SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "WFRF:(Ehrlén Johan) srt2:(2000-2004)"

Sökning: WFRF:(Ehrlén Johan) > (2000-2004)

  • Resultat 1-10 av 12
  • [1]2Nästa
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • de Kroon, Hans, et al. (författare)
  • Elasticities : a review of methods and model limitations
  • 2000
  • Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81:3, s. 607-618
  • Tidskriftsartikel (refereegranskat)abstract
    • Elasticity is a perturbation measure in matrix projection models that quantifiesthe proportional change in population growth rate as a function of a proportionalchange in a demographic transition (growth, survival, reproduction, etc.). Elasticities thusindicate the relative "importance" of life cycle transitions for population growth and maintenance.In this paper, we discuss the applications of elasticity analysis, and its extension,loop analysis, in life history studies and conservation. Elasticity can be interpreted as therelative contribution of a demographic parameter to population growth rate. Loop analysisreveals the underlying pathway structure of the life cycle graph. The different kinds ofresults of the two analyses in studies of life histories are emphasized. Because elasticitiesquantify the relative importance of life cycle transitions to population growth rate, it isgenerally inferred that management should focus on the transitions with the largest elasticities.Such predictions based on elasticities seem robust, but we do identify three situationswhere problems may arise. The mathematical properties and biological constraints thatunderlie these pitfalls are explained. Examples illustrate the additional information thatneeds to be taken into account for a sensible use of elasticities in population management.We conclude by indicating topics that are in need of research.
  •  
2.
  • Ehrlén, Johan, et al. (författare)
  • Dispersal limitation and patch occupancy in forest herbs
  • 2000
  • Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81, s. 1667-1674
  • Tidskriftsartikel (refereegranskat)abstract
    • The distribution of species depends on the availability of suitable habitats, the capacity to disperse to these habitats, and the capacity of populations to persist after establishment. Dispersal limitation implies that not all suitable habitat patches will be occupied by a species. However, the extent to which dispersal limits local distribution is poorly known. In this study, we transplanted seeds, bulbils, and juvenile plants to examine patterns of dispersal limitation and patch occupancy in seven temperate-forest herbs. Recruitment was recorded during four years in 48 patches. The investigated species varied considerably in their natural abundance in the patches. Patterns of seedling emergence and establishment among patches were not related to any of nine investigated abiotic factors. In contrast, the availability of seeds or bulbils was found to limit recruitment in six of the investigated species. Establishment was also successful in many patches where the species did not occur naturally. Estimated patch occupancy in the investigated species ranged from 17.2% to 94.6%. Seed size was positively correlated with the probability of successful establishment of seeds and negatively correlated with patch occupancy. The results suggest that dispersal limitation is an important structuring factor in temperate-forest herb communities. The distribution of species can be perceived as the result of processes operating both among and within patches. Seed size is a key trait in these processes.
  •  
3.
  • Ehrlén, Johan, et al. (författare)
  • How perennial are perennial plants?
  • 2002
  • Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 98:2, s. 308-322
  • Tidskriftsartikel (refereegranskat)abstract
    • Trade-offs involving life span are important in the molding of plant life histories. However, the empirical examination of such patterns has so far been limited by the fact that information on life span is mainly available in terms of discrete categories; annuals, semelparous perennials and iteroparous perennials. We used transition matrix models to project continuous estimates of conditional life spans from published information on size- or stage-structured demography for 71 perennial plant species. The projected life span ranged from 4.3 to 988.6 years and more than half of the species had a life span of more than 35 years. Woody plants had on average a projected life span more than four times as long as non-woody plants. Life spans were higher in forests than in open habitats and individuals of non-clonal species tended to have a longer life span than ramets of clonal species. Self-incompatible plants on average lived longer than self-compatible plants. There were no clear relations between life span and geographical region, dispersal syndrome, pollination mode, seed size or the presence of a seed bank. We conclude that accurate estimates of life span are central to understand how longevity is correlated to other traits within the group of perennial plants.
  •  
4.
  • Ehrlén, Johan, et al. (författare)
  • Pollen limitation, seed predation and scape length in Primula farinosa
  • 2002
  • Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 97:1, s. 45-51
  • Tidskriftsartikel (refereegranskat)abstract
    • Floral display and reward production may affect the attractiveness of a plant to a range of interacting animals including pollinators, herbivores, and vectors of pathogenic fungi. The optimal floral phenotype should therefore depend on the relative importance of selection exerted by both mutualistic and antagonistic animals. The perennial, rosette herb Primula farinosa is polymorphic for scape length. Natural populations may include both plants with flowers displayed well above the ground (the long-scaped morph) and those with flowers positioned very close to the ground (the short-scaped morph). In this study, we conducted a field experiment to examine how the relative fitness of the two scape morphs is affected by interactions with pollinators and fruit predators in two different microhabitats (high and low vegetation). As predicted based on the difference in floral display, supplemental hand-pollination showed that fruit initiation was more strongly pollen-limited in the short-scaped than in the long-scaped morph, and that this difference was significantly larger in high than in low vegetation. Moreover, plants with a short scape experienced lower levels of fruit predation than plants with a long scape. Among open-pollinated controls, there was no significant difference in seed output between the two scape morphs. However, among plants receiving supplemental hand-pollination, short-scaped plants produced significantly more seeds than long-scaped plants. The results suggest that the positive and negative effects of a prominent floral display (increased pollination and seed predation, respectively) balance in the study population, but also that the short-scaped morph would have an advantage at higher pollination intensities. Spatial and temporal variation in pollinator activity and seed predation should result in associated variation in the relative fecundity of the two scape morphs.
  •  
5.
  • Ehrlén, Johan (författare)
  • The dynamics of plant populations : does the history of individuals matter?
  • 2000
  • Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81:6, s. 1675-1684
  • Tidskriftsartikel (refereegranskat)abstract
    • Historical events have been used to explain a wide range of phenomenaincluding geographical distributions of species, community diversity, and population structure.At the level of individuals, historical effects in which past conditions influence futureperformance are particularly likely to occur in long-lived organisms that store resourcesbetween seasons and that form organs months or years before their elaboration. Such carryovermechanisms have been documented in several perennial plant species, but the implicationsfor population processes are poorly known. In this study, I examine how the historyof individuals influences their future performance, population dynamics, and life cycle,structure in the long-lived herb Lathyrus vernus. Overall effects of plant history on populationdynamics, in terms of growth rate, reproductive values, stable stage distribution,and elasticities, are examined by comparing an ordinary first-order matrix model with asecond-order matrix model. In the latter, not only the present state of individuals, but alsotheir past state is allowed to influence future fate.The results demonstrate that the history of individuals is sometimes important in modelsof population dynamics. Plant size change over a one-year period was negatively correlatedamong time intervals. Addition of the previous year's stage in population models shiftedthe growth rate from positive (X = 1.010) to negative (X = 0.986) and increased theproportion of small established individuals in the stable stage distribution. If historicaleffects are due to a capacity to buffer environmental variation and regain size or state, asin L. vernus, then recruitment contributes less and stasis more to population growth thansuggested by ahistorical models. The presence of historical effects at the level of individuals,in any form, may have important consequences for population development and should beincluded in any interpretation of the life-cycle structure.
  •  
6.
  • Isaeus, Martin, 1964- (författare)
  • Factors structuring Fucus communities at open and complex coastlines in the Baltic Sea
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • This thesis deals with physical factors and biological interactions affecting the distribution of two fucoid species, Fucus vesiculosus and F. serratus, in the Baltic Sea. Studies have been carried out in two quite different environments: an archipelago, and an open rocky coast. The archipelago has an extremely long coastline with a heterogeneous submerged landscape of different substrate types, slopes, water qualities, and degrees of wave exposure. The factors influencing F. vesiculosus distribution, morphology and epiphyte composition were studied in the Stockholm archipelago using field surveys and spatial modelling in Geographic information systems (GIS). A GIS-method to estimate wave exposure was developed and validated by comparing the result to an index based on vertical zonation of lichens. Wave exposure was considered an important factor for predicting the distribution of F. vesiculosus by its ability to clean hard surfaces from silt, and a predictive model was constructed based on the information of wave exposure and slope of the shore. It is suggested that the lower distribution boundary of attached F. vesiculosus is set by sediment in sheltered parts of the archipelago, and by light availability in highly wave exposed parts. The morphology of F. vesiculosus was studied over a wave exposure gradient, and several characters responded in accordance with earlier studies. However, when separating effects of wave exposure from effects of other confounding water property parameters, only thallus width was significantly different. Several water property parameters were shown to be correlated with wave exposure in the Stockholm archipelago, and the mechanism responsible for the effects on F. vesiculosus morphology is discussed. The composition of epiphytes on F. vesiculosus varied over a wave exposure gradient with a positive correlation to Elachista fucicola, and a negative to Chorda filum. At an open coast the physical environment is much less heterogeneous compared to an archipelago. The distributions of F. vesiculosus, F. serratus, turf-forming algae, and the seafloor substrate, were surveyed along the open coasts of Öland and Gotland. Turf-forming algae dominated all hard substrates in the area, and Polysiphonia fucoides was most abundant. At the Gotland coast F. vesiculosus was less abundant than at the Öland coast, and F. serratus occurred only in the southern-most part. Fucus serratus was increasingly more common towards south which was interpreted as an effect mainly of the Baltic salinity gradient, or the variation of salinity that has occurred in the past. The effects of turf-forming algae and sediment on F. serratus recruitment at 7 m depth off the Öland east coast were studied in the field, and by laboratory experiments. Almost no recruits were found in the algal turf outside the F. serratus patches. More fine sediment was found in the turf than in the F. serratus patches, suggesting that the turf accumulates sediment by decreasing resuspension. Both filamentous algae and sediment decreased the attachment ability of F. serratus zygotes and survival of recruits, and sediment had the strongest effect. It is therefore suggested that F. serratus has difficulties recruiting outside its patches, and that these difficulties are enforced by the eutrophication of the Baltic Sea, which has favoured growth of filamentous algae and increased sedimentation. An overall conclusion is that Fucus distribution is affected by large-scale-factors, such as the eutrophication and salinity changes of the Baltic Sea, as well as by small-scale variation in wave exposure, substrate and slope, and by surface competition with neighbouring species.
  •  
7.
  • Leimu, Roosa, et al. (författare)
  • Pre-dispersal seed predation in Primula veris : among-population variation in damage intensity and selection on flower number
  • 2002
  • Ingår i: Oecologia. - 0029-8549 .- 1432-1939. ; 133:4, s. 510-516
  • Tidskriftsartikel (refereegranskat)abstract
    • The geographic mosaic theory of co-evolution states that evolution of interactions is driven by geographical variation in interactions between species. We investigated whether the intensity of pre-dispersal seed predation differed among nine Primula veris populations over 5 years, and whether such differences lead to geographical variation in selection on flower number. Seed predation intensity differed significantly among years and populations, and it increased with canopy closure and decreased with the density of the field layer vegetation. Individuals in open habitats also produced the highest number of flowers. Moreover, the phenotypic selection on flower number differed among years and populations. In populations of closed habitats, with high seed predation pressure, the increased number of flowers was often correlated with an increased number of damaged capsules. However, an increased flower number did not result in fewer intact fruits due to seed predation in any population.
  •  
8.
  • Lindborg, Regina, et al. (författare)
  • Evaluating the extinction risk of a perennial herb : demographic data versus historical records
  • 2002
  • Ingår i: Conservation Biology. - 0888-8892 .- 1523-1739. ; 16:3, s. 683-690
  • Tidskriftsartikel (refereegranskat)abstract
    • Demographic information is frequently used to project the long-term extinction risk of endangered species, but the limitations of this approach have not been extensively discussed. We examined demographic data for the endangered perennial herb Primula farinosa with matrix models to assess population growth rates and extinction risks. The data came from six populations in contrasting habitats followed over a 4-year period. The results of these demographic models were compared to the results of experimental manipulations and to the actual change in occurrence of P. farinosa over a 70-year period in different habitat types. According to demographic models, all managed populations had a projected negative population growth rate and experienced a high extinction risk in 100 years, whereas unmanaged populations had increasing population sizes. In contrast, experiments and historical records suggested that continuous grazing is positively correlated with population persistence. Our results thus show that demographic studies done during a transient phase of population growth after management cessation may not capture the long-term changes. In such cases, projections of population growth rates may give misleading guidance for conservation. Short-term demographic studies are in many cases unlikely to correctly assess the survival probability of a species. We therefore argue that complementary information, such as long-term historical data or experimental manipulations of the environment, should be used whenever possible.
  •  
9.
  • Lindborg, Regina, 1966- (författare)
  • Land Use Change in Space and Time : implications for plant species conservation in semi-natural grasslands
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Land use change has during the last century altered the traditional rural landscape in Sweden, resulting in a major decline in species diversity. Traditional small-scale farming, with a remarkably high small-scale species richness, has changed in favour of rationalized agriculture, and many semi-natural grasslands, i.e. traditionally managed pastures and meadows, have become abandoned. In this thesis I examine how spatio-temporal processes affect plant species in Swedish semi-natural grasslands exposed to habitat degradation as well as recovery (restoration). I also discuss how to conserve plant species associated with semi-natural grasslands. In general, species responded slowly to habitat degradation, but quickly to improvement of habitat quality. Population viability analysis (PVA) of the grazing favoured herb Primula farinosa suggested, in contrast to historical records, that populations in abandoned grasslands performed better than populations in traditionally managed grasslands, a result questioning the accuracy of PVAs. Restoration of grasslands counteracted species richness decline and the number of species increased within seven years after restoration. It was possible to recruit grassland species in grazed former arable fields by artificial seed-sowing. This may help to speed up the natural recruitment, which often is low due to dispersal limitations in modern fragmented landscapes. Studies at larger regional scales showed century long time-lags in the response of plant species richness to land use change. Species richness was not related to present-day connectivity of grasslands, but positive effects appeared for grassland configuration in 1950s and 1900s. Thus, making conservation guidelines based solely on present-day data may be strongly misleading and under-estimate the actual risk of species loss. To secure long-term survival of species, it is important to focus on processes associated with larger spatial scales. This may benefit natural dynamics at longer time-scales, where abandoned and restored grasslands, together with species-rich semi-natural grasslands, could become natural parts of sustainable landscape management.
  •  
10.
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-10 av 12
  • [1]2Nästa

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy