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15 results for “age-structure”
Data from: Dinosaurian survivorship schedules revisited: new insights from an age-structured population model
<p>Little is known on dinosaur population biology due to insufficient information on age-dependent fecundities and mortalities. So far, survivorship curves (hereafter SC) of only six dinosaurs (four tyrannosaurs, one ceratopsian, one hadrosaur) were erected from bone assemblages of aged specimens. They indicate high survival throughout most of their life with presumable higher mortalities after hatching and increasing mortalities towards its end. However, all studies ignored that assemblages must preserve stationary age distributions (i.e., the population's age distribution is stable and its size is constant over time as overall population fecundities match mortalities, hereafter SAD population) to infer a reliable SC for a taxon.</p> <p>To assess SCs of these dinosaurs, I built a simple population model with age-dependent fecundities and survival rates. Its few input parameters are maximum longevity, age at sexual maturation and maximum annual offspring number, on which information exists in these dinosaurs. As bone histological studies and scaling relationships provide estimates on its three parameters, my model is also applicable to other extinct taxa.</p> <p> Modelling suggests that bone assemblages did not preserve SAD populations. SCs determined for SAD populations of <i>Albertosaurus sarcophagus</i>,<i> Gorgosaurus libratus</i>, <i>Dasplatosaurus torosus</i> and <i>Tyrannosaurus rex</i> indicated that low mortalities follow high mortalities early in their life or that mortalities were rather constant throughout their life. In <i>Psittacosaurus lujiatuensis</i> modelling suggests low mortalities throughout most of its life that increase towards its end. The SC of <i>Maiasaura peeblesorum</i> was not questioned by my model as it is unable to capture sigmoidal or other composite SCs.</p>
Data from: Dinosaurian survivorship schedules revisited: new insights from an age-structured population model
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Data from: Changes in age-structure over four decades were a key determinant of population growth rate in a long-lived mammal
<p>1. A changing environment directly influences birth and mortality rates, and thus population growth rates. However, population growth rates in the short-term are also influenced by population age-structure. Despite its importance, the contribution of age-structure to population growth rates has rarely been explored empirically in wildlife populations with long-term demographic data.</p> <p>2. Here, we assessed how changes in age-structure influenced short-term population dynamics in a semi-captive population of Asian elephants (Elephas maximus).</p> <p>3. We addressed this question using a demographic dataset of female Asian elephants from timber camps in Myanmar spanning 45 years (1970-2014). First, we explored temporal variation in age-structure. Then, using annual matrix population models, we used a retrospective approach to assess the contributions of age-structure and vital rates to short-term population growth rates with respect to the average environment.</p> <p>4. Age-structure was highly variable over the study period, with large proportions of juveniles in the years 1970 and 1985, and made a substantial contribution to annual population growth rate deviations. High adult birth rates between 1970-1980 would have resulted in large positive population growth rates, but these were prevented by a low proportion of reproductive-aged females.</p> <p>5. We highlight that an understanding of both age-specific vital rates and age-structure is needed to assess short-term population dynamics. Furthermore, this example from a human-managed system suggests that the importance of age-structure may be accentuated in populations experiencing human disturbance where age-structure is unstable, such as those in captivity or for endangered species. Ultimately, changes to the environment drive population dynamics by influencing birth and mortality rates, but understanding demographic structure is crucial for assessing population growth.</p>
Data from: Age-structure and transient dynamics in epidemiological systems
Mathematical models of childhood diseases date back to the early twentieth century. In several cases, models that make the simplifying assumption of homogeneous time-dependent transmission rates give good agreement with data in the absence of secular trends in population demography or transmission. The prime example is afforded by the dynamics of measles in industrialized countries in the pre-vaccine era. Accurate description of the transient dynamics following the introduction of routine vaccination has proved more challenging, however. This is true even in the case of measles which has a well-understood natural history and an effective vaccine that confers long-lasting protection against infection. Here, to shed light on the causes of this problem, we demonstrate that, while the dynamics of homogeneous and age-structured models can be qualitatively similar in the absence of vaccination, they diverge subsequent to vaccine roll-out. In particular, we show that immunization induces changes in transmission rates, which in turn reshapes the age distribution of infection prevalence, which effectively modulates the amplitude of seasonality in such systems. To examine this phenomenon empirically, we fit transmission models to measles notification data from London that span the introduction of the vaccine. We find that a simple age-structured model provides a much better fit to the data than does a homogeneous model, especially in the transition period from the pre-vaccine to the vaccine era. Thus, we propose that age structure and heterogeneities in contact rates are critical features needed to accurately capture transient dynamics in the presence of secular trends.
Quantifying the age-structure of free-ranging delphinid populations: testing the accuracy of Unoccupied Aerial System-photogrammetry
<p><span>Understanding the population health status of long-lived and slow-reproducing species is critical for their management. However, it can take decades with traditional monitoring techniques to detect population-level changes in demographic parameters. Early detection of the effects of environmental and anthropogenic stressors on vital rates would aid in forecasting changes in population dynamics and therefore inform management efforts. Changes in vital rates strongly correlate with deviations in population growth, highlighting the need for novel approaches that can provide early warning signs of population decline (e.g., changes in age-structure). We tested a novel and frequentist approach, using Unoccupied Aerial System- (UAS) photogrammetry, to assess the population age-structure of small delphinids. First, we measured the precision and accuracy of UAS-photogrammetry in estimating total body length (TL) of trained bottlenose dolphins (<em>Tursiops</em> <em>truncatus</em>). Using a log-transformed linear model, we estimated TL using the blowhole-to-dorsal-fin-distance (BHDF) for surfacing animals. To test the performance of UAS-photogrammetry to age-classify individuals, we then used length measurements from a 35-year dataset from a free-ranging bottlenose dolphin community to simulate UAS-estimates of BHDF and TL. We tested five age-classifiers and determined where young individuals (<10 years) were assigned when misclassified. Finally, we tested whether UAS-simulated BHDF only or the associated TL estimates provided better classifications. TL of surfacing dolphins was overestimated by 3.3% ±3.1% based on UAS-estimated BHDF. Our age-classifiers performed best in predicting age-class when using broader and fewer (two and three) age-class bins with ~80% and ~72% assignment performance, respectively. Overall, 72.5-93% of the individuals were correctly classified within two years of their actual age-class bin. Similar classification performances were obtained using both proxies. UAS-photogrammetry is a non-invasive, inexpensive, and effective method to estimate TL and age-class of free-swimming dolphins. UAS-photogrammetry can facilitate the detection of early signs of population changes, which can provide important insights for timely management decisions.</span></p>
Social network and fitness data from age-structured populations of forked fungus beetles
<p>We investigated the relationships between age, social behavior, and fitness at three levels of organization: the individual, the local social environment, and the population. Replicate groups of forked fungus beetles (<em>Bolitotherus cornutus</em>) were engineered to have either young- or old- biased age structures, and both social and reproductive behaviors were recorded.</p>
Social network and fitness data from age-structured populations of forked fungus beetles
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Quantifying the age-structure of free-ranging delphinid populations: testing the accuracy of Unoccupied Aerial System-photogrammetry
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Data from: Changes in age-structure over four decades were a key determinant of population growth rate in a long-lived mammal
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Data from: Age-structure and transient dynamics in epidemiological systems
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Data from: Estimating phenotypic selection in age-structured populations by removing transient fluctuations
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Data from: Estimating demographic contributions to effective population size in an age-structured wild population experiencing environmental and demographic stochasticity
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Data from: The evolution of labile traits in sex- and age-structured populations
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Data from: Optimal lineage principle for age-structured populations
We present a formulation of branching and aging processes that allows distributions along lineages to be studied within populations, and provides a new interpretation of classical results in the theory of aging. We establish a variational principle for the stable age distribution along lineages. Using this optimal lineage principle, we show that the response of a population's growth rate to age-specific changes in mortality and fecundity – a key quantity which was first calculated by Hamilton – is given directly by the age distribution along lineages. We apply our method also to the Bellman-Harris process, in which both mother and progeny are rejuvenated at each reproduction event, and show that this process can be mapped to the classic aging process such that age statistics in the population and along lineages are identical. Our approach provides both a theoretical framework for understanding the statistics of aging in a population, and a new method of analytical calculations for populations with age structure. We discuss generalizations for populations with multiple phenotypes, and more complex aging processes. We also provide a first experimental test of our theory applied to bacterial populations growing in a microfluidics device.
Data from: Optimal lineage principle for age-structured populations
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Allen Brain Atlas
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DANDI Archive for NWB datasets
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International Brain Laboratory public data
The International Brain Laboratory public data releases expose standardized mouse decision-making experiments, including Neuropixels recordings, widefield calcium imaging, behavior, and session metadata accessed through the ONE API.
OpenNeuro
OpenNeuro is a free, open platform for sharing neuroimaging datasets, with public search, dataset pages, and download paths for web, S3, DataLad, and the OpenNeuro CLI.