Download Slide 1 - Lorenzo Marini

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
INTRODUCTION
Colonization
& propagule
pressure
Native region
ESTABLISHMENT
T0
SPREAD
T1
Time
Establishment is expected to depend on size and frequency
of introduction events and quality of the recipient regions
POPULATION LEVEL
1
Allee effect
0
Propagule pressure
No species established
Probability of establishment
Human-mediated introduction
n
0
COMMUNITY LEVEL
Saturation?
Colonization pressure
The more you introduce the more you get
Establishment
Quality of the recipient region acts as a
multi-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. (2009) Global Ecology & Biogeography
Marini et al. (2011) Journal of Biogeography
Marini et al. (2012) Global Ecology & Biogeography
Marini et al. (2013) Global Ecology & 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
LAND-USE CHANGE
CLIMATE CHANGE
Urbanization and alien plants
Alien species richness
Will alien and native plant species respond similarly?
Alien
?
Native
Urbanization
Human population
Increased disturbance
and movement of people
Increased available niches and
propagule pressures
Climate change and alien plants
Will alien plant species respond like natives?
Elevation optimum
Potential elevation
optimum
Realized elevation
optimum
Dispersal limitation:
Time lags in tracking
climate change
(immigration credit?)
Species B
Species A
Species temperature
requirements
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
100 km
36
km2
Species richness & composition
Floristic inventories (more than 1,000,000 records)
Comparable sampling effort in all cells
36
km2
Elevational patterns of species richness
Natives
Aliens
Drivers:
Drivers:
Population density
Temperature
Calcareous bedrock
Topographic heterogeneity
Population density
Temperature
Marini et al. (2008) Journal of Biogeography
Marini et al. (2011) Journal of Biogeography
Aliens
5.0
10.0
250Natives
Aliens
200
150
100
50
0
-5.0
0.0
5.0
10.0
1000
900
800
700
600
500
400
300
200
100
0
15.0
Mean temperature (°C)
300
Native species richness
1000
Natives
900
800
700
600
500
400
300
200
100
0
-5.0
0.0
0.0
Alien species richness
Alien species richness
Native species richness
Species-human-energy relationships
15.0
Mean temperature (°C)
Marini et al. (2009) Global Ecology and Biogeography
2.0
4.0
6.0
Log(Human density)
300
250
200
150
100
50
0
0.0
2.0
4.0
Log(Human density)
6.0
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
Structures to survive during adverse season
Perennial herbaceous
Annuals
Trees
Phanerophytes
Hemicryptophytes
Geophytes
Therophytes
For natives we know well that different life-forms present
differential response to temperature along elevational gradients
Hypotheses
Aliens=187
Natives=2301
Different life-form spectra
Temp. x Life-form (natives)=Tempe. x Life-form (aliens)
Different composition of life-history traits among alien and native
plants alters species richness response to human and climatic factors
Temp. x Life-form (natives) but no Temp. x Life-form (aliens)
An overwhelming effect of human pressures on alien species richness can
mask any life-history trait effect mediating response to the environment
Species-temperature relationship
Natives≠Aliens
Species richness
Natives
Aliens
Mean annual temperature (°C)
Species-human relationship
Natives≠Aliens
Species richness
Natives
Aliens
Log(Human population)
Dominant effect of human pressures
● 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
● Climate filtering is expected to play a secondary role
Patterns and drivers of species richness are clear
What about species composition and identity?
Level
of invasion
(%)
species
Alien
richness
70
60
Are the invaders mountain specialists or generalists?
50
Which are the pathways of introduction?
40
30
20
10
0
0
1000
2000
3000
Elevation (m)
(m)
Elevation
Which are the mechanisms that
generate this pattern?
Hypothesis: Directional environmental filtering
Recipient
mountain region
Elevation (m)
Source regions
No introductions
from cold areas
Lowland pathway
of introduction
Species pool
Mountain
This hypothesis assumes that most alien species are introduced
from lowlands to lowlands and spread up the mountain from there
Elevation range
Elevation range (m)
~ 600 ALIENS
2% restricted
>1000m
~ 3000 NATIVES
20% restricted
>1000m
Species ranking according to max elevation
Almost all alien species extend their elevation
range in the lowlands
Compositional β-diversity
Elevation (m)
0< βtot<1
cell B
βtot =1 (complete dissimilarity)
βtot =0 (100% same species)
Longitude
βtot = βrich + βrepl
n cells
Species richness
difference
n cells
cell A
β
n cells
Species
replacement
Next analyses based on distance matrices
Patterns of β-diversity
Natives
β replacement
β replacement
βtot=1
Complete
dissimilarity
Aliens
β richness difference
Aliens have larger β richness difference than natives
Aliens have smaller β replacement than natives
βrepl Natives
βrepl Aliens
Drivers of β replacement
βrich
βrepl
ALIENS: Larger replacement
between cells with similar
environmental conditions
NATIVES: Larger replacement
between cells with different
environmental conditions
Human distance Temp. distance (°C)
β
Analyses based on distance matrices
~
Explanatory
Current situation
Mechanism of invasion
Still high floristic
differentiation in the
lowlands
Future scenario
In the long-term we will cash the accumulated invasion credit
Marini et al. (in prep.)
Future scenarios of plant invasions
Assembly of alien plant communities on mountains are primarily driven by
processes occurring in the lowlands
Level of invasion (%)
70
60
Current
50
Future
In the short term we expect strong
biotic homogenization at low- and
mid-elevations and small changes at
high elevations
40
30
20
In the long-term we will probably
cash the accumulated invasion credit
10
0
0
1000
2000
3000
Elevation (m)
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
International trade facilitates the spread of these pests given that
scolytids can move:
● 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
Unlike plants, insects are mostly introduced
accidentally
Introduction
Is introduction effort more important than local
conditions?
Import
Trade
Recipient country/state
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
n=469
n=223
n=57
n=20
Aliens more frequently
Ambrosia than natives
US native EU native US alien
EU alien
Level of invasion
(alien/native)~10-15%
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
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 drivers
Sum of model weights (wi)
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
Exotic richness patterns: Climate
Climate was less important in Europe than in the USA
Does feeding strategy modify species richness response to
climatic gradients?
Ambrosia
Species
richness
Ambrosia
Bark
Rainfall
Temperature
Bark
OR
?
Rainfall
Temperature
Test was possible only in the USA (no enough species in EU)
Sum of model weights (wi)
Ambrosia vs. bark beetles
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 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
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
No regions (or very few) can be considered inherently resistant
Thank you for your attention
PRATIQUE information
https://secure.fera.defra.gov.uk/pratique/
SCALES information
http://www.scales-project.net/
Contact details:
http://www.biodiversity-lorenzomarini.eu/
Lorenzo Marini
E-mail: [email protected]