Workshop on “Invasive exotic species” B Bozen, December D b 14th 2010 Alien and native plants respond differently to human and climatic pressures L Lorenzo Marini M i i DAAPV, University of Padova Co-authors: Andrea Battisti, Alessio Bertolli, Enzo Bona Germano Federici, Bona, Federici Kevin Gaston, Gaston Phil Hulme, Fabrizio Martini, Filippo Prosser Alien plant invasions in the Alps ● Alien plant invasions are recognized as a major driver of biodiversity decline and altered lt d ecosystem t services i worldwide ld id ● Most studies of invasive alien species have concentrated on lower elevations, with little attention being directed to the most pristine hi h l high-elevation ti environments i t ● Relative isolation and harsh climatic conditions may have allowed mountain ecosystems to experience lower levels of alien species invasions than have lowland areas BUT Something has changed The constraining factors for 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 Climate change Increased temperature along the elevation gradients Relaxation of minimum temperature constraints Optimum elevation shifts for native species Upward shift Lenoir et al. (2008) Science Published by AAAS Climate change and alien plants Elevatio on optim mum Will alien plant species respond similarly? Potential elevation optimum Realized elevation optimum Dispersal p limitation: Time lags in tracking climate change (immigration credit) Species B Species A Species temperature requirements Is current alien species distribution more related to propagule pressures or climatic constraints? Land--use change dynamics Land Main processes Ellevation (m) Forest expansion 2000 Urbanization 500 0 Elevation-dependence of land use changes Urbanization and alien plants Alien spe A ecies 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 Research aim i) We tested whether the drivers of species richness patterns differ between native and alien plants ii) We examine the responsiveness of alien and native plant life-forms to human and climatic pressures Try to disentangle the effects of climatic and human pressures on the invasion of exotic plant in the Alps to make k predictions di ti off global l b l change h effects ff t Methods: data Study area: NE of Italy 36 km2 Species richness Floristic inventories of provinces of TN, BS and BG Elevational patterns of species richness Natives Aliens Drivers: Drivers: Population density Temperature Calcareous bedrock p g p heterogeneity g y Topographic Population density Temperature Marini et al. (2008) Journal of Biogeography Marini et al. (2010) Journal of Biogeography Species--human Species human--energy relationships N ti Natives Aliens Different shapes of the relationships Natives Aliens The level of invasion drastically increased both with temperature and humans Coincidence between areas with large native extinctions and large alien invasions Marini et al. (2009) Global Ecology and Biogeography Differential response of aliens and natives Two complementary hypotheses: i) Different composition life life-history history traits among alien and native species pool alter species richness response to human and climatic factors ii) Overwhelming effect of human pressures on alien species richness which can mask any life-history trait effect mediating response to the environment The low altitude filter effect (Becker et al. 2005) We tested if plant life-form modifies the species richness response to temperature and humans Marini et al. (submitted) Plant lifelife-forms Structures to survive during adverse season Perennial herbaceous Annuals Trees Phanerophytes Hemicryptophytes Geophytes Therophytes We know that different life-forms present typical response to t temperature t along l elevational l ti l gradients di t Expected results Temperature x Life-form (native)=Temperature x Life-form (alien) Different composition of life-history traits among alien and native plants alters lt species i richness i h response tto h human and d climatic li ti ffactors t Aliens=187 Natives=2301 Diffe ent life-form Different life fo m spectra spe t a Temperature x Life-form (native)≠Temperature x Life-form (alien) An overwhelming g effect of human p pressures on alien species p richness can mask any life-history trait effect mediating response to the environment Species--temperature relationship Species Species riichness S N ti Natives Aliens Native≠Alien Mean annual temperature (°C) Species--human relationship Species Species riichness S N ti Natives Aliens Native≠Alien Log(Human population) Separate elevation belts We remove the correlation between temperature and humans We tested human x lifelife-form within subsets of cells with the same temperature t t Separate elevation belts Tre ees Sta andardized d species riichness Annuals s Perennial herbaceou P us Aliens Natives Log(Human population) Conclusions ● Alien species richness was higher in areas with the most rich and diverse assemblages of native species ● Annual A l natives ti and d all ll aliens li will ill b be th the winners, i native ti tree t and d perennial species will be the losers ● Native species richness showed complex responses to both human population and temperature suggesting that life-form modifies the sensitivity of native species to environmental changes ● Human pressures are the main drivers of alien plant invasions and climatic conditions seem to have smaller direct effect on the CURRENT distribution of alien species richness (no life-form effect) ● Current distributions of alien species and also certain native species may reflect dispersal limitation rather than climatic limits and may exhibit only limited tracking of future climate ..but we are probably accumulating an invasion credit Future scenarios An increased upwards movement of human activities such as agriculture and urban development is expected under current global warming Lev vel of invasio on (%) 70 60 Current 50 Future In the short term we expect strong biotic homogenization at low- and mid-elevations and small changes at hi h elevations high l ti 40 30 20 In the long-term we will probably cash the accumulated invasion credit 10 0 0 1000 2000 3000 Elevation (m) Plantt conservation Pl ti agenda d should h ld probably b bl ffocus more on llandd use change effect than on climate change effect Thank you for your attention PRATIQUE information i f ti https://secure.fera.defra.gov.uk/pratique/ Data owners: Alessio Bertolli, Enzo Bona, Germano Federici, Fabrizio Martini, Filippo Prosser Contact details: Lorenzo Marini, PhD http://www.biodiversity-lorenzomarini.eu/ E-mail: lorenzo.marini@unipd.it