Predicting Future Ant Invasions and Assessing Community Dynamics After Establishment

Abstract

Okinawa Institute of Science and Technology Graduate UniversityDoctor of PhilosophyAs humans have spread and increasingly dominated the planet, other species have also been introduced to places beyond their natural dispersal capacity. Some of these species have become costly invasives causing severe damage in human lives and producing negative impacts on the environment and native biodiversity. Invasive ants are among the most damaging invasive species, with hundreds of species known to be spreading around the world. In this dissertation I study pre-establishment risks and post-establishment long term effects from a community perspective using the whole ant family (Hymenoptera: Formicidae). In the first chapter, I include relevant background information to the topic and study systems. In the second chapter, I forecast the risk of establishment for Japan from the global pool of alien ants. I derive potential source hotspots from around the globe using a new workflow built around species distribution modeling. These predictions are intended to help policy-makers implement better preventive programs for cargo coming from different regions of the world. I show that there is a latitudinal effect on the invasion risk and that the remote islands of Japan are at highest risk. The species identified as threats are most numerous in temperate European areas and the subtropical American continent, which could become the main sources of new invasive species to different regions of Japan. In the third chapter, I investigate how seasonality and land cover differences shape the spatial and temporal activity density of ant communities of different historical presence (native vs. alien) to the island of Okinawa in Japan using a hierarchical joint species distribution modeling approach. I demonstrate that, even long after the first introduction, alien ants have a distinct usage of the environment than native ants. Native species' activity is mainly driven by high temperatures with a strong phenological effect which results in high activity during spring and summer. Meanwhile alien species' activity have more types of responses to temperature and humidity, with most of them active at the colder and less humid seasons. Species are also spatially structured by land cover, as expected from invasion ecology, native species are most active in forested areas while alien species dominate urban environments, and both guilds are similarly active in open areas like agricultural land. In the fourth chapter, I include how these studies may be followed, general conclusions and highlight the need for extra preventive measures as the number of potential new invaders is higher than current invaders and past invasions show that alien species are able to exploit niches that native ants cannot, and include potential avenues to continue these research studies.doctoral thesi