THE IMPACT OF TICKS ON BUFO-MARINUS FROM NATIVE HABITATS

We analysed the patterns of tick distribution on 2274 adult toads from Venezuela and Brazil, to explore whether these ectoparasites have any impact on the survival of Bufo marinus. A maximum-likelihood analysis showed that aggregation levels of ticks decreased significantly with the mean intensity of infection. This decline could be attributed to a density-dependent reduction of ticks within toads, density-dependent tick-induced toad mortality and/or density-dependent tick-induced chan ges in toad susceptibility. However, the relationship between the rate of change in tick loads and tick burdens from recaptured toads indica ted that neither the loss of ticks within toads nor the toad susceptib ility to further infection were dependent upon tick burdens. Therefore , we can indirectly infer that density-dependent tick-induced toad mor tality is responsible for the observed decline in aggregation levels w ith tick age and burdens. On the other hand, a significant negative re lationship between tick burdens and the size-specific weight of toads suggested that ticks may also have a significant impact on the pattern s of weight deposition of adult toads. This evidence suggests that the se ectoparasites may play an important role in regulating the densitie s of B. marinus in native habitats.