Aim
We studied compositional turnover in two ectoparasite taxa asking whether (a) the main driver of turnover (environmental factors, host composition, or distance) is the same in both taxa; (b) the ...turnover of rare and widespread fleas and mites is driven by different factors; and (c) the turnover of either fleas or mites or both respond to the same environmental gradients as the turnover of their hosts.
Location
Northern and central Palaearctic.
Time period
1959–2004.
Main taxa studied
Fleas, gamasid mites, mammals.
Methods
We used data on fleas and mites collected from 30 and 20 regions, respectively, and applied a novel metric, zeta diversity, and a novel approach, multi‐site generalized dissimilarity modelling (MS‐GDM).
Results
In fleas, variance explained by the models with host turnover as a predictor was higher than that of models with environment and distance or environment only. In mites, similar proportions of variance were explained by models with and without a host‐associated predictor. Host turnover strongly affected the compositional turnover of fleas, whereas mite turnover was equally influenced by host turnover and dissimilarity in air temperature. When host turnover was removed from the models, temperature became the most important predictor of turnover, followed by precipitation (for both taxa) and distance (for fleas). The effects of host turnover and environment were stronger for turnover of rare than widespread species. Temperature was the most important predictor of the host turnover independently of whether distance was included in the model.
Main conclusions
We conclude that the strength and manifestation of the effects of host compositional turnover as compared to environmental dissimilarity differ between ectoparasite taxa. Moreover, the application of MS‐GDM allowed us to reveal patterns that were obscured or distorted in earlier studies.
1. We applied a Markov random fields/conditional random fields (MRF/CRF) modelling to understand whether and how species associations in ectoparasite infracommunities of small mammals vary along ...environmental gradients across space and time.
2. We analysed the variation in species associations in flea and mite infracommunities of seven host species across localities (spatial scale) and time periods (in the same locality; temporal scale).
3. The performance of the CRF models differed between ectoparasite taxa, scales, and host species. The model performance for flea and mite infracommunities in the majority of host species was satisfying although the proportions of correctly predicted positive occurrences and model sensitivity were moderate.
4. The probability of occurrence of many flea and mite species depended mostly on the occurrence of another flea and mite species (respectively), with many negative interspecific interactions, although occurrences of some species were mainly affected by environmental factors. The patterns of pairwise associations between some ectoparasite species were affected by environmental factors.
5. Although many ectoparasite pairs demonstrated stability in the strength or sign of association across space or time, interactions between other species pairs were spatially or temporally variable, with the association between the same pair of species being stable in one host species and variable in another host species.
6. We conclude that ectoparasite associations are mediated by the off‐host environment and may depend on the life histories of both host and ectoparasite species.
The occurrence of a parasite species depended on the occurrence of another parasite species or environmental factor or both.
The majority of interspecific associations were negative with associations being spatially or temporally variable and the pattern of association being affected by environmental factors.
Some associations varied with respect to host species identity.
Similarity between species plays a key role in the processes governing community assembly. The co-occurrence of highly similar species may be unlikely if their similar needs lead to intense ...competition (limiting similarity). On the other hand, persistence in a particular habitat may require certain traits, such that communities end up consisting of species sharing the same traits (environmental filtering). Relatively little information exists on the relative importance of these processes in structuring parasite communities. Assuming that phylogenetic relatedness reflects ecological similarity, we tested whether the co-occurrence of pairs of flea species (Siphonaptera) on the same host individuals was explained by the phylogenetic distance between them, among 40 different samples of mammalian hosts (rodents and shrews) from different species, areas or seasons. Our results indicate that frequency of co-occurrence between flea species increased with decreasing phylogenetic distance between them in 37 out of 40 community samples, with 14 of these correlations being statistically significant. A meta-analysis across all samples confirmed the overall trend for closely related species to co-occur more frequently on the same individual hosts than expected by chance, independently of the identity of the host species or of environmental conditions. These findings suggest that competition between closely related, and therefore presumably ecologically similar, species is not important in shaping flea communities. Instead, if only fleas with certain behavioural, ecological and physiological properties can encounter and exploit a given host, and if phylogenetic relationships determine trait similarity among flea species, then a process akin to environmental filtering, or host filtering, could favour the co-occurrence of related species on the same host.
Dark diversity (DD) is represented by species that may potentially inhabit a locality but are absent. We applied this approach to identify missing species and links in the interaction networks of ...fleas and gamasid mites with small mammals and asked (a) which factors affect host, parasite or interaction (= link) DD and (b) whether the probability of an interaction to be missing is associated with the host and/or the parasite traits.
The DD of both parasite taxa increased with an increase in host DD. The DD of interactions increased with an increase in the DD of the respective parasite taxon. The quantity of missing flea–host links was affected by environment, whereas that of mite–host links was affected by host DD.
The values of the probability of an interaction to belong to DD were similar (= repeatable) within host and flea, but not mite, species. The probability of a flea–host and a mite–host interaction to be missing was higher if social hosts that possessed complex shelter, had low population densities but large geographic ranges.
The probability of a flea–host interaction to be missing was higher if a flea species was not abundant and preferred to spend most of its life on either the body or nest of its host but not both.
In conclusion, we propose a relatively simple way to apply the dark diversity concept to assess the quantity of missing links in parasite–host networks, to identify these links, and to relate the probability of a link to be missing with parasite and/or host traits.
The quantity of flea–host links missing from a site was affected by environment, whereas that of mite–host links was affected by missing hosts. The probability of parasite–host links to be missing depended on host and parasite traits, but the latter was true for fleas, but not mites.
Ixodes apronophorus Schulze, 1924, the marsh tick, belongs to a group of so-called “neglected” ixodid ticks, which remain underexplored compared to the most well-studied species of the genus Ixodes ...(I. ricinus, I. persulcatus). In this communication, we analyze and summarize the quantitative data on the abundance of this parasite, its geographical distribution, and the diversity of its small mammal hosts in the region of West Siberia (Asiatic Russia). The analyzed data represent a continuous series of observations made between 1953 and 2007, which constitutes one of the longest timeseries ever studied by acarologists. It is shown that the marsh tick in West Siberia is most common in the northern forest steppe and southern taiga landscape zones, being distributed south of 60° N. Among 24 species of small mammals registered as hosts for I. apronophorus in the studied region, three play the most important role: the European water vole (Arvicola amphibius), the tundra vole (Microtus oeconomus), and the Northern red-backed vole (Clethrionomys rutilus). The data characterizing parasitism of the marsh tick on these three hosts in various landscape zones and subzones are provided. We can report a weak albeit significant negative relationship between the abundances of I. apronophorus and its small mammal hosts. The possible explanation lies in the mismatch between the cycles of abundance characteristic of the tick and its hosts.
We studied compositional turnover in communities of fleas and mites harboured by small mammals using zeta diversity metric (similarity between multiple communities) and asked whether the patterns of ...zeta diversity decline with an increase in the number of communities differ between taxa and hierarchical scales infracommunities (parasite assemblages on individual hosts), component communities (parasite assemblages harboured by host populations), and compound communities (all parasite species in a locality). The average number of shared species declined with an increasing number of communities (zeta order). It attained zero at higher orders in infracommunities of both taxa with the shape of the zeta decline being best fitted by the negative exponential function, and the retention rate curves being modal. In contrast, zeta diversity values for compound communities of mites and fleas did not attain zero at higher zeta orders, and the form of the zeta decline was best fitted by the power-law function, whereas the retention rate curves were asymptotic. In component communities, the form of zeta decline was best fitted by either exponential or power-law function in dependence of whether communities were considered within a host across localities or across hosts within a locality and whether ubiquitous species were taken into account. Our main conclusions are that (a) the rules governing compositional turnover in parasite communities for the lowest and the highest hierarchical scales are taxon-invariant but scale-dependent and (b) species composition of infracommunities is mainly driven by stochastic assembly processed, whereas that of compound communities is mainly driven by niche-based processes.
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•No relationship was found between latitude and intraspecific flea or mite abundance.•Environment had the greatest effect on spatial variation in parasite abundance.•Host abundance ...affected parasite abundance to a lesser extent.•These patterns were generally consistent across spatial scales.
We tested whether biogeographic patterns characteristic for biological communities can also apply to populations and investigated geographic patterns of variation in abundance of ectoparasites (fleas and mites) collected from bodies of their small mammalian hosts (rodents and shrews) in the Palearctic at continental, regional and local scales. We asked whether (i) there is a relationship between latitude and abundance and (ii) similarity in abundance follows a distance decay pattern or it is better explained by variation in extrinsic biotic and abiotic factors. We analysed the effect of latitude on mean intraspecific abundance using general linear models including proportional abundance of its principal host as an additional predictor variable. Then, we examined the relative effect of geographic distance, biotic and abiotic dissimilarities among regions, subregions or localities on the intraspecific dissimilarity in abundance among regions, subregions or localities using Generalized Dissimilarity Modelling. We found no relationship between latitude and intraspecific flea or mite abundance. In both taxa, environmental dissimilarity explained the largest part of the deviance of spatial variation in abundance, whereas the effect of the dissimilarity in the principal host abundance was of secondary importance and the effect of geographic distance was minor. These patterns were generally consistent across the three spatial scales, although environmental variation and dissimilarity in principal host abundance were equally important at the local scale in fleas but not in mites. We conclude that biogeographic patterns related to latitude and geographic distance do not apply to spatial variation of ectoparasite abundance. Instead, the geographic distribution of abundance in arthropod ectoparasites depends on their responses, mainly to the off-host environment and to a lesser extent the abundance of their principal hosts.
1. This study tested the relationships between the probability of pairwise species co‐occurrence and pairwise dissimilarity in their traits in infracommunities (across assemblages harboured by ...conspecific individual hosts within a locality), component communities (across assemblages harboured by host species within a locality), and compound communities (across assemblages in different localities) of fleas and gamasid mites parasitic on small mammals in Western Siberia.
2. A significant, albeit weak, tendency was found for flea communities harboured by conspecific host individuals, host species, and host communities to be composed of similar species. No relationship between the probability of co‐occurrence and trait dissimilarity was detected for mite communities at any hierarchical scale.
3. For fleas, this study explained the link between positive co‐occurrence and trait dissimilarity by a process resembling environmental filtering realised mainly via host traits for infracommunities and component communities and via off‐host environment for compound communities, thus suggesting that the identical shape of the relationships between co‐occurrence and trait dissimilarity at different scales was driven by different mechanisms.
4. The explanation of the lack of this relationship in mites included: (i) the paucity of the subset of mite traits used in this study and its potential inadequacy for the question at hand; and (ii) possible masking of the effect induced by one trait on co‐occurrence owing to the lack of this effect induced by another trait(s).
5. Caution is recommended regarding the compilation of a dataset involving multiple traits, its analysis, and the interpretation of the results.
The probability of pairwise co‐occurrence of flea species in infracommunities (across host individuals within a locality) and component communities (across host species within a locality) decreased with an increase in pairwise trait dissimilarity, probably due to filtering via host traits.
The probability of pairwise co‐occurrence of flea species in compound communities (across localities) decreased with an increase in pairwise trait dissimilarity, probably due to filtering via environmental factors.
The probability of pairwise co‐occurrence of gamasid mite species was not associated with pairwise trait dissimilarity at any hierarchical scale.
We studied patterns of species co-occurrence in communities of ectoparasitic arthropods (ixodid ticks, mesostigmate mites and fleas) harboured by rodent hosts from South Africa (Rhabdomys pumilio), ...South America (Scapteromys aquaticus and Oxymycterus rufus) and west Siberia (Apodemus agrarius, Microtus gregalis, Microtus oeconomus and Myodes rutilus) using null models. We compared frequencies of co-occurrences of parasite species or higher taxa across host individuals with those expected by chance. When non-randomness of parasite co-occurrences was detected, positive but not negative co-occurrences of parasite species or higher taxa prevailed (except for a single sample of mesostigmate mites from O. rufus). Frequency of detection of non-randomness of parasite co-occurrences differed among parasite taxa, being higher in fleas and lower in mites and ticks. This frequency differed also among host species independent of parasite taxon, being highest in Microtus species and lowest in O. rufus and S. aquaticus. We concluded that the pattern of species co-occurrence in ectoparasite communities on rodent hosts is predominantly positive, depends on life history of parasites and may be affected to a great extent by life history of a host.
We provide a list of the species of the family Haemogamasidae Oudemans, 1926 living in Asiatic Russia, with data on their synonymy, distribution, and relationships with mammal hosts. In total, 23 ...species of mites distributed between two genera (Eulaelaps Berlese, 1903, and Haemogamasus Berlese, 1889) are covered.
