Scale-Dependent Portfolio Effects Explain Growth Inflation and Volatility Reduction in Landscape Demography. Hui, C., Fox, G. A., & Gurevitch, J. 114(47):12507–12511.
Scale-Dependent Portfolio Effects Explain Growth Inflation and Volatility Reduction in Landscape Demography [link]Paper  doi  abstract   bibtex   
[Significance] Population demography is central to many problems in ecology, evolution, and conservation biology, yet there is a gap between the information needed about the demography of population over multiple spatial scales and the available data, which are largely local. Inspired by concepts from landscape ecology and Markowitz's investment portfolio theory, we address this lacuna by developing a method for quantifying and predicting the demography of multiple populations across spatial scales and apply it to gypsy moth populations. We show that population demography is scale-dependent due largely to a tilted portfolio effect from skewed population size distributions and covarying population growth rate; this explains why population ensembles can have growth rates greater than the mean with variance smaller than the mean. [Abstract] Population demography is central to fundamental ecology and for predicting range shifts, decline of threatened species, and spread of invasive organisms. There is a mismatch between most demographic work, carried out on few populations and at local scales, and the need to predict dynamics at landscape and regional scales. Inspired by concepts from landscape ecology and Markowitz's portfolio theory, we develop a landscape portfolio platform to quantify and predict the behavior of multiple populations, scaling up the expectation and variance of the dynamics of an ensemble of populations. We illustrate this framework using a 35-y time series on gypsy moth populations. We demonstrate the demography accumulation curve in which the collective growth of the ensemble depends on the number of local populations included, highlighting a minimum but adequate number of populations for both regional-scale persistence and cross-scale inference. The attainable set of landscape portfolios further suggests tools for regional population management for both threatened and invasive species.
@article{huiScaledependentPortfolioEffects2017,
  title = {Scale-Dependent Portfolio Effects Explain Growth Inflation and Volatility Reduction in Landscape Demography},
  author = {Hui, Cang and Fox, Gordon A. and Gurevitch, Jessica},
  date = {2017-11},
  journaltitle = {Proceedings of the National Academy of Sciences},
  volume = {114},
  pages = {12507--12511},
  issn = {1091-6490},
  doi = {10.1073/pnas.1704213114},
  url = {https://doi.org/10.1073/pnas.1704213114},
  abstract = {[Significance]

Population demography is central to many problems in ecology, evolution, and conservation biology, yet there is a gap between the information needed about the demography of population over multiple spatial scales and the available data, which are largely local. Inspired by concepts from landscape ecology and Markowitz's investment portfolio theory, we address this lacuna by developing a method for quantifying and predicting the demography of multiple populations across spatial scales and apply it to gypsy moth populations. We show that population demography is scale-dependent due largely to a tilted portfolio effect from skewed population size distributions and covarying population growth rate; this explains why population ensembles can have growth rates greater than the mean with variance smaller than the mean.

[Abstract]

Population demography is central to fundamental ecology and for predicting range shifts, decline of threatened species, and spread of invasive organisms. There is a mismatch between most demographic work, carried out on few populations and at local scales, and the need to predict dynamics at landscape and regional scales. Inspired by concepts from landscape ecology and Markowitz's portfolio theory, we develop a landscape portfolio platform to quantify and predict the behavior of multiple populations, scaling up the expectation and variance of the dynamics of an ensemble of populations. We illustrate this framework using a 35-y time series on gypsy moth populations. We demonstrate the demography accumulation curve in which the collective growth of the ensemble depends on the number of local populations included, highlighting a minimum but adequate number of populations for both regional-scale persistence and cross-scale inference. The attainable set of landscape portfolios further suggests tools for regional population management for both threatened and invasive species.},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-14472408,~to-add-doi-URL,cross-disciplinary-perspective,diversity,forest-pests,intraspecific-vs-interspecific,knowledge-integration,lymantria-dispar,multi-scale,non-linearity,population-growth,serendipity,spatial-pattern,species-distribution},
  number = {47}
}
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