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At least 127 records · Page 7Linked to original sources
PubMed2006

Historical events and allelic polymorphism at the gametophytic self-incompatibility locus in Solanaceae.

The historical migration rate of a species is often difficult to estimate with neutral markers, because the relationship between the turnover time of the markers and the age of the species commonly remains unknown. Compared with neutral markers, the plant self-incompatibility locus (S) provides a much better source of data for migration-rate estimation due to its high allelic polymorphism and antiquity. Here, the results from extensive surveys of S alleles in two wild solanaceous species, Solanum carolinense and Physalis longifolia, indicate that historical migration rates have differed significantly between the species; the higher migration rate found in S. carolinense appears to have interacted with the balancing selection at the S locus to result in fewer S alleles being maintained in the species. Historical population growth rates estimated via a modified coalescent approach also suggest a faster growing population for S. carolinense than for P. longifolia, which would have further widened their interspecific difference in S-allelle polymorphism. These historical factors may have reduced the probability of new S alleles to prevailing in S. carolinense, leaving old ones segregating at the S locus with little signature of positive selection being currently detectable.

Alleles↗
PubMed2003

Performance of the cyclic autumnal moth, Epirrita autumnata, in relation to birch mast seeding.

The mast depression hypothesis has been put forward to explain the 9- to 10-year population cycle of the autumnal moth (Epirrita autumnata; Lepidoptera: Geometridae) in northern Fennoscandia. We analysed long-term data from Finnish Lapland in order to evaluate the critical assumption of the mast depression hypothesis: that better individual performance of herbivores, followed by high annual growth rate of populations, occurs in the year following mast seeding of the host, the mountain birch ( Betula pubescens ssp. czerepanovii). Since mast seeding has been suggested to occur at the expense of chemical defence against herbivores, we bioassayed the quality of birch leaves from the same trees by means of yearly growth trials with autumnal moth larvae. We also measured the size of wild adults as a determinant of potential fecundity of the species in different years. The relative growth rate of larvae was poorer in post-mast years compared to other years, rather than better as assumed by the hypothesis. Conversely, a slight indication of the increase in potential fecundity was observed due to the somewhat larger adult size in post-mast years. Population growth rate estimates, however, showed that the increase in fecundity would have to be much higher to facilitate population increase towards a cyclic peak with outbreak density. Accordingly, our two data sets do not support the assumption of a higher annual growth rate in autumnal moth populations subsequent to mast seeding of the host, thereby contradicting the predictions of the mast depression hypothesis. Temperatures, when indexed by the North Atlantic Oscillation and accumulated thermal sums, were observed to correlate with the abundance or rate of population change of the autumnal moth. The factors underlying the regular population cycles of the autumnal moth, however, remain unidentified. Overall, we suggest that the causal agents in cyclic insect population dynamics should be clarified by field experimentation, since trophic interactions are complex and are further modified by abiotic factors such as climate.

Animals↗
PubMed2000

Statistical inference on associated fertility life table parameters using jackknife technique: computational aspects.

Knowledge of population growth potential is crucial for studying population dynamics and for establishing management tactics for pest control. Estimation of population growth can be achieved with fertility life tables because they synthesize data on reproduction and mortality of a population. The five main parameters associated with a fertility life table are as follows: (1) the net reproductive rate (Ro), (2) the intrinsic rate of increase (rm), 3) the mean generation time (T), (4) the doubling time (Dt), and (5) the finite rate of increase (lambda). Jackknife and bootstrap techniques are used to calculate the variance of the rm estimate, which can be extended to the other parameters of life tables. Those methods are computer-intensive, their application requires the development of efficient algorithms, and their implementation is based on a programming language that encompasses quickness and reliability. The objectives of this article are to discuss statistical and computational aspects related to estimation of life table parameters and to present a SAS program that uses jackknife to estimate parameters for fertility life tables. The SAS program presented here allows the calculation of confidence intervals for all estimated parameters, as well as provides one-sided and two-sided t-tests to perform pairwise or multiple comparison between groups, with their respective P values.

Animals↗
PubMedDate not supplied

A simple method for estimating the contraceptive prevalence required to reach a fertility target.

This report describes and applies a procedure for estimating the increase in contraceptive prevalence that would have to occur to achieve specified future reductions in a population's fertility. This target-setting methodology is based on a previously developed analytic model for the relationship between fertility and its proximate determinants. The basic aggregate version of the estimation procedure, which is described in detail, requires relatively few input data, but it allows changes in the mix of contraceptive methods in future years. In extended versions of the model, age specificity and adjustments for given trends in the proximate determinants other than contraceptive use are introduced.

Contraception Behavior↗
PubMed2002

Evaluating the ecological significance of laboratory response data to predict population-level effects for the estruarine amphipod Ampelisca abdita.

Ten-day acute mortality of the benthic amphipod Ampelisca abdita is used in a number of regulatory, research, and monitoring programs to evaluate chemical contamination of marine sediments. Although this endpoint has proven to be valuable for characterizing the relative toxicities of sediments, the significance of acute mortality with respect to population viability has not yet been established. In this study, population modeling along with empirical extrapolation were used to describe a relationship between acute mortality and population-level response of A. abdita. The research involved the performance of a standard 10-d sediment toxicity bioassay and a 70-d full life-cycle chronic population (including reproduction) bioassay exposing A. abdita to sediments spiked with concentrations of the divalent metal cadmium (normalized to acid volatile sulfide) expected to produce a range of biological effects. These data provided age-specific schedules of survival and fecundity that were used to parameterize an age-classified projection matrix model for A. abdita. Measured exposure data and population growth rate estimates, obtained using the demographic information collected during the 70-d assay, were used to develop exposure-response models. These data were also used to develop an empirical relationship between population growth rate (lambda) and acute mortality. This relationship describes how acute data may be used to predict concentrations that produce population-level effects. Model manipulations permit extrapolation of early life-stage mortality (the acute endpoint) to changes in population growth rate. These relationships were used to evaluate a range of ecologically acceptable acute mortality for A. abdita.

Animals↗