The Fate of a Colonizer: Successful but Lonely?
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The fate of a colonizer: successful but lonely? The establishment of inter- and intraspecific diversity in ferns by means of long-distance dispersal Gerard Arjen de Groot The research presented in this thesis was carried out within the WODAN-project of the Ecology & Biodiversity Group, Institute of Environmental Biology, Utrecht University, the Netherlands “The fate of a colonizer: successful but lonely? The establishment of inter- and intraspecific diversity in ferns by means of long-distance dispersal” By G.A. de Groot, 2011 Copyright © 2011, G.A. de Groot All rights reserved. ISBN: 978-90-393-5701-9 Key words: biodiversity, breeding systems, colonization, dispersal, DNA barcoding, genetic variation, ISSR markers, limitation, population genetics, population dynamics. Lay-out and cover design: Arjen de Groot Photographs: Main picture on front cover: Wodan the Wanderer. Adapted from a photograph of a statue near Pec pod Sneˇzkouˇ (Krkonoseˇ mountains, Czech Republic). Small picture on front cover: Ferns in a drainage trench in the Kuinderbos. (Photographer: Ernst Kremers, www.ernstkremers.nl). Pictures on back cover, from top to bottom: Asplenium scolopendrium, Asplenium trichomanes, Polystichum aculeatum, Polystichum setiferum. Printed by: GVO drukkers & vormgevers B.V. j Ponsen & Looijen, Ede. The fate of a colonizer: successful but lonely? The establishment of inter- and intraspecific diversity in ferns by means of long-distance dispersal Het lot van de kolonist: succesvol maar eenzaam? De ontwikkeling van diversiteit binnen en tussen varensoorten door middel van lange-afstandsverspreiding (met een samenvatting in het Nederlands) PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de rector magnificus, prof. dr. G.J. van der Zwaan, ingevolge het besluit van het college voor promoties in het openbaar te verdedigen op maandag 16 januari 2012 des middags te 12.45 uur door Gerard Arjen de Groot geboren op 21 juli 1984 te Warten Promotor: Prof. dr. M.J.A. Werger Co-promotoren: Dr. H.J. During Dr. R.H.J. Erkens Voor mijn ouders Contents Chapter 1: General introduction 2 Part one: Development of species diversity Chapter 2: A two-locus DNA barcode for identification of NW-European ferns: 16 an ecological perspective Chapter 3: Limitations for fern species diversity: evidence from young spore 34 banks established by long-distance dispersal Part two: Development of genotypic diversity Chapter 4: Isolation and characterization of polymorphic microsatellite 56 markers for four widespread calcicole ferns Chapter 5: Inter- and intraspecific variation in fern mating systems after 64 long-distance colonization: selection for selfing genotypes Chapter 6: Diverse spore rains and limited local exchange shaped fern genetic 82 diversity in a recently created habitat colonized by long-distance dispersal Part three: Performance of young fern populations Chapter 7: Demographic differences between closely related ferns: variation 104 in ploidy level and phenology can result in large and unexpected differences in climatic sensitivity Chapter 8: General synthesis 126 Summary 144 Nederlandse samenvatting 148 Literature cited 157 Appendices I-VII 175 Affiliation of co-authors 191 Dankwoord/Acknowledgements 192 Curriculum Vitae and publications 196 Chapter 1 General introduction G. Arjen de Groot General introduction 3 Inter- and intraspecific diversity Our earth harbours a stunning diversity of living organisms. While about 1.9 million species have been described, the estimated total number of species on earth exceeds 11 million (Chapman 2009). Moreover, modern molecular techniques make us aware of the fact that a large amount of genetic variation is often present within species. Human-induced changes are, however, threatening this reservoir of natural diversity. As a result of climatic change, habitat destruction, pollution and ecosystem invasion by alien species, both inter- and in- traspecific diversity are reduced and the remaining diversity gets more evenly distributed (UN Millennium Ecosystem Assessment 2005). Although scientists still argue about exact extinction rates (Seabloom et al. 2002; He & Hubbell 2011), we are without any doubt in the middle of a large biodiversity crisis (e.g. Ter Steege 2010). A societal and political question may be: So what? With so many species present, who cares if some go extinct? Why should we perform costly conservation projects to save all these species? An important part of the answer lies in the functions that Earth’s ecosystems serve to the well-being of human kind. Such ’ecosystem services’ include the provision of clean water and air, food, fuel, medicines and other materials, and protection against natural disasters (UN Millennium Ecosystem Assessment 2005). A loss of biodiversity inherently damages these services. Ecosystems are complex networks of many interacting organisms. It is feared that the loss of a single key-stone species might cause the entire system to collapse. Such species are, however, not easily identified and rarely are the sole determinants of ecosystem functioning (Mills et al. 1993). Therefore, ecologists argue that (multiple) representatives from all functional groups should be available (Walker 1995). There is evidence that even the sheer number of species present may affect the stability of the system (e.g. Van Ruijven & Berendse 2007). If species conservation matters, so does conservation of their genetic diversity. Most species are not driven to extinction before their genetic diversity has dropped significantly (Spielman et al. 2004). Genetic erosion results in elevated population extinction risks, ei- ther because of reduced (reproductive) fitness due to inbreeding depression (see below) or because reduced trait variation makes populations lose their ability to adapt to changes in their local environments (e.g. Lande & Shannon 1996). When this results in smaller popu- lations that can harbour even less genetic variation, this may lead into a vortex to extinction (Blomqvist et al. 2010). Moreover, genetic erosion reduces diversity on an evolutionary time scale, as allelic diversity provides the raw material for natural selection (Fisher 1930). At the ecosystem level, genetic impoverishment within species has been shown to reduce the overall species diversity (Booth & Grime 2003) and productivity (Reusch & Hughes 2006) of the system, as well as its resistance to disturbance (Hughes & Stachowitz 2004) and invasion (Vellend et al. 2010). 4 Chapter 1 The origin of plant diversity in newly created habitats Efforts to conserve plant biodiversity focus both on maintaining diversity in protected areas and developing diversity in restored or newly created areas. At timescales that are too short for speciation, the dynamics of plant diversity in such areas ultimately depend on a balance between the rates of immigration and extinction (e.g. Zobel 1997; Ter Steege & Zagt 2002). Theories on the origin and maintenance of diversity (Hubbell 2001; Tilman 2004) differ in many ways, but all agree on the crucial role of immigration for local species diversity. Likewise, immigration is a major determinant of genetic variation (Ouborg et al. 1999). Immigration rates depend on the ability of individuals to reach a system and their ability to subsequently establish in the new environment. While local dispersal has been studied extensively, long-distance immigration has proved very difficult to quantify, because track- ing propagules over large distances is extremely difficult (Cain et al. 2000). Most of our knowledge on long-distance dispersal (LDD) is therefore deduced from modelling studies (e.g. Soons et al. 2004; Sundberg 2005). More studies on LDD are needed, as current global changes likely increase its importance for local population dynamics as well as bio- geographical patterns (Cain et al. 2000). As habitat fragmentation results in increased distance between patches, colonization of new patches and exchange between existing pop- ulations require dispersal over longer distances. Meta-population dynamics thus increas- ingly depend on LDD (Bohrer et al. 2005), which affects both population extinction rates and possibilities for gene flow between populations. At the same time, distributional range limits are shifting because of climatic changes, forcing species to regularly colonize new environments (Cain et al. 2000). Quantitative information about patterns of immigration by LDD, as well as about the main determinants of such patterns, is essential for contemporary diversity conservation. B C A E D F G H Figure 1.1: Map of the central part of the Netherlands. A = Dutch mainland; B = North Sea; C = Wadden Sea; D = IJsselmeer (former Zuiderzee). E-H = The four main IJsselmeer polders: the Wieringermeerpolder (E; reclaimed in 1927; 309 km2), the Noordoostpolder (F; reclaimed in 1942; 596 km2), Oostelijk Flevoland (G; reclaimed in 1957; 540 km2) and Zuidelijk Flevoland (H; reclaimed in 1968; 430 km2). General introduction 5 The research project “WODAN ” (Windows of Opportunity and Dispersal Affect Num- ber of species), initiated in 2007 within the Ecology & Biodiversity Group at Utrecht Uni- versity, aims to gain knowledge of the processes determining dispersal and establishment of plants that colonize new areas, in order to obtain a better understanding of the development of species and genetic diversity and their spatial structure in isolated habitats (De Groot et al. 2008). Occasionally, large-scale events provide excellent opportunities to directly test the