Biology subjects

Ostbye, K.

Publications and source records attributed to Ostbye, K..

5 recordsLinked to original sources

bioRxiv2026

Mortality causes and annual survival rates of red foxes (Vulpes vulpes).

Mortality causes and survival rate estimates from individual follow-ups of GPS-collared animals provide reliable demographic data, but such estimates are rare for red foxes Vulpes vulpes. We used data from 126 GPS-collared red foxes tracked between 2011 and 2019 across a latitudinal gradient in central Sweden and Norway to quantify mortality causes and estimate annual survival probabilities using the Andersen-Gill extension of the Cox proportional hazards model. Hunting was the dominant mortality cause (63%), followed by vehicle collisions (14%), stress or malnutrition (11%), sarcoptic mange (9%), and predation (3%). Annual survival was 0.58 for adults and 0.32 for subadults. Subadults had approximately twice the hazard of adults, males had elevated hazard relative to females, and mortality risk was highest in autumn and early winter. These collar-based estimates are strikingly similar to mark-recovery estimates from the same region nearly five decades earlier, despite an intervening population collapse from sarcoptic mange, subsequent full recovery, and a major decline in harvest pressure. This convergence is consistent with density-dependent regulation at a food-determined and food-limited carrying capacity, suggesting that current harvest levels are not limiting the population. Furthermore, human-caused mortality was approximately four times greater than natural mortality, illustrating that living in close proximity to humans -- which often favours generalist predators such as red foxes -- may also come at a cost of increased mortality risk. Developing validated census methods for red foxes in boreal Scandinavia is identified as a key priority for quantitative population management.

ecology↗

bioRxiv2026

Latitudinal effects on weight and age-dependent survival of red fox Vulpes vulpes

Age-dependent survival is central to understanding population dynamics and life-history evolution. We analysed carcass weight and age-at-harvest data from 6 022 red foxes (Vulpes vulpes) collected across Sweden between 1967 and 1971 to evaluate latitudinal effects on body mass and age-dependent survival. Carcass weights decreased from south to north in both adults and sub-adults, contrary to Bergmanns rule, with southern foxes weighing approximately 1.27 times more than northern foxes. The latitudinal weight gradient exceeded the sex difference in both age classes, and no sex x region interaction was detected. The decrease in weight with latitude is consistent with reduced prey availability and harsher winter conditions in the north, which limit growth and body size during development. Using a Bayesian age-at-harvest model with region-specific population growth rates ({lambda}), we estimated age-dependent survival probabilities for four latitudinal regions and both sexes. Despite the strong latitudinal gradient in weight, survival did not show a corresponding pattern -- regional differences were uncertain, with all credible intervals spanning zero. Regional population growth rates were consistent with slight decline in the north and near-stability in the south-central region, which suggests that body condition and population dynamics are coupled at the regional scale despite no survival gradient. The decoupling of body condition and survival across regions suggests that mortality patterns are similar across the latitudinal gradient. We discuss these patterns in terms of latitudinal productivity gradients, prey availability, and life-history trade-offs in a widely distributed carnivore.

ecology↗

bioRxiv2020

The spatio-temporal axis for phenotypic change: a comparison of source and translocated Arctic charr populations after 25 generations

Evolution of morphological traits is hypothesized to act on an extended time scale, yet studies have suggested that these changes are possible within a few generations. Trophic polymorphism enabled through niche adaptations and ecological opportunity is one phenomenon that facilitate occurrence of rapid adaptive variation, common in many northern freshwater fish species. One such species is Arctic charr, which is known for its extensive variation in morphology and the occurrence of morphs. However, the speed at which such morphological variation arises is poorly studied despite the importance for understanding the onset of evolution. The aim of this study was to elucidate this process in a gradient of eight lakes that was stocked with Arctic charr in the period from 1910 to 1917 from Lake Tinnsjoen, Norway. We used morphological measurements to test for differences in traits between populations and Haldane and Darwins evolutionary rates to estimate divergence rates in traits. We also tested for correlation between putative genetic and morphological divergence. In addition, we contrasted the morphological divergence with that expected under neutral genetic expectations, using 12 microsatellite markers, to analyze whether and which morphological differences that is following early genetic divergence. A significant genetic differentiation was found between the source population and five of the translocated populations with corresponding differences in morphological traits for four of the populations. Population genetic structuring indicated six different genetic clusters. The translocated populations also exhibited trait divergence estimated with both Haldane and Darwins rates. Differences in morphological traits showed a significant correlation with genetic divergence, and the morphological differences were most likely affected by differences in lake parameters such as maximum depth, lake size and fish community. We conclude that intraspecific morphological and genetic divergence can form on short evolutionary time scales with important implications for conservation and management practices.

evolutionary biology↗

bioRxiv2019

And if you gaze long into an abyss, the abyss gazes also into thee: four morphs of Arctic charr adapting to a depth-gradient in Lake Tinnsjoen

BackgroundThe origin of species is a central topic in biology aiming at understanding mechanisms, level and rate of diversification. Ecological speciation is an important driver in adaptive radiation during post-glacial intra-lacustrine niche diversification in fishes. The Arctic charr Salvelinus alpinus L. species complex in the Northern hemisphere freshwater systems display huge morphological and life history divergence in lakes with one or several morphs present, thus offering a unique opportunity to address ongoing speciation mechanisms.\n\nWe studied Arctic charr in Lake Tinnsjoen by fishing in four nominal lake habitats (pelagial, littoral, shallow-moderate profundal, and deep-profundal habitats) down to 350 meters depth. Research topics addressed were; (1) to illuminate Holarctic phylogeography and lineages colonizing Lake Tinnsjoen, (2) to estimate reproductive isolation of morphs or fish using unbiased methods, and (3) to document eco-morphological and life history trait divergence. Also, we compared Lake Tinnsjoen with four Norwegian outgroup populations of Arctic charr.\n\nResultsFour field-assigned morphs were identified in Lake Tinnsjoen; the planktivore morph in all habitats except deep-profundal, the dwarf morph in shallow-moderate profundal, the piscivore morph in shallow-moderate profundal (less in littoral and deep-profundal), and an undescribed new morph - the abyssal morph in the deep-profundal only. The morphs displayed extensive life history variation based on age and size patterns. A moderate to high concordance was observed between field-assigned morphs and four unbiased genetic clusters obtained from microsatellite variation. MtDNA suggested the occurrence of two minor endemic clades in Lake Tinnsjoen likely originating from one widespread colonizing clade in the Holarctic. All morphs were genetically differentiated at microsatellites (FST: 0.12-0.20; with some ongoing gene flow among morphs, and for most mtDNA comparisons (FST: 0.04-0.38). Analyses of Norwegian outgroup lakes implied colonization from a river system below Lake Tinnsjoen.\n\nConclusionOur findings suggest post-glacial adaptive radiation of one colonizing mtDNA lineage with divergent niche specialization along a depth-temperature-productivity-pressure gradient. Concordance between reproductive isolation and the realized habitat of the morphs imply that ecological speciation may be the mechanism of divergence. Particularly novel is the extensive morph diversification with depth into the often unexplored deep-water profundal habitat, suggesting we may have systematically underestimated biodiversity present in lakes.

evolutionary biology↗

bioRxiv2019

Case studies and mathematical models of ecological speciation. V. Adaptive divergence of whitefish in Fennoscandia.

Modern speciation theory has greatly benefited from a variety of simple mathematical models focusing on the conditions and patterns of speciation and diversification in the presence of gene flow. Unfortunately the application of general theoretical concepts and tools to specific ecological systems remains a challenge. Here we apply modeling tools to better understand adaptive divergence of whitefish during the postglacial period in lakes of northern Fennoscandia. These lakes harbor up to three different morphs associated with the three major lake habitats: littoral, pelagic, and profundal. Using large-scale individual-based simulations, we aim to identify factors required for in situ emergence of the pelagic and profundal morphs in lakes initially colonized by the littoral morph. The importance of some of the factors we identify and study - sufficiently large levels of initial genetic variation, size- and habitat-specific mating, sufficiently large carrying capacity of the new niche - is already well recognized. In addition, our model also points to two other factors that have been largely disregarded in theoretical studies: fitness-dependent dispersal and strong predator pressure in the ancestral niche coupled with the lack of it in the new niche(s). We use our theoretical results to speculate about the process of diversification of whitefish in Fennoscandia and to identify potentially profitable directions for future empirical research.

evolutionary biology↗