Research Interests

Abiotic mediation of mutualisms and the cascading effects on species abundance

Across environmental gradients mutualisms are highly context-dependent, with their outcomes varying in strength and direction (from beneficial to antagonistic). However, the mechanisms driving this variation and the cascading effects on species abundances and distributions are often not well understood. At the Rocky Mountain Biological Laboratory (RMBL), I study how the abiotic environment alters food-for-protection mutualisms between aphids and ants, and how this variation consequently drives aphid abundance. We have found that ants provide greater protection (1) to aphids feeding on the host plant osha (Ligusticum porteri) in sunny meadows (vs. shaded understories) and (2) to aphids feeding on aspen (Populus tremuloides) at low (vs. high) elevations. Increased ant protection in the sun and at low elevations is due to increased ant abundance or activity, causing aphids to be more abundant. We compared the effects of ant protection to other factors potentially mediating aphid abundance (direct effects of the abiotic environment or effects of variation in plant quality and top-down control by natural enemies) and found that the ant mutualism is the only factor driving aphid abundance across these environmental gradients.
An ant (Formica rufa) bites my finger to protect aphids (Pterocomma populifoliae) feeding on aspen.
Myrmica sp. ants feeding from a bait containing a 20% solution of honey.
I used a GoPro to record interactions between ants at baits containing 10% honey solution, tuna, 50% honey solution, and 20% honey solution (left to right).
Competition for mutualism

For my dissertation work, I am investigating how competition shapes the outcomes of mutualistic interactions. Most mutualisms involve guilds of interacting species, and some of these species may be better mutualists than others. Many species may also compete with each other for the services provided by their shared mutualists. However, we have a limited understanding of how frequently competition for mutualistic services occurs and what the consequences are in the community. To study this topic, I am taking two approaches:

(1) I am investigating the competitive hierarchies among ants near the RMBL and comparing the mutualistic services that they provide for aphids. Near the RMBL there are five main groups of aphid-tending ants, including carpenter ants, wood ants, and odorous house ants. Importantly, these ants differ in how quickly they discover aphid colonies and how effectively they defend them from competing ants. They also differ in how effectively they protect aphids from predators. If competitively dominant ants are also better mutualists for aphids, competition between ants could benefit aphids by inhibiting their associations with less effective ant bodyguards. However, if competitively dominant ants are worse mutualists, competition between ants could be detrimental to aphids by limiting their associations with more effective ant bodyguards. In 2016 I studied ant competition for resources using artificial baits, and in 2017 I plan to  compare the effects of multiple ant taxa on aphid colony survival, population growth rates, and dispersal using a demographic modeling approach.

(2) I am evaluating how aphids compete with each other to attract mutualist ants. To do so, I am investigating whether ant tending rates of aphid colonies and the resulting effects on aphid colony growth and survival depend on aphid colony size and the distance between colonies.