Ant-mediated seed dispersal in an invaded landscape

Abstract

Human activities are modifying our environments at an unprecedented rate and scale, leading to not only a loss of biodiversity, but also a loss of ecosystem functionality. Arguably, one of the most pervasive of these destructive forces can be seen in the rise of biological invasions, and the spread of non-native invasive ant species. Despite the clear potential of the detrimental ecological and economic pressures posed by these insects, we still lack a comprehensive understanding of their impacts on ecosystem services. One such service is ant-mediated seed dispersal – otherwise known as myrmecochory. In this thesis I address some of these shortcomings by investigating how invasive ants may disrupt the process of myrmecochory in native ecosystems, across a range of different scales. Firstly, I took a broad perspective by looking at evolutionary events of myrmecochory across the ant phylogeny: these analyses revealed that myrmecochory is a diffuse interaction between many ant-plant guilds. Secondly, in-depth analyses of the effects of the non-native invasive Argentine ants ( Linepithema humile ) on both ant and plant communities in South African and Spain suggested that these invaders are ill-equipped to replace the native seed dispersers that they displace. Field observations suggested that invaded ant communities dispersed fewer seeds than non-invaded ant communities, and that this inefficiency is evident at multiple stages in the seed dispersal process. Thirdly, the modifications to the natural ant-plant interactions due to invasive ants may be making these environments more vulnerable to secondary invasions by other invasive myrmecochorous plant species. Finally, I explore the mechanism that may be driving these changes in ant-seed interactions, by exploring how differences in a range of physical and chemical seed traits may explain ant preferences to disperse certain seeds. In conclusion, while myrmecochory may be considered a rather loose ant-plant mutualism, invasive ant species do appear to be altering the nature of the biotic interactions, with impacts permeating through different levels of the ecosystem, and potentially leaving their ecological mark well beyond the mere loss of native ant biodiversity.

Date of Award	19 Mar 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jon Bridle (Supervisor) & Seirian Sumner (Supervisor)