Abstract:
The Craugastor rugulosus species series has been one of the most affected clades by the decline of amphibian
populations in Mesoamerica. These stream-dwelling frogs are threatened at all altitudinal ranges throughout their
distribution. Craugastor ranoides is categorized as Critically Endangered on the IUCN Red List due to the disappearance
of populations in the highlands and lowlands of Costa Rica. Currently the species is only found on the Santa Elena
Peninsula. Additional ecological and natural history studies are necessary to formulate conservation plans for this
species, which should include captive breeding programs and continuous monitoring of wild populations. We conducted
a study of density, habitat use, and morphometrics of C. ranoides in three streams on the Santa Elena Peninsula
Guanacaste, Costa Rica, during two consecutive dry seasons. The density of adult frogs and the probabilities of detection
were similar during both dry seasons but we found differences in both parameters between streams. Counts of juveniles
and subadults differed between seasons and between streams. Stream sector (50-m length) occupancy was approximately
80% during both dry seasons. We found most frogs motionless on boulders, but juveniles also frequented leaf litter.
Sexual dimorphism was found in snout-vent length, mass, and tympanum diameter in subadults and adults. This study
establishes a baseline for further monitoring of wild populations. Additional research and monitoring are necessary to
detect possible changes in abundance and potential decline of these populations, which might be the only ones remaining
in Costa Rica.
