Graduation Year


Document Type




Degree Granting Department


Major Professor

Kamal Alsharif, Ph.D.

Co-Major Professor

Joni Downs, Ph.D.

Committee Member

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.