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: lorenzo.marini@unipd.it

http://www.biodiversity-lorenzomarini.eu/

Contact details:

SCALES informationhttp://www.scales-project.net/