Species interactions are changing as a result of climate-induced shifts in phenology, resulting in changes in temporal overlap between species. However, overlap alone may not adequately capture the effects of species interactions on fitness. For example, two plant species growing at the same time may facilitate one another for pollinator resources, yet compete for soil resources. Therefore, jointly assessing how species interact for multiple shared resources is important for predicting future coexistence. In this study, I assessed whether two subalpine plant taxa compete with each other for pollinators and soil resources in the Rocky Mountains, USA.
Results/Conclusions
Under early snowmelt conditions, temporal overlap between Claytonia lanceolata (Montiaceae)and Mertensia fusiformis (Boraginaceae) increased, suggesting the potential for increased overlap under future climate change. Using a neighbor-removal experiment, I found that reproductive success in C. lanceolata was higher when M. fusiformis neighbors were present in 2017 year and lower in 2018. Secondly, C. lanceolata neighbor removal increased the probability of survival in M. fusiformis in 2018, suggesting competition for resources. Finally, in another experiment, I found that pollinator visitation rates to C. lanceolataand Mertensia were not affected by each other’s local floral density. Combined, these results suggested that the effects of competition and facilitation between C. lanceolata and M. fusiformis were complex, varying temporally. Future experiments are needed to uncover the mechanisms linking phenological shifts to the fitness consequences of changing species interactions and coexistence.