220 research outputs found
Population Dynamic Consequences of Context-Dependent Trade-Offs across Life Histories
No full textTrade-offs are central to life history theory and play a role in driving life history diversity. They arise from a finite amount of resources that need to be allocated among different functions by an organism. Yet covariation of demographic rates among individuals frequently do not reflect allocation trade-offs because of variation in resource acquisition. The covariation of traits among individuals can thus vary with the environment and often increases in benign environments. Surprisingly, little is known about how such context-dependent expression of trade-offs among individuals affect population dynamics across species with different life histories. To study their influence on population stability, we develop an individual-based simulation where covariation in demographic rates varies with the environment. We use it to simulate population dynamics for various life histories across the slow-fast pace-of-life continuum. We found that the population dynamics of slower life histories are relatively more sensitive to changes in covariation, regardless of the trade-off considered. Additionally, we found that the impact on population stability depends on which trade-off is considered, with opposite effects of intraindividual and intergenerational trade-offs. Last, the expression of different trade-offs can feed back to influence generation time through selection acting on individual heterogeneity within cohorts, ultimately affecting population dynamics.This work was supported by a Swiss National Science Foundation grant (31003A_182286 to A.O.).Peer reviewe
Data-driven modelling of structured populations: a practical guide to the integral projection model
No full textThis book is a “How To” guide for modeling population dynamics using Integral Projection Models (IPM) starting from observational data. It is written by a leading research team in this area and includes code in the R language (in the text and online) to carry out all computations. The intended audience are ecologists, evolutionary biologists, and mathematical biologists interested in developing data-driven models for animal and plant populations. IPMs may seem hard as they involve integrals. The aim of this book is to demystify IPMs, so they become the model of choice for populations structured by size or other continuously varying traits. The book uses real examples of increasing complexity to show how the life-cycle of the study organism naturally leads to the appropriate statistical analysis, which leads directly to the IPM itself. A wide range of model types and analyses are presented, including model construction, computational methods, and the underlying theory, with the more technical material in Boxes and Appendices. Self-contained R code which replicates all of the figures and calculations within the text is available to readers on GitHub. Stephen P. Ellner is Horace White Professor of Ecology and Evolutionary Biology at Cornell University, USA; Dylan Z. Childs is Lecturer and NERC Postdoctoral Fellow in the Department of Animal and Plant Sciences at The University of Sheffield, UK; Mark Rees is Professor in the Department of Animal and Plant Sciences at The University of Sheffield, UK
Precision measurement of and search for dark matter in the transverse momentum spectra of Z bosons
No full textThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2019Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 241-256).A measurement of the differential Z boson production cross section in proton-proton collisions is presented. It furnishes a precision test of the Standard Model, and constrains the parton distribution functions of the proton. Moreover, it is a building block for future measurements of the mass of the W± boson. A study of the efficiency of lepton identification algorithms is performed which drives the precision of the measurement at lower values of transverse momentum. In tandem, a search for new physics in events with a Z boson produced in association with large missing transverse momentum is presented. The results of this search are interpreted in the context of several dark matter models: generic spin-0 or spin-1 mediators, invisible decays of a Higgs-like boson, unparticles, and large extra spatial dimensions. A multivariate analysis was developed to enhance the sensitivity of the invisible Higgs interpretation. The theoretical uncertainty on the irreducible background from electroweak diboson processes is constrained by emulating the missing energy using pure control samples in the fully leptonic final states. The data were collected with the Compact Muon Solenoid detector at the Large Hadron Collider and correspond to an integrated luminosity of 35.9 fb-1. No significant deviations from the Standard Model are found.by Dylan George Hsu.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Physic
Multivariate signals of population collapse in a high‐throughput ecological experiment
No full textAnticipating population declines is a crucial goal of conservation ecology. Recent conceptual work suggests that populations facing growing stressors should exhibit sequential shifts in behavior, morphology, and abundance before declining to extinction. However, the lack of high‐resolution, multidimensional data has hindered empirical validation of this conceptual work. Using an autonomously monitored, high‐throughput experimental system, we generated individual‐based data on populations of the ciliate Paramecium caudatum forced to collapse due to increasingly stressful conditions. The gradual introduction of a pollutant elicited the predictable sequence of responses—declines in movement speed, followed by declines in body length, emergence of early warning signals of collapse, and finally, abundance declines. Conversely, a press disturbance generated by the introduction of predators did not induce this sequence. The time between the first detectable trait changes and population collapse depended on the statistical approach used, but the sequence remained consistent. Using general additive models, detectable behavioral signals in the polluted populations occurred one generation before abundance‐based early warning signals were detectable, and two generations before abundance decline. We highlight that multivariate monitoring, particularly individual‐based metrics, is crucial for forecasting population declines
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Detecting context dependence in the expression of life history trade-offs
Get PDF1. Life history trade-offs are one of the central tenets of evolutionary demography. Trade-offs, depicting negative covariances between individuals' life history traits, can arise from genetic constraints, or from a finite amount of resources that each individual has to allocate in a zero-sum game between somatic and reproductive functions. While theory predicts that trade-offs are ubiquitous, empirical studies have often failed to detect such negative covariances in wild populations. 2. One way to improve the detection of trade-offs is by accounting for the environmental context, as trade-off expression may depend on environmental conditions. However, current methodologies usually search for fixed covariances between traits, thereby ignoring their context dependence. 3. Here, we present a hierarchical multivariate 'covariance reaction norm' model, adapted from Martin (2023), to help detect context dependence in the expression of life-history trade-offs using demographic data. The method allows continuous variation in the phenotypic correlation between traits. We validate the model on simulated data for both intraindividual and intergenerational trade-offs. 4. We then apply it to empirical datasets of yellow-bellied marmots (Marmota flaviventer) and Soay sheep (Ovis aries) as a proof-of-concept showing that new insights can be gained by applying our methodology, such as detecting trade-offs only in specific environments. 5. We discuss its potential for application to many of the existing long-term demographic datasets and how it could improve our understanding of trade-off expression in particular, and life history theory in general
A review and framework of Control Authority Transitions in automated driving
No full textThe paper reviews some of the essentials of human-machine interaction in automated driving, focusing on control authority transitions. We introduce a driving state model describing the human monitoring level and the allocation of lateral and longitudinal control tasks. An authority transition in automated driving is defined as the process of changing from one static state of driving to another static state. Based on (1) who initiates the transition and (2) who is in control after the transition, we categorize transitions into four types: driver-initiated driver control (DIDC), driver-initiated automation control (DIAC), automation-initiated driver control (AIDC), and automation-initiated automation control (AIAC). Finally, we discuss the effects of human-machine interfaces on driving performance during transitions.Biomechatronics & Human-Machine Contro
Inferring the temperature dependence of population parameters: the effects of experimental design and inference algorithm
Get PDFUnderstanding and quantifying the temperature dependence of population parameters, such as intrinsic growth rate and carrying capacity, is critical for predicting the ecological responses to environmental change. Many studies provide empirical estimates of such temperature dependencies, but a thorough investigation of the methods used to infer them has not been performed yet. We created artificial population time series using a stochastic logistic model parameterized with the Arrhenius equation, so that activation energy drives the temperature dependence of population parameters. We simulated different experimental designs and used different inference methods, varying the likelihood functions and other aspects of the parameter estimation methods. Finally, we applied the best performing inference methods to real data for the species Paramecium caudatum. The relative error of the estimates of activation energy varied between 5% and 30%. The fraction of habitat sampled played the most important role in determining the relative error; sampling at least 1% of the habitat kept it below 50%. We found that methods that simultaneously use all time series data (direct methods) and methods that estimate population parameters separately for each temperature (indirect methods) are complementary. Indirect methods provide a clearer insight into the shape of the functional form describing the temperature dependence of population parameters; direct methods enable a more accurate estimation of the parameters of such functional forms. Using both methods, we found that growth rate and carrying capacity of Paramecium caudatum scale with temperature according to different activation energies. Our study shows how careful choice of experimental design and inference methods can increase the accuracy of the inferred relationships between temperature and population parameters. The comparison of estimation methods provided here can increase the accuracy of model predictions, with important implications in understanding and predicting the effects of temperature on the dynamics of populations
Myanmar’s semi-captive working elephant population is not sustainable without capture from the wild
No full textWildlife populations in captivity are increasingly common, but captive populations often have a higher extinction risk and may require supplementation through wild-capture. Despite this, wild-capture may actually hinder long-term conservation goals by reducing remaining wild populations, and its direct and long-term indirect consequences for captive population viability are rarely addressed using longitudinal data. Here, we explore the implications of changes in wild-capture on population viability over 54 years using a multi-generational studbook of working Asian elephants from Myanmar. We show that population viability declined between 1960 and 2014 with declines in wild-capture. Wild-caught females had reduced birth rates and high mortality risk, but despite such disadvantages their capture is required to sustain the captive population. Importantly, survival in juveniles had a large influence on population viability, suggesting that targeting juvenile mortality may have a disproportionate effect on population growth. Myanmar’s working population may constitute a third of the large captive population of Asian elephants (~16,000 individuals), and sustainable management of this population is crucial for the preservation of this species. Our results highlight the need to assess the demographic consequences of wild-capture as species are increasingly managed and conserved in altered or novel environments, to ensure the sustainability of both wild and captive populations.peerReviewedunknown accessibilityei tietoa saavutettavuudest
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