Biology subjects

Vindenes, Y.

Publications and source records attributed to Vindenes, Y..

4 recordsLinked to original sources

bioRxiv2024

Unraveling the seasonal dynamics of ixodid ticks: A flexible matrix population model with delayed life history effects

Many vector-borne diseases are sensitive to changes in land use and climate, making it crucial to understand the factors that govern the vector populations. Ixodid ticks, which serve as vectors for multiple diseases, have a slow life cycle compared to many of their hosts. The duration of each active life stage (larvae, nymph, adult) varies greatly and depends on factors such as timing of questing and development, host availability throughout the seasons, and photoperiod-related behavioral and developmental diapause. Importantly, the observable questing population only represents a fraction of the total tick population and may include overlapping generations in each stage. Mathematical models are therefore essential to understand how complex life cycle transitions and host interactions impact the dynamics of the tick population. In this study, we present a flexible seasonal matrix model for ixodid ticks that feed on small and large hosts varying in seasonal availability. This model incorporates the delayed life history effects of overwintering and seasonal timing of feeding, density regulation through limited host capacity, and scramble competition among larvae and nymphs for small hosts. We extract the equilibrium seasonal numbers of questing, feeding, and emerging ticks for each life stage, as well as the seasonal patterns of host use. We also calculate key life history characteristics including the mean generation time, stable stage structure, and reproductive values. The baseline model represents a northern life history of the sheep tick (Ixodes ricinus) feeding on a seasonal small host and constant large host, which is compared to a scenario without host seasonality and a scenario representing a southern ecosystem. Our findings support the importance of small hosts in regulating tick populations, and highlight that feeding of larvae is a critical transition. Our analyses shed light on the complex mechanisms underlying the seasonal composition of the questing population, with its important implications for disease risk. The model can be applied to other ixodid tick species and provides a framework for future investigations into population dynamics under various tick and host scenarios.

ecology↗

bioRxiv2021

Life history adaptations to fluctuating environments: Combined effects of demographic buffering and lability of vital rates

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.

ecology↗

bioRxiv2019

Estimating cause- and size- specific mortality hazard rates using mark-recapture-recovery data

O_LIEvidence-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 versus 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. C_LIO_LIHere, we estimated harvest and background (other cause) mortality of a landlocked migratory salmonid 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. C_LIO_LIWe 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 behavior and fit the model to a unique 50-year time-series of mark-recapture-recovery data on brown trout (Salmo trutta) in Norway. C_LIO_LIHarvest 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 below the dam and increased for those spawning above. 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. C_LIO_LIWe highlight the importance of body size for cause-specific mortality and demonstrate how this can be estimated using a novel hazard rate parameterisation 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. C_LI

ecology↗

bioRxiv2017

Study mortality with hazard rates, not probabilities

O_LIMortality is a key process in ecology and evolution, and much effort is spent on statistical and theoretical modelling of this process. Mortality hazard rates describe individuals instantaneous ability to survive at different times, whereas survival probabilities are defined for time-intervals of a given length. In this commentary, we argue that it is often more meaningful to model and interpret interval-specific time-averaged mortality hazard rates than survival probabilities, also when using discrete-time models.\nC_LIO_LIWe discuss three topics where the concept of hazard rates is essential for sound biological inference, but nevertheless often not used: (i) modelling of covariate effects on survival probabilities or mortality hazard rates, (ii) modelling of multiple sources of mortality and competing risks, and (iii) elasticity analyses of population growth rate to demographic parameters. To facilitate estimation of cause-specific mortality hazard rates, we provide amendments to R package marked.\nC_LIO_LIBy focusing on modelling mortality hazard rates, one avoids several inherent problems of comparing survival or mortality probabilities. In particular, interpretations about relative differences between mortality hazard rates (measurements on a ratio scale), or effects of relative changes in mortality hazard rates on population growth (elasticities), are more meaningful than similar interpretations involving survival (or mortality) probabilities or odds (measurements on an absolute scale).\nC_LIO_LIThe concept of hazard rates is essential for understanding ecological and evolutionary processes and we give an intuitive explanation for this, using several examples. We provide some practical guidelines and suggestions for further methods developments.\nC_LI

ecology↗