Yngvild Vindenes

• Vindenes, Yngvild; Broch, Catharina; Andersen, Tom; Hessen, Dag Olav & Ergon, Torbjørn (2025). Understanding the role of ageing in the thermal responses of life history and fitness in Daphnia magna. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 292(2051). doi: 10.1098/rspb.2025.0430. Full text in Research Archive Show summary

  The current climate warming has raised concerns that increased rates of ageing will lead to reduced fitness and population viability in ectotherms. However, it is currently not known whether temperature effects on the rate of ageing mainly reflect a change in pace of life or changes in the strength of ageing in the life history. Evaluating this question requires that ageing in different temperatures is compared on the same intrinsic pace-standardized time scale. We present results from a laboratory experiment with Daphnia magna , recording complete life histories of 240 individuals from four clonal lines at six temperatures (5°C to 30°C). For each clone and temperature, we calculated measures of pace and shape of ageing in survival and reproduction. Fitness (long-term population growth rate) and mean lifetime reproduction were calculated using matrix population models. Our results highlight three main points: (i) lifespan is not a good predictor of temperature effects on ageing; (ii) there is no strong consistent effect of temperature on shape of ageing; and (iii) within temperature, the shape of ageing was positively correlated with fitness. Hence, lower fitness and population viability of ectotherms in warmer environments may be driven by factors other than increased ageing rates.

• Vindenes, Yngvild & Mysterud, Atle (2025). A seasonal matrix population model for ixodid ticks with complex life histories and limited host availability. Ecology. ISSN 0012-9658. 106(1). doi: 10.1002/ecy.4511. Full text in Research Archive Show summary

  Many vector-borne diseases are sensitive to changes in land use and climate; hence, it is important to understand the factors that govern the vector populations. Ixodid ticks, which serve as vectors for multiple diseases, have a slow life cycle compared with many of their hosts. The observable questing population represents only a fraction of the total tick population and may include overlapping cohorts in each stage. The duration of each life stage (larvae, nymph, and adult) is variable and depends on factors such as the seasonal timing of questing, development, and host availability. Mathematical models are therefore essential to mediate how complex life cycle transitions and host interactions underpin the seasonal dynamics of the questing tick population. In this study, we develop a seasonal matrix population model for ixodid ticks feeding on a small and large host. The model has 17 stages representing the main life history stages (eggs, larvae, nymphs, and adults) combined with status of feeding, seasonal timing of feeding, and overwintering. The probability of finding a host depends on tick instar and host type, and density regulation is incorporated through limited host capacity. Using a life history representing Ixodes ricinus in Northern Europe as a baseline, we extract seasonal numbers of different parts of the tick population and calculate life history outcomes such as generation time and mean and variance of lifespan and of lifetime reproductive output. These results are compared with an alternative scenario of a southern life history. Secondly, we investigate (1) effects of seasonality in the small host availability on the seasonal numbers of tick stages and (2) effects of varying host availability and utilization of small versus large hosts by larvae and nymphs, on the seasonal numbers of questing ticks. Our results suggest that the small host availability is an important regulating factor through the feeding of larvae. Our model incorporates complex mechanisms underlying the seasonal composition of the tick population. It can be applied to different ixodid tick species and provides a framework for future investigations into intra- and interspecific variation in life history and population dynamics.

• Goren, Asena; Mysterud, Atle & Vindenes, Yngvild (2024). Modeling the effects of phenological mismatch in tick questing and host demographic turnover on Lyme disease hazard. Ecological Modelling. ISSN 0304-3800. 498. doi: 10.1016/j.ecolmodel.2024.110910. Full text in Research Archive Show summary

  Climate change is altering the seasonal abundance and activity patterns of ecologically interacting species. It is not yet known how changes in phenological alignment between ticks and their hosts will impact tick feeding, survival, and the timing and probability of pathogen transmission during feeding. It has been observed that the seasonal timing of human Lyme disease cases has shifted earlier, accompanying an increased incidence, which may reflect changes in tick questing phenology. We present a mathematical model framework for exploring the seasonal dynamics of a tick-borne pathogen. The model extends a recently developed seasonal population matrix model for ixodid ticks feeding on a small and a large host, to i) incorporate the transmission of a pathogen, based on the causative agent of Lyme disease, Borrelia burgdorferi sensu lato, between ticks and a reservoir-competent small mammal host, and ii) include seasonal demographic turnover in the small mammal host. Through modification of model parameters, we explored the effects of alternative scenarios for tick questing phenology, tick host selection, and seasonality of host reproduction on disease dynamics. Our model predicts that due to differences in their life history, seasonal infection prevalence is much more variable in the small mammalian host than in the tick vector. The rapid pace of host demographic turnover is important for clearing infection in the small mammal population. The alignment between the seasonal timing of host reproduction and tick questing phenology is a critical feature in the model, as it determines pathogen transmission and infection prevalence in host and vector populations. The model predicts that increased asynchrony between larval tick feeding and small host reproduction can increase the number of infected questing nymphs, a common metric for Lyme disease hazard. When larval tick feeding is misaligned with small host reproduction, the larvae feed predominantly on older hosts, which are more likely to be infected. Our model presents an adaptable framework for exploring seasonal relationships between pathogen dynamics, host demography, and vector life history traits in an emergent tick-borne disease system.

• Kauserud, Håvard; Justad, Tor Arne; Vindenes, Yngvild; Methlie, Ine-Susanne Hopland; Sønstebø, Jørn Henrik & Skrede, Inger [Show all 7 contributors for this article] (2024). Limited evidence of local adaptation of growth and decomposition rates in the widespread wood-decay fungus Fomitopsis pinicola. Fungal ecology. ISSN 1754-5048. 70. doi: 10.1016/j.funeco.2024.101353. Full text in Research Archive
• Vindenes, Yngvild; Langvatn, Rolf & Mysterud, Atle (2023). Shifting seasonality of annual growth through ontogeny for red deer at northern latitudes. Ecosphere. 14(8), p. 1–11. doi: 10.1002/ecs2.4639. Full text in Research Archive Show summary

  Large mammals at northern latitudes show annual cycles of body mass gain insummer and body mass loss in winter. The amplitude and seasonal timing ofthese cycles may vary through ontogeny depending on trade-offs towardinvestments in structural growth versus fat storage, reproduction, and futuresurvival. Despite this knowledge, there is no detailed model of how the season-ality of body mass develops through ontogeny. Here, we define a new seasonalgrowth model that accounts for shifting seasonality through two sine compo-nents: one included in the growth coefficient and the other on the asymptoticsize. We fitted 12 candidate models to longitudinal data on body mass of cap-tive male and female red deer (Cervus elaphus) in Norway, with different base-line growth structures (von Bertalanffy, Gompertz, and Brody) and includingzero, one, or both of the seasonal components. The best fitting model was theBrody model with both seasonal components included, allowing the annualpeak to shift through ontogeny: The annual peak occurred in December forcalves, shifting to November in yearlings, and October in 2- and 3-year-olds,ending with September for adults. All age classes showed an annual minimumat the end of winter around March. Males and females showed similar sea-sonal peaks through ontogeny, although males grow bigger and have largerseasonal amplitudes. Our new growth model provides a flexible framework tomodel seasonal growth changing through ontogeny, applicable to differentspecies. Brody, Gompertz, growth model, ontogenetic shift, red deer, seasonal growth, seasonality,ungulates, von Bertalanffy

• Goren, Asena; Viljugrein, Hildegunn; Rivrud, Inger Maren; Jore, Solveig; Bakka, Haakon & Vindenes, Yngvild [Show all 7 contributors for this article] (2023). The emergence and shift in seasonality of Lyme borreliosis in Northern Europe. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 290(1993). doi: 10.1098/rspb.2022.2420. Full text in Research Archive Show summary

  Climate change has had a major impact on seasonal weather patterns, resulting in marked phenological changes in a wide range of taxa. However, empirical studies of how changes in seasonality impact the emergence and seasonal dynamics of vector-borne diseases have been limited. Lyme borreliosis, a bacterial infection spread by hard-bodied ticks, is the most commonvector-borne disease in the northern hemisphere and has been rapidly increasing in both incidence and geographical distribution in many regions of Europe and North America. By analysis of long-term surveillance data (1995–2019) from across Norway (latitude 57°580–71°080 N), we demonstrate a marked change in the within-year timing of Lyme borreliosis cases accompanying an increase in the annual number of cases. The seasonal peak in cases is now six weeks earlier than 25 years ago, exceeding seasonal shifts in plant phenology and previous model predictions. The seasonal shift occurred predominantly in the first 10 years of the study period. The concurrent upsurgence in case number and shift in case timing indicate a major change in the Lyme borreliosis disease system over recent decades. This study highlights the potential for climate change to shape the seasonal dynamics of vector-borne disease systems. seasonality, vector-borne zoonoses,disease ecology, Lyme borreliosis,Lyme disease, climate change, ecology, health and disease and epidemiology

• Goren, Asena; Mysterud, Atle; Jore, Solveig; Viljugrein, Hildegunn; Bakka, Haakon & Vindenes, Yngvild (2023). Demographic patterns in Lyme borreliosis seasonality over 25 years. Zoonoses and Public Health. ISSN 1863-1959. 70(7), p. 647–655. doi: 10.1111/zph.13073. Full text in Research Archive Show summary

  Abstract Lyme borreliosis, the most common vector‐borne disease in Europe and North America, is attracting growing concern due to its expanding geographic range. The growth in incidence and geographic spread is largely attributed to climate and land‐use changes that support the tick vector and thereby increase disease risk. Despite a wide range of symptoms displayed by Lyme borreliosis patients, the demographic patterns in clinical manifestations and seasonal case timing have not been thoroughly investigated and may result from differences in exposure, immunity and pathogenesis. We analysed 25 years of surveillance data from Norway, supplemented by population demography data, using a Bayesian modelling framework. The analyses aimed to detect differences in case seasonality and clinical manifestations of Lyme borreliosis across age and sex differentiated patient groups. The results showed a bimodal pattern of incidence over age, where children (0–9 years) had the highest incidence, young adults (20–29 years) had low incidence and older adults had a second incidence peak in the ages 70–79 years. Youth (0–19 years) presented with a higher proportion of neuroborreliosis cases and a lower proportion of arthritic manifestations compared to adults (20+ years). Adult males had a higher overall incidence than adult females and a higher proportion of arthritis cases. The seasonal timing of Lyme borreliosis consistently occurred around 4.4 weeks earlier in youth compared to adults, regardless of clinical manifestation. All demographic groups exhibited a shift towards an earlier seasonal timing over the 25‐year study period, which appeared unrelated to changes in population demographics. However, the disproportionate incidence of Lyme borreliosis in seniors requires increased public awareness and knowledge about this high‐risk group as the population continues to age concurrently with disease emergence. Our findings highlight the importance of considering patient demographics when analysing the emergence and seasonal patterns of vector‐borne diseases using long‐term surveillance data.

• Coeur, Christie Le; Yoccoz, Nigel; Salguero-Gómez, Roberto & Vindenes, Yngvild (2022). Life history adaptations to fluctuating environments: Combined effects of demographic buffering and lability. Ecology Letters. ISSN 1461-023X. 25(10), p. 2107–2119. doi: 10.1111/ele.14071. Full text in Research Archive Show summary

  Demographic buffering and lability have been identified as adaptive strategies to optimise fitness in a fluctuating environment. These are not mutually exclusive, however, we lack efficient methods to measure their relative importance for a given life history. Here, we decompose the stochastic growth rate (fitness) into components arising from nonlinear responses and variance–covariance of demographic parameters to an environmental driver, which allows studying joint effects of buffering and lability. We apply this decomposition for 154 animal matrix population models under different scenarios to explore how these main fitness components vary across life histories. Faster-living species appear more responsive to environmental fluctuations, either positively or negatively. They have the highest potential for strong adaptive demographic lability, while demographic buffering is a main strategy in slow-living species. Our decomposition provides a comprehensive framework to study how organisms adapt to variability through buffering and lability, and to predict species responses to climate change.

• Thunell, Viktor; Gårdmark, Anna; Huss, Magnus & Vindenes, Yngvild (2022). Optimal energy allocation trade-off driven by size-dependent physiological and demographic responses to warming. Ecology. ISSN 0012-9658. 104(4). doi: 10.1002/ecy.3967. Full text in Research Archive Show summary

  Body size–dependent physiological effects of temperature influence individual growth, reproduction, and survival, which govern animal population responses to global warming. Considerable knowledge has been established on how such effects can affect population growth and size structure, but less is known of their potential role in temperature-driven adaptation in life-history traits. In this study, we ask how warming affects the optimal allocation of energy between growth and reproduction and disentangle the underlying fitness trade-offs. To this end, we develop a novel dynamic energy budget integral projection model (DEB–IPM), linking individuals' size- and temperature-dependent consumption and maintenance via somatic growth, reproduction, and size-dependent energy allocation to emergent population responses. At the population level, we calculate the long-term population growth rate (fitness) and stable size structure emerging from demographic processes. Applying the model to an example of pike (Esox lucius), we find that optimal energy allocation to growth decreases with warming. Furthermore, we demonstrate how growth, fecundity, and survival contribute to this change in optimal allocation. Higher energy allocation to somatic growth at low temperatures increases fitness through survival of small individuals and through the reproduction of larger individuals. In contrast, at high temperatures, increased allocation to reproduction is favored because warming induces faster somatic growth of small individuals and increased fecundity but reduced growth and higher mortality of larger individuals. Reduced optimum allocation to growth leads to further reductions in body size and an increasingly truncated population size structure with warming. Our study demonstrates how, by incorporating general physiological mechanisms driving the temperature dependence of life-history traits, the DEB–IPM framework is useful for investigating the adaptation of size-structured organisms to warming.

• Nater, Chloe Rebecca; Stubberud, Marlene Wæge; Langangen, Øystein Ole Gahr; Rustadbakken, Atle; Moe, S. Jannicke & Ergon, Torbjørn [Show all 8 contributors for this article] (2022). Towards a future without stocking: harvest and river regulation determine long-term population viability of migratory salmonids. Climate Research (CR). ISSN 0936-577X. 86, p. 37–52. doi: 10.3354/cr01644. Full text in Research Archive Show summary

  Freshwater species are particularly vulnerable to emerging threats linked to climate change because they are often already heavily impacted by habitat destruction, pollution, and exploitation. For many harvested populations of freshwater fish, these combined impacts have been mitigated for decades through stocking with captive-bred individuals. However, stocking may lead to loss of genetic variation, which may be crucial for adaptation under climate change. Exploration of sustainable alternatives is therefore paramount. We used a female-based integral projection model (IPM) to assess the consequences of terminating a long-term stocking programme for a population of landlocked, migratory brown trout Salmo trutta, and to evaluate relative effectiveness of alternative management strategies involving harvest regulations and river habitat improvement. The IPM classified individuals by body size, life history stage, and location relative to a hydropower dam, and was parameterised with 50 yr of individual-based data, supplemented with literature values. Model simulations indicated a strong population decline of 22-29% per year without stocking, much of which was attributed to high harvest mortality. Consequently, drastic reductions in fishing pressure were predicted to be necessary to ensure population viability without stocking. Mitigation measures reducing mortality associated with the hydropower dam or restoring spawning areas could further contribute to population viability when combined with changes in harvest regulations. Our results thus emphasise that large changes in management strategies, such as termination of long-term stocking programmes, require a thorough assessment of potential consequences and alternative mitigation strategies using data and models, or, at the very least, a precautionary approach under consideration of on-going climate change. Migratory salmonid · Salmo trutta · Integral projection model · Harvest · Fishing · Stocking · Dam · Hydropower · Trout

• Stubberud, Marlene Wæge; Nater, Chloe Rebecca; Vindenes, Yngvild; Vøllestad, Leif Asbjørn & Langangen, Øystein Ole Gahr (2021). Low impact of first-time spawners on population growth in a brown trout population. Climate Research (CR). ISSN 0936-577X. 86, p. 65–78. doi: 10.3354/cr01645. Full text in Research Archive Show summary

  For species with individual variation in reproductive success, experience in breeding and the distribution of different breeders is important for population productivity and viability. Human impacts, such as climate change and harvesting, can alter this distribution and thus population dynamics. Here, we investigated the effect of spawning experience on population growth in a population of migratory brown trout Salmo trutta subject to stressors including migration barriers, harvesting, and climate change. We described the population dynamics with a structured integral projection model that differentiates between first-time and repeat spawners. We then took a scenario-based approach to test to which extent spawning experience has a positive effect on the population growth of brown trout by running 3 different model simulations: a baseline scenario with no changes to the reproductive output of the population, a non-selective scenario in which the reproductive output of all spawners was reduced, and a selective scenario where the reproductive output of only first-time spawners was reduced. We found that the reproductive output of repeat spawners is more important than that of first-time spawners for population growth, in line with other studies. Moreover, the contribution of first-time spawners to the population growth through their own survival is more important than their contribution to growth through reproduction. To ensure the continued existence of the study population, survival of first-time spawners and reproductive success of repeat spawners should be prioritised. More generally, including breeding experience adds more mechanistic detail, which ultimately can aid management and conservation efforts. Integral projection model · Iteroparity · Spawning experience · Management · Selective harvesting · Population dynamics · Brown trout · Salmo trutta · Dam

• Nater, Chloe R; Vindenes, Yngvild; Aass, Per; Cole, Diana; Langangen, Øystein & Moe, S. Jannicke [Show all 10 contributors for this article] (2020). Size‐ and stage‐dependence in cause‐specific mortality of migratory brown trout. Journal of Animal Ecology. ISSN 0021-8790. 89(9), p. 2122–2133. doi: 10.1111/1365-2656.13269. Full text in Research Archive Show summary

  Evidence‐based management of natural populations under strong human influence frequently requires not only estimates of survival but also knowledge about how much mortality is due to anthropogenic vs. natural causes. This is the case particularly when individuals vary in their vulnerability to different causes of mortality due to traits, life history stages, or locations. Here, we estimated harvest and background (other cause) mortality of landlocked migratory salmonids over half a century. In doing so, we quantified among‐individual variation in vulnerability to cause‐specific mortality resulting from differences in body size and spawning location relative to a hydropower dam. We constructed a multistate mark–recapture model to estimate harvest and background mortality hazard rates as functions of a discrete state (spawning location) and an individual time‐varying covariate (body size). We further accounted for among‐year variation in mortality and migratory behaviour and fit the model to a unique 50‐year time series of mark–recapture–recovery data on brown trout (Salmo trutta) in Norway. Harvest mortality was highest for intermediate‐sized trout, and outweighed background mortality for most of the observed size range. Background mortality decreased with body size for trout spawning above the dam and increased for those spawning below. All vital rates varied substantially over time, but a trend was evident only in estimates of fishers' reporting rate, which decreased from over 50% to less than 10% throughout the study period. We highlight the importance of body size for cause‐specific mortality and demonstrate how this can be estimated using a novel hazard rate parameterization for mark–recapture models. Our approach allows estimating effects of individual traits and environment on cause‐specific mortality without confounding, and provides an intuitive way to estimate temporal patterns within and correlation among different mortality sources.

• Stubberud, Marlene Wæge; Vindenes, Yngvild; Vøllestad, Asbjørn; Winfield, Ian J.; Stenseth, Nils Christian & Langangen, Øystein (2019). Effects of size‐ and sex‐selective harvesting: An integral projection model approach. Ecology and Evolution. 9(22), p. 12556–12570. doi: 10.1002/ece3.5719. Full text in Research Archive Show summary

  Harvesting is often size‐selective, and in species with sexual size dimorphism, it may also be sex‐selective. A powerful approach to investigate potential consequences of size‐ and/or sex‐selective harvesting is to simulate it in a demographic population model. We developed a population‐based integral projection model for a size‐ and sex‐structured species, the commonly exploited pike (Esox lucius). The model allows reproductive success to be proportional to body size and potentially limited by both sexes. We ran all harvest simulations with both lower size limits and slot limits, and to quantify the effects of selective harvesting, we calculated sex ratios and the long‐term population growth rate (λ). In addition, we quantified to what degree purely size‐selective harvesting was sex‐selective, and determined when λ shifted from being female to male limited under size‐ and sex‐selective harvesting. We found that purely size‐selective harvest can be sex‐selective, and that it depends on the harvest limits and the size distributions of the sexes. For the size‐ and sex‐selective harvest simulations, λ increased with harvest intensity up to a threshold as females limited reproduction. Beyond this threshold, males became the limiting sex, and λ decreased as more males were harvested. The peak in λ, and the corresponding sex ratio in harvest, varied with both the selectivity and the intensity of the harvest simulation. Our model represents a useful extension of size‐structured population models as it includes both sexes, relaxes the assumption of female dominance, and accounts for size‐dependent fecundity. The consequences of selective harvesting presented here are especially relevant for size‐ and sex‐structured exploited species, such as commercial fisheries. Thus, our model provides a useful contribution toward the development of more sustainable harvesting regimes.

• Ohlberger, Jan Philipp; Langangen, Øystein; Winfield, Ian J & Vindenes, Yngvild (2019). The importance of variation in offspring body size for stability in cannibalistic populations. Oikos. ISSN 0030-1299. 129(1), p. 59–69. doi: 10.1111/oik.05507. Full text in Research Archive Show summary

  Animals exhibit remarkable intraspecific variation in phenotypic traits such as body size. Understanding how such trait variation affects population and ecosystem dynamics is critically important, because future environmental change and human impacts are expected to alter phenotypic trait distributions. In species with seasonal reproduction, offspring size variation within cohorts is ubiquitous, yet we know little about its implications for population stability. In addition, long‐term monitoring data indicate that changes in offspring size variation occur at ecologically relevant time scales. Here, we study the consequences of changing offspring size variation by developing and analysing an integral projection model (IPM). Our model accounts for size‐dependent cannibalism as well as additional density regulation occurring during the first year. The model is parameterized using literature values and long‐term monitoring data for pike Esox lucius, a common fish predator in temperate freshwater ecosystems, but the general model structure applies to a wide range of size‐structured organisms. Our analyses demonstrate that a wide size distribution of offspring promotes stable dynamics, whereas narrow distributions can be destabilizing because cannibalism increases the annual variation in mean offspring mortality. Our results indicate that the stabilizing effect of offspring size variation is likely an important property of size‐structured organisms with seasonal reproduction and cannibalistic behaviour. This work highlights the importance of intracohort trait variation and describes how variation in body size can shape the dynamics of animal populations.

• Ergon, Torbjørn; Borgan, Ørnulf; Nater, Chloé Rebecca & Vindenes, Yngvild (2018). The utility of mortality hazard rates in population analyses. Methods in Ecology and Evolution. 9, p. 2046–2056. doi: 10.1111/2041-210X.13059. Full text in Research Archive
• Färber, Leonie Anette; Durant, Joel Marcel; Vindenes, Yngvild & Langangen, Øystein (2018). Increased early offspring growth can offset the costs of long-distance spawning migration in fish. Marine Ecology Progress Series. ISSN 0171-8630. 600, p. 141–150. doi: 10.3354/meps12662. Full text in Research Archive Show summary

  For long-distance migrations to pay off for individual fish, the energetic costs must be counterbalanced by benefits. Understanding the fitness trade-offs associated with migration is essential for our ability to sustainably manage migratory species. Here, we investigated such trade-offs associated with the spawning migration of Northeast Arctic cod Gadus morhua, a stock of high historical and commercial value known to be able to migrate more than 1000 km southward to reach suitable spawning grounds. Reaching the more distant spawning grounds requires more energy and hence leaves less energy available for processes such as egg production. Previous studies have indicated that increased larval survival (e.g. from rapid early development in warmer southern waters) may offset the parental costs of migration. However, it was suggested that spatial variability in survival of early life stages might cancel out this survival benefit. As an alternative, we ask if the fitness benefit of long-distance migration may reside in increased offspring growth. Using an integral projection model incorporating effects of body length and migration distance, we quantified the increase in offspring growth needed to offset parental costs of long-distance migration on fitness. Our results suggest that a 12.5% length in crease of juvenile cod is required to offset parental costs of long-distance migration. This is within the estimated growth benefit of 20% suggested by drift models of early life stages of cod. These results highlight the potential importance of offspring growth as another factor explaining the benefit of long distance migration, broadening our knowledge on spawning migration.

• Nater, Chloé Rebecca; Rustadbakken, Atle; Ergon, Torbjørn; Langangen, Øystein; Moe, S. Jannicke & Vindenes, Yngvild [Show all 8 contributors for this article] (2018). Individual heterogeneity and early life conditions shape growth in a freshwater top predator. Ecology. ISSN 0012-9658. 99(5), p. 1011–1017. doi: 10.1002/ecy.2178. Full text in Research Archive Show summary

  Body size can have profound impacts on survival, movement, and reproductive schedules shaping individual fitness, making growth a central process in ecological and evolutionary dynamics. Realized growth is the result of a complex interplay between life history schedules, individual variation, and environmental influences. Integrating all of these aspects into growth models is methodologically difficult, depends on the availability of repeated measurements of identifiable individuals, and consequently represents a major challenge in particular for natural populations. Using a unique 30‐yr time series of individual length measurements inferred from scale year rings of wild brown trout, we develop a Bayesian hierarchical model to estimate individual growth trajectories in temporally and spatially varying environments. We reveal a gradual decrease in average juvenile growth, which has carried over to adult life and contributed to decreasing sizes observed at the population level. Commonly studied environmental drivers like temperature and water flow did not explain much of this trend and overall persistent and among‐year individual variation dwarfed temporal variation in growth patterns. Our model and results are relevant to a wide range of questions in ecology and evolution requiring a detailed understanding of growth patterns, including conservation and management of many size‐structured populations.

• Caswell, Hal & Vindenes, Yngvild (2018). Demographic variance in heterogeneous populations: matrix models and sensitivity analysis. Oikos. ISSN 0030-1299. 127(5), p. 648–663. doi: 10.1111/oik.04708. Full text in Research Archive Show summary

  The demographic consequences of stochasticity in processes such as survival and reproduction are modulated by the heterogeneity within the population. Therefore, to study effects of stochasticity on population growth and extinction risk, it is critical to use structured population models in which the most important sources of heterogeneity (e.g. age, size, developmental stage) are incorporated as i‐state variables. Demographic stochasticity in heterogeneous populations has often been studied using one of two approaches: multitype branching processes and diffusion approximations. Here, we link these approaches, through the demographic stochasticity in age‐ or stage‐structured matrix population models. We derive the demographic variance, σ2d, which measures the per capita contribution to the variance in population growth increment, and we show how it can be decomposed into contributions from transition probabilities and fertility across ages or stages. Furthermore, using matrix calculus we derive the sensitivity of σ2d to age‐ or stage‐specific mortality and fertility. We apply the methods to an extensive set of data from age‐classified human populations (long‐term time‐series for Sweden, Japan and the Netherlands; two hunter–gatherer populations, and the high‐fertility Hutterites), and to a size‐classified population of the herbaceous plant Calathea ovandensis. For the human populations our analysis reveals substantial temporal changes in the demographic variance as well as its main components across age. These new methods provide a powerful approach for calculating the demographic variance for any structured model, and for analyzing its main components and sensitivities. This will make possible new analyses of demographic variance across different kinds of heterogeneity in different life cycles, which will in turn improve our understanding of mechanisms underpinning extinction risk and other important biological outcomes.

• Carim, Kellie; Vindenes, Yngvild; Eby, Lisa A.; Barfoot, Craig & Vøllestad, Leif Asbjørn (2017). Life history, population viability, and the potential for local adaptation in isolated trout populations. Global Ecology and Conservation. 10, p. 93–102. doi: 10.1016/j.gecco.2017.02.001. Full text in Research Archive Show summary

  Habitat loss and fragmentation have caused population decline across taxa through impacts on life history diversity, dispersal patterns, and gene flow. Yet, intentional isolation of native fish populations is a frequently used management strategy to protect against negative interactions with invasive fish species. We evaluated the population viability and genetic diversity of 12 isolated populations of Oncorhynchus clarkii lewisi located on the Flathead Indian Reservation in Montana, USA. Length-structured integral projection models (IPMs) were used to project population growth rate (lambda) and its sensitivity to underlying vital rates and parameters. We examined relationships between lambda, genetic diversity, and habitat size and quality. Lambda ranged from 0.68 to 1.1 with 10 of 12 populations projected to be in decline. A sensitivity analysis of lambda with respect to projection matrix elements indicated that lambda was generally sensitive to changes in early life history stages (survival/growth), but patterns differed among populations. Another sensitivity analysis with respect to underlying model parameters showed highly consistent pattern across populations, with lambda being most sensitive to the slope of probability of maturity (estimated from published literature), generally followed by adult survival, and the slope of somatic growth rate (directly measured from each population). Lambda was not correlated with genetic diversity. For populations residing in small isolated streams (≤5 km of occupied habitat), lambda significantly increased with base flow discharge (r2=0.50, p<0.02). Our results highlight the potential importance of local adaptation for persistence of small, isolated populations. Specifically we saw evidence for higher probability of maturity at smaller sizes in the smallest, coldest isolated systems, increasing probability of persistence for these populations. Climate change threatens to further fragment populations of aquatic organisms and reduce summertime base flows in much of western North America. Insights from studies such as ours will inform management strategies for long-term persistence of species facing these challenges.

• Vindenes, Yngvild & Engen, Steinar (2017). Demographic stochasticity and temporal autocorrelation in the dynamics of structured populations. Oikos. ISSN 0030-1299. 126(4), p. 462–471. doi: 10.1111/oik.03958. Full text in Research Archive
• Vindenes, Yngvild; Langangen, Øystein; Winfield, Ian J. & Vøllestad, Leif Asbjørn (2016). Fitness consequences of early life conditions and maternal size effects in a freshwater top predator. Journal of Animal Ecology. ISSN 0021-8790. 85(3), p. 692–704. doi: 10.1111/1365-2656.12489. Full text in Research Archive
• Vindenes, Yngvild & Langangen, Øystein (2015). Individual heterogeneity in life histories and eco-evolutionary dynamics. Ecology Letters. ISSN 1461-023X. 18(5), p. 417–432. doi: 10.1111/ele.12421. Full text in Research Archive
• Lawson, Callum; Vindenes, Yngvild; Bailey, Liam & Pol, Martijn Van de (2015). Environmental variation and population responses to global change. Ecology Letters. ISSN 1461-023X. 18(7), p. 724–736. doi: 10.1111/ele.12437. Full text in Research Archive
• Vindenes, Yngvild; Edeline, Eric; Ohlberger, Jan; Langangen, Øystein; Winfield, Ian J. & Stenseth, Nils Christian [Show all 7 contributors for this article] (2014). Effects of climate change on trait-based dynamics of a top predator in freshwater ecosystems. The American Naturalist. ISSN 0003-0147. 183(2), p. 243–256. doi: 10.1086/674610. Full text in Research Archive Show summary

  Predicted universal responses of ectotherms to climate warming include increased maximum population growth rate and changes in body size through the temperature-size rule. However, the mechanisms that would underlie these predicted responses are not clear. Many studies have focused on proximate mechanisms of physiological processes affecting individual growth. One can also consider ultimate mechanisms involving adaptive explanations by evaluating temperature effects on different vital rates across the life history and using the information in a population dynamical model. Here, we combine long-term data for a top predator in freshwater ecosystems (pike; Esox lucius) with a stochastic integral projection model to analyze concurrent effects of temperature on vital rates, body size, and population dynamics. As predicted, the net effect of warming on population growth rate (fitness) is positive, but the thermal sensitivity of this rate is highly size- and vital rate–dependent. These results are not sensitive to increasing variability in temperature. Somatic growth follows the temperature-size rule, and our results support an adaptive explanation for this response. The stable length structure of the population shifts with warming toward an increased proportion of medium-sized but a reduced proportion of small and large individuals. This study highlights how demographic approaches can help reveal complex underlying mechanisms for population responses to warming. © 2014 University of Chicago Press

• Vindenes, Yngvild; Sæther, Bernt-Erik & Engen, Steinar (2012). Effects of demographic structure on key properties of stochastic density-independent population dynamics. Theoretical Population Biology. ISSN 0040-5809. 82(4), p. 253–263. doi: 10.1016/j.tpb.2011.10.002. Full text in Research Archive
• Pol, Martijn Van de; Vindenes, Yngvild; Sæther, Bernt-Erik; Engen, Steinar; Ens, Bruno J & Oosterbeek, Kees [Show all 7 contributors for this article] (2011). Poor environmental tracking can make extinction risk insensitive to the colour of environmental noise. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 278(1725), p. 3713–3722. doi: 10.1098/rspb.2011.0487. Full text in Research Archive
• Vindenes, Yngvild; Engen, Steinar & Sæther, Bernt-Erik (2011). Integral projection models for finite populations in a stochastic environment. Ecology. ISSN 0012-9658. 92(5), p. 1146–1156. doi: 10.1890/10-0500.1. Full text in Research Archive
• Vindenes, Yngvild; Lee, Aline Magdalena; Engen, Steinar & Sæther, Bernt-Erik (2010). FIXATION OF SLIGHTLY BENEFICIAL MUTATIONS: EFFECTS OF LIFE HISTORY. Evolution. ISSN 0014-3820. 64(4), p. 1063–1075. doi: 10.1111/j.1558-5646.2009.00868.x. Full text in Research Archive
• Pol, Martijn Van de; Vindenes, Yngvild; Sæther, Bernt-Erik; Engen, Steinar; Ens, BJ & Oosterbeek, K [Show all 7 contributors for this article] (2010). Effects of climate change and variability on population dynamics in a long-lived shorebird. Ecology. ISSN 0012-9658. 91(4), p. 1192–1204. Full text in Research Archive
• Vindenes, Yngvild; Engen, Steinar & Sæther, Bernt-Erik (2008). Individual heterogeneity in vital parameters and demograpiic stochasticity. The American Naturalist. ISSN 0003-0147. 171, p. 455–467. doi: 10.1086/528965. Full text in Research Archive

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• Vindenes, Yngvild (2025). Ageing, fitness, and ectotherm responses to climate warming: Do increased rates of ageing reduce population viability in a warmer world? Full text in Research Archive
• Vindenes, Yngvild (2024). Seasonality, demography and Lyme disease in Northern Europe. Full text in Research Archive
• Vindenes, Yngvild; Coeur, Christie Le & Caswell, Hal (2021). Introduction to Matrix Population Models. In Roberto, Salguero-Gomez & Marlène, Gamelon (Ed.), Demographic methods across the tree of life. Oxford University Press. ISSN 9780198838609. p. 163–180. doi: 10.1093/oso/9780198838609.003.0009. Full text in Research Archive
• Che-Castaldo, Judy; Jones, Owen R.; Kendall, Bruce E.; Burns, Jean H.; Childs, Dylan Z. & Ezard, Thomas H.G. [Show all 16 contributors for this article] (2020). Comments to “Persistent problems in the construction of matrix population models”. Ecological Modelling. ISSN 0304-3800. 416. doi: 10.1016/j.ecolmodel.2019.108913. Full text in Research Archive
• Vindenes, Yngvild (2019). Using demographic approaches to understand ecological and evolutionary responses to a warmer and more variable world. Full text in Research Archive
• Vindenes, Yngvild (2019). Effects of climate change in size-structured populations. Full text in Research Archive
• Vindenes, Yngvild; Broch, Catharina & Heuschele, Jan David (2018). Når oppveksten styres av temperatur - bidrag til Forskningstorget 2018. Full text in Research Archive Show summary

  For de aller fleste dyr på jorda, er lengden på barndommen ikke et spørsmål om alder alene, men om hvor kaldt eller varmt miljøet i oppveksten har vært. For 99% av alle dyr på jorda er det temperaturen som bestemmer hvor raskt livsklokken tikker. Blant disse dyrene finner vi dafnier (vannlopper) som lever i små og store dammer der temperaturen kan skifte raskt og mye. Kom til vår bod og regn ut din egen dafnie-alder, hils på kalde og varme dafnier, og lær mer om hvordan temperatur påvirker lengden på barndommen og levealderen til disse dyrene.

• Vindenes, Yngvild & Engen, Steinar (2018). A simple formula for the complex effects of individual heterogeneity on stochastic population dynamics: the role of temporal autocorrelation. Full text in Research Archive
• Vindenes, Yngvild & Engen, Steinar (2018). A simple formula for the complex effects of individual heterogeneity. Full text in Research Archive
• Hamel, Sandra; Gaillard, Jean-Michel; Yoccoz, Nigel Gilles; Bassar, Ron D.; Bouwhuis, Sandra & Caswell, Hal [Show all 14 contributors for this article] (2018). General conclusion to the special issue Moving forward on individual heterogeneity. Oikos. ISSN 0030-1299. 127(5), p. 750–756. doi: 10.1111/oik.05223. Full text in Research Archive
• Färber, Leonie Anette; Durant, Joel Marcel; Vindenes, Yngvild & Langangen, Øystein (2017). Benefit of long distance migration for Barents Sea cod. Full text in Research Archive
• Vindenes, Yngvild (2017). Why individual variation is important for ecology and evolution. Full text in Research Archive
• Vindenes, Yngvild; Broch, Catharina; Lawson, Callum & Pol, Martijn Van de (2017). Eco-evolutionary responses to changing climate variability. Full text in Research Archive
• Vindenes, Yngvild (2016). Individual variation and eco-evolutionary dynamics: Towards more flexible model frameworks and new applications. Full text in Research Archive
• Vindenes, Yngvild; Langangen, Øystein; Winfield, Ian J. & Vøllestad, Leif Asbjørn (2016). The relative impacts of early life conditions and maternal size effects in determining average fitness and population growth of pike. Full text in Research Archive
• Vindenes, Yngvild (2016). Life history: Pike. In Kliman, Richard M. (Eds.), Encyclopedia of Evolutionary Biology. Elsevier. ISSN 9780128000496. p. 372–383. doi: 10.1016/B978-0-12-800049-6.00094-9. Full text in Research Archive
• Vindenes, Yngvild; Langangen, Øystein; Winfield, Ian J. & Vøllestad, Leif Asbjørn (2015). Relative fitness importance of a size-mediated maternal effect – an integral projection model approach. Full text in Research Archive
• Vindenes, Yngvild; Langangen, Øystein; Winfield, Ian J. & Vøllestad, Leif Asbjørn (2015). Relative fitness consequences of early life conditions and maternal length in Windermere pike. Full text in Research Archive
• Vindenes, Yngvild; Langangen, Øystein; Winfield, Ian J. & Vøllestad, Leif Asbjørn (2015). Fitness consequences of early life conditions and maternal size effects in pike (Esox lucius). Full text in Research Archive
• Vindenes, Yngvild (2014). Klimaat maakt snoek middelmatig. [Journal]. Netherlands. Full text in Research Archive
• Vindenes, Yngvild (2014). Advancing integral projection models for size-structured populations. Full text in Research Archive
• Vindenes, Yngvild; Edeline, Eric; Ohlberger, Jan; Langangen, Øystein; Winfield, Ian J. & Stenseth, Nils Christian [Show all 7 contributors for this article] (2013). Trait-based dynamics of a top predator in freshwaters and effects of climate change. Full text in Research Archive
• Vindenes, Yngvild; Edeline, Eric; Ohlberger, Jan; Langangen, Øystein; Winfield, Ian J. & Stenseth, Nils Christian [Show all 7 contributors for this article] (2013). Effects of climate warming on trait-based dynamics in a freshwater top predator. Full text in Research Archive
• Pol, Martijn Van de; Vindenes, Yngvild; Sæther, Bernt-Erik; Engen, Steinar; Ens, Bruno J & Oosterbeek, Kees [Show all 7 contributors for this article] (2013). Effects of climate change on stochastic demography in a population of Eurasian Oystercatchers. Full text in Research Archive
• Vindenes, Yngvild; Ohlberger, Jan; Langangen, Øystein & Winfield, Ian J. (2013). How does carrying capacity depend on temperature? A density dependent IPM for pike (Esox lucius). Full text in Research Archive
• Vindenes, Yngvild (2012). Climate warming and evolutionary demography of pike. Full text in Research Archive
• Vindenes, Yngvild (2012). Integral Projection Modeling (IPM) reveals effects of temperature change on the stochastic demography and population dynamics of pike (Esox lucius). Full text in Research Archive
• Vindenes, Yngvild (2012). Predicting the impacts of climate change on populations with demographic models. Full text in Research Archive
• Vindenes, Yngvild; Engen, Steinar & Sæther, Bernt-Erik (2011). Stochastic integral projection models for finite populations: Key population parameters and consequences for extinction risk. Full text in Research Archive
• Vindenes, Yngvild; Lee, Aline Magdalena; Engen, Steinar & Sæther, Bernt-Erik (2011). Fixation of slightly beneficial alleles in finite-sized structured populations: Effects of life history. Full text in Research Archive
• Vindenes, Yngvild; Engen, Steinar & Sæther, Bernt-Erik (2009). Effects of demographic heterogeneity in life histories on estimation of extinction risk. Full text in Research Archive Show summary

  Population viability analysis is a cornerstone in conservation biology, which depends on reliable predictions of the risk of extinction. A neglected topic in such risk-analyses has been the basic fact that individuals are different, and therefore typically have varying opportunities for survival and reproduction. For instance, in plants with random dispersal the survival of seedlings depend on where they happen to germinate. Moreover, these differences generally persist over time, creating temporal autocorrelation in the vital parameters of each individual. Here we show that ignoring such a fundamental aspect of populations has important consequences for the estimation of key population parameters and extinction risk. We have based our analysis on stochastic matrix and integral equation models with demographic heterogeneity incorporated. Estimates from these models are compared with estimates from models that ignore the heterogeneity and assume that all variation among individuals is merely random. Our results show that estimates of extinction risk may either increase or decrease compared to when heterogeneity is ignored. The direction of the error depends on the type of heterogeneity and on how it is maintained in the population, and the error becomes larger as the heterogeneity becomes more persistent over time. We emphasize that in order to predict extinction risk it is not enough to consider heterogeneity in only some aspects of life history (e.g. survival) without also taking the rest of the life history into account. Our general modeling approach allows us to study various combinations of heterogeneity in survival and reproduction, as well as different mechanisms for maintaining heterogeneity. An important implication of these results is that the majority of current models used in population viability analysis may in many cases underestimate the extinction risk of small, threatened populations.

• Vindenes, Yngvild; Engen, Steinar & Sæther, Bernt-Erik (2008). Individual heterogeneity in vital parameters and population viability. Full text in Research Archive Show summary

  Individuals in a population often have more‐ or less‐consistent differences in their opportunities for survival and reproduction, as a result of various biological mechanisms. For instance, the survival of a plant seedling can depend on where the seed happens to germinate. An important question is how such individual heterogeneity affects the viability of a population. The expected time to extinction of a population is determined by the amount of demographic stochasticity in the population process, which is influenced by individual heterogeneity. However, whether the heterogeneity increases or decreases the demographic stochasticity has been an unresolved question, except for special cases. We have used a stochastic matrix population model to study the effects of individual heterogeneity on demographic stochasticity. This approach is more general than other methods which have previously been used to study this type of problem. Results/Conclusions We found that individual heterogeneity can increase, decrease, or have no effect on population viability, depending on the heterogeneity itself and on how it is maintained over time. This contrasts with some earlier results which have indicated that heterogeneity should always have a positive effect. Given certain assumptions, these can be shown to be special cases of our model. We can analyze several special cases, such as permanent heterogeneity and source-sink dynamics, as well as cases where individual heterogeneity is a function of age or stage. Thus, we provide a general theoretical framework for studying how individual heterogeneity, created by various biological mechanisms, affects the fluctuations of especially small populations.

• Vindenes, Yngvild (2007). Pedagogisk opplegg for ungdomsskole-elever. Full text in Research Archive
• Vindenes, Yngvild; Engen, Steinar & Sæther, Bernt-Erik (2007). Effective size of fluctuating heterogeneous populations. Full text in Research Archive
• Vindenes, Yngvild (2010). Stochastic modeling of finite populations with individual heterogeneity in vital parameters. Norges teknisk-naturvitenskapelige universitet. ISSN 9788247123911. Full text in Research Archive Show summary

  Natural populations show large variation among individuals in patterns of survival and reproduction over time, that can often be associated with differences in state variables such as age, size or spatial location. Some of the variation is random, due to environmental fluctuations and inherent stochasticity in the processes of survival and reproduction. Several mechanisms can give rise to individual heterogeneity in natural populations, including spatial heterogeneity in the environment, maternal effects, cohort effects, and physiological differences. In this thesis I investigate how such heterogeneity affects properties of stochastic population dynamics, how it affects the fixation probability of slightly beneficial alleles, and how it influences effects of climate change on population dynamics. A demographic modeling framework for heterogeneous populations is developed based on stochastic matrix modeling and integral projection modeling, and I focus especially on (small) finite populations that are often of conservation concern. One can never be sure to have detected all sources of heterogeneity in a natural population, and individual-based data are often not available. Therefore an important question is whether estimates of parameters describing long-term population dynamics and population viability will be biased due to hidden heterogeneity, and if so in which direction and to which extent. Results given in this thesis indicate that while estimates of the expected population growth rate are not affected, estimates of the demographic and environmental variance of the population growth will be biased if the reproductive value varies between individuals. These results highlight the importance of reproductive value in stochastic models of structured populations, as it is not differences in survival or reproduction per se&nbsp;that affect the long-term stochasticity in population growth, but differences in reproductive value. Individual heterogeneity may affect the rate of evolution via the fixation probability of slightly beneficial alleles. Finding this probability is a classical problem in population genetics, dating from the work of Haldane in the 1920s. Here some earlier results are extended to include overlapping generations (individual heterogeneity) and stochastic fluctuations in a population with finite size (demographic stochasticity). The fixation probability of a slightly beneficial allele is shown to depend on the reproductive value of the individual(s) carrying the allele and the demographic variance of the population growth, in addition to the selective advantage of the allele and the population size. The reproductive value and demographic variance both depend on individual heterogeneity and can reflect general life history properties of the population. If the reproductive value of the individual(s) carrying the allele is low and the demographic variance is high, the probability of ultimate fixation will be low. In the presence of climate change individual heterogeneity can influence predictions of future population dynamics, because the effect of climatic variables on vital parameters can depend on individual state. Both the mean and variability of climatic variables are predicted to change in the future, so it is also important to assess their relative influence on population dynamics. Using data from a population of long-lived eurasian oystercatchers (Haematopus ostralegus) and a stochastic stage structured matrix model, we investigated effects of mean and variability in an important climatic variable (winter temperature) and predicted future population dynamics for different climate scenarios. The mean and variability of winter temperature had opposite effects on survival and fecundity, and the median time to extinction was most sensitive to changes in vital parameters of breeders in high-quality habitats. The population dynamics were overall more sensitive to changes in survival rates than in fecundity, in line with predictions from life-history theory for long-lived species. We hypothesize that general life history properties may be used to predict effects of changes in mean and variability in climatic variables. This study illustrates that if we want to understand how climate change affects future population dynamics, it is crucial to consider individual-level processes.

• Vindenes, Yngvild & Sæther, Bernt-Erik (2007). Population Dynamics and Consistent Individual Differences in Vital Parameters. NTNU, Institutt for biologi. Full text in Research Archive

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