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.