| 1. |
- Christiansen, Ditte M., 1990-, et al.
(författare)
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High-resolution data are necessary to understand the effects of climate on plant population dynamics of a forest herb
- 2024
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 105:1
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Tidskriftsartikel (refereegranskat)abstract
- Climate is assumed to strongly influence species distribution and abundance. Although the performance of many organisms is influenced by the climate in their immediate proximity, the climate data used to model their distributions often have a coarse spatial resolution. This is problematic because the local climate experienced by individuals might deviate substantially from the regional average. This problem is likely to be particularly important for sessile organisms like plants and in environments where small-scale variation in climate is large. To quantify the effect of local temperature on vital rates and population growth rates, we used temperature values measured at the local scale (in situ logger measures) and integral projection models with demographic data from 37 populations of the forest herb Lathyrus vernus across a wide latitudinal gradient in Sweden. To assess how the spatial resolution of temperature data influences assessments of climate effects, we compared effects from models using local data with models using regionally aggregated temperature data at several spatial resolutions (≥1 km). Using local temperature data, we found that spring frost reduced the asymptotic population growth rate in the first of two annual transitions and influenced survival in both transitions. Only one of the four regional estimates showed a similar negative effect of spring frost on population growth rate. Our results for a perennial forest herb show that analyses using regionally aggregated data often fail to identify the effects of climate on population dynamics. This emphasizes the importance of using organism-relevant estimates of climate when examining effects on individual performance and population dynamics, as well as when modeling species distributions. For sessile organisms that experience the environment over small spatial scales, this will require climate data at high spatial resolutions.
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| 2. |
- Dahlgren, Johan P., et al.
(författare)
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Nonlinear relationships between vital rates and state variables in demographic models
- 2011
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 92:5, s. 1181-1187
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Tidskriftsartikel (refereegranskat)abstract
- To accurately estimate population dynamics and viability, structured population models account for among-individual differences in demographic parameters that are related to individual state. In the widely used matrix models, such differences are incorporated in terms of discrete state categories, whereas integral projection models (IPMs) use continuous state variables to avoid artificial classes. In IPMs, and sometimes also in matrix models, parameterization is based on regressions that do not always model nonlinear relationships between demographic parameters and state variables. We stress the importance of testing for nonlinearity and propose using restricted cubic splines in order to allow for a wide variety of relationships in regressions and demographic models. For the plant Borderea pyrenaica, we found that vital rate relationships with size and age were nonlinear and that the parameterization method had large effects on predicted population growth rates, lambda (linear IPM, 0.95; nonlinear IPMs, 1.00; matrix model, 0.96). Our results suggest that restricted cubic spline models are more reliable than linear or polynomial models. Because even weak nonlinearity in relationships between vital rates and state variables can have large effects on model predictions, we suggest that restricted cubic regression splines should be considered for parameterizing models of population dynamics whenever linearity cannot be assumed.
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| 3. |
- Dahlgren, Johan P., et al.
(författare)
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The demography of climate-driven and density-regulated population dynamics in a perennial plant
- 2016
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 97:4, s. 899-907
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Tidskriftsartikel (refereegranskat)abstract
- Identifying the internal and external drivers of population dynamics is a key objective in ecology, currently accentuated by the need to forecast the effects of climate change on species distributions and abundances. The interplay between environmental and density effects is one particularly important aspect of such forecasts. We examined the simultaneous impact of climate and intraspecific density on vital rates of the dwarf shrub Fumana procumbens over 20 yr, using generalized additive mixed models. We then analyzed effects on population dynamics using integral projection models. The population projection models accurately captured observed fluctuations in population size. Our analyses suggested the population was intrinsically regulated but with annual fluctuations in response to variation in weather. Simulations showed that implicitly assuming variation in demographic rates to be driven solely by the environment can overestimate extinction risks if there is density dependence. We conclude that density regulation can dampen effects of climate change on Fumana population size, and discuss the need to quantify density dependence in predictions of population responses to environmental changes.
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| 4. |
- Edelfeldt, Stina, et al.
(författare)
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Demographic senescence and effects on population dynamics of a perennial plant
- 2019
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Ingår i: Ecology. - : WILEY. - 0012-9658 .- 1939-9170. ; 100:8
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Tidskriftsartikel (refereegranskat)abstract
- Demographic rates in plants are usually assumed to be more stage or size dependent than age dependent, and aging is therefore not considered in demographic models. However, little is known about the effect of age on demographic rates, as there still are few studies based on long-term individual-based plant population data that consider both individual age and size. In addition, little is known about how aging of individuals may affect population dynamics. We present analyses of demographic data for three populations of Fumana procumbens collected 1985-2013, on individuals with known year of germination. We modeled age- and size-dependence of the vital rates of survival, growth, fruiting probability, and fruit number using thin plate spline regressions, and constructed an age x size integral projection model (IPM) to project population-level effects of aging. We found strong correlations between age and vital rates in solely age-based vital rate models, where vital rates initially increased with age, after which they stabilized and, in some cases, eventually declined. In survival models with both age and size, the effects of age were statistically significant, whereas size effects were insignificant at two of the sites. For other vital rates, most of the effect of age could be explained by size alone. In addition, including the age effects on survival in the IPM led to lower population growth rates compared to predictions of a size-only IPM. These results illustrate that demographic senescence does occur in perennial plants, which has only been demonstrated clearly in a few recent detailed studies. Moreover, we show that population projections may be overly optimistic if they do not consider plant age. We conclude that the possibility of demographic senescence should be considered in demographic population models, such as those used in viability analyses of threatened species.
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| 5. |
- Ehrlén, Johan, et al.
(författare)
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Flowering schedule in a perennial plant; life-history trade-offs, seed predation, and total offspring fitness
- 2015
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 96:8, s. 2280-2288
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Tidskriftsartikel (refereegranskat)abstract
- Optimal timing of reproduction within a season may be influenced by several abiotic and biotic factors. These factors sometimes affect different components of fitness, making assessments of net selection difficult. We used estimates of offspring fitness to examine how pre-dispersal seed predation influences selection on flowering schedule in an herb with a bimodal flowering pattern, Actaea spicata. Within individuals, seeds from flowers on early terminal inflorescences had a higher germination rate and produced larger seedlings than seeds from flowers on late basal inflorescences. Reproductive value, estimated using demographic integral projection models and accounting for size-dependent differences in future performance, was two times higher for intact seeds from early flowers than for seeds from late flowers. Fruits from late flowers were, however, much more likely to escape seed predation than fruits from early flowers. Reproductive values of early and late flowers balanced at a predation intensity of 63%. Across 15 natural populations, the strength of selection for allocation to late flowers was positively correlated with mean seed predation intensity. Our results suggest that the optimal shape of the flowering schedule, in terms of the allocation between early and late flowers, is determined by the trade-off between offspring number and quality, and that variation in antagonistic interactions among populations influences the balancing of this trade-off. At the same time they illustrate that phenotypic selection analyses that fail to account for differences in offspring fitness might be misleading.
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| 6. |
- Fogelström, Elsa, et al.
(författare)
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Plant-herbivore synchrony and selection on plant flowering phenology
- 2017
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 98:3, s. 703-711
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Tidskriftsartikel (refereegranskat)abstract
- Temporal variation in natural selection has profound effects on the evolutionary trajectories of populations. One potential source of variation in selection is that differences in thermal reaction norms and temperature influence the relative phenology of interacting species. We manipulated the phenology of the butterfly herbivore Anthocharis cardamines relative to genetically identical populations of its host plant, Cardamine pratensis, and examined the effects on butterfly preferences and selection acting on the host plant. We found that butterflies preferred plants at an intermediate flowering stage, regardless of the timing of butterfly flight relative to flowering onset of the population. Consequently, the probability that plant genotypes differing in timing of flowering should experience a butterfly attack depended strongly on relative phenology. These results suggest that differences in spring temperature influence the direction of herbivore-mediated selection on flowering phenology, and that climatic conditions can influence natural selection also when phenotypic preferences remain constant.
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| 7. |
- Kolb, Annette, et al.
(författare)
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Population size affects vital rates but not population growth rate of a perennial plant
- 2010
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 91:11, s. 3210-3217
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Tidskriftsartikel (refereegranskat)abstract
- Negative effects of habitat fragmentation on individual performance have been widely documented, but relatively little is known about how simultaneous effects on multiple vital rates translate into effects on population viability in long-lived species. In this study, we examined relationships between population size, individual growth, survival and reproduction, and population growth rate in the perennial plant Phyteuma spicatum. Population size positively affected the growth of seedlings, the survival of juveniles, the proportion of adults flowering, and potential seed production. Analyses with integral projection models, however, showed no relationship between population size and population growth rate. This was due to the fact that herbivores and pathogens eliminated the relationship between population size and seed production, and that population growth rate was not sensitive to changes in the vital rates that varied with population size. We conclude that effects of population size on vital rates must not translate into effects on population growth rate, and that populations of long-lived organisms may partly be able to buffer negative effects of small population size on vital rates that have a relatively small influence on population growth rate. Our study illustrates that we need to be cautious when assessing the consequences of habitat fragmentation for population viability based on effects on only one or a few vital rates.
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