Australian Mountain Pollinators in a Changing World

Abstract

Pollinators play a central role in plant reproduction and, by extension, in shaping plant communities and supporting ecosystem function. In cold environments, pollinators encounter challenges that influence both survival and reproductive success. Because insects are ectothermic, their body temperature depends on external climatic conditions. Sustaining the heat needed for activity is energetically costly in climates where temperatures are low and unpredictable. These constraints often result in pollinator assemblages that differ from those in warmer habitats. Species that persist in cold regions must exhibit specialised life history traits that enable them to tolerate low temperatures.

This thesis explores how mountain pollinators respond to abiotic and biotic factors across multiple ecological scales. I examine patterns at broad spatial scales, such as community turnover with elevation, and at finer scales, including the microclimates insects experience within individual flowers. I begin by characterising whole-community responses before focusing on a few focal insect species, allowing me to consider how life history traits interact with environmental limits. By linking community- to species-level processes and climate- to microclimate-level patterns, this work aims to provide an integrated understanding of how environmental conditions shape mountain pollinators, particularly under climate change.

In Chapter 1, I assess how pollinator assemblages vary with climate. Surveys along an elevational gradient showed that flies dominated higher elevations, while bees and beetles were more common at lower sites. These shifts reflected both direct temperature effects and the distribution of floral resources, demonstrating how climate and vegetation jointly structure pollinator communities.

Chapter 2 investigates a previously unstudied bee that persists in subalpine woodlands. Nest surveys, behavioural observations, and biophysical modelling revealed that it withstands cold conditions through a distinctive nesting strategy in dead snow gum branches. While activity windows were strongly limited by temperature, modelling suggests these windows may expand under projected warming scenarios.

In Chapter 3, I examine how floral microclimates influence insect thermoregulation. Thermal imaging of flowers and visiting insects showed that flowers were consistently warmer than ambient conditions, with flower morphology affecting both floral warming and insect body heat. This indicates that alpine flowers can act as thermal refuges, allowing pollinators to decouple from an otherwise cold climate with variable conditions.

Finally, Chapter 4 focuses on the Bogong moth (Agrotis infusa), an Endangered alpine migrant. By trapping moths during aestivation and analysing pollen loads, I found that individuals regularly forage on alpine flowers, including several endemic plant species. This provides new evidence that Bogong moths contribute to alpine pollination networks, highlighting previously unrecognised ecological role during the migratory phase of their lifecycle. Show more