Avancerad sökning

Hittade 5 avhandlingar som matchar ovanstående sökkriterier.

1. 1. Reproductive patterns of birches (Betula spp.) in northern Sweden

   Författare :Stig-Olov Holm; Umeå universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Reproduction; Betula; seed-quality; seed-set; pollination; pollen-limitation; pollen-competition; tree-line; environmental gradient; seed weight; seedling survival; Semudobia;

   Sammanfattning : The aim of this thesis was to study patterns of reproduction of Betula pendula and B. pubescens coll. along an altitudinal, coastal-inland, gradient in northern Sweden. The altitudinal variation was related to the distribution of the birch taxa along the gradient. LÄS MER

3. 2. Effects of climate change on boreal wetland and riparian vegetation

   Författare :Lotta Ström; Roland Jansson; Christer Nilsson; Sarah Gergel; Umeå universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; biomass; flooding; hydrologic niche; invasibility; riparian zone; riparian plant species; river margin; climate scenario; seed sowing experiment; species composition; species richness; transplant experiment; Terrestrial ecology; Terrestrisk ekologi;

   Sammanfattning : Models of climate change predict that temperature will increase during the 21th century and the largest warming will take place at high northern latitudes. In addition to warming, predictions for northern Europe include increased annual precipitation and a higher proportion of the precipitation during winter falling as rain instead of snow. LÄS MER

4. 3. Effects of seed size and habitat on recruitment patterns in grassland and forest plants

   Författare :Karin Lönnberg; Ove Eriksson; Per Milberg; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Seed size; seedling establishment; seedling survival; recruitment; seed removal; co-existence; game-theory; Plant Ecology; växtekologi;

   Sammanfattning : A trade-off between seed size and seed number is central in seed ecology, and has been suggested to be related to a trade-off between competition and colonization, as well as to a trade-off between stress tolerance and fecundity. Large seeds endure hazards during establishment, such as shading, drought, litter coverage and competition from other plants, better than do small seeds, due to a larger amount of stored resources in the seed. LÄS MER

5. 4. Wooded or treeless pastures? : Linking policy, farmers' decisions and biodiversity

   Författare :Simon Jakobsson; Regina Lindborg; Sara A O Cousins; Jan Plue; Tim Benton; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; bat; biodiversity; bird; canopy cover; Common Agricultural Policy; European Union; farmer; functional diversity; germination; grassland; multi-taxa; pasture; plant; policy; seed sowing; tree density; trees; Physical Geography; naturgeografi;

   Sammanfattning : Worldwide, biodiversity conservation is one of the key challenges for a sustainable future of nature and society. It is particularly important to preserve high quality habitats within otherwise intensively managed agricultural landscapes. LÄS MER

7. 5. Pollinator-mediated selection and the evolution of floral traits in orchids

   Författare :Judith Trunschke; Jon Ågren; Nina Sletvold; Allan G. Ellis; Uppsala universitet; []
   Nyckelord :Among-population variation; Ecotype; Field experiment; Floral evolution; Germination; Local adaptation; Orchidaceae; Platanthera bifolia; Phenotypic selection; Pollination; Reciprocal transplant; Trait manipulation; Biology with specialization in Ecological Botany; Biologi med inriktning mot ekologisk botanik;

   Sammanfattning : In this thesis, I combined manipulations of traits and pollination environment with analysis of phenotypic selection to examine causes of variation in strength and mode of selection on floral traits, and I conducted a reciprocal sowing experiment to test for local adaptation in germination success. I tested the following predictions (1) the opportunity for selection, and the strength of pollinator-mediated and net selection increase with increasing pollen limitation, (2) the effects of traits affecting pollinator attraction and traits affecting pollination efficiency are non-additive and this leads to pollinator-mediated correlational selection, (3) the effects of spur length on pollen removal, pollen receipt, and female fitness differ between populations with short-tongued and populations with long-tongued pollinators, and (4) local adaptation at the stage of germination contributes to the maintenance of ecotypes growing in grasslands and woodlands, respectively. LÄS MER