In the face of rapid global change, a crucial question in ecology and evolution is how species will respond to changes in climate and whether they will be able to adapt quickly enough to persist under novel abiotic and biotic conditions. Changes in plant phenology and herbivory regimes are already occurring due to climate change and have the potential to impact species interactions, community structure, and biodiversity. However, little is known about how within-species differences in phenology affect adaptation and persistence. Here, we examine population-level responses to herbivory regime in Streptanthus tortuosus, which occupies a wide range of environments and displays remarkable morphological and physiological variation. We conducted a common garden experiment mimicking mammalian herbivory on individuals from three alpine populations of S. tortuosus to determine the effects of varying timing and frequency of herbivory on phenology, fitness, and life history.
Results/Conclusions
Our results suggest that timing and frequency of herbivory significantly affects both flowering time and fitness. Individuals that experienced herbivory flowered significantly later than controls, and individuals experiencing later or more frequent herbivory experienced the most pronounced delays in flowering. Additionally, herbivory depressed fecundity in all treatments, and individuals exposed to more frequent herbivory experienced a significant reduction in fecundity. This suggests that plants are unable to compensate when herbivorized, especially when tissue damage occurs multiple times throughout the season. Plants were also more likely to survive for longer periods of time in response to herbivory (significantly so if herbivorized more than once), potentially leading to increased perenniality and iteroparity. Overall, results suggest that individual variation in the timing and frequency of herbivory impacts population-level variation in phenology, fitness, and life history. Future plant phenological responses to climate change will depend on how the timing of biotic pressures interacts with changing environmental conditions. If plants and their herbivores respond differently to changing environmental cues as summers become drier and hotter in alpine regions, such varying responses may alter temporal overlap between plants and herbivores, affecting plant fitness and persistence. Understanding the abiotic and biotic factors that currently drive phenological responses is essential for accurately predicting the potential for adaptation to future climate-induced environmental change.