How parasites divide resources: a test of the niche apportionment hypothesis

Abstract

Summary1. Modelling species abundance patterns, i.e. the distribution of relative abundance among species within the same community, has become a common framework in community ecology. To describe species abundance patterns several statistical models have been proposed, e.g. the log-normal distribution, but these do not provide an ecological explanation of the underlying processes. 2. Tokeshi introduced (1990) and developed (1993, 1996, 1999) a series of niche-orientated stochastic models to fit species abundance patterns. They suggest that abundance of species are proportional to the resources they apportion. Following this hypothesis, Tokeshi defined some processes in resource partitioning to explain species abundance patterns. 3. To study the rules which govern species assemblages, parasite communities present advantages because each host harbours a replicate community, the total niche is limited to the body of the host and demographic processes are usually similar for all parasite species in a community. Using five Tokeshi models, we searched for common rules structuring the parasite communities of six species of marine fish from the coast of Chile. The biovolume of each parasite species was preferred as a measure of its 'abundance' over actual numerical abundance, to account for the considerable variation in body size among parasite species. 4. The random assortment model, which suggests a lack of competition and interaction and independent apportionment of resources between species in the community, was fitted successfully to the parasite communities of three fish species for both means and variances of abundance ranks using a new Monte-Carlo method. 5. These results are in accordance with current knowledge on parasite coexistence rules, i.e. that most parasite communities appear non-saturated with species, with many empty niches and with interspecific competition not playing a major structuring role.

Helminth communities in three sympatric rodents from the Brazilian Atlantic Forest: contrasting biomass and numerical abundance

“…As noted by GeorgeNascimento et al (2002), in fishes, low abundant but large biovolumetric species could generate a different infracommunity pattern than those based on numerical data alone. Our results are similar to those observed in fishes: when an individual host harbours a high parasite biomass, one or a few dominant parasite species account for most of the biovolume (Mouillot et al, 2003). Muñoz and Cribb (2005) showed that different parasite species can differ widely in size, such that two species with equal numerical abundance can show variability (one or more times) in their biomass, as observed for A. lenzi and R. akodontis in A. cursor.…”

“…Nevertheless, the size of the parasites is relevant information in order to understand how much parasite biomass can be sustained and how it can determine the helminth community structure. Moreover, parasite biomass could be a more relevant measure of parasite abundance than the total number of parasite individuals, because the parasite body size can be used as a proxy for productivity (Mouillot et al, 2003) and estimates of parasite energetic requirements (GeorgeNascimento et al, 2004). In the present study the species with more biomass (biovolume) represented less than 10% of total numeric abundance, reinforcing the importance of include the parasite biovolume in the analysis of the structure of helminth communities.…”

“…GeorgeNascimento et al (2004) applied biomass as an indicative of parasite infracommunity productivity. Mouillot et al (2003) used biomass as a measure of abundance in an investigation of parasite community ecology and the results indicate that interspecific competition does not play a major structure role in parasite community. In mammals, little is known about helminth community structure and biomass.…”

Comments about some species abundance patterns: classic, neutral, and niche partitioning models

“…In general ecology, experimental tests are the more direct way to link the observed patterns and the causal process involved. Considering the theoretical expectation of increasing equitability patterns following the natural succession in community organization (Harvey et al, 1983), the Power Fraction model allows several species abundance patterns between the extremes of dominance (≈ geometric series) and uniformity (≈ broken-stick) just by adjusting the parameter k. Until now, the Tokeshi resource partitioning models have only been applied to parasites communities (Naeem and Hawkins, 1994;Mouillot et al, 2003), dragonflies (Johansson et al, 2006), beetles (Ulrich and Zalewski, 2006), birds (Bersier and Sugihara, 1997), chironomidae (Tokeshi, 1990) and stream fishes (Higgins and Strauss, 2008). The process of community building is done without great mathematical or computational difficulties, making them an accessible analysis tool to most scientists.…”

“…On the other hand, the niche partitioning models remained little explored after the Sugihara and Tokeshi papers (Sugihara, 1980;Tokeshi, 1990; and except for some field tests (Naem and Hawkins, 1994;Bersier and Sugihara, 1997;Cassey and King, 2001;Fesl, 2002;Mouillot et al, 2003;Johansson et al, 2006;Higgins and Strauss, 2008), only Sugihara et al (2003) discussed theoretically its close relationship with other ecological patterns.…”