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Biogeographic origins and drivers of alien plant invasions in the Canary Islands

January 2023
Journal of Biogeography 50(1)

DOI:10.1111/jbi.14556

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CC BY-NC 4.0

Authors:

Javier Morente Lopez

Spanish National Research Council

Yurena Arjona

Universidad de La Laguna

Marcos Salas Pascual

Universidad de Las Palmas de Gran Canaria

Jorge Alfredo Reyes-Betancort

Instituto Canario de Investigaciones Agrarias

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Understanding the historical and contemporaneous drivers of invasion success in island systems can decisively contribute to identifying sources and pathways that are more likely to give rise to new invaders. Based on a floristic‐driven approach, we aimed at determining the origins of the invasive alien flora of the Canary Islands and shedding light in the mechanisms shaping their distribution within the archipelago. Canary Islands. Vascular plants. An updated checklist of the invasive alien flora of the Canary Islands was assembled along with complementary information related to the native biogeographical regions, stage of invasiveness and dates of naturalization. Statistical models were employed to describe differences in the number of species over space and time. We also used multivariate techniques to evaluate competing hypotheses related to the mechanisms driving invasive floristic composition within the archipelago. We provided a list of 149 alien plant species with a certain degree of invasiveness. The greatest number of invasive species originated from the Neotropics followed by the Cape Region, tropical Africa and the Mediterranean Basin. We observed a slow but steady increase in numbers of invasive species until the 1950s, followed by a stronger rise thereafter. In order to explain composition dissimilarity of the invasive flora among islands, a climatic matching hypothesis was fully supported, with geographic isolation and contemporary human‐mediated connectivity hypotheses receiving less and null support respectively. We showed that the Neotropical region is the main source of plant invasions to the Canary Islands, outnumbering those from other regions with a Mediterranean‐type bioclimate. The assembly of the invasive flora within the archipelago appears to be driven primarily by climate, but with geographic distance also playing a role. This study calls for archipelago‐dependent assessments of the underlying mechanisms that contribute to plant invasion success within insular systems.

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Journal of Biogeography. 2023;00:1–15.

1wileyonlinelibrary.com/journal/jbi

Received: 18 April 2022

Revised: 13 November 2022

Accepted: 20 November 2022

DOI : 10.1111/j bi.14 556

RESEARCH ARTICLE

Biogeographic origins and drivers of alien plant invasions in the

Canary Islands

Javier Morente- López1,2 | Yurena Arjona1,2 | Marcos Salas- Pascual3 |

J. Alfredo Reyes- Betancort4 | Marcelino J. del Arco- Aguilar2 | Brent C. Emerson1 |

Antonio García- Gallo2 | Louis S. Jay- García2 | Agustín Naranjo- Cigala5 |

Jairo Patiño1,2

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction

in any medium, provided the original work is properly cited and is not used for commercial purposes.

Javier Morente- López a nd Yurena Arjona e qual contribu tion

1Island Ecology and Evolution Research

Group, Instituto de Productos Naturales

y Agrobiología (IPNA- CSIC), La L aguna,

Spain

2Departamento de Botánica, Ecología y

Fisiología Vegetal, Facultad de Farmacia,

Universidad de La Laguna, La L aguna,

Spain

3Instituto de Estudios Ambientales y

Recursos Naturales (IUNAT), Universidad

de Las Palmas de Gran Canaria,

Edificio Polivalente I, Parque Científico

Tecnológico, Las Palmas de Gran Canaria,

Spain

4Jardín de Aclimatación de L a Orotava,

Instituto Canario de Investigaciones

Agrarias (ICIA), Puerto de La Cruz, Spain

5Departamento de Geografía, Universidad

de Las Palmas de Gran Canaria, Las Palmas

de Gran C anaria, Spain

Correspondence

Jairo Patiño, Island Ecology and Evolution

Research Group, Instituto de Productos

Naturales y Agrobiología (IPNA- CSIC),

Astrofísico Francisco Sánchez 3, La

Laguna, Tenerife, Canar y Islands, 38206,

Spain.

Email: jpatino@ipna.csic.es

Funding information

Fundación BBVA, Grant/Award Number:

INVASION - PR19_ECO_0046; Spanish

Ministry of Science and Innovation, Grant/

Award Number: ASTERALIEN - PID2019-

110538GA- I00; Juan de la Cier va-

Formación Fellowship, Grant/Award

Number: FJC2020- 046353- I; Ramón y

Cajal Program, Grant/Award Number:

Abstract

Aim: Understanding the historical and contemporaneous drivers of invasion success

in island systems can decisively contribute to identifying sources and pathways that

are more likely to give rise to new invaders. Based on a floristic- driven approach, we

aimed at determining the origins of the invasive alien flora of the Canary Islands and

shedding light in the mechanisms shaping their distribution within the archipelago.

Location: Canary Islands.

Tax o n: Vascular plants.

Methods: An updated checklist of the invasive alien flora of the Canary Islands was

assembled along with complementary information related to the native biogeographi-

cal regions, stage of invasiveness and dates of naturalization. Statistical models were

employed to describe differences in the number of species over space and time. We

also used multivariate techniques to evaluate competing hypotheses related to the

mechanisms driving invasive floristic composition within the archipelago.

Results: We provided a list of 149 alien plant species with a certain degree of inva-

siveness. The greatest number of invasive species originated from the Neotropics fol-

lowed by the Cape Region, tropical Africa and the Mediterranean Basin. We observed

a slow but steady increase in numbers of invasive species until the 1950s, followed

by a stronger rise thereafter. In order to explain composition dissimilarity of the in-

vasive flora among islands, a climatic matching hypothesis was fully supported, with

geographic isolation and contemporary human- mediated connectivity hypotheses re-

ceiving less and null support respectively.

Main Conclusions: We showed that the Neotropical region is the main source of

plant invasions to the Canary Islands, outnumbering those from other regions with a

Mediterranean- type bioclimate. The assembly of the invasive flora within the archi-

pelago appears to be driven primarily by climate, but with geographic distance also

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MORENTE-LÓPEZ et a l.

1 | INTRODUC TION

Global trade, transport and horticulture have become driving forces

promoting human- assisted dispersal of plant species across oce-

anic and continental regions (Capinha et al., 2015; van Kleunen

et al., 2020). As a consequence, an increasing number of species have

been introduced beyond their native ranges, with a fraction natural-

ized by forming self- replacing populations in natural or human- made

habitats (naturalized alien species sensu Lambdon et al., 2008; Pyšek

et al., 2004). A subset of these naturalized alien species has also be-

come invasive (invasive alien species sensu Lambdon et al., 2008;

Pyšek et al., 2004), emerging as important drivers of global change

and species extinctions (Bellard et al., 2016; Bellard et al., 2017;

Russell & Kueffer, 2019).

The number and origins of invasive alien plant species vary

across spatial and temporal scales depending on several interacting

factors, including history and timing of human transport pathways,

geographic isolation and distance, abiotic conditions and species

traits (Capinha et al., 2015; Irl et al., 2021; Kusumoto et al., 2021;

Monnet et al., 2020; Moser et al., 2018; van Kleunen et al., 2015).

Consequently, different underlying mechanisms of biological in-

vasion have been proposed (Catford et al., 2009; Di Castri, 1989;

Theoharides & Dukes, 2007). Among them, the ‘climate matching’

hypothesis (Richardson & Thuiller, 2007; Thuiller et al., 2005), which

postulates that alien species are most likely to establish in areas that

are climatically similar to their native range, has received mounting

evidence (e.g., Cao Pinna et al., 2021; Capinha et al., 2015; Monnet

et al., 2020). Recently, Yang et al. (2021) showed that the level of

floristic homogenization due to plant introductions increases with

climatic similarity, even among geographically distant regions.

Floristic homogenization of invasive alien floras among regions

can be further fostered by historical or current administrative re-

lationships due to enhanced intensive trade and transport (Yang

et al., 2021). Indeed, anthropogenic introductions can be highly

as ymmetric and subst a ntially relate d to the history of human occupa-

tion and trade networks (Hulme, 2015; Monnet et al., 2020; Turbelin

et al., 2 017). From the 15th to the early 20th century, European im-

perialism expanded, displacing and replacing not only native societ-

ies but also their biotas (Di Castri et al., 1990 ; Simberloff, 2004). The

historical legacy of these trade and political relationships led to the

development of the ‘Imperialist Dogma’ hypothesis (Crosby, 2004).

This hypothesis proposes that, due to human colonization history,

Old World European species have spread more frequently and widely

outside their native ranges than New World species (Di Castri, 1989;

Pyšek, 1998). Contemporary global trade still has its roots on the

historical legacy of the European imperialism, which perpetuates

trade patterns in many geographic regions (Gokmen et al., 2020).

Accordingly, van Kleunen et al. (2015) have shown that continents

in the Northern Hemisphere have been key sources of alien species

to all other continents, with North America accumulating the largest

number of non- native plants. Eurasian species were proposed to be

at clear advantage everywhere (van Kleunen et al., 2015) because of

their long coevolution with humans and their disturbance regimes

(Jeschke & Strayer, 2005; Kalusová et al., 2017; Monnet et al., 2020).

The main European sources of alien plant species have included re-

gions such as the Mediterranean Basin (Fridley, 2008) in general, and

the Iberian Peninsula in particular (Casado et al., 2018).

The geographic origins of invasive alien plants have been shown

to be different when time periods related to important socio-

economic events are considered. For instance, evidence points to

the rising importance of extra- European regions as sources of alien

species, in parallel with the development of emergent economies

and global increase in trade activity (Seebens et al., 2015). This pat-

tern is contrary to the ‘Imperialist Dogma’ and seems to have glob-

ally emerged 60 years ago with the globalization of anthropogenic

transport networks (Seebens et al., 2015). In fact, it has been in-

creasingly shown that socio- economic variables, such as trade net-

works, can be as (or even more) important drivers of plant invasion

as climate similarity and geographic distance (Chapman et al., 2017;

Essl et al., 2019). Nonetheless, increased residence time on a given

region and limited geographic distance among invaded and non-

invaded areas within that region can increase the probability of alien

plant naturalization and invasion (Lambdon et al., 2008).

Despite the importance of studying source– sink dynamics in

order to gain insights related to spatial and temporal invasiveness pat-

terns (Fridley & Sax, 2014; Kusumoto et al., 2021; Visser et al., 2016),

the main sources of invasive alien floras remain unknown and con-

troversial for many regions (Fridley, 2008; Pyšek, 1998). This is par-

ticularly true for many insular systems (Lenzner et al., 2020; Patiño

et al., 2017 ), which calls for regional assessments of the major forces

for ongoing biotic homogenization of island floras (Otto et al., 2020).

Here, we investigate the origins of the invasive alien vascular

flora of the Canary Islands to determine which biogeographic regions

have played a dominant role as sources of invasion. Fox (1990) pro-

posed that the five Mediterranean- climate regions (Mediterranean

Basin, California, central Chile, South Africa and south- western

Australia) have exchanged significant numbers of invasive plant

species, but with the Iberian Peninsula as the main source to the

RYC- 2016- 20506; Academia Canaria de

Investigación Gobierno de Canarias FPI

2021 Fellowship, Grant/Award Number:

TESIS2021010101

Handling Editor: Daniel Chapman

playing a role. This study calls for archipelago- dependent assessments of the underly-

ing mechanisms that contribute to plant invasion success within insular systems.

KEY WORDS

climatic matching, floristic assembly, geographic distance, invasive alien species, island

biogeography, Mediterranean climate type, naturalized species, transport networks

MORENTE-LÓPEZ et al.

other regions (Casado et al., 2018). In addition, it is expected that

plant species from other Mediterranean- climate regions, largely

preadapted to these environments, would have a higher probability

of naturalization and spread across the Mediterranean Basin (Cao

Pinna et al., 2021; Casado et al., 2018). We anticipate that such phe-

nomena should have left an important imprint in the Canarian ar-

chipelago, which is in general characterized by both strong climatic

similarity and floristic relationships with the Mediterranean Basin

(del Arco- Aguilar & Rodríguez- Delgado, 2018).

The Canary Islands exhibit very contrasted features in terms

of geological history, topographical complexity and associated cli-

matic gradients. Such differences help to explain the broader array

of ecosystem types found on the highest islands compared with the

lowest ones (from arid and semiarid coastal scrubs, through semi-

arid thermophilous woodlands, montane cloud laurel forests and

xeric pine forests to summit scrub). Thus, the western and central

islands are characterized by high, complex topographies, relatively

humid climates and a full range of ecosystem types, while the east-

ern ones are flatter, drier and less ecologically diverse (del Arco-

Aguilar et al., 2010; del Arco- Aguilar & Rodríguez- Delgado, 2018).

For at least 2000 years, these zonal ecosystems have been subject to

anthropogenic pressures and even more so following the European

conquest in the 15th century (de Nascimento et al., 2020). The level

of human occupation, land use history and transportation network

also vary depending on the island, with human pressure decreasing

from the central islands to both the easternmost and westernmost

edges of the archipelago. We also investigate the relative impor-

tance of geographic, climatic and transportation factors in shaping

the within- archipelago composition of the invasive flora.

Specifically, we test the four following hypotheses:

‘Imperialist Dogma’ Hypothesis (H1): Following the ‘Imperialist

Dogma’, the Mediterranean Basin has been the prevalent source of

invasive alien plants to the Canary Islands, given its strong macrocli-

matic matching, long- term commercial exchange and relatively short

geographic distance to the archipelago.

Naturalization Rate Hypothesis (H2): Rates of first introduction

and naturalization should have increased in recent years, when

global trade has peaked (Hulme, 2009; Seebens et al., 2017 ).

Furthermore, the rates of naturalization from specific biogeographic

regions are expected to differ when the colonial times (i.e., 1500–

1900) are compared with more recent times (i.e., last 50 years), when

predominant routes of human migration through the Canary Islands

have changed.

Within- archipelago Climate Matching Hypothesis (H3): Following

the climate matching hypothesis, insular floras within a given archi-

pelago should converge towards more similar assemblages of inva-

sive species with increased climatic similarity. The Canary islands

of Lanzarote and Fuerteventura are much flatter and drier than the

central and western islands. Thus, we expe ct greater floristic similar-

ities among environmentally similar islands.

Enhanced Connectivity Hypothesis (H4): It is plausible that the

positive correlation observed between trade volumes and inva-

sion patterns at the global scale (Chapman et al., 2017; Seebens

et al., 2015) can exhibit a similar correspondence at the regional scale

(Hulme, 2021). Under such an assumption, the explanatory power of

current interisland transport networks for compositional dissimilar-

ity of invasive floras within the Canarian archipelago should parallel

that of climatic similarity and geographic distance among islands.

2 | MATERIALS AND METHODS

2.1 | Study area

The Canary Islands, a volcanic archipelago situated in the north-

eastern Atlantic Ocean, is one of the most biodiverse oceanic in-

sular systems of plants on the planet (Patiño et al., 2014), being

one of the most relevant hotspots of plant biodiversity within the

Mediterranean Basin (Médail & Quézel, 1999). The Canary archipel-

ago not only exhibits high levels of endemism (539 vascular plants

which means almost 40% of the native flora) but also of alien spe-

cies (del Arco- Aguilar & Rodríguez- Delgado, 2018). The archipelago

is characterized by a general subtropical Mediterranean climate with

strong gradients in temperature and precipitation depending on el-

evation, topography and longitude (del Arco- Aguilar et al., 2010). In

addition to the elevational zonation (del Arco- Aguilar & Rodríguez-

Delgado, 2018), the archipelago exhibits a strong precipitation

gradient from west to east, with the western islands much wetter

than those to the east (Sánchez- Benítez et al., 2017 ). The Canary

archipelago was first colonized by humans, from North Africa, dur-

ing the first millennia CE (Fregel et al., 2019), and then subsequently

by the Castilian conquest during the 15th century AD. As a result,

an important increase in trade and land use transformation caused

a significant reduction of the main zonal vegetation types as well as

a noteworthy increase in the introductions of alien plants (del Arco-

Aguilar & Rodríguez- Delgado, 2018). Since Castilian colonization,

the archipelago has been a crossroad of several intercontinental

trade routes (Bosa, 2004; James, 1985; Santana- Pérez, 2018), which

makes it challenging to track the origins of alien plant species.

2.2 | Information sources

A thorough search of primary and secondary references, including

the web database BIOTA (https://www.biodi versi dadca narias.es/)

and other sources of information, such as peer- reviewed indexed

and non- indexed journals, technical reports, books and other publi-

cations, allowed us to obtain an up- to- date checklist of the invasive

alien plant species of the Canary Islands. In order to refine the list,

we first excluded species records which we could not confidently

delineate a precise geographic native range. Following the approach

proposed by Pyšek et al. (2004), widely cultivated species across

the archipelago were also discarded due to the idea that the envi-

ronmental and anthropogenic factors that shape their distributions

are likely to be different from those of non- cultivated alien species

(Monnet et al., 2020). As proposed by Capinha et al. (2015), we also

MORENTE-LÓPEZ et a l.

discarded all records for which, according to BIOTA, the invasive-

ness or alien status was mentioned as uncertain (e.g., probable inva-

sive, probable alien). In total, we used approximately 64 data sources

(Appendix S1). The scientific names of species were standardized

with global (Plants of the World Online, http://www.plant softh

eworl donli ne.org/) and regional (BIOTA) databases.

We then classified each alien species as naturalized or invasive

following the framework proposed by Blackburn et al. (2 011), which

relies on the magnitude and irreversibility of their negative ecolog-

ical impacts. The statistical analyses were performed for the group

of invasive alien species separately, and for the invasive and the nat-

uralized groups together (see Statistical analyses).

Next, we compiled information regarding the native geographic

range of each alien species (see Appendix S1 for the complete list of

references used). We defined a set of biogeographic regions intended

to represent the native areas for the human- mediated introduced

diaspores (Figure 1). Biogeographic regions were thus demarcated

following Takhtajan (1986), Cowling et al. (1996) and Cox's (20 01)

works, as follows: (A) the five regions with a Mediterranean- type cli-

mate separately, including, the Mediterranean Basin, Cape Floristic

region, California Floristic Province, central Chile and south- western

Australia (Cowling et al., 1996); (B) Palearctic Europe, excluding the

Mediterranean Basin; (C) North America as Nearctic, excluding the

California Province; (D) Neotropics which extends from tropical re-

gions of Mexico through Central America and into South America,

the Galapagos and the Revillagigedo archipelagos, but excluding

central Chile; (E) Tropical Africa, excluding the African areas of

the Mediterranean Basin and the Cape region; (F) Palaearctic East

Asia, including non- tropical areas of Asia from the Palearctic; (G)

Indo- Malayan or tropical Asia, including tropical areas of south and

southeast Asia and extends through the Malay Archipelago; (H)

Australasia, which combines Australia and New Zealand into a single

region following Cox (2001), and extends as far as New Guinea and

Polynesia. A final category, including species extending across two

FIGURE 1 Biogeographic regions defined to represent the source regions for the human- mediated introduced plant species into

the Canary Islands. CAL, Mediterranean California; NEA, Nearctic region; NEO, Neotropical region; EUR, Palearctic Europe; MED,

Mediterranean Basin including Europe, North Africa and Middle East; AFT, Tropical Africa; CAP, Cape Region of South Africa; ASN,

Palearctic Asia; AST, Tropical Asia; AUM, Mediterranean Australia; AUS, Australasia; DES, cold and hot (semi)deserts; LAK, lakes and inner

seas. Mediterranean Chile is only highlighted in the map (see Methods). Examples of the best represented floristic regions in the invasive

flora of the Canar y Islands: NEA , Robinia pseudoacacia L.; MED, Pinus pinea L.; ASN, Ailanthus altissima (Mill.) Swingle; NEO, Opuntia

tomentosa Salm- Dyck; AFT, Cenchrus purpureus (Schumach.) Morrone; AUS, Myoporum laetum G. Forst.; CAL, Cylindropuntia prolifera

(Engelm.) F.M. Knuth; CAP, Malephora crocea (Jacq.) Schwantes; AUM, Paraserianthes lophantha (Willd.) I.C. Nielsen. A version of the figure

suitable for colour blindness is provided in Supporting Information.

ASN CAP

NEA

NEO

CAL

MED

AUM

AFT AUS

MORENTE-LÓPEZ et al.

or more of the aforementioned regions (widespread), was defined

but not considered in the subsequent analyses due to the impedi-

ment for addressing signals of macroclimatic similarity and the lack

of a predominant biogeographic pattern.

2.3 | Time of introduction and naturalization

Data on the first year of record (i.e. species introduced associated

with anthropogenic environments such as gardens and urban areas)

and naturalization (i.e. species spontaneously growing and repro-

ducing in the wild) in the Canary Islands for each alien species were

gathered from several information sources including personal obser-

vations (Appendix S1). Following Seebens et al. (2017 ), when records

of time shorter than 10 years were provided, a year within the speci-

fied range was randomly selected to avoid arbitrary peaks at, for ex-

ample, the mean value of the ranges. Records of time periods longer

than 10 years were not considered for the subsequent analysis. We

restricted the analysis to species introduced after 1500 due to the

lack of data prior the conquest of the Canary Islands by Europeans

that finished in 1496 (Fregel et al., 2009).

2.4 | Characterization of islands

Three mechanisms that can govern floristic dissimilarities of alien

floras among oceanic islands were tested, including climatic similar-

ity, geographic distance and recent connectivity by human trans-

portation (see Statistical analyses). To assess climate similarity, we

used climatic data at the finest resolution available (30 seconds)

from WorldClim (Fick & Hijmans, 2017 ). After evaluating correla-

tion between the 19 WorldClim variables and using a threshold of a

Pearson's correlation coefficient r < |0.7|, we selected three variables

with low correlation (r < |0.39|): mean diurnal temperature range,

temperature seasonality and precipitation seasonality. These three

variables describe the level of seasonality of a given region, which

have been identified as suitable proxies to explain plant invasion

success in introduced ranges across Mediterranean- type regions

(González- Moreno et al., 2015; Hierro et al., 2009). Geographic dis-

tances were calculated as the minimum distance following a straight

line between each pair of Canary islands. The recent connectivity

by human transportation was estimated considering regular connec-

tions between islands by air and sea. Data for the last 16 years (be-

tween 2004 and 2020) of commercial flights between island airports

were obtained from the ‘Instituto Canario de Estadística’ (ht tp://

w w w . g o b i e r n o d e c a n a r i a s . o r g / i s t a c / e s t a d i s t i c a s / s e c t o r s e r v i c i o s / ).

Data from linear shipping connectivity were obtained from the cur-

rent offer of the two linear shipping companies working on the ar-

chipelago (https://www.fredo lsen.es/es; https://www.navie raarm

as.com/es). The human transportation connectivity was estimated

adding up information obtained from the two above- mentioned

sources: (i) the average number of commercial flights per pair of is-

lands per year; and (ii) the number of boat trips between each pair

of islands in a year. The inverse of this connectivity matrix (M−1) was

used as a proxy for the cost or distance between islands by human

transportation.

2.5 | Statistical analyses

To test the ‘Imperialist Dogma’ Hypothesis (H1) that Mediterranean

climate regions in general, and the Mediterranean Basin in particu-

lar, have been predominant sources of invasive alien plants for the

Canary Islands, we fitted generalized linear mixed models (GLMMs)

with a Poisson distribution following a top- down strategy for model

selection (e.g. Bunnefeld & Phillimore, 2012). Specifically, we used

the number of invasive alien species from a particular region to a

given island as the response variable, and the biogeographic origin

as a predictor (fixed effect with 11 levels corresponding to each of

the source regions). In order to test if the Mediterranean Basin has

played a role in being a predominant source of invasive species, the

Mediterranean region was set as the first level of the biogeographic

origin factor. This allowed direct testing of deviations from zero of the

estimators for the remaining biogeographic regions. First, the best

ran dom effect structure, wi th the bio geo grap hic or igin factor con sid -

ered, was selected using the Akaike information criterion corrected

for small sample size (AICc) approach (Burnham & Anderson, 2002).

We ran models with and without a varying intercept across islands

as a grouping variable (seven levels corresponding to each of the

main Canary islands). A more complex model structure including a

random slope of island did not converge. Second, after finding the

best random effect structure, the importance of the fixed effect was

evaluated using the same model selection procedure based on AICc

and compared with a model only including an intercept. Models with

ΔAICc >2 relative to the best model were discarded, as they have

less statistical support (Burnham & Anderson, 2002). We also used

pairwise Tukey post hoc tests to check for differences in number of

invasive alien species between biogeographical origins. The models

were fit using ‘glmmTMB’ (Brooks et al., 2017) and ‘mixlm’ (Liland &

Sæbø, 2022) R packages.

Generalized linear models (GLM) were used to investigate the

relationship between the temporal dynamics of the naturalization

and the trend of invasive alien species accumulations at the scale

of the whole archipelago (Naturalization Rate Hypothesis, H2). The

number of invasive alien species for a given period of 50 years and

from a particular biogeographic region was set as the response vari-

able following a Poisson distribution, and the naturalization time

and the biogeographic source were the two predictor variables of

these models. In order to accept the Naturalization Rate Hypothesis, a

model including the two predictors should show a superior fit iden-

tified by AICc values, as it is expected that the accumulation rates

and origins of the alien flora naturalized in the Canary archipelago

has changed during the last 50– 60 years. To determine the goodness

of fit of the models, we calculated the adjusted amount of deviance

(adjD2) accounted for (Guisan & Zimmermann, 2000). The adjD2

takes into account the number of observations and the number of

MORENTE-LÓPEZ et a l.

predictors, thus allowing direct comparison among different models.

These analyses were performed using the R packages ‘lmtest’ (Zeileis

& Hothorn, 2002), ‘ModEvA’ (Barbosa et al., 2013) and ‘AICcmodavg’

(Mazerolle, 2020) in the R environment.

After their arrival and establishment, invasive alien species can

spread across the archipelago, potentially establishing distinctive as-

semblages in each island. In order to describe floristic relationships

among islands, we chose the weighted arithmetic average clustering

method (WPGMA) derived from the UPGMA (unweighted), a clus-

teri ng algo rit hm that has pr ov ed to perf orm well in bi ogeog rap hic re-

gionalization studies (Holt et al., 2013). To provide a complementary

non- hierarchical description of floristic relationships, islands were

plotted in a two- dimensional ordination using principal coordinates

analysis (PCoA). Then, we used a permutational multivariate analysis

of variance (PERMANOVA; Anderson, 2017 ) to compare differences

in the species composition between the groups identified by the

WPGMA and PCoA approaches; all these analyses were performed

using the R package ‘vegan’ (Oksanen et al., 2020).

To investigate the correlation between several potential driv-

ers and the variation in invasive alien plant assemblages across the

Canary Islands (Within- archipelago Climatic Matching and Enhanced

Connectivity Hypotheses, H3– 4), we performed generalized dis-

similarity models (GDM). The GDM approach accounts for the

non- linearity of the relationship between floristic dissimilarity and

distance in wide environmental and geographic gradients, consider-

ing the deviations from linearity along each individual abiotic vari-

able. For that, several monotonic I- spline basis functions are linearly

combined for each predictor, and pairwise differences among sites

are calculated along this derived function. For distance- matrix pre-

dictors, the I- spline fitting is performed directly to the distances

(Ferrier et al., 2007). A GDM was fitted using Jaccard floristic dis-

similarities between islands as the response variable, and the geo-

graphical distance matrix, the human transportation cost matrix and

three non- correlated untransformed environmental variables (diur-

nal temperature range, temperature seasonality and precipitation

seasonality) as predictors. Correlations between predictor variables

were assessed prior to analyses using the Pearson's rank correlation

coefficient r. The criterion value of r to identify multicollinearity is-

sues was set to r < |0.7| following Dormann et al. (2013). As all ab-

solute values of r were < 0.5, we assumed there was no or very low

multicollinearity. This model was then fit using the R package ‘gdm’

(Fitzpatrick et al., 2021) and the number of I- spline basis functions

to fit each predictor in the model was left as default (three). We set

100 permutations to evaluate model and variable significance and

estimate variable importance by using gdm.varImp function, in which

a backward elimination process is implemented to drop the least im-

portant variable in each step, retaining in the model only significant

predictors (p- value < 0.05). The magnitude of floristic dissimilarity

accounted for each predictor is given by the sum of coefficients of

the fitted I- splines, and the rate of change along the gradient by the

slope of the derived function (Ferrier et al., 2007). All the statistical

analyses were repeated for the invasive and naturalized alien species

groupings together (see Appendix S2).

3 | RESULTS

3.1 | The invasive alien flora of the Canary Islands

The updated list comprises 137 alien species with different levels of

invasiveness: 90 invasive and 47 naturalized plant species. If wide-

spread taxa are considered, there were 101 invasive and 48 natural-

ized species (Appendix S1). The families with the highest invasive

alien diversity in the Canary Islands are Cactaceae (18 species),

Poaceae (18), Asparagaceae (13) and Fabaceae (11), which account

for 38.5% of the alien flora with a certain level of invasiveness.

Genera such as A gave, Opuntia and Cylindropuntia had the highest

number of species (Appendix S1). Around 39.4% were herbaceous

species, while 61.6% were woody species, with only 16 tree species

(Appendix S1). The highest number of invasive alien species is found

on Gran Canaria (79 species) and Tenerife (78), while the lowest on

Lanzarote (35) and El Hierro (31) respectively.

The distribution patterns of the two groupings of species (in-

vasive vs. naturalized) are centred- skewed, with most species oc-

curring in three or four islands (3.9 ± 2.0 for invasive and 3.4 ± 2.1

for naturalized respectively). All the subsequent statistical analyses

conducted in the present study that considered only invasive alien

plants and both invasive and naturalized taxa showed a practically

identical outcome (for comparisons, see Appendix S2). For this rea-

son, hereafter, we only discuss the results for the grouping exclu-

sively including invasive alien species.

3.2 | Native ranges of invasive alien plant species

The greatest number of invasive alien species was originated from

the Neotropics (39 species), with Cape Region in South Africa

(12), tropical Africa (8) and the Mediterranean Basin (7) displaying

important complementary roles as sources to the Canary Islands

(Figure 2). These four regions account for 73.3% of the invasive alien

flora. When the proportion of each biogeographic region acting as a

source of invasive alien species was estimated within each island, the

pattern of an overrepresentation of species with a Neotropical ori-

gin followed by the Cape Region, tropical Africa and Mediterranean

Basin was consistent across the archipelago (Figure 3).

According to the GLMM analyses, the best random effect struc-

ture consistently included a random intercept of island (Table S2.1),

based on the ΔAICc and AICc- w. Using this random structure,

GLMM fits were substantially improved by including effects of

the biogeographic region acting as a source, compared with a null

model including only an intercept in the fixed structure (Table 1; see

also Table S2.2). This result supports that the number of invasive

species on each island substantially differs depending on their bio-

geographic origin. According to GLMM coefficient estimates and

Tukey post hoc tests (Figure S2.1), the number of invasive plants

was significantly higher in the Neotropical grouping compared with

groups from a Mediterranean, Cape Region, tropical African and

Australasian origins.

MORENTE-LÓPEZ et al.

3.3 | Timing of the first naturalization records

A pattern emerged in the first naturalization records of invasive

plant species. This main pattern described slow but steady increases

until approximately the 1950s, followed by stronger increases

thereafter (Figure 4). This pattern is observed in all biogeographic

groupings, with the exception of Californian species due to its re-

cent record of naturalizations. We found statistical support for the

influence of the naturalization time and biogeographic origin on the

number of invasive alien species (model 3: time and biogeographic

origin as predictors; χ2 = 53.85, p- value = 2.01*10 −08); being the

amount of variance explained high (adjD2 = 0.63). The rest of the

models had from a similar (model 1: time; ΔAICc = 0.11; χ2 = 3 7. 81,

p- value = 4.12*10 −07, adjD2 = 0.42) to an inferior fit (model 2: bio-

geographic origin; ΔAICc = 18.73; χ2 = 16.0 41, p- value = 2.96*10−03,

adjD2 = 0.09). The significance of the interaction between naturali-

zation time and biogeographic origin could not be estimated because

we did not have all the potential combinations for the two predictors

across the whole series of 50- year periods.

We also considered the time since introduction (i.e. first record),

with the goal of studying the role of residence time in determining

invasion success. Nonetheless, available information on the time

since introduction was scarce (n = 51), preventing us from achieving

such a goal. The average difference between the time of introduction

and the time of expansion was around 100 years (92.1 ± 60.3 years).

3.4 | Inter- island floristic relationships

The first PCoA axis separates the richer in number of invasive alien

plants from the poorer islands, while the second PCoA axis supports

three groupings (Lanzarote- Fuerteventura; El Hierro- La Palma- La

Gomera; and Gran Canaria- Tenerife; Figure 5a). The WPGMA clus-

tering analysis was largely consistent with the PCoA, supporting

the existence of three groupings of islands (Figure 5b). In contrast,

the PERMANOVA test failed to show significant differences in the

floristic composition of invasive species among these island groups

(pseudo- F1,6 = 1.488, p- value > 0.05).

FIGURE 2 Total number of invasive (and naturalized) alien

plant species across the Canary Islands grouped according to

the biogeographic origin. CAL, California; NEA , Nearctic; NEO,

Neotropics; EUR, Palearctic Europe; MED, Mediterranean Basin

including Europe, North Africa and Middle East; AFT, Tropical

Africa; CAP, Cape Region of South Africa; ASN, Palearctic Asia;

AST, Tropical Asia; AUM, Mediterranean Australia; AUS, Australasia.

Naturalized

Invasive

Number of species

nigiro cihpargoegoiBnigiro cihpargoegoiB

Invasive alien status

FIGURE 3 (a) Geographic extent of the archipelago of the

Canary Islands. LZ, Lanzarote; FV, Fuerteventura; GC, Gran

Canaria; TF, Tenerife; LG, La Gomera; LP, La Palma; EH, El Hierro;

(b) Bar plot showing the total number of invasive alien plant species

per island and the relative contribution of the main biogeographical

regions. CAL, Mediterranean California; NEA , Nearctic; NEO,

Neotropics; EUR, Palearctic Europe; MED, Mediterranean Basin

including Europe, North Africa and Middle East; AFT, Tropical

Africa; CAP, Cape Region of South Africa; ASN, Palearctic

Asia; AST, Tropical Asia; AUM, Mediterranean Australia; AUS,

Australasia. A version of the figure suitable for colour blindness is

provided in Supporting Information.

(a)

(b)

MORENTE-LÓPEZ et a l.

3.5 | Which factor best explains invasion

within the archipelago?

The GDM results showed that the full model that includes the three

environmental variables (diurnal temperature range, temperature

seasonality and precipitation seasonality), pairwise geographic dis-

tances and pairwise distances by human transportation explained

68.5% of the deviance. When the significance of the model and

the importance of the variables were assessed, we found that

only two variables have a significant contribution to the model (p-

value < 0.05; Figure 6): precipitation seasonality (sum of I- spline

coefficients = 0.5) and geographic distance (0.27). The final model,

including these two variables as predictors, explained 67.96% of the

deviance and was statistically highly significant (p- value < 0.001).

4 | DISCUSSION

We showed that the Neotropical region is the main source of plant

invasions to the Canary Islands, outnumbering those from other

regions with a general Mediterranean- type biogeographic region.

Our results thus provide additional evidence that floristically dis-

tant regions can become important sources of harmful invaders

(Daehler, 2003; Fridley, 2008; Seastedt & Pyšek, 2011), arguing

for alternative context- dependent explanations for the underlying

mechanisms that might contribute to invasion success on islands.

Although we observed a slow increase in numbers of invasive spe-

cies until the 1950s, followed by a stronger rise subsequently, we

failed to detect significant differences in naturalization rates among

groupings defined by their biogeographic origins. In order to explain

composition dissimilarity of the invasive flora among islands, a cli-

matic similarity hypothesis was fully su pported, with geographic iso-

lation and human- mediated connectivity hypotheses receiving less

and null support respectively. The assembly of the invasive plant

flora within the archipelago thus appears to be driven primarily by

climate, but with geographic distance also playing a role.

4.1 | Biogeographic origins of an invasive alien

island flora

Based on a floristic- driven approach, we showed that vascular

plant introductions from Neotropical regions to the Canary Islands

outnumbered those from other regions with a similar Mediterranean-

type bioclimate. Indeed, the most diverse alien genera (e.g. A gave,

Opuntia and Cylindropuntia) were of Neotropical origin. Our results

are thus at odds with the often- invoked ‘Imperialist Dogma’ (sensu

Di Castri et al., 1990) and previous findings supporting that plant

introductions are predominant from Europe to elsewhere (Monnet

et al., 2020; Seebens et al., 2017; van Kleunen et al., 2015), and

from the Iberian Peninsula to other Mediterranean- type regions

or vice versa (Cao Pinna et al., 2021; Casado et al., 2018; Di Castri

et al., 1990; Fox, 1990). In doing so, we rejected our first hypothesis

and provided novel evidence for the importance of the historical

socio- economic factors when explaining the underlying mechanisms

of plant invasion (Chapman et al., 2017; Seebens et al., 2015).

The present study is not the first that would appear to lead to

rejection of the climate matching hypothesis between source and

sink regions of invasive alien plants. The historical exchange of

goods (Jaksic & Castro, 2021) and a disproportionate representation

of plants with economic value (van Kleunen et al., 2020) have been

indeed suggested as more important drivers explaining the overrep-

resentation of European taxa elsewhere rather than actual biologi-

cal pre- adaptation. However, the archipelago of the Canar y Islands

is an environmentally complex territory, which exhibits important

climatic variations in longitude and elevation (del Arco- Aguilar &

Rodríguez- Delgado, 2018). For instance, the level of precipitation

ranges from hyperarid to humid, depending on the island, with the

coastlands exhibiting lower levels of precipitation (i.e. 50– 500 mm)

compared with northern slopes (800– 1300 mm; del Arco- Aguilar &

Rodríguez- Delgado, 2018). Hence, our study provides support for

the role of a non- Mediterranean biogeographic region as a main

source of invasive species to the archipelago rather than evidence

for the acceptance or the rejection of the climate matching hypoth-

esis. Three potential limitations of the present study can explain this

lack of resolution.

A first drawback would be related to the fact that the Neotropics

is home to more than twice as many plant species as, for instance, the

Cape Region and tropical Africa together, or as tropical Asia alone

(Raven et al., 2020). Although our study does not account for these

differences in species richness across all the source regions, recent

evidence supports the crucial role of transport and trade networks

as well as human disturbance in explaining global patterns of emerg-

ing alien species (Seebens et al., 2018). Second, we used a coarse

spatial- grained biogeographic classification to explore source– sink

relationships of an invasive alien flora in an oceanic archipelago.

TAB LE 1 Fixed effect optimization rank of the generalized mixed models performed for species richness of invasive alien plants in the

Canary Islands. df, degrees of freedom; Log (L), maximized log- likelihood; the AICc, AICc difference (ΔAICc); and Akaike weights derived

from the AICc (AICcw) are given for each model. The proportion of the total variation in species richness among islands (R2) that is accounted

for by selected GLMMs is indicated

df log (L)AICc ΔAICc AICcw

Conditional Marginal

Species Richness ~ Intercept + Origin +

(1|Island)

12 −12 3 . 2 276 . 0 0.0 10.83 0.77

Species Richness ~ Intercept + (1|Island) 2−323.2 650.6 374 . 6 0.0 0.24 0

MORENTE-LÓPEZ et al.

Lastly, the main transport hubs are located in the low, dry, warm

south- eastern areas in each of the Canary islands, which might have

increased the introduction risk of species with such ecological re-

quirements. Our approach, therefore, renders the question of the

extent to which climate matches between the main species source

pools and the Canary archipelago open.

4.2 | The tempo of invasion

It has previously been proposed that introductions peaked during

the last 200 years due to (i) major migration waves of European set-

tlers in the 18th and 19th century and (ii) the acceleration of global

trade in the 20th century, with Europeans bringing most species

they liked or needed from home (Hulme, 2009; Seebens et al., 2015;

Seebens et al., 2017). Accordingly, our study demonstrates that most

of the floristic groupings considered, including the Mediterranean

Basin, did not show any sign of saturation, rather their rates of natu-

ralization increased during the 1950s or thereafter. Moreover, the

magnitude of the increase in the number of invasive alien species

varies considerably among biogeographic regions, with a different

balance of source regions in recent times compared to historical

FIGURE 4 Temporal patterns in first record rates of

naturalization represented by accumulation curve areas of

invasive alien plant species. For visualization, 20- year and 50- year

periods are distinguished for all origins and each biogeographical

region respectively. Time series for biogeographic regions with

low numbers of first records are not shown. NEO, Neotropics;

AFT, Tropical Africa; CAP, Cape Region of South Africa; MED,

Mediterranean Basin including Europe, North Africa and Middle

East; AUS, Australasia; CAL, California. The dashed line denotes the

beginning of the 1950s.

All origins

Species accumulation

CAL

AFT

AUS

MED

CAP

NEO

Date of naturalization

FIGURE 5 Clustering of the seven main Canary Islands

according to their differences in invasive alien plant species

assemblages. General biogeographical patterns inferred from: (a)

principal coordinate ordination (PCoA) analysis and (b) hierarchical

classification using weighted arithmetic average clustering

(WPGMA) as the linkage method. Acronyms in each plot represent

each island as follows: LZ, Lanzarote; FV, Fuerteventura; GC, Gran

Canaria; TF, Tenerife; LG, La Gomera; LP, La Palma; EH, El Hierro.

(a)

(b)

MORENTE-LÓPEZ et a l.

times. All these findings lead to the support of the Naturalization

Rate Hypothesis (H2).

Ba sed on ou r results, we pr o p ose that th e in cidenc e of naturali za-

tions of Mediterranean (and European) plants in the Canary archipel-

ago during the historical European human diaspore was insignificant.

Since the first colonial European voyages, through to the present,

commercial routes from Europe were established as bidirectional,

transiting through the Canary Islands for connections with central

and South America and tropical Africa (Aldrich & Connell, 1998;

Armenteros Martínez, 2018; Bosa, 200 4; Parsons, 1983; Santana-

Pérez, 2018). This historical dynamic provides support for two non-

exclusive potential explanations.

The first explanation implicates the Canarian and European mi-

grant groups that have travelled back to the Canary Islands during

different waves from regions such as Mexico, Cuba, Venezuela

and Uruguay (Parsons, 1983), particularly under flourishing socio-

political periods in the archipelago. From where, and how many of

these returned remain open questions (James, 1985). In addition,

the Canary archipelago has played a historical role as a hub for

European– American trading routes, with trade connectivity increas-

ing over time (Aldrich & Connell, 1998; Bosa, 2004; Parsons, 1983).

These migration and trade circumstances have produced concen-

trated migration that likely explains the high rates of invasion by

alien plant species from Central and South America, mainly for ag-

ricultural and horticultural purposes (e.g. González, 2008; Verloove

et al., 2019). All these historical changes in networks of human

migration and commerce from and to the Canarian archipelago ex-

emplify the need for revisiting the original ‘Imperialist Dogma’ hy-

pothesis (Crosby, 2004; Di Castri, 1989; Di Castri et al., 199 0), in

order to accommodate the emerging patterns and challenges arising

from accelerating rates of global change associated with increasing

human trade and transport.

With regard to the second explanation, it may be possible

that additional alien species of Mediterranean Basin origin have

been incorrectly considered as native, due to an apparent limited

geographic and environmental distance between these continen-

tal and insular regions. This could significantly reduce the number

of species categorized as ‘invasive’ or ‘naturalized’ and inflate the

number of species wrongly considered as ‘probably native’ in-

cluded in the regional species checklist BIOTA (https://www.biodi

v e r s i d a d c a n a r i a s . e s / ). This potential source of uncertainty calls

for genetic approaches to identify and confirm the alien status of

cryptogenic plant species (Brandes et al., 2019; Briski et al., 2016),

namely if they exhibit efficient dispersal capabilities (Patiño &

Vanderpoorten, 2015).

4.3 | Within- archipelago assembly mechanisms

Our analyses show that the floristic composition of invasive plants

is strongly determined by climatic similarity within the archipelago

and, to some extent, by geographic distance. This result is puzzlin g

because of the signature of floristic homogenization evidenced by

the fact that: (i) the different floristic elements exhibited consist-

ent proportions across the Canary Islands; (ii) most invasive alien

species occur in several islands; and (ii) PERMANOVA tests were

not significant. However, consistent with the Within- archipelago

Climate Matching Hypothesis (H3 ), Lanzaro te and Fue rtev entur a are

floristically more similar, which can be explained by the fact that

these two islands are the driest, topographically simplest and geo-

graphically nearest (del Arco- Aguilar & Rodríguez- Delgado, 2018).

Indeed, the arrangement and apparent groupings of the islands

along the second PCoA axis reveal a pattern that could be ex-

plained, to some extent, by differences in precipitation, topogra-

phy and longitude (del Arco- Aguilar & Rodríguez- Delgado, 2018).

Overall , there is indeed congr uence between the inter- island com-

position differences in invasive floras identified here and the clas-

sic floristic delineation inferred from Canarian native assemblages

(de Nicolás et al., 1989). The latter has often identified two floris-

tic entities, Lanzarote- Fuerteventura versus central and western

FIGURE 6 Generalized dissimilarity modelling (GDM) results. (a) Relationship between the observed pairwise floristic dissimilarity in

invasive alien species between islands and the ecological distance predicted by the preferred GDM model (predicted ecological distance

between islands). (b– c) GDM- fitted I- splines for each predictor of the preferred model: Precipitation seasonality and geographic distance.

The sum of coefficients of the fitted I- splines (maximum height of the curve) indicates the predictor importance in explaining the floristic

composition dissimilarity of invasive alien species.

0.40.5 0.60.7 0.8 0.9

0.00.2 0.40.6 0.81.0

Predicted Ecological Distance

Observed Compositional

Dissimilarity

84 85 86 87 88 89 90 91

0.00.1 0.20.3 0.40.5

Precipitation seasonality

Partial ecological distance

0e+001e+05 2e+053e+05

Geographical distance (m)

(a) (b) (c)

MORENTE-LÓPEZ et al.

islands (del Arco- Aguilar & Rodríguez- Delgado, 2018). Therefore,

our data imply that climate similarity and geographic distance can

interact (i.e. closer islands have a more similar climate than more

distant islands) to shape assemblages of invasive plants on islands.

Such an observation is in line with former evidence for other flo-

ristic and geographic contexts (e.g. Cao Pinna et al., 2021; Capinha

et al., 2015; Monnet et al., 2020).

However, our proxies for environmental distance are based

on temperature and precipitation at the scale of 1- km2 cells (Fick

& Hijmans, 2017) that can be poor descriptors of actual climatic

gradients in topographically complex small islands (e.g. Ferreira

et al., 2016). In addition, climate similarity has been shown to be less

evident on subtropical, high- elevation islands, which often exhibit a

broad array of climate zones due their high topographic complexity

(Essl et al., 2019; Kueffer et al., 2010). Although such distributional

patterns on islands and their underlying mechanisms need further

research (Lenzner et al., 2020; Patiño et al., 2017), we expect that

climatic similarity would gain importance versus geographic isola-

tion, if finer spatial- scale species distribution and climate data can

be considered in future studies.

Our statistical approach provided no support for a pattern

of human- mediated connectivity mechanisms. This result is at

odds with our Enhanced Connectivity Hypothesis (H4) and for-

mer evidence supporting the role of trade networks (Chapman

et al., 2017; Hulme, 2009; Seebens et al., 2015). Such a finding

is likely the combined result of different factors. First, the avail-

able transport network datasets cover a short period of time (i.e.

less than 20 years), while most introduction and naturalization ep-

isodes have happened earlier (76%; see Appendix S1). Second, as

demonstrated for other regions and taxonomic groups (Chapman

et al., 2017), we expect that the live plant trade in the Canary

Islands might have significantly contributed to explain recent in-

troduction episodes of invasive plants to and across the Canarian

archipelago. This is remarkable at the regional scale because the

journeys bet ween islands experien ce d by alien li ve plants and thei r

propagule are short, which ultimately facilitates invasion success

driven by live plant imports (Seebens et al., 2015; van Kleunen

et al., 2018). Despite the high uncertainty in the directionality and

intensity of historical trade networks (Cao Pinna et al., 2021), re-

cent trade networks (i.e. after the 1950s) might explain invasion

success due to the increasing volumes handled by sailing container

shipping and commercial jet aviation, and the rise of the interna-

tional e- commerce (Hulme, 2021). Thus, to what extent invasions

driven by live plant trade have taken place among already invaded

or native- invaded ecological systems remains largely untested in

many regions, like the Canary Islands.

5 | CONCLUSIONS

We provide evidence that biogeographic affinities are not al-

ways the most important factors determining the predominant

continental sources of alien plant species to insular recipients,

even if they differ in their invasiveness status (i.e. invasive vs.

naturalized). Both climate similarity and geographic distance are

clearly important in explaining floristic relationships of the in-

vasive flora within the Canarian archipelago. Nevertheless, our

results also illustrate how archipelago- dependent processes can

cause idiosyncratic, yet prevalent patterns of invasion success, ul-

timately reinforcing the view of biotic homogenization as a main

driver of insular floras (Castro et al., 2010; Kueffer et al., 2010;

Sánchez- Ortiz et al., 2020).

From a more applied perspective, our study helps to understand

the biogeographic origins of the invasive alien flora of the Canary

Islands, highlighting the need to control and monitor alien species of

non- Mediterranean origin. Among these taxa, we find many exam-

ples within the most biodiverse Neotropical group (e.g. Opuntia spp.,

Agave spp., Cylindropuntia spp., Austrocylindropuntia spp., Furcraea

foetida, Prosopis juliflora), which are predominantly composed of spe-

cies with ecological affinity for arid habitats such as deserts or savan-

nahs (Eguiarte et al., 2021; Filip et al., 2 017; Guerrero et al., 2019).

In this respect, these species often occur in disturbed lowlands

(e.g. cliffs next to sea; Filip et al., 20 17; Haider et al., 2010) and an-

thropogenic corridors (e.g. roadsides; Arévalo et al., 20 05; Bacaro

et al., 2015; Irl et al., 2021) across arid areas in the archipelago. The

heavily human- disturbed lowlands and coastlands, including arid

and semiarid coastal scrubs and semiarid thermophilous woodlands

(del Arco- Aguilar & Rodríguez- Delgado, 2018), are therefore more

likely to be invaded by new arrivals from within this biogeographical

grouping, particularly under ongoing climate change. A similar pat-

tern has been proposed for continental Spain (Andreu & Vilà, 2010),

which might be particularly aggravated by global warming. Effective

biosecurity policies to regulate ornamental trade, especially those

promoted by xero- gardening, and importations from Neotropics and

arid regions should become a management priority in the Canarian

and, most probably, Macaronesian regions. This conclusion urgently

calls for the cooperation of the horticultural and tourism industries.

ACKNO WLE DGE MENTS

This research was supported by the Fundación BBVA pro-

ject (INVASION - PR19_ECO_0046) and the Spanish Ministry of

Science and Innovation (MICINN) project (ASTERALIEN - PID2019-

110538GA- I00). J.M.- L. was funded by the INVASION Fundación

BBVA project and by a Juan de la Cierva- Formación Fellowship

(MICIIN; reference FJC2020- 046353- I). Y.A. by the ASTERALIEN

MICINN project. J.P. was funded by the MICINN through the Ramón y

Caj al Pr ogram (RYC- 2 016 - 2 0506) . L. S.J.G . wa s funded by the Acad emi a

Canaria de Investigación Gobierno de Canarias FPI 2021 Fellowship

(TESIS2021010101). The authors also thank Dr. D. Chapman and two

anonymous reviewers for their constructive comments and sugges-

tions. No permits were needed to perform this study.

CONFLICT OF INTEREST

The authors declare that we have no conflict of interest.

MORENTE-LÓPEZ et a l.

DATA AVA ILAB ILITY STATE MEN T

The data that support the findings of this research can be found in

the Supporting Information.

ORCID

Javier Morente- López https://orcid.org/0000-0001-9141-8581

Yurena Arjona https://orcid.org/0000-0002-1851-1664

Marcos Salas- Pascual https://orcid.org/0000-0003-2882-4469

J. Alfredo Reyes- Betancort https://orcid.

org/0000-0003-0732-3219

Marcelino J. del Arco- Aguilar https://orcid.

org/0000-0001-9063-2594

Brent C. Emerson https://orcid.org/0000-0003-4067-9858

Louis S. Jay- García https://orcid.org/0000-0003-3764-7919

Agustín Naranjo- Cigala https://orcid.org/0000-0002-3966-2592

Jairo Patiño https://orcid.org/0000-0001-5532-166X

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Nature Communications, 12(1), 7290.

Zeileis, A., & Hothorn, T. (2002). Diagnostic checking in regression rela-

tionships. R News, 2(3), 7– 10.

BIOSKETCH

Javier Morente- López is a postdoctoral researcher at Instituto

de Productos Naturales y Agrobiología (IPNA- CSIC) in the

Department of Life and Earth Sciences (Tenerife). His research

addresses the mechanisms that influence the success of plant in-

vasive species at the community level.

Yurena Arjona is a postdoctoral researcher at Department of

Botany, Ecology and Plant Physiology in the La Laguna University

(Tenerife). Her research addresses the evolutionary mechanisms

that influence the success of plant invasive species within certain

families at the Canary Islands.

Jairo Patiño is a researcher at Instituto de Productos Naturales y

Agrobiología (IPNA- CSIC) interested in island biogeography and

the study of ecological and evolutionary processes shaping the

changes in the distribution of biodiversity facets over time and

space. Additional information about the lab and ongoing research

projects can be found at http://iecoe volab.com/.

Author contributions: Jairo Patiño and Marcos Salas-Pascual

conceived the idea and designed the study. Marcos Salas-Pascual,

J. Alfredo Reyes- Betancort, Antonio García-Gallo and Jairo Patiño

assembled the data. Agustín Naranjo-Cigala prepared the car-

tography. Javier Morente-López, Yurena Arjona and Louis S. Jay-

García carried out all statistical analyses. JP wrote the first draft

of the manuscript. All co- authors contributed substantially to

revisions. Editor: Daniel Chapman.

SUPPORTING INFORMATION

Additional supporting information can be found online in the

Supporting Information section at the end of this article.

How to cite this article: Morente- López, J., Arjona, Y.,

Salas- Pascual, M., Reyes- Betancort, J. A., del Arco- Aguilar,

M. J., Emerson, B. C., García- Gallo, A., Jay- García, L. S.,

Naranjo- Cigala, A., & Patiño, J. (2023). Biogeographic origins

and drivers of alien plant invasions in the Canary Islands.

Journal of Biogeography, 00, 1–15. https://doi.org/10.1111/

jbi.14556

ResearchGate has not been able to resolve any citations for this publication.

Biological Invasions in the Anthropocene. In book Biological invasions in the South American Anthropocene: Global causes and local impacts.

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Apr 2021

The global loss of floristic uniqueness

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Dec 2021

The global loss of floristic uniqueness

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Dec 2021

Regional species assemblages have been shaped by colonization, speciation and extinction over millions of years. Humans have altered biogeography by introducing species to new ranges. However, an analysis of how strongly naturalized plant species (i.e. alien plants that have established self-sustaining populations) affect the taxonomic and phylogenetic uniqueness of regional floras globally is still missing. Here, we present such an analysis with data from native and naturalized alien floras in 658 regions around the world. We find strong taxonomic and phylogenetic floristic homogenization overall, and that the natural decline in floristic similarity with increasing geographic distance is weakened by naturalized species. Floristic homogenization increases with climatic similarity, which emphasizes the importance of climate matching in plant naturalization. Moreover, floristic homogenization is greater between regions with current or past administrative relationships, indicating that being part of the same country as well as historical colonial ties facilitate floristic exchange, most likely due to more intensive trade and transport between such regions. Our findings show that naturalization of alien plants threatens taxonomic and phylogenetic uniqueness of regional floras globally. Unless more effective biosecurity measures are implemented, it is likely that with ongoing globalization, even the most distant regions will lose their floristic uniqueness.

Unwelcome exchange: International trade as a direct and indirect driver of biological invasions worldwide

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Full-text available

May 2021

Philip Hulme

Biological invasions are synonymous with international trade. The direct effects of trade have largely been quantified using relationships between imports and the number of alien species in a region or patterns in the global spread of species linked to shipping and air traffic networks. But trade also has an indirect role on biological invasions by transforming the environments and societies of exporting and importing nations. Here, both the direct and indirect roles of trade on biological invasions, as well as their interaction, are examined for the first time. Future trends in international trade, including e-commerce, new trade routes, and major infrastructure developments, will lead to the pressure on national borders soon outstripping the resources available for intervention. The current legislative and scientific tools targeting biological invasions are insufficient to deal with this growing threat and require a new mindset that focuses on curbing the pandemic risk posed by alien species.

Biogeographical origin effects on exotic plants colonization in the insular flora of Japan

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Sep 2021
BIOL INVASIONS

Understanding the mechanisms of biological invasion is fundamental for biodiversity conservation in the Anthropocene. This study focused on a large-scale colonization pattern of exotic seed plants, which include 1094 species characterized by different geographical origins, into the insular flora of Japan. We investigated a nation-wide pattern of species richness and phylogenetic structure (clustering/over-dispersion) of exotic and its recipient native species (4664 species). We tested the invasion hypotheses associated with environmental filtering, biological resistance of recipient assemblages, human disturbance and biogeographical origins of exotics. The exotics originated from the same (Palearctic and Indo-Malay) and adjacent (Nearctic and Oceanic) biogeographical regions were widely distributed across the country under temperate climate condition, whereas tropical exotic plants from remote regions (Afrotropic, Australasian, and Neotropical) colonized mainly the south-western parts of Japan. Exotic species richness and phylogenetic structure, especially those from the same/adjacent regions, were well explained by climatic, edaphic, and topographic factors, supporting the environmental filtering hypothesis. For all the biogeographical origins, exotic richness was positively associated with native richness, opposing the biological resistance hypothesis. Human disturbance was positively associated with exotic richness, while its relationships with the exotics’ phylogenetic structure varied according to their biogeographical origins. These findings indicate that site’s invasibility was determined by the combination of exotic’s biogeographical origins and abiotic/biotic conditions of its recipient native flora. Our results suggest that global warming may accelerate the northward expansion of tropical exotic plants while future land-use changes can promote biological invasion regardless of exotics’ origins.

Human impact, climate and dispersal strategies determine plant invasion on islands

Article

Full-text available

May 2021

Aim Biological invasions are likely determined by species dispersal strategies as well as environmental characteristics of a recipient region, especially climate and human impact. However, the contribution of climatic factors, human impact, and dispersal strategies in driving invasion processes is still controversial and not well embedded in the existing theoretical considerations. Here, we study how climate, species dispersal strategies, and human impact determine plant invasion processes on islands distributed in all major oceans in the context of directional ecological filtering. Location Six mountainous, tropical, and subtropical islands in three major oceans: Island of Hawai'i and Maui (Pacific), Tenerife and La Palma (Atlantic), and La Réunion and Socotra (Indian Ocean). Taxon Vascular Plants. Methods We recorded 360 non‐native species in 218 plots along roadside elevational transects covering the major temperature, precipitation and human impact (i.e., road density) gradients of the islands. We collected dispersal strategies for a majority of the recorded species and calculated the environmental niche per species using a hypervolume approach. Results Non‐native species’ generalism (i.e., mean community niche width) increased with precipitation, elevation and human impact but showed no relationship with temperature. Increasing precipitation led to environmental filtering of non‐native species resulting in more generalist species under high precipitation conditions. We found no directional filtering for temperature but an optimum range of most species between 10 and 20°C. Niche widths of non‐native species increased with the prevalence of certain dispersal strategies, particularly anemochory and anthropochory. Main conclusions Plant invasion on tropical and subtropical islands seems to be mainly driven by precipitation and human impact, while temperature seems to be of little importance. Furthermore, anemochory and anthropochory are dispersal strategies associated with large niche widths of non‐native species. Our study allows a more detailed look at the mechanisms behind directional ecological filtering of non‐native plant species in non‐temperature‐limited ecosystems.

Ecological impacts. In book Biological invasions in the South American Anthropocene: Global causes and local impacts.

Chapter

Full-text available

Apr 2021

As we have seen in the previous chapter, the presence of invasive species is often associated with the extinction of native species (Wilcove et al. 1998; Ricciardi 2004). Although the generality of this fact has been questioned by some authors (Didham et al. 2005; Davis 2009), there is no doubt that once arrived and established, invasive species can affect to a greater or lesser extent the structure and functioning of the ecosystems they invade (Vitousek et al. 1987; Chesson 2000; Crooks 2002).

Biological Invasions in the South American Anthropocene: Global Causes and Local Impacts

Book

Jan 2021

Evolutionary ecology of Agave: distribution patterns, phylogeny, and coevolution (an homage to Howard S. Gentry)

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Feb 2021
AM J BOT

With more than 200 species, the genus Agave is one of the most interesting and complex groups of plants in the world, considering for instance its great diversity and adaptations. The adaptations include the production of a single, massive inflorescence (the largest among plants) where after growing for many years, sometimes more than 30, the rosette dies shortly afterward, and the remarkable coevolution with their main pollinators, nectarivorous bats, in particular of the genus Leptonycteris. The physiological adaptations of Agave species include a photosynthetic metabolism that allows efficient use of water and a large degree of succulence, helping to store water and resources for their massive flowering event. Ecologically, the agaves are keystone species on which numerous animal species depend for their subsistence due to the large amounts of pollen and nectar they produce, that support many pollinators, including bats, perching birds, hummingbirds, moths, and bees. Moreover, in many regions of Mexico and in the southwestern United States, agaves are dominant species. We describe the contributions of H. S. Gentry to the understanding of agaves and review recent advances on the study of the ecology and evolution of the genus. We analyze the present and inferred past distribution patterns of different species in the genus, describing differences in their climatic niche and adaptations to dry conditions. We interpret these patterns using molecular clock data and phylogenetic analyses and information of their coevolving pollinators and from phylogeographic, morphological, and ecological studies and discuss the prospects for their future conservation and management.

The biogeography of alien plant invasions in the Mediterranean Basin

Article

Dec 2020

Aims Humans have deeply eroded biogeographic barriers, causing a rapid spread of alien species across biomes. The Mediterranean Basin is a biodiversity hotspot but is also known as a hub of alien plant invasions, particularly in its European part. Yet, a comprehensive inventory of alien species in the area is missing and understanding of the drivers of Mediterranean invasions is poor. Here we aim to identify the main alien plant species in the European part of the Mediterranean Basin and quantify their invasion success in order to understand the plant species flows from other biomes of the world. Location The Mediterranean region of Europe, Anatolia and Cyprus. Methods We analysed 130 000 georeferenced vegetation plots from the European Vegetation Archive (EVA) and identified 299 extra‐European alien plant species. We identified their biomes of origin and quantified the mean geographic distance, trade exchange and climatic similarity from each biome to the study area. After estimating the invasion success of each species in the study area, we tested which biomes have donated more alien species than expected by chance and which drivers best explain these non‐random patterns. Results We found that other Mediterranean climatic regions, as well as Temperate and Xeric biomes of the world, are the main donors of successful alien species to Mediterranean Europe, beyond what would be expected by chance. Our results suggest that climatic matching, rather than geographic proximity or trade, has been the most important driver of invasion. However, climatic pre‐adaptation alone also does not appear to predict the invasion success of established species in the study area. Conclusions Our results highlight the need to pay special attention to alien plant species from the same or climatically similar biomes, but also suggest that further research is needed for early screening of the most problematic alien species.