Research

We study the ecology of mutualisms involving plants, insects, and microbes, with a focus on how these interactions shape populations, communities, and ecosystems. We integrate field and laboratory experiments, behavioral assays, analytical chemistry, and demographic modeling to understand how these interactions function—and how they change—across environmental contexts.

With ant-hemipteran mutualisms, bumble bee gut symbioses, and seed dispersal mutualisms, we ask:
1. How do mutualisms generate and maintain biodiversity?
2. How do global changes—including biodiversity loss, climate change, and species invasions—shape mutualisms?
3. How do changes in mutualisms affect populations and communities across space and time?

Ant-Hemipteran Mutualisms

Ant–hemipteran interactions are classic food-for-protection mutualisms in which ants aggressively defend sap-feeding insects—such as aphids and treehoppers—from predators and parasitoids in exchange for a sugary reward called “honeydew.” Rather than simple pairwise interactions, these mutualisms often involve diverse communities of ants and hemipterans that differ dramatically in their effectiveness as partners. As biodiversity is lost, the balance of costs and benefits in these systems can shift, altering outcomes for the ants, the hemipterans, and the broader food webs in which they are embedded. One major research focus in our lab is uncovering the factors that generate and maintain biodiversity—and conversely contribute to its loss—in ant-hemipteran mutualisms, and determining how changes in biodiversity modify the strength, stability, and ecological function of these interactions.

Ph.D. Student Lemon Lynch collecting honeydew from aphids feeding on fireweed in Colorado. Credit: Annika Nelson.

Bumble Bee Gut Symbioses

Pollination is vital for global food production, yet key pollinators—including bumble bees—are declining at alarming rates. Reversing these declines will require new strategies to promote pollinator health. One promising avenue is improving gut microbiome function through probiotic interventions. The bumble bee gut microbiome is composed of a small set of core bacterial species that provide important benefits to host health. However, microbiome composition varies widely among individuals, and many wild bees harbor disrupted gut communities dominated by non-core bacterial species with unknown impacts on host health. How this variation influences host physiology, behavior, and performance, and whether it can be harnessed to enhance bumble bee health, remain largely unknown. Our lab investigates how gut microbial diversity and composition shape bumble bee health and function through controlled laboratory experiments, with the goal of identifying microbiome-based mechanisms and interventions that support pollinator resilience.

Bombus impatiens workers inside a colony. Credit: Steve Zylius/UC Irvine.

Annika collecting bumble bees in Wisconsin. Credit:  Annika Nelson

Seed Dispersal Mutualisms

Because plants are rooted in place, many species produce fleshy fruits to attract animals that disperse their seeds. At the same time, fruits are vulnerable to attack by seed predators and pathogens, which may explain why they often contain high concentrations and diverse mixtures of toxic or deterrent secondary metabolites. Our lab investigates how diversity in fruit chemical traits shapes the wide range of species interactions surrounding fruits, and how plants navigate trade-offs between attracting mutualistic seed dispersers and defending against antagonists.

Ectatomma sp. ants dispersing seeds of the plant Piper reticulatum at La Selva Biological Station in Costa Rica. Credit: Annika Nelson