Volume Eleven Conservation Science 2016 Western Australia Review and synthesis of knowledge of insular ecology, with emphasis on the islands of Western Australia IAN ABBOTT and ALLAN WILLS i TABLE OF CONTENTS Page ABSTRACT 1 INTRODUCTION 2 METHODS 17 Data sources 17 Personal knowledge 17 Assumptions 17 Nomenclatural conventions 17 PRELIMINARY 18 Concepts and definitions 18 Island nomenclature 18 Scope 20 INSULAR FEATURES AND THE ISLAND SYNDROME 20 Physical description 20 Biological description 23 Reduced species richness 23 Occurrence of endemic species or subspecies 23 Occurrence of unique ecosystems 27 Species characteristic of WA islands 27 Hyperabundance 30 Habitat changes 31 Behavioural changes 32 Morphological changes 33 Changes in niches 35 Genetic changes 35 CONCEPTUAL FRAMEWORK 36 Degree of exposure to wave action and salt spray 36 Normal exposure 36 Extreme exposure and tidal surge 40 Substrate 41 Topographic variation 42 Maximum elevation 43 Climate 44 Number and extent of vegetation and other types of habitat present 45 Degree of isolation from the nearest source area 49 History: Time since separation (or formation) 52 Planar area 54 Presence of breeding seals, seabirds, and turtles 59 Presence of Indigenous people 60 Activities of Europeans 63 Sampling completeness and comparability 81 Ecological interactions 83 Coups de foudres 94 LINKAGES BETWEEN THE 15 FACTORS 94 ii THE TRANSITION FROM MAINLAND TO ISLAND: KNOWNS; KNOWN UNKNOWNS; AND UNKNOWN UNKNOWNS 96 SPECIES TURNOVER 99 Landbird species 100 Seabird species 108 Waterbird species 108 Plant species 108 Mammal species 115 Reptile species 115 Vegetation change 115 BIOGEOGRAPHIC POINTS OF INTEREST, SURPRISES AND ANOMALIES: EXAMPLES OF GENERA AND SPECIES UNDER- REPRESENTED OR OVER-REPRESENTED ON WA ISLANDS 116 ENIGMATIC ISLANDS 126 Dirk Hartog, Bernier and Dorre islands 126 Rottnest and Garden islands 126 Barrow Island, Montebello Group and Lowendal Group 127 REMEDIATION AND MITIGATION MEASURES APPLIED TO WESTERN AUSTRALIAN ISLANDS: RE-INTRODUCTION OF NATIVE SPECIES THAT HAVE BECOME EXTINCT ON ISLANDS; AND ERADICATION OF INTRODUCED SPECIES 127 Discussion 128 Extinct species 129 Extinction of insular populations 129 Introduced species 131 Endemic species 132 Evolutionary change 133 Species turnover 133 Small-island effect 137 The dynamic equilibrium theory of island biogeography (DETIB) 138 An alternative approach: Comprehensive synthesis of existing empirical information 144 Location and cultural history 144 Primary factors differ among species and higher taxa 145 Productivity and disturbance 145 Special local factors 146 Change in biodiversity in terms of a punctuated equilibrium model 146 A proposed new global ‘research program’ for island ecology and biogeography 147 Nature conservation on Western Australian islands 149 Recommendations for future research on, and management of, Western Australian islands 150 CONCLUSIONS 152 ACKNOWLEDGEMENTS 153 REFERENCES 153 Conservation Science W. Aust. 11 (2016) Review and synthesis of knowledge of insular ecology, with emphasis on the islands of Western Australia IAN ABBOTT* AND ALLAN WILLS Science and Conservation Division, Department of Parks and Wildlife, Locked Bag 104, Bentley Delivery Centre, Western Australia 6983 *Corresponding author: [email protected] ABSTRACT 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. © The Government of Western Australia, 2016 Recommended citation: Abbott I, Wills A (2016) Review and synthesis of knowledge of insular ecology, with emphasis on the islands of Western Australia. Conservation Science Western Australia 11 [online]. https://www.dpaw.wa.gov.au/CSWAjournal 2 I Abbott & A Wills Key words: biodiversity, biogeography, explanatory frameworks, insular processes, island, MacArthur and Wilson. ‘24th [June 1865]…Passing islands [of the Kimberley region of WA] all day…25th…Still passing islands…26th…There seemed…an unbroken continuity of islands…Still islands, islands, islands. After leaving Cape Bougainville we passed at least 500, of every shape, size, and appearance…Infinitely varied as these islands are – wild and picturesque, grand sometimes almost to sublimity – there is about them all an air of dreariness and gloom…They seem abandoned by nature to complete and everlasting desolation…It was a relief from weariness, anxiety, and danger, when we escaped from this Archipelago.’ JP Stow, Voyage of the Forlorn Hope. The South Australian Advertiser 22.8.1865: 3. ‘understanding is not achieved by generality alone, but by a relation between the general and the particular’ (Levins 1966: 430). ‘La verité consiste dans les nuances’ (JR Renan, 1832–1892). INTRODUCTION of islands have contributed disproportionately to knowledge about the evolution and ecology of species About 70% of Earth’s surface is covered by ocean, (Mayr 1942). The reason for this is that islands are very 8 2 comprising an area of c. 3.6 × 10 km . Pieces of land numerous; have smaller and simpler biotas than completely surrounded by water are a fundamental comparably-sized areas on the nearby mainland; constituent of Earth’s land surface, with perhaps one demonstrate interesting ecological idiosyncrasies (such million islands in existence at present (Fig. 1). as unexpected occurrences of species and unexpected Knowledge about islands has contributed significantly absences of