Climate change has become an ever-increasing problem for contemporary ecological communities and ecosystems. These anthropogenically driven effects are changing the way that these organisms interact with their environment, and even affecting interactions between organisms. For species engaged in mutualistic interactions, these changes may be especially important and alter host fitness responses because of these symbioses as well as subsequent interactions within the community. In this experiment, we full-factorially manipulate two mutualisms associated with the legume Chamaecrista fasciculata, nitrogen fixing soil bacteria (Rhizobiaspp) and protective ants, under field conditions of ambient and anticipated global warming.
Ceramic heaters were used to increase the ambient air temperature by 3C and additional plots were used as controls with ambient field conditions. Our experimental treatments are temperature (ambient or elevated), rhizobia inoculation (presence or absence), and ants (with or without, using Tanglefoot). The experiment was regularly censused by counting the number of ants per plant, measuring plant growth and flowering, and fitness was measured at the end of season by counting fruits and seeds.
We found increased temperature resulted in plants flowering earlier and producing more flowers. Ant presence increased fitness. This increased fitness is likely in response to a reduction in herbivory from ant defense. However interestingly, fitness decreased due to rhizobia inoculation in ambient temperature but increased in elevated temperature. Our results indicate that there may be a trade-off for carbon from C. fasciculata between ants and rhizobia in ambient temperature. Yet in elevated temperature, rhizobia availability does not significantly influence ant abundance. This may be a result of decreased carbon limitation in elevated temperature. Overall, spatiotemporal variation in herbivory and nutrient limitation may influence differences in plant fitness from these two different mutualisms over time.