Stable Isotope Insights into the Trophic Interactions of Invasive Ants: Are Sugar and Sharing Promoting Abundance?
Abstract
The complex interplay between trophic interactions, species abundance, and competition helps explain the distribution of a species and can have important evolutionary consequences. Stable isotope analysis is one of the leading tools that ecologists use to quantify trophic interactions. Although authors commonly estimate trophic position from stable isotopes, there is incredible variation in the baselines and methodologies used in the literature. I conducted a literature review to determine the causes and consequences of this variation. Baseline and methodology significantly impacted the trophic position estimates of individual species, as well as conclusions about food web structure. Increased sample size may mitigate some of the variation caused by different baselines and methodologies, but an alarmingly large proportion of studies collected only one sample or did not report how many they collected at all, highlighting a critical need to increase stable isotope sample size in trophic ecology research. Next, I used stable isotope analysis and direct observation to determine the relationship between trophic position and abundance of the invasive tawny crazy ant (Nylanderia fulva). Classical food web theory predicts that individuals at the base of the food web will be more abundant than those at the top, but I found that tawny crazy ant densities were highest when ants were more predaceous. Rather than feeding as herbivores, tawny crazy ants were actually highly omnivorous. Another factor that may promote the spread and establishment of many invasive ant species is their proclivity towards intraspecific cooperation. To quantify cooperation between colonies in the field, I developed methods to label food using stable isotope tracers. I then applied these methods to examine inter- and intracolonial cooperation using the red imported fire ant (Solenopsis invicta; hereafter fire ant). My results suggest that multiple-queen fire ant colonies are not cooperating and may engage in high levels of intraspecific competition with neighboring colonies and may exhibit low levels of nepotism within the colony. My dissertation helps develop best practices for stable isotope analysis, which is a critical tool in ecological research. It also tests fundamental questions about food web structure and kin selection theory.
Citation
Kjeldgaard, Mackenzie Kate (2020). Stable Isotope Insights into the Trophic Interactions of Invasive Ants: Are Sugar and Sharing Promoting Abundance?. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /192689.