Behavioural responses of humpback whales to food-related chemical stimuli

Publisher's version (útgefin grein)Baleen whales face the challenge of finding patchily distributed food in the open ocean. Their relatively well-developed olfactory structures suggest that they could identify the specific odours given off by planktonic prey such as krill aggregations. Like other marine predators, they may also detect dimethyl sulfide (DMS), a chemical released in areas of high marine productivity. However, dedicated behavioural studies still have to be conducted in baleen whales in order to confirm the involvement of chemoreception in their feeding ecology. We implemented 56 behavioural response experiments in humpback whales using two food-related chemical stimuli, krill extract and DMS, as well as their respective controls (orange clay and vegetable oil) in their breeding (Madagascar) and feeding grounds (Iceland and Antarctic Peninsula). The whales approached the stimulus area and stayed longer in the trial zone during krill extract trials compared to control trials, suggesting that they were attracted to the chemical source and spent time exploring its surroundings, probably in search of prey. This response was observed in Iceland, and to a lesser extend in Madagascar, but not in Antarctica. Surface behaviours indicative of sensory exploration, such as diving under the stimulus area and stopping navigation, were also observed more often during krill extract trials than during control trials. Exposure to DMS did not elicit such exploration behaviours in any of the study areas. However, acoustic analyses suggest that DMS and krill extract both modified the whales’ acoustic activity in Madagascar. Altogether, these results provide the first behavioural evidence that baleen whales actually perceive prey-derived chemical cues over distances of several hundred metres. Chemoreception, especially olfaction, could thus be used for locating prey aggregations and for navigation at sea, as it has been shown in other marine predators including seabirds.This research was funded by the Fondation Total (www.fondation.total.com), grant #144903 to A.C., and the Ministère de l'Enseignement Supérieur et de la Recherche (www.enseignementsup-recherche.gouv.fr) to B.B., Bourse doctorale. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer Reviewe

Relating Habitat and Climatic Niches in Birds

Predicting species' responses to the combined effects of habitat and climate changes has become a major challenge in ecology and conservation biology. However, the effects of climatic and habitat gradients on species distributions have generally been considered separately. Here, we explore the relationships between the habitat and thermal dimensions of the ecological niche in European common birds. Using data from the French Breeding Bird Survey, a large-scale bird monitoring program, we correlated the habitat and thermal positions and breadths of 74 bird species, controlling for life history traits and phylogeny. We found that cold climate species tend to have niche positions in closed habitats, as expected by the conjunction of the biogeographic history of birds' habitats, and their current continent-scale gradients. We also report a positive correlation between thermal and habitat niche breadths, a pattern consistent with macroecological predictions concerning the processes shaping species' distributions. Our results suggest that the relationships between the climatic and habitat components of the niche have to be taken into account to understand and predict changes in species' distributions

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