Population biology of Carlina vulgaris and Hypochoeris radicata in fragmented European grasslands [Elektronische Ressource] / vorgelegt von Ute Becker
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2005
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132
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2005
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Publié par
Publié le
01 janvier 2005
Nombre de lectures
17
Langue
English
Poids de l'ouvrage
2 Mo
Publié par
Publié le
01 janvier 2005
Nombre de lectures
17
Langue
English
Poids de l'ouvrage
2 Mo
Population biology
of Carlina vulgaris and Hypochoeris radicata
in fragmented European grasslands
Dissertation
zur
Erlangung des Doktorgrades
der Naturwissenschaften
(Dr. rer. nat.)
dem Fachbereich Biologie
der Philipps-Universität Marburg
vorgelegt von
Ute Becker
aus Einbeck
Marburg/Lahn 2005
___________________________________________________________________________
Vom Fachbereich Biologie der Philipps-Universität Marburg
als Dissertation am 11.03.2005 angenommen.
Erstgutachter: Prof. Dr. D. Matthies
Zweitgutachter: Prof. Dr. R. Brandl
Tag der mündlichen Prüfung am 24.05.2005
aus: Götz (2003)
The endless variety of organisms, in their beauty, complexity and diversity
gives to the biological sciences a fascination which is unrivalled by the physical world.
(D. Briggs & S. M.Walters 1997, Plant variation and evolution)
Contents
CHAPTER 1
General Introduction 7
CHAPTER 2
Plant size, fecundity and offspring performance in relation to habitat quality, population
size and isolation in the monocarpic Carlina vulgaris in seven European regions 17
CHAPTER 3
Quantitative genetic variation at different geographical scales – a comparison of two
Asteraceae with different life history traits 39
CHAPTER 4
Local adaptation at different spatial scales across Europe in the fragmented monocarpic
perennial Carlina vulgaris 69
CHAPTER 5
Effects of pollination distance on reproduction and offspring performance in the wide
spread perennial Hypochoeris radicata: Experiments with plants from three European
regions 91
REFERENCES 107
SUMMARY / ZUSAMMENFASSUNG123
DANK131
CHAPTER 1
General Introduction 8 CHAPTER 1
In this thesis I study the effects of habitat fragmentation on individual fitness, quantitative
genetic variation and local adaptation in the grassland species Carlina vulgaris L. and
Hypochoeris radicata L. In this introductory chapter I describe the consequences of habitat
fragmentation for plant populations and give a short theoretical background on the processes
involved. I outline the possible importance of this study for purposes of species conservation
and habitat restoration, and finally I give an overview of the contents of this thesis.
Causes and consequences of habitat fragmentation
The massive extinction of species has become a severe problem in species conservation
during the last decades (Clarke & Young 2000, Davies et al. 2001). Worldwide 12.5% of all
vascular plants are at risk of extinction (in Frankham et al. 2002), and also in European
countries, a considerable number of plant species is threatened (e.g. Landolt 1991, Korneck et
al. 1996, van Groenendael et al. 1998). The main causes for these extinction processes are
changes in land use during the last decades, e.g. intensification of agricultural use and
abandonment of extensively used farmland, and also building of new residential or industrial
areas and roads. As a consequence many large natural or semi-natural habitats were destroyed
or became fragmented. This process is much faster than the formerly natural fragmentation
that was mainly caused by different environmental conditions (Saunders et al. 1991, Young et
al. 1996, Clarke & Young 2000). Populations in fragmented habitats become smaller in size
or even extinct, leading to increased isolation among populations. Small and isolated
populations are more threatened by extinction than those that are large and well connected,
because they are more susceptible to demographic and environmental stochasticity (Menges
1991a, 1992, Matthies et al. 2004). Moreover, genetic erosion due to random genetic drift and
inbreeding is stronger in small populations and may negatively affect the fitness of individual
plants and whole populations (e.g. Barrett & Kohn 1991, Oostermeijer et al. 1996, Young et
al. 1996). The negative effects of small population size and isolation are called Allee effects
(Allee et al. 1949, Groom 1998, Stephens & Sutherland 1999). However, some authors regard
only the negative effects of reduced density within populations as Allee effects.
Genetic variation
Genetic variation is the sum of the genetic richness of all individuals of a species, between
populations (population genetic variation) and among the individuals within one population. It
is determined by four evolutionary processes: mutation, heterogeneous selection, random
General Introduction 9
genetic drift and gene flow (Barrett & Kohn 1991). Most studies of genetic variation have
used molecular markers that are selectively neutral and have measured the allelic richness per
locus or the proportion of heterozygous individuals, i.e. gene diversity (Waldmann &
Andersson 1999). These markers thus provide insights into random evolutionary processes,
i.e. genetic drift, pollination and dispersal processes, rather than into adaptive processes of
ecological significance (Thompson 1999, but see Petit et al. 2001). Moreover, the variation in
morphological traits (i.e. quantitative genetic variation) partly reflects genetic variation
(Young et al. 1996). The quantitative genetic variation is a result of the reaction of plants to
environmental conditions due to selection and is under polygenetic control (Young et al.
1996, Lynch et al. 1999). The study of quantitative genetic variation provides information
about variation in fitness-related traits and can be useful for suggesting management strategies
for species conservation (Storfer 1996, Knapp & Rice 1998, McKay et al. 2001, Frankham et
al. 2002).
The importance of genetic diversity for the evolution of a species and thus for its
persistence is manifold (Frankel & Soulé 1981, Gilpin & Soulé 1986, Frankham 1995). As
example, the genetic diversity (i.e. heterozygosity) of an individual may positively influence
its fitness, because it decreases the susceptibility to pathogens or increases plant size (Boyce
1992, Reed & Frankham 2003). Lower individual fitness in small populations in combination
with reduced genetic variation has been found in a number of studies (e.g. Fischer & Matthies
1998a, Kéry et al. 2000, Paschke et al. 2002a, Hooftman et al. 2003, Vergeer et al. 2003a).
Reduced genetic variation in small and isolated populations is the result of genetic drift,
which is the random change of the allelic composition between generations, and may result in
the loss of rare alleles (Lacy 1987, Hartl & Clark 1989, Barrett & Kohn 1991, Ellstrand &
Elam 1993). Decreased genetic variability in small and isolated plant populations has been
found in a number of studies based on molecular markers (e.g. Ouborg et al. 1991, Raijmann
et al. 1994, Fischer & Matthies 1998b, Young et al. 1999), but little is known about the
effects of population size and isolation on phenotypic variation of plant populations
(Oostermeijer et al. 1994a, Ouborg & van Treuren 1995, Podolsky 2001).
Gene flow and local adaptation
The long-term ability of a population to react to changing environmental conditions depends
on its genetic diversity (Frankel & Soulé 1981, Barrett & Kohn 1991, Eberhart et al. 1991,
Mitton 1993, Helenurm 1998, Frankham 1999). The local adaptation to environmental
10 CHAPTER 1
conditions is a process that drives population differentiation (Linhart & Grant 1996, Kassen
2002), but may be counteracted by gene flow between populations (Linhart & Grant 1996,
Nagy & Rice 1997)
Plants with locally adapted genotypes may show a home-site advantage, i.e. they grow
better in their site of origin than plants from other sites (McGraw & Antonovics 1983, van
Andel 1998, Hufford & Mazer 2003, Kawecki & Ebert 2004). This home-site advantage is a
consequence of selection and is supposed to increase with increasing environmental or genetic
dissimilarity between populations (Frankham et al. 2002). In total these differences increase
with increasing geographic distance and thus home-site advantages also might increase. How-
ever, local adaptation on large geographical scales has rarely been studied (Galloway &
Fenster 2000, Montalvo & Ellstrand 2000, Joshi et al. 2001, Santamaria et al. 2003).
Local adaptation can be constrained by increased gene flow among populations
(Futuyama 1998, Lenormand 2002). Furthermore, gene flow can counteract the loss of
genetic variation (Slatkin 1987). Gene flow in plants may occur through pollen or seeds and is
a force that is opposed to population differentiation (Dewey & Heywood 1988). The extent of
gene flow decreases with increasing geographical distance and mainly depends on foraging
distances of pollinators, on the breeding system of a species and on a species’ ability t
