M. Lampo et P. Bayliss, DENSITY ESTIMATES OF CANE TOADS FROM NATIVE POPULATIONS BASED ON MARK-RECAPTURE DATA, Wildlife research, 23(3), 1996, pp. 305-315
The cane toad (Bufo marinus) has received considerable attention becau
se of its rapid spread in Australia and the potential threat it may re
present to native species. Although the introduction of pathogens from
native populations is now being considered to control this species, p
opulation estimates based on comparable methods that demonstrate that
native populations are in fact less dense than the introduced ones are
not available. Accurate population estimates are necessary to evaluat
e potential techniques for the control of the cane toad. We estimated
population densities of cane toads over a wide range of habitat types
and climate conditions by means of mark-recapture data. The capture hi
story and location of toads each night were analysed to explore the va
lidity of some of the assumptions of mark-recapture models. Because mi
grations, deaths and recruitment over three nights appear to be unimpo
rtant, populations may be legitimately regarded as closed for that per
iod. However, cane toads seem highly sensitive to disturbance effects
due to trapping and/or handling. Consequently, density estimates based
on removal methods seem the most reliable because they are not sensit
ive to handling and trapping effects. Similarly, analyses of residuals
of regressions between I-night counts and density estimates suggested
that toad nightly activity is affected by the air temperature during
sampling. However, only 60% of the variation in estimated densities ca
n be predicted by I-night counts and air temperature. Estimates of pop
ulation density over a wide range of habitats in South America were on
e order of magnitude lower than estimates in Australia. We speculate o
n the possible factors that may account for the lower densities in pop
ulations in the native range of the species.