Investigators:	Kenneth G. Rice H. Franklin Percival Timothy S. Gross
		Additional Project Information at:

Project Topic: Ecological Processes & Indicator Species

Start Date: 1997
End Date: 2000 (Projected)

This work is associated with the U.S. Geological Survey, Biological Resources Division "Across Trophic Level System Simulation" (ATLSS) program and has the objective of supplying empirical information needed to develop a population model for the American alligator (Alligator mississippiensis). The American alligator is not only a top consumer and a keystone species in the Everglades, but also physically influences the system through construction and maintenance of alligator holes and trails. It is presumed that the existence of this species is important to the faunal and floral character of the Everglades as it has evolved. Despite its prominence biologically and publicly in the system, many important questions about basic behavioral and population parameters of alligators remain unanswered. Although many assumptions can be made, we are not certain of movements or survival of varying size classes of alligators under either stable or fluctuating water levels. The reproductive contribution of an individual animal or of different size/age classes in any given year has been a principal stumbling block for attempts at modeling any crocodilian population. For effective modeling of alligators, more definitive answers to those latter two questions are essential.

The main objectives of this study are the following:

1. To determine daily and seasonal movements and survival of varying age/size and habitat (canal, interior marsh) classes of Everglades alligators;
2. To determine the proportion of female alligators in the population that might be expected to nest in a given year;
3. To elaborate on existing hypotheses of thermoregulation in Everglades alligators; and,
4. To relate the above objectives to the dynamic hydroperiod of the Everglades and to two geographic compartments of the Everglades (Water Conservation Area-3A (WCA-3A) North and Everglades National Park).

To achieve these objectives, 29 alligators are currently being tracked in WCA-3A North and 25 alligators in Everglades National Park. Of these, 29 have been implanted with temperature data loggers. Weekly fixes have been made since the project was initiated in November 1996. Therefore, 2 years of data on home range size, movement patterns, habitat preference, and thermoregulation have been collected. Intensive week-long samples to further investigate habitat preference and daily movement patterns have been conducted as well, once in each season of the year, and the data are currently being analyzed.

Several patterns have become clear through the preliminary analysis of the data. First, in the summer, Evergladesí alligators maintain very high body temperatures due to the constant, high ambient temperature of their environment. In conditions where food is plentiful and temperatures are consistently high, such as in an alligator farm, growth is extremely rapid. However, the Everglades is currently thought to be a food limited environment for alligators. High body temperature results in high rates of metabolism, which leads to increased food demands to fuel increased maintenance cost. The poor body condition of Evergladesí alligators will likely be better understood in light of their thermal regime.

In winter, Evergladesí alligator body temperatures follow the declines of ambient temperatures. This is to be expected from the habits of northern alligators that over-winter in dens. When body temperatures remain below 22°C, alligators stop eating. By greatly reducing body temperature during over-wintering, alligators reduce metabolic cost. Preliminary analysis of body temperature during winter suggests that alligators seek the colder regions available to them. However, body temperatures rarely drop below 15°C. During winter, Evergladesí alligators frequently warm up for short periods of time. This suggests that winters in the Everglades may represent a limbo period where temperatures are not cold enough to force over-wintering in dens, but not warm enough to allow optimality in such functions as feeding. A thorough examination of winter data will likely reveal unique habits of Evergladesí alligators and lead to a better understanding of alligator biology in general.

Data from early spring reveals an interesting pattern as well. While temperatures are often as low as in winter, high body temperatures are attained much more frequently. There are two factors that are likely to be responsible for this trend. First, animals are preparing to breed. Higher temperatures are likely to aid in development of reproductive hormones and tissues. The second factor is that this is the height of the dry season, when food is concentrated in holes. In order for alligators to take advantage of this resource, they must maintain high body temperature in order to digest prey items and assimilate them into body tissues.

Once the data set has been decomposed and trends analyzed, more sophisticated data analysis techniques will be employed in order to thoroughly investigate the data. Water levels and environmental temperatures will be analyzed to determine their effect on the thermal regime of the alligator. Never before has such a complete picture of a free ranging animalís thermal biology been quantified.

A significant part of the funding for this research was provided from the U.S. Department of the Interior South Florida Ecosystem Restoration Program "Critical Ecosystems Studies Initiative" (administered through the National Park Service) and from the U.S. Geological Survey, Florida Caribbean Science Center. Additional funding for the "Atlas Tropic Level System Simulation" was also provided by the U.S. Environmental Protection Agency and the U.S. Army Corps of Engineers.

(This abstract was taken from the Proceedings of the South Florida Restoration Science Forum Open File Report)