Interactive life‐history traits predict sensitivity of plants and animals to temporal autocorrelation

Temporal autocorrelation in demographic processes is an important aspect of population dynamics, but a comprehensive examination of its effects on different life‐history strategies is lacking. We use matrix population models from 454 plant and animal populations to simulate stochastic population growth rates (log λ_s) under different temporal autocorrelations in demographic rates , using simulated and observed covariation among rates. We then test for differences in sensitivities, or changes of log λ_s to changes in autocorrelation among two major axes of life‐history strategies, obtained from phylogenetically informed principal component analysis: the fast‐slow and reproductive‐strategy continua. Fast life histories exhibit highest sensitivities to simulated autocorrelation in demographic rates across reproductive strategies. Slow life histories are less sensitive to temporal autocorrelation, but their sensitivities increase among highly iteroparous species. We provide cross‐taxonomic evidence that changes in the autocorrelation of environmental variation may affect a wide range of species, depending on complex interactions of life‐history strategies.     

Variability of important vital rates challenges the demographic buffering hypothesis

Selection is assumed to eliminate life-histories showing high variability in vital rates that have the greatest influence on population performance. Therefore, an inverse variability-importance relationship of vital rates is believed to be a universal pattern for diverse life-histories. We tested for such a relationship using multi-year demographic data on a large number of populations of two perennial plant species. Applying different approaches, we first examined the overall variability-importance relationship for the average main vital rates (survival, growth, retrogression, fecundity) per species, and then separately for each population. We found an overall inverse relationship between temporal variation and importance of the average main vital rates for both study species, but these negative species-level correlations were mainly caused by different scales of the examined vital rates. When variability-importance relationships were examined across individual demographic transitions within populations, the abundance of positive and negative correlations depended largely on the method used, and positive correlations were more common after correcting vital rates for sampling variation than when using uncorrected vital rates. Our results cast doubt on the generality of the demographic buffering hypothesis, suggesting that the inverse variability-importance relationship may not be a universal pattern when vital rates are examined for multiple populations of the same plant species.     

Demographic response of plant populations to habitat fragmentation and temporal environmental variability

Many plant species currently exist in fragmented populations of different sizes, while they also experience unpredictable climatic fluctuation over time. However, we still understand little about how plant demography responds to such spatial and temporal environmental variability. We studied population dynamics of an understory perennial herb Trillium camschatcense in the Tokachi plain of Hokkaido, Japan, where a significant effect of forest fragmentation on seedling recruitment was previously reported. Four populations across a range of fragment sizes were studied for 6 years, and the data were analyzed using matrix population models. Per capita fecundity (the number of recruits per plant) varied greatly among populations, but the variation in population growth rates (λ) was mainly driven by the variation in stasis and growth rates, suggesting that the general trend of reduced fecundity in fragmented populations may not be readily translated into subsequent dynamics. Temporal variation in λ among years was more than 2 times larger than spatial variation among populations, and this result was likely attributable to the contrasting response of correlation structures among demographic rates. The among-population variation in λ was dampened by negative covariation between matrix elements possibly due to density-dependent regulation as well as an inherent constraint that some elements are not independent, whereas positive covariation between matrix elements resulted in large temporal variation in λ. Our results show that population dynamics responded differently to habitat fragmentation and temporal variability of the environment, emphasizing the need to discriminate these spatial and temporal variations in demographic models. Although no populations were projected to be declining in stochastic simulations, correlation between current habitat size and plant density implies historical λ is positively related to habitat size.     

Demographic compensation among populations: what is it,how does it arise and what are its implications?

Most species are exposed to significant environmental gradients across their ranges, but vital rates (survival, growth, reproduction and recruitment) need not respond in the same direction to those gradients. Opposing vital rate trends across environments, a phenomenon that has been loosely called ‘demographic compensation’, may allow species to occupy larger geographical ranges and alter their responses to climate change. Yet the term has never been precisely defined, nor has its existence or strength been assessed for multiple species. Here, we provide a rigorous definition, and use it to develop a strong test for demographic compensation. By applying the test to data from 26 published, multi‐population demographic studies of plants, we show that demographic compensation commonly occurs. We also investigate the mechanisms by which this phenomenon arises by assessing which demographic processes and life stages are most often involved. In addition, we quantify the effect of demographic compensation on variation in population growth rates across environmental gradients, a potentially important determinant of the size of a species’ geographical range. Finally, we discuss the implications of demographic compensation for the responses of single populations and species’ ranges to temporal environmental variation and to ongoing environmental trends, e.g. due to climate change.     

Demographic variation in the U.K. serotine bat: filling gaps in knowledge for management

Species of conservation concern, or those in conflict with man, are most efficiently managed with an understanding of their population dynamics. European bats exemplify the need for successful and cost‐effective management for both reasons, often simultaneously. Across Europe, bats are protected, and the concept of Favourable Conservation Status (FCS) is used as a key tool for the assessment and licensing of disruptive actions to populations. However, for efficient decision‐making, this assessment requires knowledge on the demographic rates and long‐term dynamics of populations. We used capture–mark–recapture to describe demographic rates for the Serotine bat (Eptesicus serotinus) at two sites in England and investigate the transition rates between three stages: juveniles, immatures, and breeders. We then use these rates in an individual‐based population dynamics model to investigate the expected trajectories for both populations. Our results demonstrate for the first time the presence and scale of temporal variation in this species' demography. We describe the lengthy prereproductive period (3.5 years) that female Serotines experience. Finally, we show how site‐specific variation in demographic rates can produce divergent population trajectories. Effective management of European bat populations can be achieved through the understanding of life histories, and local demographic rates and population dynamics, in order to anticipate the presence of source and sink sites in the landscape. Using the Serotine bat in England, we show that these can be obtained from rigorous and systematic studies of long‐term demographic datasets.     

Stochastic LTRE analysis of the effects of herbivory on the population dynamics of a perennial grassland herb

Herbivores can have strong deleterious effects on vital rates (growth, reproduction, and survival) and thus negatively impact the population dynamics of plant species. In practice, however, these effects might be strongly correlated, for example as a result of tradeoffs between vital rates. To get better insights into the effects of herbivory on the population dynamics of the long‐lived grassland plant Primula veris population projection matrices were constructed from demographic data collected between 1999 and 2008 (nine annual transitions). Data were collected in two large grassland populations, each of which was subjected to two treatments (grazing by cattle versus a mowing treatment), yielding a total of 36 matrices. We applied a lower‐level vital rate life table response experiment (LTRE) using the small noise approximation (SNA) of the stochastic population growth rate to disentangle the contributions of changes in mean vital rates, variability in vital rates, correlations between vital rates and vital rate elasticities to the difference in the stochastic growth rate. Stochastic growth rates (a= log λ_S) were significantly lower in grazed than in mown plots (a= 0.0185 and 0.1019, respectively). SNA LTRE analysis showed that contributions of mean vital rates by far made the largest contribution to the observed difference in a between grazed and control plots. In particular, changes in sexual reproduction rates made the largest contributions to lower the stochastic growth rate in grazed plots: both adult flowering probabilities and flower and seed production were importantly lower in grazed populations, but these negative effects were largely buffered by increased establishment and seedling survival rates. Among the stochastic terms of the SNA decomposition, contributions of covariance and correlations between vital rates had the largest impact, whereas contributions of elasticities were smaller. The strongest correlation driver was the association between adult survival and seedling establishment, suggesting that environmental conditions favouring adult survival also are beneficial for seedling establishment. Overall, our results show that herbivory had a strong negative effect on the long‐term population growth rate of P. veris that was primarily mediated by differences in fecundity (flower and seed production) and germination.     

Incorporating the temporal autocorrelation of demographic rates into structured population models

Population dynamics are typically temporally autocorrelated: population sizes are positively or negatively correlated with past population sizes. Previous studies have found that positive temporal autocorrelation increases the risk of extinction due to ‘inertia’ that prolongs downward fluctuations in population size. However, temporal autocorrelation has not yet been analyzed at the level of life cycle transitions. We developed an R package, colorednoise, which creates stochastic matrix population projections with distinct temporal autocorrelation values for each matrix element. We used it to analyze long-term demographic data on 25 populations from the COMADRE and COMPADRE databases and simulate their stochastic dynamics. We found a broad range of temporal autocorrelation across species, populations and life cycle stages. The number of stage-classes in the matrix strongly affected the temporal autocorrelation of the growth rate. In the plant populations, reproduction transitions had more negative temporal autocorrelation than survival transitions, and matrices dominated by positive temporal autocorrelation had higher extinction risk, while in animal populations transition type was not associated with noise color. Our results indicate that temporal autocorrelation varies across life cycle transitions, even among populations of the same species. We present the colorednoise package for researchers to analyze the temporal autocorrelation of structured demographic rates.     

Demographic strategies of plant invaders in temporally varying environments

Plant populations may have evolved different demographic strategies to cope with temporal environmental variation. According to the demographic buffering hypothesis, vital rates that are most critical to population persistence are buffered against environmental variation and vary little over time, whereas the demographic lability hypothesis suggests that populations may track and benefit from environmental variation. While the hypotheses of demographic strategies have been widely tested in plant and animal species, they have not been explicitly examined for invasive plants, or in relation to different modelling methods (deterministic vs. stochastic). Here, we tested the demographic buffering and lability hypotheses for 23 populations of eight invasive plant species in relation to life form (woody vs. herbaceous species) and population growth rate using deterministic and stochastic modelling methods, and absolute and relative scales. We found that conclusions of demographic strategies depended on scale, with an absolute scale resulting in stronger negative correlations between the variability and importance of vital rates (i.e., buffering) than a relative scale. Conclusions of demographic strategies were also affected by life form that interacted with method. The populations of woody invaders exhibited buffering regardless of the method used, while for the populations of herbaceous species, deterministic calculations suggested buffering and stochastic calculations suggested lability. Overall, our findings emphasise the role of life form and methodological issues that need to be considered when exploring demographic strategies in fluctuating environments.     

Accounting for uncertainty in dormant life stages in stochastic demographic models

Dormant life stages are often critical for population viability in stochastic environments, but accurate field data characterizing them are difficult to collect. Such limitations may translate into uncertainties in demographic parameters describing these stages, which then may propagate errors in the examination of population‐level responses to environmental variation. Expanding on current methods, we 1) apply data‐driven approaches to estimate parameter uncertainty in vital rates of dormant life stages and 2) test whether such estimates provide more robust inferences about population dynamics. We built integral projection models (IPMs) for a fire‐adapted, carnivorous plant species using a Bayesian framework to estimate uncertainty in parameters of three vital rates of dormant seeds – seed‐bank ingression, stasis and egression. We used stochastic population projections and elasticity analyses to quantify the relative sensitivity of the stochastic population growth rate (log λs) to changes in these vital rates at different fire return intervals. We then ran stochastic projections of log λs for 1000 posterior samples of the three seed‐bank vital rates and assessed how strongly their parameter uncertainty propagated into uncertainty in estimates of log λs and the probability of quasi‐extinction, P_q(t). Elasticity analyses indicated that changes in seed‐bank stasis and egression had large effects on log λs across fire return intervals. In turn, uncertainty in the estimates of these two vital rates explained > 50% of the variation in log λs estimates at several fire‐return intervals. Inferences about population viability became less certain as the time between fires widened, with estimates of P_q(t) potentially > 20% higher when considering parameter uncertainty. Our results suggest that, for species with dormant stages, where data is often limited, failing to account for parameter uncertainty in population models may result in incorrect interpretations of population viability.     

Recruitment rates exhibit high elasticity and high temporal variation in populations of a short-lived perennial herb

Empirical studies for different life histories have shown an inverse relationship between elasticity (i.e. the proportional contribution to population growth rate) and temporal variation in vital rates. It is accepted that this relationship indicates the effect of selective pressures in reducing variation in those life‐history traits with a major impact on fitness. In this paper, we sought to determine whether changes in environmental conditions affect the relationship between elasticity of vital rates and their temporal variation, and whether vital rates with simultaneously large elasticity and temporal variation might represent a characteristic life‐history strategy. We used demographic data on 13 populations of the short‐lived Hypericum cumulicola over 5–6 years, in three time‐since‐fire classes. For each population of each time‐since‐fire, we computed the mean matrix over years and its respective elasticity matrix, and the coefficients of variation in matrix entries over study years as an estimate of temporal variability. We found that mean elasticity negatively significantly correlated with temporal variation in vital rates in populations (overall eight out of 13) included in each time‐since‐fire. However, seedling recruitment exhibited both high elasticity and high temporal variation in almost all study populations. These results indicated that (1) the general relationship between elasticity and temporal variation in vital rates was not modified by environmental changes due to time‐since‐fire, and (2) high elasticity and high temporal variation in seedling recruitment in H. cumulicola is a particular trait of the species' life history. After seed survival in the soil seed bank, seedling recruitment represents the most important life‐history trait influencing H. cumulicola population growth rate (and fitness). The high temporal variability in seedling recruitment suggests that this trait is determined by environmental cues, leading to an increase in population size and subsequent replenishment of the seed bank in favorable years.     

Spatio‐temporal variation in European starling reproductive success at multiple small spatial scales

Understanding population dynamics requires spatio‐temporal variation in demography to be measured across appropriate spatial and temporal scales. However, the most appropriate spatial scale(s) may not be obvious, few datasets cover sufficient time periods, and key demographic rates are often incompletely measured. Consequently, it is often assumed that demography will be spatially homogeneous within populations that lack obvious subdivision. Here, we quantify small‐scale spatial and temporal variation in a key demographic rate, reproductive success (RS), within an apparently contiguous population of European starlings. We used hierarchical cluster analysis to define spatial clusters of nest sites at multiple small spatial scales and long‐term data to test the hypothesis that small‐scale spatio‐temporal variation in RS occurred. RS was measured as the number of chicks alive ca. 12 days posthatch either per first brood or per nest site per breeding season (thereby incorporating multiple breeding attempts). First brood RS varied substantially among spatial clusters and years. Furthermore, the pattern of spatial variation was stable across years; some nest clusters consistently produced more chicks than others. Total seasonal RS also varied substantially among spatial clusters and years. However, the magnitude of variation was much larger and the pattern of spatial variation was no longer temporally consistent. Furthermore, the estimated magnitude of spatial variation in RS was greater at smaller spatial scales. We thereby demonstrate substantial spatial, temporal, and spatio‐temporal variation in RS occurring at very small spatial scales. We show that the estimated magnitude of this variation depended on spatial scale and that spatio‐temporal variation would not have been detected if season‐long RS had not been measured. Such small‐scale spatio‐temporal variation should be incorporated into empirical and theoretical treatments of population dynamics.     

From stochastic environments to life histories and back

Environmental stochasticity is known to play an important role in life-history evolution, but most general theory assumes a constant environment. In this paper, we examine life-history evolution in a variable environment, by decomposing average individual fitness (measured by the long-run stochastic growth rate) into contributions from average vital rates and their temporal variation. We examine how generation time, demographic dispersion (measured by the dispersion of reproductive events across the lifespan), demographic resilience (measured by damping time), within-year variances in vital rates, within-year correlations between vital rates and between-year correlations in vital rates combine to determine average individual fitness of stylized life histories. In a fluctuating environment, we show that there is often a range of cohort generation times at which the fitness is at a maximum. Thus, we expect ‘optimal’ phenotypes in fluctuating environments to differ from optimal phenotypes in constant environments. We show that stochastic growth rates are strongly affected by demographic dispersion, even when deterministic growth rates are not, and that demographic dispersion also determines the response of life-history-specific average fitness to within- and between-year correlations. Serial correlations can have a strong effect on fitness, and, depending on the structure of the life history, may act to increase or decrease fitness. The approach we outline takes a useful first step in developing general life-history theory for non-constant environments.     

Plant performance in central and northern peripheral populations of the widespread Plantago coronopus

Peripheral populations have long been predicted to show lower vital rates, higher demographic fluctuations, and lower densities than central populations. However, recent research has questioned the existence of clear patterns across species’ ranges. To test these hypotheses, we monitored five central and six northern peripheral populations of the widespread herb Plantago coronopus along the European Atlantic coast during 5 yr. We estimated population density, and calculated mean values and temporal variability of four vital rates (survival, individual growth, fecundity and recruitment) in hundreds of plants in permanent plots. Central populations showed higher fecundity, whereas peripheral populations had higher recruitment per reproductive plant, indicating a higher overall reproductive success in the periphery. Central populations showed a marginally significant tendency for higher growth, and there were no differences between range positions in survival. Fecundity and growth were affected by intraspecific competition, and recruitment was affected by precipitation, highlighting the importance of local environmental conditions for population performance. Central and peripheral populations showed no significant differences in temporal variability of vital rates. Finally, density was significantly higher in peripheral than in central populations, in discrepancy with the abundant‐centre model. Density was correlated to seedling recruitment, which would counterbalance in peripheral populations the lower fecundity and the tendency for lower growth of established plants. Such compensations among vital rates might be particularly common in widespread plants, and advise against simplistic assumptions of population performance across ranges. The whole species’ life cycle should be considered, since different arrangements of vital rates are expected to maximize fitness in local environments. Our results show also the importance of discerning between geographical periphery and ecological marginality. In a context of climate‐induced range shifts, these considerations are crucial for the reliability of niche‐models and the management of plant peripheral populations.     

Life‐history trade‐offs vary with resource availability across the geographic range of a widespread plant

• Trade‐offs between reproduction, growth and survival arise from limited resource availability in plants. Environmental stress is expected to exacerbate these negative correlations, but no studies have evaluated variation in life‐history trade‐offs throughout species geographic ranges. Here we analyse the costs of growth and reproduction across the latitudinal range of the widespread herb Plantago coronopus in Europe.
• We monitored the performance of thousands of individuals in 11 populations of P. coronopus, and tested whether the effects of growth and reproduction on a set of vital rates (growth, probability of survival, probability of reproduction and fecundity) varied with local precipitation and soil fertility. To account for variation in internal resources among individuals, we analysed trade‐offs correcting for differences in size.
• Growth was negatively affected by previous growth and reproduction. We also found costs of growth and reproduction on survival, reproduction probability and fecundity, but only in populations with low soil fertility. Costs also increased with precipitation, possibly due to flooding‐related stress. In contrast, growth was positively correlated with subsequent survival, and there was a positive covariation in reproduction between consecutive years under certain environments, a potential strategy to exploit temporary benign conditions.
• Overall, we found both negative and positive correlations among vital rates across P. coronopus geographic range. Trade‐offs predominated under stressful conditions, and positive correlations arose particularly between related traits like reproduction investment across years. By analysing multiple and diverse fitness components along stress gradients, we can better understand life‐history evolution across species’ ranges, and their responses to environmental change.

     

Small-scale spatial and temporal variation in the demographic processes underlying the large-scale decline of eiders in the Baltic Sea

The application of uniform conservation schemes often fails to account for small-scale spatial variation in the drivers of population decline. Demographic comparisons of imperilled populations across locations are therefore crucial for successful conservation, but progress is hampered by lack of long-term data from more than a single population. The recent large-scale decline of eider ducks (Somateria mollissima) in the Baltic Sea is ideal for determining to what extent mechanisms underlying population decline can be extrapolated over larger areas. We utilized stochastic demographic methods incorporating both environmental and sampling variation to assess small-scale spatial and temporal variation in the population dynamics of eiders at Söderskär (eastern range-margin) and Tvärminne (core breeding area), situated 130 km apart. The stochastic growth rate models accurately predicted the observed differences in the rate of decline between sites and time periods. At Söderskär, established breeder survival had by far the greatest elasticity, whereas elasticity was more evenly distributed among vital rates at Tvärminne. Although the study sites showed the single largest difference in fecundity, stochastic life table response experiment analyses revealed that reduced adult female survival at Tvärminne mainly determined the observed difference in growth rates between sites. In contrast, reduced fecundity primarily differentiated the past population increase from the present population decline at Söderskär. Our results demonstrate that different mechanisms may be associated with population decline across adjacent geographic locations, and indicate that dispersal of first-time breeders may be important for population dynamics. Safeguarding adult female survival and/or fecundity should be prioritized in management efforts.     

The generality of management recommendations across populations of an invasive perennial herb

Demographic models are widely used to produce management recommendations for different species. For invasive plants, current management recommendations to control local population growth are often based on data from a limited number of populations per species, and the assumption of stable population structure (asymptotic dynamics). However, spatial variation in population dynamics and deviation from a stable structure may affect these recommendations, calling into question their generality across populations of an invasive species. Here, I focused on intraspecific variation in population dynamics and investigated management recommendations generated by demographic models across 37 populations of a short-lived, invasive perennial herb (Lupinus polyphyllus). Models that relied on the proportional perturbations of vital rates (asymptotic elasticities) indicated an essential role for plant survival in long-term population dynamics. The rank order of elasticities for different vital rates (survival, growth, retrogression, fecundity) varied little among the 37 study populations regardless of population status (increasing or declining asymptotically). Summed elasticities for fecundity increased, while summed elasticities for survival decreased with increasing long-term population growth rate. Transient dynamics differed from asymptotic dynamics, but were qualitatively similar among populations, that is, depending on the initial size structure, populations tended to either increase or decline in density more rapidly than predicted by asymptotic growth rate. These findings indicate that although populations are likely to exhibit transient dynamics, management recommendations based on asymptotic elasticities for vital rates might be to some extent generalised across established populations of a given short-lived invasive plant species.     

Interaction of climate,demography and genetics: a ten-year study of <Emphasis Type="Italic">Brassica insularis</Emphasis>, a narrow endemic Mediterranean species

Long-term demographic surveys, needed to obtain accurate information on population dynamics and efficiently manage rare species, are still very scarce. Matrix population models are useful tools to identify key demographic transitions and thus help setting up conservation actions. Furthermore, the combination of ecological, demographic and genetic data is likely to improve the identification of the threats acting upon populations and help conservation decisions. In this paper we illustrate the power of this approach on Brassica insularis, a Mediterranean endemic plant species, rare and endangered in Corsica (France). In four populations of this species, a long-term demographic survey (2000–2009), genetic analyses (in 2000 and 2009) and survey of ecological variables (climatic variables, competition and herbivory) were performed. By using both deterministic and stochastic matrix model analyses, we assessed the viability of each population and tested for both spatial and temporal variations in demographic vital rates. Populations exhibited differing demographic behaviours and environmental stochasticity occurred in populations. Significant correlations between climatic variables and vital rates were detected. Stochastic simulations suggested that three out of the four populations studied might present a high risk of extinction on the short-term and should actively be managed, or at least surveyed. It could be, however, that two of these populations are experiencing density-dependent regulation, rather than being declining. Microsatellite diversity was slightly reduced in a single population and similar in the three others, consistently with expectations based on population census size and geographic area, as well as with diversity at the S-locus observed in 2000. The combination of all data led to specific recommendations for managing each population. We discuss the implications for conservation of such a general approach.     

The influence of herbivory and weather on the vital rates of two closely related cactus species

Herbivory has long been recognized as a significant driver of plant population dynamics, yet its effects along environmental gradients are unclear. Understanding how weather modulates plant–insect interactions can be particularly important for predicting the consequences of exotic insect invasions, and an explicit consideration of weather may help explain why the impact can vary greatly across space and time. We surveyed two native prickly pear cactus species (genus Opuntia) in the Florida panhandle, USA, and their specialist insect herbivores (the invasive South American cactus moth, Cactoblastis cactorum, and three native insect species) for five years across six sites. We used generalized linear mixed models to assess the impact of herbivory and weather on plant relative growth rate (RGR) and sexual reproduction, and we used Fisher's exact test to estimate the impact of herbivory on survival. Weather variables (precipitation and temperature) were consistently significant predictors of vital rate variation for both cactus species, in contrast to the limited and varied impacts of insect herbivory. Weather only significantly influenced the impact of herbivory on Opuntia humifusa fruit production. The relationships of RGR and fruit production with precipitation suggest that precipitation serves as a cue in determining the trade‐off in the allocation of resources to growth or fruit production. The presence of the native bug explained vital rate variation for both cactus species, whereas the invasive moth explained variation only for O. stricta. Despite the inconsistent effect of herbivory across vital rates and cactus species, almost half of O. stricta plants declined in size, and the invasive insect negatively affected RGR and fruit production. Given that fruit production was strongly size‐dependent, this suggests that O. stricta populations at the locations surveyed are transitioning to a size distribution of predominantly smaller sizes and with reduced sexual reproduction potential.     

Population structure and dynamics of the clonal dwarf-shrub Linnaea borealis

Abstract. The demography of the long-lived clonal dwarf-shrub Linnaea borealis was studied during four years in a coniferous forest in central Sweden. The main object was to infer patterns of temporal variation in population dynamics of this species. The shoot population is organized in fragments, i.e. physically connected systems of shoots partly covered by the moss carpet. The age and size structure of the fragment population is described, but shoots are more convenient units for a study of population dynamics. A stochastic model of shoot population dynamics was constructed, and simulations indicated a considerable temporal variation in population size and flowering. Hence, variability as such is an essential aspect of the dynamics of established populations of Linnaea. Simulations of extinction risks revealed that small-sized shoot populations (ca. 250 shoots) are likely to be long-lived when experiencing environmentally induced demographic variation of the range observed. Mortality agents for established genets, such as large-scale disturbances, were not incorporated in the models. Some implications of variable population growth rates in clonal plants in woodlands are discussed.     

Climate structures genetic variation across a species' elevation range: a test of range limits hypotheses

Gene flow may influence the formation of species range limits, and yet little is known about the patterns of gene flow with respect to environmental gradients or proximity to range limits. With rapid environmental change, it is especially important to understand patterns of gene flow to inform conservation efforts. Here we investigate the species range of the selfing, annual plant, Mimulus laciniatus, in the California Sierra Nevada. We assessed genetic variation, gene flow, and population abundance across the entire elevation‐based climate range. Contrary to expectations, within‐population plant density increased towards both climate limits. Mean genetic diversity of edge populations was equivalent to central populations; however, all edge populations exhibited less genetic diversity than neighbouring interior populations. Genetic differentiation was fairly consistent and moderate among all populations, and no directional signals of contemporary gene flow were detected between central and peripheral elevations. Elevation‐driven gene flow (isolation by environment), but not isolation by distance, was found across the species range. These findings were the same towards high‐ and low‐elevation range limits and were inconsistent with two common centre‐edge hypotheses invoked for the formation of species range limits: (i) decreasing habitat quality and population size; (ii) swamping gene flow from large, central populations. This pattern demonstrates that climate, but not centre‐edge dynamics, is an important range‐wide factor structuring M. laciniatus populations. To our knowledge, this is the first empirical study to relate environmental patterns of gene flow to range limits hypotheses. Similar investigations across a wide variety of taxa and life histories are needed.