Questioning the roles of resources nutritional quality in ecology

International audienceOur understanding of ecosystem functioning is strongly linked to the study ofpredator–prey relationships and food web structures. However, trophic ecology hasoften focused on identifying taxonomic relationships and quantifying the biomassor energy ingested by consumers, but has often failed to integrate the importanceof the nutritional quality of resources in ecological dynamics. Underlying this gap isthe multi-dimensional nature of resource quality which has hampered any consensuson the definition of resource nutritional quality. In this special issue, we aimed atgathering a subset of articles exemplifying the diversity of variables by which resourcesquality is quantified, the diversity of research topics that can be tackled in ecology– from physiological or evolutionary aspects to ecosystem processes – and proposesome perspectives on the integration of nutritional quality within broader ecologicalconcepts. Using a semi-automated literature analysis, we map the current landscapeof the ‘resources nutritional quality’ research of the last 30 years. We depict how ithas been quantified through physical, biological or chemical indicators, the use ofthese parameters being largely dependent on the type of ecosystem studied and on theinvestigated ecological process. We then position the articles published in this specialissue of Oikos within this landscape, showing they cover a small but relatively wellrepresentative subset of the domains of resources quality-related issues. Articles in thisspecial issue browse a range of individual and population-level approaches (embracingevolutionary questions) to community related questions, include methodologicalissues and ecosystem-wide approaches using trophic quality indicators as tracers ofresources origin. Based on these studies and on the literature review, we identify a nonexhaustivelist of challenges and perspectives of research that we consider of highestpriority in the large topic of trophic ecology

MesopTroph, a database of trophic parameters to study interactions in mesopelagic food webs

Mesopelagic organisms play a crucial role in marine food webs, channelling energy across the predator-prey network and connecting depth strata through their diel vertical migrations. The information available to assess mesopelagic feeding interactions and energy transfer has increased substantially in recent years, owing to the growing interest and research activity in the mesopelagic realm. However, such data have not been systematically collated and are difficult to access, hampering estimation of the contribution of mesopelagic organisms to marine ecosystems. Here we present MesopTroph, a georeferenced database of diet, trophic markers, and energy content of mesopelagic and other marine taxa compiled from 203 published and non-published sources. MesopTroph currently includes data on stomach contents, carbon and nitrogen stable isotopes, major and trace elements, energy density, fatty acids, trophic positions, and diet proportion estimates for 498 species/genera. MesopTroph will be expanded with new data emerging from ongoing studies. MesopTroph provides a unique tool to investigate trophic interactions and energy flow mediated by mesopelagic organisms, and to evaluate the ecosystem services of this community

Long-term ecological segregation among the NW Iberian peninsula odontocete as evidenced using ecological tracers

25th Annual Conference of the European Cetacean Society, Long-term datasets on marine mammals: learning from the past to manage the future, 21st – 23rd March 2011, Cádiz, SpainThe waters off the Northwest of the Iberian Peninsula are characterised by high marine biodiversity and productivity, supported by the nutrients made available by seasonal upwellingN

Investigating the role of prey depletion in cetacean distributions and population dynamics

34th European Cetacean Society Conference, O Grove, 16-20 April 2023A key driver in determining the distribution and demography of cetaceans is the dispersion of their prey, in terms of availability, abundance and quality. A Working Group on Resource Depletion has been established within ASCOBANS to review current knowledge and develop recommendations for research and action. It includes members with expertise in veterinary and fishery science, cetacean biology, ecology and conservation. The group has eight terms of reference - reviewing and collating recent information on resource depletion and its impacts, prey distribution and abundance, health and condition indicators, small cetacean diet, spatio-temporal trends in small cetacean species, emerging technologies, integrating information from multiple data sources, and making recommendations for possible mitigation measures to aid conservation. As a first step, the group has summarised information on the diets of all small cetacean species regularly occurring in the ASCOBANS Agreement Area, and explored the parameters required to assess cetacean health and condition at both an individual and population level. The need to better understand prey choice in terms of prey availability and caloric content is highlighted along with the development of indicators of food shortage through necropsies of dead animals and photographic assessments of body condition in live animals. Future research, monitoring and conservation needs include refining the definition of prey depletion, developing prey depletion reference points, and articulating associated conservation objectives. We also need a better understanding of the relationships between cetacean physiology, energetics, body condition, health and diet, and of the population and ecosystem level consequences of prey depletion (e.g. based on the use of ecosystem models). Improved monitoring of prey and cetacean distribution and abundance at relevant spatiotemporal scales would facilitate estimation and mapping of resource depletion riskN

Assessment of the toxicological status of small cetacean species from the North West Iberian Peninsula

27th Conference of the European Cetacean Society, Interdisciplinary Approaches in the Study of Marine Mammals, 8th-10th April 2013, Setúbal, PortugalIn order to determine the contamination status and vulnerability of five of the most frequent small cetaceans from the NW Iberian Peninsula (NWIP) (common dolphin Delphinus delphis, harbour porpoise Phocoena phocoena, bottlenose dolphin Tursiops truncatus, striped dolphin Stenella coeruleoalba and long-finned pilot whale Globicephala melas), 32 congeners of polychlorinated biphenyls (PCBs) were analysed in their blubber and 14 trace elements (Ag, As, Cd, Co, Cu, Cr, Fe, Hg, Mn, Ni, Pb, Se, V, Zn) in liver and kidneyN

Grey and harbour seals in France : distribution at sea, connectivity and trends in abundance at haulout sites

Grey (Halichoerus grypus) and harbour seals (Phoca vitulina) are sympatric seal species, but they display distinct strategies of habitat use and connectivity between haulout sites. The distribution patterns and variations in relative abundance of both species were investigated along the French coast of the English Channel, at the southern limit of their range where seal numbers are increasing. Regular censuses conducted at all main haulout sites in mainland France showed significant seasonal variations at most sites, with more harbour seals counted during summer (breeding and moulting seasons), and more grey seals during summer only in the eastern English Channel. Trends in maximum haulout numbers at haulout sites showed a significant increase over the last five years, ranging from 9.7 to 30.9% per year for harbour seals, and from 5.8% (in the western English Channel) to 49.2% (in the eastern English Channel) per year for grey seals. These rates of increase in grey seal numbers are not linked to local pup production and most probably result from seal movements from the southwest British Isles and the North Sea, respectively. Aerial surveys conducted across the English Channel showed that most seal observations at sea were concentrated in the north-eastern English Channel. Telemetry showed that the 28 harbour seals tracked remained highly coastal, within a radius of 100 km from their haulout sites, and did not move to other known colonies. Grey seals moved much greater distances, reaching up to 1200 km from their capture site. More than half of the 45 grey seals tracked crossed the English Channel, especially during the breeding season, moving to known colonies in the southwest British Isles and the North Sea. Combining individual tracks and long-term surveys of the seal populations allowed a better understanding of the dynamics of these populations and their connectivity at a larger regional scale. The findings provide direct information for the management of grey and harbour seals within the frame of the Marine Strategy Framework Directive, and highlight focus areas where potential interactions between the two species should be monitored.PostprintPeer reviewe

Foraging strategies and energetic of predation among marine mammals

Les stratégies alimentaires peuvent être définies comme la mise en place d'ensembles cohérents de réponses morphologiques, physiologiques, écologiques ou comportementales permettant d’optimiser le succès alimentaire d’une espèce. Le présent travail s'est proposé d'aller au-delà de la simple analyse taxonomique des régimes alimentaires en utilisant les caractéristiques des proies pour explorer certains aspects des stratégies alimentaires et de l’énergétique de la prédation chez les mammifères marins de l’atlantique nord-est. L'objectif majeur était de contribuer à une meilleure compréhension du "pourquoi une proie est une proie ?" La valeur énergétique des proies est apparue comme un élément central des stratégies de prédation. Il en résulte que des coûts d'existence importants chez les mammifères marins doivent être soutenus par une alimentation de qualité élevée et ne peuvent pas être satisfaits simplement par une plus grande quantité de proies de qualité moyenne ou faible. Les résultats obtenus lors de cette thèse ont ainsi permis de progresser de la description des régimes alimentaires vers la compréhension de certaines relations fonctionnelles entre proies et prédateurs. Ainsi, les traits descriptifs de la qualité des proies, comme la teneur en lipides et la valeur énergétique, et les traits descriptifs des coûts d’existence des mammifères marins, comme l’indice mitochondrial et la teneur en lipides des muscles, sont significativement corrélés. Enfin, ce travail souligne que pour comprendre l'écologie alimentaire d'un prédateur, il faut surtout bien connaitre les caractéristiques de ses proies.Foraging strategies can be defined as the establishment of a consistent set of morphological, physiological, ecological and behavioural responses allowing the optimization of foraging success. Beyond the simple description of the diet, the present work attempted to explore some aspects of foraging strategies and of the energetic of predation among northeast Atlantic marine mammals. The main goal of the study was to contribute to a better understanding of "why a prey is a prey?" Prey energy density appeared to be a key point of predation strategies. Hence, marine mammal species with high existence costs would need high quality prey items, and cannot fulfil their energy requirement just by ingesting more prey items of low to medium quality. The results of this thesis permitted to progress from a taxonomic description of marine mammal diets to the identification of functional relationships between prey and predators. Hence, traits of prey quality such as lipid content or energy density, and traits of predator cost of existence such as muscle mitochondrial density or muscle lipid content, were significantly correlated. Finally, this work underlines that in order to understand the foraging ecology of a predator, its prey characteristics have to be known