Some plants don’t play games: An ideal free distribution explains the root production of plants that do not engage in a tragedy of the commons game.

Abstract

This is the pre-peer-reviewed version of the following article: G.G. McNickle and J.S. Brown. (2014) An ideal free distribution explains the root production of plants that do not engage in a tragedy of the commons game. Journal of Ecology. DOI: 10.1111/1365-2745.12259, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/1365-2745.12259/abstract\n\nO_LIGame theoretic models that seek to predict the most competitive strategy plants use for competition in soil are clear; they generally predict that over-proliferation of roots is the only evolutionarily stable strategy. However, empirical studies are equally clear that not all plants employ this strategy of over-proliferation of roots. Here, our goal was to develop and test an alternative non-game theoretic model that can be used to develop alternative hypotheses for plants that do not appear to play games.\nC_LIO_LIThe model is similar to previous models, but does not use a game theoretic optimization criterion. Instead, plants use only nutrient availability to select a root allocation strategy, ignoring neighbours. To test the model we compare root allocation and seed yield of plants grown either alone or with neighbours.\nC_LIO_LIThe model predicted plants that do not sense neighbours (or ignore neighbours) should allocate roots relative to resource availability following an ideal free distribution. This means that if a soil volume of quality R contains x roots, then a soil volume of quality R/n will contain x/n roots. The experimental data were consistent with this prediction. That is, plants grown with 1.2g of slow release fertilizer resources produced 0.043 g of roots, while plants grown with neighbours, or plants grown with half as much fertilizer produced half as much root mass (0.026g, and 0.24g respectively). Seed yield followed a similar pattern.\nC_LIO_LIThis model presents an alternative predictive framework for those plant species that do not seem to play a tragedy of the commons game for belowground competition.\nC_LIO_LISynthesis: It remains unclear why some plants do not engage in belowground games for competition. Models suggest over-proliferation is an unbeatable evolutionary stable strategy, yet plants that do not play the game apparently coexist with plants that do. We suggest that a greater understanding of trade-offs among traits that are important for other biotic interactions (above-ground competition, enemy defence, mutualisms) will lead to a greater understanding of why some species over-proliferate roots when in competition but other species do not.\nC_LI