Population Persistence and Offspring Fitness in the Rare Bellflower Campanula cervicaria in Relation to Population Size and Habitat Quality

Authors

  • Anna-Kaija Eisto,

    1. Department of Biological and Environmental Science, University of Jyväskylä, P.O Box 35 (YAC), FIN-40351 Jyväskylä, Finland
    2. Forest and Park Service, Urheilukatu 3 A, FIN-81700 Lieksa, Finland
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  • Markku Kuitunen,

    1. Department of Biological and Environmental Science, University of Jyväskylä, P.O Box 35 (YAC), FIN-40351 Jyväskylä, Finland
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  • Antti Lammi,

    1. Department of Biological and Environmental Science, University of Jyväskylä, P.O Box 35 (YAC), FIN-40351 Jyväskylä, Finland
    2. South West Finland Regional Environment Centre, P. O. Box 47, FIN-20801 Turku, Finland
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  • Veli Saari,

    1. Department of Biological and Environmental Science, University of Jyväskylä, P.O Box 35 (YAC), FIN-40351 Jyväskylä, Finland
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  • Jukka Suhonen,

    1. Department of Biological and Environmental Science, University of Jyväskylä, P.O Box 35 (YAC), FIN-40351 Jyväskylä, Finland
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  • Susanna Syrjäsuo,

    1. Department of Biological and Environmental Science, University of Jyväskylä, P.O Box 35 (YAC), FIN-40351 Jyväskylä, Finland
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  • Päivi M. Tikka

    Corresponding author
    1. Department of Biological and Environmental Science, University of Jyväskylä, P.O Box 35 (YAC), FIN-40351 Jyväskylä, Finland
       Address correspondence to P.M. Tikka, email pmt@cc.jyu.fi
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 Address correspondence to P.M. Tikka, email pmt@cc.jyu.fi

Abstract

Abstract: Data from several animal species and a few plant species indicate that small populations face an elevated risk of extinction. Plants are still underrepresented in these studies concerning the relation between population size and persistence. We studied the effect of population size on persistence among natural populations of the rare bellflower Campanula cervicaria in Finland. We monitored 52 bellflower populations for 8 years and found that the mean population size decreased from 24 to 14 during this period. Small populations with ≤5 individuals were more prone to losing all fertile plants than were larger ones. Reduction in population size was nevertheless unrelated to the degree of population isolation, measured as the distance to the nearest known population. To test the hypothesis that offspring fitness is lower in small populations, we germinated bellflower seeds from different-sized populations in a laboratory and found that seed germination ability was independent of population size. The seedlings raised from seeds of small populations grew faster than those taken from larger populations. Population size was negatively related to the amount of shade in the habitats. In conclusion, decreasing population sizes of C. cervicaria seemed not to be caused by lowered germination ability or growth rate in small populations; rather, population size reductions appeared to be due to closing of vegetation in the habitats.

Abstract

Resumen: Los datos de varias especies de animales y de unas pocas especies de plantas indican que las poblaciones pequeñas enfrentan un riesgo elevado de extinción. Las plantas están aún menos representadas en estos estudios concernientes a la relación entre el tamaño poblacional y la persistencia. Nosotros estudiamos el efecto del tamaño poblacional sobre la persistencia de poblaciones naturales de la rara Campanula cervicaria en Finlandia. Monitoreamos 52 poblaciones de C. cervicaria por 8 años y encontramos que el tamaño promedio poblacional disminuyó de 24 a 14 durante este período. Las poblaciones pequeñas con ≤5 individuos fueron más propensas a perder todas las plantas fértiles que las poblaciones grandes. Sin embargo, la reducción en el tamaño poblacional no estuvo relacionada con el grado de aislamiento poblacional, medido como la distancia a la población más cercana. Para evaluar la hipótesis de que la adaptabilidad de la progenie es menor en poblaciones pequeñas, germinamos semillas de C. cervicaria de diferentes tamaños poblacionales en un laboratorio y encontramos que la germinación de semillas fue independiente del tamaño poblacional. Las plántulas provenientes de poblaciones pequeñas crecieron más rápido que aquéllas tomadas de poblaciones más grandes. El tamaño poblacional estuvo negativamente relacionado con la cantidad de sombra en los hábitats. En conclusión, la disminución del tamaño poblacional de C. cervicaria aparentemente no es causada por una disminución en la habilidad de germinación o en la tasa de crecimiento, más bien, parece ser que las reducciones en el tamaño poblacional son debidas a lo cerrado de la vegetación en los hábitats.

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