Mind the Gap:

: the importance of flowering phenology in pollinator conservation

Abstract

Pollinator declines pose a major threat to global food security and the integrity of natural ecosystems, making their conservation a high priority. Understanding the ecological factors that limit pollinator populations is central to ensuring their survival in the face of ongoing land use change and climate change. The availability of suitable floral resources is known to be one of the most important of these limiting factors, but the exact mechanisms by which floral resources affect pollinators are not well understood. In this thesis I investigated the different ways in which floral resources, in particular their phenology, affect bumblebees, a particularly important group of UK pollinators. My thesis had three main aims:
The first was to characterise and quantify the phenology of nectar resources in UK farmland and compare this with the phenology of common farmland bumblebees to identify periods of nectar deficit. Comparing the phenology of nectar supply with the phenology of bumblebee nectar demand revealed ‘hunger gaps’ during March and September when supply did not meet demand. My results suggest the phenology of nectar supply may be as important as total nectar production in limiting bumblebee populations.
The second aim was to determine how different components of an agricultural landscape contribute to resource availability in different periods of the year, and how this affects the density of farmland bumblebee colonies. Nectar resources in September were found to have the greatest effect on bumblebee colony density but the proportion of garden cover in the surrounding landscape was also important. No other landscape factors, including semi-natural habitat cover, showed any relationship with colony density. In-silico farmland manipulation simulations which increased September nectar supply resulted in substantial increases in bumblebee colony density, highlighting the potential value of phenologically-informed conservation actions.
The final aim was to measure the foraging preferences, foraging patterns and diet breadth of farmland bumblebees and investigate how these changed through the year. Bumblebees showed preferences for certain plant taxa and appeared to actively expand their diet breadth, feeding on a wider and more consistent number of plant species than expected from relative resource abundance. The results suggest the quantity and diversity of floral resources is important in driving bumblebee foraging choices.
From a conservation perspective, this study demonstrates the importance of considering the phenology, spatial arrangement and nutritional value of floral resources in the design of pollinator conservation schemes. Overall, my study provides an improved understanding of how food resources, and their variation across time and space, can shape pollinator communities.

Date of Award	28 Nov 2019
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Jane Memmott (Supervisor)