Brian M. Jeffery

Factors affecting individual foraging specialization and temporal diet stability across the range of a large “generalist” apex predator

Individual niche specialization (INS) is increasingly recognized as an important component of ecological and evolutionary dynamics. However, most studies that have investigated INS have focused on the effects of niche width and inter- and intraspecific competition on INS in small-bodied species for short time periods, with less attention paid to INS in large-bodied reptilian predators and the effects of available prey types on INS. We investigated the prevalence, causes, and consequences of INS in foraging behaviors across different populations of American alligators (Alligator mississippiensis), the dominant aquatic apex predator across the southeast US, using stomach contents and stable isotopes. Gut contents revealed that, over the short term, although alligator populations occupied wide ranges of the INS spectrum, general patterns were apparent. Alligator populations inhabiting lakes exhibited lower INS than coastal populations, likely driven by variation in habitat type and available prey types. Stable isotopes revealed that over longer time spans alligators exhibited remarkably consistent use of variable mixtures of carbon pools (e.g., marine and freshwater food webs). We conclude that INS in large-bodied reptilian predator populations is likely affected by variation in available prey types and habitat heterogeneity, and that INS should be incorporated into management strategies to efficiently meet intended goals. Also, ecological models, which typically do not consider behavioral variability, should include INS to increase model realism and applicability.

Estimating trends in alligator populations from nightlight survey data

Nightlight surveys are commonly used to evaluate status and trends of crocodilian populations, but imperfect detection caused by survey- and location-specific factors makes it difficult to draw population inferences accurately from uncorrected data. We used a two-stage hierarchical model comprising population abundance and detection probability to examine recent abundance trends of American alligators (Alligator mississippiensis) in subareas of Everglades wetlands in Florida using nightlight survey data. During 2001–2008, there were declining trends in abundance of small and/or medium sized animals in a majority of subareas, whereas abundance of large sized animals had either demonstrated an increased or unclear trend. For small and large sized class animals, estimated detection probability declined as water depth increased. Detection probability of small animals was much lower than for larger size classes. The declining trend of smaller alligators may reflect a natural population response to the fluctuating environment of Everglades wetlands under modified hydrology. It may have negative implications for the future of alligator populations in this region, particularly if habitat conditions do not favor recruitment of offspring in the near term. Our study provides a foundation to improve inferences made from nightlight surveys of other crocodilian populations.

Home range and movements of American alligators (Alligator mississippiensis) in an estuary habitat

BackgroundUnderstanding movement patterns of free-ranging top predators throughout heterogeneous habitat is important for gaining insight into trophic interactions. We tracked the movements of five adult American alligators to delineate their estuarine habitat use and determine drivers of their activity patterns in a seasonally-fluctuating environment. We also compared VHF- and satellite-tracks of one of the alligators to examine tradeoffs in data quality and quantity.ResultsAll tracked alligators showed high site fidelity in the estuary, but estimated home range size and core-use areas were highly variable. Two alligators were relatively sedentary and remained in the upper stream zone. One alligator traveled to a transition zone between freshwater marsh and estuary habitat, but primarily remained in the upstream area. Two alligators traveled to the downstream zone into saline conditions and showed high salinity tolerance. Overall movement rates were highly influenced by salinity, temperature, and season. Both satellite and VHF radio telemetries resulted in similar home range, core-use area, and activity centers.ConclusionsThis study reveals consistent use of estuary habitat by American alligators. The alligators showed variations in their movement pattern and seasonal habitat, with movement attributable to environmental factors. Although satellite-derived locations were more dispersed compared to locations collected using VHF radio-tags, data collected from VHF tracking omitted some habitat used for a short period of time, indicating the effectiveness of satellite telemetry to continuously track animals for ecosystem-scale studies.

Body Condition of Morelet's Crocodiles (Crocodylus moreletii) from Northern Belizea

Abstract Body condition factors have been used as an indicator of health and well-being of crocodilians. We evaluated body condition of Morelets Crocodiles (Crocodylus moreletii) in northern Belize in relation to biotic (size, sex, and habitat) and abiotic (location, water level, and air temperature) factors. We also tested the hypothesis that high water levels and warm temperatures combine or interact to result in a decrease in body condition. Size class, temperature, and water level explained 20% of the variability in condition of Morelets Crocodiles in this study. We found that adult crocodiles had higher condition scores than juveniles/subadults but that sex, habitat, and site had no effect. We confirmed our hypothesis that warm temperatures and high water levels interact to decrease body condition. We related body condition of Morelets Crocodiles to natural fluctuations in air temperatures and water levels in northern Belize, providing baseline conditions for population and ecosystem monitoring.

Implications of the 2013 Python Challenge® for Ecology and Management of Python molorus bivittatus (Burmese Python) in Florida

Abstract The 2013 Python Challenge® provided an opportunity to learn more about the ecology and management of Python molorus bivittatus (Burmese Python). Goals of the 2013 Python Challenge were to raise awareness about Burmese Pythons, remove pythons, increase public participation and agency cooperation in removal and reporting of pythons, increase knowledge of python ecology, and examine effectiveness of incentives to increase public participation in invasive wildlife management. Over 1500 participants registered for the competition. Sixty-eight Burmese Pythons were removed during the Challenge. Thirteen females (19%), 54 males (79%), and 1 young-of-the-year (1%) python of undetermined sex were captured. More pythons—73 (68 from the Challenge and 5 incidental)—were removed during the 2013 Python Challenge period than during similar time periods during 2008–2012. We found no evidence of unintended consequences such as removal of native species. We identified 13 prey species: 6 mammals (46%), 6 birds (46%), and 1 alligator (8%). The potential of recreational-harvest incentive programs to impact python populations is uncertain. Incentive programs are potential tools in invasive-species management programs, but they should be managed diligently and evaluated for effectiveness.