Climatic disturbances are major forces regulating the population dynamics of terrestrial fauna, particularly amphibians. In Puerto Rico (PR), a severe drought occurred between 2015 and 2016, which would have profound consequences for many of our amphibians. In this study, we examined the responses of three species of Puerto Rican Eleutherodactylus frogs to this drought in a tropical mountain forest in the Sierra de Cayey, PR. We monitored the abundance of the highland E. wightmanae (leaflitter-dweller), and the generalist species, E. coqui (arboreal) and E. brittoni (grass-dweller) monthly using visual and acoustic surveys in four 4x30m2 transects (480m2) for a 4-year period (2014 to present). Our main objective is to determine if these species also differ in their population dynamics in response to this drought. We conducted a literature review and contrasted the number of days with less than the minimum rainfall required to avoid the hydric stress for these species. We collected data on rainfall from our study site from June 2014 to present and contrasted the deficit in rainfall compared to the historic deficit (50-years of data for the region). We used the mean abundance of adults and large-sized juveniles combined and production of egg clutches (only for E. wightmanae) to examine their relationship with rainfall at our study site.
Results/Conclusions
The abundance of all species, and production of egg clutches of E. wightmanae, increased during months with more rainfall and higher temperature, and decreased during months with lower temperature and less rainfall. Compared to historic deficits, 13 months exceeded the total number of days resulting in hydric stress at our study site: between 2014-2015 (425 days covering the period of drought), 91.5% of the time consisted of days with rainfall below the threshold to avoid hydric stress. However, responses differed among species: the abundance of E. coqui increased after the drought (r=0.5672, p<0.0001, n=44); the abundance of non-arboreal species showed no changes attributed to the drought (E. brittoni: r=0.1034, p=0.5042, n=44; E. wightmanae: r=0.0447, p<0.7733, n=44). Another study showed that the arboreal highland-specialist E. portoricensis decreased instead, which suggests that responses to climatic disturbances may result from behavioral modification, physiological adaptations, and the use of the vertical environment in this forest. Unfortunately, category 4 Hurricane María stroke PR in September 2017, devastated our study-site, and generated microclimate conditions typical of lowland areas, which may influence the persistence of species from highlands in this assemblage of Eleutherodactylus frogs.