projects > across trophic level system simulation (atlss) > alligators > 2001 Proposal
American alligator distribution, thermoregulation, and biotic potential relative to hydroperiod in the Everglades
Project Proposal for 2001
Continuation Research Plan [Year 5 of 7 Years]
Principal Investigator: Dr. H. Franklin Percival, Leader
Co- Principal Investigator: Dr. Kenneth G. Rice
Over the last one hundred years the hydrology of the Everglades has been greatly altered by mankind. Efforts to repair the functioning of the ecosystem are using a multicomponent model, the Across Trophic Level System Simulation (ATLSS), to predict the response of native flora and fauna to alterative water delivery scenarios. This study was designed to provide information on the natural history and population functioning of the American alligator in the Everglades for construction of an ATLSS American alligator population model and to investigate restoration needs and status of the alligator in the Everglades ecosystem.
We initiated a five year study on the home range, daily movement, habitat use, thermoregulation, and body temperature patterns of alligators in both Shark Slough, Everglades National Park, and in Water Conservation area 3A North. A total of 66 alligators were captured and surgically implanted with radio-transmitters. A subset of 29 of these also were implanted with temperature recording data loggers. Data loggers recorded core body temperature simultaneously at 72 minute intervals for 1 year.
Weekly aerial telemetry locations were collected beginning 1 January 1997 to estimate home range size. Weeklong intensive sampling efforts conducted from 7 November 1997 to 31 July 1998 were used to estimate daily movement and habitat use.
INFORMATION NEEDS AND USES
Based on a preliminary analysis of data (findings subject to change with increased sample size and hydrological conditions), the following key results have been obtained:
Purpose and Goals
The American alligator (Alligator mississippiensis) is not only a top consumer and a keystone species in the Everglades, but also physically influences the system through construction and maintenance of gator holes and trails(Mazzotti and Brandt 1994). 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 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. Further, Everglades restoration requires an understanding of the ecological impact of various restoration alternatives. This study not only provides keys to this understanding through contribution to ecological modeling but is designed to answer questions related to the effects of decompartmentalization on alligator populations, fertilization failure of eggs, and hydrological effects on thermoregulatory function.
Urgency or Timelines
This study provides information critical the construction of the ATLSS American alligator population model which will be used as a tool for evaluation of restoration alternatives during adaptive implementation of the Comprehensive Ecosystem Restoration Plan. We also provide other timely investigations involving the effects of canals and fertilization failure on alligator populations. The alligator is both a keystone and indicator species in the Everglades ecosystem. Therefore, it is critical to understand the effects of restoration alternatives on this species and to include the alligator in restoration alternative selection, evaluation, and monitoring.
Synopsis of Research Methods
The Everglades is believed to be a harsh environment for alligators. Everglades alligators weigh less than alligators the same length from other parts of their range (Jacobson and Kushlan 1989, Barr 1997). Further, maximum length is decreased, and sexual maturity is delayed (Kushlan and Jacobsen 1990, Dalrymple 1996). Jacobsen and Kushlans (1989) model for growth in the Everglades of Southern Florida predicted alligators reaching a mere 1.26 meters in 10 years and requiring at least 18 years to reach sexual maturity. It is currently suspected that the reason for this poor condition is a combination of low food availability and high temperatures (Jacobson and Kushlan 1989, Dalrymple 1996, Barr 1997).
Two study sites were chosen from within the Everglades ecosystem. Water Conservation Area 3A North (WCA) represented a drier and more dynamic hydropattern while Shark Slough, Everglades National Park (ENP) typified the more stable conditions of the central drainage of the Everglades ecosystem.
After a series of consultations with researchers familiar with radio telemetry and the conditions under which this study was to be performed, an AVM model SB2 transmitter in the 166-170 MHz range was chosen. Three different sized radio-transmitters were utilized. The various sized radio-transmitters allowed alligators of different size to be implanted (K-16-H size with a life expectancy of 1.5 years for small animals, C-cell size with a life expectancy of 3 years for intermediate animals and D-cell size with a life expectancy of 5 years for the larger animals). Radio-transmitters were equipped with a single 30 cm to 40 cm external whip antenna. Transmitters were tested under laboratory and field conditions (both from the ground and air) to determine effective ranges.
The disk shaped data loggers (Tidbit Stowaway Temperature Loggers manufactured by Onset Computer Corporation) had a diameter of 3.0 cm and a thickness of 1.5 cm. Each data logger was capable of recording 7944 temperature readings from a range of -5 to 37° C with an accuracy of +/- 0.2° C. Data loggers were programmed to record temperature every 72 minutes, allowing 396 days of continuous data collection. Data collection times were synchronized using Logbook software (Onset Computer Corporation) so that they recorded temperature simultaneously. Once recovered, data loggers were recalibrated using a water bath.
Data loggers were also used to record environmental temperatures. Environmental temperatures were recorded in the marsh near the home ranges of implanted alligators. Environmental temperatures were recorded with both the -5 to 37° C range data logger and data loggers that recorded from -20 to 70° C. The air temperature data logger was shielded from direct solar radiation by a glossy white 14 l plastic bucket with slotted vents for ventilation. The deep water temperature data logger was attached to a concrete block that anchored it at the bottom of the water column. Shallow water temperatures were recorded using data loggers suspended from floats approximately 5 cm from the surface of the water. Black body temperature data loggers were placed in a 600 cm3 copper spheroid painted flat black and positioned to maximize solar input.
Alligators were captured at night from airboats. Suitable habitat was searched using 400,000 candlepower spotlights, and alligators were located by the reflection of the light in their eyes. Alligators were then captured using snares or toggle darts. The location was recorded using GPS along with time of capture and a description of the habitat. Alligators were transported to the University of Florida Fort Lauderdale Research and Education Center in Davie, Florida. The total length, snout-vent length (to the end of the vent), head length, hind foot length, tail girth, mass, and sex were recorded. Each alligator was then permanently marked with two individually numbered Monel tags, a size 6 tag on the first sagittal scute on the tail and a size 3 tag in the webbing of the right hind foot.
Alligators were anesthetized using a combination of medetomindine and isoflurine (T.S. Gross, USGS, unpublished data). Data loggers were cold sterilized and surgically implanted intraperitoneally on the left flank between the last rib and the hind limb. This technique allowed low impact access to the center of the body, which provided accurate core body temperature readings. Two sterilized radio transmitters were then implanted between the peritoneum and the muscle layer on each side of the alligator, one accessed via the incision used to implanted the data logger, and the other through an additional incision on the right flank. After incisions were sutured, the medetomindine was reversed using atipamezole hydrochloride and the alligators were monitored for signs of ill health. The alligators were then released within 24 hours at the exact capture location.
After one year of temperature recording, alligators were recaptured, data loggers were removed using the same surgical techniques, and the animals were released at the recapture site. Animals that were not implanted with temperature data loggers and those implanted but not recaptured were located weekly for the entirety of the study. A sample of the animals were located on a 24 hour basis for an investigation of seasonal movement patterns.
Statistical analyses involved calculation of several variants of home-range estimates (White and Garrott 1990, Seaman and Powell 1996, Staus 1998), time series analysis (SAS Institute 1988), Fourier decomposition (Wilkinson, 1996), cluster analysis (Milligan and Cooper 1985), habitat use (Aebischer et al. 1993), and analysis of variance and other standard statistical tests (SAS Institute 1988).
During this study, 79 alligators were captured and surgically implanted with radio transmitters. A total of 66 alligators were subsequently radio tracked for a sufficient period of time for inclusion in home range, movement, and habitat use analyses. These analyses include 31 animals from Shark Slough, Everglades National Park and 35 from Water Conservation Area 3A North. A subset of 29 of these alligators were implanted with temperature recording data loggers. Of the data logger implanted alligators, 18 have been recaptured and 15 functioning data loggers recovered. Finally, 15 of these animals nested at lease once during the course of the study.
See www.fcsc.usgs.gov. (see http://cars.er.usgs.gov/)
Percival, H.F., K.G. Rice, C.R. Morea, and S.R. Howarter. 1997-1999. American alligator distribution, thermoregulation, and biotic potential relative to hydroperiod in the Everglades. Interim/Annual Reports. USGS-BRD. Gainesville, Fl.
Percival, H.F., K.G. Rice, and S.R. Howarter. 2000. American alligator distribution, thermoregulation, and biotic potential relative to hydroperiod in the Everglades. Contract Final Report. USGS-BRD. Gainesville, Fl.155 pp.
Data & Models
All data from this project have been stored in a database (MS Access) maintained at both the USGS-BRD, Florida Cooperative Fish and Wildlife Research Unit in Gainesville Florida and at the USGSBRD, Florida Caribbean Science Center, Restoration Ecology Branch, Everglades National Park Field Station in Homestead Florida. The data also have been reported in the two masters theses. Stanley R. Howarter's "Thermal Ecology of the American Alligator in the Everglades" and Cory R. Morea's "Home range, Movement, and Habitat Use of the American Alligator in the Everglades" are deposited at the University of Florida's science library and available as reprints from the Florida Cooperative Fish and Wildlife Unit.
Permits for alligator capture, surgical implantation of data loggers and radio transmitters, alligator nest/egg investigations, and survey were obtained annually (1996 to present) from the following agencies:
Publications and Presentations
1. Abercrombie, C.L., S. Howarter, C.R. Morea, K.G. Rice, and H.F. Percival. 2000. Thermoregulation of alligators (Alligator mississippiensis) in southern Florida. J. Thermal Biology. SUBMITTED.
2. Barnett, J., K.G. Rice, H.F. Percival, and P.T. Cardeilhac. 1997. A method for the intramuscular implantation of transmitters in alligators. Proc. Inter. Assoc. Aquatic Animal Medicine. 28:45-48.
3. Howarter, S.R., C.R. Morea, H.F. Percival, K.G. Rice, and C.L. Abercrombie. 1999. Thermal ecology of the American alligator in the Everglades. Abstract/Presentation in Managing Biodiversity. Fl. Chap. Wildl. Soc. Orlando, FL.
4. Morea, C.R., S.R. Howarter, K.G. Rice, H.F. Percival, and C. L. Abercrombie. 1999. Habitat preference and movement of the American alligator in the Everglades ecosystem. Abstract/Presentation in Managing Biodiversity, Fl. Chap. Wildl. Soc. Orlando, FL.
5. Rice, K.G., F.J. Mazzotti, and H.F. Percival. 1999. Effects of restoration on alligators and crocodiles in the Greater Everglades Ecosystem. South Florida Restoration Science Forum. Boca Raton, FL. Posters.
6. Howarter, S. R. 1999. Thermoregulation of the American alligator in the Everglades. M.S. Thesis. University of Florida, Gainesville, Florida. 73 pp.
7. Morea, C. R. 1999. Home range, movement, and habitat use of the American alligator in the Everglades. M.S. Thesis, University of Florida, Gainesville, Florida. 88 pp.
8. Morea, C.R., K.G. Rice, H.F. Percival, and S.R. Howarter. 2000. Home range and daily movement of the American alligator in the Everglades. 19 pp. in Crocodiles. Proceedings of the15th Working Meeting of the Crocodile Specialist Group, IUCN, Gland, Switzerland. In Press.
9. Howarter, S.R., K.G. Rice, H.F. Percival, K.M. Portier, and C.R. Morea. 2000. Thermal ecology of the American alligator in the Everglades. 18 pp. in Crocodiles. Proceedings of the15th Working Meeting of the Crocodile Specialist Group, IUCN, Gland, Switzerland. In Press.
10. Morea, C.R., K.G. Rice, H.F. Percival, and S.R. Howarter. 2000. Home range and daily movement of the American alligator in the Everglades. 15th Working Meeting of the Crocodile Specialist Group, IUCN, Varadero, Cuba. Poster.
11. Howarter, S.R., K.G. Rice, H.F. Percival, K.M. Portier, and C.R. Morea. 2000. Thermal ecology of the American alligator in the Everglades. 15th Working Meeting of the Crocodile Specialist Group, IUCN, Varadero, Cuba. Poster.
12. Morea, C.R., K.G. Rice, H.F. Percival, and S.R. Howarter. 2000. Movement of the American alligator in the Everglades. Wildl. Soc. Bull. IN PREP.
13. Howarter, S.R., K.G. Rice, H.F. Percival, and C.R. Morea. 2000. Alligator thermal ecology in the Everglades. J. Herp. SUBMITTED.
PLANNED ACTIVITIES - 1999/2000:
SCHEDULE OF ACTIVITIES AND DELIVERABLE - 2000/2001:
Literature Cited and Related References
Aebischer, N.J., P. A. Robertson, and R. E. Kenward. 1993. Compositional analysis of habitat use from animal radio-tracking data. Ecology. 74(5):1313-1325.
Barr, B. 1997. Food Habits of the American alligator, Alligator mississippiensis, in the southern Everglades. Unpublished Ph.D. Thesis, Univ. Miami, Florida.
Dalrymple, G. H. 1996. Growth of American Alligators in the Shark Valley Region of Everglades National Park. Copeia. 1996(1): 212-216.
Jacobsen, T. and J. A. Kushlan. 1989. Growth dynamics in the American alligator (Alligator mississippiensis). J. Zool., Lond. 219(2): 309-328.
Kushlan, J. A. and T. Jacobsen. 1990. Environmental variability and the reproductive success of Everglades alligators. J. Herpetol. 24(2):176-184.
Lang, J. W. 1987. Crocodilian thermal selection. in G. J. W. Webb, S. C. Manolis, and P. J. Whitehead (eds.), Wildlife Management: Crocodiles and Alligators, pp. 301-317. Surrey Beatty and Sons, Ltd., New South Wales, Australia.
Mazzotti, F. J. and L. A. Brandt. 1994. Ecology of the American alligator in a seasonally fluctuating environment. In S. Davis and J. Ogden, (eds.), Everglades: The Ecosystem and its Restoration, pp. 485-505. St. Lucie Press, Delray Beach, Florida.
Milligan, G. W, and M. C. Cooper. 1985. An examination of procedures for Determining the number of clusters in a data set. Psychometrika 50(2):159-179.
SAS Institute Inc. 1988. SAS/STAT users guide, release 6.03 edition. SAS Institute Inc., Cary, NC. 1028 pp.
Seaman, D. E. and R. A. Powell. 1996. An evaluation of the accuracy of kernel density estimators for home range analysis. Ecology, 77(7):2075-2085.
Staus, N. L. 1998. Habitat use and home range of West Indian whistling-ducks. J. Wildl. Manag. 62(1):171-178.
White, G. C. and R. A. Garrott. 1990. Analysis of Wildlife Radio-Tracking Data. Academic Press Inc., New York.
Wilkinson, L. 1996. SYSTAT 6.0 for Windows: Statistics. SPSS Inc., Chicago.