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To understand the consequences of anthropogenic and environmental changes for wildlife populations, it is important to study how individuals differ in their sensitivity to environmental change and whether this depends on individual characteristics. An individual's reproductive performance may provide an integrative, unidimensional proxy of an individual's characteristics. In this study, we define an individual's characteristics by three such reproductive states, namely successful, failed and non‐breeders in the previous year. We used a 16‐year dataset of individually marked breeding Eurasian Oystercatchers Haematopus ostralegus to examine the interannual fluctuations in reproductive success and survival among breeding states, and their state‐dependent sensitivity to environmental conditions. Environmental conditions included available biomass of the main prey species of breeding Oystercatchers (Ragworm, Baltic Tellin and Lugworm), tidal height, which reflects one of the main causes of nest loss (flooding), and conditions that may impact the energetic requirements during incubation, such as temperature. We also included environmental variables measured in winter, including available biomass of the main winter prey species (Blue Mussel and Common Cockle) along with factors that may affect food availability and energetic requirements for homeostasis, namely bivalve weight loss, windchill, winter severity and precipitation. Breeding birds that were successful the previous year had higher survival and were more likely to remain successful, in comparison with failed or non‐breeders. The effects of environmental conditions acted in the same direction on reproductive success but had opposite effects on survival among the three breeding states, especially for windchill and Blue Mussel biomass. The contrasting state‐dependent effects of the environment on survival thus averaged out when examining consequences for lifetime reproductive nest success (LRnS); instead, LRnS was largely influenced by environmental conditions acting upon reproduction. Our study indicates that an individual's previous breeding state provides an integrative measure of heterogeneity in individuals' sensitivity of reproduction and survival to environmental change. Incorporating previous breeding state as a source of individual heterogeneity in population modelling may improve predictions of future population dynamics in a rapidly changing world. [ABSTRACT FROM AUTHOR]

Understanding which factors cause populations to decline begins with identifying which parts of the life cycle, and which vital rates, have changed over time. However, in a world where humans are altering the environment both rapidly and in different ways, the demographic causes of decline likely vary over time. Identifying temporal variation in demographic causes of decline is crucial to assure that conservation actions target current and not past threats. However, this has rarely been studied as it requires long time series. Here we investigate how the demography of a long‐lived shorebird (the Eurasian Oystercatcher Haematopus ostralegus) has changed in the past four decades, resulting in a shift from stable dynamics to strong declines (−9% per year), and recently back to a modest decline. Since individuals of this species are likely to respond differently to environmental change, we captured individual heterogeneity through three state variables: age, breeding status, and lay date (using integral projection models). Timing of egg‐laying explained significant levels of variation in reproduction, with a parabolic relationship of maximal productivity near the average lay date. Reproduction explained most variation in population growth rates, largely due to poor nest success and hatchling survival. However, the demographic causes of decline have also been in flux over the last three decades: hatchling survival was low in the 2000s but improved in the 2010s, while adult survival declined in the 2000s and remains low today. Overall, the joint action of several key demographic variables explain the decline of the oystercatcher, and improvements in a single vital rate cannot halt the decline. Conservations actions will thus need to address threats occurring at different stages of the oystercatcher's life cycle. The dynamic nature of the threat landscape is further supported by the finding that the average individual no longer has the highest performance in the population, and emphasizes how individual heterogeneity in vital rates can play an important role in modulating population growth rates. Our results indicate that understanding population decline in the current era requires disentangling demographic mechanisms, individual variability, and their changes over time. [ABSTRACT FROM AUTHOR]

Interactions between plants and soil biota are increasingly shown to play critical roles in plant species coexistence processes. Plant species coexistence is thought to be promoted via biotic legacies that plant species leave behind in the soil after a plant disappears. These soil legacies are hypothesised to supress colonisation success when the preceding plant is of the same species, that is, when a plant species encounters its own, species‐specific soil antagonists.However, colonisation of vacant spots in plant communities is in the first place determined by the ability of plants to reach such vacant locations. We currently lack an understanding of the explicit role of soil legacy effects and their relative contribution to colonisation processes in plant communities consisting of plant species inherently differing in colonisation ability.In experimental, outdoor plant communities consisting of eight grassland species, we tested the effect of five differently conditioned soil patches on plant species colonisation success over three consecutive growing seasons. We found that colonisation success was largely determined by the species' reproductive strategy, lateral spread and growth rate, and not by the plant species that conditioned the soil patch. Fast spreading, clonal plant species reached the soil patches first and initially attained the highest biomass inside the patch. One year later, slower spreading plant species colonised the patch via seedlings. Species with intrinsically high growth rates attained the highest biomass, decreasing biomass of the initial colonisers. While subtle differences between conditioned soil patches did occur, these were not strong enough to overcome the inherent differences in colonisation ability between the various plant species.Synthesis. Our results reject the hypothesis that colonisation of vacant soil patches in plant communities is strongly affected by the legacy that is left behind by the preceding plant species. Instead, plant species life‐history strategy plays a prominent role, driving sequential plant species replacements. Based on our results and recent accounts in literature we present a conceptual model for local cyclic dynamics in grassland communities, where soil legacy plays a role in affecting the performance of established plant species rather than colonisation of vacant patches. [ABSTRACT FROM AUTHOR]

Aim: In many species, density‐dependent effects on reproduction are an important driver of population dynamics. However, it is rarely considered that the direction of density dependence is expected to vary over space and time depending on anti‐predator behaviour and predator community. Aggregation may allow for effective group mobbing against avian nest predators while aggregation may also attract mammalian predators, causing negative density dependence. We aim to quantify spatial variation in the effect of conspecific breeding density on nest survival in a mobbing bird species (Eurasian oystercatcher; Haematopus ostralegus) and identify whether this variation in density dependence can be explained by the predator community. Location: Country‐wide (The Netherlands). Methods: We integrated reproductive data with breeding territory maps of Eurasian oystercatchers and occupancy maps of avian and mammalian predator species across the Netherlands for a 10‐year period. Results: Spatial variation in the composition of the predator community explained the effects of neighbour density, showing decreasing nest survival when both conspecific density and mammalian dominance increased. Also, heterospecific density (from breeding godwits and lapwing) has an additional effect on the oystercatcher nest survival. Strikingly, this pattern did not extend to mammal‐free island populations. Main conclusions: Our study provides evidence that both the strength and sign of density dependence can vary spatially within species, implying that it is dangerous to generalize results from a single local population to large‐scale management implications and modelling exercises. The study also suggests that conservation actions that aim to attract breeding birds should be prioritized in areas with fewer mammalian predators, but this idea requires further testing on island populations. [ABSTRACT FROM AUTHOR]

Body condition is an important concept in behaviour, evolution and conservation, commonly used as a proxy of an individual's performance, for example in the assessment of environmental impacts. Although body condition potentially encompasses a wide range of health state dimensions (nutritional, immune or hormonal status), in practice most studies operationalize body condition using a single (univariate) measure, such as fat storage. One reason for excluding additional axes of variation may be that multivariate descriptors of body condition impose statistical and analytical challenges.Structural equation modelling (SEM) is used in many fields to study questions relating multidimensional concepts, and we here explain how SEM is a useful analytical tool to describe the multivariate nature of body condition. In this 'Research Methods Guide' paper, we show how SEM can be used to resolve different challenges in analysing the multivariate nature of body condition, such as (a) variable reduction and conceptualization, (b) specifying the relationship of condition to performance metrics, (c) comparing competing causal hypothesis and (d) including many pathways in a single model to avoid stepwise modelling approaches. We illustrated the use of SEM on a real‐world case study and provided R‐code of worked examples as a learning tool.We compared the predictive power of SEM with conventional statistical approaches that integrate multiple variables into one condition variable: multiple regression and principal component analyses. We show that model performance on our dataset is higher when using SEM and led to more accurate and precise estimates compared to conventional approaches.We encourage researchers to consider SEM as a flexible framework to describe the multivariate nature of body condition and thus understand how it affects biological processes, thereby improving the value of body condition proxies for predicting organismal performance. Finally, we highlight that it can be useful for other multidimensional ecological concepts as well, such as immunocompetence, oxidative stress and environmental conditions. [ABSTRACT FROM AUTHOR]

The temporal and spatial dynamics of soil water are closely interlinked with terrestrial ecosystems functioning. The interaction between plant community properties such as species composition and richness and soil water mirrors fundamental ecological processes determining above‐ground–below‐ground feedbacks. Plant–water relations and water stress have attracted considerable attention in biodiversity experiments. Yet, although soil scientific research suggests an influence of ecosystem productivity on soil hydraulic properties, temporal changes of the soil water content and soil hydraulic properties remain largely understudied in biodiversity experiments. Thus, insights on how plant diversity—productivity relationships affect soil water are lacking.Here, we determine which factors related to plant community composition (species and functional group richness, presence of plant functional groups) and soil (organic carbon concentration) affect soil water in a long‐term grassland biodiversity experiment (The Jena Experiment).Both plant species richness and the presence of particular functional groups affected soil water content, while functional group richness played no role. The effect of species richness changed from positive to negative and expanded to deeper soil with time. Shortly after establishment, increased topsoil water content was related to higher leaf area index in species‐rich plots, which enhanced shading. In later years, higher species richness increased topsoil organic carbon, likely improving soil aggregation. Improved aggregation, in turn, dried topsoils in species‐rich plots due to faster drainage of rainwater. Functional groups affected soil water distribution, likely due to plant traits affecting root water uptake depths, shading, or water‐use efficiency. For instance, topsoils in plots containing grasses were generally drier, while plots with legumes were moister.Synthesis. Our decade‐long experiment reveals that the maturation of grasslands changes the effects of plant richness from influencing soil water content through shading effects to altering soil physical characteristics in addition to modification of water uptake depth. Functional groups affected the soil water distribution by characteristic shifts of root water uptake depth, but did not enhance exploitation of the overall soil water storage. Our results reconcile previous seemingly contradictory results on the relation between grassland species diversity and soil moisture and highlight the role of vegetation composition for soil processes. The effect of plant species richness on soil water content in the Jena Experiment changed with time after establishment, and was related at the beginning to aboveground (canopy) and later to belowground (soil organic carbon, roots) processes. In contrast, each plant functional group affected soil water distribution in a characteristic fashion that did not change with time, but varied in strength between years. Overall, the analysis suggests that recovery of soil functions after abandonment of arable farming may benefit from higher grassland diversity as a follow up land use, which likely feeds back on other ecosystem functions. [ABSTRACT FROM AUTHOR]

Abstract: Below‐ground resource partitioning is among the most prominent hypotheses for driving the positive biodiversity–ecosystem function relationship. However, experimental tests of this hypothesis in biodiversity experiments are scarce, and the available evidence is not consistent. We tested the hypothesis that resource partitioning in space, in time or in both space and time combined drives the positive effect of diversity on both plant productivity and total community resource uptake. At the community level, we predicted that total community resource uptake and biomass production above‐ and below‐ground will increase with increased species richness or functional group richness. We predicted that, at the species level, resource partition breadth will become narrower, and that overlap between the resource partitions of different species will become smaller with increasing species richness or functional group richness. We applied multiple resource tracers (Li and Rb as potassium analogues, the water isotopologues—H218O and 2H2O, and 15N) in three seasons at two depths across a species and functional group richness gradient at a grassland biodiversity experiment. We used this multidimensional resource tracer study to test if plant species partition resources with increasing plant diversity across space, time or both simultaneously. At the community level, total community resource uptake of nitrogen and potassium and above‐ and below‐ground biomass increased significantly with increasing species richness but not with increasing functional group richness. However, we found no evidence that resource partition breadth or resource partition overlap decreased with increasing species richness for any resource in space, time or both space and time combined. Synthesis. These findings indicate that below‐ground resource partitioning may not drive the enhanced resource uptake or biomass production found here. Instead, other mechanisms such as facilitation, species‐specific biotic feedback or above‐ground resource partitioning are likely necessary for enhanced overall ecosystem function. [ABSTRACT FROM AUTHOR]

Summary: There is consensus that plant species richness enhances plant productivity within natural grasslands, but the underlying drivers remain debated. Recently, differential accumulation of soil‐borne fungal pathogens across the plant diversity gradient has been proposed as a cause of this pattern. However, the below‐ground environment has generally been treated as a ‘black box’ in biodiversity experiments, leaving these fungi unidentified. Using next generation sequencing and pathogenicity assays, we analysed the community composition of root‐associated fungi from a biodiversity experiment to examine if evidence exists for host specificity and negative density dependence in the interplay between soil‐borne fungi, plant diversity and productivity. Plant species were colonised by distinct (pathogenic) fungal communities and isolated fungal species showed negative, species‐specific effects on plant growth. Moreover, 57% of the pathogenic fungal operational taxonomic units (OTUs) recorded in plant monocultures were not detected in eight plant species plots, suggesting a loss of pathogenic OTUs with plant diversity. Our work provides strong evidence for host specificity and negative density‐dependent effects of root‐associated fungi on plant species in grasslands. Our work substantiates the hypothesis that fungal root pathogens are an important driver of biodiversity‐ecosystem functioning relationships. [ABSTRACT FROM AUTHOR]

Abstract: Lianas are structural parasites of trees and reduce individual host tree growth, survival and fecundity. Thus, liana infestation is expected to affect tree population growth rates, with potentially different effects in different species depending on the frequency of liana infestation and the impact of liana infestation on population growth rates. Previous studies have documented the myriad negative effects of lianas on trees and variation in liana infestation among tree species; however, no study has quantified the impact of liana infestation on individual tree species population growth rates. Lianas are increasing in abundance in multiple Neotropical sites, which may have profound consequences for tree species composition if lianas differentially affect host tree species population growth. Here, we use long‐term data to evaluate the effects of liana infestation on the reproduction, growth, survival and ultimately population growth rates of dozens of tree species from Barro Colorado Island, Panama. We then test whether liana infestation affects tree species differentially with respect to two axes of life‐history variation: adult stature and position along the fast–slow axis, a measure of shade tolerance. Liana infestation decreased tree growth, survival and reproduction, with the strongest effects on survival in fast‐growing, light‐demanding species and on reproduction in large‐statured species. In combination, these effects reduced tree population growth rates such that liana‐infested populations declined by an average of 1.4% annually relative to conspecific liana‐free populations. The reduction in population growth rates was greatest among fast‐growing species and smaller in slow‐growing species. Synthesis. Our results demonstrate that liana infestation has strong negative effects on tree population growth rates, which vary systematically among tree species with tree life history. The finding that liana infestation is more harmful to fast‐growing tree species appears to be at odds with the general expectations in the literature. We propose that this is likely due to survivorship bias, as infestation greatly decreases survival in fast‐growing species such that the observable sample is biased towards those that survived and liana‐free. In combination with data on how tree species vary in liana infestation rates, these results provide a basis for predicting the impacts of changes in liana abundance on tree species composition. [ABSTRACT FROM AUTHOR]

Abstract: Questions: The rapid climate warming in tundra ecosystems can increase nutrient availability in the soil, which may initiate shifts in vegetation composition. The direction in which the vegetation shifts will co‐determine whether Arctic warming is mitigated or accelerated, making the understanding of successional trajectories urgent. One of the key factors influencing the competitive relationships between plant species is their access to nutrients, depending on the depth where they take up most nutrients. However, nutrient uptake at different soil depths by tundra plant species that differ in rooting depth is unclear. Location: Kytalyk Nature Reserve, northeast Siberia, Russia. Methods: We injected 15N to 5 cm, 15 cm and the thaw front of the soil in a moist tussock tundra. The absorption of 15N by grasses, sedges, deciduous shrubs and evergreen shrubs from the three depths was compared. Results: The results clearly show a vertical differentiation of N uptake by these plant functional types, corresponding to their rooting strategy. Shallow‐rooting dwarf shrubs were more capable of absorbing nutrients from the upper soil than from deeper soil. Deep‐rooting grasses and sedges were more capable of absorbing nutrients from deeper soil than the dwarf shrubs. The natural 15N abundances in control plants also indicate that graminoids can absorb more nutrients from the deeper soil than dwarf shrubs. Conclusions: Our results show that graminoids and shrubs in the Arctic differ in their N uptake strategies, with graminoids profiting from nutrients released at the thaw front, while shrubs mainly forage in upper soil layers. Our results suggest that tundra vegetation will become graminoid‐dominated as permafrost thaw progresses and nutrient availability increases in the deep soil. [ABSTRACT FROM AUTHOR]

Below-ground resource partitioning is often proposed as the underlying mechanism for the positive relationship between plant species richness and productivity. For example, if species have different root distributions, a mixture of plant species may be able to use the available resources more completely than the individual species in a monoculture. However, there is little experimental evidence for differentiation in vertical root distributions among species and its contribution to biodiversity effects., We determined species-specific root standing biomass over depth using molecular techniques (real-time qPCR) in a large grassland biodiversity experiment (one to eight plant species mixtures), in 2 years. Species-specific root biomass data were used to disentangle the effects of positive interactions between species (complementarity effects) and effects due to dominance of productive species (selection effects) on root biomass in mixtures. In a next step, these biodiversity effects were linked to the diversity of rooting depths and the averaged rooting depth of the community., Root biomass increased with species richness. This was mainly due to positive interactions (the complementarity effect), which increased with species richness below-ground. In contrast, the selection effect decreased with species richness. Although there was considerable variation in vertical root distribution between species in monocultures, the diversity of rooting strategies did not explain the complementarity effect. Rather, the abundance of deep-rooting species in mixtures (i.e. high community-weighted mean) was significantly related to the complementarity effect. Comparing the 'predicted' root distribution (based on monocultures) to the actual distribution in mixtures, we found that mixtures rooted deeper than expected, but this did not better explain the complementarity effect., Synthesis. This study demonstrates that vertical root distributions of species provide only subtle evidence for resource partitioning. We found no evidence that functional diversity in vertical rooting patterns was important for the complementarity effect, in contrast to our expectation that the enhancement of productivity was due to resource partitioning. Alternatively, we found significant but weak relationships between the complementarity effect and deep-rooting communities, based on the community-weighted mean root distribution. This suggests that factors other than below-ground resource partitioning alone may drive the biodiversity-productivity relationship. [ABSTRACT FROM AUTHOR]

1. Plant roots selectively forage for soil nutrients when these are heterogeneously distributed. In turn, effects of plant roots on biotic and abiotic conditions in the soil, which result in socalled plant–soil feedback can be heterogeneously distributed as well, but it is unknown how this heterogeneity affects root distribution, nutrient uptake and plant biomass production. Here, we investigate plant root distribution patterns as influenced by spatial heterogeneity of plant–soil feedback in soil and quantify consequences for plant nitrogen uptake and biomass production. 2. We conditioned soils by four grassland plant species to obtain ‘own’ and ‘foreign’ soils that differed in biotic conditions similar as is done by the first phase of plant–soil feedback experiments. We used these conditioned soils to create heterogeneous (one patch of own and three patches of foreign soils) or homogeneous substrates where own and foreign soils were mixed. We also included sterilized soil to study the effect of excluding soil biota, such as pathogens, symbionts and decomposers. We supplied 15N as tracer to measure nutrient uptake. 3. In nonsterile conditions, most plant species produced more biomass in heterogeneous than in homogeneous soil. Root biomass and 15N uptake rates were higher in foreign than own soil patches. These differences between heterogeneous and homogeneous soil disappeared when soil was sterilized, suggesting that the effects in non-sterilized soils were due to species-specific soil biota that had responded to soil conditioning. 4. We conclude that plants produce more biomass when own and foreign soils are patchily distributed than when mixed. We show that this enhanced productivity is due to nutrient uptake being overall most efficient when own and foreign soils are spatially separated. We propose that spatial heterogeneity of negative plant–soil feedback in species diverse plant communities may provide a better explanation of overyielding than assuming that plant–soil feedback effects are diluted. [ABSTRACT FROM AUTHOR]

Biodiversity experiments generally report a positive effect of plant biodiversity on aboveground biomass (overyielding), which typically increases with time. Various studies also found overyielding for belowground plant biomass, but this has never been measured over time. Also, potential underlying mechanisms have remained unclear. Differentiation in rooting patterns among plant species and plant functional groups has been proposed as a main driver of the observed biodiversity effect on belowground biomass, leading to more efficient belowground resource use with increasing diversity, but so far there is little evidence to support this. We analyzed standing root biomass and its distribution over the soil profile, along a 1-16 species richness gradient over eight years in the Jena Experiment in Germany, and compared belowground to aboveground overyielding. In our long-term dataset, total root biomass increased with increasing species richness but this effect was only apparent after four years. The increasingly positive relationship between species richness and root biomass, explaining 12% of overall variation and up to 28% in the last year of our study, was mainly due to decreasing root biomass at low diversity over time. Functional group composition strongly affected total standing root biomass, explaining 44% of variation, with grasses and legumes having strong overall positive and negative effects, respectively. Functional group richness or interactions between functional group presences did not strongly contribute to overyielding. We found no support for the hypothesis that vertical root differentiation increases with species richness, with functional group richness or composition. Other explanations, such as stronger negative plant-soil feedbacks in low-diverse plant communities on standing root biomass and vertical distribution should be considered. [ABSTRACT FROM AUTHOR]

The importance of competition has been defined as the impact or role of competition relative to the total impact of the environment, and the intensity of competition is its absolute impact. Understanding the distinction has been proposed as key in reconciling long-running ecological debates., An index of competition importance, Cimp, has been used in a number of recent studies. Rees, Childs & Freckleton (2012) present a strong attack on the competition index Cimp (and the associated interaction index Iimp) and question the underlying rationale for the concept of competition importance. We assess their critique and challenge it in a number of areas., Rees et al. conflate criticism of the index Cimp with criticism of the concept of competition importance. Their approach to assessing the properties of Cimp (and Iimp), including the use of target plant success in the absence of neighbours ( PNC) as a measure of environmental severity, is biased towards demonstrating a simple linear relationship between severity and Cimp, and supporting the argument that there is no need for separate measurements of importance., We consider the proposal by Rees et al. for the use of variance partitioning to assess importance. Although providing a measure of the relative role of competition, it is unable to assess the shape of the importance-severity relationship, something central to testing important ecological theories such as those of Grime (1979) or Bertness & Callaway (1994). We discuss alternative approaches which might address this question., Synthesis. Responding to Rees et al. has been beneficial in clarifying points of difference between our approaches, and the need to visualize the shape of the importance-severity relationship. From this response we draw three broad conclusions. We need: (i) metrics of environmental severity that are independent of the success of target species; (ii) analytical approaches that avoid the statistical problems associated with ratios whilst enabling us to assess the shape of the severity-importance relationship; (iii) new data to assess the generality of proposed relationships. Studies incorporating these elements will take forward our understanding of the role of competition in plant communities. [ABSTRACT FROM AUTHOR]

Summary [ABSTRACT FROM AUTHOR]

Summary 1. Plants are known to respond to heterogeneous distribution of nutrients in the soil, and they also respond to the presence of neighbouring roots. However, it is unclear whether plants are able to distinguish between these factors and adjust their root responses accordingly. 2. We investigated whether the simultaneous response to nutrient heterogeneity and competition could be predicted from the responses to these factors separately. As a null model, we hypothesized that the responses to nutrients and competition are additive and thus no interactions occur. We performed a short-term competition experiment in the greenhouse with two floodplain species in homogeneous and heterogeneous conditions. The consequences of different root distributions for nutrient uptake were tested using 15N pulse-labelling. 3. Both species responded to nutrient heterogeneity by investing significantly more roots in the nutrient-rich patch, and both species showed a significant reduction in root growth in response to competition, albeit that the reduction was much more pronounced for the grass species. For Rumex palustris, the effects of heterogeneity and competition were additive. However, the response to nutrient heterogeneity of Agrostis stolonifera was reversed by competition: instead of proliferating in the nutrient-rich patch, it significantly increased root investments in the 'empty' (nutrient-poor) patches. As the partitioning of total N was less asymmetric than 15N uptake from the nutrient-rich patch, it appears that these altered root investments of A. stolonifera in the 'empty' patches have also been functional with respect to compensating N uptake. 4. Our results suggest that root responses to nutrient distribution in a competitive environment depend on the competitive strength of the neighbouring species. The foraging response of the superior species ( R. palustris) was hardly affected, but that of the inferior species ( A. stolonifera) was greatly inhibited and even reversed by competition: instead of proliferating in the nutrient-rich patch, it increased root growth and foraging activity in less favourable patches. Incorporating competitive hierarchy into root foraging studies may help to explain the ambiguous results found in previous studies. [ABSTRACT FROM AUTHOR]

Summary 1. Although a major part of plant biomass is underground, we know little about the contribution of different species to root biomass in multispecies communities. We summarize studies on root distributions and plant responses to species-specific soil biota and formulate three hypotheses to explain how root responses may drive species coexistence and ecosystem productivity. 2. Recent studies suggest that root growth of some species may be stimulated in species mixtures compared with monocultures without hampering the growth of other species, leading to below-ground overyielding. Further studies suggest that these responses are the result of reduced impairment of growth by species-specific plant pathogens that accumulate in monocultures. 3. First, we hypothesize that due to pathogen-constrained growth, monocultures are 'under-rooted', i.e. they do not have enough roots for optimal acquisition of nutrients. Although elevated root production in mixtures represents a cost to the plant, improved nutrition will eventually result in improved plant performance. 4. Second, due to the plant species specificity of the soil biotic communities, we suggest that plant species in mixtures develop an intransitive competitive network in which none of the species is competitively superior to all other species. Competitive intransitivity is proposed as a mechanism of species coexistence. 5. As a final hypothesis, we suggest that pathogen-mediated root overproduction in species mixtures determines the patterns of community productivity and overyielding, both directly, by improving plant performance, and indirectly, by releasing more carbon into the soil, resulting in enhanced availability of nutrients. 6. Synthesis.Recent evidence suggests that species coexistence and ecosystem productivity may be the result of an interplay between pathogen-driven plant responses and nutritional consequences. We suggest that responses of the roots are an important yet mostly overlooked intermediary between soil biota and plant community responses to biodiversity. [ABSTRACT FROM AUTHOR]

Summary 1. Scaling theory predicts that organisms respond to different scales of resource patchiness in relation to their own size. We tested the hypothesis that the scale of nutrient patchiness mediates resource partitioning between large trees and small grasses in a semi-arid savanna. 2. In a factorial field experiment, Colophospermum mopane trees and associated grasses were fertilized at either a fine or coarse scale of patchiness with nitrogen (N), phosphorus (P) or N + P. The growth of marked tree shoots, herbaceous biomass and leaf N and P concentrations were monitored for 2 years following fertilization. 3. Responses of trees were partly scale dependent. Tree leaf N concentration and shoot length relatively increased with fertilization at a coarse scale. Tree leaf mass decreased when P was supplied at a fine scale of patchiness, suggesting intensified grass competition. 4. Phosphorus fertilization increased leaf P concentrations more in grasses than trees, whereas N fertilization increased leaf N concentration moderately in both trees and grasses. Herbaceous above-ground biomass around focal trees was negatively correlated with tree size when fertilized with N, suggesting intensified tree competition. 5. Synthesis. Our results support the hypothesis that trees benefit more from nutrients supplied at a relatively coarse scale of patchiness. No direct responses of grasses to scale were detected. In trees, the scale effect was surpassed by the effect of sample year, when rainfall varied. [ABSTRACT FROM AUTHOR]

• Plants can respond to their environment by morphological plasticity. Generally, the potential benefits of adaptive plastic responses are beyond doubt under predictable environmental changes. However, the net benefits may be less straightforward when plants encounter temporal stresses, such as flooding in river flood plains. • Here, we tested whether the balance of costs and benefits associated with flooding-induced shoot elongation depends on the flooding regime, by subjecting Rumex palustris plants with different elongation capacity to submergence of different frequency and duration. • Our results showed that reaching the surface by shoot elongation is associated with fitness benefits, as under less frequent, but longer, flooding episodes plants emerging above the floodwater had greater biomass production than plants that were kept below the surface. As we predicted, slow-elongating plants had clear advantages over fast-elongating ones if submergence was frequent but of short duration, indicating that elongation also incurs costs. • Our data suggest that high costs select for weak plasticity under frequent environmental change. In contrast to our predictions, however, fast-elongating plants did not have an overall advantage over slow-elongating plants when floods lasted longer. This indicates that the delicate balance between benefits and costs of flooding-induced elongation depends on the specific characteristics of the flooding regime. [ABSTRACT FROM AUTHOR]

1. Plant diversity has profound effects on primary production. Plant diversity has been shown to correlate with increased primary production in nutrient-limited grassland ecosystems. This overyielding has been attributed to vertical niche differentiation among species below-ground, allowing for complementarity in resource capture. However, a rigorous test of this longstanding hypothesis is lacking because roots of different species could not be distinguished in diverse communities. 2. Here, we present the first application of a DNA-based technique that quantifies species abundances in multispecies root samples. We were thus able to compare root distributions in monocultures of two grasses and two forbs with root distributions in four-species mixtures. In order to investigate if vertical niche differentiation is driven by soil nutrient depletion, the topsoil layer of the communities were either nutrient-rich or -poor. 3. Immediately in the first year, 40% more root biomass was produced in mixtures than expected from the monocultures, together with significant below-ground complementarity effects, probably preceding above-ground overyielding. This below-ground overyielding appeared not to be the result of vertical niche differentiation, as rooting depth of the community tended to decrease, rather than increase in mixtures compared to monocultures. Roots thus tended to clump in the very dense topsoil layer rather than segregate over the whole profile in mixtures. The below-ground overyielding was mainly driven by enhanced root investments of one species, Anthoxanthum odoratum, in the densely rooted topsoil layer without retarding the growth of the other species. 4. Synthesis. Conventional ecological mechanisms, such as competition for nutrients, do not seem to be able to explain the increased root investments of A. odoratum in mixtures compared to monocultures, with apparently little effect on the root growth of the other species. Instead, the observed root responses are consistent with species-specific root recognition responses. From a community perspective, the observed early below-ground overyielding may initiate the recently reported increased soil organic matter, mineralization and N availability and thus may ultimately be responsible for the higher productivity at high plant species diversity. [ABSTRACT FROM AUTHOR]

Ecology Letters (2010) 13: 736–743 Climate change not only affects mean temperature and precipitation but also exacerbates temporal fluctuations in these conditions. However, we know relatively little about how species respond to such climate fluctuations, with respect to variation in vital rates (i.e. survival, growth and reproduction of individuals) and population fluctuations. We examine whether populations display evidence of buffering against environmental variation in one of two ways: (1) through negative covariances among vital rates, or (2) reduction of variation in those vital rates to which population growth is most sensitive. We analyse time series of demographic data for 40 plant species and show that there is no evidence for either of these mechanisms. In species in which there is evidence for vital rate covariation, positive covariances between reproduction and survival rates predominate, and tend to magnify the effect of variability. Increasing climate variability is therefore expected to increase population fluctuations and extinction risks. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 λ) 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 λs) 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. [ABSTRACT FROM AUTHOR]

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 (λ) 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 λ 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 λ 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. [ABSTRACT FROM AUTHOR]

1. An increasing body of evidence suggests that within-species diversity plays an important role for community and ecosystem functioning, alters complex trophic interactions and affects patterns of species diversity and coexistence. Nonetheless, we lack a good understanding of how genotypic trait variation translates into shifts in the relative abundance of genotypes within populations. 2. In this study, we show that genotypic selection strongly alters dominance relationships among genotypes over a period of 5 years. This resulted in remarkably consistent changes in the proportional representation of genotypes, and in a concomitant decline of diversity and evenness in our experimental populations. 3. High growth rates and the production of large offspring were positively associated with genotypic performance. Vegetative abundances of genotypes translated monotonically into flowering frequencies. 4. Synthesis. We conclude that genotypic selection markedly affects patterns of diversity and consistently alters genotypic abundance and mean trait distributions in plant populations over a relatively short period of time. [ABSTRACT FROM AUTHOR]

In this paper we examined the notion that plant foraging for resources in heterogeneous environments must involve: (1) plasticity at the level of individual modules in reaction to localized environmental signals; and (2) the potential for modification of these responses either by the signals received from connected modules that may be exposed to different conditions, or by the signals reflecting the overall resource status of the plant. A conceptual model is presented to illustrate how plant foraging behaviour is achieved through these processes acting in concert, from the signal reception through signal transduction to morphological or physiological response. Evidence to support the concept is reviewed, using selective root placement under nutritionally heterogeneous conditions and elongation responses of stems and petioles to shade as examples. We discussed how the adoption of this model can promote understanding of the ecological significance of foraging behaviour. We also identified a need to widen the experimental repertoires of both molecular physiology and ecology in order to increase our insight into both the regulation and functioning of foraging responses, and their relationship with the patterns of environmental heterogeneity under which plants have evolved. [ABSTRACT FROM AUTHOR]

1. Globally, both climatic patterns and nitrogen deposition rates show directional changes over time. It is uncertain how woody seedlings, which coexist with herbaceous plants in savannas, respond to concurrent changes in water and nutrient availability. 2. We investigated competition effects between herbaceous vegetation and tree seedlings ( Colophospermum mopane) under changed water and nutrient (fertilized) conditions in a garden experiment situated in a semi-arid savanna. 3. Herbaceous competition significantly suppressed woody seedling growth. The effect of herbaceous competition on woody seedling growth remained constant with both increasing water and nutrient availability. However, during a wet-season drought, herbaceous competition apparently caused premature leaf senescence in non-irrigated treatments. Fertilization exacerbated negative competition effects during the drought, while irrigation prevented leaf loss of tree seedlings in spite of herbaceous competition and fertilization. 4. Based on a conceptual model, we propose that the vigorous response of herbaceous plants to increased nutrient availability leads to faster depletion of soil water, which increasingly causes water stress in woody seedlings if the interval between watering events is prolonged, e.g. during wet-season droughts. 5. Synthesis. Our data support the notion that changes in drought frequency are of greater importance to woody recruitment success than changes in annual rainfall amount. Based on the water and nutrient interactions observed in our experiment, we suggest that the effect of increased nitrogen deposition on woody seedling recruitment is contingent on water availability. [ABSTRACT FROM AUTHOR]

• Ethylene is a strong controller of root development, and it has been suggested that it is involved in the increase of lateral root development in nutrient-rich soil patches (selective root placement). Here, this contention was tested by comparing selective root placement of an ethylene-insensitive transgenic tobacco ( Nicotiana tabacum) genotype (Tetr) with that of wild-type (Wt) plants. • Wt and Tetr plants were grown in pots with locally increased nitrate or phosphate concentrations, after which the root growth patterns were compared with those of plants grown in pots with homogeneous nutrient distribution. • Tetr plants responded to nutrient patches in a similar way to Wt plants, by placing their roots preferentially at locations with higher nutrient content, and other aspects of plant morphology were also not greatly influenced by ethylene insensitivity. The response of both Wt and Tetr plants to high-nitrate patches was considerably stronger than to locally high phosphate, suggesting that the two responses are not linked in any functional or regulatory way. • As the response to nutrient patches was similar in ethylene-sensing and ethylene-insensitive plants, it is concluded that selective root placement in response to nitrate or phosphate is, at least in tobacco, not mediated or modified by ethylene action. [ABSTRACT FROM AUTHOR]

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 oil 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. [ABSTRACT FROM AUTHOR]

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 Hylocolmium 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 seventies. Under the same average disturbance severity, H. splendens population growth rates are highest in acyclic scenarios and are progressively reduced with increasing peak disturbance seventies (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. [ABSTRACT FROM AUTHOR]

1 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. 2 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. 3 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. 4 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. 5 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. 6 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. [ABSTRACT FROM AUTHOR]

The article presents a study that introduces and applies a new approach in evaluating the sustainability of nontimber forest products, such as palms, in the U.S. tropical forests. The new approach combines the two demographic analyses of matrix population models, the prospective and retrospective analyses. The first analysis relates harvest effect on vital rates with their importance for population growth rate, while the second analysis includes a life table response experiment (LTRE) to detect the contributions of vital rate changes to change in population growth rate. The LTRE analysis was then applied to Geonoma deversa, a clustered forest understory palm, which shows that commercial leaf cutting in the palm is potentially sustainable.

• We tested whether the degree of shade-induced plasticity in petiole length and leaf area is related to the mean trait value expressed under high-light conditions, and to what extent trait values expressed under high-light and shaded conditions affect plant performance. • Thirty-four Trifolium repens genotypes were used with a wide range of petiole lengths and leaf areas. Plants were subjected to a high-light environment and two shading regimes: homogeneous shading and a vertical light gradient. • Absolute petiole elongation in response to both shading treatments and absolute leaf area expansion in response to homogeneous shading were independent of the trait values expressed in high light. Consequently, relative plasticity was higher for genotypes with lower high-light trait values. Plasticity was associated with enhanced plant performance in a vertical light gradient but not in homogeneously shaded conditions. We also found costs associated with the ability to express plasticity. • Our results suggest that selection can act separately on trait values expressed under high-light conditions and on the degree of plasticity. [ABSTRACT FROM AUTHOR]

1 Plant performance of species in river floodplains is negatively affected by submergence, due to severely hampered gas exchange under water. Several individual traits have been shown to determine flooding tolerance, but the interrelationships among these traits and their effects on plant performance still remain largely unknown. 2 Here, we aim for a more coherent understanding of submergence tolerance, by investigating whether different traits are alternative strategies to enhance survival under water or whether these traits act in concert. 3 Because responses to submergence may be taxon-specific, we chose a multiple-species approach that allowed phylogenetic comparisons. The phenotypic traits investigated in the current study were constitutively different in species originating from frequently flooded habitats than in species from dry habitats: wet species were taller and had a higher specific leaf area (SLA), chlorophyll content, aerenchyma content, and longer longevity of terrestrial and ‘aquatic’ leaves compared with species from dry habitats. Moreover, the frequently flooded species appeared to be more plastic for these traits in response to submergence. Neither the phylogenetic component nor the light climate under water were important for the expression of the submergence-related traits. 4 Principal component analysis (PCA) showed that these traits were divided in two independent clusters structured either around the petiole (i.e. aerenchyma content and shoot length) or the leaf lamina (i.e. SLA, chlorophyll content and leaf longevity). Shoot length and aerenchyma content of the petiole were also positively correlated, albeit not significantly. A positive correlation between SLA and leaf longevity was observed under water, indicating that thinner leaves may have an increased potential for gas exchange, resulting in increased leaf longevity and plant survival. 5 Path analyses indicated significant positive effects of the two trait clusters on plant performance during full submergence. 6 Our study shows that multiple ecophysiological traits act in concert to fine tune responses to dynamic and unpredictable environments such as river floodplains. [ABSTRACT FROM AUTHOR]

1 Many plant species are currently restricted to small and isolated populations as a result of habitat destruction and fragmentation. Lack of sufficient data often leads to spatial variation being substituted for temporal variation in models to evaluate management options, but variation in population growth rate (λ) between sites or over years may be caused by variation in different life history components. 2 We studied the demography of three coexisting and related perennial herbs (the long-lived perennial Succisa pratensis, the shorter-lived Hypochaeris radicata and the long-lived, but more clonal Centaurea jacea) in the same plots over 4 years (1999–2003). 3 Life table response experiment analysis revealed that temporal and spatial variation in the life history components of S. pratensis and H. radicata were qualitatively different: variation in fecundity contributed most to variation in λ between sites, but variation in growth contributed most to variation between years. 4 In years with a below average λ, most life history components of S. pratensis and H. radicata had lower transition probabilities, whereas the reasons for low population growth differed between the three poor sites. All major life history components of S. pratensis had lower probabilities in the most productive of these sites, but in the other two, negative contributions from some components (fecundity or growth) were partly compensated for by positive contributions from others (growth or stasis). 5 Centaurea jacea showed a different pattern: in poor years, negative contributions from some life history components were buffered by positive contributions from other components; however, this buffering did not occur in poor sites. 6 Our analysis shows that the population dynamics of perennial plants may respond differently to temporal and spatial variation in environmental conditions. Moreover, co-occurring species with similar life histories responded differently to the same spatiotemporal variation. We conclude that temporal and spatial dynamics cannot readily be interchanged in population viability analyses and management studies, as such substitution may lead to incorrect projections of a species’ population dynamics in time. Journal of Ecology (2005) doi: 10.1046/j.0022-0477.2005.01003.x [ABSTRACT FROM AUTHOR]

• Terrestrial plants experience multiple stresses when they are submerged, caused both by oxygen deficiency due to reduced gas diffusion in water, and by shade due to high turbidity of the floodwater. It has been suggested that responses to submergence arede factoresponses to low light intensity.• We investigated the extent to which submergence and shade induce similar acclimation responses by comparing two terrestrialRumexspecies that differ in their responses to flooding.• Our study confirms that there are strong similarities between acclimation responses to shade and submergence. Petiole length, specific leaf area (SLA), chlorophyll parameters and underwater light-compensation points changed at least qualitatively in the same direction. Maximum underwater photosynthesis rate, however, did discriminate between the functionality of the responses, as the acclimation to submergence appeared to be more effective than acclimation to shade at saturating light.• We conclude that acclimation to submergence involves more than an increase in SLA to achieve the significant reduction of diffusion resistance for gas exchange between leaves and the water column.New Phytologist(2005)doi: 10.1111/j.1469-8137.2005.01404.x© New Phytologist(2005) [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Based on empirical evidence from the literature we propose that, in nature, phenotypic plasticity in plants is usually expressed at a subindividual level. While reaction norms (i.e. the type and the degree of plant responses to environmental variation) are a property of genotypes, they are expressed at the level of modular subunits in most plants. We thus contend that phenotypic plasticity is not a whole-plant response, but a property of individual meristems, leaves, branches and roots, triggered by local environmental conditions. Communication and behavioural integration of interconnected modules can change the local responses in different ways: it may enhance or diminish local plastic effects, thereby increasing or decreasing the differences between integrated modules exposed to different conditions. Modular integration can also induce qualitatively different responses, which are not expressed if all modules experience the same conditions. We propose that the response of a plant to its environment is the sum of all modular responses to their local conditions plus all interaction effects that are due to integration. The local response rules to environmental variation, and the modular interaction rules may be seen as evolving traits targeted by natural selection. Following this notion, whole-plant reaction norms are an integrative by-product of modular plasticity, which has far-reaching methodological, ecological and evolutionary implications.New Phytologist(2005)doi: 10.1111/j.1469-8137.2004.01310.x© New Phytologist(2005) [ABSTRACT FROM AUTHOR]

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 site 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. [ABSTRACT FROM AUTHOR]

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. Journal of Ecology (2004) 92, 696–706 [ABSTRACT FROM AUTHOR]

Question: Does disturbance reduce competition intensity and thus favour weak competitors that are presumably less affected by disturbance than strong competitors? Methods: We used a single flooding event with increasing duration to simulate disturbance with increasing intensity. Six flood-plain grass species, typical of different flood regimes were grown in monocultures and in an additive species mixture. Flooding took place early in the first growing season and changes were monitored until the end of the second growing season. Results: Longer flooding durations initially decreased competition, but only a single species (Agrostis) increased its abundance in mixtures after flooding. The two weakest competitors in our selection (Poa trivialis and Elytrigia repens) failed to benefit them flooding because direct losses from flooding exceeded gains from reduced competition. Accordingly, we found no trade-off between flooding tolerance and competitive ability indicating that floods affect strong and weak competitors equally, although some species tolerated floods better than others. Conclusions: Since competition is only temporarily weakened after disturbance, increased competitive ability relative to other species may provide a more effective strategy for persistence in flood-disturbed sites. Above-ground runners seem an important prerequisite for enhanced competitive ability of clonal species in flood-disturbed sites. [ABSTRACT FROM AUTHOR]

Plants growing at high densities express shade avoidance traits as a response to the presence of neighbours. Enhanced shoot elongation is one of the best researched shade avoidance components and increases light capture in dense stands. We show here that also leaf movements, leading to a more vertical leaf orientation (hyponasty), may be crucial in the early phase of competition. The initiation of shade avoidance responses is classically attributed to the action of phytochrome photoreceptors that sense red:far-red (R:FR) ratios in light reflected by neighbours, but also other signals may be involved. It was recently shown that ethylene-insensitive, transgenic (Tetr) tobacco plants, which are insensitive to the gaseous plant hormone ethylene, have reduced shade avoidance responses to neighbours. Here, we report that this is not related to a reduced response to low R:FR ratio, but that Tetr tobacco plants are unresponsive to a reduced photon fluence rate of blue light, which normally suppresses growth inhibition in wild-type (WT) plants. In addition to these light signals, ethylene levels in the canopy atmosphere increased to concentrations that could induce shade avoidance responses in WT plants. Together, these data show that neighbour detection signals other than the R:FR ratio are more important than previously anticipated and argue for a particularly important role for ethylene in determining plant responses to neighbours. [ABSTRACT FROM AUTHOR]

In a garden experiment we investigated the response to continuous removal of either flower buds or rosette buds in three perennial grassland species ( Hypochaeris radicata, Succisa pratensis and Centaurea jacea), which differ in longevity and flowering type. We distinguished two possible responses: compensation for lost buds by making more buds of the same type, and switching towards development of other life history functions. Both responses were demonstrated in our experiment, but bud removal had significantly different effects in each of the three species. The degree of compensation and the expression of trade-offs between life history functions differed markedly between species and seem related to longevity and developmental constraints. With respect to switching, our results suggest costs of reproduction and a trade-off between life history functions, at least for Hypochaeris and Succisa. For these species weight of new rosettes increased when resource allocation to flowering was inhibited. In Hypochaeris, we see that both compensation for lost flower buds and switching from lost rosette buds increased production of flower buds, underscoring the pivotal role of sexual reproduction in this short-lived species. The most prominent response seen in Centaurea is compensation for lost rosette buds, indicating that this long-lived species with monocarpic rosettes relies on rosette formation. Although Succisa does respond to bud removal, time is an important constraint in this species with long-lived rosettes and preformed flowering stalks. Trade-offs in Succisa seem to operate at a larger time scale, requiring long-lasting experiments to reveal them. We conclude that the response of these species to inflicted damage is likely to be linked to their longevity and developmental constraints. [ABSTRACT FROM AUTHOR]

Summary 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... [ABSTRACT FROM AUTHOR]

Investigates the effects of nutrient heterogeneity on the competition between the perennial grass species Anthoxanthum odoratum L. and Festuca rubra L. Relation of root foraging ability of species with a competitive advantage in heterogeneous soils; Root activity assessment through the determination of the amount of strontium captured by a species; Role of physiological plasticity in obtaining a long-term competitive advantage.

Savanna trees have a multitude of positive and negative effects on understorey grass production, but little is known about how these effects interact. We report on a fertilization and shading experiment carried out in a Tanzanian tropical dry savanna around Acacia tortilis trees. In two years of study there was no difference in grass production under tree canopies or in open grassland. Fertilization, however, indicate that trees do affect the nutrient limitation of the grass layer with an N-limited system in open grassland to a P-limited system under the trees. The N:P ratios of grass gave a reliable indication of the nature of nutrient limitation, but only when assessed at the end of the wet season. Mid-wet season nutrient concentrations of grasses were higher under than outside the tree canopy, suggesting that factors other than nutrients limit grass production. A shading experiment indicated that light may be such a limiting factor during the wet season when water and nutrients are sufficiently available. However, in the dry season when water is scarce, the effect of shade on plant production became positive. We conclude that whether trees increase or decrease production of the herbaceous layer depends on how positive effects (increased soil fertility) and negative effects (shade and soil availability) interact and that these interactions may significantly change between wet and dry seasons. [ABSTRACT FROM AUTHOR]

Summary 1The 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. 2Canopy 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). 3Both 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. 4The 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, λ = 1.012), with the survival of mature segments making an overwhelming contribution to its growth rate. The higher λ (1.740) in the Removal population was associated with higher elasticities of branching. Clipping reduced λ 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. 5Life table response experiment analyses revealed that almost all demographic processes including branching and the survival of mature segments contributed to the increased λ in Removal treatment. The relatively small decrease in λ 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... [ABSTRACT FROM AUTHOR]

Studies vegetation pattern formation in semi-arid grazing system. Spatially explicit model describing the dynamics of three state variables; Turing conditions for pattern formation; Homogenous equilibiria.

Investigates the applications of elasticity analysis, its extension, loop analysis, in demographic studies and conservation. Definition of elasticity; Details on the results of two analyses in studies of life histories; Mathematical properties and biological constraints explaining the limitations of elasticity models.