RECRUITMENT-DRIVEN, SPATIALLY DISCONTINUOUS COMMUNITIES - A NULL MODEL FOR TRANSFERRED PATTERNS IN TARGET COMMUNITIES OF INTESTINAL HELMINTHS

Populations and therefore communities of intestinal helminths of verte brates are fueled by recruitment of new individuals from outside the h ost. The source of new individuals is often an intermediate host that harbors several infective propagules of 1 or more species. Hence these source communities are transmitted in packets of infective propagules to target communities in definitive hosts. Packets not only provide r ecruits to target communities, but, because a packet of propagules pos sesses its own structure, it may also transmit structure to the target community. We use this system to examine the contribution that struct ure in the source pool of propagules makes to the structure of recruit ment-driven target populations and communities. By treating the dynami cs of such target populations and communities as immigration-death pro cesses, we conclude: (1) Unlike a birth-driven population a recruitmen t-driven target population will grow to an asymptotic limit even in th e absence of density-dependent processes or reaching carrying capacity ; (2) the frequency distribution of the number of recruits entering ta rget populations will determine the frequency distribution of adults i n target populations; (3) interspecific associations among species in the source community will be transmitted to target communities, but th e magnitude of the transmitted associations will depend upon the relat ive survival rates of the species; and (4) for associations of equal m agnitude in a source community, the magnitude of a transferred negativ e association will be less than the magnitude of a positive associatio n in a target community. Two examples of source communities in salt ma rsh crabs reveal that source infracommunities exist with the hypothesi zed structure. Further, the source helminth communities display a grea ter number of positive than negative interspecific associations. The i nequity in transfer and the existence of a greater proportion of posit ive associations in source communities may explain the widespread occu rrence of excess positive associations that has been noted in recruitm ent-driven communities.