Niche packing and expansion account for species richness-productivity relationships in global bird assemblages

Aim: Niche theory proposes that increases in species richness along an environmental gradient are associated with a packing of species inside the niche space or an expansion of the niche space. We test whether and under what conditions an increase in bird species richness along a gradient of resource availability is associated with an expansion or packing of the niche as measured based on traits related to resource use. Location: Global. Time period: Current. Major taxa studied: Birds. Methods: We measured birds' realized niche space as the standardized departure between observed total trait range and its null expectation (functional richness: SES.FRic) in 12,188 cells worldwide. We first correlated both species richness and this measurement along the global net primary productivity (NPP) gradient using linear regressions. Second, we investigated the non‐stationarity of the species richness–NPP relationship with Lee's bivariate correlation, a measure of the spatial association of two variables. We then assessed the number of cells exhibiting a significant positive species richness–NPP association and a significant negative or positive SES.FRic. Third, we assessed whether species of species‐rich assemblages occur within or outside the niche space of species‐poor assemblages. Results: At a global scale, we found that species richness and SES.FRic increased with NPP. We also showed that cells with a significant positive association between species richness and NPP exhibited niche packing (1,699 assemblages out of 12,188) more than niche expansion (five assemblages). Niche packing was associated with complex biomes such as tropical rain forests. Finally, by showing that species in species‐rich assemblages predominantly occur within the niche space of species‐poor assemblages, we showed that the increase in SES.FRic with NPP contributed little to the increase in species richness. Main conclusion: Although niche volume increases with species richness along an NPP gradient, we confirmed that niche packing is the pattern most associated with the species richness–NPP relationship at a global scale

Biogeographic, environmental and anthropogenic determinants of global patterns in taxonomic and trait turnover in birds

Aim:To assess contemporary and historical determinants of taxonomic and ecological trait turnover in birds worldwide. We tested whether taxonomic and trait turnover (1) are structured by regional bioclimatic conditions, (2) increase in relationship with topographic heterogeneity and environmental turnover and change according to current and historical environmental conditions, and (3) decrease with human impact. Major Taxa: Birds Location: Global Methods: We used computationally efficient algorithms to map the taxonomic and trait turnover of 8,040 terrestrial bird assemblages worldwide, based on a grid with 110 km × 110 km resolution overlaid on the extent-of-occurrence maps of 7,964 bird species, and nine ecological traits reflecting six key aspects of bird ecology (diet, habitat use, thermal preference, migration, dispersal and body size). We used quantile regression and model selection to quantify the influence of biomes, environment (temperature, precipitation, altitudinal range, net primary productivity, Quaternary temperature and precipitation change) and human impact (human influence index) on bird turnover. Results: Bird taxonomic and trait turnover were highest in the north African deserts and boreal biomes. In the tropics, taxonomic turnover tended to be higher, but trait turnover was lower than in other biomes. Taxonomic and trait turnover exhibited markedly different or even opposing relationships with climatic and topographic gradients, but at their upper quantiles both types of turnover decreased with increasing human influence. Main conclusions: The influence of regional, environmental and anthropogenic factors differ between bird taxonomic and trait turnover, consistent with an imprint of niche conservatism, environmental filtering and topographic barriers on bird regional assemblages. Human influence on these patterns is pervasive and demonstrates global biotic homogenization at a macroecological scale

Ecological traits influence the phylogenetic structure of bird species co-occurrences worldwide

The extent to which species’ ecological and phylogenetic relatedness shape their co-occurrence patterns at large spatial scales remains poorly understood. By quantifying phylogenetic assemblage structure within geographic ranges of >8000 bird species, we show that global co-occurrence patterns are linked - after accounting for regional effects - to key ecological traits reflecting diet, mobility, body size and climatic preference. We found that co-occurrences of carnivorous, migratory and cold-climate species are phylogenetically clustered, whereas nectarivores, herbivores, frugivores and invertebrate eaters tend to be more phylogenetically overdispersed. Preference for open or forested habitats appeared to be independent from the level of phylogenetic clustering. Our results advocate for an extension of the tropical niche conservatism hypothesis to incorporate ecological and life-history traits beyond the climatic niche. They further offer a novel species-oriented perspective on how biogeographic and evolutionary legacies interact with ecological traits to shape global patterns of species coexistence in birds

Drivers of black grouse trends in the French Alps: The prevailing contribution of climate

International audienceAim Mountains host complex ecosystems whose wide range of ecological conditions over small geographical distances makes them biodiversity hotspots. To ensure their long-term conservation, a better understanding of the interaction between climate change and modifications in land use is necessary. Most studies have focused on only one of these factors at a time, leading to incomplete predictions. In this study, we explored the relative contribution of both recreative activities and climate change on the population dynamics of the black grouse (Tetrao tetrix), an emblematic cold-adapted species of the Alps.Methods We used data from a network of 47 monitoring sites dispersed around the French Alps and surveyed since the 1980s or 1990s. We estimated black grouse population growth rates using state-space models and tested for effects of biotic and abiotic pressures on both long-term trends and inter-annual variations in these rates.Results Population trajectories were strongly heterogeneous in space; nevertheless, a general decline at the edge of the black grouse distribution area was revealed in the southern pre-Alps. We found very little influence of hunting and new ski lift cables installation on inter-annual variability in population growth rate. In contrast, our results suggest strong impact of climatic conditions and phenology. While temperature positively influenced growth rate, precipitation had a negative effect. Early snowmelt and vegetation season were correlated with high positive values of annual population growth rates.Main conclusions Birds in mountain habitats may be drastically affected by ongoing climate change, perhaps to a greater extent than by an increase in recreational activities. However, other human activities in the mountains (such as animal grazing or forest exploitation) that were not taken into consideration in this study might also have a strong impact on habitat structure and indirectly affect populations' growth