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Metapopulation and metacommunity processes, dispersal strategies and life-history trade-offs in epiphytes
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany. (Ecology of mire plants and bryophytes)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this thesis was to increase knowledge about metapopulation and metacommunity processes in patchy, dynamic landscapes, using epiphytic bryophytes as a model system. Host trees and deciduous forest stands in the coniferous landscape are patchy, temporal and undergo changes in habitat quality during succession. Epiphytes must track this dynamic habitat network for their long-term survival. Community patterns at different spatial scales were explored and linked to regional metapopulation processes and local population dynamics.

Spatial structuring in species richness both at a local and regional scale indicated stronger dispersal limitation but lower sensitivity to habitat quality in species with large asexual than in species with small sexual diaspores. In sexually dispersed species, a strong rescue effect was indicated by a bimodal frequency distribution of the species and by increasing local abundance with increasing patch connectivity. Present connectivity to other deciduous forest patches had positive effects on richness of asexually dispersed species, whereas richness of sexually dispersed species was instead related to the landscape connectivity 30 years ago. A study of local growth and reproduction suggested that this is caused by delayed sexual, but not asexual, reproduction. Habitat conditions affected the production of sporophytes, but not of asexual diaspores. No differences in either growth rates or competitive abilities among species with different dispersal and life-history strategies were found. In vitro experiments showed that establishment is higher from large asexual diaspores than from small sexual. Establishment of all diaspore types was limited by pH. There were indications of trade-offs between high germination and protonemal growth rates, desiccation tolerance and a rapid development of shoots from protonema.

The results indicated that the epiphyte metacommunity is structured by two main trade-offs: dispersal distance (diaspore size) versus age at first reproduction, and dispersal distance versus sensitivity to habitat quality. Trade-offs in species traits may have evolved as a consequence of conflicting selection pressures imposed by habitat turnover, connectivity and irregular water supply rather than by species interactions. Syndromes of interrelated species traits imply that fairly small changes in habitat conditions can lead to distinct changes in metacommunity diversity: the results indicate that increasing distances among patches cause most harm to asexually dispersed species, whereas cuttings of forests of high age and quality as well as increasing patch dynamics are most harmful to sexually dispersed species.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2009. , p. 37
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 661
Keywords [en]
asexual, biodiversity, bryophytes, dispersal limitation, establishment, evolution of reproductive traits, germination, growth, habitat fragmentation, landscape dynamics, local processes, patch-tracking, pH, reproduction, species richness, species interactions
National Category
Other Biological Topics
Research subject
Ecological Botany
Identifiers
URN: urn:nbn:se:uu:diva-106847ISBN: 978-91-554-7578-9 (print)OAI: oai:DiVA.org:uu-106847DiVA, id: diva2:228852
Public defence
2010-05-20, Lindahlsalen, EBC, Norbyvägen 18B, 752 36, Uppsala, 10:00 (English)
Opponent
Supervisors
Note
Senarelagd disputation från: 2009-09-26, Lindahlsalen, EBC, Villavägen 9, 75236 Uppsala, Uppsala, 10:00 Available from: 2010-03-09 Created: 2009-07-06 Last updated: 2011-03-02Bibliographically approved
List of papers
1. Species richness patterns and metapopulation processes evidence from epiphyte communities in boreo-nemoral forests
Open this publication in new window or tab >>Species richness patterns and metapopulation processes evidence from epiphyte communities in boreo-nemoral forests
2006 (English)In: Ecography, Vol. 29, p. 169-182Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-24126 (URN)
Available from: 2007-02-03 Created: 2007-02-03 Last updated: 2019-02-01
2. Metapopulation processes in epiphytes inferred from patterns of regional distribution and local abundance in fragmented forest landscapes
Open this publication in new window or tab >>Metapopulation processes in epiphytes inferred from patterns of regional distribution and local abundance in fragmented forest landscapes
2006 (English)In: Journal of Ecology, Vol. 94, p. 856-868Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-24128 (URN)
Available from: 2007-02-03 Created: 2007-02-03 Last updated: 2019-02-01
3. Mating system, reproduction mode and diaspore size affect metacommunity diversity
Open this publication in new window or tab >>Mating system, reproduction mode and diaspore size affect metacommunity diversity
2009 (English)In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 97, no 1, p. 176-185Article in journal (Refereed) Published
Abstract [en]

1. Metapopulation persistence and metacommunity diversity in patchy dynamic landscapes critically depend on efficient dispersal. Dispersal strategies could involve trade-offs that result in different species responses to habitat fragmentation, alteration in habitat quality and changes in landscape dynamics. 2. We studied spatial structuring in species richness of obligate epiphytic bryophytes in 135 deciduous forest patches in a largely coniferous landscape in Sweden. We tested the effects of forest patch size (0.01-15 ha), patch quality and present and historic connectivity (as revealed by air photographs) on species richness of species groups with different mating systems, reproduction modes and diaspore sizes. 3. Present connectivity to other deciduous forest patches had positive effects on richness of dioecious species with predominant asexual reproduction, whereas richness of monoecious species with predominant sexual reproduction was affected by historic connectivity only. The scale of spatial structuring in species richness increased with decreasing diaspore sizes. Forest patch quality affected richness of monoecious species reproducing sexually but not of dioecious species reproducing asexually. 4. Our results suggest shorter dispersal distances, but higher establishment rates, of large asexual diaspores than of small sexual ones. In monoecious species with sexual reproduction, it may take several decades from establishment to first spore production, and this may explain the strong effect of historic, but not present, forest patch connectivity on species richness of this group. This suggests a trade-off between dispersal distance and age at first reproduction, which may explain the parallel evolution of asexual reproduction and monoecism in species inhabiting patchy, transient habitats. 5. Synthesis. We conclude that dispersal success of metacommunity members is influenced both by species traits and habitat characteristics. In patch-tracking metacommunities, trade-offs in species traits may have evolved as a consequence of conflicting selection pressures imposed by habitat patchiness and dynamics. Syndromes of interrelated species traits imply that fairly small changes in habitat conditions may lead to distinct changes in metacommunity diversity: Species reproducing asexually may drastically decline with increasing distances among patches, whereas sexually reproducing species may decline with increasing patch dynamics.

Keywords
asexual reproduction, bryophytes, dispersal strategies, epiphytes, habitat fragmentation, landscape dynamics, life-history trade-offs, metapopulation, patch-tracking, species richness
National Category
Biological Sciences
Research subject
Ecological Botany
Identifiers
urn:nbn:se:uu:diva-107313 (URN)10.1111/j.1365-2745.2008.01459.x (DOI)000261684400020 ()
Available from: 2009-08-05 Created: 2009-08-05 Last updated: 2019-02-01Bibliographically approved
4. Dispersal and life-history strategies in epiphyte metacommunities: alternative solutions to survival in patchy, dynamic landscapes
Open this publication in new window or tab >>Dispersal and life-history strategies in epiphyte metacommunities: alternative solutions to survival in patchy, dynamic landscapes
2009 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 161, no 3, p. 569-579Article in journal (Refereed) Published
Abstract [en]

Host trees for obligate epiphytes are dynamic patches that emerge, grow and fall, and metacommunity diversity critically depends on efficient dispersal. Even though species that disperse by large asexual diaspores are strongly dispersal-limited, asexual dispersal is common. The stronger dispersal limitation of asexually reproducing species compared to species reproducing sexually via small spores may be compensated by higher growth rates, lower sensitivity to habitat conditions, higher competitive ability or younger reproductive age.

We compared growth and reproduction of different groups of epiphytic bryophytes with contrasting dispersal (asexual vs sexual) and life-history strategies (colonists, short- and long-lived shuttle species, perennial stayers) in an old-growth forest stand in the boreo-nemoral region in Eastern Sweden.

No differences were seen in relative growth rates between asexual and sexual species. Long-lived shuttles had lower growth rates than colonists and perennial stayers. Most groups grew best at intermediate bark pH. Interactions with other epiphytes had a small, often positive effect on growth. Neither differences in sensitivity of growth to habitat conditions nor differences in competitive abilities among species groups were found. Habitat conditions, however, influenced the production of sporophytes, but not of asexual diaspores. Presence of sporophytes negatively affected growth, whereas presence of asexual diaspores did not. Sexual species had to reach a certain colony size before starting to reproduce, whereas no such treshold existed for asexual reproduction.

The results indicate that the epiphyte metacommunity is structured by two main trade-offs: dispersal distance vs reproductive age, and dispersal distance vs sensitivity to habitat quality. There seems to be a trade-off between growth and sexual reproduction, but not asexual. Trade-offs in species traits may be shaped by conflicting selection pressures imposed by habitat turnover and connectivity rather than by species interactions.

Keywords
Growth, Local processes, Metapopulation, Reproduction, Trade-offs
National Category
Biological Sciences
Research subject
Ecological Botany
Identifiers
urn:nbn:se:uu:diva-107314 (URN)10.1007/s00442-009-1402-1 (DOI)000269010300012 ()
Available from: 2009-08-05 Created: 2009-08-05 Last updated: 2019-02-01Bibliographically approved
5. Trade-offs and habitat constraints in the establishment of epiphytic bryophytes
Open this publication in new window or tab >>Trade-offs and habitat constraints in the establishment of epiphytic bryophytes
2010 (English)In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 24, no 4, p. 887-897Article in journal (Refereed) Published
Abstract [en]

1. Diversity of patch-tracking epiphyte metacommunities depends on successful colonization of new habitats. Habitat constraints and critical stages in the establishment have gained little attention in metacommunity studies, but a trade-off between dispersal ability and establishment rate is often assumed. This assumption remains largely untested, and alternative dispersal and reproductive strategies offer several trade-offs to be explored.

2. We used in vitro experiments to identify critical stages in the establishment of obligate epiphytic bryophytes with contrasting dispersal strategies [sexual via small (< 20 mu m) or large (> 20 mu m) spores, asexual via gemmae or gemmae-like branchlets], and to identify habitat constraints of diaspore establishment and trade-offs among species traits.

3. Across all stages of the establishment process, large asexual diaspores performed better than small sexual ones. Asexual species also had a higher ability to establish from fragments than sexual species. Germination of all diaspore types was limited by pH with highest germination rates at intermediate pH. Large moss spores showed a higher desiccation tolerance than small ones, but lower germination and protonemal growth rates. Liverwort spores had the lowest desiccation tolerance, germination and protonemal growth rates, but rapidly developed gametophytic shoots once they had germinated.

4. Combining the results with earlier studies on dispersal distances in epiphytes, our study demonstrated a trade-off between dispersal distance and establishment ability, which may be central for the evolution of asexual dispersal in epiphytes. The evolution of spore size may additionally involve trade-offs between high germination and protonemal growth rates, desiccation tolerance, and a rapid development from protonema to shoots. We suggest that trade-offs in epiphytes are shaped by conflicting selection pressures imposed by habitat patchiness, landscape dynamics and irregular water supply.

Keywords
desiccation, germination, life-history trade-offs, metacommunity, pH, patch-tracking, protonema, reproductive strategies
National Category
Biological Sciences
Research subject
Ecological Botany
Identifiers
urn:nbn:se:uu:diva-107315 (URN)10.1111/j.1365-2435.2010.01705.x (DOI)000279837700022 ()
Note
Part of PhD-thesis which will be defended the 26th of September 2009Available from: 2009-08-05 Created: 2009-08-05 Last updated: 2019-02-01Bibliographically approved

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