Effects of temperature on resource competition in marine phytoplankton

Background/Question/Methods

Predicting how species will respond to climate change remains a challenge for ecologists, in part because climate change has hard-to-predict effects on species interactions. For example, changing temperatures can alter competitive dynamics by changing a species’ ability to compete with other species for limited resources. Tilman’s R* theory predicts a winner of resource competition based on minimum resource requirements, and these resource requirements and uptake rates have predictable changes with temperature. Therefore, we might expect to see changes in competitive dominance for a resource as temperatures increase. However, there have been few tests of whether the temperature dependence of species’ minimum resource requirements can be used to predict switches in competitive dominance in different thermal environments.Here we empirically test Tilman’s R* theory using marine phytoplankton species competing for limited nitrate. We first measure minimum nitrate requirements at population equilibrium at two temperatures in five marine phytoplankton species in monocultures, from which we can predict switches in competitive outcomes according to Tilman’s R* theory. Next, we test the accuracy of our predictions by running pairwise competition experiments, in which two species of phytoplankton are grown together under each temperature in continuous flow environments until one species competitively excludes the other.

Results/Conclusions

We present preliminary results on whether competitive switches with temperature can be predicted by species minimum nitrate requirements measured in monocultures. Nitrate commonly limits phytoplankton growth in marine ecosystems and is declining with climate change due to altered ocean circulation patterns.This project will empirically test theory about how resource competition changes with temperature, which is a critical step towards understanding and predicting how climate change will affect community dynamics.