Anolis gundlachi, Photo taken by Johann Crespo Zapata
Disturbance events can be important drivers of population dynamics for many different species. Puerto Rico, an island in the Caribbean, experienced two major disturbances over the course of a few years – a drought in 2015 and a hurricane in 2017 – that caused stress to the herpetofauna living in the region. The yellow-chinned anole, Anolis gundlachi, is particularly susceptible to disturbance events because it is a thermoconformer and vulnerable to dehydration. Johann Crespo-Zapata and his team wanted to track the population of yellow-chinned anoles in the tropical mountain forest of Sierra de Cayey during and after these disturbance events to determine how the population would change.
Johann and his collaborators counted A. gundlachi along four 30-meter transects to determine population size. The crew split its groups into adults (> 45 snout to vent length, SVL), large juveniles (20-45 SVL) and juveniles (<20 SVL). The team also collected precipitation levels using a local weather station to determine if each month had less rain than average, which is called a rain deficit. Following the population subsets over the last four years allowed Johann to understand how the population responded to hydric stress. He recorded a decrease in juvenile abundance as rain deficit increased (r = -0.352, p < 0.0482, n = 32), which suggests a decrease in recruitment. There was no overall trend for large juveniles in response to the drought. Adults displayed a similar pattern to that of juveniles, as they experienced a decrease in abundance with increased deficit. After a time lag, adults experienced an increase in abundance when the drought lifted (r = 0.4469, p <0.0024, n = 44) that could be attributed to increased mortality during the drought events.
Sierra de Cayey forest after Hurricane Maria, photo taken by Johann Crespo Zapata
Following this study period, hurricane Maria struck Puerto Rico, causing structural changes to the forest canopy and decreases in humidity. Immediately following the hurricane, Johann saw the anole abundance decrease to its lowest point. Johann plans to continue to follow this population for the foreseeable future to observe population dynamics in A. gundlachi populations following major hurricane disturbances. Understanding the population dynamics of these anoles is critical to comprehending how this species and others like it will cope with increased disturbance events that will become more frequent according to current climate change projections.