Fire reduces parasite load in a Mediterranean lizard

Abstract

Wildfires are a natural disturbance in many ecosystems. However, their effect on biotic interactions has been poorly studied. Fire consumes the vegetation and the litter layer where many parasites spend part of their life cycles. We hypothesize that wildfires reduce habitat availability for parasites with consequent potential benefits for hosts. We tested this for the lizard Psammodromus algirus and its ectoparasites in a Mediterranean ecosystem. We predicted that lizards in recently burned areas would have lower parasite load (cleaning effect) than those in unburned areas and that this phenomenon implies that lizards spending their entire lives in postfire conditions experience a lower level of parasitism than those living in unburned areas. We compared the ectoparasite load of lizards between eight paired burned/unburned sites, including recent (less than 1 year postfire) and older fires (2-4 years). We found that lizards' ectoparasites prevalence was drastically reduced in recently burned areas. Likewise, lizards in older burned areas showed less evidence of past parasitic infections. Fire disrupted the host-parasite interaction, providing the opportunity for lizards to avoid the negative effects of ectoparasites. Our results suggest that wildfires probably fulfil a role in controlling vector-borne diseases and pathogens, and highlight ecological effects of wildfires that have been overlooked.

Keywords: Ophionyssus; Psammodromus algirus; ectoparasites; global change; mite; wildfire.

Figure 1.

(a) Lizards' mite load in relation to lizards’ size (SVL) for recently burned areas (less than 1 year from fire; red, lower line) and the corresponding paired unburned (blue, upper line). Lines are predicted values (and confidence intervals) of conditioned on the zero-inflation component (probability of mite infection) of the hurdle mixed model. For the statistical significance, table 1a. Raw binomial data (n = 117) are represented as short vertical lines on the horizontal axes at y = 0 and 1. The data split by populations is represented in electronic supplementary material, figure S6. (b) Number of raised scales in relation to lizards' size (SVL) for burned areas (older wildfires, 2–4 years; in red, lower line) and the corresponding paired unburned (in blue, upper line). Lines are predicted values (with confidence intervals) of the zero-inflation component of the hurdle mixed model. Symbols are the raw data (n = 241). For the statistical significance, table 1b. The data split by populations is represented in electronic supplementary material, figure S7. (Online version in colour.)