Root foraging behaviour of plants: New theory, new methods and new ideas

All organisms, including plants, experience variability in the environment which puts pressure on organisms to evolve flexible responses. The study of these responses by organisms falls into the discipline of behavioural ecology. In this thesis, I am interested in the foraging behaviour of plant roots and I have two goals. First, I will use foraging theory from the animal literature to determine whether plants forage in ways that are similar to animals. Second, I will show how the adoption of foraging theory for plants can lead to a better theoretical understanding of coexistence of plants. I begin with a discussion of the major differences between plants and animals in their foraging behaviour and how this can be incorporated in to a more general predictive framework of plant foraging behaviour. I follow this discussion with two empirical tests of classic foraging models. First, I test a patch use model from the animal literature to determine if it can predict plant foraging behaviour. My results show that plants foraged for patches using the same strategies used by animals. Second, I test a resource choice model from the animal literature. These data indicated that plants select different types of nitrogen using the same resource choice strategies as foraging animals. These two studies reveal some basic foraging abilities of plants, however the experiments were performed in the absence of resource competition, a condition seldom experienced by plants in nature. To overcome difficulties in studying plant roots grown with neighbours I developed a molecular method for the identification of visually indistinguishable plant roots from competition experiments. Finally, I apply the molecular method to examine whether resource patchiness in soil can increase the intensity of competition experienced by foraging plants, and that the presence of neighbours influences the foraging strategies of plants. Together the results presented in this thesis show that plants use the same basic foraging strategies as animals, and that foraging behaviour can be linked to competition and coexistence of plant species.