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| 2. |
- 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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| 3. |
- Vanhoenacker, Didrik, 1971-, et al.
(författare)
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Spatial variability in seed predation in Primula farinosa: local population legacy vs. patch selection
- 2009
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 160:1, s. 77-86
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Tidskriftsartikel (refereegranskat)abstract
- Spatio-temporal variation in seed predation may strongly influence both plant population dynamics and selection on plant traits. The intensity of seed predation may depend on a number of factors, but the relative importance of previous predator abundance (“local legacy”), spatial distribution of the host plant, environmental factors and plant characteristics has been explored in few species. We monitored seed predation in the perennial herb Primula farinosa, which is dimorphic for scape length, during 5 consecutive years, in a 10-km × 4-km area comprising 79 P. farinosa populations. A transplant experiment showed that the seed predator, the oligophagous tortricid moth Falseuncaria ruficiliana, was not dispersal limited at the spatial scale corresponding to typical distances between P. farinosa populations. Correlations between population characteristics and incidence and intensity of seed predation varied among years. The incidence of the seed predator was positively correlated with host population size and mean number of flowers, while intensity of seed predation in occupied patches was positively related to the frequency of the long-scaped morph in 2 years and negatively related to host population size in 1 year. In both scape morphs, predation tended to increase with increasing frequency of the long morph. There was no evidence of a local legacy; incidence and intensity of seed predation were not related to the abundance of the seed predator in the population in the previous year. Taken together, the results indicate that among-population variation in seed predation intensity is determined largely by patch selection and that the seed predator’s preference for tall and many-flowered inflorescences may not only affect selection on plant traits within host plant populations, but also the overall intensity of seed predation.
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| 4. |
- Herben, T, et al.
(författare)
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Longterm spatial dynamics of Succisa pratensis in a changing rural landscape : linking dynamical modelling with historical maps
- 2006
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Ingår i: Journal of Ecology. - : Wiley-Blackwell. - 0022-0477 .- 1365-2745. ; 94:1, s. 131-143
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Tidskriftsartikel (refereegranskat)abstract
- We attempt to explain the current distribution of a long-lived perennial plant, Succisa pratensis, in a rural landscape in southern Sweden by linking its population biology with documented changes in the landscape, using a dynamical, spatially explicit model incorporating population dynamics and spatial spreading of the plant. Changes in the landscape were inferred from historical maps (1850 and 1900) and aerial photographs (1945 and 2001). We tested whether predictions for the current species distribution are affected by assumptions about its early 19th century distribution, to determine whether recent history and current processes are dominant, and how past landscape changes determine current distributions. Initial conditions influence predictions of current distribution, suggesting that the current distribution still partly reflects the distribution of the species in the early 19th century. A period of 150 years is too short for Succisa to have spread extensively if dispersal parameters are given realistic values. Simulations in which present-day land-use patterns were imposed at earlier dates showed that changes in landscape structure over the past 175 years also had a strong effect on the present-day habitat occupancy and population sizes of Succisa. The dominant process for Succisanow is extinction from marginal habitats. It is therefore likely that the (relatively) high present-day occupation patterns are still due to much larger areas having been available in the past rather than to successful dispersal. Although the species has responded to landscape changes, there is little evidence of population sizes reaching equilibrium. Our approach shows that the wealth of landscape information available from historical maps can be linked with data on population biology by means of dynamical models that can make predictions about species dynamics.
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| 5. |
- Toräng, Per, 1978-
(författare)
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Pollinators, Enemies, Drought, and the Evolution of Reproductive Traits in Primula farinosa
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, I combined comparative and experimental approaches to examine selection on reproductive traits and population differentiation in the insect-pollinated, self-incompatible, perennial herb Primula farinosa. More specifically, I (1) determined whether the effects of floral display and interactions with pollinators and seed predators, and plant reproductive success were frequency-dependent and affected by surrounding vegetation context, (2) examined the consequences of intermittent drought years on population dynamics using numerical simulations based on demographic data collected over seven years, (3) analyzed among-population differentiation in flowering phenology and reproductive allocation, and its relationship to soil-depth at the site of origin.A field experiment suggested that conspicuous plants facilitate inconspicuous plants in terms of pollinator attraction, and that the facilitation effect is contingent on the height of the surrounding vegetation. Further experiments revealed that both mutualistic and antagonistic interactions can result in frequency-dependent selection on floral display. Among inconspicuous plants, both fruit initiation, and damage from seed predators increased with the proportion of the conspicuous morph. The relative strength of these effects, and therefore their net outcome on the relationship between morph ratio and seed production varied among years.I combined information on vital rates and their relation to environmental conditions in simulations to predict future population viability in changing environments. Simulated stochastic population growth rate decreased with increasing frequency of drought years.Reproductive allocation varied significantly among populations both in the field and in a common-garden experiment, but was correlated with soil depth at the site of origin only in the field. The results suggest that among-population variation in reproductive effort in the field mainly reflects plastic responses to environmental conditions, and that this plasticity may be adaptive. The common-garden experiment suggested that the study populations have diverged genetically in flowering time.
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| 6. |
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| 7. |
- Lehtilä, Kari, et al.
(författare)
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Seed size as an indicator of seed quality : a case study of Primula veris
- 2005
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Ingår i: Acta Oecologica. - : Elsevier BV. - 1146-609X .- 1873-6238. ; 28:3, s. 207-212
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Tidskriftsartikel (refereegranskat)abstract
- Seed size is a widely accepted measure of seed quality, because many earlier studies have shown that large seeds have high seedling survival, growth and establishment. We tested whether ovule loss increases size of the remaining seeds and whether such size increase affects seedling establishment. We removed all except one flower from inflorescences of Primula veris L. (Primulaceae), a perennial hemicryptophyte herb, at a late stage of flowering. Flower removal (FR) increased seed size by 33% compared to the control plants. We then divided the seeds within each treatment to small, middle-sized and large seeds and carried out a sowing experiment in the field, Within each experimental group, seedling establishment was positively associated with seed size. However, despite size differences, seeds from the FIR and control groups had the same seedling establishment probability. Seeds from FR plants had a higher seedling emergence in May than those from control plants, but the number of seedlings alive per sowing plot in the late summer was the same in both experimental groups. Increase in seed mass after partial FR thus did not enhance seedling performance, although seed size variation due to other causes was positively correlated with seedling establishment. Further studies are needed to show whether plastic changes of seed size are usually adaptive or not.
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| 8. |
- Mildén, Mikael, 1973-
(författare)
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Local and regional dynamics of Succisa pratensis
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Land use change is considered to be one of the biggest threat to global species diversity. In Sweden, abandonment of grazing is one of the most common reasons for decline in species richness in semi-natural grasslands. Today semi-natural grasslands often occur as more or less isolated fragments. The result for species that benefits from grazing is a smaller area of suitable habitat and higher extinction risks and a lowered ability to colonize new areas. Succisa pratensis is a long-lived perennial plant that benefits from grazing and is common in Swedish semi-natural grasslands. I have assessed the performance of Succisa pratensis at various spatial and temporal scales, in a Swedish rural landscape. I performed demographic matrix modelling of populations at grazed and ungrazed sites. A regional level was then added, by incorporating data collected from a large number of populations and habitat types into the matrix models and extinction risks over 50 years were calculated. A dynamic metapopulation model was created and the regional dynamics, in terms of colonisations resulting from long distance dispersal and population extinctions were examined. The effects of management history were incorporated into the model by using historical maps. In addition, I made an analysis of the impact of management history on the distribution and performance of four grassland species, using vegetation maps from 1945 and 2001. Local dynamics of Succisa pratensis was negatively affected by abandonment of grazing. Recorded population sizes were ten times higher in grazed sites than in ungrazed. The turnover rate of the system was estimated to about one extinction or colonisation per year. Both the simulation study and the analyses of vegetation maps suggested a pronounced legacy of management history in Succisa pratensis in the study landscape. Overall, the results of this thesis demonstrate the importance of management history for species in the rural landscape.
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| 9. |
- Mildén, Mikael, et al.
(författare)
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Metapopulation dynamics of a perennial plant, Succisa pratensis, in an agricultural landscape
- 2006
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Ingår i: Ecological Modelling. - : Elsevier B.V.. - 0304-3800 .- 1872-7026. ; 199:4, s. 464-475
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Tidskriftsartikel (refereegranskat)abstract
- Most metapopulation models neglect the local dynamics, and systems characterized by slow population turnover, time lags and non-equilibrium, are only rarely examined within a metapopulation context. In this study we used a realistic, spatially explicit, dynamic metapopulation model of a long-lived grassland plant, Succisa pratensis, to examine the relative importance of local population dynamics, and short and long-distance dispersal of seeds. Using both vegetation composition and sowing experiments we identified 94 occupied and 43 unoccupied, but suitable, habitat patches in a 7-km2 landscape. Local population dynamics were studied in permanent plots in five populations. Simulation results showed that the colonization and extinction dynamics of S. pratensis were slow with about one colonization or extinction per year and the time frame for the population system to attain equilibrium in a constant landscape was several thousands of years. Sensitivity analyses demonstrated that occasional long-distance dispersal had a large influence on population turnover rates whereas regular short-distance dispersal had little effect. Our model also allowed us to assess how demographic processes affect not only local population growth but also regional dynamics. Fecundity was more important, compared with growth and survival, in a metapopulation context than when considered only within populations. The effect of landscape development was examined through different land-use scenarios and suggested that S. pratensis only very slowly colonizes new habitats that are made available. Our results with S. pratensis in an agricultural landscape show that long-distance dispersal and colonization dynamics play an important role for the regional distribution in long-lived plants but that time lags, and thus the effect of landscape history, are also very important.
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| 10. |
- Pico, Xavier, et al.
(författare)
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Modelling the effects of genetics and habitat on the demography of a grassland herb
- 2009
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Ingår i: Basic and Applied Ecology. - : Elsevier BV. - 1439-1791 .- 1618-0089. ; 10, s. 122-130
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Tidskriftsartikel (refereegranskat)abstract
- There is growing evidence that genetic and ecological factors interact in determining population persistence. The demographic effects of inbreeding depression can largely depend on the ecological milieu. We used demographic data of the perennial herb Succisa pratensis from six populations in grazed and ungrazed sites with different soil moisture. We built an individual-based model assessing the demographic consequences of inbreeding depression in populations with different management and habitat. Today this plant has to cope with severe landscape fragmentation, deteriorating habitat conditions in terms of decreasing grazing intensity, and the effects of inbreeding depression. For each population we performed simulations testing two inbreeding depression hypotheses (partial dominance and overdominance) and three epistatic functions among loci. The results indicated stronger inbreeding depression effects for populations in unfavourable sites without grazing or in xeric habitats compared to populations in favourable mesic sites with grazing. Overall, we found stronger effects with overdominance, a result that emphasizes the importance of understanding the genetic mechanisms of inbreeding depression. Hence, management practices can interact with the genetic consequences of inbreeding depression in population dynamics, which may have important implications for plant population ecology and evolutionary dynamics of inbreeding depression.
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