Competition dynamics can be inferred from a single ‘snapshot’ of plant communities’ spatial distribution

Background/Question/Methods

Plant competition models have played a significant role in the development of ecological theory, but explicit empirical testing of model predictions has proven to be notoriously difficult. One of the obstacles to empirical testing is that model analyses do not always lead to concrete and testable predictions. Even in cases where such predictions can be derived, empirical testing would often require experimental manipulation under controlled conditions, hampering extrapolation to natural ecosystems. Using three general individual-based, spatially explicit competition models, we show that these models can be used to generate specific predictions of how plant competition dynamics within ecotones are reflected in the spatial organization of the plant communities involved. As these competition dynamics can be inferred from a single ‘snapshot’ (e.g. an aerial photograph or satellite image) of ecotones in time, these predictions can be tested relatively easily with Earth Observation data from natural ecosystems.   

Results/Conclusions

Our analyses suggest that a key diagnostic attribute of competition dynamics is the average spatial position of frontrunners of both communities along the ecotone. Mathematical analyses and simulation modeling show that this average frontrunner position of retreating communities is always farther away from a so-called optimal vegetation boundary as compared to that of the expanding community. Importantly, this feature does not depend on assumptions about plant dispersal or competition characteristics.  In addition, we show that the velocity of expansion is reflected by the relative difference in boundary position between the two communities. With the availability of snapshot data rapidly increasing, this method may provide an easy tool to test the extent to which plant community dynamics are driven by competition processes as described in classical model frameworks. In ecosystems where plant competition processes are dominant, the method could serve as a diagnostic tool indicating areas where rapid changes in plant distributions are occurring. Application of the method may therefore be particularly useful in ecosystems subject to invasion by exotic species or in mountain ecosystems where ecotones might be shifting upward due to climate change.