Local adaptation and species distribution limits along climatic gradients

Abstract

Climate change threatens the persistence of species with loss of biodiversity and ecosystem function. Species and populations may differ in their ability to adapt to changes, and those with restricted distributions may be particularly vulnerable. Genetic adaptation and phenotypic plasticity can provide species with the capacity to respond to changing climatic conditions. This study aims to determine the adaptive capacity of widespread and restricted Acacia species under climate change through a multifaceted approach: (1) develop species distribution models (SDMs) to determine climatic suitability under current and projected future climate scenarios; (2) conduct a controlled glasshouse, temperature manipulation experiment incorporating populations sourced from distinct bioclimatic regions into contrasting growth temperatures to explore genetic adaptation and phenotypic plasticity; and (3) a field reciprocal transplant experiment to determine local adaptation and species distribution limits along altitudinal gradients. SDMs predicted that species with restricted distributions, especially those from tropic climates will be most vulnerable to habitat loss under 2050 climate projections, while species from temperate origins may have greater capacity to maintain larger areas of climate refugia as climate changes. Maximum temperatures were predicted to drive local extinctions on the warm edges of species ranges. However, tropic origin species also showed greater potential to gain suitable habitat in cooler regions compared to temperate species that are more geographically restricted with limited potential to gain suitable habitat which may make them vulnerable to competition from warm origin species longer term. These areas of climate refugia and gained habitat could provide potential sites for range shifts or assisted migration. The glasshouse supported vulnerability of restricted species from tropic climate which showed local adaptation to warm climates while temperate species were able to adjust their growth across temperatures. Patterns of local adaptation were driven mean and maximum temperatures at species climate of origin. Asat and dark respiration were positively correlated with growth and contributed to variation in growth strategies between biomes where tropic species showed lower biomass and greater allocation to leaves as well as allocation to roots in cooler environments and temperate origin species had greater biomass and lower SLA. Intraspecific comparisons between populations suggested that widespread species and species from temperate environments showed greater genotypic differences in growth that may allow for some adaptive capacity through selection of better adapted genotypes. Tropic genotypes showed a stronger response to temperature with limited genotypic differences. However, it is clear that temperature is an important factor in contributing to plant establishment and performance which are determined by coordinated resource allocation and physiological processes. These findings provide critical information to guide conservation and restoration efforts under climate change. Specifically, climate refugia for protection, target populations for assisted migration to enhance resilience and translocation to suitable habitat in the future.

Date of Award	2023
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Paul Rymer (Supervisor), Mark Tjoelker (Supervisor) & Linda J. Beaumont (Supervisor)