Climate and extreme weather independently affect population growth, but neither is a consistently good predictor

Abstract

AbstractClimate change involves changes in mean temperature and precipitation as well as increases in extreme weather events; thus, determining how species will respond to climate change requires understanding how organisms respond to change in both mean and extreme conditions. Previously, we have shown that the growth of 21 interconnected populations of the alpine butterfly, Parnassius smintheus, is affected by prevailing climatic conditions during its overwintering period. More recently, we have shown that population growth is affected by extreme weather events during early overwintering. Here, we compare the descriptive and predictive abilities of models based on climate, weather, and their combination. We found that both climate‐ and weather‐based models explain significant, but independent, variation in year‐to‐year changes in population abundance; the combination of both was not better than either individual model. None of the models showed consistently good predictive ability. The climate model was accurate in predicting relatively small changes in year‐to‐year abundance, but not large changes. In contrast, the weather model was poor at predicting small changes in abundance, but accurately predicted large changes. Our results indicate that a more mechanistic approach, linking specific conditions to vital rates and population growth, will be needed to predict population responses to changing abiotic conditions.