Conservationists are far from able to assist all species under threat, if only for lack of funding. This places a premium on priorities: how can we support the most species at the least cost? One way is to identify 'biodiversity hotspots' where exceptional concentrations of endemic species are undergoing exceptional loss of habitat. As many as 44% of all species of vascular plants and 35% of all species in four vertebrate groups are confined to 25 hotspots comprising only 1.4% of the land surface of the Earth. This opens the way for a 'silver bullet' strategy on the part of conservation planners, focusing on these hotspots in proportion to their share of the world's species at risk.

Biodiversity hotspots for conservation priorities

Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

Summary

1
Most theory and empirical research on exotic invasions is based on the assumption that problematic exotics are much more abundant in the regions where they invade than in the regions where they are native. However, the overwhelming majority of studies on exotic plants have been conducted solely within the introduced range. With few exceptions, ecologists know surprisingly little about the abundance, interaction strengths and ecosystems impacts of even the best-studied exotics in their native range.

2
We argue that taking a biogeographical approach is key to understanding exotic plant invasions. On a descriptive level, unambiguous quantification of distributions and abundances of exotics in native and introduced ranges are crucial. Experiments conducted at a biogeographical scale are also necessary to elucidate the mechanisms that enable highly successful exotics to occur at substantially higher abundance in their introduced vs. native communities.

3
We summarize the leading hypotheses for exotic plant success. We assert that tests of these major hypotheses for invasions (the natural enemies, evolution of invasiveness, empty niche and novel weapons hypotheses) require comparative biogeographical approaches.

4
In addition to focusing on comparative work in the native and introduced range, we also suggest other approaches that could yield important insight into processes that influence exotic success.

5
Increased understanding of invasions has the potential to provide unique insight into fundamental ecological theory, including that on individualistic-holistic structure, the role of trophic interactions in population regulation, and the importance of co-evolution in communities.

A biogeographical approach to plant invasions: the importance of studying exotics in their introduced and native range

Biological invasions are caused by human-mediated extra-range dispersal and, unlike natural extra-range dispersal, are often the result of multiple introductions from multiple sources to multiple locations. The processes and opportunities that result in propagules moving from one area to another can be used more broadly to differentiate all types of extra-range dispersal. By examining key properties of dispersal pathways (notably propagule pressure, genetic diversity and the potential for simultaneous movement of coevolved species), the establishment and evolutionary trajectories of extra-range dispersal can be better understood. Moreover, elucidation of the mechanistic properties of dispersal pathways is crucial for scientists and managers who wish to assist, minimise or prevent future movements of organisms.

Something in the way you move: dispersal pathways affect invasion success

Species Diversity in Space and Time

Oceanic islands have long been considered to be particularly vulnerable to biotic invasions, and much research has focused on invasive plants on oceanic islands. However, findings from individual islands have rarely been compared between islands within or between biogeographic regions. We present in this study the most comprehensive, standardized dataset to date on the global distribution of invasive plant species in natural areas of oceanic islands. We compiled lists of moderate (5–25% cover) and dominant (>25% cover) invasive plant species for 30 island groups from four oceanic regions (Atlantic, Caribbean, Pacific, and Western Indian Ocean). To assess consistency of plant behaviour across island groups, we also recorded present but not invasive species in each island group. We tested the importance of different factors discussed in the literature in predicting the number of invasive plant species per island group, including island area and isolation, habitat diversity, native species diversity, and human development. Further we investigated whether particular invasive species are consistently and predictably invasive across island archipelagos or whether island-specific factors are more important than species traits in explaining the invasion success of particular species. We found in total 383 non-native spermatophyte plants that were invasive in natural areas on at least one of the 30 studied island groups, with between 3 and 74 invaders per island group. Of these invaders about 50% (181 species) were dominants or co-dominants of a habitat in at least one island group. An extrapolation from species accumulation curves across the 30 island groups indicates that the total current flora of invasive plants on oceanic islands at latitudes between c. 35°N and 35°S may eventually consist of 500–800 spermatophyte species, with 250–350 of these being dominant invaders in at least one island group. The number of invaders per island group was well predicted by a combination of human development (measured by the gross domestic product (GDP) per capita), habitat diversity (number of habitat types), island age, and oceanic region (87% of variation explained). Island area, latitude, isolation from continents, number of present, non-native species with a known invasion history, and native species richness were not retained as significant factors in the multivariate models. Among 259 invaders present in at least five island groups, only 9 species were dominant invaders in at least 50% of island groups where they were present. Most species were invasive only in one to a few island groups although they were typically present in many more island groups. Consequently, similarity between island groups was low for invader floras but considerably higher for introduced (but not necessarily invasive) species – especially in pairs of island groups that are spatially close or similar in latitude. Hence, for invasive plants of natural areas, biotic homogenization among oceanic islands may be driven by the recurrent deliberate human introduction of the same species to different islands, while post-introduction processes during establishment and spread in natural areas tend to reduce similarity in invader composition between oceanic islands. We discuss a number of possible mechanisms, including time lags, propagule pressure, local biotic and abiotic factors, invader community assembly history, and genotypic differences that may explain the inconsistent performance of particular invasive species in different island groups.

A global comparison of plant invasions on oceanic islands

The native flora of tropical oceanic islands is known to be particularly susceptible both to displacement and extinction, following the invasion of alien organisms. Miconici ccrlvescem DC. (Melastomataceae), first introduced to Tahiti (French Polynesia. South Pacific Ocean) in 1937 as an ornamental plant, now covers over two-thirds of the island. As it forms dense monotypic stands which have progressively overwhelmed the native forests, this plant pest is a direct threat to the rich Tahitian indigenous flora. Between 40 and 50 species of the 107 species endemic to Tahiti are thought to be on the verge of extinction. hl. calvescens was finally declared a 'noxious species in French Polynesia' in 1990. Without efficient control efforts and effective endangered plant conservation and protection legislation, M. culvesceiis could cause Tahiti and all the high islands of French Polynesia to become ecological descrts.

Tahiti's native flora endangered by the invasion of Miconia calvescens DC. (Melastomataceae)

Invasive alien species (IASs) on islands have broad impacts across biodiversity, agriculture, economy, health and culture, which tend to be stronger than on continents. Across small-island developing states (SIDSs), although only a small number of IASs are widely distributed, many more, including those with greatest impact, are found on only a small number of islands. Patterns of island invasion are not consistent across SIDS geographic regions, with differences attributable to correlated patterns in island biogeography and human development. We identify 15 of the most globally prevalent IASs on islands. IAS impacts on islands are exacerbated through interactions with a number of other global change threats, including over-exploitation, agricultural intensification, urban development and climate change. Biosecurity is critical in preventing IAS invasion of islands. Eradication of IASs on islands is possible at early stages of invasion, but otherwise is largely restricted to invasive mammals, or otherwise control is the only option. Future directions in IAS management and research on islands must consider IASs within a broader portfolio of threats to species, ecosystems and people's livelihoods on islands. We advocate for stronger collaborations among island countries and territories faced with the same IASs in similar socio-ecological environments.

/pdf/invasive-alien-species-on-islands-impacts-distribution-4tm8xhmq9k.pdf

Invasive alien species on islands: impacts, distribution, interactions and management

Eastern Polynesia, a phytogeographical subregion of Polynesia in the Pacific Ocean, comprises the archipelagoes of the Cook Islands, the Austral Islands, the Society Islands, the Tuamotu Islands, the Marquesas Islands, the Gambier Islands, the Pitcairn Islands, and Rapa Nui, which is the easternmost inhabited island of Polynesia. It consists of a total of about 140 tropical to subtropical oceanic islands that are among the most remote in the world, being over 3,000 km distant from the nearest continents. Because of this strong geographic isolation, the relatively young geological age, and small terrestrial surface (less than 4,000 km2) of these islands, the native flora of eastern Polynesia is impoverished, disharmonic, and with a relative low number of endemic genera (12). However, some high volcanic islands within these archipelagoes display a great diversity of habitats and a highly endemic flora (e.g., 50% for the vascular plants in Nuku Hiva, 45% in Tahiti) with striking cases of adaptative radiation (e.g., in the genera Bidens, Cyrtandra, Glochidion, Myrsine, and Psychotria). Most of these endemic taxa are restricted to montane rain forests and cloud forests. These upland wet forests are not directly threatened by habitat destruction by humans or disturbance by large mammals but rather by invasive alien plants. Native forests of eastern Polynesian islands are invaded by aggressive introduced species (e.g., Lantana camara and Psidium cattleianum in most island groups; Syzygium jambos in Pitcairn, Tahiti, and Nuku Hiva; Ardisia elliptica, Cestrum nocturnum, Spathodea campanulata in Tahiti and Rarotonga; Rubus rosifolius in the Society Islands, Hiva Oa, and Rapa Iti). Therefore, one of the highest priorities for the long-term conservation of the original native flora and forest vegetation of eastern Polynesia should be given to the study (invasion dynamics and ecological impacts) and control (strategy and methods) of the current invasive alien plants and to the early detection and eradication of potential plant invaders. Eastern Polynesia, with its small, diverse, and isolated oceanic islands, also offers opportunities to test hypotheses on the vulnerability of islands to invasion by alien species, with or without disturbance.

/pdf/threat-of-invasive-alien-plants-to-native-flora-and-forest-44n3pydmbe.pdf

Threat of Invasive Alien Plants to Native Flora and Forest Vegetation of Eastern Polynesia

Miconia caluescens DC (Melastomataceae) is a dominant invasive species in the tropical oceanic island of Tahiti (French Polynesia, South Pacific Ocean), where it was introduced as an ornamental plant. Whereas this small tree is sparse in its native range of Central America, it has spread in ‘Tahiti into a wide variety of habitats including native wet forests. The remarkable success of this invasion is due in great part to prolific reproduction: a mature tree can bear up to 220 inflorescences with an average of 1330 AowerslinHorescence, 208 fruitslinfructescence and 175 seeddfruit. lwo and a half years of phenological observations in a highly invaded site indicated that three major peaks of flowering occurlyear over brief periods: Hower anthesis lasted a few days and pollen grain germination suggested a short stigmatic receptivity of only a few hours; no pollinators were observed foraging on flowers during our survey; the production of fruits containing viable seeds in bagged inflorescences showed that self-fertilization can occur; pollen-ovule ratio (log PI0 = 2.68) suggested facultative xenogamy; bagged isolated flowers to test for autogamy and style cutting to learn whether apomixis occured or not were not conclusive. The flowering phenology and the breeding system of M. caluescens enable this plant to build up rapidly successful populations from even a single propagule on the island of Tahiti and on other sites of introducrion. The vegetation structure of Polynesian native forests compared to Neotropical rain forests probably plays an important role in determining the reproductive success of M. caluescens and could provide a complementary explanation of the biological invasion processes in tropical oceanic islands.

Observations on the Reproductive Biology of Miconia calvescens DC (Melastomataceae), an Alien Invasive Tree on the Island of Tahiti (South Pacific Ocean)1

Jean-Yves Meyer

Papers

A global comparison of plant invasions on oceanic islands

Tahiti's native flora endangered by the invasion of Miconia calvescens DC. (Melastomataceae)

Invasive alien species on islands: impacts, distribution, interactions and management

Threat of Invasive Alien Plants to Native Flora and Forest Vegetation of Eastern Polynesia

Observations on the Reproductive Biology of Miconia calvescens DC (Melastomataceae), an Alien Invasive Tree on the Island of Tahiti (South Pacific Ocean)1