HELMINTH COMMUNITY STRUCTURE AND PATTERN IN A MIGRATORY HOST (ANAS-PLATYRHYNCHOS)

The helminth community at the southern periphery of the mallard (Anas plyatyrhynchos) breeding range on the Southern High Plains of Texas co nsisted of species commonly reported in this host at northern latitude s. Although prevalence, abundance, and dominance values Varied and thi s helminth community was species-rich and diverse, species composition was relatively consistent over temporal and host variables. Mallards had higher mean abundances of helminths in summer than winter; 80% of all helminth individuals occurred in juveniles. Recurrent groups forme d during summer and within juvenile mallards were larger and more comp lex than groups formed during winter or in adults. Of the 15 helminth species forming group memberships, only Cloacotaenia megalops, Microso macanthus hopkinsi, Amidostomum acutum, and Tetrameres spp. commonly c o-occurred during each of four seasons in juvenile mallards, whereas C . megalops and Capillaria contorta persisted temporally in adult malla rds. These species occupy different host microhabitats, suggesting lit tle or no interaction between temporally persistent species that commo nly co-occur in mallards. The results of our study suggest that helmin th communities reflect the density distribution of the host species ac ross their annual geographic range, where the breeding range represent s the epicenter of origin for this host-helminth system.