Bernt-Erik Sæther

Environmental stochasticity and population dynamics of large herbivores: a search for mechanisms

Recently, the results from several long-term individual-based population studies of ungulates have been published. One major conclusion is that the population dynamics of ungulates in predator-free environments is strongly influenced by a combination of stochastic variation in the environment, and population density. Both density dependence and environmental stochasticity operate through changes in life history traits, correlated with variation in body weight. This generates delays in the response of the population to changes in environment. In the absence of predation, a stable equilibrium is therefore unlikely to exist between an ungulate population and its food resources. This thorough understanding of the mechanisms generating population fluctuations suggests that studies of ungulates will provide an important source for examining effects of long-term changes in the environment, for instance, resulting from a climatic change.

Sex biases in avian dispersal : a reappraisal

We reviewed the avian literature for quantitative studies of sex biases in dispersal and found continued and strengthened support for the general pattern of female biased dispersal established by Greenwood in 1980. We report sex differences in dispersal patterns in natal and breeding dispersal as measured by 1) proportion leaving and 2) distance moved. Greenwoods review found evidence for male biased dispersal only within four species of the Anatidae. We find there is now evidence for male biased dispersal in twenty-two species representing twelve families.

Senescence rates are determined by ranking on the fast-slow life-history continuum

Comparative analyses of survival senescence by using life tables have identified generalizations including the observation that mammals senesce faster than similar-sized birds. These generalizations have been challenged because of limitations of life-table approaches and the growing appreciation that senescence is more than an increasing probability of death. Without using life tables, we examine senescence rates in annual individual fitness using 20 individual-based data sets of terrestrial vertebrates with contrasting life histories and body size. We find that senescence is widespread in the wild and equally likely to occur in survival and reproduction. Additionally, mammals senesce faster than birds because they have a faster life history for a given body size. By allowing us to disentangle the effects of two major fitness components our methods allow an assessment of the robustness of the prevalent life-table approach. Focusing on one aspect of life history - survival or recruitment - can provide reliable information on overall senescence.

Spatial Scale of Population Synchrony: Environmental Correlation versus Dispersal and Density Regulation.

A stochastic model is developed to analyze the equilibrium spatial pattern of population synchrony, the correlation of temporal fluctuations in population density between localities. The expected population dynamics and the distribution of individual dispersal distance are homogeneous in space. Environmental stochasticity is caused by temporal fluctuations in the intrinsic rate of increase and/or carrying capacity of local populations that are correlated in space (but not time), the environmental correlation decreasing with distance. We analyze a linearized model for small fluctuations. Employing the standard deviation of a function in a given direction as a measure of scale, the spatial scale of population synchrony, lρ, is related to the spatial scales of environmental correlation, le, and individual dispersal, l, by the simple general formula \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Climate Influences on Avian Population Dynamics

l^{2}_{\rho }=l^{2}_{e}+ml^{2}/ \gamma

Optimal Harvesting of Fluctuating Populations with a Risk of Extinction

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THRESHOLD HARVESTING FOR SUSTAINABILITY OF FLUCTUATING RESOURCES

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