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Selection on flowering time in plants is often mediated by multiple agents, including climatic conditions and the intensity of mutualistic and antagonistic interactions with animals. These selective agents can have both direct and indirect effects. For example, climate might not only influence phenotypic selection on flowering time directly by affecting plant physiology, but it can also alter selection indirectly by modifying the seasonal activity and relative timing of animals interacting with plants. We used 21 years of data to identify the drivers of selection on flowering time in the perennial herb Lathyrus vernus, and to examine if antagonistic plant-animal interactions mediate effects of climate on selection. We examined the fitness consequences of vertebrate grazing and pre-dispersal seed predation, and how these effects varied among years and among individuals within years. Although both antagonistic plant-animal interactions had important negative effects on plant fitness, only grazing intensity was consistently related to plant phenology, being higher in early-flowering individuals. Spring temperature influenced the intensity of both plant-animal interactions, as well as the covariance between seed predation and plant phenology. However, only differences in grazing intensity among years were associated with differences in selection on flowering time; the strength of selection for early flowering being stronger in years with lower mean intensity of grazing. Our results illustrate how climatic conditions can influence plant-animal interactions that are important selective agents for plant traits. A broader implication of our findings is that both ecological and evolutionary responses to climatic changes might be indirect, and largely mediated by species interactions.

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.

Identifying the environmental drivers of population dynamics is crucial to predict changes in species abundances and distributions under climate change. Populations of the same species might differ in their responses as a result of intraspecific variation. Yet the importance of such differences remains largely unexplored. We examined the responses of latitudinally distant populations of the forest moss Hylocomiastrum umbratum along microclimate gradients in Sweden. We transplanted moss mats from southern and northern populations to 30 sites with contrasting microclimates (i.e., replicated field common gardens) within a forest landscape, and recorded growth and survival of individual shoots over 3 yr. To evaluate the importance of intraspecific variation in responses to environmental factors, we assessed effects of the interactions between population origin and microclimate drivers on growth and survival. Effects on overall performance of transplanted populations were estimated using the product of survival and growth. We found differences between southern and northern populations in the response to summer temperature and snowmelt date in one of three yearly transitions. In this year, southern populations performed better in warm, southern‐like conditions than in cold, northern‐like conditions; and the reverse pattern was true for northern populations. Survival of all populations decreased with evaporation, consistent with the high hydric demands and poikilohydric nature of mosses. Our results are consistent with population adaptation to local climate, and suggest that intraspecific variation among populations can have important effects on the response of species to microclimate drivers. These findings highlight the need to account for differential responses in predictions of species abundance and distribution under climate change.

Variation in selection among populations and years has important implications for evolutionary trajectories of populations. Yet, the agents of selection causing this variation have rarely been identified. Selection on the time of reproduction within a season in plants might differ both among populations and among years, and selection can be mediated by both mutualists and antagonists. We investigated if differences in the direction of phenotypic selection on flowering phenology among 20 populations of Gentiana pneumonanthe during 2 yr were related to the presence of the butterfly seed predator Phengaris alcon, and if butterfly incidence was associated with the abundance of the butterfly's second host, Myrmica ants. In plant populations without the butterfly, phenotypic selection favored earlier flowering. In populations where the butterfly was present, caterpillars preferentially attacked early-flowering individuals, shifting the direction of selection to favoring later flowering. Butterfly incidence in plant populations increased with ant abundance. Our results demonstrate that antagonistic interactions can shift the direction of selection on flowering phenology, and suggest that such shifts might be associated with differences in the community context.

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.

Selection mediated by one biotic agent will often be modified by the presence of other biotic interactions, and the importance of such indirect effects might change over time. We conducted an 11-yr field experiment to test the prediction that large grazers affect selection on floral display of the dimorphic herb Primula farinosa not only directly through differential grazing damage, but also indirectly by affecting vegetation height and thereby selection mediated by pollinators and seed predators. Exclusion of large grazers increased vegetation height and the strength of pollinator-mediated selection for tall inflorescences and seed-predator-mediated selection for short inflorescences. The direct effect of grazers on selection resulting from differential grazing damage to the two scape morphs showed no temporal trend. By contrast, the increase in vegetation height in exclosures over time was associated with an increase in selection mediated by pollinators and seed predators. In the early years of the experiment, the indirect effects of grazers on selection mediated by pollinators and seed predators were weak, whereas at the end of the experiment, the indirect effects were of similar magnitude as the direct effect due to differential grazing damage. The results demonstrate that the indirect effects of a selective agent can be as strong as its direct effects, and that the relative importance of direct vs. indirect effects on selection can change over time. A full understanding of the ecological processes governing variation in selection thus requires that both direct and indirect effects of biotic interactions are assessed.

Variation in mutualistic and antagonistic interactions are important sources of variation in population dynamics and natural selection. Environmental heterogeneity can influence the outcome of interactions by affecting the intensity of interactions, but also by affecting the demography of the populations involved. However, little is known about the relative importance of environmental effects on interaction intensities and demographic sensitivity for variation in population growth rates. We investigated how soil depth, soil moisture, soil nutrient composition, and vegetation height influenced the intensity of seed predation as well as host plant demography and sensitivity to seed predation in the perennial herb Primula farinosa. Intensity of seed predation ranged from 0% to 80% of seeds damaged among the 24 study populations and was related to soil moisture in two of four years. The effect of seed predation on plant population growth rate (lambda) ranged from negligible to a reduction in lambda by 0.70. Sensitivity of population growth rate to predation explained as much of the variation in the reductions in population growth rate due to seed predation as did predation intensity. Plant population growth rate in the absence of seed predation and sensitivity to predation were negatively related to soil depth and soil moisture. Both intensity of predation and sensitivity to predation were positively correlated with potential population growth rate and, as a result, there was no significant relationship between predation intensity and realized population growth rate. We conclude that in our study system environmental context influences the effects of seed predation on plant fitness and population dynamics in two important ways: through variation in interaction intensity and through sensitivity to the effects of this interaction. Moreover, our results show that a given abiotic factor can influence population growth rate in different directions through effects on potential growth rate, intensity of biotic interactions, and the sensitivity of population growth rate to interactions.

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.

7 páginas, 3 figuras, 1 tabla.-- El documento en word es la versión de autor., 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, λ (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., This study was financially supported by the Strategic Research Programme EkoKlim at Stockholm University (J.P.D.), the National Parks project (ref 018/2008) (M.B.G), and the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) (J.E.).

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.

Theory predicts that, with conflicting selection pressures mediated by mutualists and antagonists, alternative reproductive strategies can be maintained by negative frequency-dependent selection if it results in rare-morph advantage. We combined field experiments and surveys of natural populations to determine whether selection on floral display is frequency dependent in the self-incompatible herb Primula farinosa, which is polymorphic for inflorescence height and occurs in a short-scaped and a long-scaped morph. Among short-scaped plants, both pollination success, quantified as initiation of fruits and seeds, and seed predation were positively correlated with the relative frequency of the long-scaped morph. The relative strength of these effects and the direction of the resulting frequency-dependent selection on scape morph varied among years and populations. The results suggest that both mutualists and antagonists may mediate frequency-dependent selection and that frequency dependence may vary from positive to negative with rare-morph advantage, depending on the relative strength of these interactions.

Population context should influence pollination success and selection on floral display in animal-pollinated plants because attraction of pollinators depends not only on the characteristics of individual plants, but also on the attractiveness of co-occurring conspecifics. The insect-pollinated herb Primula farinosa is polymorphic for inflorescence height. Natural populations may include both long-scaped plants, which present their flowers well above the soil surface, and short-scaped plants, with their flowers positioned close to the ground. We experimentally tested whether seed production in short-scaped P. farinosa varied with local morph frequency and surrounding vegetation height. In tall vegetation, short-scaped plants in polymorphic populations produced more fruit and tended to produce more seeds than short-scaped plants did in monomorphic populations. In low vegetation, population composition did not significantly affect fruit and seed output of short-scaped plants. The results suggest that long-scaped plants facilitate short-scaped plants in terms of pollinator attraction and that the facilitation effect is contingent on the height of the surrounding vegetation. The documented facilitation should contribute to the maintenance of the scape length polymorphism in ungrazed areas where litter accumulates and vegetation grows tall.

Metapopulation dynamics have received much attention in population bi- ology and conservation. Most studies have dealt with species whose population turnover rate is much higher than the rate of patch turnover. Models of the dynamics in such systems have assumed a static patch landscape. The dynamics of many species, however, are likely to be significantly affected by the dynamics of their patches. We tested the relative im- portance of local conditions, connectivity, and dynamics of host tree patches on the meta- population dynamics of a red-listed epiphytic moss, Neckera pennata, in Sweden. Repeated surveys of the species and its host trees were conducted at three sites over a period of six years. There was a positive effect of connectivity, and colonizations mainly occurred in the vicinity of occupied trees. Colonizations were also less likely on strongly leaning trees. Local extinctions sometimes occurred from small trees with low local abundances but were most often caused by treefall. Simulations of the future (100 years) dynamics of the system showed that the metapopulation size will be overestimated unless the increased local ex- tinction rate imposed by the dynamics of the trees is accounted for. The simulations also suggested that local extinctions from standing trees may be disregarded in dynamic models for this species. This implies that the dynamics of N. pennata can be characterized as a patch-tracking metapopulation, where local extinctions are caused by patch destruction.

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.

Historical events have been used to explain a wide range of phenomena including geographical distributions of species, community diversity, and population struc- ture. At the level of individuals, historical effects in which past conditions influence future performance are particularly likely to occur in long-lived organisms that store resources between seasons and that form organs months or years before their elaboration. Such carry- over mechanisms have been documented in several perennial plant species, but the impli- cations for population processes are poorly known. In this study, I examine how the history of individuals influences their future performance, population dynamics, and life cycle, structure in the long-lived herb Lathyrus vernus. Overall effects of plant history on pop- ulation dynamics, in terms of growth rate, reproductive values, stable stage distribution, and elasticities, are examined by comparing an ordinary first-order matrix model with a second-order matrix model. In the latter, not only the present state of individuals, but also their past state is allowed to influence future fate. The results demonstrate that the history of individuals is sometimes important in models of population dynamics. Plant size change over a one-year period was negatively correlated among time intervals. Addition of the previous year's stage in population models shifted the growth rate from positive (X = 1.010) to negative (X = 0.986) and increased the proportion of small established individuals in the stable stage distribution. If historical effects are due to a capacity to buffer environmental variation and regain size or state, as in L. vernus, then recruitment contributes less and stasis more to population growth than suggested 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 be included in any interpretation of the life-cycle structure.

Elasticity is a perturbation measure in matrix projection models that quantifies the proportional change in population growth rate as a function of a proportional change in a demographic transition (growth, survival, reproduction, etc.). Elasticities thus indicate 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 the relative contribution of a demographic parameter to population growth rate. Loop analysis reveals the underlying pathway structure of the life cycle graph. The different kinds of results of the two analyses in studies of life histories are emphasized. Because elasticities quantify the relative importance of life cycle transitions to population growth rate, it is generally inferred that management should focus on the transitions with the largest elasticities. Such predictions based on elasticities seem robust, but we do identify three situations where problems may arise. The mathematical properties and biological constraints that underlie these pitfalls are explained. Examples illustrate the additional information that needs 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.

Demographic transition matrices are among the most commonly applied population models for both basic and applied ecological research. The relatively simple framework of these models and simple, easily interpretable summary statistics they produce have prompted the wide use of these models across an exceptionally broad range of taxa. Here, we provide annual transition matrices and observed stage structures/population sizes for 20 perennial plant species which have been the focal species for long-term demographic monitoring. These data were assembled as part of the “Testing Matrix Models” working group through the National Center for Ecological Analysis and Synthesis (NCEAS). The data represent 82 populations with >460 total population-years of observations. It is our hope that making these data available will help promote and improve our ability to monitor and understand plant population dynamics. The complete data sets corresponding to abstracts published in the Data Papers section of the journal are publ...