Abstract
Foreseeing population collapse is an on-going target in ecology, and this has led to the development of early warning signals based on expected changes in leading indicators before a bifurcation. Such signals have been sought for in abundance time-series data on a population of interest, with varying degrees of success. Here we move beyond these established methods by including parallel time-series data of abundance and fitness-related trait dynamics. Using data from a microcosm experiment, we show that including information on the dynamics of phenotypic traits such as body size into composite early warning indices can produce more accurate inferences of whether a population is approaching a critical transition than using abundance time-series alone. By including fitness-related trait information alongside traditional abundance-based early warning signals in a single metric of risk, our generalizable approach provides a powerful new way to assess what populations may be on the verge of collapse.
Highlights
Foreseeing population collapse is an on-going target in ecology, and this has led to the development of early warning signals based on expected changes in leading indicators before a bifurcation
Including body size within composite early warning metrics generally improved the accuracy of predictions, especially at a 2s threshold for early warning signals (Fig. 3a,b)
Recent work on the detectability of critical transitions has tended to focus on the change in single leading indicators, and how reliable these methods may be in predicting future population crashes[10,19]
Summary
Foreseeing population collapse is an on-going target in ecology, and this has led to the development of early warning signals based on expected changes in leading indicators before a bifurcation. Such an approach has previously been used to combine the trends in coefficient of variation, autocorrelation, skewness, and spatial autocorrelation into a single composite early warning signal, and has been shown to provide better estimates of an approaching transition than single leading indicators alone[11] Such abundance-based measures of the stability of a system may not be the only indicators that a population is being stressed; recent studies have shown that demographic change, driven by environmental perturbation, is often accompanied by simultaneous change in individual traits[21]. This will be especially true if estimates of trends in body size are less prone to error than abundance data
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