| Summary: | The thesis contains studies of animal life histories at high latitudes. Several topics are covered; from ecosystem consequences of life histories to tests of specific behavioural predictions put forward based on life history arguments. Work on complete life histories is also included in an attempt to understand the evolution of capital and income breeding in marine copepods. My main research questions, followed by main topics and findings, are as follows: • How are seasonal environments influencing life history traits and phenology? • What are the roles of storage as a reproductive adaptation? • How are individual states, particularly energy reserves, influencing optimal life histories and behaviour? Paper 1 deals with how growth of a high-latitude pelagic fish, the Norwegian spring-spawning herring, is scheduled during the annual cycle. Body mass data reveal a short period of rapid annual increase in body mass at the time when the copepod Calanus finmarchicus is the main prey. The food consumption (energy units) of the entire herring population is estimated, using a bioenergetics model, and compared with production estimates of C. finmarchicus. Large herring populations, particularly because of their selective predation on older stages, can influence population dynamics of C. finmarchicus, and may explain some of the copepod’s life history adaptations. Finally, estimates of spatial energy transport are presented; caused by herring migrating from oceanic feeding grounds to coastal overwintering and spawning sites. The large herring stock may be responsible for the world’s largest biomass transport caused by a migrating population. This flux of energy and nutrients is important for coastal species, and potentially for interactions not yet studied, such as between herring eggs and benthic invertebrates. Paper 2 is a short comment on recent studies of copepod life cycles that have suggested that the large lipid stores serve as a means of obtaining neutral buoyancy at a given depth - an ultimate explanation of ...
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