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Ecology of Everglades Alligator Holes

Poster presented April 2003, at the Greater Everglades Ecosystem Restoration Conference

Frank J. Mazzotti1, Mark R. Campbell1, Michelle L. Palmer1, Jocie A. Graham1,
Karen Minkowski1, Laura A. Brandt2, Kenneth G. Rice3

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Description

The American alligator (Alligator mississippiensis) creates small ponds, called alligator holes, by excavating substrate and vegetation. These holes are common in the Everglades and Frank Craighead in 1968 characterized alligator holes by these three components:

  1. A depression in the muck or limestone bedrock;
  2. Water to fill the resulting basin; and,
  3. Alligators to create and maintain the hole.
photo of alligator's head sticking out of water
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photo of alligator hole
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Function
  • Provide water necessary for mating;
  • Act as dry season refugia for aquatic organisms;
  • Provide concentrated area for birds and mammals to forage;
  • Provide disturbance site for plant establishment through soil enrichment and removal of vegetation; and,
  • Increase overall diversity of Everglades

flow chart of hydroperiod effects on alligators
Flow Chart of Hydroperiod Effects on Alligators. Redrawn from Marl Prairie Rocky Glades Workshop by: Steve Davis and Tomma Barnes [larger image]

Questions
  1. Where are alligator holes?
  2. What do alligator holes look like?
  3. How are alligator holes arranged in space?

Methods
methodology flow chart

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Mapping Summary
map of alligator hole locations in WCA-3

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  • Holes are classified in three categories by vegetation type.
  • Color, infrared aerials (1:24,000) are adequate to map alligator holes.
  • Spatial accuracy is 60 m.
  • Commission accuracy depends on size, location, and vegetation. Holes in sloughs are more difficult to identify than in wet prairies and sawgrass.

Ecological Characterization
  • Small holes are structurally and vegetatively distinct from larger holes.
  • Larger holes surrounded by woody vegetation provide upland habitat and increase the diversity and richness of the surrounding vegetation.
  • Larger alligators (and hatchlings) are found in larger holes, while juveniles are found in surrounding smaller ponds – holes act as social refugia.

[Note: The image to the right is a thumbnail version of a digital enlargement of an alligator hole.]

Click on the image to the right to view a digital enlargement of an alligator hole at 1 meter resolution. These field maps assist in classifying vegetation types, identifying alligator holes, and mapping vegetation. Yellow dot indicates location of picture below, on right.

 digital enlargement of an alligator hole at 1 meter resolution
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photo of scientist surveying
[larger image]		 photo of scientists in alligator hole
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legend of vegetation types
composition of vegetation in three meter rings from edge of open water for woody area composition of vegetation in three meter rings from edge of open water for marsh area composition of vegetation in three meter rings from edge of open water for artificial area
Woody
[larger image]		 Marsh
[larger image]		 Artificial
[larger image]
Composition of Vegetation in Three Meter Rings from Edge of Open Water

example of transect data for an alligator hole showing water and muck depths in the North to South direction
Example of transect data for an alligator hole showing water and muck depths in the North to South direction. Note vertical scale exaggeration. [larger image]


Spatial Analysis
  • Holes are clustered, but clusters are not clustered.
  • Clusters are 3 km apart.
  • Vegetation and canals have an effect on overall hole distribution.
  • Fewer holes than expected are found within 1 km of a canal.

density map of all holes
Density Map: All Holes [larger image]

graph of number of alligator holes as compared to distance from canal
Number of Alligator Holes as compared to distance from canal. [larger image]

map showing canal influence, the number of alligator holes as compared to distance from canal at 1 km increments
Canal Influence. Number of Alligator Holes as Compared to Distance from Canal at 1 km increments. [larger image]

Number of Alligators Observed at Different Hole Types
  #Active-Spring # Active-Fall Trails Adult Hatch. Juven. Nest Other*
Type 1 5 (56%) 7 (78%) 9 2 7 0 1 3
Type 2 6 (55%) 8 (73%) 11 0 0 5 0 3
Type 3 7 (78%) 8 (89%) 9 3 5 1 2 6
Total 18 (62%) 23 (79%) 29 5 12 6 3 12
*Other signs include; tail drags, footprints, sunning spots, or gator dens.


Acknowledgements:
This research was supported in significant part by the Everglades Agricultural Area Environmental Protection District and the National Fish and Wildlife Foundation.

University of Florida IFAS Extension logo 1University of Florida
Ft. Lauderdale Research & Education Center
3205 College Avenue
Fort Lauderdale, Florida 33314
U.S. Fish and Wildlife Service logo 2U.S. Fish and Wildlife Service
Arthur R. Marshall Loxahatchee National Wildlife Refuge
10216 Lee Road
Boynton Beach, Florida 33437
U.S. Geological Survey logo 3U.S. Geological Survey
Center for Water and Restoration Studies
University of Florida Field Station
3205 College Avenue
Fort Lauderdale, Florida 33314

PDF icon Click here to download an 8.5 x 11 PDF version of the original poster (744 KB). PDF files require the Free Adobe Acrobat Reader ® to be read.

Related information:

SOFIA Project:

American Alligator Distribution, Thermoregulation, and Biotic Potential Relative to Hydroperiod in the Everglades

American Alligator Ecology and Monitoring for CERP

Parameter Estimation and Population-Based Simulation Modeling of American Alligator Populations in Support of ATLSS



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Last updated: 13 July, 2009 @ 11:54 AM(TJE)