THE NUMBER OF NICHES IN INTESTINAL HELMINTH COMMUNITIES OF ANGUILLA-ANGUILLA - ARE THERE ENOUGH SPACES FOR PARASITES

The suggestion that there may be a limit to the number of niches avail able to helminth species in the intestine of Anguilla anguilla was inv estigated by examining the frequency distributions of the number of he lminth species per eel and the relationships between maximum and mean infracommunity richness and component community richness in 1 locality over 17 years and in 64 localities throughout Ireland and England. Th e maximum number of species per eel did not exceed 4 in the 1 locality , or 3 in the 64 localities. In both the single and the several locali ties, the relationship between maximum and mean infracommunity richnes s and component community richness was curvilinear and best described by a power or polynomial function. This was interpreted to mean that i nfracommunity richness became increasingly independent of component co mmunity richness, and that infracommunities were saturated at values w ell below the higher level of helminth richness immediately available for colonization i.e. component community richness. It is argued that these findings cannot be explained by supply-side ecology, pool exhaus tion or transmission rates, but only by infracommunity processes actin g to impose a fixed limit to the number of species in an infracommunit y. Most infracommunities are species poor, and the limiting factors wi ll only operate as species richness rises to determine a maximum. Acce ptance of a limit to the number of niches available also resolves the apparent inconsistency between the occurrence and importance of inters pecific competition and the nature of isolationist communities.