Effect of seasonality on abomasal helminth community in alpine ibex (Capra ibex ibex).

Abomasal helminths of 81 adult female ibex (Capra ibex ibex) from Piz Albris colony (CH) culled monthly from December 1989 to May 1991 were analyzed. Subjects were divided into six quarterly groups (I: December 1989-February 1990; II: March-May 1990; III: June-August 1990; IV: September-November 1990; V: December 1990-February 1991; VI: March-May 1991) in order to investigate the seasonal fluctuation of helminth community parameters (abundance, richness, sex-ratio, Berger-Parker dominance index, importance index, overall association between species by Schluter's variance test). All parameters showed considerable seasonality. Abundance was highest in group III, while richness was highest and Berger-Parker index lowest in group IV. Overall associations between species were positive in winter-spring groups and negative in summer-autumn. The importance index of the two dominant species (Teladorsagia circumcincta and Marshallagia marshalli) showed a symmetrical and opposite seasonal development. A significant negative correlation (Spearman r = -.30; p < .01) has been demonstrated between the Berger-Parker dominance index and factor scores descriptive of age and weight of the subjects. These results suggest that seasonal factors determine the community composition while host control can act as a filter maintaining a stable community structure.