Effects of New Land Management Regimes on Florida Scrub lizard Communities, Michael Brennan (Georgia Southern University)
Each year, GTC awards 1-2 grants of up to $3,000 each to undergraduate and/or graduate students researching gopher tortoise biology and ecology, or other relevant aspects of upland habitat conservation and management within the range of the gopher tortoise. Michael Brennan was a Landers Grant recipient in 2022. Keep reading to learn more about his research on Florida scrub lizards in peninsular Florida.
My thesis research focuses on the effects of land management in the Ocala National Forest (ONF) on native lizard communities. Historically, ONF has been managed predominantly for pulpwood production. When managed for pulpwood, areas are clearcut and seeded with sand pine and allowed to mature for 30-40 years before being clearcut once again. Also, ONF manages several large sandhill habitats for longleaf pine, wiregrass, and associated flora and fauna. The longleaf pine islands receive prescribed burns biennially, keeping them at early successional stages. Collectively, this management approach has kept ONF with a variety of different successional stage habitats with varying connectivity year to year. While the variety of successional stages is desirable for many species, populations with low dispersal potential may be vulnerable to shifting habitat quality as some stages age.
In 2015, the ONF adopted a new management plan to better mimic the frequent disturbance regimes desired by the endangered Florida scrub jay. The plan calls for large, connected areas of land to be clearcut, then allowed to grow without any seeding and receive prescribed burns on a 5–12-year cycle. This will create large islands of early to intermediate successional Florida scrub habitat that have the potential to benefit many early succession-reliant species, such as scrub jays, gopher tortoises, and my model species, Florida scrub lizards (Sceloporus woodi, henceforth scrub lizard).
Since scrub lizards are associated with early successional scrub habitat, I expect to find increased densities of the species in early succession Florida scrub habitat. Populations in pulpwood managed areas will decrease in density as the stand ages, while populations in scrub jay managed areas will persist with similar densities. I also investigate if different habitat types and ages affect lizard endoparasite communities. The goal of this study is to establish a baseline status as management continues to be carried out and expanded within ONF.
Scrub lizards are a near-threatened endemic species to Florida yet remain abundant in the ONF such that they are reliably encountered on surveys. I collected data over the summer of 2022 by conducting encounter surveys in both scrub jay and pulpwood managed areas to quantify lizard densities. I chose early successional (<5 years since disturbance) and intermediate succession (5-12 years since disturbance) sites in both pulpwood and longleaf management areas. Each site was surveyed 2-3 times with equal distances walked on the edge and 5-10m into the interior of each site. Any vertebrate encountered was recorded to species level, but the search pattern was focused on lizard detection. By assuming I could spot any vertebrate within a 3m radius of my path, I calculated the total area surveyed to obtain densities of each species as well as site richness.
Preliminary results show that there are higher densities of lizards in land that is managed for scrub jays. Most early successional scrub habitats, from both pulpwood and scrub jay management, had a similar abundance of lizards. However, intermediate ages of pulpwood managed areas often lacked scrub lizards. Intermediate-aged scrub jay management had lower densities when compared to younger Florida scrub but maintained populations.
In parallel with this project, I also surveyed scrub lizards and racerunners for gut parasites (helminths). I chose separate sites of Florida scrub (early successional and 25-40 years post-disturbance), and longleaf pine to collect lizards. These lizards were euthanized and had their gastrointestinal and respiratory tracts dissected for parasite communities. I will compare how management plans and habitat type affect endoparasite communities within lizards of ONF. I can then calculate prevalence, intensity, and the exact composition of communities using molecular identification to compare between habitats and successional stages.
Overall, parasite prevalence and intensity are low in scrub lizards across the forest. Most infections are attributed to stomach nematodes. Scrub lizards caught from mature habitat had the highest infection prevalence (~1/3) followed by lizards from longleaf pine (~1/5). Lizards in young scrub had a low infection prevalence (~1/10) with most cases being larval migrans where large nematodes were present in the body cavity. Intensity of infection is stable across habitat and age with an average of about 2 worms in infected lizards.
These results indicate that Scrub Jay management benefits scrub lizards and likely other early successional scrub species. This is likely due to both the increase in disturbance frequency keeping habitat at younger stages and increased connectivity between habitats. Both combined for one robust population to exist in an area rather than many small disjunct populations across the mosaic of suitable habitat. The patterns seen with endoparasite communities are likely driven by habitat use and diet. Both longleaf pine sandhills and mature scrub have mature trees and other vertical microhabitats used by scrub lizards. It is likely the insect intermediate host of the nematodes uses these vertical microhabitats as well, resulting in increased prevalence in these habitats. The larval migrans seen in early scrub is likely an insect-driven parasite targeting birds or mammals, but the lizards became incidental hosts. Molecular identification will help tell this full story and perhaps unlock further interactions within the greater Florida scrub community.
I would like to thank the Gopher Tortoise Council and my advisers Lance McBrayer and Stephen Greiman for supporting my research. As of writing this, I am completing a fellowship through Georgia Sea Grant and am starting a part-time position studying eastern diamondback rattlesnakes on Jekyll Island while I finish analyzing my thesis data. I expect to finish by the summer of 2024.