Alligators and crocodiles as indicators for restoration of Everglades ecosystems

Abstract

Alligators and crocodiles integrate biological impacts of hydrological operations, affecting them at all life stages through three key aspects of Everglades ecology: (1) food webs, (2) diversity and productivity, and (3) freshwater flow. Responses of crocodilians are directly related to suitability of environmental conditions and hydrologic change. Correlations between biological responses and environmental conditions contribute to an understanding of species' status and trends over time. Positive or negative trends of crocodilian populations relative to hydrologic changes permit assessment of positive or negative trends in restoration. The crocodilian indicator uses monitoring parameters (performance measures) that have been shown to be both effective and efficient in tracking trends. The alligator component uses relative density (reported as an encounter rate), body condition, and occupancy rates of alligator holes; the crocodile component uses juvenile growth and hatchling survival. We hypothesize that these parameters are correlated with hydrologic conditions including depth, duration, timing, spatial extent and water quality. Salinity is a critical parameter in estuarine habitats. Assessments of parameters defined for crocodilian performance measures support these hypotheses. Alligators and crocodiles are the charismatic megafauna of the Everglades. They are both keystone and flagship species to which the public can relate. In addition, the parameters used to track trends are easy to understand. They provide answers to the following questions: How has the number of alligators or crocodiles changed? Are the animals fatter or thinner than they should be? Are the animals in the places (in terms of habitat and geography) where they should be? As surely as there is no other Everglades, no other single species defines the Everglades as does the American alligator. The Everglades is the only place in the world where both alligators and crocodiles exist. Crocodilians clearly respond to changes in hydrologic parameters of management interest. These relationships are easy to communicate and mean something to managers, decision makers, and the public. Having crocodilians on the list of system-wide, general indicators provides us with one of the most powerful tools we have to communicate progress of ecosystem restoration in Greater Everglades ecosystems to diverse audiences.