| 1. |
- Caruso, Alexandro, et al.
(författare)
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Colonization-extinction dynamics of epixylic lichens along a decay gradient in a dynamic landscape
- 2010
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 119, s. 1947-1953
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Tidskriftsartikel (refereegranskat)abstract
- Metapopulation models are often used for understanding and predicting species dynamics in fragmented landscapes. Several models have been proposed depending on e.g. the relative importance of patch dynamics on the metapopulation dynamics. Dead wood is a dynamic substrate patch, and species that are confined to such patches have experienced a high degree of habitat loss in managed forests. Little is, however, known about how the population dynamics of epixylic species are affected by the fast dynamics of their substrate patches. We quantified the effect of local patch conditions and metapopulation processes on colonizations and extinctions of epixylic lichen species in a managed boreal forest landscape. This was done by twice surveying seven lichen metapopulations on 293 stumps in 30 stands of ages covering the duration of the dynamic patches (stumps). We also investigated the relative importance of local stochastic extinctions from stumps that remained available, and deterministic extinctions due to stump surface disappearance. We found importance of a decay gradient, surrounding metapopulation size, and local population sizes, in driving the colonization-extinction dynamics of epixylic lichens. The species were sorted along the stump decay gradient. Increasing surrounding metapopulation size was associated with increased colonization rates, and increasing local population size decreased lichen extinction rates. Finally, both local stochastic extinctions and deterministic extinctions due to patch disappearance occur, confirming that the long-term persistence of epixylic lichens depends on colonization rates that compensate for stochastic population extinctions as well as deterministic extinctions.
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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. |
- Svensson, Måns, et al.
(författare)
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Combined observational and experimental data provide limited support for facilitation in lichens
- 2016
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 125, s. 278-283
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Tidskriftsartikel (refereegranskat)abstract
- It is increasingly recognized that facilitative interactions can shape communities. One of the mechanisms through which facilitation may operate is when one species facilitates the colonization of another through the exchange of shared symbionts. Lichens are symbiotic associations composed of a mycobiont (lichenised-fungus) and one or two photobionts (algae or cyanobacteria). Different lichen species may have overlapping specificity for photobionts, creating the possibility that facilitation drives lichen community assembly. To investigate whether facilitation occurs in lichens, we combined an observational study (a) with a manipulative field experiment (b). For (a), we quantified the effect of local patch conditions, facilitation and the size of the surrounding metapopulation on colonizations of an epixylic lichen species (Cladonia botrytes) in an area of managed boreal forest. This was done by twice surveying lichens on 293 stumps, located in stands of three age classes. For (b), we treated unoccupied surfaces of 56 cut stumps with algal mixtures of an Asterochloris photobiont and recorded C. botrytes colonizations over three years. In (a), colonization rates of C. botrytes increased with increasing abundance of other lichen species with specificity for Asterochloris photobionts, consistent with an effect of facilitation. However, in the field experiment (b), colonizations of the focal species did not provide support for facilitation. We conclude that our study provides limited support for facilitation in green-algal lichens, underscoring the importance of combining observational studies with experiments when studying species interactions.
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