Population size and habitat quality affect genetic diversity and fitness in the clonal herb Cirsium dissectum


Remaining populations of plant species in fragmented landscapes are threatened by declining habitat quality and reduced genetic diversity, but the interactions of these major factors are rarely studied together for species conservation. In this study, the interactions between population size, habitat quality, genetic diversity and fitness were investigated in 22 populations of the clonal herb Cirsium dissectum throughout the British Isles. Regression analysis was used to identify significant factors, and a structural equation model was developed to illustrate and integrate these interactions. It was found that smaller populations (measured as the total number of plants) had lower genetic diversity (proportion of polymorphic loci), and that reduced genetic diversity (allelic richness) had a negative impact on the survival of seedlings grown under standard conditions. Habitat quality also had a large effect on C. dissectum. Unmanaged sites with tall vegetation, no bare soil and higher nutrient levels had smaller populations of C. dissectum, but flowering was promoted. Flowering was suppressed in heavily grazed sites with short vegetation. Higher levels of bare soil and phosphorus both had a positive relationship with genetic diversity, but probably for distinctly different reasons: bare soil provides safe sites for establishment, whilst phosphorus may promote flowering and improve seed germination. In order to conserve C. dissectum, management needs to maintain site heterogeneity so that C. dissectum can flower and establishment gaps are still available for seedlings; when either component is reduced, negative feedbacks through reduced genetic diversity and individual fitness can be expected. This study therefore highlights the importance of considering both conservation genetics and habitat quality in the conservation of plant species.

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The authors would like to thank Colin Ford for help with fieldwork, and Ian Turner, Wayne Edwards, Ann Chapman, Sarah Cunningham and Maxine Chavner for help growing and potting on plants; Ann Smithson and Mark MacNair for allowing us to use the molecular genetics laboratory at Exeter University and for providing training in molecular techniques; and two anonymous referees for valuable comments and critical reading of the manuscript. Many thanks to the landowners and conservation bodies who allowed us access to field sites and to the vice county recorders of the Botanical Society of the British Isles for suggesting suitable sites. This project was funded by the Whitley Wildlife Conservation Trust. E.J. acknowledges support from the Netherlands Organization for Scientific Research (NWO project 805-33-452).

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Correspondence to Natasha de Vere.

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Communicated by Bernhard Schmid.

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de Vere, N., Jongejans, E., Plowman, A. et al. Population size and habitat quality affect genetic diversity and fitness in the clonal herb Cirsium dissectum . Oecologia 159, 59–68 (2009).

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  • Plant species conservation
  • Ecological genetics
  • Habitat management
  • Structural equation model