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 Colonization & propagule pressure 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 Probability of establishment Colonization pressure No species established COMMUNITY LEVEL Allee effect Saturation? n 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. (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 CHANGE LAND-USE CHANGE

Urbanization and alien plants Will alien and native plant species respond similarly? Increased disturbance and movement of people Alien species richnessUrbanization Human population Increased available niches and propagule pressures Native Alien ?

Climate change and alien plants Will alien plant species respond like natives? Elevation optimum 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 km 2

Elevational patterns of species richness 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 Natives Aliens

Species-human-energy relationships Natives Natives Aliens Aliens 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 Therophytes Geophytes Hemicryptophytes 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 spectra Natives=2301 Aliens=187

Species-temperature relationship Natives Aliens Species richness Mean annual temperature (°C) Natives≠Aliens

Species-human relationship Natives≠Aliens Natives Aliens Log(Human population) Species richness

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 Alien species richness 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 that generate this pattern?

Lowland pathway of 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 Elevation (m) Source regions Recipient 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 Elevation range (m) Almost all alien species extend their elevation range in the lowlands

Compositional β-diversity 0< β tot <1 Elevation (m) Latitude Longitude Species richness difference Species replacement n cells β β tot = β rich + β repl β tot =1 β tot =0 (100% same species) (complete dissimilarity) Next analyses based on distance matrices cell Acell B

Patterns of β-diversity β richness difference β replacement β tot =1 Complete dissimilarity NativesAliens β replacement Aliens have larger β richness difference than natives Aliens have smaller β replacement than natives

Drivers of β replacement β Explanatory ~ β repl Natives β repl Aliens ALIENS: Larger replacement between cells with similar environmental conditions NATIVES: Larger replacement between cells with different environmental conditions β rich β repl 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 Current situation Future scenario Still high floristic differentiation in the lowlands

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 drivers Sum of model weights (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 Rainfall Temperature Species richness Ambrosia Bark Ambrosia Bark ? Rainfall Temperature

Ambrosia vs. bark beetles Sum of model weights (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 information Lorenzo Marini Contact details: SCALES information