Regularity underlies erratic population abundances in marine ecosystems

TL;DR

This study reveals that marine species populations fluctuate following a Laplace distribution, enabling a stochastic model that highlights the importance of ecosystem-level management to mitigate extinction risks.

Contribution

The paper introduces a novel stochastic model based on a Laplace distribution of growth rates, emphasizing the role of reduced growth at low densities and shared stochasticity across species.

Findings

Population growth rates follow a Laplace distribution.

Reduced growth at low densities is crucial for accurate extinction risk assessment.

Shared stochasticity dominates single-species growth rates.

Abstract

The abundance of a species' population in an ecosystem is rarely stationary, often exhibiting large fluctuations over time. Using historical data on marine species, we show that the year-to-year fluctuations of population growth rate obey a well-defined double-exponential (Laplace) distribution. This striking regularity allows us to devise a stochastic model despite seemingly irregular variations in population abundances. The model identifies the effect of reduced growth at low population density as a key factor missed in current approaches of population variability analysis and without which extinction risks are severely underestimated. The model also allows us to separate the effect of demographic stochasticity and show that single-species growth rates are dominantly determined by stochasticity common to all species. This dominance---and the implications it has for interspecies correlations, including co-extinctions---emphasizes the need of ecosystem-level management approaches to reduce the extinction risk of the individual species themselves.