Right now I am working on this paper with several collaborators "The impact of the invasive Argentine ant (Linepithema humile) on association network structure of native ant species in Northern California." We are using an 18 year dataset of Argentine ant presence in Jasper Ridge Biological Preserve to answer questions about how the Argentine ant invasion affects native ant species.We use null models to examine native ant community structure in conjunction with log-linear models to clarify associations among specific pairs of species by creating association networks in three types of ant community: those with long-term Argentine ant presence (invaded), fluctuating Argentine ant presence (where Argentine ants were present in some surveys but not others), and no Argentine ant presence (intact). We have found that the presence of Argentine ants affected co-occurrence patterns and diversity in native ant assemblages. From 1994-2000, co-occurrence patterns of native ant species were random, and native ant diversity was low. During that same time period, native ants in intact areas co-occurred less than expected by chance and diversity was high. Ant communities in fluctuating areas, in contrast, were randomly assembled similar to those in invaded areas, but native ant diversity was high, as in the intact assemblages. Co-occurrence patterns did not change over time in either fluctuating or invaded areas. However, native species in intact areas shifted from co-occurring less than expected by chance to occurring randomly with respect to one another after 2000. Concurrently, diversity in intact communities and fluctuating communities increased, and the Argentine ant invasion stopped progressing in 2001. Preliminary results suggest that changes in interactions between key native species may be the driver for these shifts in co-occurrence patterns among native species.
An investigation of synergistic interaction among invasive species
Invasive species cause a great deal of harm both to native ecosystems and to human economies. Because of the large numbers of currently problematic invasive species, the continually increasing rate of introduction of new species, and the pressing conservation concerns, invasive species require study. Though there have been many studies of individual invasive species, few studies explore how invasions interact with one another. Furthermore, we know even less about the mechanisms underlying both individual and interacting invasions.
My thesis research explored the potentially synergistic interactions among invasive species in grasslands on Robinson Crusoe Island, Chile.
The island has no native mammals, but a variety of mammals and plants invaded following human discovery. To clarify the mechanisms of interaction among European rabbits (Oryctolagus cuniculus) and invasive plants, I set up a large-scale experiment manipulating soil disturbance and rabbit presence using exclosures, which I maintained for four years.
Using Markov chain models to examine species transitions over time for each treatment, I found that native plants were most successful without rabbits or disturbance, epizoochorous exotic plants did not improve colonization success in the presence of rabbits, elimination of rabbits but not disturbance decreases native plant presence, and native plants lose in competition with exotic plants in all treatments. The Markovian models also provided predictions of future community structure within treatment and in novel situations.
As the exotic plant community on Robinson Crusoe originates from five continents, I also examined the role of origin in invasion success. Surprisingly, I found that plants from the native range of European rabbits were not more successful than other invasive plants in the presence of rabbits. Instead, almost all exotic plants benefited from soil disturbance, while native plants were negatively impacted.
Lastly, I explored the association between native status and population dynamic parameters, for dominant plants. There was no statistical difference between parameters of native species and exotic species. However, treatment and life form (annual / perennial) did influence parameters to some extent. Overall, idiosyncratic species effects were the most important factor in determining population dynamics.
In the future, I plan to continue collecting data at this field site to establish a long-term study of plant community dynamics of invasive plants and response to invasive rabbits, and to compare invasion dynamics of species found in Chile with the same species invading in other locations.
This research was conducted with the help of my amazing graduate advisor, Timothy Wootton, at the University of Chicago, in the Committee on Evolutionary Biology. Please check out links to my publications on my publications web page.