Stocking with livestock results in ectoparasite increases in resident Mediterranean wildlife

Background/Question/Methods

The spread of invasive pathogens or parasites into new host species constitutes one of the greatest drivers of global biodiversity declines. Invasive parasites are generally spread into new ecosystems through anthropogenic activities either directly or indirectly through the introduction of infected hosts. Introduced livestock can function as reservoir hosts, facilitating the transmission of novel parasites into host wildlife populations. Here, we explore the effects of exotic ticks (Haemaphysalis sp.) on island populations of native Aegean wall lizards (Podarcis erhardii, Lacertidae, Reptilia). Our study, based on the Cyclades Islands (Aegean Sea, Greece), included two surveys to evaluate the potential of livestock to introduce lizards both in diverse large island communities as well as in simplified small islet ecosystems. In addition we evaluate the possible impact of ticks on lizard biology through laboratory manipulations. 

Results/Conclusions

On 15 islets located in the central Cyclades Isl. and stocked with varying numbers of livestock we evaluated the relationship between goat density and lizard ectoparasite burdens (N = 15; R² = 0.96; p < 0.01). Both lizard tick numbers as well as prevalence of Haemaphysalis tick parasitism increased linearly with goat density. To evaluate these relationships in a more realistic, complex environment, we repeated these analyses on 12 study plots covered by xerophytic sclerophyllous scrub (‘phrygana’) on the nearby large (429Km²) island of Naxos (Cyclades). Again, we found that in these realistic, complex landscapes settings, lizard tick loads increased with stocking density (N = 12; R² = 0.48; p < 0.01). Lastly we evaluated whether tick burden affects lizard life history. Tick parasitism led to significant decreases in the size of young hatchlings (both snout-to-vent length and mass), metrics known to be correlated with later survival.  Our investigation indicates that introducing goats into previously ungrazed landscapes induces the spillover of ticks onto lizards. Understanding how livestock can mediate parasite transmission into native wildlife is critical for further management and conservation of Mediterranean fauna.