The ecology of insular plants was examined at several levels and on several geographic and temporal scales. First, the factors affecting numbers of species on islands of the Torres Strait and Great Barrier Reef regions were analysed. Then, the geographic scale was narrowed to the Capricornia Section and the change in species-richness and composition of the flora over time was assessed. Still further narrowing focused on a single island, One Tree Island, where the effect of variations in weather (drought) was studied, as was the impact of insects on the vegetation. The small cays of the Swain Reefs were used to examine the dynamics of vegetation under geomorphological instability and disturbance by sea birds and sea turtles.
The predictions of the equilibrium theory of insular biogeography were fulfilled in that immigration, extinction and species-turnover occurred, and species-richness was related to insular area. It was also related to insular height. The expectations of the theory were not fulfilled in that species-richness on islands was not strongly related to distance from the mainland and there was a general increase in species-number, rather than an equilibrium number, on islands of the Capricornia Section; furthermore, local instability of very small cays in the Swain Reefs influenced vegetation dynamics to such an extent that the concept of an equilibrium species-number was not realistic.
Other findings were:
(i) Incidence of most species of plants increased with increasing insular size and species-richness; a few species, however, had higher incidence on islands of intermediate-richness than on either richer or more depauperate ones.
(ii) Drought can cause large changes in plant biomass and may result in shifts in species-dominance that require a period of years for restoration to the previous condition.
(iii) Insect grazing may be high, and in extreme cases can lead to local extinction of some species of plants.
(iv) Vegetation is zoned, even on very small, unstable cays. That zonation seems related to the effect of seabirds, sea turtles, and erosion and deposition of sand as well as gradients in physical factors such as salinity, moisture and soil nutrients.
Finally, a geomorphological-successional model was constructed which accounts for the new findings, compensates for inadequacies in the equilibrium theory, and incorporates aspects of that theory as well as parts of models proposed by Sauer, Buckely and others. It accounts for vegetation dynamic s and zonation on islands during their development and degradation, and allows for temporal instability as well as persistent conditions.