Trophic roles of black rats and seabird impacts on tropical islands: Mesopredator release or hyperpredation?

Abstract

Corre. Trophic roles of black rats and seabird impacts on tropical islands: Mesopredator release or hyperpredation?. Biological Conservation, Elsevier, 2015Elsevier, , 185, pp.75-84. 10.1016Elsevier, /j.biocon.2014 a b s t r a c tRats contribute to the decline of tropical seabird populations by affecting their breeding success through direct predation of eggs and chicks. When they coexist with other predators, invasive rats may also generate indirect interactions via the changes they impose on the structure of communities and trophic interactions following invasion ('hyperpredation process'), or when apex predators are eradicated from the ecosystem ('mesopredator release effect'). Understanding these effects is necessary to implement restoration operations that actually benefit threatened seabird populations. We investigated these processes on two French tropical seabird islands of the western Indian Ocean, Europa and Juan de Nova, where black rats coexist with two different apex predator species (introduced cats and potentially native barn owls). The parallel use of several methods (diet analysis, stable isotopes, seabird monitoring) to identify trophic roles of rats revealed that the direct impact of rats on seabirds was particularly high on Europa where only rats and owls occur, with high consumption of chicks resulting in low breeding success for several seabird species. We also suggested that hyperpredation associated with top-down regulation of cats is occurring on Juan de Nova, although territoriality of cats may buffer this process. Conversely we found evidence that mesopredator release effect is unlikely, irrespective of the apex predator identity. Considering the most likely effects on both islands we provided recommendations on eradication priorities to mitigate the risk of local extinction that seabirds are currently facing.

Feral cats threaten the outstanding endemic fauna of the New Caledonia biodiversity hotspot

“…This abundant food resource can help sustain feral cat abundance at a high level, thereby exacerbating predation pressure on native wildlife via the "hyperpredation" process (Courchamp et al, 1999;Ringler et al, 2015). This result is consistent with the FO found by Bonnaud et al (2011) (44.05 ± 28.3, 55 studies) in their review of the cat diet on islands worldwide.…”

“…Introduced mammals (rodents and lagomorphs) generally constitute staple prey that can facilitate the establishment and expansion of abundant feral cat populations, indirectly increasing predation risk for native species through a so-called "hyperpredation" mechanism (e.g. Courchamp et al, 1999;Ringler et al, 2015).…”

Field data and worldwide literature review reveal that alien crayfish mitigate the predation impact of the American bullfrog on native amphibians

“…At the same time, introduced crayfish naturally adapted to predation by American bullfrogs, and with a high growth rate, may inflate L. catesbeianus numbers and consequently increase their impact on native amphibians (i.e. ‘hyperpredation’; Zavaleta et al, ); however, hyperpredation has been described for island ecosystems (Courchamp et al, ; Ringler, Russell, & Le Corre, ; Russell, ), but has rarely been described in freshwater environments (Ricciardi & MacIsaac, ; but see Pope, Garwood, Welsh, & Lawler, ).…”

Estimating Burdens of Neglected Tropical Zoonotic Diseases on Islands with Introduced Mammals

“…28 In particular, efficiency in public services such as solid waste management and access to waste disposal centers lead to decreased rodent population sizes, and decreased contact with commensal rodents and rodentborne pathogens. [29][30][31] This in turn may have a cascading effect on cat abundance through bottom-up processes, 32 and in consequence affect the environmental load of parasites like Toxoplasma gondii. 33,34 However, this pattern has only been studied in large metropolitan areas, and whether it persists at smaller population sizes is currently unknown.…”