Abstract
It is well established in theory that short-term environmental fluctuations could affect the long-term growth rates of wildlife populations, but this theory has rarely been tested and there remains little empirical evidence that the effect is actually important in practice. Here we develop models to quantify the effects of daily, seasonal, and yearly temperature fluctuations on the average population growth rates, and we apply them to long-term data on the endangered Black-faced Spoonbill (Platalea minor); an endothermic species whose population growth rates follow a concave relationship with temperature. We demonstrate for the first time that the current levels of temperature variability, particularly seasonal variability, are already large enough to substantially reduce long-term population growth rates. As the climate changes, our results highlight the importance of considering the ecological effects of climate variability and not just average conditions.
Highlights
Population growth rate is fundamental to understanding the relationship between populations and environmental conditions [1]
Our results show that the relationship between population growth rate and temperature is nonlinear, with a significant negative quadratic component in the function (Table 1, Fig 1)
The overall effect of temperature variability is considerable compared to previous studies and our analyses demonstrate here that wildlife population growth rates can be substantially reduced by environmental variation
Summary
Population growth rate is fundamental to understanding the relationship between populations and environmental conditions [1]. Population growth is determined not just by the well-documented effects of average environmental conditions [2,3,4], and by more complex effects of environmental variability [5] This may include the well-known effects of variability on extinction risk [6, 7], with fluctuations reducing populations to the critically low numbers where they become vulnerable, but in theory environmental variability can impact the long-term growth rates of wildlife populations more directly [8, 9]. The average of concave-down functions is lower, but the average of convex functions is higher and the average of functions that switch concavity could be either, so the magnitude of the inequality is determined not just by the variability and by the degree of concavity in the function [10, 11]
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