Abstract
According to the principle of competitive exclusion, the number of resources determines the number of different plant types that are able to coexist. In this thesis, it is investigated whether plant types can maintain themselves in a homogeneous environment that has only one limiting resource, simply by possessing different traits.
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To investigate growth and competitive interactions of plants that possess different traits, a model was developed. Light availability was presumed as the only limiting resource. The plant growth was mechanistic in the way that growth of plant organs was not superimposed on the plant, but was at any time determined by the allocation to organs and the costs and benefits this brought about in relation to neighbouring plants. Only one trait at a time was varied in value. This provided a good way to isolate the role of particular traits and assess the adaptiveness of different values of the trait. A closer look was taken on the role of investment in height growth, crown architecture, seed production and dispersal as determinants for growth, competition, and coexistence between plants. Additionally, the effects of density and frequency dependency were investigated with help of game theory.
In the different simulations reported in this thesis, several factors promoting coexistence under light limitation were found. Interestingly, the role of any plant trait in itself for generating coexistence was limited. These plant traits, however, were the basis for less tangible factors that did affect coexistence. It was the interplay of plant traits with frequency and density dependent processes and the inclusion of space that generated possibilities for plants to live together. By the different susceptibility of plants with different traits to frequency, density and space, situations were created where each of the types could be successful. It is noted explicitly here that the investment patterns of plants and the emerging traits were the actual mechanism through which all other processes worked.
By including mechanisms at the plant and organ scale in the simulations of processes at population or community scale, self-assembling communities were achieved without inserting community-level specifications. The community structures obtained were truly a result of underlying mechanisms. Some general statements could be formulated on the influence of plants’ investment patterns on competition, population development and coexistence, independent of variation in external factors for growth.
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