| 1. |
- Osorio-Zuniga, Felipe, et al.
(författare)
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Evidence of mutualistic synzoochory between cryptogams and hummingbirds
- 2014
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 123:5, s. 553-558
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Tidskriftsartikel (refereegranskat)abstract
- Endozoochory is usually involved in seed dispersal mutualisms, whereas ectozoochory is non-rewarding, and therefore neutral (or even negative) for the animal vector. Synzoochory is an intermediate dispersal type between endo and ectozoochory in which propagules are deliberately transported (usually in the mouth) but with no ingestion or gut passage involved. We present empirical evidence of synzoochoric mutualism between the hummingbird Sephanoides sephaniodes and cryptogams (one fern and seven moss species). Two species (Lophosoria quadripinnata and Ancistrodes genuflexa) constituted the bulk of nest biomass, and another six moss species were present in lesser quantity. The hummingbird was selective when collecting nest material so that the nests contained a higher density of reproductive structures (that could be dispersed further) than natural patches of the cryptogam species. Even after one year, the nests maintained half of the original reproductive structures (sporangia, sporophytes) and biomass, constituting an important dispersal source. These results show a new type of mutualism in which mosses could be dispersed throughout longer distances (several km) by hummingbirds and to higher positions (particularly for ground-living species, promoting dispersal potential). The hummingbird benefits from collecting cryptogam material for nest building, and cryptogams benefit from the concentration and relocation of diaspore sources into more effective recruiting sites. Similar mutualistic relationships could be a general phenomenon, of importance in many ecosystems.
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| 2. |
- Snäll, Tord, et al.
(författare)
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Spatial occurrence and colonisations in patch-tracking metapopulations : local conditions versus dispersal
- 2003
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 103:3, s. 566-578
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Tidskriftsartikel (refereegranskat)abstract
- We studied the relative importance of local variables and dispersal for the occurrence and colonisation of the epiphytic bryophytes Orthotricum speciosum (spore dispersed), and O. obtusifolium (spore and asexual gemmae) on aspen trees ('patches') in two forest landscapes (one old-growth and one fragmented) using multiple logistic regression. The relative importance of dispersal was quantified as the reduction of residual deviance for a connectivity variable. In modelling dispersal, we assumed that trees with low local abundance were recent colonisations, and that trees with high local abundance were diaspore sources for colonisation. The occurrence of O. speciosum in the fragmented landscape was most affected by shading, but also by connectivity, aspen diameter and vitality. In the old-growth landscape, connectivity was the single most important variable for recent colonisations, but its effect was lower than the sum of the effects of all local environmental variables. The occurrence of O. obtusifolium in the fragmented landscape was related to similar variables but the relative importance of these variables was different, and connectivity did not affect the probability of a recent colonisation in this species. We describe the epiphyte-tree system in the patch-tracking metapopulation model. In this model colonisations are distance dependent, but in contrast to the classical metapopulation model local extinctions are caused by deterministic patch destruction - once the epiphyte has colonised the tree it remains until the tree dies.
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| 3. |
- Frost, Ingela, et al.
(författare)
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Effects of competition, grazing and cotyledon nutrient supply on growth of Quercus robur seedlings
- 1997
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Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 79:1, s. 53-58
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Tidskriftsartikel (refereegranskat)abstract
- In this greenhouse experiment we examined how competition and herbivory affects the growth of Quercus robur seedlings and if the cotyledon nutrient reserve is of importance for survival and growth during unfavourable conditions. We planted oak seedlings with or without a strong competitor (grass turf) and subjected them to factorial grazing and cotyledon removal, in a split-plot design. After one growing season (20 weeks) we found large negative main effects from competition, grazing and cotyledon removal on all biomass components of the seedling. Seedling mortality was also significantly increased by competition. We observed an additional effect of cotyledon removal if the seedlings were also grazed or were growing in competition with grass. This gives some support to the hypothesis that cotyledon nutrient reserves are used under unfavourable conditions, but the effect was often relatively small and not detectable in the growth of all plant parts.
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| 4. |
- Granath, Gustaf, et al.
(författare)
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Tradeoffs and scaling of functional traits in Sphagnum as drivers of carbon cycling in peatlands
- 2014
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 123:7, s. 817-828
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Tidskriftsartikel (refereegranskat)abstract
- Growth and decomposition of Sphagnum controls turnover of a large global store of soil organic carbon. We investigated variation in morphological and physiological traits of Sphagnum shoots, and related this variation to canopy variables relevant to peatland carbon cycling. We sampled Sphagnum along a bog plateau-swamp forest gradient and measured a suite of shoot traits and canopy variables. Major axes of variation were identified using principal component analysis and correlated with canopy variables such as growth, biomass and decomposition. We also examined scaling of shoot traits with one another and with canopy variables. Two distinct tradeoffs in shoot traits emerged. From dry to wet habitats, individual metabolic rates and capitulum size increased while numerical density decreased, leading to faster growth and elongation on an individual basis. From treed to open habitats, photosynthetic efficiency decreased and photosynthetic biomass increased, driving faster growth on an area basis and slower litter mass loss. The tradeoffs identified have important implications for peatlands undergoing climate-related changes in water and light availability. Sphagnum trait comparisons, combined with scaling analyses, offer a promising approach to understanding and predicting the effects of environmental change on peatland carbon cycling.
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