Bridging ecophysiological trade-offs and population dynamics - How competition and climate shape community structure

The regional climate is the primary selective factor for whether a plant species is successful or not. Under favorable climatic conditions more species can thrive than under unfavorable conditions. Furthermore, it is competitive interactions that strongly affect the relative abundances of plant species within communities through competition for light, water, or space. Additionally disturbances such as fire or wind throw can strongly affect community composition. Examine the abundances of plants in a realistic community therefore still remains as challenging. In my thesis I investigate the role of competition, disturbances and climate on the development of vegetation community structure and diversity patterns. To answer these research questions the model DIVE (Dynamics and Interactions of VEgetation) has been developed. It determines population dynamics of plant communities while calculating the abundances of each plant species dependent on its establishment at open sites, competition for occupied sites and mortality in the presence of different rates of disturbances and strengths of r- and K-selection. Thereby r-selection favors the selection of colonizers that quickly establish on open sites and K-selection favors the selection of competitors that grow slowly but can exclude less competitive plants. As follows, r-selection influences establishment, K-selection competition and the disturbance rate mortality. DIVE is a simple general model linking plant strategies to their competitive dynamics, using growth and reproduction characteristics. These characteristics serve as input information for DIVE. The input information for DIVE is gains from simulations with the JeDi (Jena Diversity) model. This model simulates a variety of hypothetical functional plant strategies that emerge from climatic constraints. Thereby our approach bridges from theoretical population dynamics models such as Lotka-Volterra to realistic vegetation models, which calculate biogeochemical exchange fluxes but usually simulate only a few so called plant functional types instead of diverse communities. In the first study of my thesis examined the dynamics of DIVE using a community out of 5 plant strategies under different sensitivities of strength of r- and K-selection and disturbances. The results show that the simulated successional dynamics are reasonable if K-selection is present. Under K-selection big competitive strategies slowly overgrow the smaller ones. The highest levels of diversity are found in simulations in the absence of selection. Under high levels of selection strength, intermediate levels of disturbances are required to obtain coexistence. The second study investigates the relation of diversity to disturbances. The results show that, depending on the presence or absence of r- or K-selection, four different diversity-disturbance curves appear: flat under absence of selection, increasing under K-selection, decreasing under r-selection and hump-shaped under r- and K-selection. We show that these curves develop through the different realizations of the colonization-competition trade-off. This trade-off means, that either a plant strategy can quickly occupy open sites or it can competitively exclude smaller strategies. The second study blocked out the role of climate, as simulation were done for a moist tropical climate only. But climate in fact represents a first filter that sorts out plant strategies, while competition can be seen as second additional filter. The third study therefore explores the effects of climate onto the relation of diversity to disturbances using four different climates: a moist and a dry tropical climate and a warm and a cold temperate climate. First of all, in absence of selection the model reproduces the observed diversity gradient from the poles towards the tropics. The temperate climates are more restricted to high disturbances than the tropical ones. Therefore in our simulations flat diversity-disturbance curves are only observed in the tropical climates. Nevertheless an additional increase in disturbances would also lead in the tropical climates to no strategies surviving. Further r- and K-selection show the same effects in the different climates, as already proposed in the second study. Interestingly the tropics are highly influenced by strong r-selection which means that diversity proportionally decreases while in the cold temperate climates r-selection takes the less influence. Remarkably under both strong r- and K-selection the warm temperate climate reach highest diversity. My thesis shows the importance of competition for population dynamics. During this thesis the first model has been developed that independently controls strength of r- and K-selection. The results can help to explain found diversity-disturbance relations with strength of selection. Furthermore, because of the simplicity and generality of DIVE, it could be used to understand vegetation structure and functioning at the global scale and the response of vegetation to global change.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2014

Author dc:creator

• Bohn, Kristin

Contributors dc:contributor

• Reineking, Björn

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/1700/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:1700