No evidence for a dilution effect of high vertebrate diversity on tick-borne disease hazard in Dutch forests

Abstract

Abstract Background Maintaining high vertebrate diversity is promoted as a potential strategy to control Lyme disease hazard via a so-called dilution effect, which occurs when increasing diversity of an ecological community reduces the transmission of a pathogen. However, empirical evidence from Europe is limited at best, while it remains unclear whether dilution effects operate for other tick-borne diseases. Here, we evaluated how often the dilution effect occurs for a wide range of tick-borne pathogens and symbionts in forest areas in the Netherlands. Methods Data on wildlife, tick densities, and tick-borne microorganisms were collected in 19 forest sites. We calculated six different biodiversity indices based on camera trapping and live trapping data to characterize the vertebrate community of each forest site. These indices were correlated with the nymphal infection prevalence (NIP) and density of infected nymphs (DIN) of three Borrelia burgdorferi sensu lato genospecies as well as seven other tick-borne pathogens and symbionts. Results Vertebrate host species diversity, tick densities and infection prevalence varied widely among sites. However, neither the NIP nor the DIN of any of the ten tick-borne pathogens or symbionts was significantly correlated with any of the six indices of vertebrate species diversity or with total host availability. These results were consistent regardless of whether we used the relative abundance of vertebrate species or the proportion of larvae fed by each host species to calculate the diversity indices. Conclusions Our results do not support evidence for a dilution effect in Dutch forests, suggesting that facilitating high species diversity of native wildlife is unlikely to reduce tick-borne disease hazard at the scale of local forest patches. Whether (other) nature conservation strategies in other types of habitats and at other spatial scales can reduce tick-borne disease hazard warrants further investigation.