Øyvind Fiksen

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Industrial fishing has been identified as a cause for life history changes in many harvested stocks, mainly because of the intense fishing mortality and its size-selectivity. Because these changes are potentially evolutionary, we investigate evolutionarily stable life-histories and yield in an energy-allocation state-dependent model for Northeast Arctic cod(More)
That sexually mature fish skip reproduction, especially in response to poor condition, has been documented in many species. We present results from an energy-allocation life history model that shed light on the underlying logic of skipped spawning, based on the Northeast Arctic stock of Atlantic cod (Gadus morhua). The model predicts that skipped spawning(More)
Mate choice is common in most animals, but the issue has largely been ignored in regard to pelagic copepods—the most abundant zooplankton group in the oceans. Contemporary demographic models of copepods assume that all encounters lead to successful copulation and viable egg production. We revisit the subject of copepod mating biology in the framework of(More)
In microbial competition theory, the Michaelis-Menten (MM) half-saturation coefficient is often considered to be a trait of an organism defining competitive strength in a trade-off conflict with maximum uptake rate. Theoretical studies have shown that a quadratic model characterizes the uptake rate, and that this model can be approximated by a MM model.(More)
When prey and predator are seasonal migrants, encounters depend on migration phenologies and environmental constraints on predation. Here we investigate the relative contribution of seasonality in irradiance and prey abundance in shaping the rapid seasonal body condition increase of a migrating predator searching visually for its prey: the Norwegian(More)
A central simplifying assumption in evolutionary behavioral ecology has been that optimal behavior is unaffected by genetic or proximate constraints. Observations and experiments show otherwise, so that attention to decision architecture and mechanisms is needed. In psychology, the proximate constraints on decision making and the processes from perception(More)
Studies on the relationship between the optimal phenotype and its environment have had limited focus on genotype-to-phenotype pathways and their evolutionary consequences. Here, we study how multi-layered trait architecture and its associated constraints prescribe diversity. Using an idealized model of the emotion system in fish, we find that trait(More)
Nutrient uptake affinity affects the competitive ability of microbial organisms at low nutrient concentrations. From the theory of diffusion limitation it follows that uptake affinity scales linearly with the cell radius. This is in conflict with some observations suggesting that uptake affinity scales to a quantity that is closer to the square of the(More)
Foraging processes in plankton and planktivorous fish are constrained by relative prey and predator size and therefore, these are important variables to include in a foraging model. The distribution of prey biomass across different size classes can be characterized by a size spectrum slope. We present a foraging model for anchovy larvae including the most(More)