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Significance Invasive mammalian predators are arguably the most damaging group of alien animal species for global biodiversity. Thirty species of invasive predator are implicated in the extinction or endangerment of 738 vertebrate species—collectively contributing to 58% of all bird, mammal, and reptile extinctions. Cats, rodents, dogs, and pigs have the most pervasive impacts, and endemic island faunas are most vulnerable to invasive predators. 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.
Invasive predators and global biodiversity loss
Tim S. Doherty
, Alistair S. Glen
, Dale G. Nimmo
, Euan G. Ritchie
, and Chris R. Dickman
Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Geelong, VIC 3216, Australia;
Centre for Ecosystem
Management, School of Natural Sciences, Edith Cowan University, Joondalup, WA 6027, Australia;
Landcare Research, Auckland 1072, New Zealand;
Institute for Land, Water and Society, School of Environmental Science, Charles Sturt University, Albury, NSW 2640, Australia; and
Desert Ecology
Research Group, School of Life and Environmental Sciences, University of Sydney, Sydney, NSW 2006, Australia
Edited by Daniel S. Simberloff, The University of Tennessee, Knoxville, TN, and approved July 20, 2016 (received for review February 12, 2016)
Invasive species threaten biodiversity globally, and invasive mam-
malian 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 extinctions58% of these groupscontemporary extinc-
tions worldwide. These figures are likely underestimated because
23 critically endangered species that we assessed are classed as
possibly extinct.Invasive mammalian predators endanger a fur-
ther 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.
feral cat
invasive mammal
trophic cascade
Invasive mammalian predators (invasive predatorshereafter)
are arguably the most damaging group of alien animal species
for global biodiversity (13). 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, pre-
dation by feral cats and red foxes (Vulpes vulpes) has led to the
decline or extinction of two thirds of Australias 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, pre-
dation of seabirds by introduced Arctic foxes (Alopex lagopus)has
lowered nutrient input and soil fertility, ultimately causing vege-
tation to transform from grasslands to dwarf shrub/forb-dominated
systems (12).
Mitigating the negative impacts of invasive mammalian pred-
ators 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
Results and Discussion
In total, 596 threatened and 142 extinct species (total 738) have
suffered negative impacts from 30 species of invasive mammalian
predators from 13 families and eight orders. These species
include three canids, seven mustelids, five rodents, two procyo-
nids, three viverrids, two primates, two marsupials, two mon-
gooses, and single representatives from four other families, with
60% from the order Carnivora (Table S1). The 738 impacted
species consist of 400 bird species from 78 families, 189 mammal
species from 45 families, and 149 reptile species from 26 families
(Dataset S1). Invasive mammalian predators emerge as causal
factors in the extinction of 87 bird, 45 mammal, and 10 reptile
species, which equates to 58% of modern bird, mammal, and reptile
species extinctions globally (including those species classed as ex-
tinct in the wild). Invasive predators also threaten 596 species
classed as vulnerable(217 species), endangered(223), or criti-
cally endangered(156), of which 23 are classed as possibly extinct.
To assess the comparative severity of predator impacts, we
assigned each of 1,439 predator-threatened species cases a value
of either 0.25 (secondary cause of species decline), 0.75 (primary
cause of species decline), or 1.0 (species extinction attributed to
the predator), and we weighted these values by the strength of
evidence available, drawing on a total of 996 supporting references
(Methods). The severity of predator impacts and the strength of
evidence supporting them [the inverse of the width of confidence
intervals (CIs)] was higher for bird and mammal species compared
with reptile species (Fig. 1).
Rodents are linked to the extinction of 75 species (52 bird, 21
mammal, and 2 reptile species; 30% of all extinctions) and cats
to 63 extinctions (40, 21, and 2 species, respectively; 26%)
whereas red foxes, dogs (Canis familiaris), pigs (Sus scrofa), and
small Indian mongoose (H. auropunctatus) are implicated in 911
extinctions each (Fig. 2). For all threatened and extinct species
combined, cats and rodents threaten similar numbers of species
(430 and 420 species, respectively), followed by dogs (156 spe-
cies), pigs (140 species), mongoose (83 species), red foxes (48
species), stoats (30 species) (Fig. 2), and the remaining predators
Invasive mammalian predators are arguably the most damag-
ing group of alien animal species for global biodiversity. Thirty
species of invasive predator are implicated in the extinction or
endangerment of 738 vertebrate speciescollectively contrib-
uting to 58% of all bird, mammal, and reptile extinctions. Cats,
rodents, dogs, and pigs have the most pervasive impacts, and
endemic island faunas are most vulnerable to invasive preda-
tors. 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 re-
ducing the rate of global biodiversity loss.
Author contributions: T.S.D., A.S.G., D.G.N., E.G.R., and C.R.D. designed research; T.S.D.
and A.S.G. performed research; T.S.D. analyzed data; and T.S.D., A.S.G., D.G.N., E.G.R., and
C.R.D. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
To whom correspondence should be addressed. Email:
This article contains supporting information online at
1073/pnas.1602480113/-/DCSupplemental. PNAS Early Edition
(range 114 species). The lower number of species impacted by
some predators, such as red foxes and stoats, reflects the limited
number of locations in which these predators have established
alien populations (16). The frequency of impacted species in each
taxonomic class differed among predators (χ
=112.27, P<
0.001). Cats, rodents, and stoats threaten more bird than mammal
or reptile species whereas red foxes threaten more mammal
species (Fig. 2). Dogs threaten fewer reptile species, and pigs and
mongoose threaten fewer mammal species, compared with other
taxonomic classes (Fig. 2). Although cats and rodents negatively
affect the most bird species, birds experience similar impact
across predator species (Fig. 3). Mammals experience lower, but
more variable, impacts from pigs and stoats compared with the
other predators (Fig. 3). The greatest impact on reptile species is
from stoats, and the lowest from foxes (no impact) and pigs (Fig.
3). The significanceof differing relationships between invasive
predators and impacted species classes is uncertain, however,
because confidence intervals overlapped in most cases.
Central America (including the Caribbean) has experienced
the most extinctions (33 species), followed by Micro-/Mela-/
Polynesia (25), Australia (21), the Madagascar region (20), New
Zealand (15), and Hawaii (11), with the remaining regions having
07 species extinctions each (Fig. 4). The taxonomy of impacted
species varied among regions, with the highest numbers of im-
pacted mammal species occurring in Australia and Central
America, and most of the impacted reptile species occurring in
Micro-/Mela-/Polynesia and Central America (Fig. 4). Most im-
pacted bird species are in Micro-/Mela-/Polynesia, New Zealand,
the Madagascar region, Central America, and Hawaii (Fig. 4).
Insular endemics accounted for 87% of extinct species (124
species) and 81% of the sum of all threatened/extinct species
(601 species). The proportions of total threatened/extinct species
that were insular endemics varied between taxonomic classes
=117.29, P<0.001; birds 90%, mammals 55%, reptiles
91%). Insular endemic reptile species were more negatively af-
fected by invasive mammalian predators than continental species,
whereas mammal and bird species experienced similar impacts
between the two groups (Fig. 1). If Australia is reclassified as an
island, insular endemic mammals experience more severe predator
impacts than continental species (Fig. S1). We sourced evolu-
tionary distinctiveness scores from published databases (Methods)
to show that species negatively affected by invasive predators were
more evolutionarily distinct than nonimpactedspecies for both
bird (t=3.32, P=0.001) and mammal species (t=3.31, P=0.001)
(Fig. S2).
Although it is often stated that invasive predators have con-
tributed to many modern extinctions (1, 2, 11, 17), our findings
reveal the magnitude and pervasiveness of their impacts and link
them to the majority (58%) of modern bird, mammal, and reptile
species extinctions. This figure is likely an underestimate because
23 critically endangered species negatively affected by invasive
predators are currently classed as possibly extinct. Evolutionarily
distinct species are most affected, meaning that invasive preda-
tors are drivers of irreversible loss of global phylogenetic di-
versity, affecting both mainland and island-endemic species.
Introduced rodents and cats are major agents of extinction,
collectively being listed as causal factors in 44% of modern bird,
mammal, and reptile species extinctions. We pooled the impacts
of rodents across five species, but previous studies indicate that
R. rattus has negatively affected the most species, followed by
Rattus norvegicus and Rattus exulans (1820). The role of the
house mouse (Mus musculus) is less well understood, but there is
emerging evidence of severe predatory impacts on insular sea-
bird (21) and lizard species (22). We found that cats, rodents,
dogs, and pigs have had the most pervasive effects across regions
and taxonomic classes, supporting recent work by Bellard et al.
(3), who identified these four taxa as the invasive species af-
fecting the greatest number of threatened vertebrates globally,
after chytrid fungus (Batrachochytrium dendrobatidis). However,
other predators have had large impacts in particular regions;
stoats remain a major threat to New Zealand bird and reptile
species (23), and the red fox, along with the feral cat, is an im-
portant driver of Australian mammal species extinctions (11).
Fewer reptile species were negatively affected by invasive
mammalian predators, compared with bird and mammal species.
Reptiles also had a lower average impact score, which may be
because reptiles are less studied than birds and mammals (9),
with only 40% of the worlds reptiles having been assessed for the
Red List thus far (compared with 99% for birds and mammals)
(24). Further insights will likely emerge once the conservation
status of most reptiles has been determined. Detailed studies
from individual regions nonetheless demonstrate that invasive
predators can have severe impacts on local reptile assemblages
Birds Mammals Reptiles
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.
Number of extinct
and threatened species
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.
| Doherty et al.
(e.g., ref. 25). Evolutionary exposure to native mammalian
predators might moderate such effects; few Australian reptiles
are threatened by cat and fox predation whereas more than 100
reptile species in the Caribbean/Central America and Micro-/
Mela-/Polynesia are threatened with extinction by rodents, cats,
pigs, dogs, and mongoose (25, 26).
Insular regions are most affected by invasive predators, and
insular endemic reptile species, but not bird and mammal species,
are more heavily affected than continental species. This last
finding contrasts with Blackburn et al. (13), who reported such an
effect for birds, as did Medina et al. (1) for all three taxonomic
classes. The difference in our results could arise because both
previous studies assessed insular species only and used individual
populations (species ×island) as the experimental unit whereas
we assessed all species across their entire geographic ranges. The
isolation of many islands and a lack of natural predators mean
that insular species often lack appropriate defensive traits, thus
making them naive to the threat of invasive predators (9, 27). The
high extinction rates of ground-dwelling birds in Hawaii (28) and
New Zealand (29)both of which lack native mammalian
predatorsare cases in point.
That most impacted species are insular indicates that man-
agement of invasive predators on islands should be a global
conservation priority. Given the many islands on which invasive
predators occur and the high costs involved in controlling or
eradicating them, prioritization of islands for eradications is an
important exercise (3033). Facilitation between multiple in-
vasive species (e.g., rodents providing abundant food for cats,
thus maintaining high densities of the latter) can exacerbate their
respective impacts on native species (1, 9). Thus, it is essential
that eradications adopt a whole-ecosystem approach to avoid the
ecological release of undesirable species (5, 34). Modeling can
help determine the order in which multiple species should be
eradicated (35) and how best to allocate resources (36). On
continents or large islands where eradications are difficult, al-
ternative approaches are needed, such as predator-proof fencing
(37), improved land management (38, 39), restoration of top
predators (40, 41), and lethal control (42).
Although we have documented the comparative severity of
impacts of invasive mammalian predators, we note that the
strength of evidence available to quantify predator impacts was
often low (Dataset S1), particularly for reptile species. While
invasive predators are named as causal factors in large numbers
Galapagos South
StH, Asc, TdC
Amsterdam &
St Paul Islands
Number of extinct species
Total number of extinct and threatened species
SE Asia
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 extinctinthe
wild). StH, Asc, and TdC indicate the islands of St. Helena, Ascension, and Tristan da Cunha, respectively.
Birds Mammals Reptiles
Model-estimated impact
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 yaxis, but the values can be found in Table S5.
Doherty et al. PNAS Early Edition
of extinctions and as key threats to many threatened species, the
lack of strong evidence suggests that there remains an urgent
need for research on the impacts of invasive predators relative to
other threats (e.g., habitat loss). Teasing apart the impacts of
different threatening processes is challenging for extinct species
and for those that have suffered historical declines, have small
populations, and/or inhabit remote islands but should be more
feasible for many other threatened species. Understanding and
mitigating the impact of invasive mammalian predators is es-
sential for reducing the rate of global biodiversity loss.
Data Collation. For all threatened species in the taxonomic classes Aves,
Mammalia, and Reptilia, we downloaded data on taxonomy and conserva-
tion status from the International Union for Conservation of Nature and
Natural Resources (IUCN) Red List in December 2014 (version 2014.3) using
the inbuilt search and export functions (n=3,745 species) (Dataset S2). We
did not assess amphibians here because our preliminary research indicated
that the invasive predators impacting them are mostly nonmammalian (e.g.,
snakes, fish, crayfish, and other amphibians). Threatened species were those
listed as vulnerable, endangered, critically endangered, extinct, or extinct in
the wild. We then used a custom R script (Dataset S3) to download addi-
tional Red List information on each speciesrange and major threats.
We filteredthis database (n=3,745 species) in Microsoft Accessby searching
the major threatssection for any of the following keywords: predator*,
predation, cat, cats, fox*, dog, dogs, rat, rats, rodent*, Rattus,mouse,mice,
stoat*, mongoose*, pig, pigs, mink, ferret*, weasel*, mustelid*, possum*,
macaque*, coati*, and civet*. These predators were chosen based on consul-
tation of the Global Invasive Species Database (43) and Long (16). This search
returned 771 records, which we inspected to determine whether invasive alien
predators were identified as a known or likely threat to each species (n=703
species identified as negatively impacted by invasive predators). We cross-
checked this list against previous reviews (1, 18, 20, 4448) and added 35 ad-
ditional threatened species recorded as being negatively affected by invasive
predators, but not revealed in our Red List search. Given the small number of
additional species identified and the broad geographic coverage of the pre-
vious studies used for cross-checking, we do not consider that this exercise
brings any systematic bias to our analyses.
For each of the 738 study species, we recorded information on taxonomic
classification (class, order, family), Red List status, insularity (insular endemic
or found on continents also), and region (Fig. S3 and Table S2). Information
on species distributions was sourced primarily from the Red List although
other sources were consulted in a small number of cases. For the analyses,
we included in the extinct category four species classed as extinct in the wild.
To find information on the impact of invasive predators on each of the
study species, we initially searched the Red List and Scopus database for
relevant material using species names and synonyms, followed by consul-
tation of primary and gray literature cited therein. We defined impact as any
inference that an invasive predator had caused a decline in the abundance or
distribution of a species. In most cases, predation was inferred as the primary
mechanism of predator impacts although competition, disease transmission,
and habitat disturbance were also cited in some cases. For accounts that
referred only to introduced/invasive predatorsand not a specific species,
we assigned the impact to a generic predator group. We took any reference
to domestic predators/carnivores/petsto mean cats (F. catus) and dogs
(C. familiaris). We did not distinguish the impacts of individual rodent species
because many accounts did not provide sufficient information to allow dis-
crimination of individual species effects and because the relative impacts of
the different rodent species have been reviewed elsewhere (1820, 49, 50).
Given the difficulties in attributing causation in species declines and ex-
tinctions, most inferences regarding the impact of invasive predators were
based on observational evidence, rather than experimental data. For this
reason, we used a similarapproach to that of previous studies(1, 19) and coded
the degree of predator impacts as follows: mixed (0.25, when the predator
was a secondary cause of species decline); high (0.75, when the predator was a
primary cause of species decline); and strong (1.0, when the extinction of the
species was attributed to the predator). Unlike previous studies (1, 19), how-
ever, we did not include a nil impactlevel (e.g., 0.01) because such in-
formation is not systematically reported in the literature. Other threats may
have contributed to the speciesdeclines/extinctions although assessing their
relative importance was beyond the scope of this study. We assessed species
across their entire geographic ranges and thus did not code predator impacts
for individual populations (e.g., multiple islands). This exercise was con-
ducted between March and September 2015, and it revealed 1,381 individual
predator-threatened species cases, plus an additional 58 cases where the
predator species were not named. The 996 references supporting the
rankings are listed in Dataset S4.
Statistical Analyses. We first summarized numbers of extinct and threatened
species impacted by invasive predators, based on taxonomic classes and
geographic regions where they occur, or occurred. We then used meta-
analysis in the metafor package version 1.9-6 in R version 3.1.2 (51, 52) to
analyze these trends based on three categorical variables: (i) taxonomic class
model (levels: Aves, Mammalia, Reptilia); (ii ) insularity model [levels: insular
endemic, or continental (either wholly or partially)]; and (iii) predator model
[levels: rodent (Rodentia), cat, dog, red fox (V. vulpes), stoat (M. erminea),
small Indian mongoose (H. auropunctatus), and pig (S. scrofa)].
For the predator model, we excluded 19 predator species that impacted
fewer than 15 threatened species each (range 30430 threatened species
impacted by each of the seven remaining predators). We conducted separate
tests for each of these variables using the restricted maximum-likelihood
estimator. We pooled impacts across all predators for the taxonomic class
and insularity models; if a threatened species was impacted by multiple
predators, we used the highest impact and its associated weight. For ex-
ample, if a bird species was impacted by both cats (impact =0.75, weight =
10) and rodents (impact =0.25, weight =100), we used the former pair of
values for the pooled category, which means that the models estimate the
strongest predator impacts across taxonomic classes and insularity. To ex-
amine individual responses of the three taxonomic classes, we conducted
separate analyses for birds, mammals, and reptiles across insular endemism
and predators. The response variable was the impact rankings described
above, such that higher effect sizes represented greater predator impacts.
We inferred significanteffects where the 90% confidence intervals of the
different predictor variable levels did not overlap. Data used in the analyses
are available as Dataset S1 (see also Table S3).
Metaanalysis traditionally weights effect sizes based on each studys
sample variance and/or size. However, these data do not exist for our da-
tabase because each case consists of a predator ×threatened species com-
bination that is assigned a categorical level of impact. Instead, we used a
weighting system similar to that of Jones et al. (19) and Medina et al. (1) that
weights individual cases based on the type and strength of evidence pro-
vided in each case. Assigned weights were as follows: 1 (lowest: no evidence
provided apart from stating that the predator is thought to be a cause of
species decline or extinction), 10 (single line of correlative evidence), 100
(multiple lines of correlative evidence), or 1,000 (highest: experimental evi-
dence in a beforeafter and/or controlimpact design). We used the inverse
of the weights as the variance component in the metaanalysis. Examples of
correlative evidence included artificial nest experiments, correlation be-
tween species decline and predator introduction, absence of a species from
parts of its historical range now inhabited by predators, monitoring of
predation events, and analysis of predator diet. Examples of experimental
evidence included monitoring of population parameters in response to
predator removal, and comparison of islands with and without predators.
The weights were assigned during the impact ranking exercise described
above. We conducted a fail-safe analysis to determine the number of cases
showing no effect that would be needed to eliminate a significant overall
effect size (SI Text). We also conducted a sensitivity analysis to determine
how the selection of impact values and the use of weights influenced the
results (SI Text and Figs. S4 and S5).
We used χ
analyses to determine (i) whether the proportion of impacted
species that were insular endemics varied among taxonomic classes and (ii )
whether the proportion of impacted species in each taxonomic class differed
among predators. We restricted the second analysis to those seven predators
included in the predator model described above. Significant effects were
inferred at the 0.05 level.
Evolutionary Distinctiveness. We used evolutionary distinctiveness (ED) scores
to examine whether invasive predators have had a disproportionate impact
on evolutionarily distinct species. ED scores were calculated based on the fair
proportionmetric: i.e., the weighted sum of branch lengths along phylo-
genetic tree roots to tips, with weights based on the number of tips sharing
that branch (see refs. 5355 for detailed descriptions). This analysis was re-
stricted to extant birds (53) and mammals (54, 55) because data limitations
currently prevent ED scores being calculated for reptiles and extinct taxa
from all classes. We used general linear models to compare the ED scores of
the impacted species against threatened species for which invasive predators
were not identified as a threat (nonimpactedspecies hereafter). We used
a gamma error distribution because the data were positive, continuous,
and skewed. Significant effects were inferred at the 0.05 level. Taxonomic
| Doherty et al.
differences between the Red List version 2014.3 and the source databases
(53, 55) are detailed in Table S4. Because ED scores were not available for
extinct species, the values presented here are likely to be an underestimate
of the true effect sizes.
ACKNOWLEDGMENTS. The IUCN and its many contributors are acknowl-
edged for maintaining the Red List, which provided information on species
taxonomy, sta tus, threats, and range. Grant Williamson is thanked for
writing and testing the custom R script. Comments from Corey Bradshaw,
Chris Johnson, and three anonymous reviewers greatly improved earlier
versions of this manuscript. T.S.D. was supported by scholarships from Edith
Cowan University and Earthwatch Institute Australia during the initial stages
of this study, and C.R.D. by a fellowship from the Australian Research
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Doherty et al. PNAS Early Edition
... Anthropogenic disturbances represent increasingly pervasive threats to native fauna [1][2][3][4][5][6]. One of the most prominent drivers of biodiversity loss and homogenization is the introduction and establishment of invasive species [7,8]. Many domestic animals of non-native taxa serve as human-subsidized predators and cause substantial wildlife mortality annually [9][10][11][12]. ...
... Domestic dogs (Canis lupus familiaris) in particular, including owned and feral, threaten a wide variety of species globally [13][14][15][16][17][18][19][20][21][22][23][24][25][26]. These canids have become a notable and ubiquitous conservation challenge, ranking just below cats and rats as the third most-damaging invasive predator [8]. ...
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Human-introduced predators, primarily the domestic dog (Canis lupus familiaris), and human-modified landscapes conjointly threaten wildlife across Costa Rica. For arboreal species, including the two-fingered sloth (Choloepus hoffmani), the impact of domestic dogs is amplified in areas of habitat fragmentation. In efforts to navigate discontinuous canopies associated with urban development and human encroachment, C. hoffmani is forced to utilize terrestrial locomotion. This unnatural behavior leaves sloths increasingly vulnerable to predation by domestic dogs, which occupy altered landscapes in high densities. In this report, we detail the ante and postmortem findings associated with C. hoffmani following an extensive attack by three large-breed dogs. The patient sustained severe and fatal polytraumatic injuries targeting the abdominothoracic region. Gross lesions were not readily evident, obscured by unique anatomical characteristics of the species. This report aims to highlight the threat imposed by dogs to sloths and the severity of injuries, with considerations for clinical management in light of C. hoffmani morphology. We review the scope of domestic dog–wildlife conflict in Costa Rica, and propose collaborative mitigation strategies including habitat preservation, domestic dog population control, installation of wildlife corridors, policy initiatives, and dog owner education and public outreach.
... These invasive species not only cause harm to agriculture, economies, and ecosystems but also pose a threat to human health [3][4][5]. Invasive species have a strong ability to spread under different environmental conditions, and that spread may threaten biodiversity, lead to the extinction of local species, and drastically change local ecosystems [6][7][8][9]. When invasive species are introduced to a new area, their niche may change due to a lack of natural enemies or due to adaptations motivated by local conditions [10][11][12]. ...
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Determining whether the climatic ecological niche of an invasive alien plant is similar to that of the niche occupied by its native population (ecological niche conservatism) is essential for predicting the plant invasion process. Ragweed (Ambrosia artemisiifolia L.) usually poses serious threats to human health, agriculture, and ecosystems within its newly occupied range. We calculated the overlap, stability, unfilling, and expansion of ragweed’s climatic ecological niche using principal component analysis and performed ecological niche hypothesis testing. The current and potential distribution of A. artemisiifolia was mapped by ecological niche models to identify areas in China with the highest potential risk of A. artemisiifolia invasion. The high ecological niche stability indicates that A. artemisiifolia is ecologically conservative during the invasion. Ecological niche expansion (expansion = 0.407) occurred only in South America. In addition, the difference between the climatic and native niches of the invasive populations is mainly the result of unpopulated niches. The ecological niche model suggests that southwest China, which has not been invaded by A. artemisiifolia, faces an elevated risk of invasion. Although A. artemisiifolia occupies a climatic niche distinct from native populations, the climatic niche of the invasive population is only a subset of the native niche. The difference in climatic conditions is the main factor leading to the ecological niche expansion of A. artemisiifolia during the invasion. Additionally, human activities play a substantial role in the expansion of A. artemisiifolia. Alterations in the A. artemisiifolia niche would help explain why this species is so invasive in China.
... Cats (Felis catus) pose a considerable ongoing threat to wildlife in Australia (Woinarski et al., 2015(Woinarski et al., , 2019 and globally (Doherty et al., 2016) through predation, competition and disease transmission (Medway, 2004;Nishimura et al., 1999;Phillips et al., 2007). Across Australia, the predation impacts of feral cats are thought to be greatest in areas with sparse groundlayer vegetation cover (Lawes et al., 2015). ...
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Predation by feral cats (Felis catus) has caused the extinction of many native species in Australia and globally. There is growing evidence that the impacts of feral cats can be amplified in post‐fire environments, as cats are drawn to hunt in or around recently burnt areas and are also more effective hunters in open habitats. In 2018–2019, we established arrays of camera traps to estimate the abundance of feral cats on Kangaroo Island, South Australia. Much of the island (including five of our seven survey sites) was subsequently burnt in a severe wildfire (December 2019–February 2020). We re‐sampled the sites 3–8 months post‐fire (seven sites) and 11–12 months post‐fire (three sites). At two unburnt sites sampled post‐fire, it was possible to produce density estimates of cats using a spatially explicit capture–recapture approach. Where estimating density was not possible (due to low detections or individual cats not being distinguishable), the number of individuals and percentage of trap nights with detections was compared between the sampling periods. Some low‐level cat control occurred within 2 km of three of the seven arrays (all within the burn scar) within 3 months of the fire. Across the five burnt sites, there was a decline in cat detections post‐fire (including those without post‐fire cat control). At 3–8 months post‐fire, there was, on average, a 57% reduction in the number of individual cats, and a 65% reduction in the number of nights with cat detections, relative to pre‐fire levels. Although cat detections declined following the fire, reduced population sizes of prey species and reduced cover as a result of the fire might still mean that cat predation is a threat to some surviving prey species. Management that reduces feral cat predation pressure on wildlife following wildfire should enhance the likelihood of post‐fire wildlife persistence and recovery. We examined the impact of a large, high‐severity fire on the abundance and detection of the feral cat on a temperate southern Australian island. The abundance and activity of the cat declined markedly following fire. Despite post‐fire reductions in feral cat populations, the species is likely to pose a considerable threat to the survival of native species.
... Predatory invasive species have been identified as a major driver of species extinctions, with invasive predatory mammals implicated in the extinction or endangerment of 738 vertebrate species (Doherty et al. 2016). In freshwaters, invasive piscivorous fishes are a key driver of fish diversity loss (Britton 2022). ...
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Freshwater ecosystems are highly vulnerable to the detrimental impacts of both biological invasions and climate change. Piscivorous alien fishes drive populations of small-bodied native fishes to extinction and warming is already driving extreme temperature events in lakes and rivers globally. Here, we use Ecological Niche Modelling (ENM) to predict how climate change will alter the geographical space of six alien fishes and five native fish genera (which include multiple endemic species) in Turkey, a hotspot of freshwater fish diversity. The models predicted that the geographical space of the alien fishes already present in Turkey would generally increase (including pikeperch Sander lucioperca and perch Perca fluviatilis), but with the most substantial increases in largemouth bass Micropterus salmoides, a species not yet present in Turkey but that is invasive in countries nearby and is highly popular for sport angling. For the native fish genera, general predictions were for reduced geographical space, especially in the south and east of the country, suggesting the endemic species will become increasingly imperilled in future. Their populations will also be at increasing risk of deleterious impacts from the alien piscivores, as the predictions were also for increasing overlaps in the geographical space of both the alien fishes and native fish genera. These predictions suggest that the conservation of these endemic species need to consider measures on preventing both the introduction of alien species (e.g. largemouth bass) and the further dispersal of extant alien species (e.g. pikeperch), as well as habitat interventions that will limit the effects of climate change on their populations. These results also indicate that the combination of climate change and alien invasions could have substantial impacts on-and similar-hotspots of freshwater diversity.
... Invasive species are considered among the most significant threats to global biodiversity (Bellard et al. 2016a;Pyšek et al. 2020), with invasive mammalian predators being the most damaging group of alien animal species (Bellard et al. 2016b). Through competition (Smith and Banks 2014), predation (Doherty et al. 2016), disease transmission (Chinchio et al. 2020), hybridization (Parker et al. 1999) and facilitation of other invasive species , they can cause the decline and extinction of native species with cascading effects throughout entire ecosystems (White et al. 2006). The economic consequences of invasive species are just as severe, with costs associated with mitigating their impacts exceeding €116 billion between 1960 and 2020 in Europe only (Haubrock et al. 2021). ...
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Raccoons (Procyon lotor) are worldwide invaders, due to deliberate or accidental releases, and their impacts exceed hundred of billions of Euros in Europe only. In France, raccoons have currently established three separate, expanding populations. Identifying the current spatial genetic structure, dispersal events and phylogeography of these populations is needed to infer the invasion history and identify management units. We used wild and captive individuals sampled in France and Belgium to characterize the genetic diversity and current population genetic structure of French raccoon populations and identify potential genetic connectivity with the Belgium population using both mitochondrial DNA and microsatellite loci. Results confirm that French populations are the result of at least three independent introductions. While the three populations display low genetic diversity and sign of recent bottleneck, they are still expanding, suggesting that in addition to their ecological plasticity, the remaining genetic diversity is sufficient to successfully adapt to their new environment and allow a quick colonization. Particular attention must be given to the North-Eastern population, which shows genetic admixture with the Belgium population, as admixed individuals may exhibit hybrid vigor facilitating their expansion. The comparison of captive and wild individuals did not allow to identify a potential captive origin of the wild populations. The current regulation in France allowing captivity in zoos without enforcement to tighten the biosecurity of detention facilities might dampen any management measure as few introduced founders might be enough to create new populations.
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イエネコは,最も身近な動物であると同時に,野外にあふれるネコがさまざまな問題を引き起こしている.本稿では,これらの問題を整理するとともに,ネコをあふれさせる行為や現状に対して,目をそらし続ける人間社会の歪みを指摘し,イエネコ問題の本質と問題解決のために必要な制度について議論する.(生物の科学 遺伝 Vol. 77 p124-129)
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Roaming domestic cats (Felis catus) are recognised as a threat to wildlife globally. Yet management of pet cats in urbanised areas is not regularly mandated, and management of feral cats in urbanised areas is rarely implemented. Mounting evidence emphasises the value of urban environments as hot spots of wildlife activity, which as the human population continues to grow may become the best or only habitats available to some wildlife species. Wildlife in urban environments must navigate introduced stressors that can compound with natural stressors. Additional, often novel, predators such as free-roaming pet and feral cats that are prevalent in urban environments could have high nonconsumptive fear/stress impacts on urban wildlife that influence their activity and adversely affect their health and reproduction capabilities, possibly more so than direct predation effects do. Cat roaming activity, particularly that of pet cats, could be managed with the support of the community, though motivation needs to be ensured. Understanding if roaming cat activity influences urban wildlife activity via perceived fear/stress impacts will help to build community motivation for the need for domestic cat management in urbanised areas. Using infrared motion sensor cameras positioned in both yards and green space edge habitats, we observed whether the presence and times active of native and introduced small mammals, and native birds, were impacted by domestic cat activity within a 24-h period and by their activity in the prior-24-h period. We found evidence of cat roaming activity during the hours of most wildlife activity, and show that wildlife navigated “landscapes of fear” relative to cat activity, as wildlife observed across a 24-h period increased their activity in the absence of cats in the same 24-h period and in the previous 24-h period. We also tested if cat activity was relative to previous cat activity, or disturbances, and found that cats reduced activity in response to each, but were still consistently present. Our results provide justification for the need to increase management of domestic cats in urbanised areas and offer fear/stress impacts as a novel approach to engender community support of such management.
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Deployment of mouse carcasses laced with acetaminophen has become a common management tool to control invasive brown tree snakes (Boiga irregularis; BTS) on Guam. Additionally, anticoagulant rodenticides may be used to control invasive rats (Rattus spp.) if their populations increase due to predator release in the wake of BTS eradication. However, there has been little research examining how scavengers on Guam could be incidentally exposed to toxicants by scavenging carcasses of animals that die from these population control strategies. Furthermore, there is a limited understanding of how the proliferation of invasive species on Guam has influenced the composition of the scavenger community. We investigated these topics by examining scavenger consumption of mouse, rat, and BTS carcasses on Guam in both a coastal and upland site during the wet (May–Aug 2016) and dry season (Jan–Apr 2017). We documented carcass consumption by 9 species, which scavenged 48% of carcasses. Interactions between season, habitat, and carcass type influenced probability of scavenging, and appeared to be driven by consumption by the two main scavenger species, BTS and cane toads (Rhinella marina), both of which are invasive on Guam. Baiting programs should consider the potential for toxin exposure to land crabs (Coenobita spp., Birgus latro), native species that scavenged at every combination of carcass type, habitat, and season. Overall, 60% of scavenging events were attributed to species considered pests that are recent introductions to Guam. Invasive species on Guam are the primary scavengers of small vertebrate carrion, suggesting a substantial role in trophic dynamics that extends beyond predation.
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Invasive mammalian predators are major drivers of species extinctions globally. To protect native prey, lethal control is often used with the aim of reducing or exterminating invasive predator populations. The efficacy of this practice, however, is often not considered despite multiple practical and ecological factors that can limit success. Here, we summarize contemporary knowledge regarding the use and challenges of both lethal control and alternative approaches for reducing invasive predator impacts. As the prevailing management approach, we outline four key issues that can compromise the effectiveness of lethal control: release of herbivore and mesopredator populations, disruption of predator social systems, compensatory predator immigration, and ethical concerns. We then discuss the relative merits and limitations of four alternative approaches that may enhance conservation practitioner's ability to effectively manage invasive predators: top-predator conservation or reintroduction, maintaining habitat complexity, exclusion fencing, and behavioral and evolutionary ecology. Considerable uncertainty remains regarding the effectiveness of management approaches in different environmental contexts. We propose that the deficiencies and uncertainties outlined here can be addressed through a combination of adaptive management, expert elicitation, and cost-benefit analyses. Improved management of invasive predators requires greater consideration and assessment of the full range of management approaches available.
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More than US$21 billion is spent annually on biodiversity conservation. Despite their importance for preventing or slowing extinctions and preserving biodiversity, conservation interventions are rarely assessed systematically for their global impact. Islands house a disproportionately higher amount of biodiversity compared with mainlands, much of which is highly threatened with extinction. Indeed, island species make up nearly two-thirds of recent extinctions. Islands therefore are critical targets of conservation. We used an extensive literature and database review paired with expert interviews to estimate the global benefits of an increasingly used conservation action to stem biodiversity loss: eradication of invasive mammals on islands. We found 236 native terrestrial insular faunal species (596 populations) that benefitted through positive demographic and/or distributional responses from 251 eradications of invasive mammals on 181 islands. Seven native species (eight populations) were negatively impacted by invasive mammal eradication. Four threatened species had their International Union for the Conservation of Nature (IUCN) Red List extinction-risk categories reduced as a direct result of invasive mammal eradication, and no species moved to a higher extinction-risk category. We predict that 107 highly threatened birds, mammals, and reptiles on the IUCN Red List—6% of all these highly threatened species—likely have benefitted from invasive mammal eradications on islands. Because monitoring of eradication outcomes is sporadic and limited, the impacts of global eradications are likely greater than we report here. Our results highlight the importance of invasive mammal eradication on islands for protecting the world’s most imperiled fauna.
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We assessed the prevalence of alien species as a driver of recent extinctions in five major taxa (plants, amphibians, reptiles, birds and mammals), using data from the IUCN Red List. Our results show that alien species are the second most common threat associated with species that have gone completely extinct from these taxa since AD 1500. Aliens are the most common threat associated with extinctions in three of the five taxa analysed, and for vertebrate extinctions overall. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
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We support the call of Wallach et al. (2015a) for a compassionate approach to conservation, and agree that any lethal control must be justified by a high probability of conservation gains and supported by relevant stakeholders. We believe that lethal control of invasive predators is justified when it will reverse the negative impacts of predators introduced by humans on native species and ecosystems, and when the extent of that predation endangers the survival of entire populations or species. Globally a few key introduced predator species are having disproportionately large effects on island ecosystems and their constituent species (e.g. Towns et al. 2006; Medina et al. 2011). Where invasive predators are killed to achieve conservation goals, we believe this can come from compassion for all of the ecosystem, its species, the individuals being protected, and the invasive animals themselves. This view is well supported by literature and policies relating to the role of animal welfare, animal rights, and environmental ethics in pest control programmes (e.g. Gunn 2007; Dunlevy et al. 2011). This article is protected by copyright. All rights reserved.
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Biological invasions as drivers of biodiversity loss have recently been challenged. Fundamentally, we must know where species that are threatened by invasive alien species (IAS) live, and the degree towhich they are threatened. We report the first study linking 1372 vertebrates threatened by more than 200 IAS from the completely revised Global Invasive Species Database. New maps of the vulnerability of threatened vertebrates to IAS permit assessments of whether IAS have a major influence on biodiversity, and if so, which taxonomic groups are threatened and where they are threatened.We found that centres of IAS-threatened vertebrates are concentrated in the Americas, India, Indonesia, Australia and New Zealand. The areas in which IAS-threatened species are located do not fully match the current hotspots of invasions, or the current hotspots of threatened species. The relative importance of biological invasions as drivers of biodiversity loss clearly varies across regions and taxa, and changes over time, with mammals from India, Indonesia, Australia and Europe are increasingly being threatened by IAS. The chytrid fungus primarily threatens amphibians, whereas invasive mammals primarily threaten other vertebrates. The differences in IAS threats between regions and taxa can help efficiently target IAS, which is essential for achieving the Strategic Plan 2020 of the Convention on Biological Diversity. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
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Many highly diverse island ecosystems across the globe are threatened by invasive species. Eradications of invasive mammals from islands are being attempted with increasing frequency, with their success aided by geographical isolation and increasing knowledge of eradication techniques. There have been many attempts to prioritize islands for invasive species eradication; however, these coarse methods all assume managers are unrealistically limited to a single action on each island: either eradicate all invasive mammals, or do nothing. We define a prioritization method that broadens the suite of actions considered, more accurately representing the complex decisions facing managers. We allow the opportunity to only eradicate a subset of invasive mammals from each island, intentionally leaving some invasive mammals on islands. We consider elements often omitted in previous prioritization methods, including feasibility, cost, and complex ecological responses (i.e. trophic cascades). Using a case study of Australian islands, we show that for a fixed budget this method can provide a higher conservation benefit across the whole group of islands. Our prioritization method outperforms simpler methods for almost 80% of the budgets considered. On average, by relaxing the restrictive assumption that an eradication attempt must be made for all invasives on an island, ecological benefit can be improved by 27%. Synthesis and applications. Substantially higher ecological benefits for threatened species can be achieved for no extra cost if conservation planners relax the assumption that eradication projects must target all invasives on an island. It is more efficient to prioritize portfolios of eradication actions, rather than islands. This article is protected by copyright. All rights reserved.
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Prioritization is indispensable for the management of biological invasions, as recognized by the Convention on Biological Diversity, its current strategic plan, and specifically Aichi Target 9 that concerns invasive alien species. Here we provide an overview of the process, approaches and the data needs for prioritization for invasion policy and management, with the intention of informing and guiding efforts to address this target. Many prioritization schemes quantify impact and risk, from the pragmatic and action-focused to the data-demanding and science-based. Effective prioritization must consider not only invasive species and pathways (as mentioned in Aichi Target 9), but also which sites are most sensitive and susceptible to invasion (not made explicit in Aichi Target 9). Integrated prioritization across these foci may lead to future efficiencies in resource allocation for invasion management. Many countries face the challenge of prioritizing with little capacity and poor baseline data. We recommend a consultative, science-based process for prioritizing impacts based on species, pathways and sites, and outline the information needed by countries to achieve this. This should be integrated into a national process that incorporates a broad suite of social and economic criteria. Such a process is likely to be feasible for most countries.
The Action Plan for Australian Mammals 2012 is the first review to assess the conservation status of all Australian mammals. It complements The Action Plan for Australian Birds 2010 (Garnett et al. 2011, CSIRO Publishing), and although the number of Australian mammal taxa is marginally fewer than for birds, the proportion of endemic, extinct and threatened mammal taxa is far greater. These authoritative reviews represent an important foundation for understanding the current status, fate and future of the nature of Australia. This book considers all species and subspecies of Australian mammals, including those of external territories and territorial seas. For all the mammal taxa (about 300 species and subspecies) considered Extinct, Threatened, Near Threatened or Data Deficient, the size and trend of their population is presented along with information on geographic range and trend, and relevant biological and ecological data. The book also presents the current conservation status of each taxon under Australian legislation, what additional information is needed for managers, and the required management actions. Recovery plans, where they exist, are evaluated. The voluntary participation of more than 200 mammal experts has ensured that the conservation status and information are as accurate as possible, and allowed considerable unpublished data to be included. All accounts include maps based on the latest data from Australian state and territory agencies, from published scientific literature and other sources. The Action Plan concludes that 29 Australian mammal species have become extinct and 63 species are threatened and require urgent conservation action. However, it also shows that, where guided by sound knowledge, management capability and resourcing, and longer-term commitment, there have been some notable conservation success stories, and the conservation status of some species has greatly improved over the past few decades. The Action Plan for Australian Mammals 2012 makes a major contribution to the conservation of a wonderful legacy that is a significant part of Australia’s heritage. For such a legacy to endure, our society must be more aware of and empathetic with our distinctively Australian environment, and particularly its marvellous mammal fauna; relevant information must be readily accessible; environmental policy and law must be based on sound evidence; those with responsibility for environmental management must be aware of what priority actions they should take; the urgency for action (and consequences of inaction) must be clear; and the opportunity for hope and success must be recognised. It is in this spirit that this account is offered. Winner of a 2015 Whitley Awards Certificate of Commendation for Zoological Resource.
Winner in the Scholarly Reference section of the 2004 Australian Awards for Excellence in Educational Publishing. Introduced Mammals of the World provides a concise and extensive source of information on the range of introductions of mammals conducted by humans, and an indication as to which have resulted in adverse outcomes. It provides a very valuable tool by which scientists can assess future potential introductions (or re-introductions) to avoid costly mistakes. It also provides tangible proof of the need for political decision makers to consider good advice and make wise and cautious decisions. Introduced Mammals of the World also provides a comprehensive reference to students of ecological systems management and biological conservation. This book is a companion volume to Introduced Birds of the World, by the same author, published in 1981, and which remains the premier text of its kind in the world more than twenty years after it was published. Introduced Mammals of the World provides the most comprehensive account of the movement of mammals around the world providing details on the date(s) of introduction, the person/agency responsible, the source populations, the location(s) of release, the fate of the introductions, and the impact if known, for over 300 species of mammal.