Defining Parasite Communities Is a Challenge for Neutral Theory

The neutral theory of biodiversity and biogeography is a null model of community structure that suggests that it may be possible to explain the richness and relative abundance of species through neutral processes of immigration, extinction, and speciation, without resort to interactive processes such as competition. There have been no attempts to fit neutral models to parasite communities to date. The nature of parasite communities, however, challenges the basic assumptions of neutral theory. In particular, the spatially dynamic relationships between hosts as habitat patches result in immigration rates that are in a constant state of flux. In addition, the partial compositional overlap of many component communities means that they can affect each other's process rates, which violates the zero-sum assumptions of neutral theory. Despite these obstacles, many of the patterns that neutral theory seeks to explain are still present in parasite communities. Far from being an esoteric special case, parasite communities are ubiquitous in nature and, therefore, any attempts to produce unified theoretical frameworks should accommodate the characteristics of parasite communities, or risk obsolescence.