This article reviews the role of migration in determining population size in Australia, and suggest ways of achieving a stationary population, or zero population growth (ZPG), when fertility is below replacement. There is a narrow range of feasible options. It is argued that achievement of ZPG is feasible only with net migration of 60,000-100,000 annually and with a fertility rate of 1.65-1.8...

Genetic data are often used to assess 'population connectivity' because it is difficult to measure dispersal directly at large spatial scales. Genetic connectivity, however, depends primarily on the absolute number of dispersers among populations, whereas demographic connectivity depends on the relative contributions to population growth rates of dispersal vs. local recruitment (i.e. survival a...

Recent imaging data for single bacterial cells reveal that their mean sizes grow exponentially in time and that their size distributions collapse to a single curve when rescaled by their means. An analogous result holds for the division-time distributions. A model is needed to delineate the minimal requirements for these scaling behaviors. We formulate a microscopic theory of stochastic exponen...

The literature comparing fully funded (FF) and pay-as-you-go (PAYG) financed public pension systems in small, open economies stresses the importance of the Aaron condition as an empirical measure to decide which system can be expected to lead to a higher long-run welfare. A country with a PAYG system has a higher level of utility than a country with a FF system if the growth rate of total wage...

We consider three individual-based models describing growth in stochastic environments. Stochastic differential equations (SDEs) with identical von Bertalanffy deterministic parts are formulated, with a stochastic term which decreases, remains constant, or increases with organism size, respectively. Probability density functions for hitting times are evaluated in the context of fish growth and ...

The establishment and spreading of biological populations depends crucially on population growth at low densities. The Allee effect is a problem in those populations where the per capita growth rate at low densities is reduced. We examine stochastic spatial models in which the reproduction rate changes across a gradient g so that the population undergoes a 2D-percolation transition. Without the...

We examined the long-term, 15-year pattern of population change in a network of 21 Rocky Mountain populations of Parnassius smintheus butterflies in response to climatic variation. We found that winter values of the broadscale climate variable, the Pacific Decadal Oscillation (PDO) index, were a strong predictor of annual population growth, much more so than were endogenous biotic factors relat...

Forest ecologists often evaluate how well the species composition of saplings in the understory matches that of the canopy: absence of juveniles suggests that a tree species is suffering population decline. Here we offer a theoretical and empirical test of this assertion using data from a 50-ha census plot in Panama. Theory indicates that higher rates of population change, lambda, lead to more ...

A study on the new role of the elderly as caretakers of orphans was conducted in a rural part of Kenya applying a combination of qualitative and quantitative methods. One out of three children had lost at least one biological parent and one of nine had lost both. These figures are increasing exponentially. Most orphans were cared for by relatives, and about one out of five caretakers was 55 yea...