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- Dahlgren, Johan Petter, 1978-
(författare)
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Linking plant population dynamics to the local environment and forest succession
- 2008
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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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- Hambäck, Peter A., et al.
(författare)
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Plant trait-mediated interactions between early and late herbivores on common figwort (Scrophularia nodosa) and effects on plant seed set
- 2011
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Ingår i: Ecoscience. - : Informa UK Limited. - 1195-6860 .- 2376-7626. ; 18:4, s. 375-381
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Tidskriftsartikel (refereegranskat)abstract
- This study examined the interactive effects of early and late season herbivory on the growth and reproductive output of figwort (Scrophularia nodosa). The early season herbivore is a pentatomid bug that feeds on and kills the apical meristem, while the late season herbivores are 2 weevil species and a sawfly that all feed on leaves and flowers. The direct effect of early season meristem damage on plant reproduction was quite limited, although meristem damage did cause increased branching. This change in plant morphology may entail that early season herbivores have profound indirect effects on plant reproduction by affecting the abundance of and damage caused by late season herbivores. Comparisons of plants with and without early season meristem damage, natural and artificial, also suggest that plants with meristem damage are significantly shorter throughout most of the summer and receive less damage late in season. However, the reduced damage translated to increased flowering but not to increased fruit production, suggesting that the plants were able to compensate for late season damage. In the end, and despite damage, figwort was well able to tolerate the observed meristem and leaf damage.
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- van der Meer, Sascha, et al.
(författare)
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Differential effects of abandonment on the demography of the grassland perennial Succisa pratensis
- 2014
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Ingår i: Population Ecology. - : Wiley. - 1438-3896 .- 1438-390X. ; 56:1, s. 151-160
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Tidskriftsartikel (refereegranskat)abstract
- Abandonment of traditional land-use practices can have strong effects on the abundance of species occurring in agricultural landscapes. However, the precise mechanisms by which individual performance and population dynamics are affected are still poorly understood. To assess how abandonment affects population dynamics of Succisa pratensis we used data from a 4-year field study in both abandoned and traditionally grazed areas in moist and mesic habitats to parameterize integral projection models. Abandoned populations had a lower long-term stochastic population growth rate (lambda (S) = 0.90) than traditionally managed populations (lambda (S) = 1.08), while lambda (S) did not differ between habitat types. The effect of abandonment differed significantly between years and had opposed effects on different vital rates. Individuals in abandoned populations experienced higher mortality rates and lower seedling establishment, but had higher growth rates and produced more flower heads per plant. Population viability analyses, based on a population survey of the whole study area in combination with our demographic models, showed that 32 % of the populations face a high risk of extinction (> 80 %) within 20 years. These results suggest that immediate changes in management are needed to avoid extinctions and further declines in population sizes. Stochastic elasticity analyses and stochastic life table response experiments indicated that management strategies would be most effective if they increase survival of small plants as well as seedling establishment, while maintaining a high seed production. This may be achieved by varying the grazing intensity between years or excluding grazers when plants are flowering.
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- Dahlgren, Johan Petter, et al.
(författare)
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Actuarial senescence in a long-lived orchid challenges our current understanding of ageing
- 2016
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 283:1842
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Tidskriftsartikel (refereegranskat)abstract
- The dominant evolutionary theory of actuarial senescence-an increase in death rate with advancing age-is based on the concept of a germ cell line that is separated from the somatic cells early in life. However, such a separation is not clear in all organisms. This has been suggested to explain the paucity of evidence for actuarial senescence in plants. We used a 32 year study of Dactylorhiza lapponica that replaces its organs each growing season, to test whether individuals of this tuberous orchid senesce. We performed a Bayesian survival trajectory analysis accounting for reproductive investment, for individuals under two types of land use, in two climatic regions. The mortality trajectory was best approximated by a Weibull model, showing clear actuarial senescence. Rates of senescence in this model declined with advancing age, but were slightly higher in mown plots and in the more benign climatic region. At older ages, senescence was evident only when accounting for a positive effect of reproductive investment on mortality. Our results demonstrate actuarial senescence as well as a survival-reproduction trade-off in plants, and indicate that environmental context may influence senescence rates. This knowledge is crucial for understanding the evolution of demographic senescence and for models of plant population dynamics.
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- Wiig Tholstrup, Ditte, et al.
(författare)
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Actuarial senescence progresses similarly across sites and species in four boreal orchids
- 2024
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Ingår i: Journal of Ecology. - : British Ecological Society. - 0022-0477 .- 1365-2745. ; 112:3, s. 461-469
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Tidskriftsartikel (refereegranskat)abstract
- Whole-plant senescence, defined as a decrease in individual fitness as an organism grows older, has often been assumed to not occur in plants; however, it has now been detected in a range of plant taxa. Still, reported senescence patterns vary substantially, and it remains unknown how consistent patterns are within phylogenetic groups and how they may be affected by environmental factors. Plants show a high diversity in life-history traits within phylogenetic groups and environments, but shared traits among related species are also common, making both diverse and similar patterns probable.Here, we explore how mortality changes with advancing age in four closely related species (Dactylorhiza incarnata, D. lapponica, D. maculata and Gymnadenia conopsea) across two sites in Norway: the coastal Nordmarka and inland Sølendet. Using data collected over 34 years, following more than 2500 individual plants, we conduct Bayesian survival trajectory analysis to assess mortality age trajectories.A simple Weibull model, illustrating increasing mortality at a decelerating rate with age, was the best fit for all species at both sites. From these models, we calculate rates of senescence and compare them using Kullback–Leibler divergences, finding no notable differences in rates between species or sites.Synthesis. Our findings suggest that actuarial senescence, an increase in mortality with advancing age, may be common in orchids and show that demographic ageing can proceed similarly in closely related taxa across different environments.
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