E. crucis Maiden occurs as small, isolated populations confined to granite outcrops in south-western Australia. The level and distribution of genetic diversity at 11 allozyme loci in 10 populations were estimated. Ten loci were polymorphic. However, many alleles were fixed in populations and occurred at low frequencies in others. The mean expected panmictic heterozygosity for populations was low when compared with tree species in general but similar to other tree species occurring in small, isolated populations. The level of population differentiation was high, as expected for small, isolated populations undergoing genetic fixation through genetic drift. The majority of the differentiation was attributable to between-population rather than between-subspecies differentiation. Analyses of allozyme data suggest that the mating system of E. crucis may be adapted to maintain diversity within populations by selection favouring heterozygous, presumably outcrossed progeny. The optimal strategy for the conservation of the genetic resources of E. crucis and other eucalypts with similar distribution patterns is considered in the light of this and previous studies.

Mating system parameters of the rare and endangered species Banksia brownii were estimated for two populations using both the mixed mating and effective selfing models. Estimates of outcrossing rate were similar in both populations for both models (mixed mating t Pop. 1=0.68, Pop. 2=0.75; effective selfing t Pop. 1=0.65, Pop. 2=0.73) and were among the lowest reported for undisturbed Banksia populations. Banksia brownii is killed by fire and the high level of selfing found may be associated with this trait. Multilocus and minimum variance mean i estimates were similar and the covariance of selfing with gene fixation (D) was not significantly different from zero indicating that populations were not structured and that most of the inbreeding was the result of self-fertilisation. The absence of structure was attributed to gene dispersal through pollen disperse by birds, and selection against inbred seed. It is suggested that several entire, large populations of this species together with habitat sufficient to support pollinators be reserved to conserve this species.

Estimates of parameters of the mixed mating model were made for three populations of the bird-pollinated arid zone eucalypt, Eucalyptus rameliana F. Muell. Levels of outcrossing ((t) over cap) varied significantly between populations from mixed mating with substantial selfing ((t) over cap = 0.54) to almost completely outcrossed ((t) over cap = 0.95). Comparison of single-locus and multilocus estimates suggested that the drop in outcrossing was due to increased self-pollination. The lowest outcrossing rate was attributed to the reduced ability of a population with low numbers of buds to attract bird pollinators. Outcrossing rates in E. rameliana are proposed to be a more direct reflection of pollination than estimates made for mass flowering, i.e. small-fruited eucalypts. The distribution of allozyme diversity in E. rameliana also appeared to reflect the impact of bird pollinators in promoting gene flow as well as the species capacity for outcrossing and introgression. Levels of diversity were comparable with other eucalypts, but the proportion of diversity between populations (GST = 9.2%) was only about half the mean for other eucalypts. Genetic distances between populations were low, but there was same significant differentiation of populations which was attributed to non-random bird migrations. The importance of bird pollination in the mating system and the distribution of genetic diversity in E. rameliana emphasises that enough habitat to support nomadic birds should be preserved in order to conserve this eucalypt species.