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.

Keywords: extinction; feral cat; invasive mammal; island; trophic cascade.

Fig. 1.

Model-estimated severity of impact of invasive predators on birds, mammals, and reptiles for all species combined (Total), insular endemics (Insular), and species found on continents (Continental). Error bars are 90% confidence intervals. Model estimates and confidence intervals are weighted by the strength of evidence available. See Table S5 for model estimates.

Fig. 2.

Numbers of threatened and extinct bird (B), mammal (M), and reptile (R) species negatively affected by invasive mammalian predators. Gray bars are the total number of extinct and threatened species, and red bars are extinct species (including those classed as extinct in the wild). Predators affecting <15 species are not shown here. Predators (L to R) are the cat, rodents, dog, pig, small Indian mongoose, red fox, and stoat.

Fig. 3.

Severity of model-estimated impacts of invasive predator species on birds, mammals, and reptiles. Error bars are 90% confidence intervals. Model estimates and confidence intervals are weighted by the strength of evidence available. See Table S5 for model estimates. To aid visual interpretation across all estimates, the error bars for the effects of pigs and stoats on mammals are truncated at the limits of the y axis, but the values can be found in Table S5.

Fig. 4.

Numbers of threatened and extinct bird, mammal, and reptile species impacted by invasive predators in 17 regions (Fig. S3 and Table S2). Gray bars represent the total number of extinct and threatened species, and red bars represent the number of extinct species (including those classed as extinct in the wild). StH, Asc, and TdC indicate the islands of St. Helena, Ascension, and Tristan da Cunha, respectively.

Fig. S1.

Model-estimated severity of impact of invasive predators on birds, mammals, and reptiles for all species combined (Total), insular endemics (Insular), and species found on continents (Continental) with Australia reclassified as insular instead of continental. Error bars are 90% confidence intervals. Model estimates and confidence intervals are weighted by the strength of evidence available.

Fig. S2.

Mean evolutionary distinctiveness scores for extant threatened birds and mammals. Impacted, identified as being negatively affected by invasive predators (Dataset S1); Nonimpacted, not identified as being negatively affected by invasive predators. Error bars are SEs.

Fig. S3.

Classification of regions (Table S2).

Fig. S4.

Comparison of weighted and unweighted model-estimated severity of impact of invasive predators on birds, mammals, and reptiles for all species combined (Total), insular endemics (Insular), and species found on continents (Continental). Error bars are 90% confidence intervals.

Fig. S5.

Influence of different impact-ranking values on the model-estimated severity of impact of invasive predators on birds, mammals, and reptiles for all species combined (Total), insular endemics (Insular), and species found on continents (Continental). Error bars are 90% confidence intervals.