The effect of warming temperatures on the physiology and behaviour of pollinating insects

Abstract

Pollination is an important ecosystem service for both agricultural and natural systems. However, climate change is driving changes in the delivery of pollination services. One of the main influencing factors of climate change is rising temperatures. Most research on this issue has focused on phenological shifts (resulting in temporal mismatches between pollinators and plants), while the influence of warming on insect pollinator metabolism and pollination behaviour has not received equal attention. My research aims to fill both gaps by first testing if pollinator metabolism scales with temperature in pollinator body size according to the Metabolic Theory of Ecology (MTE). The MTE aims to explain a range of biological patterns and processes based on the underlying energetic constraints of organisms arising from metabolism. These constraints are primarily dependent on organismal body size and temperature, making the MTE highly relevant for predicting the impacts of warming on pollinating insects. Secondly, I tested if differences in air temperature can change pollinator foraging behaviour and if it can influence how pollinators alter their foraging behaviour in response to predation risk. I experimentally studied the patterns of foraging behaviour and metabolic scaling in four different pollinator species, Apis mellifera (honeybee), Bombus terrestris (bumblebee), Eristalis tenax (drone fly), and Lucilia sericata (blow fly) across a range of temperatures that represent a rise in average and maximum temperatures across New Zealand. My findings suggested that the MTE predictions only hold for certain species and only for the temperature-metabolism relationship for all species combined. Thus, the MTE may not be adequate for predicting the full impacts of warming on insect pollinators without further development, but the underlying theory itself still has uses in providing us with information on species-specific temperature sensitivities. Furthermore, I discovered that temperature and predation risk both affect insect pollinator behaviour, though not interactively, suggesting that warming will alter insect pollinator foraging behaviour, but not in concert with predation risk. In summary, this thesis provides meaningful insights into individual and species-level responses of pollinator behaviour and physiology to climate warming and the potential consequences for future pollination services.