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Metapopulation and Metacommunity Processes, Dispersal Strategies And !"# ! $%&' $#()*(%%')%)*( + , ++ + -.*') Till alla som har hjälpt mig att bli frisk igen List of Papers This thesis is based on the following papers, which are referred to in the text by their Roman numerals. I Löbel, S., Snäll, T., Rydin, H. (2006a) Species richness patterns and metapopulation processes – evidence from epiphyte com- munities in boreo-nemoral forests. Ecography, 29(2):169–182 II Löbel, S., Snäll, T., Rydin, H. (2006b) Metapopulation pro- cesses in epiphytes inferred from patterns of regional distribu- tion and local abundance in fragmented forest landscapes. Jour- nal of Ecology, 94(4): 856–868 III Löbel, S., Snäll, T., Rydin, H. (2009) Mating system, reproduc- tion mode and diaspore size affect metacommunity diversity. Journal of Ecology, 97(1): 176–185 IV Löbel, S., Rydin, H. (in press) Dispersal and life-history strate- gies in epiphyte metacommunities: alternative solutions to sur- vival in patchy, dynamic landscapes. Oecologia, DOI: 10.1007/s00442-009-1402-1 V Löbel, S., Rydin, H. Bottle-necks and trade-offs in the establish- ment of epiphytes. Manuscript Reprints were made with kind permission from the publishers. I planned all studies, conducted the field and laboratory work, analyzed the data and wrote the texts. T. Snäll and H. Rydin contributed with valuable discussions of the study concepts, data analyses, results and manuscripts. Contents Introduction.....................................................................................................1 Habitat loss and fragmentation as threats to biodiversity...........................1 Metapopulation theory ...............................................................................1 Metacommunity theory ..............................................................................2 Dynamic landscapes and system non-equilibrium .....................................3 Epiphytic bryophytes as model organisms.................................................4 Aims of this thesis......................................................................................5 Material and methods......................................................................................7 Study system, species and sites ..................................................................7 Species richness pattern at a local scale (I) ................................................9 Community pattern at a regional scale (II, III).........................................10 Growth, reproduction and species interactions (IV).................................12 Establishment experiments (V) ................................................................12 Results and discussion ..................................................................................14 Habitat patch quality ................................................................................14 Local scale (I) ......................................................................................14 Regional scale (II, III)..........................................................................14 Growth and reproduction (IV).............................................................15 Establishment (V) ................................................................................15 Habitat patch size (I-III)...........................................................................16 Spatial structure and dispersal..................................................................17 Local scale (I) ......................................................................................17 Regional scale (II, III)..........................................................................18 Landscape dynamics and species reproduction (II-IV)............................19 Dispersal strategies and life-history trade-offs.........................................20 Dispersal ability versus reproductive age and frequency (I-IV)..........20 Reproduction versus local growth and competitive ability (IV)..........20 Dispersal ability versus establishment ability (V) ...............................21 Trade-offs in the establishment (V).....................................................22 Evolution of dispersal strategies in patch-tracking metacommunities .....23 Conclusions and implications...................................................................25 Acknowledgements.......................................................................................26 References.....................................................................................................28 Biologisk mångfald av trädlevande mossor..................................................33 Folgen der Flächenreduktion und Verinselung natürlicher Wälder für die Artenvielfalt epiphytischer Moose................................................................36 Introduction Habitat loss and fragmentation as threats to biodiversity Habitat loss and fragmentation are major threats to biodiversity (Heywood 1995). In present day landscapes many forest species are restricted to rem- nants of a formerly more or less contiguous forest cover. In Fennoscandia, modern forestry has led to a great decrease of old-growth forests and a low proportion of deciduous trees (Berg et al. 2002). Host trees and deciduous forest stands in the coniferous landscape are patchy, temporal and undergo changes in habitat quality during succession. Many species must track this dynamic habitat network for their long-term survival (Snäll et al. 2005a). Increased dispersal distance, as imposed by landscape fragmentation, may lead to species extinctions and reduced biodi- versity. Reduced habitat quality of small forest fragments due to forest edge effects may be fatal for many highly specialized species (Harrison & Bruna 1999; Moen & Jonsson 2003). Forest fires were the main disturbance regime in the natural forest landscape which stochastically varied in space and time (Niklasson & Granström 2000). Current forestry practice promotes conifers, and thus does not provide alternative means of host tree generation. Cutting rotation times are often shorter than natural forest fire rotation times, poten- tially causing harm to species with slow population dynamics such as many epiphytes (Snäll et al. 2005a, b). Metapopulation theory Metapopulation theory has increased our understanding of the dynamics of species in fragmented landscapes, and has become an important tool for na- ture conservation. According to theory, the most critical aspects of habitat fragmentation are reduced patch sizes and increasing distances between habitat patches (Hanski & Gaggiotti 2004). Population sizes are expected to increase with the patch size which reduces the local extinction risk (Hanski 1999). In addition, with increasing patch size the ‘target area’ for dispersing diaspores increases. In temporary habitats such as trees, the patch area in- cludes yet an additional dimension: the time, as reflected by tree diameter, under which a patch has been available for colonization (Snäll et al. 2003). However, empirical data suggest that reduced habitat quality of small 1 patches and edge effects are more important than area or distance effects per se (Debinsky & Holt 1999; Moen & Jonsson 2003). Further complexity is added by the fact that the time-lag between passing the extinction threshold and regional metapopulation extinction can be long, implying that effects of habitat fragmentation may first be detected after many years (Ovaskainen & Hanski 2002). Epiphytes that have inertia to stochastic local extinctions be- long to this group of species (Snäll et al. 2005a; Ellis & Coppins 2009). The core-satellite hypothesis (Hanski 1982) suggests that the importance of metapopulation processes can be assessed from regional frequency distri- butions and local abundances. The model predicts that within a region, most species are either core species, which are abundant within patches and occur in > 90% of all patches, or satellite species, which are sparse within patches and occur in < 10% of all patches. This bimodality is explained by meta- population dynamics including a rescue effect, i.e. recurrent immigration reduces the rate of local extinction (Hanski & Gaggiotti 2004). Inferences about metapopulation processes can be further made from spatial species occupancy patterns by applying the incidence function model approach (Hanski 1994), and rescue effects may be detected by analyzing the impact of patch connectivity (sensu Hanski 1999) on local species abundances. De- clining local abundances may be detected long before species extinctions, and thus, may serve as an early warning system. Metacommunity theory The metacommunity approach extends the metapopulation concept to the community level. The most basic issue is to address what regulates coexis- tence of species in a system of connected habitat patches (Leibold & Miller 2004). There are four main frameworks: ‘patch dynamics’, ‘species-sorting’, ‘mass-effects’ and the ‘neutral model’ (Leibold & Miller 2004).
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