Causes and consequences of ontogenetic dietary shifts: a global synthesis using fish models

Accepted manuscript version. Published version available at https://doi.org/10.1111/brv.12468. Ontogenetic dietary shifts (ODSs), the changes in diet utilisation occurring over the life span of an individual consumer, are widespread in the animal kingdom. Understanding ODSs provides fundamental insights into the biological and ecological processes that function at the individual, population and community levels, and is critical for the development and testing of hypotheses around key concepts in trophic theory on model organisms. Here, we synthesise historic and contemporary research on ODSs in fishes, and identify where further research is required. Numerous biotic and abiotic factors can directly or indirectly influence ODSs, but the most influential of these may vary spatially, temporally and interspecifically. Within the constraints imposed by prey availability, we identified competition and predation risk as the major drivers of ODSs in fishes. These drivers do not directly affect the trophic ontogeny of fishes, but may have an indirect effect on diet trajectories through ontogenetic changes in habitat use and concomitant changes in prey availability. The synthesis provides compelling evidence that ODSs can have profound ecological consequences for fish by, for example, enhancing individual growth and lifetime reproductive output or reducing the risk of mortality. ODSs may also influence food‐web dynamics and facilitate the coexistence of sympatric species through resource partitioning, but we currently lack a holistic understanding of the consequences of ODSs for population, community and ecosystem processes and functioning. Studies attempting to address these knowledge gaps have largely focused on theoretical approaches, but empirical research under natural conditions, including phylogenetic and evolutionary considerations, is required to test the concepts. Research focusing on inter‐individual variation in ontogenetic trajectories has also been limited, with the complex relationships between individual behaviour and environmental heterogeneity representing a particularly promising area for future research

The influence of food web structure on the growth and bioenergetics of lake trout (Salvelinus namaycush) /

Most fish species tend to feed on larger prey as their size increases. The lack of suitable prey during critical periods of their life can prevent them from shifting their diet to larger prey and also from reaching larger body sizes. In this study, we compared the energy budget of lake trout ( Salvelinus namaycush) populations with contrasting food webs. Non-piscivorous lake trout (NPLT) populations reached a much smaller size and grew at a much slower rate than picivorous lake trout (PLT) populations. Food consumption rates were on average, 2--3 times higher in NPLT when they were expressed on a wet weight basis. However, only a slight difference in their energy intake was detected (less than 10%) once consumption rates were corrected for differences in prey caloric content. Growth efficiency was about two times lower in NPLT compared to PLT, while their metabolic costs were higher and assimilation efficiency was lower. It is most likely that the increased metabolic costs were associated with higher foraging costs, since more feeding attempts must be made to acquire a given quantity of food when fish are feeding on smaller prey. Furthermore, the portion of indigestible matter is likely to be higher in the diet of NPLT than in PLT (e.g. chitin versus bone). These results are consistent with theoretical models of fish growth that have showed that lake trout must have access to larger prey, even if they are rare, to reach larger body sizes. Our study also illustrates how the restructuring of a prey community by the arrival of an exotic species into a food web could alter the growth rate of a top predator. Furthermore, our study suggests that age at first maturity is influenced by growth efficiency in indigenous populations of fish. Therefore, the dynamic of a population and its vulnerability to exploitation are likely to be influenced by their energy allocation strategy

An exploratory study of derogation in Quebec : the case of three students

This qualitative study investigates the consequences of advancing three preschoolers into kindergarten in the province of Quebec, where the derogation exemption enables younger children to start school before they reach the age of admission of five years by September 30th. The rationale for this study came from an interest to discover the perspectives of the students, their teachers, and their parents on the topic of derogation. This study examines how these students, one in grade 4 and two in grade 6, feel about being the youngest in the class, and how teachers and parents perceive them as learners and socializers. The research design is based on an exploratory qualitative case study approach. The methods used to collect the data consist of interviews conducted with the three selected students, their homeroom teachers, and two parents; observations of the students in their school settings, and the analysis of documents such as field notes and journal entries. The interviews are analyzed within a socio-cultural interpretive framework in order to examine the way that derogation has affected the social and emotional lives of the three selected children. Vygotsky's zone of proximal development is explored. This concept presents the idea that children develop their learning potential in a setting where they can learn with more capable peers and adults who provide guidance and support. When these younger children are advanced into a kindergarten class, they are placed in a setting with older peers and adult teachers. One of the issues addressed in this study is how the social milieu encourages derogated children to develop their cognitive approach to problem solving and learning. The themes that emerged from this study include the importance of parental support, peer acceptance, and self-esteem. The younger derogated students are more likely to experience success in their academic and social-emotional lives if they have good parental support,