The role of habitat in structuring Halipegus occidualis metapopulations inthe green frog

The transmission dynamics of the trematode Halipegus occidualis in its defi nitive host, Rana clamitans, have been examined over a 5-yr period in a Nor th Carolina pond. The breeding season of green frogs coincides with the per iod of worm recruitment, during which time male frogs are territorial and f emales show strong site fidelity. This site fidelity allows inferences to b e made regarding the suitability of a particular habitat for worm transmiss ion based on frog infection intensities within that habitat. Four foci of i nfection were identified in the pond by plotting worm infrapopulation size against site of host capture. Sites within infection foci are characterized by shallow water and emergent vegetation, factors favorable for overlappin g distributions of the 4 hosts in the life cycle of H. occidualis. Consiste nt year-to-year worm prevalences and intensities, despite fluctuations in f rog population size, are thought to be the result of a relatively constant proportion of the frog population being present in infection foci each year . Removal of worms from heavily infected frogs in the fifth year resulted i n further heavy worm recruitment by treated frogs suggesting that site sele ction can predispose a frog to heavy infection. Further, the sum of removed parasites and those recruited after parasite removal by treated frog hosts was higher than worm infrapopulations observed in previous years, indicati ng that worm density regulates parasite infrapopulation size in heavily inf ected frogs.