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Recent studies have shown that neonicotinoid insecticides have adverse effects on non-target invertebrate species (1-6). Invertebrates constitute a substantial part of the diet of many bird species during the breeding season and are indispensable for raising offspring (7). We investigated the hypothesis that the most widely used neonicotinoid insecticide, imidacloprid, has a negative impact on insectivorous bird populations. Here we show that, in the Netherlands, local population trends were significantly more negative in areas with higher surface-water concentrations of imidacloprid. At imidacloprid concentrations of more than 20 nanograms per litre, bird populations tended to decline by 3.5 per cent on average annually. Additional analyses revealed that this spatial pattern of decline appeared only after the introduction of imidacloprid to the Netherlands, in the mid-1990s. We further show that the recent negative relationship remains after correcting for spatial differences in land-use changes that are known to affect bird populations in farmland. Our results suggest that the impact of neonicotinoids on the natural environment is even more substantial than has recently been reported and is reminiscent of the effects of persistent insecticides in the past. Future legislation should take into account the potential cascading effects of neonicotinoids on ecosystems., Although concerns have been raised about the direct effects of neonicotinoids on non-target vertebrate species (8), neonicotinoids are in general thought to be less harmful to mammals and birds than [...]

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2009.01635.x Byline: Roberto Salguero-Gomez (1), Hans de Kroon (2) Keywords: demographic buffering; integral projection model; plant demography; population dynamics; projection matrix; stochastic elasticity; stochastic life table response experiment (SLTRE); transient dynamics Abstract: Summary 1. Projection matrices have become the dominant modelling approach in plant demography because they (i) are relatively easy to formulate, (ii) compile complex data in a structured and analytically tractable manner, (iii) provide numerous parameters with direct biological meaning, (iv) allow the investigator to address broad or specific, experimental and/or theoretical, ecological and evolutionary questions, and (v) produce uniform outputs, enabling direct comparisons between the results of different studies. 2. The last decade has witnessed major advancements in this field that have brought demographic models much closer to the real world, in particular in the analysis of effects of spatial and temporal environmental variation on populations. The present Special Feature contributes to that progress with novel methodologies and applications on Integral Projection Models, stochastic Life Table Response Experiment analyses, stochastic elasticities, transient dynamics and phylogenetic analyses. 3.Synthesis. Environmental stochasticity is an integral part of ecosystems, and plant populations exhibit a tremendous array of demographic strategies to deal with its effects. The analytical challenge of understanding how populations avoid, tolerate or depend on stochasticity is finally overcome with the new matrix approaches. The tools are now available to interpret the effects of changes in temporal and spatial variation on plant populations. Author Affiliation: (1)Department of Biology, University of Pennsylvania, 215 South University Avenue, 321 Leidy Laboratories, Philadelphia, PA 19104, USA (2)Department of Experimental Plant Ecology, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands Article History: Received 3 December 2009; accepted 9 December 2009 Handling Editor: Michael Hutchings Article note: (*) Correspondence author. E-mail: salguero@sas.upenn.edu

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2009.01612.x Byline: Eelke Jongejans (1), Linda D. Jorritsma-Wienk (1), Ute Becker (2), Petr Dostal (3), Mikael Milden (4), Hans de Kroon (1) Keywords: Asteraceae; climate fluctuations at different spatial scales; demography; elasticity; gross LTRE contributions; life table response experiments (LTRE); net variance contributions; population dynamics; short-lived perennials Abstract: Summary 1. When range shifts or invasions of plant species are studied, it is important to know whether large-scale spatial variation in a species' demography can be ignored or approximated by variation observed over smaller spatial scales. 2. Here, we studied the population dynamics of three similar (as shown by elasticity analysis) short-lived perennial plant species in multiple sites in different European countries over 2 years. We constructed a total of 40 transition matrices and analysed the spatio-temporal variation in the projected population growth rate ([lambda]) with spatially nested life table response experiments (LTRE). 3. All species (Carlina vulgaris, Tragopogon pratensis and Hypochaeris radicata) showed considerable life-history variation among regions on top of variation among sites within regions. 4. Net variance contributions (NVC), a novel LTRE statistic, revealed that in each species, variation in one group of vital rates contributed most to variation in [lambda] among regions as well as among sites. However, that most important type of vital rates differed between species: plant growth in C. vulgaris, flower head production in T. pratensis and establishment probability of seedlings in H. radicata. The rankings of the NVCs of other vital rates varied between site and region effects, suggesting that buffering through negative vital rate correlations varies over different spatial scales, while the identity of the main contributor to [lambda] variation is more constant. 5. Temporal effects were smaller than spatial effects, but the LTREs showed strong interactions between time and space (region or site), suggesting that the effect of, e.g. climate fluctuations are not synchronized throughout the distribution of a species. 6. Synthesis. This study shows that the life histories of plant species are distinguishable even when mean elasticity values show only small differences, and that life histories vary over the distribution range of a species. Demographic differences over large spatial scales can therefore only be partly substituted by small scale spatial variation in modelling studies on the population dynamics of a species across its entire distribution. Author Affiliation: (1)Department of Experimental Plant Ecology, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands (2)Department of Biology, Plant Ecology, University of Marburg, Karl-von-Frisch-Strasse 8, D-35032 Marburg, Germany (3)Institute of Botany, Academy of Sciences of the Czech Republic, Zamek 1, 252 43 Pruhonice, Czech Republic (4)Department of Botany, Stockholm University, 106 91 Stockholm, Sweden Article History: Received 13 August 2009; accepted 4 November 2009 Handling Editor: Hans Jacquemyn Article note: (*) Correspondence author. E-mail: e.jongejans@science.ru.nl

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2009.01611.x Byline: Raziel Davison (1), Hans Jacquemyn (2), Dries Adriaens (3), Olivier Honnay (2), Hans de Kroon (4), Shripad Tuljapurkar (1) Keywords: Anthyllis vulneraria; climate change; life table response experiment (LTRE); population growth; stochastic elasticities Abstract: Summary 1. Life table response experiment (LTRE) analyses have been widely used to examine the sources of differences in the long-term deterministic growth rate (r = log [lambda]) of stage-structured populations that live in spatially distinct habitats or under distinct experimental conditions. However, existing methods for LTRE analysis ignore the fact that persistent temporal variation in matrix elements results in a long-term stochastic growth rate (a = log [lambda].sub.s) that is different from the deterministic growth rate (r) and thus do not take into account environmental stochasticity. 2. Here, we develop a stochastic extension of LTRE methods that can be used to compare stochastic growth rates among populations that differ in the observed variability of their matrix elements over time. We illustrate our method with actual data and explore a range of questions that may be addressed with these new tools. Specifically, we investigate how variability in weather conditions affected the population dynamics of the short-lived perennial plant species Anthyllis vulneraria and examine how differences in stochastic growth rates (a) are determined by contributions of mean matrix elements and variability in matrix elements. 3. We find that, consistent with the life history of the species, differences in mean fertility and growth made the largest contribution to differences in a, whereas in terms of variability fertility made the largest contribution in most populations. However, we also find that in all populations, the magnitude of the total contribution of mean matrix elements outweighed that of variability. Finally, increasing soil depth significantly lowered contributions of variability in matrix elements, but it was not related to contributions of differences in mean matrix elements. 4.Synthesis. Stochastic life table response experiment analysis described here provides the first systematic way of incorporating observed differences in temporal variability into the comparison of natural populations. A key finding from this study is that populations occurring on relatively deeper soils were better buffered against climatic variation than populations occurring on shallow soils. We expect this new approach to analyse temporal variability to prove especially useful in the analysis of natural populations experiencing environmental change. Author Affiliation: (1)Department of Biology, Stanford University, Stanford, CA 94305, USA (2)Division of Plant Ecology and Systematics, University of Leuven, Arenbergpark 31, B-3001 Heverlee, Belgium (3)Research Institute for Nature and Forest, Kliniekstraat 25, B-1070 Brussels, Belgium (4)Department of Experimental Plant Ecology, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands Article History: Received 13 August 2009; accepted 27 October 2009 Handling Editor: Pieter Zuidema Article note: (*) Correspondence author. E-mail: rdavison@stanford.edu

In stoloniferous species, the length of petioles is of pivotal importance because it determines the position of leaf blades within the canopy. From a mechanistic perspective, two developmental processes, cell division and cell elongation, are responsible for the length of a given petiole. This study aimed at quantifying the relative contributions of cell division and cell elongation to genotypic and plastic variation in petiole length of the stoloniferous herb Trifolium repens. Thirty-four genotypes of T. repens were grown under high light conditions and simulated canopy shade. Cells were counted and their lengths measured on epidermal prints from fully grown petioles of leaves that had been initiated in the experimental light conditions. Cell number was the main trait explaining petiole length differences among genotypes grown under high light, while both cell number and length changed in response to shading. Our study revealed a strong negative correlation between shade-induced changes in cell number and cell length: genotypes that responded to shading by increasing cell numbers hardly changed in cell length, and vice versa. Our results suggest that genotypic and phenotypic variation in petiole length results from a complex interplay between the developmental processes of cell elongation and cell division. Key words: cell number; cell size; petiole elongation; plasticity; shade avoidance; trade-off; Trifolium repens.

Bryophytes have increased in abundance in northern regions, and climate changes have been proposed to account for this change. However, changes in the population dynamics of microtine rodents may also contribute to changes in bryophyte abundance. New evidence indicates a tendency for microtine rodent population oscillations to change from periodicity of 3-5 years to become irregular or acyclic. The impact on ecosystem functioning is potentially great. We study the impact of variation in microtine rodent population characteristics, such as cycle length and amplitude, on the population dynamics of the boreal, clonal moss Hylocomium splendens. We use experimental and observational demographic data to construct 127 scenarios representing all combinations of disturbance type (gap formation and/or clipping), period (cyclic with 4, 6, 12, or 24 years between rodent peaks: or acyclic with constant or stochastically varying annual disturbance severity) and disturbance severity (fraction of individuals affected by disturbance in each year relative to the maximum disturbance carried out in the field experiment: seven levels). Population data collected in the field during 13 years were used as a baseline scenario. By subjecting all scenarios to stochastic matrix modeling, we demonstrate considerable impact of microtine rodent on the population dynamics of H. splendens, most notably when rodent populations fluctuate with short periods and high peak disturbance severities. Under the same average disturbance severity, H. splendens population growth rates are highest in acyclic scenarios and are progressively reduced with increasing peak disturbance severities (i.e., with increasing period). Stochastic elasticity analyses show that in less variable environments mature segment survival contributes more to the population growth rate, while in more variable environments the regeneration pathway (branching of older parts of the plant) plays a stronger role, inevitably leading to lower population fitness. Our results support the hypothesis that breakdown of cyclic rodent population dynamics accentuates increase in the abundance of H. splendens and other large bryophytes in boreal forests in Norway, observed empirically in recent years and primarily ascribed to climatic change. Key words: boreal clonal moss; bryophytes; climatic change; disturbance; elasticity; Hylocomium splendens; matrix population models; microtime rodent cycles; resistance to herbivory; stochastic growth rate.

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2006.01204.x Byline: LINDE HESS, HANS DE KROON (*) Keywords: roots; root growth; rooting volume; nutrients; self/non-self discrimination; root recognition; allocation; split-root design; competition Abstract: Abstract An increasing number of studies have shown that plants produce more root mass when sharing rooting space with an intraspecific neighbour as compared with plants growing alone. This so-called self/non-self discrimination has been suggested as a mechanism by which plants may prevent wasteful competition with their own roots and enhance their competitive ability for nutrients with roots of neighbouring plants. The overproduction of root biomass is said to result in a 'tragedy of the commons', because it appears to occur at the expense of reproductive biomass. Studies on self/non-self root discrimination have commonly used a split-root design to distinguish self from non-self competition, while keeping the total amount of nutrients available per plant the same. This design has recently been criticized because the rooting volume differs between treatments. Here, we use three general hypotheses to explain the published results without invoking the mechanism of self/non-self discrimination. The hypotheses propose that differences in root mass are due to differences in rooting volume, and differences in nutrient availability determine whole plant growth. More root mass without more growth results in less reproductive biomass. A reanalysis of the results of root self/non-self discrimination confirms these hypotheses. Root overproduction in the presence of another plant, as found in nearly all studies, is consistent with effects of a larger soil volume available to these plants as compared with plants growing alone. Under the same total nutrient availability, total plant weight was the same or higher when more roots were produced. Inevitably, a larger root production with the same total biomass implies that less reproductive biomass is produced. Although our analysis can explain most of the results of the split-root experiments, we cannot rule out the possibility that self/non-self root discrimination did take place. We discuss a limited set of experiments for which volume effects cannot explain the results, suggesting, in fact, that direct self/non-self root interactions have operated. We suggest experimental designs that can demonstrate their ecological significance in the future. We conclude that there is ample evidence that plants can sense the volume of available rooting space, and a limited number of studies on individual roots show that plant roots may sense the identity of neighbouring roots and respond accordingly. The significance of these responses for whole plant growth and reproduction in relation to well-known resource competition effects is yet largely unknown and in urgent need of further study. Author Affiliation: (*)Department of Experimental Plant Ecology, Radboud University of Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands Article History: Received 11 July 2006 revision accepted 26 October 2006Handling Editor: David Gibson Article note: Present address and correspondence: Linde Hess, Crop and Soil Systems Research Group, SAC, King's Buildings, West Mains Road, Edinburgh EH9 3JG, UK (tel. +44 131 5354000; e-mail lhess@ed.sac.ac.uk).

Spatial models predict that long-distance dispersal of offspring provides competitive superiority in open environments. We tested this prediction by artificially aggregating ramets of the spreading clonal species Agrostis stolonifera in an undisturbed environment and in an environment where flooding increased open space. We compared the competitive response of this manipulated Agrostis with both the natural ramet distribution of Agrostis and with the naturally aggregated clonal species Alopecurus pratensis. Our phenotypic manipulation of ramet dispersal significantly increased aggregation of clonal offspring, without altering the number of offspring, and thus provided an adequate test of spatial effects. Regardless of flooding, both Alopecurus and the aggregated Agrostis were more suppressed in species mixtures than the natural dispersed form of Agrostis. This demonstrates that long distance dispersal of ramets enhances competitive ability, at least in early stages of succession. Key words: competition--colonization trade-off; disturbance; flooding; phenotypic manipulation; spatial pattern.

Many studies have focused on the ecology of seed dimorphism, the production of two seed types by a single plant. Morphology and seed size are usually correlated, but how morphology affects germination percentage and seedling growth is poorly understood. Here we explicitly separate these effects for nine populations of the dimorphic species Tragopogon pratensis subsp, pratensis. Larger seeds yielded higher germination percentages, yet seed morphology had no additional direct effect on germination. Neither seed size nor seed morphology affected seedling growth. Neither germination nor seedling growth varied among populations, but seed head varied significantly. Results show that germination is mainly controlled by seed size rather than by seed morphology. This study is one of the few to distinguish explicitly between seed size and seed morphology effects on ecological characteristics and suggests that seed dimorphism may exert its ecological effects predominantly through its correlated size. Key words: Asteraceae; germination; The Netherlands; population; seed dimorphism; seed morphology; seed size; seedling growth.

The Mediterranean perennial herb Lobularia maritima shows an exceptionally extended flowering and fruiting that lasts for 10 months, from early September to late June. We hypothesized that such an extended phenology may be a flexible mechanism that enhances population persistence in variable Mediterranean environments, as fecundity in one part of the season could compensate for reproductive failure in another part of the season. We predicted that (1) fecundities throughout the year would significantly contribute to mean population growth rate [lambda], (2) negative covariances among fecundities in different periods of the year would reduce variance in population growth rate, and (3) extended flowering and fruiting would enhance long-term stochastic population growth rates. We used a periodic matrix model to describe the demography of a L. maritima population over five years, in which each year was divided into six periods of two months each. Population growth rates varied from a low of 0.25 to a high of 4.81 over the five years of study. Periodic elasticity analyses revealed that fecundities in the first two periods of the year, i.e., the autumn periods, were the major determinants of population growth in most of the years, rather than fecundities over the whole flowering and fruiting season. Variation in the autumn fecundities also made the largest contribution to the observed variance in [lambda]. Hence, unlike earlier generalizations, highly variable parameters also had relatively high elasticities. As predicted, negative covariances appeared between the fecundities, but only between those of the two autumn periods. These negative covariances were interpreted as a flexible mechanism to tailor the onset of reproduction to the start of the autumn rains, thereby reducing the variance in [lambda]. We used stochastic matrix models to investigate the effect of different reproductive strategies on stochastic population growth rate. We created hypothetical populations with either an even distribution of fecundity throughout the year or with concentrated flowering and fruiting in autumn or in spring. Stochastic population growth rates were high if a major part of the reproduction remained in autumn. A hypothetically even distribution of fecundities over the entire flowering season increased both the mean and the variance in [lambda], with little overall effect on stochastic population growth rate. All together, our results indicate that a reproductive failure of L. maritima in autumn cannot be compensated for by reproduction in winter and spring. The extended flowering and fruiting season thus has very little effect on the population dynamics of the species. Alternative explanations for the unusual phenology of L. maritima in the Mediterranean environment are discussed. Key words: elasticity analysis; extended flowering and fruiting; Lobularia maritima; Mediterranean environments; periodic matrix model; population growth rate; stochastic simulations; temporal variation; variance decomposition analysis.

1 In natural habitats, essential resources for plant growth are heterogeneously distributed in space, resulting in environmental patchiness with favourable and less favourable microhabitats. Clonal plants may benefit from their ability to share resources between connected ramets experiencing contrasting levels of resource supply. This hypothesis was tested with clones of Potentilla reptans and P. anserina, consisting of a mother rosette and a number of daughters on an attached stolon, grown under homogeneously high and low light conditions, as well as in spatially heterogeneous light environments in which either mother or daughters were shaded. Biomass data were used to carry out an analysis of the costs and benefits of clonal integration. 2 Both species showed high benefits of integration. In P. reptans, connections to unshaded clone-parts enhanced biomass production of the shaded part. In contrast to the prediction that clonal integration would result in costs to unshaded clone-parts connected to shaded parts, unshaded ramets of both species developed higher instead of lower dry weights when connected to a shaded part. Thus, unshaded ramets actually benefitted from integration. 3 It is hypothesized that these unexpected benefits of integration were due to mutual support of connected clone-parts growing in shaded and unshaded patches. The high evaporative demands of the unshaded clone-parts probably resulted in water being translocated from shaded to unshaded ramets while, at the same time carbohydrates were translocated from unshaded to shaded ramets. 4 We discuss implications of this suggested bidirectional transport of two different resources for the ecological significance of physiological integratio in clonal plants and for the notion of habitat heterogeneity.

1 Plant species are known to segregate along small-scale flooding gradients. We tested whether differences in flooding duration can also result in genetic differentiation in the clonal species Ranunculus reptans, which naturally grows in both a lakeside microhabitat and a landside microhabitat with shorter periods of flooding. 2 We compared traits related to fitness, and clonal life-history traits, of 432 plants representing nine genotypes from each microhabitat, grown without flooding or with short or long flooding duration. We also determined aerenchyma contents and carbohydrate use efficiencies during flooding in plants of these 18 genotypes. 3 In the flooding treatments, genotypes from the lakeside microhabitat produced significantly more rosettes and rooted rosettes than genotypes from the landside microhabitat. This indicates small-scale local adaptation to flooding duration in R. reptans. 4 Unexpectedly, genotypes from the landside microhabitat had a higher proportion of aerenchyma in their roots than those from the lakeside microhabitat. Carbohydrate use efficiency was high in all genotypes. These physiological traits cannot therefore explain the observed local adaptation. 5 Genotypes from the lakeside microhabitat produced shorter stolon internodes than genotypes from the landside microhabitat when flooded. Moreover, in the treatment with long flooding duration, there was selection for reduced stolon internode lengths, which might help to reduce respiratory losses. This suggests that local adaptation is a consequence of differences in plasticity of internode length. 6 Our results indicate an important role for flooding in plant microevolution by demonstrating that variation in flooding duration can induce intraspecific specialization even within populations. Physiological traits that determine differences in flooding tolerance between species do not, however, seem to have played a key role in this differentiation.

1 The long-term benefits of root foraging in heterogeneous environments are unclear. The short duration of many previous studies may have overlooked the effects of patch depletion and root turnover, which may limit the long-term rewards of root foraging for perennial plants. 2 The benefits of root foraging were investigated for Holcus lanatus and Nardus stricta over two growing seasons. Shoot biomass of each species was measured in homogeneous nutrient-rich and nutrient-poor treatments and in a heterogeneous treatment consisting of a nutrient-rich and a nutrient-poor side, at a high and a low overall level of nutrient availability at the same patch contrast. Large initial differences in nitrate concentrations in the soil solution between the soil types disappeared so that, after several months, nitrate levels were low in all soil types. 3 In heterogeneous treatments, Holcus was able to proliferate roots in the nutrient-rich side compared with the nutrient-poor side, but only at the high overall level of nutrient availability. Nardus did not selectively place roots in the nutrient-rich side of the heterogeneous treatment at either nutrient level. 4 Root longevity, as determined by minirhizotron observations, revealed that roots of Holcus tended to be shorter lived than those of Nardus, and to live longer in nutrient-poor soils. 5 Initially, Holcus produced more shoot biomass in the heterogeneous treatments, at both overall levels of nutrient availability, than expected from values in the homogeneous treatments, but this advantage disappeared by the end of the first growing season and, after 2 years, shoot biomass in the heterogeneous treatments was much less than expected. At the high overall level of nutrient availability, Holcus shoot biomass was not significantly greater than that produced in the homogeneous nutrient-poor treatment. In contrast, shoot biomass of Nardus in the heterogeneous treatment was similar to the expected value, both after the first and second growing seasons. 6 For Holcus, fast root proliferation and presumably a high nutrient uptake resulted in increased shoot biomass in the short term, but this was then curtailed by rapid patch depletion and high losses due to a limited root life span. We discuss the implications for the long-term rewards of root proliferation in perennial species of heterogeneous environments. Key-words: foraging, minirhizotrons, nutrient heterogeneity, root proliferation, root longevity

Differences in root foraging behavior between species have been well documented, but the effects of these differences on belowground competitive ability are only beginning to be studied. Here we report the results of a competition experiment in homogeneous and heterogeneous soils between two species that differ in their ability to acquire nutrients from patchy environments. The perennial grasses Festuca rubra and Anthoxanthum odoratum have comparable growth rates, but results of previous studies with isolated plants designated the latter species as the more effective forager, probably due to its higher physiological plasticity (stronger increase in nutrient uptake rates per unit root mass in enriched nutrient patches). We introduced nutrient soil heterogeneity at two spatial scales. In a fine-grained heterogeneous treatment, the nutrient-rich patches were smaller and more concentrated than in a coarse-grained heterogeneous (checkerboard) treatment. Overall, the level of nutrient availability in these heterogeneous treatments was similar to a third treatment with homogeneous soils. The species were grown in monocultures and mixtures in a standard replacement design during two growing seasons. In the homogeneous treatment, the relative competitive ability of F. rubra was higher than of A. odoratum, but F. rubra's advantage declined in the heterogeneous environments, and the relative competitive abilities became the same. Both species produced higher root densities in the richer patches of the fine-grained heterogeneous treatment, but not significantly so in the coarse-grained heterogeneous treatment, and these responses were the same for both species. The root activity of the species was assessed by determining the amount of strontium captured by a species at the end of the experiment, after injecting Sr[Cl.sub.2] in the nutrient-rich patches and in equivalent locations in the homogeneous treatment. F. rubra acquired significantly more Sr in the mixtures in the homogeneous treatments, but in the coarse- and fine-grained heterogeneous treatment the nutrient acquisition abilities of the species were equal. These results suggest that a more effective root foraging behavior confers a higher competitive ability in heterogeneous environments. Moreover, the results on root-proliferation and nutrient-acquisition ability suggest that a higher physiological (rather than morphological) plasticity is critical in obtaining a long-term competitive advantage. Analyses of shoot size inequalities suggest that competitive interactions were size-symmetric in homogeneous soil and size-asymmetric in the heterogeneous treatments. However, in the long term, competition becomes more size-symmetric in the heterogeneous soils, consistent with the increasing importance of physiological plasticity. Key words: Anthoxanthum odoratum; competition; Festuca rubra; grasses, perennial; heterogeneity, soil nutrients; morphological and physiological plasticity; nutrients in soils; plant competition underground; replacement design; root foraging; soil nutrient heterogeneity changes competition.

1 The boreal forest is subject to disturbance but the effects on population dynamics are poorly understood. We investigated how a prominent species of the forest floor, the clonal moss Hylocomium splendens, responded to different types of fine-scale disturbance. 2 Canopy gap formation was simulated in H. splendens populations by removing 50% of the bryophyte layer (Removal treatment) and herbivory by clipping all of its growing points (Clipped treatment). Demographic parameters and population dynamics were compared with an unmanipulated reference population (Ref). 3 Both types of disturbance caused a significant decrease in mean segment size (particularly following clipping) and an increase in branching rates. Branching rates in the Removal population were enhanced at all architectural opportunities for enhanced branching, but only the Clipped segments themselves were affected during the 2 years following disturbance. 4 The population effects of disturbance were analysed by a periodic matrix model, with 3-year as the period, followed by elasticity analysis. The Ref population was approximately stable (growth rate, [Lambda] = 1.012), with the survival of mature segments making an overwhelming contribution to its growth rate. The higher [Lambda] (1.740) in the Removal population was associated with higher elasticities of branching. Clipping reduced [Lambda] to 0.841 by blocking segment survival, although regeneration of new growing points on the remnant main shoot axis after 1 year, and its subsequent maturation in the next year, then made a major contribution. 5 Life table response experiment analyses revealed that almost all demographic processes including branching and the survival of mature segments contributed to the increased [Lambda]. in Removal treatment. The relatively small decrease in [Lambda] following clipping was mainly due to the absence of mature segment survival, being almost balanced by the pulse of regeneration of growing points the year after disturbance. 6 We conclude that H. splendens populations show a good ability to recover from common types of disturbances in their environment. The general mechanisms behind the responses are discussed. Key-words: boreal forest, bryophytes, clonal plants, demography, elasticity, fine-scale disturbance, life table response experiment, Norway, periodic matrix model, population growth rate Journal of Ecology (2001) 89, 395-405

The general statement made by Mills et al., that elasticities can give inaccurate predictions of lambda remains unfounded and it is argued that unequal variation is not a problem of elasticities. It is concluded that elasticities in spite of their limitations, when applied cautiously are a core and vital tool in conservation biology.

Hypotheses about the origin of vegetation pattern formation in semi-arid areas around the world almost all include a common feature of semi-arid areas: the presence of a positive feedback between plant density and water infiltration. We investigate whether this positive feedback and the spatial redistribution of runoff water are sufficient to explain vegetation pattern formation. For this purpose, we analyze a spatially explicit model consisting of partial differential equations using a method for demonstrating pattern formation (Turing analysis). Our analysis reveals that pattern formation can occur in semi-arid areas given only the positive feedback between plant density and local water infiltration coupled with the spatial redistribution of runoff water. Thus, slope and underlying heterogeneity are not essential conditions. Other factors in the model, such as herbivory, plant dispersal, rainfall, and drought tolerance of plants, appear to determine under what conditions pattern formation is likely but are not the primary factors that generate the patterns. The model is in agreement with field observations and indicates the conditions for which vegetation pattern formation can be expected in arid and semi-arid grazing systems. Key words: grazing; herbivory; patchiness; plant dispersal; plant-soil interaction; positive feedback; runoff; semi-arid grazing systems; spatially explicit model; Turing analysis; vegetation patterns.