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Environmental stochasticity is important in explaining the persistence and establishment of invasive species, but the simultaneous effects of environmental and demographic factors are difficult to separate. Understanding how demography and environmental factors affect invasive species abundance over large temporal and spatial scales is essential to anticipate populations at risk of becoming established and setting appropriate management measures., Using a hierarchical mixed modelling approach, we analysed the spatial and interannual dynamics of the invasive raphidophyte Gonyostomum semen, a noxious flagellate which is spreading in northern Europe, in response to demographic and environmental variation. We used data from 76 lakes distributed across two biogeographical regions in Sweden (Central Plains in the south and Fennoscandian region in the north) and sampled during 14 years., We found a strong asynchrony in the density dynamics of G. semen populations between the two regions. G. semen showed positive trends (i.e. increasing frequency of high density peaks) in most southern lakes, forming established populations with recurrent blooms in successive years in some of them. In contrast, G. semen populations were smaller and more stochastic in the north., G. semen previous year's abundance, a proxy for cyst production and recruitment, had a strong control on the dynamics, likely contributing to the stability of high density populations in southern lakes. Conversely, the effects of climate and habitat were weaker and their influence varied across regions. Temperature was the limiting factor in the north whereas local habitat was more important in the south., Synthesis. A full understanding of the mechanisms driving abundance changes across large scales can only be gained if endogenous and environmental factors are analysed together. For phytoplankton species, and specially, noxious microalgae, this implies that proxies for cyst production and recruitment, which are the inoculum for next year population, should be included in e.g. distribution, bloom formation and climate models, as these may modify establishment and population response to environmental variation. Asynchronous changes in abundance across regions also indicate that management plans should be developed for small regions, as inference at a large scale may obscure the mechanisms driving local population changes. [ABSTRACT FROM AUTHOR]

The relationship between the performance of individuals and the surrounding environment is fundamental in ecology and evolutionary biology. Assessing how abiotic and biotic environmental factors influence demographic processes is necessary to understand and predict population dynamics, as well as species distributions and abundances., We searched the literature for studies that have linked abiotic and biotic environmental factors to vital rates and, using structured demographic models, population growth rates of plants., We found 136 studies that had examined the environmental drivers of plant demography. The number of studies has been increasing rapidly in recent years. Based on the reviewed studies, we identify and discuss several major gaps in our knowledge of environmentally driven demography of plants. We argue that some drivers may have been underexplored and that the full potential of spatially and temporally replicated studies may not have been realized., We also stress the need to employ relevant statistical methods and experiments to correctly identify drivers. Moreover, assessments of the relationship between drivers and vital rates need to consider interactive, nonlinear and indirect effects, as well as effects of intraspecific density dependence., Synthesis. Much progress has already been made by using structured population models to link the performance of individuals to the surrounding environment. However, by improving the design and analyses of future studies, we can substantially increase our ability to predict changes in plant population dynamics, abundances and distributions in response to changes in specific environmental drivers. Future environmentally explicit demographic models should also address how genetic changes prompted by selection imposed by environmental changes will alter population trajectories in the face of continued environmental change and investigate the reciprocal feedback between plants and their biotic drivers. [ABSTRACT FROM AUTHOR]

Understanding how variation in growth, survival and reproduction affect population dynamics is a fundamental question in ecology. Although the effects of among-year variation (environmental stochasticity) are well understood, the effects of among-site variation (spatial heterogeneity) are less clearly defined., I evaluated the effects of spatial and temporal variation on the population dynamics of Pulsatilla patens, pasqueflower, a perennial prairie forb. I conducted a 10-year demographic monitoring study, and quantified vital rate variation among sites and years using generalized linear models. I incorporated vital rate functions using this variation into integral projection models for stochastic and spatially heterogeneous environments., I also explored the effects of temporal and spatial autocorrelation, by exploring model predictions over the range of possible values for temporal autocorrelation and local seed dispersal., Vital rates varied more among years than among sites. However, environmental stochasticity and spatial heterogeneity had similar magnitude effects on population dynamics. These effects were also qualitatively different: environmental stochasticity reduced population growth rates relative to the average, whereas spatial heterogeneity increased population growth rates., Spatial autocorrelation and negative temporal autocorrelation led to higher population growth rates, although environmental stochasticity still reduced growth rates for all autocorrelation values, and spatial heterogeneity increased growth rates for all autocorrelation values. Some form of autocorrelation would be necessary for model projections to match observed population trends., Synthesis. Spatial heterogeneity is as important as environmental stochasticity for population dynamics, but it is much less often incorporated into population projection models. This study points to a number of interesting avenues for future research into the roles of spatial heterogeneity and spatiotemporal variation for long-term population dynamics. [ABSTRACT FROM AUTHOR]

The dynamics of structured plant populations in variable environments can be decomposed into the 'asymptotic' growth contributed by vital rates, and 'transient' growth caused by deviation from stable stage structure., We apply this framework to a large, global data base of longitudinal studies of projection matrix models for plant populations. We ask, what is the relative contribution of transient boom and bust to the dynamic trajectories of plant populations in stochastic environments? Is this contribution patterned by phylogeny, growth form or the number of life stages per population and per species?, We show that transients contribute nearly 50% or more to the resulting trajectories, depending on whether transient and stable contributions are partitioned according to their absolute or net contribution to population dynamics., Both transient contributions and asymptotic contributions are influenced heavily by the number of life stages modelled. We discuss whether the drivers of transients should be considered real ecological phenomena, or artefacts of study design and modelling strategy. We find no evidence for phylogenetic signal in the contribution of transients to stochastic growth, nor clear patterns related to growth form. We find a surprising tendency for plant populations to boom rather than bust in response to temporal changes in vital rates and that stochastic growth rates increase with increasing tendency to boom., Synthesis. Transient dynamics contribute significantly to stochastic population dynamics but are often overlooked in ecological and evolutionary studies that employ stochastic analyses. Better understanding of transient responses to fluctuating population structure will yield better management strategies for plant populations, and better grasp of evolutionary dynamics in the real world. [ABSTRACT FROM AUTHOR]

1. Environmental stochasticity can play a major role in population dynamics with consequences for population viability and the evolution of life-history traits. However, in empirical studies it is necessary to verify that environmental stochasticity is actually present and that the observed variability is not simply a consequence of sampling variation. 2. We propose a non-parametric method to detect environmental variability in demographic parameters of structured populations based on data randomization using an estimated Kullback–Leibler distance as a test statistic. 3. The Kullback–Leibler distance is an established information-theoretic measure of the deviance between distributions and we show, with empirical and simulated data sets, that it can be adapted effectively to detect variability in demographic fates among populations. 4. This metric has the potential to reveal the importance of relatively rare transitions for understanding temporal variability in demography that would not be revealed by log-linear analysis. 5. Synthesis: Using an estimated Kullback–Leibler distance as a test statistic allows variability at the level of demographic rates to be economically assessed as an adjunct to the randomization tests that many researchers currently perform to assess variability in λ, and would provide additional and complementary insight. [ABSTRACT FROM AUTHOR]

1. Habitat fragmentation, degradation and abiotic disturbances may strongly affect population dynamics and genetic diversity of plant populations. 2. In this study, a Life Table Response Experiment (LTRE) and stochastic simulations were used to investigate how different types of disturbance affected the fitness and population dynamics of small, fragmented populations of the long-lived perennial Primula vulgaris and how this was related to genetic diversity. Nested factors were included in the LTRE analysis in order to assess population-specific contributions to changes in population growth rate and to contrast these with contributions derived for year and type of disturbance. 3. Stochastic growth rates (λs) varied considerably among disturbance types: sites continuously disturbed throughout the year had a mean stochastic growth rate smaller than one, whereas sites receiving low or cyclic disturbance had stochastic growth rates larger than one. 4. LTRE analysis revealed that disturbance had a major impact on variation in growth rate, whereas year effects were less pronounced. However, contributions of individual populations equalled or exceeded those of the disturbance regime and mainly originated from negative or positive contributions of seedling recruitment and growth. 5. Linear regression analysis showed that these deviations of population demography from the disturbance type contribution were positively related to genetic diversity and effective population size, whereas inbreeding and isolation had no effect. Similar analyses revealed a positive effect of effective population size on λs. 6. Our data indicate that disturbance has an important impact on population dynamics of this plant species, but that populations containing a higher number of reproductive adults are buffered against large fluctuations due to environmental stochasticity so that stochastic growth rates are higher. However, because population specific contributions to changes in population growth rate were as large as the contributions of disturbance itself, and because they were significantly related to population genetic diversity, our study suggests that, along with local and regional environmental variables, genetic diversity may also play a key role in determining population viability of perennial plant species. [ABSTRACT FROM AUTHOR]

Summary 1 Transition matrix models were used to evaluate the effects of environmental stochasticity and four different methods of grassland management on dynamics and viability of a population of the biennial Gentianella campestris (Gentianaceae) in species-rich grassland. Data were collected between 1990 and 1995. 2 Continuous summer grazing, the prevailing management strategy in Scandinavian grasslands, resulted in high recruitment of new plants, mainly because litter accumulation was prevented and gaps were created by trampling. Trampling and repeated grazing, however, caused damage which reduced seed production. Lambda for the average matrix was c. 0.77, and a stochastic matrix model yielded an extinction probability for the total population of c. 0.08 within 50 years. 3 Mowing in mid-July (used as a conservation tool) increased seed production, but litter accumulation following re-growth of the vegetation prevented establishment. Lambda and extinction risk were similar to continuous grazing. 4 Mowing in October (another conservation tool) promoted recruitment because of low litter accumulation, but the seed output decreased because plant growth was impaired by tall vegetation. Lambda was 0.64, while the extinction probability was very high (c. 0.98 within 50 years). 5 Mid-July mowing followed by autumn grazing (the historical management regime) yielded high values for both seed production and establishment of rosettes. Lambda was 0.94 and the probability of extinction within 50 years was below detection level. 6 Log-linear analysis showed that the matrices differed significantly both between treatments and between years. The latter indicates environmental stochasticity, here caused by summer drought that increased the extinction risk. Lambda may be slightly underestimated because drought occurred in one out of five summers during the study period, which is high compared with the natural frequency. 7 We conclude that traditional grassland management is more... [ABSTRACT FROM AUTHOR]

1 The annual plant Eichhornia paniculata occurs in discrete, ephemeral habitats formed by pools, wet ditches and flooded pastures in arid north-eastern Brazil. We conducted a large-scale geographical survey of populations four times over a 7-year period (1982–89) and measured population size, population persistence and patch occupancy. In total, 167 populations were censused. 2 To investigate the importance of local and regional influences on population size, we posed the following specific questions. Are fluctuations in population size independent of their initial size and independent among years? Is persistence uniform among populations of different size and age? Are the proportion of patches occupied related to the density of habitat patches in a region? What are the relations between the size, persistence and density of populations? 3 Population size averaged 86 over the 4-year period with 52% of populations containing less than 100 individuals. Sixty-four per cent of populations persisted from one year to the next, but the rate at which populations became absent from a patch was independent of initial population size and time since the last census. For populations that persisted, there was a significant positive correlation between the initial census number and their size in subsequent years. 4 In 29 transects through different regions of north-eastern Brazil, an average of 21.6% (range 3.8–47.2%) of suitable habitat patches were occupied by E. paniculata. The proportion of patches occupied was positively correlated with the density of patches in a region. No populations were found when the density of patches fell below 0.23 patches km-1 or 0.18 patches km-1 in 1988 and 1989, respectively, indicating the probable existence of a habitat threshold for species persistence within a region. There was no correlation between patch occupancy and either the average number of individuals per population or the probability of... [ABSTRACT FROM AUTHOR]

1 Long-term demographic field studies combined with simulation models that incorporated two types of stochasticity were used to investigate the relative impact of reproduction and survival on the persistence of populations of the North American woodland herb, Asarum canadense. 2 Field data were collected over 7 years in replicate plots located in early and late successional forest habitat. By following marked ramets from year to year it proved possible to investigate the demography both of ramets and of groups of genetically identical ramets (clones). 3 A. canadense exhibited considerable temporal and spatial variation in reproductive success, survivorship, and population growth rates. Populations of ramets and clones in late successional forest habitats held their own, while those in early successional forest habitats declined. 4 Sexual and clonal reproduction had less impact on population growth than did survival. Nonetheless, seedling recruitment was important, as indicated by the relatively high rates of genet turnover in A. canadense populations. 5 Results from simulations indicated that the vast majority of genets in both habitat types failed to reproduce. Over their lifetime, simulated genets produced a maximum of 44 and 77 seedlings in early and late successional forest habitat, respectively. 6 Although A. canadense genets are potentially immortal, the maximum life span for 2000 simulated genets was 104 years. Simulated genets lived a mean of 3.0 and 4.8 years in early and late successional forest habitat, respectively. 7 Simulated A. canadense populations only persisted in late successional forest habitat. Within simulated late successional forest populations, the number of ramets tended to decrease over time, while the number of genets tended to increase over time. 8 The minimum viable population size for A. canadense ramets in late successional forest was 25 individuals with environmental stochasticity only, and 1000 individuals with both environmental and demographic stochasticity; for genets in late successional forest, the corresponding numbers were 20 and 25, respectively. 9 Ramet and genet dynamics differed greatly in A. canadense, highlighting the importance of long-term demographic studies at each of these levels. [ABSTRACT FROM AUTHOR]

Summary1 The clonal perennial herb Helianthus divaricatus and the clonal shrub Rhus aromatica reach the northern limit of their distribution in southern Québec (Canada), where both are rare, but they are more common southwards in the adjacent province of Ontario. We tested whether peripheral populations of these species maintain themselves by having highly variable individual growth and survival rates. Their annual rates of population growth, λ, would then vary more, from year to year, than those of more southern populations in neighbouring Ontario, where the species are common. 2 Demographic analyses compared, over two transition intervals, size-based transition matrices for two northern (Gatineau Park, southern Québec) and two southern populations (Pinery Park, southern Ontario) of each species. Comparisons used log-linear analyses, bias-corrected λ-values with 95% confidence intervals, and elasticity values. 3 For both species, the northern populations showed a larger variation between transition intervals and local populations in some of their vital rates and in λ-values. For H. divaricatus, elasticity values combined with log-linear analyses indicated that differences in the growth and survival of medium-sized ramets contributed most to the differences in λ-values between northern and southern populations. For R. aromatica, they indicated that differences in the fate of both medium and large ramets contributed to variation in λ. 4 Most of our data indicated a greater demographic variability in the northern populations of H. divaricatus and R. aromatica. At the northern periphery, these species grow in very few of the numerous habitat patches that appear to be suitable for them, whereas the two species together present a near continuous cover in all suitable habitats further south. High demographic variability therefore appears to contribute to determining the distribution of plant species, by increasing the extinction... [ABSTRACT FROM AUTHOR]