| 1. |
- de Kroon, Hans, et al.
(författare)
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Elasticities : a review of methods and model limitations
- 2000
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81:3, s. 607-618
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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.
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| 2. |
- Ehrlén, Johan, et al.
(författare)
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Dispersal limitation and patch occupancy in forest herbs
- 2000
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81, s. 1667-1674
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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.
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| 3. |
- Ehrlén, Johan, et al.
(författare)
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Pollen limitation, seed predation and scape length in Primula farinosa
- 2002
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 97:1, s. 45-51
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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.
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| 4. |
- Ehrlén, Johan
(författare)
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The dynamics of plant populations : does the history of individuals matter?
- 2000
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81:6, s. 1675-1684
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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.
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| 5. |
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| 6. |
- Snäll, Tord, 1969-
(författare)
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Distribution Patterns and Metapopulation Dynamics of Epiphytic Mosses and Lichens
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis examines the relative importance of local conditions, dispersal and dynamics of the trees on epiphyte distribution patterns and colonization-extinction dynamics. Study species are the mosses Orthotrichum speciosum and O. obtusifolium, and the red-listed Neckera pennata. The thesis also includes an attempt to parameterize a model for a lichen metapopulation (Lobaria pulmonaria) in a dynamic landscape, based on only presence/absence data of the epiphyte and its host trees. The results show that epiphyte colonization of trees is affected by both local conditions, and by connectivity to occupied trees. The positive effect of connectivity, implying a restricted dispersal range, was established by both demographic and genetic studies. The important local conditions were tree diameter and vitality, and shade. Local extinctions from trees occurred among small trees with low local epiphyte abundance, but more often, were the results of tree fall.The observed importance of connectivity on epiphyte colonization agrees with the assumptions of the classic metapopulation model. However, the classic metapopulation model assumes that the landscape is static, and that local extinctions occur for stochastic reasons. The dynamics of epiphytes are different. A new conceptual model is therefore suggested, the patch-tracking metapopulation model. It differs from the classic metapopulation model in that it includes dynamics of the patches, and in that local extinctions only occur as patches are destroyed.Simulations of the dynamics of N. pennata showed that its future metapopulation size will be overestimated unless the dynamics of the trees are accounted for. The simulation results further suggest that the dynamics of N. pennata can be characterised by the patch-tracking metapopulation model. The attempt to parameterize the L. pulmonaria metapopulation model showed that more information are required for rigorous parameterization, preferably of the past historic fire regime.
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| 7. |
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