Global warming responses within the New Zealand alpine radiation of acridid grasshoppers : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatu, New Zealand

Abstract

We are living in the Anthropocene, where humans are directly and indirectly altering climatic regimes, leading to warmer conditions with multifarious effects on the biosphere. Well-documented ecological responses to planetary heating include distributional, phenological, and/or phenotypical shifts. Anthropogenic global warming is predicted to significantly impact alpine ecosystems, yet our current understanding of alpine species responses to both ongoing and future global warming is limited. My thesis bridges this gap by investigating the influence of past and future climates on New Zealand’s endemic alpine short-horn grasshoppers (Orthoptera: Acrididae), as representatives of New Zealand’s alpine fauna. As one of the most ubiquitous herbivores in alpine areas worldwide, grasshoppers provide a marvellous lens to examine responses of native systems to increasing temperatures and explore the mechanisms behind such responses. For this, I used an integrative approach combining phylogeographic tools, demographic statistics, phenotypic data (size and shape), niche models and niche metrics, and genotype–phenotype–environment associations. My findings indicate that (1) distinct climatic, biological, and geophysical factors controlled population structuring of grasshopper species during the Pleistocene with a legacy of spatially separate intraspecific lineages; (2) departures from current climatic conditions are projected to vary with geography, and so species exposure and vulnerability to climate change will vary; (3) habitat loss predicted over the next 50 years of warming will lead to smaller and more-fragmented populations with reduced adaptive potential; (4) differences in niche features between diverging intraspecific lineages may lead to lineage-specific responses; (5) distinct climatic factors influence body size clines, and this might strongly influence potential phenotypic responses. An unexpected and important result is that closely related species are predicted to respond in different ways to climate change, suggesting such responses are more evolutionarily labile than conserved. Collectively, this body of research offers valuable insights into the eco-evolutionary responses of alpine organisms to global warming with broad implications for alpine biota everywhere in the world. The thermal environment is a powerful abiotic driver of evolution, and as we face unparalleled rates of warming, understanding how temperature hinder or foster evolution is critical for assisting management decisions that embrace evolutionary resilience.