| Summary: | Resumen del trabajo presentado al 3rd International Congress on Parasites of Wildlife, celebrado en Kruger National Park (South Africa) del 24 al 27 de septiembre de 2017. By experimentally adding or removing parasites, it has been shown that macro-parasites may regulate populations of their hosts. At an individual level, ecto-parasites can affect body condition, growth, life span, energy expenditure, litter size, foraging, and juvenile survival of hosts, which could translate into effects on host population abundances. We investigated the effect of a flea community (Cenophthalmus apertus, Nosopsyllus fasciatus, Leptopsylla taschenbergi) on free-living common vole (Microtus arvalis) populations from agricultural landscapes of NW Spain, where voles regularly fluctuate in numbers. We evaluated the numerical response of fleas to vole abundance (direct vs. delayed density-dependence, DD), also considering the abundance of alternative rodent hosts. We tested for negative associations between vole population growth rates (PGR) in spring, summer and winter and species-specific flea abundances. Finally, we investigated whether the body condition of voles (mass relative to size) and the reproductive effort of females (number of embryos) co-varied with flea abundance. We found that: flea abundance had a delayed DD pattern, increasing with previous (8 month before) vole abundance; at population level, a greater flea abundance was associated with a reduced vole PGR in summer and winter; and male body condition in spring and winter and the number of embryos per pregnant female were negatively associated with individual-level flea abundance. These effects varied depending on the flea species, but support the hypothesis that fleas have a regulating influence on common vole populations and have a destabilizing effect in the studied system. Experiments are required to confirm these findings. Peer Reviewed
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