Abstract
The goal of this thesis is to advance the field of community ecology by looking for evidence that viruses, like other collections of biological organisms, exist within communities that are shaped by ecological processes. It focuses on picobirnaviruses, which are small bipartite double-stranded RNA viruses that are commonly found in the faeces of many eukaryotic species, but which are actually believed to be viruses of bacteria. Diverse assemblages of picobirnaviruses were sequenced from the faeces of 2664 macaques over 19 different sites in Bangladesh, which were used to explore the relative contribution of stochastic and deterministic processes in shaping viral communities at different scales. Two ecological frameworks were used, one where community assembly was dichotomized into processes that are either stochastic or deterministic, and one where the role of these processes were jointly considered (Vellend’s model of community assembly) and where different stochastic and deterministic processes (dispersal and selection respectively) were investigated. The findings from this work show that viral communities, like macroecological communities, are structured by both stochastic and deterministic forces – but highlight selection, a deterministic process, as being particularly important. The strongest findings overall were that (geographic) site represents the most relevant community scale, and that closely related picobirnaviruses were prevented from occupying the same individual macaque, either because of competition for the same resources (i.e., competitive exclusion) or because of priority effects driven by host immunity (i.e., immune exclusion).