Publications by authors named "Bernt-Erik Saether"

128 Publications

Structure of the G-matrix in relation to phenotypic contributions to fitness.

Theor Popul Biol 2021 Apr 19;138:43-56. Epub 2021 Feb 19.

Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway. Electronic address:

Classical theory in population genetics includes derivation of the stationary distribution of allele frequencies under balance between selection, genetic drift, and mutation. Here we investigate the simplest generalization of these single locus models to quantitative genetics with many loci, assuming simple additive effects on a set of phenotypes and a linear approximation to the fitness function. Genetic effects and pleiotropy are simulated by a prescribed stochastic model. Our goal is to analyze the structure of the G-matrix at stasis when the model is not very close to being neutral. The smallest eigenvalue of the G-matrix is practically zero by Fisher's fundamental theorem for natural selection and the fitness function is approximately a linear function of the corresponding eigenvector. Evolution of genetic trade-offs is closely linked to the fitness function. If a single locus never codes for more than two traits, then additive genetic covariance between two phenotype components always has the opposite sign of the product of their coefficients in the fitness function under no mutation, a pattern that is likely to occur frequently also in more complex models. In our major examples only 1-2 percent of the loci are over-dominant for fitness, but they still account for practically all dominance variance in fitness as well as all contributions to the G-matrix. These analyses show that the structure of the G-matrix reveals important information about the contribution of different traits to fitness.
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http://dx.doi.org/10.1016/j.tpb.2021.01.004DOI Listing
April 2021

Density-Dependent Adaptive Topography in a Small Passerine Bird, the Collared Flycatcher.

Am Nat 2021 01 3;197(1):93-110. Epub 2020 Dec 3.

AbstractAdaptive topography is a central concept in evolutionary biology, describing how the mean fitness of a population changes with gene frequencies or mean phenotypes. We use expected population size as a quantity to be maximized by natural selection to show that selection on pairwise combinations of reproductive traits of collared flycatchers caused by fluctuations in population size generated an adaptive topography with distinct peaks often located at intermediate phenotypes. This occurred because - and -selection made phenotypes favored at small densities different from those with higher fitness at population sizes close to the carrying capacity . Fitness decreased rapidly with a delay in the timing of egg laying, with a density-dependent effect especially occurring among early-laying females. The number of fledglings maximizing fitness was larger at small population sizes than when close to . Finally, there was directional selection for large fledglings independent of population size. We suggest that these patterns can be explained by increased competition for some limiting resources or access to favorable nest sites at high population densities. Thus, - and -selection based on expected population size as an evolutionary maximization criterion may influence life-history evolution and constrain the selective responses to changes in the environment.
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http://dx.doi.org/10.1086/711752DOI Listing
January 2021

Connecting the data landscape of long-term ecological studies: The SPI-Birds data hub.

Authors:
Antica Culina Frank Adriaensen Liam D Bailey Malcolm D Burgess Anne Charmantier Ella F Cole Tapio Eeva Erik Matthysen Chloé R Nater Ben C Sheldon Bernt-Erik Saether Stefan J G Vriend Zuzana Zajkova Peter Adamík Lucy M Aplin Elena Angulo Alexandr Artemyev Emilio Barba Sanja Barišić Eduardo Belda Cemal Can Bilgin Josefa Bleu Christiaan Both Sandra Bouwhuis Claire J Branston Juli Broggi Terry Burke Andrey Bushuev Carlos Camacho Daniela Campobello David Canal Alejandro Cantarero Samuel P Caro Maxime Cauchoix Alexis Chaine Mariusz Cichoń Davor Ćiković Camillo A Cusimano Caroline Deimel André A Dhondt Niels J Dingemanse Blandine Doligez Davide M Dominoni Claire Doutrelant Szymon M Drobniak Anna Dubiec Marcel Eens Kjell Einar Erikstad Silvia Espín Damien R Farine Jordi Figuerola Pınar Kavak Gülbeyaz Arnaud Grégoire Ian R Hartley Michaela Hau Gergely Hegyi Sabine Hille Camilla A Hinde Benedikt Holtmann Tatyana Ilyina Caroline Isaksson Arne Iserbyt Elena Ivankina Wojciech Kania Bart Kempenaers Anvar Kerimov Jan Komdeur Peter Korsten Miroslav Král Miloš Krist Marcel Lambrechts Carlos E Lara Agu Leivits András Liker Jaanis Lodjak Marko Mägi Mark C Mainwaring Raivo Mänd Bruno Massa Sylvie Massemin Jesús Martínez-Padilla Tomasz D Mazgajski Adèle Mennerat Juan Moreno Alexia Mouchet Shinichi Nakagawa Jan-Åke Nilsson Johan F Nilsson Ana Cláudia Norte Kees van Oers Markku Orell Jaime Potti John L Quinn Denis Réale Tone Kristin Reiertsen Balázs Rosivall Andrew F Russell Seppo Rytkönen Pablo Sánchez-Virosta Eduardo S A Santos Julia Schroeder Juan Carlos Senar Gábor Seress Tore Slagsvold Marta Szulkin Céline Teplitsky Vallo Tilgar Andrey Tolstoguzov János Török Mihai Valcu Emma Vatka Simon Verhulst Hannah Watson Teru Yuta José M Zamora-Marín Marcel E Visser

J Anim Ecol 2020 Nov 17. Epub 2020 Nov 17.

Department of Animal Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands.

The integration and synthesis of the data in different areas of science is drastically slowed and hindered by a lack of standards and networking programmes. Long-term studies of individually marked animals are not an exception. These studies are especially important as instrumental for understanding evolutionary and ecological processes in the wild. Furthermore, their number and global distribution provides a unique opportunity to assess the generality of patterns and to address broad-scale global issues (e.g. climate change). To solve data integration issues and enable a new scale of ecological and evolutionary research based on long-term studies of birds, we have created the SPI-Birds Network and Database (www.spibirds.org)-a large-scale initiative that connects data from, and researchers working on, studies of wild populations of individually recognizable (usually ringed) birds. Within year and a half since the establishment, SPI-Birds has recruited over 120 members, and currently hosts data on almost 1.5 million individual birds collected in 80 populations over 2,000 cumulative years, and counting. SPI-Birds acts as a data hub and a catalogue of studied populations. It prevents data loss, secures easy data finding, use and integration and thus facilitates collaboration and synthesis. We provide community-derived data and meta-data standards and improve data integrity guided by the principles of Findable, Accessible, Interoperable and Reusable (FAIR), and aligned with the existing metadata languages (e.g. ecological meta-data language). The encouraging community involvement stems from SPI-Bird's decentralized approach: research groups retain full control over data use and their way of data management, while SPI-Birds creates tailored pipelines to convert each unique data format into a standard format. We outline the lessons learned, so that other communities (e.g. those working on other taxa) can adapt our successful model. Creating community-specific hubs (such as ours, COMADRE for animal demography, etc.) will aid much-needed large-scale ecological data integration.
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http://dx.doi.org/10.1111/1365-2656.13388DOI Listing
November 2020

Phenotypic evolution in stochastic environments: The contribution of frequency- and density-dependent selection.

Evolution 2020 09 26;74(9):1923-1941. Epub 2020 Jul 26.

Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, Trondheim, N-7491, Norway.

Understanding how environmental variation affects phenotypic evolution requires models based on ecologically realistic assumptions that include variation in population size and specific mechanisms by which environmental fluctuations affect selection. Here we generalize quantitative genetic theory for environmentally induced stochastic selection to include general forms of frequency- and density-dependent selection. We show how the relevant fitness measure under stochastic selection relates to Fisher's fundamental theorem of natural selection, and present a general class of models in which density regulation acts through total use of resources rather than just population size. In this model, there is a constant adaptive topography for expected evolution, and the function maximized in the long run is the expected factor restricting population growth. This allows us to generalize several previous results and to explain why apparently " -selected" species with slow life histories often have low carrying capacities. Our joint analysis of density- and frequency-dependent selection reveals more clearly the relationship between population dynamics and phenotypic evolution, enabling a broader range of eco-evolutionary analyses of some of the most interesting problems in evolution in the face of environmental variation.
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http://dx.doi.org/10.1111/evo.14058DOI Listing
September 2020

Multi-event capture-recapture analysis in Alpine chamois reveals contrasting responses to interspecific competition, within and between populations.

J Anim Ecol 2020 10 10;89(10):2279-2289. Epub 2020 Aug 10.

Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway.

Understanding components of interspecific competition has long been a major goal in ecological studies. Classical models of competition typically consider equal responses of all individuals to the density of competitors, however responses may differ both among individuals from the same population, and between populations. Based on individual long-term monitoring of two chamois populations in sympatry with red deer, we built a multi-event capture-recapture model to assess how vital rates of the smaller chamois are affected by competition from the larger red deer. In both populations, mortality and breeding probabilities of female chamois depend on age and in most cases, breeding status the preceding year. Successful breeders always performed better the next year, indicating that some females are of high quality. In one population where there was high spatial overlap between the two species, the survival of old female chamois that were successful breeders the preceding year (high-quality) was negatively related to an index of red deer population size suggesting that they tend to skip reproduction instead of jeopardizing their own survival when the number of competitors increases. The breeding probability of young breeders (ages 2 and 3) was similarly affected by red deer population size. In contrast, in the second site with low spatial overlap between the two species, the vital rates of female chamois were not related to red deer population size. We provide evidence for population-specific responses to interspecific competition and more generally, for context-, age- and state-dependent effects of interspecific competition. Our results also suggest that the classical assumption of equal responses of all individuals to interspecific competition should be relaxed, and emphasize the need to move towards more mechanistic approaches to better understand how natural populations respond to changes in their environment.
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http://dx.doi.org/10.1111/1365-2656.13299DOI Listing
October 2020

Consistent scaling of inbreeding depression in space and time in a house sparrow metapopulation.

Proc Natl Acad Sci U S A 2020 06 8;117(25):14584-14592. Epub 2020 Jun 8.

Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway.

Inbreeding may increase the extinction risk of small populations. Yet, studies using modern genomic tools to investigate inbreeding depression in nature have been limited to single populations, and little is known about the dynamics of inbreeding depression in subdivided populations over time. Natural populations often experience different environmental conditions and differ in demographic history and genetic composition, characteristics that can affect the severity of inbreeding depression. We utilized extensive long-term data on more than 3,100 individuals from eight islands in an insular house sparrow metapopulation to examine the generality of inbreeding effects. Using genomic estimates of realized inbreeding, we discovered that inbred individuals had lower survival probabilities and produced fewer recruiting offspring than noninbred individuals. Inbreeding depression, measured as the decline in fitness-related traits per unit inbreeding, did not vary appreciably among populations or with time. As a consequence, populations with more resident inbreeding (due to their demographic history) paid a higher total fitness cost, evidenced by a larger variance in fitness explained by inbreeding within these populations. Our results are in contrast to the idea that effects of inbreeding generally depend on ecological factors and genetic differences among populations, and expand the understanding of inbreeding depression in natural subdivided populations.
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http://dx.doi.org/10.1073/pnas.1909599117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7322018PMC
June 2020

The Demographic Buffering Hypothesis: Evidence and Challenges.

Trends Ecol Evol 2020 06 24;35(6):523-538. Epub 2020 Mar 24.

Department of Biology, Centre for Biodiversity Dynamics, NTNU, Norwegian University of Science and Technology, 7491 Trondheim, Norway.

In (st)age-structured populations, the long-run population growth rate is negatively affected by temporal variation in vital rates. In most cases, natural selection should minimize temporal variation in the vital rates to which the long-run population growth is most sensitive, resulting in demographic buffering. By reviewing empirical studies on demographic buffering in wild populations, we found overall support for this hypothesis. However, we also identified issues when testing for demographic buffering. In particular, solving scaling problems for decomposing, measuring, and comparing stochastic variation in vital rates and accounting for density dependence are required in future tests of demographic buffering. In the current context of climate change, demographic buffering may mitigate the negative impact of environmental variation and help populations to persist in an increasingly variable environment.
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http://dx.doi.org/10.1016/j.tree.2020.02.004DOI Listing
June 2020

Grow fast at no cost: no evidence for a mortality cost for fast early-life growth in a hunted wild boar population.

Oecologia 2020 Apr 2;192(4):999-1012. Epub 2020 Apr 2.

Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, 7491, Trondheim, Norway.

From current theories on life-history evolution, fast early-life growth to reach early reproduction in heavily hunted populations should be favored despite the possible occurrence of mortality costs later on. However, fast growth may also be associated with better individual quality and thereby lower mortality, obscuring a clear trade-off between early-life growth and survival. Moreover, fast early-life growth can be associated with sex-specific mortality costs related to resource acquisition and allocation throughout an individual's lifetime. In this study, we explore how individual growth early in life affects age-specific mortality of both sexes in a heavily hunted population. Using longitudinal data from an intensively hunted population of wild boar (Sus scrofa), and capture-mark-recapture-recovery models, we first estimated age-specific overall mortality and expressed it as a function of early-life growth rate. Overall mortality models showed that faster-growing males experienced lower mortality at all ages. Female overall mortality was not strongly related to early-life growth rate. We then split overall mortality into its two components (i.e., non-hunting mortality vs. hunting mortality) to explore the relationship between growth early in life and mortality from each cause. Faster-growing males experienced lower non-hunting mortality as subadults and lower hunting mortality marginal on age. Females of all age classes did not display a strong association between their early-life growth rate and either mortality type. Our study does not provide evidence for a clear trade-off between early-life growth and mortality.
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http://dx.doi.org/10.1007/s00442-020-04633-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7165149PMC
April 2020

Opposing fitness consequences of habitat use in a harvested moose population.

J Anim Ecol 2020 07 28;89(7):1701-1710. Epub 2020 Apr 28.

Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, Trondheim, Norway.

Landscape changes are happening at an unprecedented pace, and together with high levels of wildlife harvesting humans have a large effect on wildlife populations. A thorough knowledge of their combined influence on individual fitness is important to understand factors affecting population dynamics. The goal of the study was to assess the individual consistency in the use of risky habitat types, and how habitat use was related to fitness components and life-history strategies. Using data from a closely monitored and harvested population of moose Alces alces, we examined how individual variation in offspring size, reproduction and survival was related to the use of open grasslands; a habitat type that offers high-quality forage during summer, but at the cost of being more exposed to hunters in autumn. The use of this habitat type may therefore involve a trade-off between high mortality risk and forage maximization. There was a high repeatability in habitat use, which suggests consistent behaviour within individuals. Offspring number and weight were positively related to the mothers' use of open grasslands, whereas the probability of surviving the subsequent harvest season was negatively related to the use of the same habitat type. As a consequence, we found a nonsignificant relationship between habitat use and lifetime fitness. The study suggests that harvesting, even if intended to be nonselective with regard to phenotypes, may be selective towards animals with specific behaviour and life-history strategies. As a consequence, harvesting can alter the life-history composition of the population and target life-history strategies that would be beneficial for individual fitness and population growth in the absence of hunting.
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http://dx.doi.org/10.1111/1365-2656.13221DOI Listing
July 2020

Spatial Scales of Population Synchrony in Predator-Prey Systems.

Am Nat 2020 02 18;195(2):216-230. Epub 2019 Dec 18.

Many species show synchronous fluctuations in population size over large geographical areas, which are likely to increase their regional extinction risk. Here we examine how the degree of spatial synchrony in population dynamics is affected by trophic interactions using a two-species predator-prey model with spatially correlated environmental noise. We show that the predator has a larger spatial scale of population synchrony than the prey if the population fluctuations of both species are mainly determined by the direct effect of stochastic environmental variations in the prey. This result implies that in ecosystems regulated from the bottom up, the spatial scale of synchrony of the predator population increases beyond the scale of the spatial autocorrelation in the environmental noise and in the prey fluctuations. Harvesting the prey increases the spatial scale of population synchrony of the predator, while harvesting the predator reduces the spatial scale of the population fluctuations of its prey. Hence, the development of sustainable harvesting strategies should also consider the impact on unharvested species at other trophic levels as well as human perturbations of ecosystems, whether the result of exploitation or an effect on dispersal processes, as they can affect food web structures and trophic interactions over large geographical areas.
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http://dx.doi.org/10.1086/706913DOI Listing
February 2020

Stabilizing selection and adaptive evolution in a combination of two traits in an arctic ungulate.

Evolution 2020 01 16;74(1):103-115. Epub 2019 Dec 16.

Natural Resources Institute Finland (Luke), Terrestrial Population Dynamics, FIN-999870, Kaamanen, Inari, Finland.

Stabilizing selection is thought to be common in wild populations and act as one of the main evolutionary mechanisms, which constrain phenotypic variation. When multiple traits interact to create a combined phenotype, correlational selection may be an important process driving adaptive evolution. Here, we report on phenotypic selection and evolutionary changes in two natal traits in a semidomestic population of reindeer (Rangifer tarandus) in northern Finland. The population has been closely monitored since 1969, and detailed data have been collected on individuals since they were born. Over the length of the study period (1969-2015), we found directional and stabilizing selection toward a combination of earlier birth date and heavier birth mass with an intermediate optimum along the major axis of the selection surface. In addition, we demonstrate significant changes in mean traits toward earlier birth date and heavier birth mass, with corresponding genetic changes in breeding values during the study period. Our results demonstrate evolutionary changes in a combination of two traits, which agree closely with estimated patterns of phenotypic selection. Knowledge of the selective surface for combinations of genetically correlated traits are vital to predict how population mean phenotypes and fitness are affected when environments change.
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http://dx.doi.org/10.1111/evo.13894DOI Listing
January 2020

Decomposing demographic contributions to the effective population size with moose as a case study.

Mol Ecol 2020 01 13;29(1):56-70. Epub 2019 Dec 13.

Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway.

Levels of random genetic drift are influenced by demographic factors, such as mating system, sex ratio and age structure. The effective population size (N ) is a useful measure for quantifying genetic drift. Evaluating relative contributions of different demographic factors to N is therefore important to identify what makes a population vulnerable to loss of genetic variation. Until recently, models for estimating N have required many simplifying assumptions, making them unsuitable for this task. Here, using data from a small, harvested moose population, we demonstrate the use of a stochastic demographic framework allowing for fluctuations in both population size and age distribution to estimate and decompose the total demographic variance and hence the ratio of effective to total population size (N /N) into components originating from sex, age, survival and reproduction. We not only show which components contribute most to N /N currently, but also which components have the greatest potential for changing N /N. In this relatively long-lived polygynous system we show that N /N is most sensitive to the demographic variance of older males, and that both reproductive autocorrelations (i.e., a tendency for the same individuals to be successful several years in a row) and covariance between survival and reproduction contribute to decreasing N /N (increasing genetic drift). These conditions are common in nature and can be caused by common hunting strategies. Thus, the framework presented here has great potential to increase our understanding of the demographic processes that contribute to genetic drift and viability of populations, and to inform management decisions.
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http://dx.doi.org/10.1111/mec.15309DOI Listing
January 2020

Spatial covariation of competing species in a fluctuating environment.

Ecology 2020 01 19;101(1):e02901. Epub 2019 Nov 19.

Centre for Biodiversity Dynamics, Department of Mathematical Sciences, Norwegian University of Science and Technology, 7491, Trondheim, Norway.

Understanding how stochastic fluctuations in the environment influence population dynamics is crucial for sustainable management of biological diversity. However, because species do not live in isolation, this requires knowledge of how species interactions influence population dynamics. In addition, spatial processes play an important role in shaping population dynamics. It is therefore important to improve our understanding of how these different factors act together to shape patterns of abundance across space within and among species. Here, we present a new analytical model for understanding patterns of covariation in space between interacting species in a stochastic environment. We show that the correlation between two species in how they experience the same environmental conditions determines how correlated fluctuations in their densities would be in the absence of competition. In other words, without competition, synchrony between the species is driven by the environment, similar to the Moran effect within a species. Competition between the two species causes their abundances to become less positively or more negatively correlated. The same strength of competition has a greater negative effect on the correlation between species when one of them has a more variable growth rate than the other. In addition, dispersal or other movement weakens the effect of competition on the interspecific correlation. Finally, we show that movement increases the distance over which the species are (positively or negatively) correlated, an effect that is stronger when the species are competitors, and that there is a close connection between the spatial scaling of population synchrony within a species and between species. Our results show that the relationships between the different factors influencing interspecific correlations in abundance are not simple linear ones, but this model allows us to disentangle them and predict how they will affect population fluctuations in different situations.
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http://dx.doi.org/10.1002/ecy.2901DOI Listing
January 2020

Spatial heterogeneity in climate change effects decouples the long-term dynamics of wild reindeer populations in the high Arctic.

Glob Chang Biol 2019 11 21;25(11):3656-3668. Epub 2019 Aug 21.

Centre for Biodiversity Dynamics (CBD), Department of Biology, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.

The 'Moran effect' predicts that dynamics of populations of a species are synchronized over similar distances as their environmental drivers. Strong population synchrony reduces species viability, but spatial heterogeneity in density dependence, the environment, or its ecological responses may decouple dynamics in space, preventing extinctions. How such heterogeneity buffers impacts of global change on large-scale population dynamics is not well studied. Here, we show that spatially autocorrelated fluctuations in annual winter weather synchronize wild reindeer dynamics across high-Arctic Svalbard, while, paradoxically, spatial variation in winter climate trends contribute to diverging local population trajectories. Warmer summers have improved the carrying capacity and apparently led to increased total reindeer abundance. However, fluctuations in population size seem mainly driven by negative effects of stochastic winter rain-on-snow (ROS) events causing icing, with strongest effects at high densities. Count data for 10 reindeer populations 8-324 km apart suggested that density-dependent ROS effects contributed to synchrony in population dynamics, mainly through spatially autocorrelated mortality. By comparing one coastal and one 'continental' reindeer population over four decades, we show that locally contrasting abundance trends can arise from spatial differences in climate change and responses to weather. The coastal population experienced a larger increase in ROS, and a stronger density-dependent ROS effect on population growth rates, than the continental population. In contrast, the latter experienced stronger summer warming and showed the strongest positive response to summer temperatures. Accordingly, contrasting net effects of a recent climate regime shift-with increased ROS and harsher winters, yet higher summer temperatures and improved carrying capacity-led to negative and positive abundance trends in the coastal and continental population respectively. Thus, synchronized population fluctuations by climatic drivers can be buffered by spatial heterogeneity in the same drivers, as well as in the ecological responses, averaging out climate change effects at larger spatial scales.
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http://dx.doi.org/10.1111/gcb.14761DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6851690PMC
November 2019

Spatial scaling of population synchrony in marine fish depends on their life history.

Ecol Lett 2019 Nov 4;22(11):1787-1796. Epub 2019 Aug 4.

Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, 7491, Trondheim, Norway.

The synchrony of population dynamics in space has important implications for ecological processes, for example affecting the spread of diseases, spatial distributions and risk of extinction. Here, we studied the relationship between spatial scaling in population dynamics and species position along the slow-fast continuum of life history variation. Specifically, we explored how generation time, growth rate and mortality rate predicted the spatial scaling of abundance and yearly changes in abundance of eight marine fish species. Our results show that population dynamics of species' with 'slow' life histories are synchronised over greater distances than those of species with 'fast' life histories. These findings provide evidence for a relationship between the position of the species along the life history continuum and population dynamics in space, showing that the spatial distribution of abundance may be related to life history characteristics.
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http://dx.doi.org/10.1111/ele.13360DOI Listing
November 2019

Towards a predictive conservation biology: the devil is in the behaviour.

Philos Trans R Soc Lond B Biol Sci 2019 09 29;374(1781):20190013. Epub 2019 Jul 29.

Department of Mathematical Sciences, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, 7491 Trondheim, Norway.

One of the most important challenges in conservation biology is to predict the viability of populations of vulnerable and threatened species. This requires that the demographic stochasticity strongly affecting the ecological and evolutionary dynamics of especially small populations is correctly estimated and modelled. Here, we summarize theoretical evidence showing that the demographic variance in population dynamics is a key parameter determining the probability of extinction and also is directly linked to the magnitude of the genetic drift in the population. The demographic variance is dependent on the mating system, being larger in a polygynous than in monogamous populations. Understanding factors affecting intersexual differences in mating success is therefore essential in explaining variation in the demographic variance. We hypothesize that the strength of sexual selection, for example, quantified by the Bateman gradient, may be a useful predictor of the magnitude of the demographic stochasticity and hence the genetic drift in the population. We provide results from a field study of moose that support this claim. Thus, including central principles from behavioural ecology may increase the reliability of population viability analyses through an improvement of our understanding of factors affecting stochastic influences on population dynamics and evolutionary processes. This article is part of the theme issue 'Linking behaviour to dynamics of populations and communities: application of novel approaches in behavioural ecology to conservation'.
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http://dx.doi.org/10.1098/rstb.2019.0013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6710570PMC
September 2019

Density-dependent population dynamics of a high Arctic capital breeder, the barnacle goose.

J Anim Ecol 2019 08 20;88(8):1191-1201. Epub 2019 May 20.

Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway.

Density regulation of the population growth rate occurs through negative feedbacks on underlying vital rates, in response to increasing population size. Here, we examine in a capital breeder how vital rates of different life-history stages, their elasticities and population growth rates are affected by changes in population size. We developed an integrated population model for a local population of Svalbard barnacle geese, Branta leucopsis, using counts, reproductive data and individual-based mark-recapture data (1990-2017) to model age class-specific survival, reproduction and number of individuals. Based on these estimates, we quantified the changes in demographic structure and the effect of population size on age class-specific vital rates and elasticities, as well as the population growth rate. Local density regulation at the breeding grounds acted to reduce population growth through negative effects on reproduction; however, population size could not explain substantial variation in survival rates, although there was some support for density-dependent first-year survival. With the use of prospective perturbation analysis of the density-dependent projection matrix, we show that the elasticities to different vital rates changed as population size increased. As population size approached carrying capacity, the influence of reproductive rates and early-life survival on the population growth rate was reduced, whereas the influence of adult survival increased. A retrospective perturbation analysis revealed that density dependence resulted in a positive contribution of reproductive rates, and a negative contribution of the numbers of individuals in the adult age class, to the realised population growth rate. The patterns of density dependence in this population of barnacle geese were different from those recorded in income breeding birds, where density regulation mainly occurs through an effect on early-life survival. This indicates that the population dynamics of capital breeders, such as the barnacle goose, are likely to be more reproduction-driven than is the case for income breeders.
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http://dx.doi.org/10.1111/1365-2656.13001DOI Listing
August 2019

Ecological dynamics and large scale phenotypic differentiation in density-dependent populations.

Theor Popul Biol 2019 06 22;127:133-143. Epub 2019 Apr 22.

Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway. Electronic address:

Spatial differentiation of phenotypes is assumed to be determined by a combination of fluctuating selection producing adaptations to the local environment and a homogenizing effect of migration. We present a model with density regulation and a density-dependent fitness function affected by spatio-temporal variability in population size driven by spatially correlated fluctuations in the environment causing fluctuating r- and K-selection on a set of traits. We derive the variance in local mean phenotypes and show how the spatial scales of the correlations between the components of the mean phenotype depend on ecological parameters. The degree of spatial differentiation of phenotypes is strongly influenced by parameters affecting ecological dynamics. In the case of a one-dimensional character the geographical scale of variation in the mean phenotype has simply an additive term corresponding to the Moran effect in population dynamics as well as a term determined by dispersal and strength of local selection. The degree of phenotypic differentiation increases with decreasing strength of local density dependence and decreasing strength of local selection. These results imply that the form of the spatial autocorrelation function can reveal important information about ecological and evolutionary processes causing phenotypic differentiation in space.
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http://dx.doi.org/10.1016/j.tpb.2019.04.005DOI Listing
June 2019

More frequent extreme climate events stabilize reindeer population dynamics.

Nat Commun 2019 04 8;10(1):1616. Epub 2019 Apr 8.

Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway.

Extreme climate events often cause population crashes but are difficult to account for in population-dynamic studies. Especially in long-lived animals, density dependence and demography may induce lagged impacts of perturbations on population growth. In Arctic ungulates, extreme rain-on-snow and ice-locked pastures have led to severe population crashes, indicating that increasingly frequent rain-on-snow events could destabilize populations. Here, using empirically parameterized, stochastic population models for High-Arctic wild reindeer, we show that more frequent rain-on-snow events actually reduce extinction risk and stabilize population dynamics due to interactions with age structure and density dependence. Extreme rain-on-snow events mainly suppress vital rates of vulnerable ages at high population densities, resulting in a crash and a new population state with resilient ages and reduced population sensitivity to subsequent icy winters. Thus, observed responses to single extreme events are poor predictors of population dynamics and persistence because internal density-dependent feedbacks act as a buffer against more frequent events.
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http://dx.doi.org/10.1038/s41467-019-09332-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6453938PMC
April 2019

Accounting for interspecific competition and age structure in demographic analyses of density dependence improves predictions of fluctuations in population size.

Ecol Lett 2019 May 28;22(5):797-806. Epub 2019 Feb 28.

Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, 7491, Trondheim, Norway.

Understanding species coexistence has long been a major goal of ecology. Coexistence theory for two competing species posits that intraspecific density dependence should be stronger than interspecific density dependence. Great tits and blue tits are two bird species that compete for food resources and nesting cavities. On the basis of long-term monitoring of these two competing species at sites across Europe, combining observational and manipulative approaches, we show that the strength of density regulation is similar for both species, and that individuals have contrasting abilities to compete depending on their age. For great tits, density regulation is driven mainly by intraspecific competition. In contrast, for blue tits, interspecific competition contributes as much as intraspecific competition, consistent with asymmetric competition between the two species. In addition, including age-specific effects of intra- and interspecific competition in density-dependence models improves predictions of fluctuations in population size by up to three times.
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http://dx.doi.org/10.1111/ele.13237DOI Listing
May 2019

Characterizing morphological (co)variation using structural equation models: Body size, allometric relationships and evolvability in a house sparrow metapopulation.

Evolution 2019 03 17;73(3):452-466. Epub 2019 Jan 17.

Department of Biology, Centre for Biodiversity Dynamics (CBD), Norwegian University of Science and Technology (NTNU), N-7491, Trondheim, Norway.

Body size plays a key role in the ecology and evolution of all organisms. Therefore, quantifying the sources of morphological (co)variation, dependent and independent of body size, is of key importance when trying to understand and predict responses to selection. We combine structural equation modeling with quantitative genetics analyses to study morphological (co)variation in a meta-population of house sparrows (Passer domesticus). As expected, we found evidence of a latent variable "body size," causing genetic and environmental covariation between morphological traits. Estimates of conditional evolvability show that allometric relationships constrain the independent evolution of house sparrow morphology. We also found spatial differences in general body size and its allometric relationships. On islands where birds are more dispersive and mobile, individuals were smaller and had proportionally longer wings for their body size. Although on islands where sparrows are more sedentary and nest in dense colonies, individuals were larger and had proportionally longer tarsi for their body size. We corroborated these results using simulations and show that our analyses produce unbiased allometric slope estimates. This study highlights that in the short term allometric relationships may constrain phenotypic evolution, but that in the long term selection pressures can also shape allometric relationships.
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http://dx.doi.org/10.1111/evo.13668DOI Listing
March 2019

Environmental drivers of varying selective optima in a small passerine: A multivariate, multiepisodic approach.

Evolution 2018 11 9;72(11):2325-2342. Epub 2018 Oct 9.

Centre for Biodiversity Dynamics CBD, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway.

In changing environments, phenotypic traits are shaped by numerous agents of selection. The optimal phenotypic value maximizing the fitness of an individual thus varies through time and space with various environmental covariates. Selection may differ between different life-cycle stages and act on correlated traits inducing changes in the distribution of several traits simultaneously. Despite increasing interests in environmental sensitivity of phenotypic selection, estimating varying selective optima on various traits throughout the life cycle, while considering (a)biotic factors as potential selective agents has remained challenging. Here, we provide a statistical model to measure varying selective optima from longitudinal data. We apply our approach to analyze environmental sensitivity of phenotypic selection on egg-laying date and clutch size throughout the life cycle of a white-throated dipper population. We show the presence of a joint optimal phenotype that varies over the 35-year period, being dependent on altitude and temperature. We also find that optimal laying date is density-dependent, with high population density favoring earlier laying dates. By providing a flexible approach, widely applicable to free-ranging populations for which long-term data on individual phenotypes, fitness, and environmental factors are available, our study improves the understanding of phenotypic selection in varying environments.
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http://dx.doi.org/10.1111/evo.13610DOI Listing
November 2018

Inferences of genetic architecture of bill morphology in house sparrow using a high-density SNP array point to a polygenic basis.

Mol Ecol 2018 09 11;27(17):3498-3514. Epub 2018 Aug 11.

Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, Trondheim, Norway.

Understanding the genetic architecture of quantitative traits can provide insights into the mechanisms driving phenotypic evolution. Bill morphology is an ecologically important and phenotypically variable trait, which is highly heritable and closely linked to individual fitness. Thus, bill morphology traits are suitable candidates for gene mapping analyses. Previous studies have revealed several genes that may influence bill morphology, but the similarity of gene and allele effects between species and populations is unknown. Here, we develop a custom 200K SNP array and use it to examine the genetic basis of bill morphology in 1857 house sparrow individuals from a large-scale, island metapopulation off the coast of Northern Norway. We found high genomic heritabilities for bill depth and length, which were comparable with previous pedigree estimates. Candidate gene and genomewide association analyses yielded six significant loci, four of which have previously been associated with craniofacial development. Three of these loci are involved in bone morphogenic protein (BMP) signalling, suggesting a role for BMP genes in regulating bill morphology. However, these loci individually explain a small amount of variance. In combination with results from genome partitioning analyses, this indicates that bill morphology is a polygenic trait. Any studies of eco-evolutionary processes in bill morphology are therefore dependent on methods that can accommodate polygenic inheritance of the phenotype and molecular-scale evolution of genetic architecture.
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http://dx.doi.org/10.1111/mec.14811DOI Listing
September 2018

The effect of harvesting on the spatial synchrony of population fluctuations.

Theor Popul Biol 2018 09 31;123:28-34. Epub 2018 May 31.

Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, N-7491 Trondheim, Norway. Electronic address:

Harvesting in space affects, in general, the spatial scale of the synchrony in the population fluctuations, which determines the size of the areas subjected to simultaneous quasi-extinction risk. Here we show that harvesting reduces the population synchrony scale if it depends more strongly on population fluctuations than the density dependence of the growth rate in the absence of harvesting. We show that constant and proportional harvesting always increases the spatial scale, using a theta-logistic model for density regulation. We also provide exact scaling results under harvesting for the Beverton-Holt and the Ricker stock-recruitment models that are commonly applied, e.g. in fisheries. Our results indicate that harvest in areas with large abundances should be encouraged to avoid increase of the spatial scale of synchrony in the population fluctuations that can lead to unexpected quasi-extinction of populations over large areas. Our results quantify this harvesting impact giving the resulting scales of spatial synchrony of population fluctuations. This emphasizes the importance of estimating the form of density dependence as well as the dependency of harvest upon population density of exploited populations, in order to get reliable predictions of the size of areas that can undergo simultaneous quasi-extinction.
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http://dx.doi.org/10.1016/j.tpb.2018.05.001DOI Listing
September 2018

Spatial distribution and optimal harvesting of an age-structured population in a fluctuating environment.

Math Biosci 2018 02 11;296:36-44. Epub 2017 Dec 11.

Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim N-7491, Norway. Electronic address:

We analyze a spatial age-structured model with density regulation, age specific dispersal, stochasticity in vital rates and proportional harvesting. We include two age classes, juveniles and adults, where juveniles are subject to logistic density dependence. There are environmental stochastic effects with arbitrary spatial scales on all birth and death rates, and individuals of both age classes are subject to density independent dispersal with given rates and specified distributions of dispersal distances. We show how to simulate the joint density fields of the age classes and derive results for the spatial scales of all spatial autocovariance functions for densities. A general result is that the squared scale has an additive term equal to the squared scale of the environmental noise, corresponding to the Moran effect, as well as additive terms proportional to the dispersal rate and variance of dispersal distance for the age classes and approximately inversely proportional to the strength of density regulation. We show that the optimal harvesting strategy in the deterministic case is to harvest only juveniles when their relative value (e.g. financial) is large, and otherwise only adults. With increasing environmental stochasticity there is an interval of increasing length of values of juveniles relative to adults where both age classes should be harvested. Harvesting generally tends to increase all spatial scales of the autocovariances of densities.
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http://dx.doi.org/10.1016/j.mbs.2017.12.003DOI Listing
February 2018

Fitness correlates of age at primiparity in a hunted moose population.

Oecologia 2018 02 2;186(2):447-458. Epub 2017 Dec 2.

Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, Trondheim, Norway.

Trade-offs between fitness-related traits are predicted from the principle of resource allocation, where increased fecundity or parental investment leads to reduced future reproduction or survival. However, fitness traits can also be positively correlated due to individual differences (e.g. body mass). Age at primiparity could potentially explain variation in individual fitness either because early primiparity is costly, or it may lead to higher lifetime reproductive success. Based on long-term monitoring and genetic parentage assignment of an island population of moose, we quantified reproductive performance and survival, and examined whether early maturing females have higher total calf production than late maturing females. We explored if harvesting of calves affected the subsequent reproductive success of their mothers, i.e. also due to a post-weaning cost of reproduction, and whether there are any intergenerational effects of female reproductive success. There was a positive relationship between current and future reproduction. The probability to reproduce was lower for females that were unsuccessful the year before, indicating a strong quality effect on productivity. Females that started to reproduce as 2-year olds had a slightly higher total calf production compared to those starting at age three or four. High-performing mothers were also correlated with daughters that performed well in terms of reproductive success. Our results suggest that the observed individual heterogeneity in fitness could be associated with differences in age at primiparity. This heterogeneity was not affected by reproductive costs associated with tending for a calf post-weaning.
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http://dx.doi.org/10.1007/s00442-017-4021-2DOI Listing
February 2018

Evolution of stochastic demography with life history tradeoffs in density-dependent age-structured populations.

Proc Natl Acad Sci U S A 2017 10 10;114(44):11582-11590. Epub 2017 Oct 10.

Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.

We analyze the stochastic demography and evolution of a density-dependent age- (or stage-) structured population in a fluctuating environment. A positive linear combination of age classes (e.g., weighted by body mass) is assumed to act as the single variable of population size, [Formula: see text], exerting density dependence on age-specific vital rates through an increasing function of population size. The environment fluctuates in a stationary distribution with no autocorrelation. We show by analysis and simulation of age structure, under assumptions often met by vertebrate populations, that the stochastic dynamics of population size can be accurately approximated by a univariate model governed by three key demographic parameters: the intrinsic rate of increase and carrying capacity in the average environment, [Formula: see text] and [Formula: see text], and the environmental variance in population growth rate, [Formula: see text] Allowing these parameters to be genetically variable and to evolve, but assuming that a fourth parameter, [Formula: see text], measuring the nonlinearity of density dependence, remains constant, the expected evolution maximizes [Formula: see text] This shows that the magnitude of environmental stochasticity governs the classical trade-off between selection for higher [Formula: see text] versus higher [Formula: see text] However, selection also acts to decrease [Formula: see text], so the simple life-history trade-off between [Formula: see text]- and [Formula: see text]-selection may be obscured by additional trade-offs between them and [Formula: see text] Under the classical logistic model of population growth with linear density dependence ([Formula: see text]), life-history evolution in a fluctuating environment tends to maximize the average population size.
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http://dx.doi.org/10.1073/pnas.1710679114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5676918PMC
October 2017

Modelling time to population extinction when individual reproduction is autocorrelated.

Ecol Lett 2017 Nov 18;20(11):1385-1394. Epub 2017 Sep 18.

Centre for Biodiversity Dynamics, Department of Mathematical Sciences, Norwegian University of Science and Technology, Trondheim, Norway.

In nature, individual reproductive success is seldom independent from year to year, due to factors such as reproductive costs and individual heterogeneity. However, population projection models that incorporate temporal autocorrelations in individual reproduction can be difficult to parameterise, particularly when data are sparse. We therefore examine whether such models are necessary to avoid biased estimates of stochastic population growth and extinction risk, by comparing output from a matrix population model that incorporates reproductive autocorrelations to output from a standard age-structured matrix model that does not. We use a range of parameterisations, including a case study using moose data, treating probabilities of switching reproductive class as either fixed or fluctuating. Expected time to extinction from the two models is found to differ by only small amounts (under 10%) for most parameterisations, indicating that explicitly accounting for individual reproductive autocorrelations is in most cases not necessary to avoid bias in extinction estimates.
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http://dx.doi.org/10.1111/ele.12834DOI Listing
November 2017

Extinction Risk and Lack of Evolutionary Rescue under Resource Depletion or Area Reduction.

Am Nat 2017 07 25;190(1):73-82. Epub 2017 Apr 25.

Evolutionary adaptations following environmental deterioration can sometimes rescue populations from extinction. Here we provide a scenario in which such evolutionary rescue will be difficult. Using a rather general model for fluctuating r- and K-selection in a density-dependent population, we show that reduction of available resources will not necessarily induce evolution of adaptations to counteract such changes provided that density regulation acts through available resources per individual. In large populations, resource depletion may induce a change in stationary distribution of population size while the optimal phenotype remains unchanged. Under a period of continuous reduction in available resources, increased strength of K-selection will occur in the sense that individuals are able to live and reproduce under less favorable conditions. Smaller growth rates as a consequence of K-selection and trade-offs between intrinsic growth rate r and carrying capacity K may then have a considerable negative effect on the persistence of the population even after the reduction of available resources is stopped. This negative effect comes in addition to the purely ecological effect of reduced time to extinction because of a reduction in K and increased demographic stochasticity. Continuous reduction in the available area or in available resources per individual may result in long-run maladaptation even if demographic noise increases and, finally but too late, induces r-selection.
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http://dx.doi.org/10.1086/692011DOI Listing
July 2017

Reversal of response to artificial selection on body size in a wild passerine.

Evolution 2017 08 20;71(8):2062-2079. Epub 2017 Jun 20.

Centre for Biodiversity Dynamics (CBD), Department of Biology, Norwegian University of Science and Technology (NTNU), NO-7491, Trondheim, Norway.

A general assumption in quantitative genetics is the existence of an intermediate phenotype with higher mean individual fitness in the average environment than more extreme phenotypes. Here, we investigate the evolvability and presence of such a phenotype in wild bird populations from an eleven-year experiment with four years of artificial selection for long and short tarsus length, a proxy for body size. The experiment resulted in strong selection in the imposed directions. However, artificial selection was counteracted by reduced production of recruits in offspring of artificially selected parents. This resulted in weak natural selection against extreme trait values. Significant responses to artificial selection were observed at both the phenotypic and genetic level, followed by a significant return toward preexperimental means. During artificial selection, the annual observed phenotypic response closely followed the predicted response from quantitative genetic theory (ryears = 0.96, rcohorts = 0.56). The rapid return to preexperimental means was induced by three interacting mechanisms: selection for an intermediate phenotype, immigration, and recombination between selected and unselected individuals. The results of this study demonstrates the evolvability of phenotypes and that selection may favor an intermediate phenotype in wild populations.
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http://dx.doi.org/10.1111/evo.13277DOI Listing
August 2017