In a recent publication in the Journal of Tropical Ecology, we found that the herpetofauna communities of Virgin Islands National Park, on the island of St. John, USVI, were resistant to the large disturbances of hurricanes Irma and Maria, showing no significant change in habitat associations eight months post-hurricane. These findings were born from undergraduate research that grew, due to ample encouragement and funding from the National Geographic Society, into an in-depth examination of community recovery from some of the nastiest storms to hit the Caribbean region.
Anolis stratulus dewlapping. Photo by Sam DiGiulio
I started this work in 2016 as a third-year undergraduate at Northern Michigan University (NMU). My research partner, Sam DiGiulio, and I jumped at the chance to enroll in Dr. Jill Leonard’s class, Field Marine Biology, which took students on a spring-break field excursion to St. John, USVI. During our stay at the Virgin Islands Environmental Resource Station (VIERS), we experienced the biodiversity of Caribbean coral reefs, observed marine sampling techniques, and learned how terrestrial processes affect marine environments. As an additional component to the class, Sam and I designed an independent research project to carry out during our time on St. John. Due our shared passion for herpetofauna, we decided to implement a herpetological inventory of Virgin Islands National Park (VINP), following up on work done by the US Geological Survey (USGS) in 2001 (Rice et al. 2001). The initial goal of our survey was to provide the National Park Service (NPS) with a report that would act as a snapshot of the herp communities 15 years after the USGS survey, but it ended up being a lot more than that.
There is not much better field work than that in VINP. We hiked the trails and conducted visual encounter surveys; documenting the anoles, dwarf geckos (Sphaerodactylus macrolepis), and the occasional green iguana (Iguana iguana). Each transect we walked was classified by one of five landcover types (moist forest, dry forest, scrub, estuarine, and gut – small areas that hold freshwater for extended periods), per the USGS inventory. We also set out to the trails at night to conduct vocalization surveys for the island’s frog species. VINP is home to 19 species of reptile and amphibian, though this number fluctuates as populations of introduced species wink in and out. St. John is the smallest of the US Virgin Islands and does not host some of the rarer endemic species like St. Croix, such as Anolis acutus, or Ameiva polops, or hold the diversity found on Puerto Rico. However, that doesn’t make its residents any less charming, and with over 56% of the island of St. John included within VINP, there are ample places to observe them.
Anolis cristatellus. Photo by Sam DiGiulio
The most common anole on the island is the Puerto Rican crested anole (Anolis cristatellus). We observed all age classes, sizes, and crest shapes of these lizards and in every habitat type on the island. It was a treat to see two huge males duke it out on a tree trunk, head bobbing, dewlapping, and charging at one another, turning almost black, as opposed to their usual brown hues. The fight ended with one tossing the other off the trunk with its mouth.
We were also fortunate to find some of the rarer island residents, flipping just the right logs and rocks to reveal blind snakes (Antillotyphlops richardii) and a Virgin Islands worm lizard (Amphisbaena fenestrata). We conducted our surveys anywhere that we could hitch a ride with the class, or with staff from VIERS as they traveled to and from town for camp supplies. Even without our own vehicle, we were able to cover much of the park on foot in the course of the week and after returning to NMU for the end of the semester, we wrote up the report for the NPS, and presented the data at several scientific conferences.
Come September of 2017, category 5 Hurricanes Irma and Maria struck St. John within the course of two weeks. The forests and infrastructure of the islands sustained serious damage. Countless trees had fallen, and those that were still standing were completely defoliated. I anxiously stayed informed about the damage, but it wasn’t until November of 2017 that we talked about the potential of returning to resurvey the herps of VINP. Jill pointed us in the direction of the program. With encouragement from our advisor, we applied for a National Geographic Society’s Early Careers grant and in March of 2018 we received the funds necessary to return to St. John to re-conduct our herp survey.
Early that summer, Sam and I arrived back on St. John. This time, we were able to secure a vehicle and cover even more of the park, in addition to resurveying the areas that we had visited in 2016. We hit the ground running, first by revisiting our previous survey areas to ensure we repeated the same procedures as 2016. As we had arrived nine months after the storms hit, there were already plenty of signs of recovery. Canopy gaps created by the storms were being filled by early successional growth. Vines covered fallen trees and standing trees were quickly replacing lost leaves. The red mangroves were very slowly sprouting new shoots and leaves from the standing skeletons of prop roots. Clean-up operations and construction projects were coming along in the developed areas of the island. Unfortunately, VINP infrastructure had yet to be repaired, and VIERS had been destroyed. As of writing this post in 2021, the incredible education center is still not functional. However, as we traversed the trails and conducted our visual encounter surveys, the herps of the island appeared to be rather unperturbed.
Anolis pulchellus. Photo by Sam DiGiulio
While the vegetation structure appeared different from our initial surveys in 2016, community composition and the landcover types in which they were found remained unchanged. Puerto Rican crested anoles remained the most abundant species across the landcover types, taking full advantage of the coarse woody debris as display platforms to show off their dewlaps. The male anoles retained their cantankerous attitude towards conspecifics; this time around, we observed two dueling sharp-mouth anoles (Anolis pulchellus). These anoles are much lighter than the bulky crested anoles, favoring grasses and shrubbery to perch, allowing their background to more easily match their greenish hues. As diligently as we searched, we were unable to find more blind snakes and worm lizards, although this was no surprise due to the rarity of specimens recorded in previous surveys. Sufficient planning allowed the 2018 surveys to unfold even more smoothly than in 2016, and after canvasing the national park, we headed home to work through our results.
As a conclusion to our expedition, we determined that the reptile and amphibian communities of VINP had no observable changes in community composition, or landcover associations after hurricanes Irma and Maria. Interestingly, the communities appear resistant to large disturbances, indicating that they are either able to survive and adapt to the habitat changes, or underwent rapid population growth. Because the hurricanes struck the island over the course of just two weeks, they may have been perceived as a single disturbance event for the island fauna.
While the herpetofauna communities appeared to survive the hurricanes intact, they remain under pressure from many other threats, including invasive species like rats (Rattus rattus) and Indian mongoose (Herpestes auropunctatus), increasing human impact in VINP, and climate change. We recommend a regular monitoring program that would allow managers to observe abundance and population changes of both the herpetofauna species and invasive predators on the island, and give further insight to how these animals deal with disturbances, especially in a time of global biodiversity loss.
The findings from this study were recently published in the Journal of Tropical Ecology (Richter et al. 2021). What started as a class project was able to grow into grant writing, presentation, and publication opportunities that have helped me gain critical skills I’ll be using while pursuing my master’s degree at the University of Georgia’s Warnell School of Forestry and beyond. This work would not have been possible without the encouragement and guidance of our advisors and coauthors, and serves as an example of the advances that can be made by investing in undergraduate research.
Rice KG, Waddle JH, Crockett ME, Carthy RR and Percival HF (2005) Herpetofaunal Inventories of the National Parks of South Florida and the Caribbean. U.S. Geological Survey Professional Paper 1631. Open-File Report 2005-1301: 2, 1-45.
Richter, C. J., S. M. DiGiulio, C. D. Marshall, and J. B. K. Leonard. 2021. Herpetofaunal community response to hurricanes Irma and Maria in Virgin Islands National Park. Journal of Tropical Ecology 37(4): 185-192.