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  • Ehrlén, Johan, et al. (författare)
  • Climate drives among-year variation in natural selection on flowering time
  • 2020
  • Ingår i: Ecology Letters. - 1461-023X .- 1461-0248. ; 23:4, s. 653-662
  • Tidskriftsartikel (refereegranskat)abstract
    • To predict long-term responses to climate change, we need to understand how changes in temperature and precipitation elicit both immediate phenotypic responses and changes in natural selection. We used 22 years of data for the perennial herb Lathyrus vernus to examine how climate influences flowering phenology and phenotypic selection on phenology. Plants flowered earlier in springs with higher temperatures and higher precipitation. Early flowering was associated with a higher fitness in nearly all years, but selection for early flowering was significantly stronger in springs with higher temperatures and lower precipitation. Climate influenced selection through trait distributions, mean fitness and trait-fitness relationships, the latter accounting for most of the among-year variation in selection. Our results show that climate both induces phenotypic responses and alters natural selection, and that the change in the optimal phenotype might be either weaker, as for spring temperature, or stronger, as for precipitation, than the optimal response.
  • 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.
  • 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.
  • Ehrlén, Johan, et al. (författare)
  • Land use and population growth of Primula veris : an experimental demographic approach
  • 2005
  • Ingår i: Journal of Applied Ecology. - 0021-8901 .- 1365-2664. ; 42:2, s. 317-326
  • Tidskriftsartikel (refereegranskat)abstract
    • 1. Changes in land use are the primary cause of decline for many plant species. Efficient management actions for such species must be based on knowledge of the key phases of the plant life cycles that respond most to changes in environmental factors. 2. To assess how grazing influences population viability of the perennial rosette herb Primula veris, we applied four experimental treatments to abandoned grasslands and recorded the demographic response in permanent plots and seed sowing experiments over 3 years. 3. Treatments had strong effects on population viability. Transition matrix models showed that cutting the surrounding vegetation had no effect on population growth rate (lambda). However, when this was combined with litter removal lambda increased to 1.46, compared with 1.11 in controls. With disturbance and complete removal of the surrounding vegetation the effect was even stronger, and lambda increased to 1.60. 4. Increases in lambda were primarily a result of increased growth of the smallest rosettes, and increased seedling production. In contrast, the performance of larger P. veris individuals was not affected by experimental treatments. 5. The higher the elasticity of a particular life cycle transition, the less the change in the transition rate caused by treatments. This suggests that plants are able partly to buffer the effects of environmental variation by minimizing changes in the life cycle transitions that are most important to population growth rate. 6. Synthesis and applications. Experimental demographic approaches provide an important tool for assessing how grazing and other types of management influence species viability, and help to unravel the mechanisms underlying such relationships. With such information it is possible to predict the effects of novel types of management and land-use scenarios on population viability. For P. veris, we identified seedling establishment as a key phase in the life cycle, and litter accumulation as a key environmental factor, suggesting that these should be prime targets for management. One practice that is likely to favour as well as seedling establishment preventing litter accumulation is late summer grazing.
  • 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.
  • Ehrlen, Johan, et al. (författare)
  • Predicting changes in the distribution and abundance of species under environmental change
  • 2015
  • Ingår i: Ecology Letters. - 1461-023X .- 1461-0248. ; 18:3, s. 303-314
  • Forskningsöversikt (refereegranskat)abstract
    • Environmental changes are expected to alter both the distribution and the abundance of organisms. A disproportionate amount of past work has focused on distribution only, either documenting historical range shifts or predicting future occurrence patterns. However, simultaneous predictions of abundance and distribution across landscapes would be far more useful. To critically assess which approaches represent advances towards the goal of joint predictions of abundance and distribution, we review recent work on changing distributions and on effects of environmental drivers on single populations. Several methods have been used to predict changing distributions. Some of these can be easily modified to also predict abundance, but others cannot. In parallel, demographers have developed a much better understanding of how changing abiotic and biotic drivers will influence growth rate and abundance in single populations. However, this demographic work has rarely taken a landscape perspective and has largely ignored the effects of intraspecific density. We advocate a synthetic approach in which population models accounting for both density dependence and effects of environmental drivers are used to make integrated predictions of equilibrium abundance and distribution across entire landscapes. Such predictions would constitute an important step forward in assessing the ecological consequences of environmental changes.
  • Ehrlén, Johan (författare)
  • Selection on flowering time in a life-cycle context
  • 2015
  • Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 124:1, s. 92-101
  • Tidskriftsartikel (refereegranskat)abstract
    • The main way in which plants can exert control over their local environment is by the timing of different events within their life cycles. Regarding timing of flowering as an integrated part of both the annual cycle and of the whole life cycle, rather than as an isolated event, has important implications for how we assess selection on timing of reproduction and interpret existing phenological patterns in perennial plants. I argue that: 1) we have little unequivocal evidence of pollinator-mediated selection on flowering time, but perhaps more evidence of antagonist-mediated selection; 2) much of selection on flowering time might occur before flowers have developed and after reproduction; 3) vital rates of non-flowering individuals can influence the strength and direction of selection on flowering time, and 4) differences in the direction of selection on flowering date between years might well correspond to consistent selection on the mechanisms determining flowering time. Overall, a life cycle perspective on timing of flowering is likely to facilitate the identification of selective agents and the understanding of the complex mechanisms underlying spatial and temporal variation in selection as well as to enable more accurate predictions of responses to environmental change.
  • 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.
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