890 research outputs found
The relative importance of life-history variables to population growth rate in mammals: Cole's prediction revisited
No full textThe relative importance of life-history variables to population growth rate (lambda) has substantial consequences for the study of life-history evolution and for the dynamics of biological populations. Using life-history data for 142 natural populations of mammals, we estimated the elasticity of lambda to changes in age at maturity (alpha), age at last reproduction (omega), juvenile survival (P-j), adult survival (P-a), and fertility (F). Elasticities were then used to quantify the relative importance of alpha, omega, P-j, P-a, and F to lambda and to test theoretical predictions regarding the relative influence on lambda of changes in life-history variables. Neither alpha nor any other single life-history variable had the largest relative influence on lambda in the majority of the populations, and this pattern did not change substantially when effects of phylogeny and body size were statistically removed. Empirical support for theoretical predictions was poor at best. However, analyses of elasticities on the basis of the magnitude (F) and onset (alpha) of reproduction revealed that alpha, followed by F, had the largest relative influence on lambda in populations characterized by early maturity and high reproductive rates, or when F/alpha > 0.60. When maturity was delayed and reproductive rates were low, or when F/alpha < 0.15, survival rates were overwhelmingly most influential, and reproductive parameters (alpha and F) had little relative influence on lambda. Population dynamic consequences of likely responses of biological populations to perturbations in life-history variables are examined, and predictions are made regarding the numerical dynamics of age-structured populations on the basis of values of the F/alpha ratio.PublishedYe
BODY-MASS, STRUCTURAL SIZE, AND LIFE-HISTORY PATTERNS OF THE COLUMBIAN GROUND-SQUIRREL
No full textColumbian ground squirrels (Spermophilus columbianus) exhibit an elevational cline in several life-history traits and in body mass. Body mass is a trait that might interact with the elevational changes in life histories, but it could reflect either or both of two underlying factors: structural size and physiological condition. I studied these factors in several populations of ground squirrels. Structural size was estimated from first principal component scores in an analysis of postcranial bone lengths. Physiological condition was inferred from differences in body mass that were independent of structural size. Field body mass and structural size of yearlings decreased with increasing elevation, which indicates slower growth at higher elevations. For adults, physiological condition was not measured directly, but evidence suggested that it was reflected by changes in body mass: body mass declined with increasing elevation but structural size did not, residuals of body mass on structural size showed the same patterns of change as body mass, most of the variation in body mass was orthogonal to a general size factor in principal components analyses, and significant changes in body mass of individuals could be stimulated by experimental supplementation of food. Life-history traits and physiological condition covaried along the elevational cline and were phenotypically plastic, but the structural size of adult ground squirrels was not an extremely plastic trait.PublishedYe
Replication Data for: "Estimating a key parameter of mammalian mating systems: the chance of siring success for a mated male"
No full textContains R code and data to analyze the probability of multiple paternity among litters using both simulations and real data from 60 mammalian species, of which 10 exemplar species are examined. Data on multiple paternity were obtained as described in Dobson et al. (2018).
JAGS must be installed on the computer/machine before being able to run this code. Please visit https://mcmc-jags.sourceforge.io/ for more info.
References Cited:
Dobson F. Stephen, Abebe Ash, Correia Hannah E., Kasumo Christian and Zinner Bertram. 2018. Multiple paternity and number of offspring in mammals. Proc. R. Soc. B. 285:20182042. 20182042. http://doi.org/10.1098/rspb.2018.2042 </p
MATERNAL TRAITS AND REPRODUCTION IN RICHARDSONS GROUND-SQUIRRELS
No full textDifferences among conspecifics in body mass result from underlying differences in structural size and physiological condition. To determine whether the structural or physiological component of body mass has a stronger influence on reproductive traits at parturition, we studied the body composition (lean dry mass and fat content), structural size (1st principal component scores computed from 10 skeletal measurements), and body condition (residuals from regression of body mass on structural size) of yearling and older female Richardson's ground squirrels (Spermophilus richardsonii). At parturition, differences among yearlings in body mass primarily reflected differences in structural size associated with continuing structural growth. Older females appeared to reach a deterministic adult structural size, and body mass of older females was most strongly associated with body condition. Structural size of yearling females and body condition of older females had significant positive effects on litter mass. For older females, date of parturition had a significant negative influence on litter size. Both yearling and older females exhibited significant positive effects of parturition date and body condition on neonate mass. In older females, a trade-off resulted in smaller litters of heavier neonates as the breeding season progressed, perhaps reflecting the need for rapid growth of offspring before hibernation. Maternal size, maternal condition, and seasonal timing were important aspects of reproduction in Richardson's ground squirrels, but these characteristics are seldom considered concurrently in studies of life histories.PublishedYe
Fitness implications of seasonal climate variation in Columbian ground squirrels
No full textThe influence of climate change on the fitness of wild populations is often studied in the context of the spring onset of the reproductive season. This focus is relevant for climate influences on reproductive success, but neglects other fitness‐relevant periods (e.g., autumn preparation for overwintering). We examined variation in climate variables (temperature, rainfall, snowfall, and snowpack) across the full annual cycle of Columbian ground squirrels (Urocitellus columbianus) for 21 years. We investigated seasonal climate variables that were associated with fitness variables, climate variables that exhibited directional changes across the study period, and finally observed declines in fitness (−0.03 units/year; total decline = 37%) that were associated with directional changes in climate variables. Annual fitness of adult female ground squirrels was positively associated with spring temperature (r = 0.69) and early summer rainfall (r = 0.56) and negatively associated with spring snow conditions (r = −0.44 to −0.66). Across the 21 years, spring snowmelt has become significantly delayed (r = 0.48) and summer rainfall became significantly reduced (r = −0.53). Using a standardized partial regression model, we found that directional changes in the timing of spring snowmelt and early summer rainfall (i.e., progressively drier summers) had moderate influences on annual fitness, with the latter statistically significant (ρ = −0.314 and 0.437, respectively). The summer period corresponds to prehibernation fattening of young and adult ground squirrels. Had we focused on a single point in time (viz. the onset of the breeding season), we would have underestimated the influences of climate change on our population. Rather, we obtained a comprehensive understanding of the influences of climate change on individual fitness by investigating the full lifecycle.Ye
Reproductive Value and the Stochastic Demography of Age-Structured Populations
No full textThe dynamics of an age-structured population in a fluctuating environment is determined by the stochastic individual contributions from annual survival and fecundity to the total reproductive value of the population the next year. All parameters required to describe the population dynamics are simple properties of the distribution of these individual demographic contributions, which we call individual reproductive value. The asymptotic population growth rate in the average environment and the demographic and environmental variances are respectively the mean individual reproductive value over individuals through time and the variance within and between years. Our approach leads to an intuitive understanding of demographic and environmental variances in age-structured populations and their decomposition into additive age-specific components due to survival and reproduction. We show how to apply this approach to estimate the demographic and environmental variances and their components. The estimates are based on yearly random samples of individual vital rates and require no information about the total population size.PublishedYe
1975 RDA 1 (A-F)
No full textBlack and white photo; mounted on paper, with names.Back - Trevor Adams, Vicky Adams, Peter Amos, Archie Baker, Stephen Bell, Stephen Berris, Timothy Carden; centre - Philip Cleary, Chris Conroy, John Cooper, William Cormack, Gregory Cottle, Mark Cunningham, Joanne Curkpatrick; front - Peter Delbridge, Andrew Dixon, Anne Dobson, Steven Earle, Wayne Edwards, Michael Faulkner
Race, Religion and Politics: Evangelicals, Conservatives and Liberals Look for Common Ground
No full textIncludes descriptive metadata provided by producer in MP4 file: "Politics, Economics and Social Issues - Video - Race, Religion and Politics: Evangelicals, Conservatives and Liberals Look for Common Ground." Pastor and best-selling author Stephen Mansfield and Vanderbilt Divinity School Dean James Hudnut-Beumler speak at Vanderbilt's Commons Center on Oct. 1, 2008. Frank Dobson, director of Vanderbilt's Bishop Joseph Johnson Black Cultural Center and Faculty Head of Gillette House in the Commons, opens the program. Commons student leaders David Curran and Harry Stimmel introduce the speakers
An approach to situation recognition based on learned semantic models
No full textA key enabler of pervasive computing is the ability to drive service delivery through the analysis of situations: Semantically meaningful classifications of system state, identified through analysing the readings from sensors attached to the everyday objects that people interact with.
Situation recognition is a mature area of research, with techniques primarily falling into two categories. Knowledge-based techniques use inference rules crafted by experts; however often they compensate poorly for sensing peculiarities. Learning-based approaches excel at extracting patterns from noisy training data, however their lack of transparency can make it difficult to diagnose errors.
In this thesis we propose a novel hybrid approach to situation recognition that combines both techniques. This offers improvements over each used individually, through not sacrificing the intelligibility of the decision processes that the use of machine learning alone often implies, and through providing better recognition accuracy through robustness to noise typically unattainable when developers use knowledge-based techniques in isolation.
We present an ontology model and reasoning framework that supports the uniform modelling of pervasive environments, and infers additional knowledge from that which is specified, in a principled way. We use this as a basis from which to learn situation recognition models that exhibit comparable performance with more complex machine learning techniques, while retaining intelligibility. Finally, we extend the approach to construct ensemble classifiers with either improved recognition accuracy, intelligibility or both.
To validate our approach, we apply the techniques to real-world data sets collected in smart-office and smart-home environments. We analyse the situation recognition performance and intelligibility of the decision processes, and compare the results to standard machine learning techniques and results published in the literature
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