Abstract

Climate change has caused widespread shifts in species’ phenology, but the consequences for population and community dynamics remain unclear because of uncertainty regarding the species‐specific drivers of phenology and abundance, and the implications for synchrony among interacting species. Here, we develop a statistical model to quantify inter‐annual variation in phenology and abundance over an environmental gradient, and use it to identify potential drivers of phenology and abundance in co‐occurring species. We fit the model to counts of 10 butterfly species with single annual generations over a mountain elevation gradient, as an exemplar system in which temporally limited availability of biotic resources and favorable abiotic conditions impose narrow windows of seasonal activity. We estimate parameters describing changes in abundance, and the peak time and duration of the flight period, over ten years (2004–2013) and across twenty sample locations (930–2,050 m) in central Spain. We also use the model outputs to investigate relationships of phenology and abundance with temperature and rainfall. Annual shifts in phenology were remarkably consistent among species, typically showing earlier flight periods during years with warm conditions in March or May–June. In contrast, inter‐annual variation in relative abundance was more variable among species, and generally less well associated with climatic conditions. Nevertheless, warmer temperatures in June were associated with increased relative population growth in three species, and five species had increased relative population growth in years with earlier flight periods. These results suggest that broadly coherent interspecific changes to phenology could help to maintain temporal synchrony in community dynamics under climate change, but that the relative composition of communities may vary due to interspecific inconsistency in population dynamic responses to climate change. However, it may still be possible to predict abundance change for species based on a robust understanding of relationships between their population dynamics and phenology, and the environmental drivers of both.

Highlights

  • As the climate has warmed, the timing of life cycle events—phenology—has advanced for a wide range of taxa (Parmesan 2007)

  • Our results suggest a link between phenological change and interannual variation in abundance, which, in some cases but seemingly not all, may be explained by common environmental drivers of these phenomena

  • Our model quantified the phenology and abundance of 10 univoltine species, detected evidence of their interannual variations, and identified how phenology varies with elevation

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Summary

Introduction

As the climate has warmed, the timing of life cycle events—phenology—has advanced for a wide range of taxa (Parmesan 2007). Phenological changes have not been consistent in direction or magnitude across populations, species, or trophic levels (Thackeray et al 2010, Scranton and Amarasekare 2018). Understanding the drivers and ecological consequences of this variation in phenology is challenging because the population sizes and activity periods of species vary across geographical gradients, such as elevation or Manuscript received 6 August 2019; accepted 11 September 2019. Phenological change could itself influence population dynamics via several mechanisms. If the duration of an activity period is extended, population growth can occur over a longer period.

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