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Predation of seabirds by invasive rats: multiple indirect consequences for invertebrate communities

TitlePredation of seabirds by invasive rats: multiple indirect consequences for invertebrate communities
Publication TypeJournal Article
Year of Publication2009
AuthorsTowns, DR, Wardle, DA, Mulder, CPH, Yeates, GW, Fitzgerald, BM, G. Parrish, R, Bellingham, PJ, Bonner, KI
JournalOikos
Volume118
Pagination420–430
Abstract

Invasive species are a global problem but most studies have focused on their direct rather than indirect ecological effects.We studied litter and soil-inhabiting invertebrate communities on 18 islands off northern New Zealand, to betterunderstand the indirect ecological consequences of rat (Rattus) invasion. Nine islands host high densities of burrowingprocellariid seabirds that transport large amounts of nutrients from the ocean to the land. The other nine have beeninvaded over the past 50150 years by rat species that have severely reduced the density of seabirds by preying on eggs andchicks. Invaded islands had lower densities of seabird burrows but deeper forest litter than did the uninvaded islands,indicative of rats reducing disturbance effects of seabirds. However, despite deeper litter on the invaded islands, eight ofthe 19 orders of invertebrates that we measured were significantly less abundant on invaded islands. Furthermore, threesoil-inhabiting micro-invertebrate groups that we measured were significantly less abundant on invaded islands. Thesedifferences probably result from rats thwarting transfer of resources by seabirds from the ocean to the land. We alsoinvestigated community-level properties of each of three test groups of invertebrates (minute land snails, spiders and soilnematodes) to illustrate this process. Spiders were equally abundant on both groups of islands, but showed lower speciesrichness on the invaded islands. The other two groups showed no difference in species richness with island invasion status,but were more abundant on uninvaded islands. Reduced abundance of soil nematodes on invaded islands provides strongevidence of indirect consequences of seabird reduction by rats, because nematodes are unavailable to rats as prey. Wepredict that if rats are eradicated from islands, components of below-ground invertebrate dependent on seabird-mediatedsoil conditions may take considerable time to recover because they require subsequent seabird recolonisation.

DOI10.1111/j.1600-0706.2008.17186.x
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