Review and synthesis of knowledge of insular ecology, with emphasis on the islands of Western Australia.

WESTERN Australia; AUSTRALIA

This paper assesses the legacy of isolation from the mainland and the influence of other factors on biodiversity, biogeography, and faunal and floral change on islands of Western Australia (WA). An empirical perspective from WA reveals numerous neglected insights and overlooked factual information, illustrating the need for improved synthesis of existing knowledge in order to understand the generality of biodiversity patterns and change on islands. A recent loss of direction in the discipline of island biogeography appears to have resulted from over-emphasis of island area, distance from mainland, and absence of competitor species as the key variables in explaining the nature and evolution of insular biodiversity. While these three factors are relevant, they are not always sufficient and should instead be considered as embedded in a more general set of 12 parameters, namely geographic location (including climatic conditions and geomorphological features); history (both geological and human); productivity (soil nutrient status); disturbance (including degree of exposure to salt-laden winds and the presence of Indigenous people); occurrence of breeding marine birds and mammals (particularly significant on small islands); and sampling compatibility. These nine factors are less unequal than is conceded in the literature. Furthermore, most of the 12 factors are interconnected and interdependent, and in combination provide a more satisfactory explanation of insular phenomena. However, the relative influence of these factors differs among species and among higher taxa. Baselines for the biotas of WA islands date from 1843 (for landbirds and seabirds), much earlier than for mammals (1906), plants (1950), and butterflies (1969). Most WA islands demonstrate no extinctions or immigrations of landbird species, evidence of a static equilibrium. On some other WA islands, immigrations of native landbird species exceed extinctions. Immigrations of seabird species also exceed extinctions. In contrast, the native mammal fauna of WA islands shows few immigrations or extinctions unrelated to human activities. The floras of WA islands show numerous immigrations of species, many of which involve plant species not native to WA. Island floras generally exhibit many extinctions and immigrations, with small islets having the most stable floras. Before Europeans settled WA, it appears that species turnover on islands was either non-existent or infrequent. The concept of punctuated equilibrium appears to provide a better explanation of ongoing biodiversity change on islands than dynamic equilibrium, with the intrusion of humans representing a turning point. Dynamic equilibrium is then a special case applicable to relatively short time scales and islands within the dispersal capabilities of species in a particular taxon. We are optimistic about the future of biodiversity on the islands of WA if current policies, management and monitoring are maintained and strengthened. Garden and Barrow islands, with their extensive naval or mining infrastructure, demonstrate successful coexistence for at least several decades between humans and biodiversity. The main challenge to protecting biodiversity on the islands of WA is to prevent the establishment of pest species, particularly of ants, rodents, cats (Felis catus), house mice (Mus musculus) and weeds, and plant and animal diseases. Continual and vigilant monitoring and public education are required. To facilitate this, we recommend that one management plan be prepared to apply to all islands of WA. Our review concludes with numerous suggestions for future research on the islands of WA, as well as on continental and oceanic islands globally. We advocate a systematic comparative approach, based on a comprehensive global synthesis of information already available on islands in the ecological and natural history literature. Fifteen themes are briefly outlined. Regional syntheses will remain important, but many more are needed in order to achieve effective global synthesis and a more complete and holistic understanding of island ecology. These suggestions should result in improved knowledge about insular biodiversity and more comprehensive protection and management of island life. [ABSTRACT FROM AUTHOR]

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