Global change and biological invasions: Why are some regions more invaded than others?

1. Global change and biological invasions:Why are some regionsmore invaded than others?

2. 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

3. Stages of alien invasion INTRODUCTION Native region SPREAD ESTABLISHMENT Colonization & propagule pressure T0 T1 Time Establishment is expected to depend on size and frequency of introduction events and quality of the recipient regions

4. Human-mediated introduction POPULATION LEVEL COMMUNITY LEVEL n 1 Saturation? Allee effect Probability of establishment No species established 0 0 Propagule pressure Colonization pressure • The more you introduce the more you get

5. Establishment • Quality of the recipient region acts as a • multi-dimensional filter

6. Main question addressed in the seminar • Is introduction effort more important than the quality of the recipient regions? • Important implications for prevention and management

7. 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

8. 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?

9. Something has changed Theconstraining factors of invasion are now changingdue to globalization and climate change, increasing the chances of plant invasions into high-elevation environments LAND-USE CHANGE CLIMATE CHANGE

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

11. Climate change and alien plants Will alien plant species respond like natives? Potential elevation optimum Realized elevation optimum Dispersal limitation: Time lags in tracking climate change (immigration credit?) Elevation optimum Species B Species A Upwards shift of the limiting thresholds Species temperature requirements

12. 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

13. Methods: data Study area: NE of Italy 36 km2 100 km Species richness & composition Floristic inventories (more than 1,000,000 records) Comparable sampling effort in all cells 36 km2

14. 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

15. Species-human-energy relationships Aliens Natives Natives Aliens Marini et al. (2009) Global Ecology and Biogeography

16. 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

17. Plant life-forms Structures to survive during adverse season Perennial herbaceous Annuals Trees Hemicryptophytes Phanerophytes Therophytes Geophytes For natives we know well that different life-forms present differential response to temperature along elevational gradients

18. 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

19. Species-temperature relationship Natives≠Aliens Natives Speciesrichness Aliens Mean annual temperature (°C)

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

21. 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

22. Patterns and drivers of species richness are clear What about species composition and identity? Are the invaders mountain specialists or generalists? Which are the pathways of introduction? Alien species richness Elevation (m) Which are the mechanisms that generate this pattern?

23. Hypothesis: Directional environmental filtering • Recipient mountain region • Source regions • No introductions from cold areas Species pool Elevation (m) • Lowland pathway • of introduction Mountain This hypothesis assumes that most alien species are introduced from lowlands to lowlands and spread up the mountain from there

24. Elevation range ~ 600 ALIENS ~ 3000 NATIVES 2% restricted >1000m 20% restricted >1000m Elevation range (m) Species ranking according to max elevation Almost all alien species extend their elevation range in the lowlands

25. Compositionalβ-diversity cell A cell B 0< βtot<1 βtot =1 (completedissimilarity) Elevation (m) (100% same species) βtot =0 Longitude βtot = βrich +βrepl Latitude Species richness difference Species replacement β n cells Next analyses based on distance matrices n cells n cells

26. Patterns of β-diversity βtot=1 Complete dissimilarity Natives Aliens βreplacement βreplacement βrichnessdifference Aliens have larger β richness difference than natives Aliens have smaller β replacement than natives

27. Drivers of β replacement βrich βrepl ALIENS: Larger replacement between cells with similar environmental conditions βreplAliens NATIVES: Larger replacement between cells with different environmental conditions βreplNatives Human distance Temp. distance (°C) Explanatory β ~ Analyses based on distance matrices

28. Mechanism of invasion Current situation Still high floristic differentiation in the lowlands In the long-term we will cash the accumulated invasion credit Future scenario Marini et al. (in prep.)

29. Future scenarios of plant invasions Assembly of alien plant communities on mountains are primarily driven by processes occurring in the lowlands In the short term we expect strong biotic homogenization at low- and mid-elevations and small changes at high elevations Current Future 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

30. Exploring the effects of trade and environment on exotic Scolytinae (Coleoptera) invasions Marini et al. (2011) Biological Invasions

31. Introduction: Alien scolytid invasions ● Bark and ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) are amongst the most important pestscausing 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

32. 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

33. Introduction Is introduction effort more important than local conditions? • Import • Trade • Recipient country/state

34. Methods: data Study area: continental USA andEurope Response variable: Number of native and alien species established in each state/country • Predictors: Two groups of variables: • Economy (Import): proxy for colonization and propagule pressures • Environment of the recipient region(forest area, temperature, rainfall, forest diversity, climatic heterogeneity)

35. General results: feeding strategies n=469 n=223 n=57 n=20 Aliens more frequently Ambrosia than natives Level of invasion (alien/native)~10-15% US native EU native US alien EU alien • Ambrosia life-history traits favoring invasion: • haplodiploidy, i.e. the ability to produce male offspring without mating, • sib-mating, i.e. brother-sister mating prior to emergence from the host tree, • symbiotic trophic specialization with fungi that obviates the need to overcome many host defenses, and • low host specificity and ability to breed in dead wood

36. 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

37. Relative importance of the drivers US native US alien Sum of model weights (wi) EU native EU alien

38. 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

39. Exotic richness patterns: Climate Climate was less important in Europe than in the USA Does feedingstrategy modifyspecies richness response to climatic gradients? Ambrosia Ambrosia Bark Species richness OR ? Bark Rainfall Temperature Rainfall Temperature Test was possible only in the USA (no enough species in EU)

40. Ambrosia vs. bark beetles Sum of model weights (wi)

41. Conclusions ●Our study suggests that growing international tradeis the primary factor contributing to escalating rates of scolytid invasionsworldwide ●Climate and land-use effects are of secondary importance ● More attention is needed to prevent or reduce the arrival rateof 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

42. 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)

43. 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

44. 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: lorenzo.marini@unipd.it