather mites was moderately repeatable (R = 0.26–0.53; Radj = 0.32–0.57); smaller values were found for intensity (R = 0.19–0.30; Radj = 0.18–0.30). These moderate repeatabilities show that prevalence and intensity of feather mites differ among species, but also that the high variation within species leads to considerable overlap among bird species. Differences in the prevalence and intensity of feather mites within bird species were small among habitats, suggesting that local factors are playing a secondary role. However, effects of local climatic conditions were partially observed for intensity.

Gradients of environmental stress may affect biotic interactions in unpredictable ways responding to climate variation, depending on the abiotic stress tolerance of interacting partners. Here, we study the effect of local climate on the intensity of feather mites in six mountain passerines along a 1400 m elevational gradient characterized by shifting temperature and rainfall. Although obligatory symbionts of warm-blooded organisms are assumed to live in mild and homeothermic environments, those inhabiting external, non-blood-irrigated body portions of the host organism, such as feather mites, are expected to endure exposure to the direct influence of a fluctuating climate. As expected, feather mite intensity declined with elevation in all bird species, a pattern that was also found in cold-adapted passerines that have typical alpine habits. The elevation cline was mainly explained by a positive effect of the average temperature upon mite intensity in five of the six species studied. Precipitation explained less variance in mite intensity than average temperature, and showed a negative correlation in half of the studied species. We found no climate-driven migration of mites along the wings of birds, no replacement of mite species along elevation gradients and no association with available food resources for mites (estimated by the size of the uropygial gland). This study suggests that ectosymbionts of warm-blooded animals may be highly sensitive to climatic variation and become less abundant under stressful environmental conditions, providing empirical evidence of the decline of specialized biotic interactions among animal species at high elevations.

Online enhancement: appendix. Dryad data: http://dx.doi.org/10.5061/dryad.g4p92.abstract: Ecosystem functioning depends on nutrient cycles and their responses to abiotic and biotic determinants, with the influence of evolutionary legacies being generally overlooked in ecosystem ecology. Along a broad elevation gradient characterized by shifting climatic and grazing environments, we addressed clines of plant N and C : N content and of d 13 C and d 15 N in producers (herbs) and in primary (grasshoppers) and secondary (birds) consumers, both within and between species in phylogenetically controlled scenarios. We found parallel and significant intra-and interspecific trends of isotopic variation with elevation in the three groups. In primary producers, nutrient and isotope distributions had a detectable phylogenetic signal that constrained their variation along the environmental gradient. The influence of the environment could not be ascribed to any single factor, and both grazing and climate had an effect on leaf stoichiometry and, thus, on the resources available to consumers. Trends in consumers matched those in plants but often became nonsignificant after controlling for isotopic values of their direct resources, revealing direct bottom-up control and little phylogenetic dependence. By integrating ecosystem and mechanistic perspectives, we found that nutrient dynamics in food webs are governed at the base by the complex interaction between local determinants and evolutionary factors.

In eight European study sites (

No abstract

The study of determinants of species' ranges along elevational gradients may shed light on the ecological factors that constrain their distribution and fundamental niche. We analysed the influence of the climate, habitat at different spatial scales and topography on Water Pipit Anthus spinoletta density in mountain landscapes across a wide elevational gradient. Variables associated with spring and annual temperature values were the main determinants of Water Pipit density, especially at the lower distributional limit (700-1200 m asl), where the species avoided warmer areas. At high-elevation sites (1600-2300 m asl), the main constraint to the species' distribution was habitat structure and composition, with steep rocky areas being avoided. Highest densities were found in open but locally heterogeneous habitat at intermediate to high elevations, and the habitat variables that played a major role at the landscape scale were medium-tall shrublands and woodlands, but with contrasting effects depending on elevation. These results suggest that different sets of variables may constrain density, and effects may differ at the upper and lower elevational limits, with climate being more important at lower elevations and local habitat more important at higher elevations. Ongoing global warming is likely to cause an upward shift in range boundaries of alpine species, but local habitat features could constrain the upward expansion, resulting in range contractions accompanying range shift.

We studied the pattern of inter‐specific association of breeding territories in a passerine assemblage of dry cereal farmland in central Spain and evaluated the role of the presence of heterospecifics in the habitat use patterns exhibited by different species. Bird territories showed a non‐random inter‐specific spatial aggregation pattern. We studied territory abundance variation in the three more abundant species: the corn bunting, the crested lark, and the fan‐tailed warbler. Crested lark and fan‐tailed warbler territories were more abundant in plots where corn bunting territories were present and vice versa, while their respective abundances did not vary with the breeding presence of the other species. We used landscape and agricultural management variables to analyze the relationships between habitat and each species’ breeding territories by means of classification trees. While the corn bunting showed a marked pattern of nesting habitat use, the crested lark and the fan‐tailed warbler exhibited a much more generalist one. Corn Bunting presence was affected negatively by intensification‐related variables, such as field size and percent cover of cereal crops. Similarly, the presence of crested larks was negatively related to high yielding areas. However, when the presence of hetero‐specific territories was considered, the presence of corn bunting territories was the most important variable explaining the occurrence of breeding fan‐tailed warblers, and the second most important in the case of the crested lark. These results suggest that inter‐specific attraction could play a role in the formation of farmland bird assemblages, while adding further evidence for the detrimental effect of agricultural intensification at the community level.