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Alien species as a driver of recent extinctions

  • Center for biodiversity and environment research, University College of London

Abstract and Figures

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.
Content may be subject to copyright.
Cite this article: Bellard C, Cassey P,
Blackburn TM. 2016 Alien species as a driver of
recent extinctions. Biol. Lett. 12: 20150623.
Received: 16 July 2015
Accepted: 18 December 2015
Subject Areas:
non-native species, amphibian, bird,
mammal, plant, reptile
Author for correspondence:
Tim M. Blackburn
An invited contribution to the special feature
‘Biology of extinction: inferring events, patterns
and processes’ edited by Barry Brook and
John Alroy.
Electronic supplementary material is available
at or
Conservation biology
Alien species as a driver of recent
´line Bellard1, Phillip Cassey2and Tim M. Blackburn1,2,3, 4
Department of Genetics, Evolution and Environment, Centre for Biodiversity and Environment Research,
Darwin Building, UCL, Gower Street, London WC1E 6BT, UK
School of Biological Sciences and the Environment Institute, The University of Adelaide, Adelaide,
South Australia 5005, Australia
Institute of Zoology, Zoological Society of London, Regent’s Park, London NW1 4RY, UK
Distinguished Scientist Fellowship Program, King Saud University, Riyadh 1145, Saudi Arabia
TMB, 0000-0003-0152-2663
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 com-
pletely 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.
1. Introduction
Biological diversity naturally varies substantially over space and time, but this vari-
ation is ultimately the product of just four key processes: speciation, immigration,
emigration and extinction [1]. These processes are increasingly being perturbed,
and subsequently shaped, by the actions of humans [2]. Human exploitation of
species and appropriation of land and water have greatly increased extinction
rates in recent centuries relative to the background levels in the fossil record [3,4].
Human activities have also greatly increased the rates of immigration [5,6], by delib-
erately or accidentally transporting and introducing large numbers of species to
areas beyond normal biogeographic barriers to their spread, where they may estab-
lish viable populations (here termed alien) [7]. Alien species have had a range of
impacts documented in their new environments [8], and there are well-documented
examples of native species that have been driven extinct by aliens [9,10]. Indeed,
alien species are often cited as the second most common cause of recent and ongoing
extinctions (since AD 1500) after habitat destruction (i.e. for the USA, see [11]).
Human activities are clearly elevating extinction rates, but it is contentious how
much of that elevation is due to direct effects of exploitation and appropriation,
and how much arises indirectly as a consequence of our elevation of species’ immi-
gration. As a consequence, the role of aliens as important drivers of past extinctions
and/or current extinction risk has been disputed [12–14], the evidence underpin-
ning the ‘second commonest cause’ claim has been questioned [15], and indeed,
speciation by aliens has even been argued to lead to a net increase in diversity
in some taxa in some regions [16]. These arguments form part of a narrative that
the detrimental effects of alien species have been overemphasized [14–18].
Some of the arguments about the impacts of alien species [12,19] have been
based on data on extinction, and extinction risk, from the IUCN (International
Union for Conservation of Nature) Red List. This is a dynamic resource, for which
regular updates add ever greater and more accurate information on the conservation
status of increasing numbers of species. Here, we revisit this resource to assess the
current state of knowledge on associated causes of extinction in five of the best-
studied taxa worldwide. Specifically, we assess the frequency with which alien
species are cited under the causes of loss of plant, amphibian, reptile, bird and
&2016 The Author(s) Published by the Royal Society. All rights reserved.
on February 17, 2016 from
mammal species considered to be extinct (category EX) and
extinct in the wild (category EW).
2. Methods
The Red-Listing process identifies and classifies 12 major threats
to the persistence of species (IUCN threat classification scheme
v. 3.0) [20]. We compiled data on the total numbers of described,
extinct and possibly extinct (category EX), and extinct in the wild
(category EW) plant, amphibian, reptile, bird and mammal
species from the 2015 IUCN Red List with threat information
(n¼247) [21]. We maintained the same classification scheme as
IUCN except for threat category number 8 (‘Invasive and other
problematic species, genes & diseases’), which we subdivided
into alien species (i.e. invasive non-native (alien) species and dis-
eases) and other problematic species (i.e. native species or species
of unknown origin).
We ascribed threats to each EX and EW species according to
the information in the IUCN Red list. For instance, if a species is
recorded as threatened by biological resource use according to
IUCN, it was given a ‘1’ in the data matrix; otherwise, it received
a value of ‘0’. We repeated this process for the 12 external threats
listed. This allows that species may have been affected by mul-
tiple threats. For each taxonomic group, we calculated the
number of EX þEW species for which alien species are cited as
a threat among species with known threats. This allowed us to
calculate the proportion of all threats that relate to alien species.
We classified EX and EW species either as an island endemic
or mainland species using the IUCN Red List database (www.; accessed June 2015). Geographical range distri-
butions were also used to assign each EX and EW species to
one of 12 biogeographic regions (figure 1).
All analyses were conducted in R v. R 3.2.0 [22].
3. Results
A total of 215 species from the five taxa considered here are
recorded as extinct in the IUCN Red List, and a further 32
are extinct in the wild (table 1). Alien species are listed as a
cause for 58% of all EX, and 31% of all EW species for
which a cause is given (see electronic supplementary
material, table S1, for the species list). These percentages
vary across taxa (table 1). Aliens are less important as an
extinction (EX þEW) driver for plants (27%, 15/55 species)
than for vertebrates (62%, 119/192), and indeed, they are
listed as a driver for more than half of the extinctions in
each of the vertebrate taxa analysed (table 1). Extinct species
commonly have more than one threat identified (mean ¼
1.90), but aliens compose from 14% (plants) to 45%
(mammals) of all listed threats for a given taxon, and
28.51% of all threats listed (table 1). For those species with
just a single extinction (EX þEW) driver listed, this driver
is alien species for 17% of plants, no amphibians, 25% of
reptiles, 27% of birds and 47% of mammals.
For all four vertebrate taxa, the top three threats ranked
by the percentage of extinct (EX) species impacted are agri-
culture and aquaculture, alien species and biological
resource use (overexploitation; table 2). Alien species is the
top-ranked threat for extinct amphibians, reptiles and mam-
mals. For plants, residential and commercial development is
one of the top three threats, displacing alien species down
to fourth (table 2). In total, 58% of EX species (125/215) in
the five taxa analysed were listed as impacted by biological
resource use, which is the highest ranked overall. Alien
species comes in a close second, with 58% of extinct species
(124/215) impacted, whereas agriculture and aquaculture
ranks a distant third (61/215; 28%).
Most recorded extinctions (EX þEW) in the taxa analysed
for which alien species are a listed driver have concerned
island endemic species (86%, 115/134 species; electronic
supplementary material, figure S1). All EX þEW plants and
reptiles were island endemic species, whereas 27% of amphi-
bians, 93% of birds and 80% of mammals were island
endemics. Nevertheless, there are eight amphibian, five bird
and six mammal species with continental mainland popu-
lations for which alien species are listed as an extinction
driver (electronic supplementary material, figure S1). Most
of the species that aliens have helped to drive extinct have
been lost from Australia, New Zealand and other locations
in the Pacific (figure 1). However, most amphibian losses
have been from the Americas (figure 1).
4. Discussion
Our results confirm that, for the five major taxa analysed
here, alien species are the second most common threat
no. of species
Central America
eastern Africa
western Africa
eastern Asia
northern America
South America
Australia and New Zealand
Figure 1. The locations of the (now lost) native ranges of the 134 extinct (EX þEW) species for which alien species are listed as a driver. Biol. Lett. 12: 20150623
on February 17, 2016 from
associated with species that have gone completely extinct
since AD 1500. They are relegated into second place by bio-
logical resource use, by the smallest possible margin (125
versus 124 species affected). In fact, alien species are the
most common threat associated with extinctions in three of
the five taxa analysed, and for vertebrate extinctions overall.
Alien species are listed as having contributed to the extinction
of more than half of all the species in our analyses (EX þEW),
and to almost two-thirds of the vertebrates. Around 30
alien taxa are implicated, including ‘bees’, rainbow trout
Oncorhynchus mykiss, ‘tortoises’, great horned owls Bubo virgi-
nianus and guinea pigs Cavia porcellus, but especially rats
Rattus spp. and cats Felis catus for extinct birds and mammals,
diseases (especially chytridiomycosis and avian malaria) for
extinct amphibians and birds, and herbivores (especially
goats Capra hircus, sheep Ovis aries and European rabbits
Oryctolagus cuniculus) and alien plants for extinct plant
species [21]. Extinctions since AD 1500 are only a small pro-
portion of the vertebrate species lost in the period following
human expansion out of Africa [23,24]. However, well-
typified fossil assemblages reveal a number of extinctions
that are most likely to have been caused by alien species
[25]. Thus, alien-driven extinctions are unlikely to be just a
modern phenomenon.
The IUCN Red List represents probably the best available
data on the factors associated with recent extinctions, and on
current extinction risk, and we have taken the causes of
extinction it records at face value. It remains possible that
the Red List may systematically overestimate the impact of
alien species, if these are not the causal agents of extinction,
but symptoms of the real causes (e.g. habitat destruction)
[13]. We doubt that any such overestimation is substantial.
Alien species may often act in synergy with other extinction
drivers—and indeed, most extinctions are associated with
more than one—but the impacts of alien species have been
well documented in multiple contexts [9,26]. Further, habitat
loss, harvesting and human disturbance co-occur randomly
with impact from aliens as threats to vertebrates on the
IUCN Red List [27]. One could argue equally convincingly
that the impacts of alien species may in many cases be
Table 1. The total number of species either extinct (EX) or extinct in the wild (EW) according to the IUCN Red List (2015) in each of five major taxa, and the
total number (S
) and percentage (%S
) for which alien species are listed as a causal threat, the mean number of threats recorded per species (+s.d.),
and the percentage of all listed threat categories that relate to aliens (%T).
taxon status species S
threats %T
plants EX 32 9 28 2 (+1) 14
EW 23 6 26 2 (+1) 15
amphibians EX 15 10 67 4 (+2) 19
EW 2 1 50 4 (+1) 13
reptiles EX 6 4 67 2 (+1) 29
EW 1 0 0 1 0
birds EX 119 71 60 2 (+1) 35
EW 4 3 75 3 (+2) 27
mammals EX 43 30 70 2 (+1) 45
EW 2 0 0 3 (+1) 0
total 247 134 54 2 (+1) 29
Table 2. The top four threats associated with extinct (EX) species in each taxon, and the percentage and (in parentheses) numbers of extinct species for which
each threat was listed. Only three threats are listed for reptiles, because the percentages for the fourth- to seventh-ranked threats were all equal (17%). Alien
species (AS) is highlighted in italics. Other threats are: AG, agriculture and aquaculture; CC, climate change and severe weather; BR, biological resource use
(overexploitation); PO, pollution; SM, natural system modifications; UR, residential and commercial development (urbanization).
taxon status rank 1 rank 2 rank 3 rank 4
plants threat AG BR UR AS
% (number) 59 (19) 44 (14) 34 (11) 28 (9)
amphibians threat AS AG BR PO
% (number) 67 (10) 60 (9) 53 (8) 47 (7)
reptiles threat AS BR AG
% (number) 67 (4) 50 (3) 33 (2)
birds threat BR AS AG SM
% (number) 70 (83) 60 (71) 17 (20) 8 (10)
mammals threat AS BR AG SM
% (number) 70 (30) 40 (17) 26 (11) 7 (3) Biol. Lett. 12: 20150623
on February 17, 2016 from
underestimated, as many interactions (especially between
alien parasites and native hosts) [28] are very hard to
detect. Nevertheless, in many cases, the true contribution of
alien species versus other extinction drivers will never be
known, given that the impacted species concerned are now
Alien species are not just a problem forisland species. While
most of the recent extinctions associated with alien species
relate to island endemics (figure 1), 14% of alien-related extinc-
tions have concerned species with mainland populations. Alien
species are a significant concern for mainland species currently
threatened with extinction. In particular, the highest absolute
number of species threatened by alien species are located in
South American countries [29]. In summary, our results do
not support arguments that the detrimental effects of alien
species have been overemphasized [14–18].
Data accessibility. The data on which this paper is based are freely avail-
able on the IUCN Red List website ( A list of extinct
species is given in the electronic supplementary material.
Authors’ contributions. C.B., P.C. and T.M.B. conceived the study; C.B.
compiled and analysed the data; C.B., P.C. and T.M.B. wrote the
paper. The authors agree to be accountable for all aspects of the
work reported.
Competing interests. The authors have no competing interests.
Funding. C.B. was supported by an AXA Fellowship. P.C. was supported
by an ARC Future Fellowship (FT0914420) and by an ARC Discovery
grant (DP140102319). T.M.B. had no funding for this work.
Acknowledgements. Wethank Barry Brookand John Alroy for inviting us to
write this paper, and three anonymous referees for helpful comments.
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Background Biological invasions threaten the functioning of ecosystems, biodiversity, and human well-being by degrading ecosystem services and eliciting massive economic costs. The European Union has historically been a hub for cultural development and global trade, and thus, has extensive opportunities for the introduction and spread of alien species. While reported costs of biological invasions to some member states have been recently assessed, ongoing knowledge gaps in taxonomic and spatio-temporal data suggest that these costs were considerably underestimated. Results We used the latest available cost data in InvaCost (v4.1)—the most comprehensive database on the costs of biological invasions—to assess the magnitude of this underestimation within the European Union via projections of current and future invasion costs. We used macroeconomic scaling and temporal modelling approaches to project available cost information over gaps in taxa, space, and time, thereby producing a more complete estimate for the European Union economy. We identified that only 259 out of 13,331 (~ 1%) known invasive alien species have reported costs in the European Union. Using a conservative subset of highly reliable, observed, country level cost entries from 49 species (totalling US$4.7 billion; 2017 value), combined with the establishment data of alien species within European Union member states, we projected unreported cost data for all member states. Conclusions Our corrected estimate of observed costs was potentially 501% higher (US$28.0 billion) than currently recorded. Using future projections of current estimates, we also identified a substantial increase in costs and costly species (US$148.2 billion) by 2040. We urge that cost reporting be improved to clarify the economic impacts of greatest concern, concomitant with coordinated international action to prevent and mitigate the impacts of invasive alien species in the European Union and globally.
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... Invasive alien species are a major contributor to the current global biodiversity crisis, impacting native biodiversity communities through competition, ecological changes, economic costs, and health risks [1,2]. Among invasive vertebrates, nutria (Myocastor coypus) are semi-aquatic rodents native to subtropical and temperate regions of South America that have now spread to every continent except Australia and Antarctica. ...
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Simple Summary This study aims to investigate the behavior and ecology of nutria (Myocastor coypus), a semi-aquatic rodent that was introduced to South Korea for commercial farming and subsequently damaged aquatic ecosystems after its release. How the behavioral ecology of introduced nutria changes over time and across seasons remains unclear. Twenty-four adult nutria (twelve males and twelve females) were radio tracked in 2015–2016 to identify their home range size and activity patterns in the Macdo wetland, South Korea. This study found that the nutria home range size varied seasonally, with males having larger home ranges than females. Additionally, nutria showed crepuscular and nocturnal activity patterns throughout the year, with no significant difference between sexes. The findings of this study provide crucial information on the home range and activity patterns of introduced nutria in the Macdo wetland, which can guide management efforts to mitigate their impacts on the ecosystem. It is the first quantitative analysis of the home range and activity patterns of introduced nutria based on radio tracking data in the Macdo wetland. Abstract Nutria (Myocastor coypus) are semi-aquatic rodents that were introduced in South Korea for commercial farming but significantly damaged aquatic ecosystems. Understanding nutria ecological behavior is essential for developing effective control and eradication strategies to mitigate their impacts. Thus, this study aimed to investigate the home range and activity patterns of 24 nutria (12 males and 12 females) in the Macdo wetland in South Korea from 2015–2016 through radio tracking. The average minimum convex polygon home range of the nutria was 0.29 ± 0.55 km², with a 95% kernel density estimation (KDE) home range of 0.43 ± 0.85 km² and a 50% KDE home range of 0.05 ± 1.1 km². The home range of males was larger than that of females; however, the winter home range of females was as large as that of males. The home range also varied seasonally, with the smallest observed in winter. The nutria showed crepuscular and nocturnal activity patterns throughout the year, with no significant difference between sexes. The activities in spring, summer, and autumn showed no significant differences, but the activity in winter was significantly different from that in the other seasons. This study may serve as a basis for developing appropriately timed and scaled management strategies to mitigate the impacts of nutria on ecosystems. In conclusion, several environmental and biological factors contribute to the behavior of nutria in South Korea.
Changes in invasion understanding have been advocated for by researchers to better forecast invasions and lessen the consequences of invasive species on the environment and socioeconomics. This chapter aims to generate new ideas and promote research on remote sensing applications to advance robust invasion science and management. Remote sensing techniques can be used to examine and identify invasive species by combining a synergistic understanding of biological invasions associated with the aquaculture and shipping industries, invasive species detection aspects, limitations of marine remote sensing for invasion science, specific invasion metrics and change detection. Using these synergies is crucial for developing long-term management strategies based on interdisciplinary collaboration among academics, policymakers and communities. By monitoring and mapping the existence and distribution of marine invasive species, remote sensing can aid in ecosystem-based management of damaged coastal zones.
Background: As an invasive pest from North America, grey squirrels (GS, Sciurus carolinensis Gmelin) are displacing native squirrels in Europe. However, the climatic niche and range dynamics of GS in Europe remain largely unknown. Through niche and range dynamic models, we investigated climatic niche and range shifts between introduced GS in Europe and native GS in North America. Results: GS in North America can survive in more variable climatic conditions, and have much wider climatic niche breadth than do GS in Europe. Based on climate, the potential range of GS in Europe included primarily Britain, Ireland, and Italy, whereas the potential range of GS in North America included vast regions of western and southern Europe. If GS in Europe could occupy the same climatic niche space and potential range as GS in North America, they would occupy an area ca. 2.45 times the size of their current range. The unfilling ranges of GS in Europe relative to those of GS in North America were primarily in France, Italy, Spain, Croatia, and Portugal. Conclusion: Our observations implied that GS in Europe have significant invasion potential, and that range projections based on their occurrence records in Europe may underestimate their invasion risk. Given that small niche shifts between GS in Europe and in North America could lead to large range shifts, niche shifts could be a sensitive indicator in invasion risk assessment. The identified unfilling ranges of the GS in Europe should be prioritized in combating GS invasions in the future.
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We provide an overview of the current state of knowledge of parasites in biological invasions by alien species. Parasites have frequently been invoked as drivers of invasions, but have received less attention as invasion passengers. The evidence to date that parasites drive invasions by hosts is weak: while there is abundant evidence that parasites have effects in the context of alien invasions, there is little evidence to suggest that parasites have differential effects on alien species that succeed versus fail in the invasion process. Particular case studies are suggestive but not yet informative about general effects. What evidence there is for parasites as aliens suggests that the same kind of factors determine their success as for non-parasites. Thus, availability is likely to be an important determinant of the probability of translocation. Establishment and spread are likely to depend on propagule pressure and on the environment being suitable (all necessary hosts and vectors are present); the likelihood of both of these dependencies being favourable will be affected by traits relating to parasite life history and demography. The added complication for the success of parasites as aliens is that often this will depend on the success of their hosts. We discuss how these conclusions help us to understand the likely effects of parasites on the success of establishing host populations (alien or native).
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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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The oft-repeated claim that Earth's biota is entering a sixth " mass extinction " depends on clearly demonstrating that current extinction rates are far above the " background " rates prevailing in the five previous mass extinctions. Earlier estimates of extinction rates have been criticized for using assumptions that might overestimate the severity of the extinction crisis. We assess, using extremely conservative assumptions, whether human activities are causing a mass extinction. First, we use a recent estimate of a background rate of 2 mammal extinctions per 10,000 species per 100 years (that is, 2 E/MSY), which is twice as high as widely used previous estimates. We then compare this rate with the current rate of mammal and vertebrate extinctions. The latter is conservatively low because listing a species as extinct requires meeting stringent criteria. Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 114 times higher than the background rate. Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear. These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way. Averting a dramatic decay of biodiversity and the subsequent loss of ecosystem services is still possible through intensified conservation efforts, but that window of opportunity is rapidly closing.
The observational evidence on non-native plants, mammals, reptiles, fish, mollusks earthworms, and insects as drivers of population declines or extinctions of native taxa suggests that non-native predators are far more likely to cause the extinction of native species than non-native competitors. Notable examples of such taxa include non-native vertebrates and mollusks as mainly predators and plants and insects as mainly competitors. The most vulnerable species are insular endemics, presumably because of the lack of coevolution between introduced predator and native prey. Island-like situations contribute to severe impacts because the affected native taxa have nowhere to escape. The presence of dormant stages in plants makes it possible to escape unfavourable conditions over time and might contribute to the lack of clear evidence of native plant species driven to extinction by plant invaders. Overall, robust evidence has accumulated during the past few decades that non-native species are drivers of local and global extinctions of threatened, often endemic, native species.
The extent to which human activity has influenced species extinctions during the recent prehistoric past remains controversial due to other factors such as climatic fluctuations and a general lack of data. However, the Holocene (the geological interval spanning the last 11,500 years from the end of the last glaciation) has witnessed massive levels of extinctions that have continued into the modern historical era, but in a context of only relatively minor climatic fluctuations. This makes a detailed consideration of these extinctions a useful system for investigating the impacts of human activity over time. This book describes and analyses the range of global extinction events which have occurred during this key time period, as well as their relationship to both earlier and ongoing species losses. By integrating information from fields as diverse as zoology, ecology, palaeontology, archaeology, and geography, and by incorporating data from a broad range of taxonomic groups and ecosystems, this text provides a fascinating insight into human impacts on global extinction rates, both past and present.
At 270,000 km2, New Zealand is one-thirtieth the area of Australia, one-third that of Madagascar, twice that of Cuba, and comparable in area to the British Isles, to the Philippines, and within the United States to the State of Colorado. Isolated in the southwestern Pacific, 1900 km east of Australia, New Zealand was the last major habitable landmass to be peopled, in this instance by Polynesians. Unlike the British Isles and the Philippines, which are partly on and partly off the continental shelf, New Zealand is so remote that despite zoogeographic and geotectonic evidence of a considerable antiquity, it lacked nonvolant land mammals when humans and their commensals colonized 700 years ago.
Significance Non-native plants dominate global lists of invasive (harmful) species, yet plants introduced to Britain are both less widespread than native species and not increasing any more than native plants, and changes to native and non-native plant diversity are positively associated. The hypothesis that competitive exclusion will eventually enable introduced plants to drive native species extinct receives no support, according to analysis of extensive British data. A more parsimonious explanation is that both native and introduced plants are responding predominantly to other drivers of environmental change. The negative effects of non-native plants on British biodiversity have been exaggerated, and may also have been exaggerated in other parts of the world.