Herbivore Survival in Changing Environments

Biotic and abiotic stressors play a pivotal role in shaping herbivore population dynamics, but their impact is far from isolated. Interactive effects, both direct and indirect, necessitate an exploration of these dynamics from a tritrophic perspective. Abiotic conditions directly affect herbivore development and, in turn, influence larvae by altering larval-food plant chemistry. Additionally, these conditions mold predator community composition, impacting hunting strategies, activity patterns, and foraging efficiency. To decipher how predator exposure and abiotic conditions, particularly water availability, influence the larval development and survival of the declining specialist herbivore the monarch butterfly (Danaus plexippus), I established four common gardens across a 513-km water-availability gradient spanning northern Nevada and California.

The North American monarch butterfly, recognized for long distance migration, faces a stark decline due to habitat loss, pesticides, and climate change. Monarch larvae, known for sequestering toxic compounds called cardenolides from their milkweed host-plants, exhibit variable toxicity influenced by environmental conditions, impacting their predation rates. This summer, I tracked larval growth and survival across four gardens to investigate the role biotic and abiotic stressors in shaping monarch performance. Larvae were divided between predator-exclusion and exposed (mock) enclosures, with each common-garden site reflecting distinct climatic conditions, including ambient temperatures, water availability, and predator communities.

As I move into the analysis phase, examining survival rates and identifying key variables through a Random Forest classifier approach, these findings will offer broader insights into how predator communities and abiotic conditions shape larval performance in herbivorous insects.