Ecological effects of a disturbance event on the black racer (Coluber constrictor) habitat use, thermoregulation, and energetic expenditures

Background/Question/Methods

All species may respond differently to disturbance events based on how that disturbance changes the availability of life requisites within the landscape. With regard to reptiles, these life requisites include not only changes in vegetation, prey resources, and shelter, but also changes in the thermal landscape which may dictate potential body temperatures (T_b). It was the objective of this project to determine how the available habitat within burned and unburned landscapes affected the habitat use, behavior, and energy expenditures of a reptile species, the black racer (Coluber constrictor) and the ability for that reptile to maintain a preferred T_b. We determined the preferred T_b of C. constrictor while at rest (T_set) and the optimal T_b while in motion (thermal breadth; B₈₀). These temperature ranges were compared to T_bs maintained by C. constrictor in the field and operative temperatures (T_e) available within each treatment. Good thermal quality habitat was defined as areas which T_e deviated less from T_set and B₈₀ ranges. We compared the behaviors and the ability for C. constrictor to thermoregulate between treatments. Further, we used doubly-labeled water to measure energy expenditures for C. constrictor in each treatment.

Results/Conclusions

Prescribed fire created more preferred habitat characteristics (more open canopy, new vegetative growth, and less leaf litter). Open canopy may be associated with better thermoregulatory opportunities and new vegetative growth may be associated with higher prey abundances. We found that burned landscapes were higher thermal quality earlier in the active season, but unburned treatments became higher thermal quality later in the field season. Regardless of T_es, C. constrictor maintained T_bs that strongly overlapped with B₈₀ ranges. This meant that individuals would have to allocate more time and energy toward thermoregulation earlier in the field season within unburned treatments when T_es were cooler, but more time and energy toward thermoregulation in the burned landscape later in the field season when T_es became warmer. Later in the field season, individuals were in fact more active and expended more energy in the burn treatment. Ultimately, prescribed fire altered the landscape which led to changes in how species interacted with the environment. These ecological effects may lead to biases in perceived abundances by researchers and detection rates by potential predators. Future research investigating the effects of disturbance on reptile species should incorporate ecological effects into their study designs.