Friends and foe: a cross-continental analysis of interactions facilitating or hindering successful introduction

Abstract

Plant introductions to novel environments, whether intentional or accidental, have occurred for centuries and are the precursor to the thousands of invasions that are currently threatening ecosystems across the globe. One of the common, well-studied mechanisms that is thought to aid in successful introduction is known as the enemy release hypothesis, which explains that organisms may thrive in their new environments as they have escaped their co-evolved natural enemies. While enemy release may facilitate introduction in some species or situations, half of the time it does not, and we did not understand the circumstances that lead to its occurrence. Using a robust, biogeographical approach, I quantified herbivore damage across 16 plant species at varying sites across their native and introduced ranges and found that neither time, space, climate, or leaf palatability explained patterns of enemy release. Most research on invasion ecology tends to focus on the negative interactions that are missed in the introduced range and fails to consider how positive interactions are affected. Here, I provide the first broad test of the missed mutualist hypothesis across ten plant species in their native and introduced ranges, that accounts for variation between locations. Following over 120 hours of in-situ observations I found plants to be visited 2.6 times less frequently and with 1.8 times lower richness of pollinators in their introduced range in comparison to their native range. I also introduce the ZAX Herbivory Trainer, a globally accessible software that can reduce researchers’ inaccuracy of herbivory estimates by 7% in less than 10 minutes, which can be retained for up to 3 months. My thesis deepens our understanding of the mechanisms that facilitate and hinder successful introduction and provides an effective tool scientists can use to further this area of research at even larger scales.