Relationship between body condition of American alligators and water depth in the Everglades, Florida

Abstract

Feeding opportunities of American alligators (Alligator mississippiensis) in freshwater wetlands in south Florida are closely linked to hydrologic conditions. In the Everglades, seasonally and annually fluctuating surface water levels affect populations of aquatic organisms that alligators consume. Since prey becomes more concentrated when water depth decreases, we hypothesized an inverse relationship between body condition and water depth in the Everglades. On average, condition of adult alligators in the dry season was significantly higher than in the wet season, but this was not the case for juveniles/ subadults. The correlation between body condition and measured water depth at capture locations was weak; however, there was a significant negative correlation between the condition and predicted water depth prior to capture for all animals except for spring juveniles/subadults which had a weak positive condition-water depth relationship. Overall, a relatively strong inverse correlation occurred at 10-49 days prior to the capture day, suggesting that current body condition of alligators may depend on feeding opportunities during that period. Fitted regression of body condition on water depth (mean depth of 10 days when condition-water depth correlation was greatest) resulted in a significantly negative slope, except for spring adult females and spring juveniles/subadults for which slopes were not significantly different from zero. Our results imply that water management practices may be critical for alligators in the Everglades since water depth can affect animal condition in a relatively short period of time.

Slow Isotope Turnover Rates and Low Discrimination Values in the American Alligator: Implications for Interpretation of Ectotherm Stable Isotope Data

“…(M/SVL ) # 10 length (Fujisaki et al 2009). At the beginning of the experiment, the alligators ranged in age from 3.3 to 8.4 yr (mean, 5.7 ‫ע‬ SD) and in total length from 78.6 to 114.8 cm (mean, 1.2 SD).…”

Responses of American Alligators (Alligator mississippiensis) to Environmental Conditions: Implications for Population and Ecosystem Monitoring

“…From a research perspective, considering our findings can allow researchers to better assess treatment effects in wetland habitats (e.g., Mazzotti et al 2009;Fujisaki et al 2009;Ugarte et al 2013) by using more accurate alligator monitoring techniques. This will produce not only more reliable results than would be available from broad-scale techniques, but will also provide a more in-depth understanding of wetland ecology and management.…”

“…Site-and age-specific responses to environmental conditions also have been detected in other species such as snakes (Henderson and Hoevers 1977;Sun et al 2001) and mammals (Härkö nen et al 1999). Foraging activity might differ between age classes of alligators because their life history, and more specifically diet, are known to differ by age (Brandt 1991;Saalfeld et al 2008;Fujisaki et al 2009). As noted by Sun et al (2001), the determinants of activity patterns of reptiles are highly complex and generalizations might not be possible within a given ecosystem.…”

Fluctuating water depths affect American alligator (Alligator mississippiensis) body condition in the Everglades, Florida, USA

“…They are a non-destructive measure and data are relatively easy to collect. Previous studies have looked at alligator body condition in the Everglades in relation to season (Barr, 1997, Dalrymple, 1996 and water depths (Fujisaki et al, 2009). These studies evaluated one hydrologic factor (water depth) that could affect alligator body condition.…”