Invasive predators and global biodiversity loss

Abstract

Invasive species threaten biodiversity globally, and invasive mammalian predators are particularly damaging, having contributed to considerable species decline and extinction. We provide a global metaanalysis of these impacts and reveal their full extent. Invasive predators are implicated in 87 bird, 45 mammal, and 10 reptile species extinctions-58% of these groups' contemporary extinctions worldwide. These figures are likely underestimated because 23 critically endangered species that we assessed are classed as "possibly extinct." Invasive mammalian predators endanger a further 596 species at risk of extinction, with cats, rodents, dogs, and pigs threatening the most species overall. Species most at risk from predators have high evolutionary distinctiveness and inhabit insular environments. Invasive mammalian predators are therefore important drivers of irreversible loss of phylogenetic diversity worldwide. That most impacted species are insular indicates that management of invasive predators on islands should be a global conservation priority. Understanding and mitigating the impact of invasive mammalian predators is essential for reducing the rate of global biodiversity loss.I nvasive mammalian predators ("invasive predators" hereafter) are arguably the most damaging group of alien animal species for global biodiversity (1-3). Species such as cats (Felis catus), rats (Rattus rattus), mongoose (Herpestes auropunctatus), and stoats (Mustela erminea) threaten biodiversity through predation (4, 5), competition (6), disease transmission (7), and facilitation with other invasive species (8). The decline and extinction of native species due to invasive predators can have impacts that cascade throughout entire ecosystems (9). For example, predation by feral cats and red foxes (Vulpes vulpes) has led to the decline or extinction of two thirds of Australia's digging mammal species over the past 200 y (10, 11). Reduced disturbance to topsoil in the absence of digging mammals has led to impoverished landscapes where little organic matter accumulates and rates of seed germination are low (10). In the Aleutian archipelago, predation of seabirds by introduced Arctic foxes (Alopex lagopus) has lowered nutrient input and soil fertility, ultimately causing vegetation to transform from grasslands to dwarf shrub/forb-dominated systems (12).Mitigating the negative impacts of invasive mammalian predators is a primary goal of conservation agencies worldwide (1,13,14). Regardless, there remains no global synthesis of the role of invasive predators in species declines and extinctions (but see refs. 3 and 15). Here, we quantify the number of bird, mammal, and reptile species threatened by, or thought to have become extinct (since AD 1500) due to, invasive mammalian predators. We use metaanalysis to examine taxonomic and geographic trends in these impacts and show how the severity of predator impacts varies according to species endemicity and evolutionary distinctiveness. Results and DiscussionIn total, 596 threatened and 142 extinc...

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

“…Feral cats have been directly responsible for the extinction of numerous bird species (e.g. Doherty et al, 2016b), especially small and medium-sized flightless island bird species, generally considered highly vulnerable to introduced alien predators (Roots, 2006). Although the Kagu is within the size and weight ranges of feral cat prey , we hypothesize that the Kagu may have developed efficient defensive behavior (Hunt et al, 1996), which could explain why no cat predation was detected.…”

“…The greatly underestimated impact it faces from feral cats is therefore unacknowledged and disproportionate. Although feral cats are known to be among the most damaging species introduced to islands (Doherty et al, 2016b), their global impact on insular fauna has so far been underestimated due to the lack of studies on islands with high biodiversity value. This intensive assessment of the feral cat threat to New Caledonian biodiversity argues strongly for investigating the feral cat diet and impacts on other islands that harbor high biodiversity and endemism rates but where there have been few or no investigations, especially in the Pacific: Polynesian, Micronesian and Melanesian islands Nogales et al, 2013).…”

“…Feral cats are known to have contributed significantly to island vertebrate extinctions and declines worldwide (Doherty et al, 2016b;Medina et al, 2011;Woinarski et al, 2015). Understanding and reducing their impacts is thus considered essential for threatened and endemic species conservation; cat population management has generally involved reducing populations through lethal operations Russell et al, 2016).…”

“…Invasive species are considered the primary cause of island biodiversity loss (Clavero and Garcia-Berthou, 2005;Sax and Gaines, 2008;Tershy et al, 2015). Alien mammal predators have been responsible for most species extinctions on islands worldwide (Blackburn et al, 2004;Doherty et al, 2016b). The domestic cat (Felis catus), is one of the most widespread introduced predators on islands (Courchamp et al, 2003;Medina et al, 2011).…”

“…They currently threaten 430 different species (birds, mammals and reptiles) with extinction and are implicated in the recent extinction of 63 species (40 bird, 21 mammal and 2 reptile species), i.e. 26% of recent extinctions (Doherty et al, 2016b). Furthermore, Doherty et al (2015a) for Australia and adjacent islands and Bonnaud et al (2011) for the rest of the world's islands, listed 16 and 29 IUCN Red-listed threatened vertebrate species respectively, in the diets of feral cats.…”