Effects of climate change on mutualisms and multi-trophic interactions
Climate is a key driver of species abundances and distributions. While climate change can have strong direct effects on species abundances, it can also have strong indirect effects by altering the complex multi-trophic food webs in which species are embedded. However, because few studies have documented the relative strengths of such direct and indirect effects, we have a limited understanding of the exact mechanisms driving species responses to climate variation. To study this topic, my work includes experimental manipulations of plant-insect multi-trophic interactions along climatic gradients at the Rocky Mountain Biological Laboratory in Gothic, Colorado. This work has shown that species at higher trophic levels (e.g., predators, parasitoids, and ants) are particularly sensitive to changes in climate, and this can have important cascading effects on the abundances and distributions of species at lower trophic levels (e.g., insect herbivores).
Nelson et al. 2019, Journal of Animal Ecology
Nelson et al. 2019, Oikos
Mooney et al. 2016, Ecology Letters
Effects of biodiversity loss on mutualisms
Mutualisms play a central role in structuring populations and maintaining biodiversity. While most mutualisms consist of complex networks of interacting species, we know little about the effects of mutualist identity and diversity on partner fitness. As a result, our ability to predict the effects of biodiversity loss on mutualisms is limited. To fill this gap, my research examines the individual and interactive effects of multiple mutualist species on the fitness and demography of their shared partners. Comparing the effectiveness of multiple ant species as mutualist partners for aphid herbivores, I have found that variation in ant traits (e.g., activity, diet, thermal tolerance, competitive dominance) can shape interactions with aphid herbivores. For example, due to dominance-discovery trade-offs in ants, the ants that typically discover mutualist aphids the fastest are the least able to defend them against competing ants, and are thus replaced over time. Using demographic models, I showed that herbivores benefit from such competition-driven shifts in ant partners and receive the greatest benefits in the most diverse ant communities. This work thus demonstrates the importance of biodiversity for maintaining mutualism functioning.
Sheard et al. 2020, Journal of Biogeography
Nelson & Mooney 2021, Annals of the Entomological Society of America
Trade-offs in plant allocation to dispersal and defense
Plants face contrasting selective pressures to attract mutualists but deter antagonists. For instance, although many plant populations produce rewards (e.g., fleshy fruits) to attract animals to disperse their seeds, fruits are also vulnerable to attack by pre- and post-dispersal seed predators and pathogens. Currently, I am investigating the causes and consequences of variation in plant allocation to dispersal and defense of fruits in southwest Virginia. I have found that defensive secondary metabolites in fruit can reduce the attraction of seed-dispersing ants, but plants may adaptively alter their allocation to defense as fruits develop, reducing defense of mature seeds that are ready to be dispersed. Currently, I am investigating how variation in fruit defense throughout development also influences rates of seed predation by a variety of vertebrates (e.g., mice, raccoons) and invertebrates (e.g., snails, crickets), as well as how allocation to fruit dispersal and defense change across space.
Nelson & Whitehead 2021, TREE
Nelson et al. 2019, Current Opinion in Insect Science
Nelson et al. 2019, Ecological Entomology
Whitehead et al. 2021, Oikos