Influences in community assembly

This dissertation is a collection of four bodies of work which have focused on issues of processes and mechanisms that influence ecological systems. The distribution and abundance of species is the central issue of ecology. To persist in the natural environment, species must coexist with other species in environments that may be periodically perturbed so that ecological systems are constantly undergoing change at some scale. Thus, ecological systems are dynamical and assemble within the bounds of certain rules. In the first of these works, the dynamics of overlapping perturbations is examined. Perturbations of the "1/f" distribution type were placed onto a model landscape. Collapses occurring from the perturbations were independently placed on the landscape and the resulting dynamics were examined. It was found that these overlapping perturbations led to a range of distributions depending on the number of perturbations and their spectral coefficients. In the second study, four green algal species were studied to examine the influence of invasion sequence and timing. A competitive hierarchy was established based upon phosphorus use efficiency. It was found that this hierarchy could be altered by varying the sequence and timing of species inoculations, as well as by varying the inoculation densities and various environmental factors of the system. The last two studies involved the modelling of community assembly. Again, invasion sequence was found to alter the community dynamics of a model system. Several previous assembly models had two key assumptions, single invaders and low inoculation densities, built in which led to the development of complete invasion resistance. When these two assumptions were relaxed, it was found that invasion resistant states did not occur. However, invasion resistance was found for most species and increased numbers of invading species resulted in increased turnover.