Population Size Parameters Research Articles

Demographic impact of AIDs on the Thai population

Thailand continues to feel the impact of a long-standing acquired immunodeficiency syndrome AIDS epidemic. Encouraged by the ready availability of epidemiological and behavioural data, a number of modelling efforts have been undertaken in an attempt to understand the impact of the epidemic since 1990. However, as better models are developed and the course of the epidemic changes, owing to behaviourial modifications as well as advances in therapy, there remains an ongoing need to provide new estimates and projections of the impact of AIDS on the Thai population. This paper projects the important demographic parameters of population size and annual growth rate. In addition, mortality indicators such as the crude death rate, agespecific death rate, infant mortality rate, child mortality rate (1-4 years) and life expectancy at birth are projected. These projections are made through a comparison of two scenarios: in the absence of AIDS and with AIDS. The paper concludes with a discussion of some of the potential social and economic impacts of AIDS.

Methods for cell cycle analysis and detection of apoptosis of teleost cells.

Flow cytometric techniques have not been previously used on a routine basis to study teleost cell growth and development. In the present chapter, flow instrumentation and cell preparation protocols are given in order to provide evaluation criteria characteristic of different phases of the cell cycle. Flow cytometry is used as an analytical and diagnostic tool to measure DNA ploidy as well as to measure alterations in cell cycle profiles characteristic of random DNA fragmentation (necrosis) compared to patterned DNA cleavage (apoptosis). The types of information obtained by flow analysis include the visualization of cell subpopulations with differing DNA content. For each identified nuclei subpopulation, the parameters of population size, fractions of nuclei in each phase of the cell cycle and computation of DNA ratios can be discerned. Data are presented of ex vivo prepared teleost nonspecific cytotoxic cells (NCC) at resting phase compared to NCC undergoing DNA hypoploid changes characteristic of apoptosis. These cells are compared with a teleost tissue cultured cell line maintained under optimum cell growth conditions versus cells undergoing necrotic cellular pathology. Finally, the requirements for optimum flow analysis are described. Techniques including gating strategies, voltage and gain settings, discrimination options and data collection and interpretation are provided.

Genetic Differentiation in Populations with Different Classes of Individuals

I formulate and analyse a model of population structure with different classes of individuals. These different classes may be age classes, other demographic classes, or different types of habitats homogeneously distributed over a geographical area. The value of population differentiation under an island model of dispersal and the increase of differentiation with geographical distance in one- and two-dimensional “isolation by distance” models are then obtained for a generalization of the FST measure of population structure, as a function of “effective” mutation, migration, and population size parameters. The relevant effective subpopulation size is related to the “mutation effective population size” of a single isolated subpopulation and, in models of age-structured populations, to the inbreeding effective population size.

Information‐Theoretic Model Selection and Model Averaging for Closed‐Population Capture‐Recapture Studies

Specification of an appropriate model is critical to valid statistical inference. Given the true model for the data is unknown, the goal of model selection is to select a plausible approximating model that balances model bias and sampling variance. Model selection based on information criteria such as AIC or its variant AIC c , or criteria like CAIC, has proven useful in a variety of contexts including the analysis of open-population capture-recapture data. These criteria have not been intensively evaluated for closed-population capture-recapture models, which are integer parameter models used to estimate population size (N), and there is concern that they will not perform well. To address this concern, we evaluated AIC, AIC c , and CAIC model selection for closed-population capture-recapture models by empirically assessing the quality of inference for the population size parameter N. We found that AIC-, AIC c -, and CAIC-selected models had smaller relative mean squared errors than randomly selected models, but that confidence interval coverage on N was poor unless unconditional variance estimates (which incorporate model uncertainty) were used to compute confidence intervals. Overall, AIC and AIC c outperformed CAIC, and are preferred to CAIC for selection among the closed-population capture-recapture models we investigated. A model averaging approach to estimation, using AIC, AIC c , or CAIC to estimate weights, was also investigated and proved superior to estimation using AIC-, AIC c -, or CAIC-selected models. Our results suggested that, for model averaging, AIC or AIC c should be favored over CAIC for estimating weights.

The breeding structure of a tropical keystone plant resource

Despite the recognized importance of maintaining viable populations of keystone plant resources in tropical wildlife parks and forested preserves, the critical question of what constitutes effective breeding units of these species has not been directly addressed. Here we use paternity analysis techniques to reconstruct the genotypes of pollen donor trees and to estimate pollen dispersal distances and breeding population size parameters for Panamanian populations of seven species of monoecious strangler figs (Ficus, Moraceae), a particularly widespread and influential group of keystone producers1,2,3. Despite the minute size (1–2 mm) and short lifespan (2–3 d) of the species-specific wasp pollinators (Agaonidae, Chalcidoidea), pollen dispersal was estimated to occur routinely over distances of 5.8–14.2 km between widely spaced host trees. As a result of such extensive pollen movement, breeding units of figs comprise hundreds of intermating individuals distributed over areas of 106–632 km2, an order of magnitude larger than has been documented for any other plant species. Moreover, these results should be generalizable to the 350 or so monoecious fig species that share this pollination system4. The large areal extent of breeding units of these keystone plant resources has important implications for our understanding of both the evolution of tropical biodiversity and its maintenance by applied conservation efforts.

Effects of measurement error on catch–-effort estimation

We have investigated the consequences of using imprecise catch and effort estimates in closed-population catch-effort analyses using traditional regression techniques and maximum likelihood to estimate the catchability coefficient and population size parameters. Our simulation study involved adding known amounts of measurement error to error-free catch and effort data to determine the effects of using such estimates of catch and effort rather than the true, and in many cases unknown, quantities. Our results suggest that naive estimation using estimates of catch and effort as true values may bias estimates of population size and the catchability coefficient. In most cases, the effects of measurement error in catch and effort were to inflate the parameter estimates, the magnitude of inflation being dependent on the size of the measurement error variance. Maximum likelihood estimation proved to be the estimation procedure most robust to the errors in measurement, but still displayed the need for correction of the measurement-error-induced bias. A recently developed simulation-extrapolation method of inference (J.R. Cook and L.A. Stefanski. 1994. J. Am. Stat. Assoc. 89: 1314-1328) is suggested as a possible means for making bias adjustments.

Molecular clock rates at loci under stabilizing selection.

Under stabilizing selection in a finite population, lambda, the rate of allelic substitutions at a locus is approximately lambda approximately mu(1 + S)-1/2, where mu is the mutation rate. S, the stringency of selection upon new mutants, is defined by S = NVm/Vs, where N is the population size and Vm/Vs is a measure of the average fitness decrease experienced by new mutants. The approximation holds both for a "lonely" locus, which is the sole provider of genetic variation for the character under selection, and for an "embedded" locus, which is not. In both cases I use the Crow and Kimura model of a continuum of alleles with Gaussian selection and mutation. Monte Carlo simulations corroborate the substitution rate formula. Some molecular evolution data suggest the potential utility and limitations of the formula for estimating population size, mutation, and selection parameters. This work agrees with the rest of nearly neutral theory in emphasizing the important role of population size for substitution rates.

Method for determining the temporal response of microbial phosphate transport affinity.

Nutrient transport affinities of nutrient-starved microbial populations were measured as initial slopes of plots of limiting-nutrient transport rates versus extracellular limiting-nutrient concentrations. A method was devised for the determination of soluble reactive phosphate (Pi) affinity in Pi-limited continuous culture (aT), which was then used as an indicator of the effects of light/dark cycle (LD) perturbations on the temporal Pi transport abilities of three species of freshwater algae. Cell division was asynchronous for the green alga Selenastrum capricornutum grown in continuous cultures exposed to LD cycles. An apparent rhythm in aT for Pi was greatly affected by the population size parameter. Cell division was phased for the green alga Scenedesmus quadricauda grown in LD continuous culture. A rhythm in aT for Pi was not greatly affected by the biomass parameter. Cell division was also phased in LD continuous culture for the blue-green alga (cyanobacterium) Synechococcus Nägeli, but rhythms in other parameters could not be detected. Synechococcus Nägeli was an extremely efficient Pi transporter at low Pi concentrations in LD continuous culture, and so aT could not be calculated. The results demonstrate that aT is well suited to describing the temporal response of Pi transport in LD-perturbed, Pi-limited continuous culture.

Energy, ecology, and cotton rat evolution

Body mass is estimated for extinct species of Sigmodon. These data are then used in appropriate equations derived among Recent mammals to estimate a suite of physiological and ecological variables which are followed through almost 4 ma of cotton rat history. A statistical trend towards large size is documented. Despite large swings in population size and other parameters, hypothetical values of population metabolism remain virtually constant, suggesting negligible population energetic benefit to size change in either direction. Studies of extant cotton rats and unrelated taxa sharing the same adaptive zone suggest that there is now, and has been in the past, negligible thermoregulatory advantage to modification of cotton rat body mass. Large size appears to be associated in Sigmodon with heightened aggression to the point that two species, particularly if of dichotomous size, cannot coexist in the same microhabitat. At least with regard to cotton rats, this conclusion represents a challenge to the comfortable hypotheses of coevolution and character displacement. The overall trend toward large size during Pleistocene time is considered then as the interplay of selection acting to favor large size in areas of sympatry and stochastic processes originating cotton rat populations of different body size. Because morphology and ecological strategies are stable within the cotton rat adaptive zone for millions of years, it is suggested that mammalian speciation events that result in exploitation of a new adaptive zone are uncommon and occasionally cross higher taxonomic categories. These events are defined as first-order speciation events, in contrast to second-order events that occur in clades within the same adaptive zone.