Host densities as determinants of abundance in parasite communities

Abstract

Several epidemiological models predict a positive relationship between host population density and abundance of directly transmitted macroparasites. Here, we generalize these, and test the prediction by a comparative study. We used data on communities of gastrointestinal strongylid nematodes from 19 mammalian species, representing examination of 6670 individual hosts. We studied both the average abundance of all strongylid nematodes within a host species, and the two components of abundance, prevalence and intensity. The e¡ects of host body weight, diet, fecundity and age at maturity and parasite body size were controlled for directly, and the phylogenetically independent contrast method was used to control for confounding factors more generally. Host population density and average parasite abundance were strongly positively correlated within mammalian taxa, and across all species when the e¡ects of host body weight were controlled for. Controlling for other variables did not change this. Even when looking at single parasite species occurring in several host species, abundance was highest in the host species with the highest population density. Prevalence and intensity showed similar patterns. These patterns provide the ¢rst macroecological evidence consistent with the prediction that transmission rates depend on host population density in natural parasite communities.

A symbiont's dispersal strategy: condition-dependent dispersal underlies predictable variation in direct transmission among hosts

“…Positive relationships between host size and symbiont density or biomass are well known, especially in parasite systems (e.g. [41][42][43][44][45]). Similarly, branchiobdellidan and cocoon abundance are frequently correlated with crayfish size [9,11,32].…”

Bat flies on phyllostomid hosts in the Cerrado region: component community, prevalence and intensity of parasitism

“…Prevalence patterns vary extensively between sites, but there is not an apparent pattern associated with phytogeographical domains. Local host abundance and shelter type are thought to affect the prevalence of streblids (Arneberg et al 1998, Patterson et al 2007). Therefore, the data available on streblids support the theory that conspecific bats use variable shelters throughout their distributional range and/or that bat species vary widely in their abundance within a phytogeographical region.…”

High host densities dilute sea lice Lepeophtheirus salmonis loads on individual Atlantic salmon, but do not reduce lice infection success

“…Classical models (Anderson & May 1978, 1979 predict that the mean number of parasites per host (i.e. infection intensity) increases with higher host densities, due to the higher probability of encountering a host (Arneberg et al 1998). However, examples of negative correlations between infection intensity and host density exist (McCallum et al 2001).…”

“…As mobile parasites, an increase in host density could result in a lower infection intensity. Few studies have tested this empirically (Arneberg et al 1998, Krasnov et al 2002, particularly in aquatic systems (Sasal 2003), where disease epidemiology is qualitatively different from terrestrial systems (McCallum et al 2004). Infection success (Sevatdal 2001), prevalence (Krasnov et al 2002, Costello 2006) and degree of aggregation (Bagge et al 2005, Stanko et al 2006, Krasnov et al 2007) also describe parasite infestation dynamics.…”