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Global change and biological invasions:Why are some regions
more invaded than others?
Presentation outline
● Brief introduction: stages of alien invasion
● Patterns and mechanisms of invasion of alien plants in temperate mountains
● Invasion of alien Scolytids across Europe and the USA
● Conclusions
Stages of alien invasion
Native region
Colo
niz
ati
on
&
pro
pag
ule
pre
ssu
re
ESTABLISHMENT
INTRODUCTION
Establishment is expected to depend on size and frequency of introduction events and quality of the recipient regions
SPREAD
T0
Time
T1
Human-mediated introduction
POPULATION LEVEL
Propagule pressure
Pro
bab
ility
of e
sta
blis
hm
en
t
Colonization pressure
No
sp
eci
es
est
abl
ish
ed
COMMUNITY LEVEL
Allee effect
0
1
0
Saturation?n
The more you introduce the more you get
Establishment
Quality of the recipient region acts as amulti-dimensional filter
Main question addressed in the seminar
Is introduction effort more important than the quality of the recipient regions?
Important implications for prevention and management
Patterns and mechanisms of invasion of alien plants in temperate mountains
Marini et al. (2012) Global Ecology & Biogeography
Marini et al. (2009) Global Ecology & Biogeography
Marini et al. (2013) Global Ecology & Biogeography
Marini et al. (2011) Journal of Biogeography
Alien plant invasions in temperate mountains
● Most studies of invasive alien species have concentrated on lower elevations, while little attention has been directed to the most pristine high-elevation environments
● Relative isolation and harsh climatic conditions may have allowed mountain ecosystems to experience lower levels of alien species invasions than have lowland areas
Are cold regions inherently resistant to alien invasions?
Something has changed
The constraining factors of invasion are now changing due to globalization and climate change, increasing the chances of
plant invasions into high-elevation environments
CLIMATE CHANGELAND-USE CHANGE
Urbanization and alien plants
Will alien and native plant species respond similarly?
Increased disturbance and movement of people
Alie
n s
peci
es
rich
ness
UrbanizationHuman population
Increased available niches and propagule pressures
Native
Alien
?
Climate change and alien plants
Will alien plant species respond like natives? E
levati
on
op
tim
um
Species temperature requirements
Potential elevation optimum
Realized elevation optimum
Dispersal limitation:Time lags in tracking
climate change(immigration credit?)
Species A
Species B
Upwards shift of the limiting thresholds
Global change and alien plants
Is introduction effort more important than climate?
Try to disentangle the effects of climatic and human pressures on the invasion of exotic plant in the Alps to
make predictions of global change effects
Methods: data
Study area: NE of Italy
Floristic inventories (more than 1,000,000 records)
Comparable sampling effort in all cells
Species richness & composition
100 km
36 km2
36 km2
Elevational patterns of species richness
Drivers: Drivers:Population density TemperatureCalcareous bedrockTopographic heterogeneity
Population densityTemperature
Marini et al. (2008) Journal of Biogeography
Marini et al. (2011) Journal of Biogeography
Natives Aliens
Species-human-energy relationships
Natives
Natives
Aliens
Aliens
-4.0
-2.0 0.
02.
04.
06.
08.
010
.012
.014
.016
.00
100200300400500600700800900
1000
Mean temperature (°C)
Na
tiv
e s
pe
cie
s r
ich
ne
ss
-4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.012.014.016.00
50
100
150
200
250
300
Mean temperature (°C)
Ali
en
sp
ec
ies
ric
hn
es
s
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.50
100
200
300
400
500
600
700
800
900
1000
Log(Human density)
Na
tiv
e s
pe
cie
s r
ich
ne
ss
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.50
50
100
150
200
250
300
Log(Human density)
Ali
en
sp
ec
ies
ric
hn
es
s
Marini et al. (2009) Global Ecology and Biogeography
Why a differential response of aliens vs. natives?
Two hypotheses:
i) Different composition of life-history traits among alien and native species pool alter species richness response to human and climatic factors
ii) Alternatively a dominant effect of human population through accidental or deliberate introduction and creation of novel niches favouring alien establishment should result in differential responses of aliens vs. natives irrespective of life-history traits
We tested if plant life-form or native/alien status modifies the species richness response to temperature and humans
Marini et al. (in press) Global Ecology and Biogeography
Plant life-forms
Trees
Perennial herbaceous Annuals
Structures to survive during adverse season
TherophytesGeophytesHemicryptophytes
Phanerophytes
For natives we know well that different life-forms present differential response to temperature along elevational gradients
An overwhelming effect of human pressures on alien species richness can mask any life-history trait effect mediating response to the environment
Hypotheses
Temp. x Life-form (natives)=Tempe. x Life-form (aliens)
Temp. x Life-form (natives) but no Temp. x Life-form (aliens)
Different composition of life-history traits among alien and native plants alters species richness response to human and climatic factors
Different life-form spectraNatives=2301Aliens=187
Species-temperature relationship
Natives
Aliens
Spec
ies r
ichn
ess
Mean annual temperature (°C)
Natives≠Aliens
Species-human relationship
Natives≠Aliens
Natives
Aliens
Log(Human population)
Spec
ies
richn
ess
Dominant effect of human pressures
● Climate filtering is expected to play a secondary role
● The differential responses of aliens vs. natives irrespective of life-forms indicates a dominant effect of human population through accidental or deliberate introduction and creation of novel niches on alien establishment
● Any effect of climate would be contingent on human pressures
Patterns and drivers of species richness are clear
Elevation (m)
0 1000 2000 3000
Leve
l of i
nva
sion
(%
)
0
10
20
30
40
50
60
70
Alie
n s
pec
ies
rich
ness
Elevation (m)
What about species composition and identity?
Are the invaders mountain specialists or generalists?
Which are the pathways of introduction?
Which are the mechanisms thatgenerate this pattern?
Lowland pathwayof introduction
Hypothesis: Directional environmental filtering
This hypothesis assumes that most alien species are introduced from lowlands to lowlands and spread up the mountain from there
Species pool
Elev
ation
(m)
Source regionsRecipient
mountain region
Mountain
No introductions from cold areas
Elevation range
~ 600 ALIENS ~ 3000 NATIVES
2% restricted >1000m
20% restricted>1000m
Species ranking according to max elevation
Ele
vati
on
ran
ge (
m)
Almost all alien species extend their elevation range in the lowlands
Compositional β-diversity
0< βtot<1El
evati
on (m
)
Latitu
de
Longitude
Species richnessdifference
Speciesreplacement
n ce
lls
n cells
n ce
lls β
βtot = βrich + βrepl
βtot =1
βtot =0 (100% same species)
(complete dissimilarity)
Next analyses based on distance matrices
cell A cell B
Patterns of β-diversity
β richness difference
β r
ep
lacem
en
t
βtot=1Complete dissimilarity
Natives Aliens
β r
ep
lacem
en
t
Aliens have larger β richness difference than natives
Aliens have smaller β replacement than natives
Drivers of β replacement
β Explanatory~
β repl
Nati
ves
β repl
Alie
ns
ALIENS: Larger replacement between cells with similar environmental conditions
NATIVES: Larger replacement between cells with different environmental conditions
βrich βrepl
Human distance Temp. distance (°C)
Analyses based on distance matrices
Mechanism of invasion
Marini et al. (in prep.)
In the long-term we will cash the accumulated invasion credit
Cu
rren
t sit
uati
on
Fu
ture
scen
ari
o
Still high floristic differentiation in the lowlands
Elevation (m)
0 1000 2000 3000
Leve
l of i
nvas
ion
(%)
0
10
20
30
40
50
60
70
Future scenarios of plant invasions
In the short term we expect strong biotic homogenization at low- and mid-elevations and small changes at high elevations
Assembly of alien plant communities on mountains are primarily driven by processes occurring in the lowlands
Future
Current
In the long-term we will probably cash the accumulated invasion credit
Investigation of the alien communities occurring in the lowlands might provide new tools to prevent invasions in high-elevation areas by predicting the potential pool of invaders and their elevational distribution
Exploring the effects of trade and environment on exotic Scolytinae (Coleoptera) invasions
Marini et al. (2011) Biological Invasions
Introduction: Alien scolytid invasions
● Bark and ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) are amongst the most important pests causing significant economic damage to forest trees worldwide
● In the past few decades, establishment of alien species has steadily increased in both Europe and North America
● Alien species might have important ecological and economic impacts
Introduction: Alien scolytid pathways
● in the actual product being transported (e.g., nuts, seeds, logs, lumber, nursery stock)
● in the associated wood packing material or dunnage, or
● as hitchhikers on ships. containers, and airplanes
International trade facilitates the spread of these pests given that scolytids can move:
Unlike plants, insects are mostly introduced accidentally
Introduction
Recipient country/state
Import
Trade
Is introduction effort more important than local conditions?
Methods: data
Study area: continental USA and Europe
Response variable: Number of native and alien species established in each state/country
Predictors: Two groups of variables:(i) Economy (Import): proxy for colonization and propagule pressures(ii) Environment of the recipient region (forest area, temperature, rainfall,
forest diversity, climatic heterogeneity)
General results: feeding strategies
Level of invasion (alien/native)~10-15%
Aliens more frequently Ambrosia than natives
Ambrosia life-history traits favoring invasion:(i) haplodiploidy, i.e. the ability to produce male offspring without mating,(ii) sib-mating, i.e. brother-sister mating prior to emergence from the host tree,(iii) symbiotic trophic specialization with fungi that obviates the need to overcome many
host defenses, and(iv) low host specificity and ability to breed in dead wood
n=20n=57n=223n=469
US native EU native US alien EU alien
General results: alien species invasion
Much higher diversity of alien species in the USA than EU
Higher levels of exotic invasions in the USA than EU
Relative importance of the driversSu
m o
f mod
el w
eigh
ts (w
i)
US native
EU native
US alien
EU alien
Alien richness patterns: Import
€€€ The consequences of being rich $$$:The more you introduce the more you get
Amongst our 6 variables IMPORT was always the best predictor
Does feeding strategy modify species richness response to climatic gradients?
Test was possible only in the USA (no enough species in EU)
Climate was less important in Europe than in the USA
Exotic richness patterns: Climate
OR
RainfallTemperature
Spec
ies
richn
ess
Ambrosia
Bark
Ambrosia
Bark ?
RainfallTemperature
Ambrosia vs. bark beetlesSu
m o
f mod
el w
eigh
ts (w
i)
Conclusions
● Our study suggests that growing international trade is the primary factor contributing to escalating rates of scolytid invasions worldwide
● Climate and land-use effects are of secondary importance
● More attention is needed to prevent or reduce the arrival rate of alien species through international trade
● Although international standards have been implemented, individual countries can further reduce the likelihood of establishment and spread of exotic organisms through pest and pathway risk assessments, improved inspection techniques, and early detection surveys
Main question addressed in the seminar
Is introduction effort more important than the quality of the recipient regions?
In most cases yes!
Pyšek et al. PNAS (2010)
Conclusions
The current growth in human population and in the volume and diversity of trade will increase the frequency of new introductions and hence the probability that an introduced species will spread and have an impact whatever the local conditions
The strong influence of demographic and economic factors on the level of invasion by alien species demonstrates that future solutions to the problem of biological invasions will be a considerable challenge
No regions (or very few) can be considered inherently resistant
Thank you for your attention
PRATIQUE informationhttps://secure.fera.defra.gov.uk/pratique/
Lorenzo MariniE-mail: [email protected]
http://www.biodiversity-lorenzomarini.eu/
Contact details:
SCALES informationhttp://www.scales-project.net/