Population Dynamics of Distoichometra bufonis (Cestoda: Nematotaeniidae) in Bufo woodhousii

Abstract

Prevalence, density, and variance/mean (=variance/density) ratios are reported for the cestode Distoichometra bufonis in 28 samples of the amphibian host, Bufo woodhousii, taken over a 3-yr period at 2 study sites on the South Platte River in Keith County, Nebraska, U.S.A. In addition, changes in host demography resulting from entry of newly metamorphosed toads into the terrestrial population are given. Prevalence and density (average number of worms per host, infected + noninfected) did not vary significantly either within or between sites and years unless newly metamorphosed toads were included in the analysis. Prevalence ranged from 70 to 100%, and density from 2.7 to 14.8 worms per host, excluding samples containing newly meta- morphosed toads. The bulk of metamorphosis occurred in late June or early July, and by August both prevalence and density had returned to their premetamorphosis values. The host/parasite system is interpreted as one in which disruption of the host population's demographic makeup only temporarily perturbs parasite population structure. The Rocky Mountain toad, Bufo woodhousii Girard, 1854, occurs throughout most of Ne- braska. Casual observations from 1976 to 1983 suggested that the toad had a relatively short breeding season in western Nebraska (late May and June), that breeding took place in ephemeral ponds on a schedule that produced a rather syn- chronous influx of newly metamorphosed indi- viduals into the terrestrial population, usually in early July, and that prevalence of the nemato- taeniid cestode, Distoichometra bufonis Dickey, 1921, was quite high. The studies reported here were done in an attempt to describe some of the population level interactions between the toads and these cestodes.