Inferring associations among parasitic gamasid mites from census data

Abstract

Within a community, the abundance of any given species depends in large part on a network of direct and indirect, positive and negative interactions with other species, including shared enemies. In communities where experimental manipulations are often impossible (e.g., parasite communities), census data can be used to evaluate the strength or frequency of positive and negative associations among species. In ectoparasite communities, competitive associations can arise because of limited space or food, but facilitative associations can also exist if one species suppresses host immune defenses. In addition, positive associations among parasites could arise merely due to shared preferences for the same host, without any interaction going on. We used census data from 28 regional surveys of gamasid mites parasitic on small mammals throughout the Palaearctic, to assess how the abundance of individual mite species is influenced by the abundance and diversity of other mite species on the same host. After controlling for several confounding variables, the abundance of individual mite species was generally positively correlated with the combined abundances of all other mite species in the community. This trend was confirmed by meta-analysis of the results obtained for separate mite species. In contrast, there were generally no consistent relationships between the abundance of individual mite species and either the species richness or taxonomic diversity of the community in which they occur. These patterns were independent of mite feeding mode. Our results indicate either that synergistic facilitative interactions among mites increase the host's susceptibility to further attacks (e.g., via immunosuppression) and lead to different species all having increased abundance on the same host, or that certain characteristics make some host species preferred habitats for many parasite species.

Body size and coexistence in gamasid mites parasitic on small mammals: null model analyses at three hierarchical scales

“…on all conspecific hosts in the same locality) and compound (i.e. on all hosts belonging to all species in the same locality) communities were taken from published surveys and unpublished data on gamasids collected from the bodies of small mammals (Soricomorpha, Erinaceomorpha, Lagomorpha, and Rodentia) in 29 different regions of the Palearctic [28 regional surveys referenced in Krasnov et al (2009) with the addition of a survey in Norway (Edler and Mehl 1972)]. The surveys reported the number of mites of each species found on each small mammal species in a particular location.…”

“…Mite infracommunities are characterized by positive species co‐occurrence, that is, different species co‐occur more frequently than expected by chance (Krasnov et al 2010). In component communities of mites, the abundance of individual species correlates positively with the combined abundances of all other mite species in this community (Krasnov et al 2009). These patterns have been explained mainly by apparent facilitation among coexisting mites mediated via the defense system of the host (Krasnov et al 2009, 2010, but see Presley 2011) or via ‘cooperative feeding’ (Furman 1966) when multiple mite individuals feed from a single skin lesion or puncture.…”

“…In component communities of mites, the abundance of individual species correlates positively with the combined abundances of all other mite species in this community (Krasnov et al 2009). These patterns have been explained mainly by apparent facilitation among coexisting mites mediated via the defense system of the host (Krasnov et al 2009, 2010, but see Presley 2011) or via ‘cooperative feeding’ (Furman 1966) when multiple mite individuals feed from a single skin lesion or puncture. Positive co‐occurrence of mite species could also arise due to reduced resource overlap which could represent ‘the ghost of competition past’ (Connell 1980).…”

“…Positive co‐occurrence of mite species could also arise due to reduced resource overlap which could represent ‘the ghost of competition past’ (Connell 1980). Although, to the best of our knowledge, competition between parasitic gamasids has never been experimentally studied, it seems likely because a) some negative interspecific interactions among parasitic gamasids have been inferred from census data (Krasnov et al 2009) and b) interspecific competition has been reported for other taxa of Acari (e.g. Tetranychidae; Morimoto et al 2006).…”

Patterns of diversity and abundance of fleas and mites in the Neotropics: host‐related, parasite‐related and environment‐related factors

“…Any parasite species is affected by both host‐related and off‐host factors. Consequently, the diversity and abundance of ectoparasites in a locality may be affected by a variety of factors, including host and parasite community structure and environmental factors (Watters, 1992; Vaughn & Taylor, 2000; Krasnov et al , 2005a, 2005b, 2009). Moreover, patterns of the relationships among ectoparasite diversity and abundance and host‐, parasite‐ and environment‐related factors differ not only among ectoparasite taxa [e.g.…”