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Sökning: WFRF:(Ehrlén Johan) > (2005-2009) > Dahlgren Johan

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1.
  • Dahlgren, Johan, et al. (författare)
  • Linking environmental variation to population dynamics of a forest herb
  • 2009
  • Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 97:4, s. 666-674
  • Tidskriftsartikel (refereegranskat)abstract
    • . Although necessary for understanding and predicting population dynamics, abiotic and biotic interactions have only rarely been coupled to demography and population dynamics. 2. We estimated effects of 11 environmental factors on survival, growth and fertility of the perennial herb Actaea spicata and incorporated significant factors into integral projection models to assess their effect on population dynamics. 3. Statistical models suggested that high soil potassium concentration increased individual growth and that seed predation and, to a lesser extent, canopy cover reduced seed production. 4. Demographic models showed that both soil potassium concentration and pre-dispersal seed predation could reverse population growth from positive to negative. The observed range of soil potassium concentration corresponded to growth rates (lambda) between 0.96 and 1.07, at mean observed seed predation intensity. At observed mean potassium concentration, growth rate ranged from 0.99 to 1.02 over observed seed predation intensities. 5. Sensitivity of population growth rate to different vital rates strongly influenced the relative effects of the two factors. Elasticity analysis suggested that proportional changes in soil potassium concentration result in seven times larger effects on population growth rate than changes in seed predation. 6. Synthesis. We conclude that relatively weak associations between environmental factors and vital rates can have substantial long-term effects on population growth. Approaches based on detailed demographic models, that simultaneously assess abiotic and biotic effects on population growth rate, constitute important tools for establishing the links between the environment and dynamics of populations and communities.
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2.
  • Dahlgren, Johan Petter, 1978- (författare)
  • Linking plant population dynamics to the local environment and forest succession
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Linking environmental variation to population dynamics is necessary to understand and predict how the environment influences species abundances and distributions. I used demographic, environmental and trait data of forest herbs to study effects of spatial variation in environmental factors on populations as well as environmental change in terms of effects of forest succession on field layer plants. The results show that abundances of field layer species during forest succession are correlated with their functional traits; species with high specific leaf area increased more in abundance. I also found that soil nutrients affect vegetative and flowering phenology of the forest herb Actaea spicata. The effect of nutrients shows that a wider range of environmental factors than usually assumed can influence plant phenology. Moreover, local environmental factors affected also the demography of A. spicata through effects on vital rates. An abiotic factor, soil potassium affecting individual growth rate, was more important for population growth rate than seed predation, the most conspicuous biotic interaction in this system. Density independent changes in soil potassium during forest succession, and to a lesser extent plant population size dependent seed predation, were predicted to alter population growth rate, and thereby the abundance, of A. spicata over time. Because these environmental factors had effects on population projections, they can potentially influence the occupancy pattern of this species along successional gradients. I conclude that including deterministic, as opposed to stochastic, environmental change in demographic models enables assessments of the effects of processes such as succession, altered land-use, and climate change on population dynamics. Models explicitly incorporating environmental factors are useful for studying population dynamics in a realistic context, and to guide management of threatened species in changing environments.
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