Impacts of introduced species on the biota of an oceanic archipelago: the relative importance of competitive and trophic interactions

Abstract

Introduced species negatively impact native species through competitive and trophic interactions, particularly on oceanic islands that have never been connected to any continental landmass. However, there are few studies on the relative importance of competitive interactions (resource competition with introduced species) and trophic interactions (predation or herbivory by introduced species) with respect to the negative impacts on native organisms on oceanic islands. A literature review on introduced and native species of the oceanic Ogasawara (Bonin) Islands in the western Pacific Ocean indicated that many native species (e.g., bees, beetles, damselflies, butterflies, land snails, birds, and plants) have been negatively impacted by introduced predators and herbivores (e.g., lizards, rats, flatworms, and goats). Several native plants and bees have been negatively affected by introduced competitors. However, the native species that have competed with introduced species have also suffered from either intense herbivory or predation by other introduced species. Thus, introduced predators and herbivores have had greater impacts on native species than introduced competitors in the Ogasawara Islands.

Massively Introduced Managed Species and Their Consequences for Plant–Pollinator Interactions

“…Species communities on islands are usually fragile and sensitive to introductions and invasions (Kaiser-Bunbury et al, 2010, see also Massol et al, 2017). The reported cases of native species extinctions after introduction of alien species on islands are usually due to predation or pathogens rather than exploitative competition (Sax and Gaines, 2008;Sugiura, 2016). Still, exploitative competition with introduced species can reduce the fitness and lead to local extinctions of the native island species, including bees (Sugiura, 2016).…”

“…The reported cases of native species extinctions after introduction of alien species on islands are usually due to predation or pathogens rather than exploitative competition (Sax and Gaines, 2008;Sugiura, 2016). Still, exploitative competition with introduced species can reduce the fitness and lead to local extinctions of the native island species, including bees (Sugiura, 2016). Several cases of exploitative competition for floral resources have been evidenced or suspected in oceanic island systems of various sizes.…”

Fates of Rare Species under Siege from Invasion: Persistence of Coccinella novemnotata Herbst in Western North America alongside an Invasive Congener

“…One major, continuing concern is that invasive species are a key cause of loss of biodiversity in threatening native species with extinction (Elton, 1958;Wilson, 1992;Wilcove et al, 1998). Reduced population sizes and, in the extreme, extinctions within many groups of native species appear most often caused by invasive species through interactions across trophic levels, such as predation, herbivory and disease, with interspecific competition playing a lesser and less clear role (Davis, 2003;Sax et al, 2007;Kraus, 2015;Sugiura, 2016). Insects and arachnids may be noteworthy exceptions in this regard, however, as Gao and Reitz (2017) review many examples of competitive displacement (p. 166: "elimination of one species by another with the same ecological niche").…”

Functional compensation by insular scavengers: the relative contributions of vertebrates and invertebrates vary among islands

“…In addition, introduced raccoon dogs are abundant on a small island of the Oki Islands (Ohdachi et al 2015). Because introduced mammals negatively impact insular communities and ecosystem functions (Courchamp et al 2003, Blackburn et al 2004, Sugiura 2016, these raccoon dogs may affect the scavengers' functions on the island. Thus, investigating ecosystem function in areas with introduced raccoon dogs may help elucidate how introduced species affect the functions of scavengers.…”