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Spatial population dynamics: Analyzing patterns and processes of population synchrony

The search for mechanisms behind spatial population synchrony is currently a major issue in population ecology. Theoretical studies highlight how synchronizing mechanisms such as dispersal, regionally correlated climatic variables and mobile enemies might interact with local dynamics to produce different patterns of spatial covariance. Specialized statistical methods, applied to large-scale survey data, aid in testing the theoretical predictions with empirical estimates.

A new test for density-dependent survival: The case of coastal cod populations

A new test based on the generalized additive model is proposed to investigate density-dependent mortality in the juvenile cohorts of cod. Density dependence implies that the function linking the count of a cohort in one year to the count in the succeeding year is convex. The method estimates (without functional assumptions) the function linking the two counts and provides a level of significance for any convexity. We investigate the power and bias of the new test on the basis of simulated data.

Cycles and trends in cod populations

Year-to-year fluctuations in fish stocks are usually attributed to variability in recruitment, competition, predation, and changes in catchability. Trends in abundance, in contrast, are usually ascribed to human exploitation and large-scale environmental changes. In this study, we demonstrate, through statistical modeling of survey data (1921–1994) of cod from the Norwegian Skagerrak coast, that both short- and long-term variability may arise from the same set of age-structured interactions.

Synchrony and scaling in dynamics of voles and mice in northern Japan

One-hundred-and-seventy-six time series of the Japanese wood mouse (Apodemus speciosus) and 185 time series of the grey-sided vole (Clethrionomys rufocanus) spanning 31 years (1962-1992) were studied with respect to synchrony and spatial correlation in population dynamics. The time series were collected at fixed sites as part of the rodent census program of the Japanese Forestry Agency. The survey locations cover a region of 115km by 270km of northern Hokkaido, Japan.

Density dependence in voles and mice: A comparative analysis

Dynamics of coastal cod populations: Intra- and intercohort density dependence and stochastic processes

Skagerrak populations of Atlantic cod (Gadus morhua L.) have been surveyed at several fixed stations since 1919. These coastal populations consist of local stocks with a low age of maturity and a short life span. We investigated 60 time-series of 0-group juveniles (i.e. young of the year) sampled annually from 1945 to 1994. An age-structured model was developed which incorporates asymmetrical interactions between the juvenile cohorts (0-group and 1-group; i.e. one-year-old juveniles) and stochastic reproduction.

Impact: Toward a framework for understanding the ecological effects of invaders

Positive interactions of nonindigenous species: Invasional meltdown?

A global database: The key to weighing on-the-ground invasive species impacts

Biological impacts of species invasions: Implications for policy makers