MODELING EFFECTS OF CHEMICALS ON A POPULATION - APPLICATION TO A WADING BIRD NESTING COLONY

An approach for the study of effects of chemical contamination of an a vian population is described. The protocol consists of four components : (1) an individual model that is coupled with (2) a chemical exposure model; and (3) a population model together with (4) an effects model. The model-based protocol is generic, delineates types of information required for ecological assessment and lays the framework for the impl ementation of toxic effects in an individual-oriented model. The proto col is illustrated by modifying an existing individual-oriented model of a wood stork colony to incorporate sublethal and lethal effects of mercury contamination. Because of the paucity of available data on eff ects of chemicals on wading birds, information from experiments on oth er avian species is, by necessity, frequently extrapolated to dose-res ponse formulations for wading birds; consequently, the results are qua litative in character and portray relationships determined to exist be tween certain species of birds and the toxic effects of mercury pollut ion. Simulation results and applications focus on a population level e ffect, colony survival of the endangered species Mycteria americana in the Everglades of Florida. Because of the lack of information about m odel processes and parameter values for mercury effects on wood storks , model sensitivity studies were performed. Given the results for subl ethal contamination levels along with the information on levels of mer cury found in fish of the Everglades, it would seem that if our assump tions are even close to accurate, this model suggests that wood stork colony losses due to mercury contamination are feasible, possibly in t he short term, but definitely in the long term.