Dispersal and Infection in Mistletoe Metapopulations

Abstract

1 The influence of dispersal patterns on the local distribution and abundance of the mistletoe, Phrygilanthus sonorae (Loranthaceae) is investigated. 2 Mistletoe and host distributions were measured at several subsites at two field sites in Baja California. Dispersal patterns were determined both by bird observation and the locations of dispersed seeds. The observed correlations between patterns of dispersal and patterns of mistletoe infection are interpreted by treating the mistletoe population as a metapopulation of the mistletoes on individual trees. 3 Mistletoe seeds were dispersed artificially to test experimentally for differences in the establishment success of mistletoe seedlings between individuals within a host species or between host species. No evidence was found for individual differences in susceptibility of hosts within a site or for host specific races of Phrygilanthus sonorae. 4 Sites and subsites differed dramatically in frugivore sets, dispersal patterns and the relative density of host trees (relative to all large trees and shrubs in the community). 5 A number of patterns of mistletoe distribution are explained by dispersal. Within subsites, the proportion of a size class infected by mistletoes (cohort occupancy) increases with the size of the class.. This size-occupancy relationship is predicted from a metapopulation model with patch (tree) turnover. Subsites within sites differ in the slope of the size-occupancy relationship and in the overall proportion of hosts infected by mistletoes (overall occupancy). These differences between subsites are explained by differences in the proportion of mistletoe seeds that are dispersed off the parent host tree and the efficiency of the off-tree dispersal, but not by overall dispersal efficiency. 6 Differences in mistletoe establishment success, adult mistletoe mortality and host turnover do not explain the observed patterns of infection.