Impacts of a millennium drought on butterfly faunal dynamics

Matthew L Forister,James H Thorne,James A Fordyce,Chris C Nice,Arthur M Shapiro,David P Waetjen

doi:10.1186/s40665-018-0039-x

Abstract

BackgroundClimate change is challenging plants and animals not only with increasing temperatures, but also with shortened intervals between extreme weather events. Relatively little is known about diverse assemblages of organisms responding to extreme weather, and even less is known about landscape and life history properties that might mitigate effects of extreme weather. Our aim was to address this knowledge gap using a multi-decadal dataset of 163 butterfly species that recently experienced a millennium-scale drought. To understand faunal dynamics in the context of the millennium drought, we investigated the behavior of phenology (including date of first flight), species richness and diversity indices through time at 10 study sites spanning an elevational gradient. Linear models were developed to understand the differential sensitivity of butterflies to climate at low and high elevations.ResultsDates of first flight advanced across the elevational gradient during the drought, leading to an overall expansion of the flight window at low elevations and a compression of the flight window in the mountains. The number of species observed per year increased at lower elevations but decreased at higher elevations, apparently as a consequence of extreme sensitivity to hot and dry conditions.ConclusionMontane populations may be more sensitive to climatic extremes than expected based on availability of microclimates and spatial heterogeneity, while low-elevation populations (despite existing in degraded habitats) are buffered by life history plasticity.

Highlights

Climate change is challenging plants and animals with increasing temperatures, and with shortened intervals between extreme weather events
While the shift in phenology is evident across elevations, the dynamics of the flight window diverge later in the season: at higher elevations, the date of last flight shifted to an earlier time during the drought, while at lower elevations the last flight dates from 2011 to 2015 are closer to the long-term average (Fig. 1c; see Additional file 1: Figure S1 for the same results without sampling filters as described above)
Along with the recent reduction in the average number of days that butterflies were observed flying at higher elevations during the drought years, there have been fewer butterfly species observed per year at the same sites (Fig. 2a-e)

Summary

Introduction

Climate change is challenging plants and animals with increasing temperatures, and with shortened intervals between extreme weather events. While many studies of species and ecosystems have looked at climate impacts by using the average change in historical or projected climatic conditions [3, 4], we know far less about the ecological impacts of extreme weather events on wild organisms [5,6,7]. In part this is due to the regional geography in which extreme weather events occur, which requires baseline biological data as well as appropriatelyscaled climatological data for a particular region prior to an event [8]. Associations with climatic variables often differ in sign among congeneric species [18], and even among populations of a single species [17]

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