Current Research - Biological Invasions

Biological invasions are a leading threat to biodiversity, agriculture and the economy. Of the many introduced organisms, ants are over-represented with 5 species considered among the top 100 invasive species worldwide. A major challenge of invasion biology lies in the development of a predictive understanding of invasion processes. However, this is inherently difficult because different characteristics may be important for different species or during different stages of invasion. Subsequently, our research on mechanisms of success for invasive ants is both comparative across species and also across each of the three distinct stages of invasion: opportunity, establishment and spread.

To examine the role of opportunity in invasion, we are developing a database of ants intercepted in quarantine in the United States. These data will be used to examine why some species succeed as invaders while others do not. Surprisingly, there is a remarkable diversity of ant species moving around the world as a result of human commerce. However, relatively few species become established suggesting that opportunity alone is insufficient for introduced species to establish and spread.

Determining a species’ pattern of spread and its potential distribution is integral for the establishment of monitoring programs and preventing new infestations. Using the literature, museum collections and personal surveys, we have assembled a dataset of over 1000 locations for the Argentine ant (Linepithema humile), one of the world’s worst invasive alien species. We have used this dataset to assess the species’ potential geographic and ecological distribution using ecological niche modeling, and to predict its spread locally. This information is essential to guide quarantine efforts and prevent the establishment of new populations and we are currently pursuing these techniques to examine the potential distribution for other ant species.

Argentine Ants tending scale insects Attempts to identify the proximate causes of invasion success or to predict rates of spread seldom emphasize behavioral characteristics or changes in the biology of organisms that occur post introduction. Recent work, however, illustrates that insight into the proximate causes of invasions often hinges upon a careful comparison between native and introduced populations of an organism. Our previous work on invasive ants has focused on variation in their colony structure (specifically the role of unicolonility in ecological success). More recently, work in our lab has employed stable isotope analysis of carbon and nitrogen to compare the trophic ecology of invasive ants between native and introduced populations. Our results suggest that Argentine ants and fire ants are able to monopolize plant-based resources in introduced populations while being more predatory in their native ranges. Changes in trophic biology may allow introduced ant populations to attain higher worker densities relative to their native range where they co-exist with other ants in species rich communities. This work also contributes to our understanding of how mutualisms with honeydew producing insects influences ant community structure, behavior and ecological success.

Current Research - Ant Polymorphism and Specializations

Evolution and biomechanics of trap-jaw ants

fig 7 from spagna et. al 2008 A range of animal taxa have evolved suites of morphological and behavioral specializations for self-propelled rapid-strike attacks on prey. These extreme strike abilities are among the fastest biological movements ever recorded and may be the results of co-evolutionary predator-prey arms races. What is the process underlying the transition from a generalized function to a specialized evolutionary adaptation? We are addressing this question using “trap-jaw” ants. “Trap-jaws” have independently evolved at least five times across four subfamilies of ants. In addition to being very effective at capturing prey, some species can use their over-sized jaws to propel themsleves into the air. Advances in measurement and video-graphic technologies allow the characterization of these incredibly fast movements with improved precision resulting in the characterization of novel mechanisms for energy storage, amplification and release. The comparative nature of this system also allows for the examination of multiple, independent origins of trap-jaw morphology as well as variation in form and function within each origin. This variation is ideal for biomechanical research on the relationship between morphology, size, energetics, maneuverability, maximum speed and endurance.

Ecological consequences of body size variation in ants

Body size is an important life history trait that affects metabolism, thermoregulation, locomotion, reproduction, abundance, longevity, and diet. As with other life history traits, investment into body size is constrained by resource availability and tradeoffs between increasing individual offspring size and increasing the total number of offspring. For social insects, investment into offspring size or number is theorized to be an important tradeoff influencing the ecological success of a colony. Moreover, as many ants have polymorphic worker castes, colonies can vary in the body size distributions they produce. Subsequently we are intersted in examining how colony investment into worker size and/or worker number contributes to a colony’s ecological success and also how such investment may be constrained developmentally of phylogenetically.