Tracking the snow line: Responses to climate change by New Zealand alpine invertebrates

Abstract

We review and test an ecological paradigm that asserts that alpine invertebrate communities may shift upslope with climate warming. Our model couples the end of summer snow line (EOSS) elevation with invertebrate populations in New Zealand’s Southern Alps, using a forty-year data set, from fifty index glaciers. We show the snow line has risen an average 3.7 m a−1. This is equivalent to raising alpine isotherms by almost 150 m and presents alpine biotic populations with four possible scenarios: upslope tracking, stasis, horizontal dispersal, or local adaptation. We characterize the alpine invertebrate biota (AIB) and present two case studies that show that high-elevation taxa have tracked the snow line within a narrow range (<20 m), whereas lower elevation taxa have potentially shifted by tens of meters. Relationships between the EOSS and Southern Oscillation Index (SOI) are investigated because precipitation and temperature influence snow line elevation by 25 percent. We also highlight the utility of invertebrates for monitoring climate change impacts on alpine ecosystems with a proposal for alpine climate monitoring units (CMUs), complementing an existing network of ecological management units (EMUs). We include an annotated list of New Zealand alpine invertebrates as potential indicators of climate change.