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Sex-ratio mediated pollen limitation in the dioecious herb Antennaria dioica
Stockholm University, Faculty of Science, Department of Botany.
Stockholm University, Faculty of Science, Department of Botany.
2007 (English)In: Ecoscience, ISSN 1195-6860, Vol. 14, no 3, 387-398 p.Article in journal (Refereed) Published
Abstract [en]

We examined how population structure affects seed set and recruitment in the dioecious plant Antennaria dioica, which is a declining species inhabiting semi-natural grasslands in Sweden. Flowering and sex ratio in A. dioica were studied over 4 y at a local (1.2 km2) scale and over 1 y at a regional (742 km2) scale in southern Sweden. Antennaria dioica was also hand-pollinated during 2y to examine whether sex ratios, male abundance, and distance to nearest male influence the degree of pollen limitation. Seed-sowing experiments were conducted to assess whether recruitment is limited by seed or microsite availability. There was a considerable spatio-temporal variation in both flowering and sex ratios. The regional scale survey showed that patch size and number of patches per site were positively correlated, and small patches of A.dioica tended to have biased sex ratios. Experimental hand-pollinations showed that the degree of pollen limitation increased with increasingly female-biased sex ratios in the closest vicinity of the experimental plants. Thus, even though A. dioica is pollinated by many different insects, a fragmented population structure has a large influence on reproductive performance of A. dioica. The seed-sowing experiments showed that recruitment is limited by a combination of seed and microsite availability. It is therefore plausible that reduced seed production due to pollen limitation translates into reduced recruitment. The results from the local and the regional scale indicate that a large fraction of local patches and populations of A. dioica have decreased sexual reproduction. The conclusion is that A. dioica is likely to be particularly sensitive to habitat fragmentation.

Place, publisher, year, edition, pages
2007. Vol. 14, no 3, 387-398 p.
Keyword [en]
dioecy, habitat fragmentation, hand-pollination, pollen limitation, seed sowing, sex ratio
National Category
URN: urn:nbn:se:su:diva-23023DOI: 10.2980/1195-6860(2007)14[387:SRMPLI]2.0.CO;2ISI: 000250040400016OAI: diva2:189931
Available from: 2006-11-23 Created: 2006-11-23 Last updated: 2011-03-11Bibliographically approved
In thesis
1. Biological diversity values in semi-natural grasslands: indicators, landscape context and restoration
Open this publication in new window or tab >>Biological diversity values in semi-natural grasslands: indicators, landscape context and restoration
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Semi-natural grasslands, which are a declining and fragmented habitat in Europe, contain a high biodiversity, and are therefore of interest to conservation. This thesis examines how plant diversity is influenced by the landscape context, and how plant and fungal diversity can be targeted by practical conservation using indicator species and congruence between species groups. Reproduction and recruitment of the dioecious herb Antennaria dioica was also investigated, providing a case study on how fragmentation and habitat degradation may affect grassland plants.

Grassland size and heterogeneity were of greater importance for plant diversity in semi-natural grassland, than present or historical connectivity to other grasslands, or landscape characteristics. Larger grasslands were more heterogeneous than smaller grasslands, being the likely reason for the species-area relationship.

A detailed study on A. dioica discovered that sexual reproduction and recruitment may be hampered due to skewed sex-ratios. Sex-ratios were more skewed in small populations, suggesting that dioecious plants are likely to be particularly sensitive to reduced grassland size and fragmentation.

A study on indicators of plant species richness, used in a recent survey of remaining semi-natural grasslands in Sweden, revealed several problems. A high percentage of all indicator species were missed by the survey, removing an otherwise significant correlation between indicator species and plant species richness. Also, a null model showed that the chosen indicator species did not perform significantly better than species chosen at random from the available species pool, questioning the selection of the indicators in the survey. Diversity patterns of the threatened fungal genus Hygrocybe were not congruent with plant species richness or composition. Plants are thus a poor surrogate group for Hygrocybe fungi, and probably also for other grassland fungi. Implications from this thesis are that conservation of semi-natural grasslands should target several species groups, and that an appropriate scale for plant conservation may be local rather than regional.

Place, publisher, year, edition, pages
Stockholm: Botaniska institutionen, 2006. 41 p.
Biodiversity, connectivity, Hygrocybe, indicators, landscape history, plants, pollen limitation, species-area effects, surrogate species
National Category
Biological Sciences
urn:nbn:se:su:diva-1352 (URN)91-7155-341-X (ISBN)
Public defence
2006-12-15, föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 13:00
Available from: 2006-11-23 Created: 2006-11-23Bibliographically approved

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Öster, MathiasEriksson, Ove
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