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Stable isotope analysis as an early monitoring tool for Community-scale effects of rat eradication
Available Online

Egmann, Alex S.

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Fisher, Robert N.

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Hathaway, Stacie A

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Katherine M Nigro

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Kuile, Ana Miller-ter

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Young, Hillary S

2017
Invasive rats have colonized most of the islands of the world, resulting in strong negative impacts on native biodiversity and on ecosystem functions. As prolific omnivores, invasive rats can cause local extirpation of a wide range of native species, with cascading consequences that can reshape communities and ecosystems. Eradication of rats on islands is now becoming a widespread approach to restore ecosystems, and many native island species showstrong numerical responses to rat eradication. However, the effect of rat eradication on other consumers can extend beyond direct numerical effects, to changes in behavior, dietary composition, and other ecological parameters. These behavioral and trophic effectsmay have strong cascading impacts on the ecology of restored ecosystems, but they have rarely been examined. In this study, we explore how rat eradication has affected the trophic ecology of native land crab communities. Using stable isotope analysis of rats and crabs, we demonstrate that the diet or trophic position of most crabs changed subsequent to rat eradication. Combined with the numerical recovery of two carnivorous land crab species (Geograpsus spp.), this led to a dramatic widening of the crab trophic niche following rat eradication. Given the established importance of land crabs in structuring island communities, particularly plants, this suggests an unappreciated mechanism by which rat eradication may alter island ecology. This study also demonstrates the potential for stable isotope analysis as a complementary monitoring tool to traditional techniques, with the potential to provide more nuanced assessments of the community- and ecosystem-wide effects of restoration.
Preliminary Analysis of Vector Routes and Selected Invasive Species for Pacific Island Countries and Territories
Available Online

Green, Wren

2004
Understanding vector routes for invasive species (i.e. the routes by which pest plants and animals move from place to place via human assistance) is a key element in global and national efforts to reduce risks and limit the further spread of invasive species. This report is divided into two main sections. The first section provides a quantitative analysis of air and sea movements between the countries and territories of the Pacific. The second section summarises information on eighty existing or potential invasive plants and animals to Pacific islands. While the GEF project with which this report is linked is limited to SPREP countries, the analysis also includes the territories of the region (with the exception of Pitcairn Island). This is essential since some territories are pivotal to understanding vector routes and transport ‘hubs’ in the region. For the same reason, flights from Pacific islands to Hawaii are included, as well as including Hawaii in the analysis of the selected invasive species. There is significant variability in the volume and patterns of ship movements and aircraft flights between the countries and territories of the Pacific, which is consistent with their diverse sizes, economies, exports, and political linkages. A few countries emerged as significant ‘hubs’ for sea and air transport within the region. (Refer to Tables 1 and 2 for summaries.) In the northern Pacific, Guam emerges as the “high risk” country, given its high levels of total merchant ship and oceanic fishing vessels as well as the largest number of weekly flights to other Pacific island countries (139) and to Asian destinations (148). In the central southern Pacific, Fiji is the major transport centre with a large volume of merchant shipping, cruise liners and itinerant yachts (585 yearly visits) and relatively high numbers of weekly flights both within and outside the region. To the east, French Polynesia has a smaller annual number of merchant ship visits, but when other shipping activity is included, as well as 26 weekly flights to the USA (including Hawaii) and more within the region, it emerges as an important vector route. (It already has a significant number of invasive species). Papua New Guinea and New Caledonia are important countries in the western Pacific for shipping volumes; New Caledonia also for visits by yachts (500/yr). Papua New Guinea has extensive air links with Australia, another source of tropical invasives, but very few within the Pacific. New Caledonia has a larger number of weekly flights than Papua New Guinea spread within the region, as well as to Asian, Australian and New Zealand destinations. The information in the second section on eighty invasive species provides evidence for the links between trade, travel and the distribution of invasives. Vector routes and methods of spread are identified. It also highlights the importance of early detection and eradication if Pacific countries are to be more effective at limiting the arrival and spread of invasive species.
Hurricane disturbance accelerates invasion by alien tree Pittosporum undulatum in Jamaican montane rain forests
Island and Ocean Ecosystems, BRB
Available Online

Bellingham, Peter J.

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Excurra, E.

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Healey, John R.

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Tanner, Edmund V. J.

2005
Questions: Do past disturbance, soil nutrients, or species diversity predict the invasion success of the alien tree Pittosporum undulatum in an island montane rain forest? What are the consequences of its invasion for forest composition and species diversity? Location: Blue Mountains, Jamaica. Methods: Censuses of trees ? 3 cm DBH in permanent plots in four sites within ca. 7 ha; 1974–2004 (intensive sites) and in 16 plots within 250 ha; 1990–2004 (extensive plots). Results: Pittosporum was unrecorded in the intensive sites before a severe hurricane in 1988: by 2004 all four sites were invaded. Pittosporum had invaded 25% of the extensive plots in 1990 and 69% in 2004, where its basal area increased from 0.5 ± 0.4 (SEM) m2.ha?1 in 1990 to 2.8 ± 1.3 m2.ha?1 in 2004. It had zero stem mortality and diameter growth rate exceeded that of native species fourfold. Pittosporum's basal area in the extensive plots in 2004 was positively related to the stand basal area damaged in the 1988 hurricane and negatively related to soil N concentrations. Pittosporum invasion was unrelated to stand-level tree species diversity in the extensive plots but as its basal area increased over time the basal area of native species and stand-level diversity declined. Conclusions: There are no obvious functional attributes of Pittosporum unrepresented in the native tree flora although it has high photosynthetic efficiency compared with native trees. More widespread invasion of these forests by Pittosporum seems inevitable since hurricanes, which accelerated the invasion, affect these forests frequently.
Funtional Roles of Invasive Non-indigenous Plants in Hurricane-Affected Subtropical Hardwood Forests
BRB
Available Online

Freedman, Andrea.

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Hoffstetter, Ronald H.

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Horvitz, Carol. C.

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McMann, Stephen.

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Pascarella, John B.

1998
Native forest species exhibit a well-known range of ecological roles with respect to natural disturbance regimes, from pioneer phase to mature phase, and they regenerate from a range of sources, including dormant seeds, seed rain, pre-established juveniles, and resprouts from damaged adults. In contrast, the ecological roles of invasive, non-indigenous species in forest communities after natural disturbances are not well understood. Some previous studies of invasive species have emphasized their weedy nature and their ability to colonize anthropogenic disturbances. Tropical hardwood hammock forest in southern Florida experience frequent disturbance by hurricanes. Our studies of forest regneration during two years following a recent severe hurricane suggest that invasive non-indigenous forest species exhibit the same range of ecological roles as native forest regeneration during two years following a recent severe hurricane suggest that invasive non-indigenous forest species exhibit the same range of ecological roles as native forest species and compete with native species for particular kinds of regeneration opportunities. To study ecological roles of non-indegenous species in regenerating forests after Hurricane Andrew, we set up four large study areas at each of three study sites that had differing amounts of hurricane-caused canopy disturbance. There were two pairs of 30 X 60 m research plots per site, and in each pair there was one control plot and one restoration plot; restoration areas were subject to an aggressive management program, focused on reducing non-indigenous vine cover. Within these study areas we subsampled vegetation in small study plots that were regularly spaced, and conducted vegetation censuses in April (the end of the dry season) and October (the end of the rainy season) for 2 yr, beginning in April 1993. We found that the source of regeneration for forest species was dependent upon the amount of canopy disturbance, the time since disturbance, and the autecology of the constituent species. Overall, 28% of the 90 species were non-indigenous: 34% of the vines (N=32) and 24% of other life-forms (N=58). Non-indigenous vines seemed to have a special role; not only could they compete with native vines, but they could also negatively affect the regeneration of other natives from a diverse array of sources including pre-established juveniles and resprouts from damaged adults. Both native and non-indigenous vine cover in unmanipulated study areas increased following the hurricane. Non-indigenous vine species had higher cover than native vine species, and many species formed dense "blankets." Non-indigenous species in general (not just vines) did not differ significantly from native species in seed mass, nor were they restricted to the pioneer type of life history. Many non-indigneous species had invaded forests prior to hurricane disturbance and had their own banks of pre-established juveniles; others recruited from dormant seeds, and seed rain, and/or respouts from pre-established adults. Based on information on source of regeneration and impact on native species, we propose a classification scheme for functional roles of non-indigenous invasive species in forests. To investigate whether non-indigenous taxa had roles in other geographic regions similar to those they had in Florida, we reviewed literature for 50 taxa belonging to genera that have species known to be invasive in southern Florida. We found that these taxa were invsive or had cogeners that were invsive in other geographic regions (Western Australis, the Mariana Islands, Hawaii, the rMascarene Islands, and South Africa). We propose that taxa predominantly retain their invasive, functional-role type across regions. Thus, studies of ecological roles of invasive species with respect to natural disturbance regimes in one region may help us predict invasive roles in other regions.