Date of Award


Publication Type

Doctoral Thesis

Degree Name



Great Lakes Institute for Environmental Research


Environmental Sciences.


Haffner, G.D. (Great Lakes Institute for Environmental Research)




Ecologists have sought to describe the Rules of Assembly - a set of basic, tenets that would regulate the composition, structure, and dynamics of groups of organisms. To date, these Rules of Assembly have proven elusive, and several authors have postulated that the inherent complexity of natural communities precludes investigators from ever describing these rules. In this dissertation, I used data from benthic diatom communities of tropical (Lake Matano, Sulawesi, Indonesia) and temperate (Mazinaw Lake, Ontario, Canada) freshwater lakes to evaluate several novel models regarding the mechanisms that regulate the composition, structure, and relative abundance of biological communities. I demonstrated that in Lake Matano, diatom communities exhibited high degrees of small-scale patchiness and were not regulated by geographic proximity or substrate characteristics. The small scale patchiness exhibited by this system was a result of a high degree of ecological specialization among the diatom taxa of the lake. Such elevated levels of ecological specialization were shown to be characteristic of low-latitude habitats. In general, groups of species with higher levels of ecological specialization exhibited higher levels of taxonomic diversity and lower species abundances, and my results demonstrate that more specialized taxa tended to partition resources while generalists were more prone to competitive effects. In colonization experiments, assemblages from low latitudes proceeded quickly through the early successional period and exhibited deterministic community structure in as little as ten days. This deterministic structure was not observed in similar experiments conducted in a temperate system and succession was frequently reset by weather events. Additionally, taxa from within the tropical assemblage responded independently when subjected to a simulated upwelling event, and neither simulated nor actual disturbances invoked changes in community composition in this system. In summary, I proposed the following Rules of Assembly as they pertain to diatom communities: 1.