A Retrospective Analysis of the Potential Environmental Stressors Responsible for the Decline of the Natural Populations of the Florida Apple Snail (Pomacea paludosa) in the A.R.M. Loxahatchee National Wildlife Refuge
Degree Granting Department
Kamal Alsharif, Ph.D.
Joni Downs, Ph.D.
Matthew Harwell, Ph.D.
Population dynamics · Toxicity · Everglades restoration · Everglades · snail kite · Drought
The purpose of this thesis is to determine the factors that contributed to
the decline of Florida apple snail ( Pomacea paludosa) populations in the A.R.M.
Loxahatchee National Wildlife Refuge with the goal of devising management
recommendations to the Refuge regarding population management strategies.
The factors examined that could have potentially contributed to population
decline include the use of copper-based herbicides, insecticide application, the
occurrence of drought, the use of other herbicides, the occurrence of fire, and
non-avian predation. Annual Narrative documents produced by Refuge
managers and staff members, dated from 1951 to 2007, were used to collect
historical data for these factors. The quality of data reporting within the Annual
Narratives was also examined. To support data on droughts documented in the
Annual Narratives, surface water and rainfall data were obtained and analyzed.
The methodology includes the use of conceptual ecological models and historical
ecology to determine whether or not the factors examined produced an
ecological effect capable of affecting the Refuge population of apple snails.
Evidence from the Annual Narratives suggests that the use of copper-based
herbicides, the occurrence of drought, and predation by alligators were
responsible for the decline of the apple snail on the Refuge. A lack of consistently
reported data regarding apple snail densities makes it difficult to determine the
degree to which each factor had an effect on the apple snails or to determine if
any spatio-temporal relationship existed between the Florida apple snail and
Everglade snail kite ( Rostrhamus sociabilis plumbeus) based on copper-based
herbicide use. The overall quality of the Annual Narratives improved throughout
the study period and eventually focused heavily on investigative studies. Several
management recommendations were suggested to improve Florida apple snail
populations on the Refuge. First, in order to monitor the health and trends of the
apple snail population, a monitoring network needs to be established with results
maintained in a geodatabase. Both apple snail density and egg cluster counts
need to be made following an established sampling method. Second, in an
attempt to sustain higher apple snail densities, stocking of the interior should be
attempted. Finall, in the event that adjacent farmlands are to be restored, soil
samples need to be analyzed to determine if concentrations are high enough that
desorption of copper from the flooded agricultural soils could pose a serious
threat to the Refuge by reintroducing toxic levels of copper.
Scholar Commons Citation
Ladd, Shannon, "A Retrospective Analysis of the Potential Environmental Stressors Responsible for the Decline of the Natural Populations of the Florida Apple Snail (Pomacea paludosa) in the A.R.M. Loxahatchee National Wildlife Refuge" (2010). Graduate Theses and Dissertations.