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Unmanned aerial systems offer a cost-effective and reproducible method for monitoring natural resources in expansive areas. But the transferability of developed models, which are often based on single snapshots, is rarely tested. This is particularly relevant in rangelands where forage resources are inherently patchy in space and time, which may limit model transfer. Here, we investigated the accuracy of drone-based models in estimating key proxies of forage provision across two land tenure systems and between two periods of the growing season in semi-arid rangelands. We tested case-specific models and a landscape model, with the expectation that the landscape model performs better than the case-specific models as it captures the highest variability expected in the rangeland system. The landscape model did achieve the lowest error when predicting herbaceous biomass and predicted land cover with better or similar accuracy to the case-specific models. This reinforces the importance of incorporating the widest variation of conditions in predictive models. This study contributes to understanding model transferability in drier rangeland systems characterized by spatial and temporal heterogeneity. By advancing the integration of drone technology for accurate monitoring of such dynamic ecosystems, this research contributes to sustainable rangeland management practices. [ABSTRACT FROM AUTHOR]

Heavy metal hyperaccumulation (MH) is a rare trait found in plant species that inhabit metal‐contaminated soils. Two main hypotheses proposed to explain the selective advantage of MH are the elemental defence hypothesis and elemental allelopathy hypothesis. The elemental defence hypothesis suggests that MH functions as defence against herbivores while the elemental allelopathy hypothesis suggests that MH acts to inhibit the growth of neighbours. Nevertheless, these hypotheses are not likely to be mutually exclusive. Here, we present the first study to test both hypotheses simultaneously. We examined these hypotheses with the Cd hyperaccumulator, Arabidopsis halleri, which inhabits both metalliferous and non‐metalliferous soils, thus providing an opportunity to test the hypotheses of both habitats.Arabidopsis halleri plants originating from several populations in both metalliferous and non‐metalliferous soils were grown in a greenhouse in soils with or without cadmium (Cd). Their leaves were used in a feeding experiment with a specialist herbivore and in a set of leaf‐leachate experiments that tested their effect on seed germination and seedling establishment of species co‐occurring with A. halleri. Finally, a field survey in several A. halleri populations was conducted to compare herbivore load between A. halleri and neighbours from metalliferous versus non‐metalliferous soils.Results of the feeding experiment and field survey suggest that Cd accumulation in A. halleri leaves could provide it with defence against herbivores. Results of the leaf‐leachate experiments reveal that Cd accumulation has no effect on seed germination of neighbouring species but inhibits seedling establishment, particularly of plant species originating from non‐metalliferous soils.Our results suggest that both herbivores and competing neighbours may jointly select for MH in plants. Moreover, MH could provide a selective advantage particularly in non‐metalliferous soils, where neighbouring plants lack metal tolerance. These results highlight the importance of including different origins and populations of both the target species and its neighbouring plant species when studying the ecological role of MH. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Invasive plants typically escape specialist herbivores but are often attacked by generalist herbivores in their introduced ranges. The shifting defense hypothesis suggests that this will cause invasive plants to evolve lower resistance against specialists, higher resistance against generalists, and greater tolerance to herbivore damage. However, the duration and direction of selective pressures can shape the evolutionary responses of resistance and tolerance for invasive plants. Two critical factors are (1) residence time (length of time that an invasive species has been in its introduced range) and (2) specialist herbivore reassociation (attack by purposely or accidentally introduced specialists). Yet, these two factors have not been considered simultaneously in previous quantitative syntheses. Here, we performed a meta-analysis with 367 effect sizes from 70 studies of 35 invasive plant species from native and invasive populations. We tested how the residence time of invasive plant species and specialist reassociation in their introduced ranges affected evolutionary responses of defenses against specialists and generalists, including herbivore resistance traits (physical barriers, digestibility reducers and toxins), resistance effects (performance of and damage caused by specialists or generalists) and tolerance to damage (from specialists or generalists). We found that residence time and specialist reassociation each significantly altered digestibility reducers, specialist performance, generalist damage, and tolerance to specialist damage. Furthermore, residence time and specialist reassociation strongly altered toxins and generalist performance, respectively. When we restricted consideration to invasive plant species with both longer residence times and no reassociation with specialists, invasive populations had lower resistance to specialists, similar resistance to generalists, and higher tolerance to damage from both herbivore types, compared with native populations. We conclude that the duration and direction of selective pressure shape the evolutionary responses of invasive plants. Under long-term (long residence time) and stable (no specialist reassociation) selective pressure, invasive plants generally decrease resistance to specialists and increase tolerance to generalist damage that provides mixed support for the shifting defense hypothesis. [ABSTRACT FROM AUTHOR]

Summary: Plant–plant interactions are reciprocal and include effects on and response to neighbours. Distinct traits confer competitive effect and response ability, but how specific traits determine effect and response in facilitative interactions has not been studied experimentally.We utilized the model species Arabidopsis thaliana to test for trait dependence of facilitative interactions. Salt‐sensitive (sos) mutants or salt‐tolerant wild‐types were exposed to an experimental salinity gradient with and without intraspecific neighbours and the intensity of plant–plant interactions was measured for three performance variables. We tested whether salt tolerance can predict facilitative effect and response and whether a tradeoff exists between competitive ability and tolerance to stress.Interactions shifted very clearly from negative to positive with increasing stress. Salt‐sensitive genotypes were less negatively affected by competition but more dependent on facilitation than were wild‐types, indicating a tradeoff between competitive ability and stress tolerance. Surprisingly, sensitive genotypes imposed stronger facilitative effects, despite being much smaller under stress, probably because they retrieved more salt from the soil.Stress tolerance defined facilitative effect and response via distinct mechanisms. We advocate more controlled experiments with model species to advance our understanding of the trait dependence of biotic interactions and their consequences for community organization. [ABSTRACT FROM AUTHOR]

Plant-plant interactions may critically modify the impact of climate change on plant communities. However, the magnitude and even direction of potential future interactions remains highly debated, especially for water-limited ecosystems. Predictions range from increasing facilitation to increasing competition with future aridification., The different methodologies used for assessing plant-plant interactions under changing environmental conditions may affect the outcome but they are not equally represented in the literature. Mechanistic experimental manipulations are rare compared with correlative approaches that infer future patterns from current observations along spatial climatic gradients., Here, we utilize a unique climatic gradient in combination with a large-scale, long-term experiment to test whether predictions about plant-plant interactions yield similar results when using experimental manipulations, spatial gradients or temporal variation. We assessed shrub-annual interactions in three different sites along a natural rainfall gradient (spatial) during 9 years of varying rainfall (temporal) and 8 years of dry and wet manipulations of ambient rainfall (experimental) that closely mimicked regional climate scenarios., The results were fundamentally different among all three approaches. Experimental water manipulations hardly altered shrub effects on annual plant communities for the assessed fitness parameters biomass and survival. Along the spatial gradient, shrub effects shifted from clearly negative to mildly facilitative towards drier sites, whereas temporal variation showed the opposite trend: more negative shrub effects in drier years., Based on our experimental approach, we conclude that shrub-annual interaction will remain similar under climate change. In contrast, the commonly applied space-for-time approach based on spatial gradients would have suggested increasing facilitative effects with climate change. We discuss potential mechanisms governing the differences among the three approaches., Our study highlights the critical importance of long-term experimental manipulations for evaluating climate change impacts. Correlative approaches, for example along spatial or temporal gradients, may be misleading and overestimate the response of plant-plant interactions to climate change. [ABSTRACT FROM AUTHOR]

Background and Aims The enemy release hypothesis assumes that invasive plants lose their co-evolved natural enemies during introduction into the new range. This study tested, as proposed by the evolution of increased competitive ability (EICA) hypothesis, whether escape from enemies results in a decrease in defence ability in plants from the invaded range. Two straightforward aspects of the EICA are examined: (1) if invasives have lost their enemies and their defence, they should be more negatively affected by their full natural pre-invasion herbivore spectrum than their native conspecifics; and (2) the genetic basis of evolutionary change in response to enemy release in the invasive range has not been taken sufficiently into account. Methods Lythrum salicaria (purple loosestrife) from several populations in its native (Europe) and invasive range (North America) was exposed to all above-ground herbivores in replicated natural populations in the native range. The experiment was performed both with plants raised from field-collected seeds as well as with offspring of these where maternal effects were removed. Key Results Absolute and relative leaf damage was higher for introduced than for native plants. Despite having smaller height growth rate, invasive plants attained a much larger final size than natives irrespective of damage, indicating large tolerance rather than effective defence. Origin effects on response to herbivory and growth were stronger in second-generation plants, suggesting that invasive potential through enemy release has a genetic basis. Conclusions The findings support two predictions of the EICA hypothesis – a genetically determined difference between native and invasive plants in plant vigour and response to enemies – and point to the importance of experiments that control for maternal effects and include the entire spectrum of native range enemies. [ABSTRACT FROM PUBLISHER]

Summary 1. Abiotic stress and interactions with neighbours are major selective forces but their relative importance for local adaptation has rarely been separated. Plant community theory predicts increasing importance of competition with decreasing stress. We experimentally separated the role of neighbours and drought stress for local adaptation of two annual plant species. We predicted that neighbours amplify patterns of local adaptation with adaptation to competition prevailing in benign habitats. 2. During one growing season, we combined reciprocal transplants with neighbour removals along a gradient of more than an eightfold increase in annual rainfall using populations from sites representative of Arid, Semi-arid, Mediterranean and Mesic Mediterranean ecosystems. We evaluated statistical interactions between origin and planting site with and without neighbours and quantified plant-plant interaction importance. 3. An extreme drought (<63% of the average annual rainfall at the arid sites) reduced the probability of detecting neighbour effects. There was weak but non-significant evidence for local adaptation and for the amplification of adaptation patterns with neighbours for populations from wetter sites of the two species. Our results together with previous findings in similar gradients suggest that detecting local adaptation to neighbours in unpredictable environments depends on the climatic conditions of the study season. 4. We coupled a central concept from plant community ecology with an evolutionary approach to separate the role of abiotic vs. biotic factors for local adaptation. This permits quantifying the importance of interactions with neighbours and we advocate its use in future studies of local adaptation, which should be conducted over several years. [ABSTRACT FROM AUTHOR]

Morphological plasticity is a striking characteristic of plants in natural communities. In the context of foraging behavior particularly, root plasticity has been documented for numerous species. Root plasticity is known to mitigate competitive interactions by reducing the overlap of the individuals' rhizospheres. But despite its obvious effect on resource acquisition, plasticity has been generally neglected in previous empirical and theoretical studies estimating interaction intensity among plants. In this study, we developed a semi-mechanistic model that addresses this shortcoming by introducing the idea of compensatory growth into the classical-zone-of influence (ZOI) and field-of-neighborhood (FON) approaches. The model parameters describing the belowground plastic sphere of influence (PSI) were parameterized using data from an accompanying field experiment. Measurements of the uptake of a stable nutrient analogue at distinct distances to the neighboring plants showed that the study species responded plastically to belowground competition by avoiding overlap of individuals' rhizospheres. An unexpected finding was that the sphere of influence of the study species Bromus hordeaceus could be best described by a unimodal function of distance to the plant's center and not with a continuously decreasing function as commonly assumed. We employed the parameterized model to investigate the interplay between plasticity and two other important factors determining the intensity of competitive interactions: overall plant density and the distribution of individuals in space. The simulation results confirm that the reduction of competition intensity due to morphological plasticity strongly depends on the spatial structure of the competitive environment. We advocate the use of semi-mechanistic simulations that explicitly consider morphological plasticity to improve our mechanistic understanding of plant interactions. [ABSTRACT FROM AUTHOR]

Bet hedging is a means to increase fitness in environments that vary unpredictably in space and time. In such environments, models predict a trade-off between the bet-hedging strategies dispersal and dormancy, while the increasing importance of risk reduction with decreasing predictability should lead to an increase in dispersal and dormancy along gradients of environmental predictability. However, so far there has been no experimental study to test these predictions in the field. Here, we used a set of novel field experiments that enabled us to quantify and separate seedling recruitment from three sources: local reproduction, dormancy, and dispersal. The study included the entire plant community from five environments differing considerably in predictability. Evidence for both the existence of a trade-off between dispersal and dormancy within environments and their increased use in unpredictable environments was very weak. The importance of dispersal for population and community dynamics in our system was extremely low relative to dormancy and local reproduction. This indicates that the role of dispersal for buffering environmental variation may be negligible compared with other risk-reducing strategies. Our findings highlight the urgent need for multispecies and multisite experiments in empirical tests of theoretical predictions. [ABSTRACT FROM AUTHOR]

1. Recent models on bet-hedging germination in annual plants assume a negative relationship between the proportion of offspring that germinate and the quality of the maternal environment. An increase in the proportion of seeds remaining dormant in the next year, when produced in seasons with high reproduction may result from selection that avoids overcrowding in the following year. 2. We present the first empirical test of this prediction by utilizing a field experiment in Israel which manipulated the entire maternal environment. We subjected semi-arid and Mediterranean annual plant communities to different rainfall treatments: control, reduced and increased rainfall. We then related maternal environment quality to offspring germination fractions for three focal species in two consecutive seasons. 3. There was a negative relationship between the quality of the maternal environment and offspring germination fraction in four out of twelve cases. The negative relationship was stronger for the least competitive species and in the environment with high competition intensity, supporting the role of competition for the observed pattern. 4. Our results suggest that competition with all neighbours is more likely to explain the pattern than sib competition. 5. Synthesis. Our findings provide the first experimental evidence of a highly reliable cue (productivity of maternal environment) that allows for plants to respond to their future biotic environment. There is an urgent need for testing predictions of theoretical models in natural populations and for incorporating the role of density dependence in studies of bet-hedging germination. [ABSTRACT FROM AUTHOR]

Question: Which mechanisms promote the maintenance of the protected pioneer grass Corynephorus canescens in a mosaic landscape? Which are the interactive effects of small-scale disturbances, successional stage and year-to-year variation on early establishment probabilities of C. canescens? Location: Brandenburg, NE Germany. Methods: We measured emergence and survival rates over 3 yr in a sowing-experiment conducted in three successional stages ( C. canescens-dominated site, ruderal forb site and pioneer forest) under two different regimes of mechanical ground disturbance (disturbed versus undisturbed control). Results: Overall, disturbance led to higher emergence in a humid year and to lower emergence in a very dry year. Apparently, when soil moisture was sufficient, the main factor limiting C. canescens' establishment was competition, while in the dry year, water became the limiting factor. Survival rates were not affected by disturbance. In humid years, C. canescens emerged in higher numbers in open successional stages while in the dry year, emergence rates were higher in late stages, suggesting an important role of late successional stages for the persistence of C. canescens. Conclusions: Our results suggest that small-scale disturbances can promote germination of C. canescens. However, disturbances should be carefully planned. The optimal strategy for promoting C. canescens is to apply disturbances just before seed dispersal and not during dry years. At the landscape scale, a mosaic of different vegetation types is beneficial for the protected pioneer grass as facilitation by late-successional species may be an important mechanism for the persistence of C. canescens, especially in dry years. [ABSTRACT FROM AUTHOR]

Question: Species composition during secondary succession is influenced by a number of factors, such as soil moisture, disturbance timing and surrounding vegetation. How does the importance of these factors change over the course of succession? Methods: We set up a full-factorial block design using molehills differing in (a) disturbance timing, (b) soil moisture and (c) composition of surrounding vegetation, and recorded the cover of all species present on the molehills over 3 years. M1ultiple regression analyses on the dissimilarity matrices of community composition and of environmental factors were applied for each of five age classes of molehills to estimate the effect of the single factors at different stages of succession. Results: The timing of disturbance did not significantly affect community composition at any stage of succession. In contrast, the effects of soil moisture and surrounding vegetation changed significantly over time, with moisture being more important at earlier stages of succession and surrounding vegetation at later stages. Conclusion: The importance of environmental factors for species composition change significantly over the course of secondary succession. Instead of aggregating the effects of environmental factors over time, future studies should consider underlying dynamics of recolonization more comprehensively. [ABSTRACT FROM AUTHOR]

The timing of seedling emergence may strongly affect fitness in competitive environments. Therefore, selection should favour mechanisms that allow sensing neighbours prior to emergence. We tested whether or not germination is affected by density and identity of neighbouring seeds or seedlings of desert perennial plants. Based on theory, we predicted that germination fractions are independent of neighbouring seeds, that germination is accelerated in dense interspecific neighbourhoods, and neighbour effects are caused by seedlings, not by seeds. We examined germination fraction and timing of four naturally coexisting sandy desert perennial species in low versus high seed densities in both intra- and interspecific neighbourhoods, and with and without removal of newly emerged seedlings. Neighbours accelerated germination independent of density and this pattern was apparently caused by the presence of early emerging seedlings. Germination fractions were lower in high seed densities even when neighbours did not germinate, indicating that seeds were able to sense each other prior to emergence. Early germination may be adaptive because fast emerging seedlings may gain a competitive edge over slow emerging ones. However, since seeds that did not germinate died, delayed germination may only be advantageous for mother plants when sib competition is intense. Another key finding was a competitive hierarchy with late successional species germinating faster and inhibiting germination of pioneer species. This indicates that successional processes may be directed as early as during germination. [ABSTRACT FROM AUTHOR]

1. Local adaptation is a major factor shaping a species’ range. Studies on adaptation to local abiotic conditions are numerous, but adaptation to neighbour conditions has been almost neglected, and these two have rarely been separated experimentally. We hypothesized that adaptation to abiotic stress (e.g. fast development, drought resistance) dominates at the stressful end of the gradient, while adaptation to competition (e.g. large plant size) is more common at the benign end of the distribution range. 2. We conducted a reciprocal sowing experiment coupled with a removal experiment in the field for two winter annual grass species Bromus fasciculatus C. Presl. and Brachypodium distachyon (L.) Beauv. from Mediterranean and arid populations in Jordan. The two species were also grown under standard conditions for evaluating whether traits indicative of competitive ability and tolerance to stress are more common for either of the ecotypes. 3. Adaptation to abiotic stress could not be tested because our experiment was performed in a favourable year where water was not limiting in either of the sites. Competition was intense in both sites for the two populations of each species but competitive exclusion was observed only in the Mediterranean site. Mediterranean populations produced consistently more biomass and exhibited later onset of flowering than arid populations, both in the field and under standard conditions. 4. Mediterranean populations also showed better competitive response ability however stress tolerance was no different to that of arid populations. 5. This study indicates that competition and length of the growing season are major selective constraints at the two extremes of the ecological range along aridity gradients. We suggest that drought stress increases in importance during dry years and studies on local adaptation along climatic gradients may help predict the effect of global change on future species’ distributions. [ABSTRACT FROM AUTHOR]

The role of local adaptation and factors other than climate in determining extinction probabilities of species under climate change has not been yet explicitly studied. Here we performed a field experiment with annual plants growing along a steep climatic gradient in Israel to isolate climatic effects for local trait expression. The focus trait was seed dormancy, for which many theoretical predictions exist regarding climate-driven optimal germination behaviour. We evaluated how germination is consistent with theory, indicating local adaptation to current and changing climatic conditions, and how it varies among species and between natural and standardised soil conditions. We reciprocally sowed seeds from three or four origins for each of three annual species, Biscutella didyma, Bromus fasciculatus and Hymenocarpos circinnatus, in their home and neighbouring sowing locations along an aridity gradient. Our predictions were: lower germination fraction for seeds from more arid origins, and higher germination at wetter sowing locations for all seed origins. By sowing seeds in both local and standard soil, we separated climatic effects from local conditions. At the arid sowing location, two species supported the prediction of low germination of drier seed origins, but differences between seed origins at the other sites were not substantial. There were no clear rainfall effects on germination. Germination fractions were consistently lower on local soil than on standard soil, indicating the important role of soil type and neighbour conditions for trait expression. Local environmental conditions may override effects of climate and so should be carefully addressed in future studies testing for the potential of species to adapt or plastically respond to climate change. [ABSTRACT FROM AUTHOR]

1 Interactions among plants strongly influence the structure and dynamics of plant populations and communities. However, most empirical studies of plant–plant interactions failed to make repeated measures of responses to neighbouring individuals and thereby neglected possible changes in interactions throughout the life history of the plants. 2 We tested the hypothesis that competition between annual species intensifies from early to late life-history stages, by sequentially measuring interactions in neighbour-removal experiments at three study sites located along a rainfall gradient in Israel. 3 Two annual species, Biscutella didyma and Hymenocarpos circinnatus, grew with and without neighbours in their natural habitats. Five response variables representing consecutive life-history stages (seedling survival, juvenile biomass, adult survival, number of seeds and final biomass) were recorded throughout the whole growing season. 4 The direction and intensity of interactions varied considerably between environments and life stages. On average, growth-related response variables indicated higher competition intensity at the productive end of the climatic gradient, while survival indicated either facilitation at the dry end or no trend along the gradient. 5 Temporal changes occurred, with moderate facilitation soon after germination shifting to strong competition at the end of the growing season. 6 Our results demonstrate that the outcome of experimental studies on plant–plant interactions may depend not only on the environmental productivity but more so on the life stage at which the target plant is studied. [ABSTRACT FROM AUTHOR]

Environmental gradients represent an ideal framework for studying adaptive variation in the life history of plant species. However, on very steep gradients, largely contrasting conditions at the two gradient ends often limit the distribution of the same species across the whole range of environmental conditions. Here, we study phenotypic variation in a winter annual crucifer Biscutella didyma persisting along a steep gradient of increasing rainfall in Israel. In particular, we explored whether the life history at the arid end of the gradient indicates adaptations to drought and unpredictable conditions, while adaptations to the highly competitive environment prevail at the mesic Mediterranean end. We examined several morphological and reproductive traits in four natural populations and in populations cultivated in standard common environment. Plants from arid environments were faster in phenological development, more branched in architecture and tended to maximize reproduction, while the Mediterranean plants invested mainly in vertical vegetative growth. Differences between cultivation and field in diaspore production were very large for arid populations as opposed to Mediterranean ones, indicating a larger potential to increase reproduction under favorable conditions. Our overall findings indicate two strongly opposing selective forces at the two extremes of the aridity gradient, which result in contrasting strategies within the studied annual plant species. [ABSTRACT FROM AUTHOR]

Annual plants in unpredictable environments maintain dormant seeds to avoid extinction. Here, we present results for four desert annual species suggesting that germination rates are variable even in the absence of abiotic cues. Namely, seeds produced in a copious year had lower germination rates than seeds produced in drought years. Inspired by our data, we have extended previous bet-hedging models by including a structured seed bank. With density-dependence, the ESS (environmental stable strategy) involved a negative relationship between seed yield and subsequent germination probability. We suggest that heterogeneous germination rates are selected for by competition among seedlings after years with high seed production. In summary, our findings are suggestive of an intriguingly simple and effective mechanism that may allow annual plants to partly predict their future success. [ABSTRACT FROM AUTHOR]

Stress experienced during development in organisms with bilateral structures could result in developmental instability, which is expressed as subtle non‐directional deviations from perfect symmetry, known as fluctuating asymmetry (FA). As such, FA has been proposed, and extensively used, as a trait indicating stress for many organisms with bilateral structures and many types of stress. However, while this concept may apply to animals, the evidence for plants' main vegetative structures, that is, leaves, remains equivocal, and a comprehensive synthesis on this topic is still missing.We designed observational field and controlled greenhouse studies, combining different growth and leaf forms across multiple stress gradients, comprising 21 species and 80 populations. We measured FA as the difference between the left and right area of the leaf, an approach that accommodates diverse leaf forms. We used high‐precision, blind, single‐person measurements and tested for other forms of symmetry and the effect of leaf size. We further complemented our study with a systematic literature review of FA in plant leaves, compiling 51 studies comprising 72 species, 23 stress types and 131 unique entries (species × stress type).We consistently found no effect of stress on leaf FA in any of the studied species in both our field and experimental gradients. In the systematic literature review, only 39% of the unique entries showed the expected increase in FA with stress, 53% showed no effect, 9% showed an opposite trend of a decrease in FA with stress and 1% showed a unimodal relationship. Importantly, only 40% of all entries fulfilled the crucial step of controlling for a high‐precision measurement, and of these 49% reported the expected increase in FA with stress.Both the results of our observational and experimental approaches and the systematic literature review failed to support a clear relationship between stress and FA in plant leaves. These results clearly show that FA in plant leaves cannot be used as a reliable trait indicating stress during development. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Belowground niche partitioning presents a key mechanism for maintaining species coexistence and diversity. Its importance is currently reinforced by climate change that alters soil hydrological conditions. However, experimental tests examining the magnitude of its change under climate change are scarce. We combined measurements of oxygen stable isotopes to infer plant water‐uptake depths and extreme drought manipulation in grasslands. Belowground niche partitioning was evidenced by different water‐uptake depths of co‐occurring species under ambient and extreme drought conditions despite an increased overlap among species due to a shift to shallower soil layers under drought. A co‐occurrence of contrasting strategies related to the change of species water‐uptake depth distribution was likely to be key for species to maintain some extent of belowground niche partitioning and could contribute to stabilizing coexistence under drought. Our results suggest that belowground niche partitioning could mitigate negative effects on diversity imposed by extreme drought under future climate. [ABSTRACT FROM AUTHOR]

Litter decomposition rates are determined by the interplay of climate, decomposer organisms and litter quality. It has been suggested that the decomposer community may be locally adapted to litter quality, providing a home‐field advantage (HFA) resulting in accelerated decomposition of local compared to non‐local litter, after accounting for decomposition differences due to litter quality and the functional capacity of microorganisms. Although widely tested in forests, this hypothesis remains controversial and lacks support of its generality across climates.We therefore tested the HFA hypothesis for litter decomposition in four contrasting ecosystems along an extensive climatic gradient in Chile, using a translocation experiment involving litter from 20 species. In addition to comparing mass loss, we adopted a novel way to disentangle decomposer effects from climate effects, based on loss rates of elements that are actively released from the litter by decomposers during its breakdown versus elements that are simply leached by precipitation. We used the ratios of nitrogen and potassium losses (N/K loss) and phosphorus and potassium losses (P/K loss) to unravel the relative role of microbial breakdown (N and P loss) versus physical leaching (K loss) along the climate gradient. Thus, at each site, we tested whether litter mass loss, N/K loss and P/K loss presented an additional loss due to a HFA for local compared to non‐local litter.Across a wide range of environments and litter types, our findings unequivocally contradicted the HFA hypothesis. We observed no significantly positive HFA along the gradient; however, litter quality and the general ability of the decomposer community influenced litter decomposition much more strongly than origin or location of the litter.Our study questions the applicability of the HFA for litter decomposition and calls for more studies that include a large range of climatic conditions to understand the context‐dependency of HFA. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Abstract: Admixture is the hybridization between populations within one species. It can increase plant fitness and population viability by alleviating inbreeding depression and increasing genetic diversity. However, populations are often adapted to their local environments and admixture with distant populations could break down local adaptation by diluting the locally adapted genomes. Thus, admixed genotypes might be selected against and be outcompeted by locally adapted genotypes in the local environments. To investigate the costs and benefits of admixture, we compared the performance of admixed and within‐population F1 and F2 generations of the European plant Lythrum salicaria in a reciprocal transplant experiment at three European field sites over a 2‐year period. Despite strong differences between site and plant populations for most of the measured traits, including herbivory, we found limited evidence for local adaptation. The effects of admixture depended on experimental site and plant population, and were positive for some traits. Plant growth and fruit production of some populations increased in admixed offspring and this was strongest with larger parental distances. These effects were only detected in two of our three sites. Our results show that, in the absence of local adaptation, admixture may boost plant performance, and that this is particularly apparent in stressful environments. We suggest that admixture between foreign and local genotypes can potentially be considered in nature conservation to restore populations and/or increase population viability, especially in small inbred or maladapted populations. [ABSTRACT FROM AUTHOR]

Bet-hedging via between-year seed dormancy is a costly strategy for plants in unpredictable environments. Theoretically, fitness costs can be reduced through a parental environmental effect when the environment is partly predictable. We tested whether populations from environments that differ in predictability diverged in parental effects on seed dormancy., Common garden-produced seeds of the two annual plant species Biscutella didyma and Bromus fasciculatus collected along an aridity gradient were grown under 12 irrigation treatments. Offspring germination was evaluated and related to environmental correlations between generations and their fitness consequences at the four study sites., One species exhibited strong seed dormancy that increased with unpredictability in seasonal precipitation. The parental effect on seed dormancy also increased proportionally with the environmental correlation between precipitation in the parental season and seedling density in the following season; this correlation increased from mesic to arid environments. Because fitness was negatively related to density, this parental effect may be adaptive. However, the lack of dormancy in the second species indicates that bet-hedging is not the only strategy for annual plants in arid environments., Our results provide the first evidence for clinal variation in the relative strength of parental effects along environmental gradients. [ABSTRACT FROM AUTHOR]

Under climate change, extreme droughts will limit water availability for plants. However, the species‐specific responses make it difficult to draw general conclusions. We hypothesized that changes in species' abundance in response to extreme drought can be best explained by a set of water economic traits under ambient conditions in combination with the ability to adjust these traits towards higher drought resistance. We conducted a 4‐year field experiment in temperate grasslands using rainout shelters with 30% and 50% rainfall reduction. We quantified the response as the change in species abundance between ambient conditions and the rainfall reduction. Abundance response to extreme drought was best explained by a combination of traits in ambient conditions and their functional adjustment, most likely reflecting plasticity. Smaller leaved species decreased less in abundance under drought. With increasing drought intensity, we observed a shift from drought tolerance, i.e., an increase in leaf dry matter content, to avoidance, i.e., a less negative turgor loss point (TLP) in ambient conditions and a constancy in TLP under drought. We stress the importance of using a multidimensional approach of variation in multiple traits and the importance of considering a range of drought intensities to improve predictions of species' response to climate change. [ABSTRACT FROM AUTHOR]

In recent years, the effects of plastic contamination on soil and plants have received growing attention. Plastic can affect soil water content and thus may interact with the effects of drought on soil and plants. However, the effects of plastic on soil are highly context-dependent, and interactions with drought have been hardly tested. We conducted two greenhouse experiments to test the combined effects of plastic fragments (of varying size and concentration), water availability and soil texture, on soil water content and performance of the plant Arabidopsis thaliana. Plastic fragments had stronger negative effects on soil water content in low water availability, and the shape of this response (linear vs. unimodal) was mediated by soil texture. Conversely, increasing concentration of plastic had positive effects on plant growth. We suggest that plastic fragments introduce fracture points within soil aggregates. This increases number and size of soil pores favoring water loss but also facilitating root growth. Our results suggest complex interactive effects of plastic and drought, that may lead to a decoupling of plant and soil response. These processes should be taken into account in ecological studies and agricultural practices. [ABSTRACT FROM AUTHOR]

Summary: Phenology has emerged as key indicator of the biological impacts of climate change, yet the role of functional traits constraining variation in herbaceous species' phenology has received little attention. Botanical gardens are ideal places in which to investigate large numbers of species growing under common climate conditions. We ask whether interspecific variation in plant phenology is influenced by differences in functional traits.We recorded onset, end, duration and intensity of initial growth, leafing out, leaf senescence, flowering and fruiting for 212 species across five botanical gardens in Germany. We measured functional traits, including plant height, absolute and specific leaf area, leaf dry matter content, leaf carbon and nitrogen content and seed mass and accounted for species' relatedness.Closely related species showed greater similarities in timing of phenological events than expected by chance, but species' traits had a high degree of explanatory power, pointing to paramount importance of species' life‐history strategies. Taller plants showed later timing of initial growth, and flowered, fruited and underwent leaf senescence later. Large‐leaved species had shorter flowering and fruiting durations.Taller, large‐leaved species differ in their phenology and are more competitive than smaller, small‐leaved species. We assume climate warming will change plant communities' competitive hierarchies with consequences for biodiversity. [ABSTRACT FROM AUTHOR]

Litter decomposition is controlled by climate, litter quality and decomposer communities. Because the decomposition of specific litter types is also influenced by the properties of adjacent types, mixing litter types may result in non‐additive effects on overall decomposition rates. The strength of these effects seems to depend on the litter functional diversity. However, it is unclear which functional traits or combination of traits explain litter mixture effects and whether these depend on the range of trait values and the ecosystems involved. These uncertainties hamper our ability to predict decomposition in plant communities.We aimed at understanding whether and how functional diversity (measured as functional dispersion, FDis) influences litter decomposition, and how this influence varies among different climates and across decomposition stages. We calculated FDis based on litter traits related to nutrient concentrations or to litter recalcitrance, and tested whether these diversity measures and climatic parameters (soil moisture and temperature) explained litter mixture effects on decomposition.Additive mixture effects (i.e. decomposition of mixtures equalling the mean decomposition of the single litter types) were common in most of the evaluated climates. Non‐additive, negative effects were mainly restricted to the driest and warmest sites, and decreased with time. Non‐additive effects increased in magnitude with the mixtures' FDis, with positive effects being related to FDis in nutrient traits and negative effects being related to FDis in recalcitrance traits.Synthesis. Litter mixing did not have strong effects on decomposition rates across the studied climatic gradient overall, and the direction and intensity of the mixture effects were context dependent. The effects were stronger and more negative in the dryer ecosystems. Where effects were found, functional diversity calculated from selected groups of traits (related to nutrients or litter recalcitrance) predicted mixture effects, especially where trait ranges were broad, though much of the variation remains unexplained. We propose that functional diversity metrics based on litter traits that are mechanistically relevant, applied to diverse site‐specific litter mixtures in different climates, can help to better understand under which conditions and in which direction litter diversity affects decomposition. [ABSTRACT FROM AUTHOR]

Parental effects ( PE) can be adaptive and improve offspring performance when parents and offspring experience similar environmental conditions. However, it is unknown whether adaptive PE exist also in habitats where such similarity is unlikely due to strong temporal variation. In particular, we do not know whether PE can adapt offspring to fluctuating levels of neighbour competition in such habitats., Here, we tested for adaptive PE in terms of two key environmental factors in a semi-arid annual system, competition and drought. While rainfall was stochastic in the study site, the competitive environment was partly predictable: higher plant densities followed after favourable (rainy) years due to high seed production. We therefore expected PE to adapt the offspring's competitive ability to these (predictable) fluctuations in plant densities, rather than to adapt the offspring's drought tolerance to the (unpredictable) occurrence of intensified drought., Parental plants of Biscutella didyma, an annual Brassicaceae, were raised under favourable watering and under drought conditions. Offspring performance was then tested under a full-factorial combination of two neighbour regimes and six watering levels in the glasshouse., Offspring of parents grown under favourable conditions were stronger competitors. This was associated with a small shift in phenology but not with higher parental seed provisioning. Offspring from parents grown under drought showed no improved drought tolerance. Moreover, no PE were detectable when offspring were grown without neighbours., Our results suggest a novel path of adaptive PE: higher competitive ability was induced in offspring that were more likely to experience high neighbour densities. Together with the lack of adaptive PE towards drought tolerance, this emphasizes that a correlation between parental and offspring environment is crucial for adaptive PE to evolve. Our results also call for the inclusion of competitive effects in future PE studies., Synthesis. This study demonstrates the important role of adaptive PE for plant fitness (regarding competition) but also their limits (regarding drought) in temporally variable environments, based on the predictability of the respective environmental factor. [ABSTRACT FROM AUTHOR]

Altered rainfall regimes will greatly affect the response of plant species to climate change. However, little is known about how direct effects of changing precipitation on plant performance may depend on other abiotic factors and biotic interactions. We used reciprocal transplants between climatically very different sites with simultaneous manipulation of soil, plant population origin, and neighbor conditions to evaluate local adaptation and possible adaptive response of four Eastern Mediterranean annual plant species to climate change. The effect of site on plant performance was negligible, but soil origin had a strong effect on fecundity, most likely due to differential water retaining ability. Competition by neighbors strongly reduced fitness. We separated the effects of the abiotic and biotic soil properties on plant performance by repeating the field experiment in a greenhouse under homogenous environmental conditions and including a soil biota manipulation treatment. As in the field, plant performance differed among soil origins and neighbor treatments. Moreover, we found plant species-specific responses to soil biota that may be best explained by the differential sensitivity to negative and positive soil biota effects. Overall, under the conditions of our experiment with two contrasting sites, biotic interactions had a strong effect on plant fitness that interacted with and eventually overrode climate. Because climate and biotic interactions covary, reciprocal transplants and climate gradient studies should consider soil biotic interactions and abiotic conditions when evaluating climate change effects on plant performance. [ABSTRACT FROM AUTHOR]

Point pattern analyses such as the estimation of Ripley's K-function or the pair-correlation function g are commonly used in ecology to characterise ecological patterns in space. However, a major disadvantage of these methods is their missing ability to deal with spatial heterogeneity. A heterogeneous intensity of points causes a systematic bias in estimates of the K- and g-functions, a phenomenon termed “virtual aggregation” in the recent literature. To address this problem, we derive a new index, called K2-index, as an extension of existing point pattern characteristics. The K2-index has a heuristic interpretation as an approximation to the first derivative of the g-function. We estimate the K-, g- and K2-functions for six different types of simulated point patterns and show that the K2-index may provide important information on point patterns that the other methods fail to detect. The results indicate that particularly the small-scale distributions of points are better represented by the K2-index. This might be important for testing hypotheses on ecological processes, because most of these processes, such as direct neighbour interactions, occur very locally. When applied to empirical patterns of molehill distribution, the results of the K2-analysis show regularity up to distances between 0.1 and 0.4 m in most of the study areas, and aggregation of molehills up to distances between 0.2 and 1.1 m. The type and scale of these deviations from randomness agree with a priori expectations on the hill-building behaviour of moles. In contrast, the estimated g-functions merely indicate aggregation at the full range from 0 to 7 m (or even above). Considering the advantages and disadvantages of the different methods, we suggest that the K2-index should be used as a complement to existing approaches, particularly for point patterns generated by processes that act on more than one scale. [ABSTRACT FROM AUTHOR]

Catchment erosion and sedimentation are influenced by variations in the rates of rock uplift (tectonics) and periodic fluctuations in climate and vegetation cover. This study focuses on quantifying the effects of changing climate and vegetation on erosion and sedimentation over distinct climate–vegetation settings by applying the Landlab–SPACE landscape evolution model. As catchment evolution is subjected to tectonic and climate forcings at millennial to million-year timescales, the simulations are performed for different tectonic scenarios and periodicities in climate–vegetation change. We present a series of generalized experiments that explore the sensitivity of catchment hillslope and fluvial erosion as well as sedimentation for different rock uplift rates (0.05, 0.1, 0.2 mm a -1) and Milankovitch climate periodicities (23, 41, and 100 kyr). Model inputs were parameterized for two different climate and vegetation conditions at two sites in the Chilean Coastal Cordillera at ∼26 ∘ S (arid and sparsely vegetated) and ∼33 ∘ S (Mediterranean). For each setting, steady-state topographies were produced for each uplift rate before introducing periodic variations in precipitation and vegetation cover. Following this, the sensitivity of these landscapes was analyzed for 3 Myr in a transient state. Results suggest that regardless of the uplift rate, transients in precipitation and vegetation cover resulted in transients in erosion rates in the direction of change in precipitation and vegetation. The transients in sedimentation were observed to be in the opposite direction of change in the precipitation and vegetation cover, with phase lags of ∼1.5 –2.5 kyr. These phase lags can be attributed to the changes in plant functional type (PFT) distribution induced by the changes in climate and the regolith production rate. These effects are most pronounced over longer-period changes (100 kyr) and higher rock uplift rates (0.2 mm yr -1). This holds true for both the vegetation and climate settings considered. Furthermore, transient changes in catchment erosion due to varying vegetation and precipitation were between ∼35 % and 110 % of the background (rock uplift) rate and would be measurable with commonly used techniques (e.g., sediment flux histories, cosmogenic nuclides). Taken together, we find that vegetation-dependent erosion and sedimentation are influenced by Milankovitch timescale changes in climate but that these transient changes are superimposed upon tectonically driven rates of rock uplift. [ABSTRACT FROM AUTHOR]

Plants have been shown to change their foraging behaviour in response to resource heterogeneity. However, an unexplored hypothesis is that foraging could be induced by environmental stressors, such as herbivory, which might increase the demand for particular resources, such as those required for herbivore defence. This study examined the way simulated herbivory affects both root foraging for and uptake of cadmium (Cd), in the metal-hyperaccumulating plant Arabidopsis halleri, which uses this heavy metal as herbivore defence. Simulated herbivory elicited enhanced relative allocation of roots to Cd-rich patches as well as enhanced Cd uptake, and these responses were exhibited particularly by plants from non-metalliferous origin, which have lower metal tolerance. By contrast, plants from a metalliferous origin, which are more tolerant to Cd, did not show any preference in root allocation, yet enhanced Cd sharing between ramets when exposed to herbivory. These results suggest that foraging for heavy metals, as well as their uptake and clonal-sharing, could be stimulated in A. halleri by herbivory impact. Our study provides first support for the idea that herbivory can induce not only defence responses in plants but also affect their foraging, resource uptake and clonal sharing responses. [ABSTRACT FROM AUTHOR]

Plants have been shown to change their foraging behaviour in response to resource heterogeneity. However, an unexplored hypothesis is that foraging could be induced by environmental stressors, such as herbivory, which might increase the demand for particular resources, such as those required for herbivore defence. This study examined the way simulated herbivory affects both root foraging for and uptake of cadmium (Cd), in the metal-hyperaccumulating plant Arabidopsis halleri, which uses this heavy metal as herbivore defence. Simulated herbivory elicited enhanced relative allocation of roots to Cd-rich patches as well as enhanced Cd uptake, and these responses were exhibited particularly by plants from non-metalliferous origin, which have lower metal tolerance. By contrast, plants from a metalliferous origin, which are more tolerant to Cd, did not show any preference in root allocation, yet enhanced Cd sharing between ramets when exposed to herbivory. These results suggest that foraging for heavy metals, as well as their uptake and clonal-sharing, could be stimulated in A. halleri by herbivory impact. Our study provides first support for the idea that herbivory can induce not only defence responses in plants but also affect their foraging, resource uptake and clonal sharing responses. [ABSTRACT FROM AUTHOR]

Plants minimize fitness losses through grazing by three fundamental strategies: tolerance, avoidance and escape. Annual species have been traditionally assumed to escape grazing through their short life cycle and seed dormancy; however, their grazing response strategies remain almost unexplored. How traits and their coordination affect species' grazing responses, and whether the generalized grazing model, which posits convergent filtering by grazing and drought, is applicable to this ecologically and economically important species group thus remain unclear.We used a trait‐based approach to evaluate grazing response strategies of winter annuals from the Middle East. Across 23 species, we examined the coordination of 16 traits hypothesized to be relevant for grazing responses, and linked them to species' fecundity responses, as proxy for fitness responses, to simulated grazing in controlled conditions, to species' abundance responses to grazing in the field and to species' distribution along a large‐scale rainfall gradient.Winter annuals exhibited both grazing escape and to a lesser extent tolerance indicated by (a) independent coordination of escape and tolerance traits, and (b) maintenance of higher fecundity in species with more pronounced escape or tolerance traits under simulated grazing. In the natural habitat, species with a more pronounced escape but not tolerance strategy maintained higher abundance under grazing in dry habitats, indicating convergent favouring of escape by both grazing and drought. However, this finding at the local scale was not mirrored by a strategy shift along a large‐scale rainfall gradient.Synthesis. The convergent favouring of escape traits by grazing and drought in annuals is consistent with the generalized grazing model. This model, which has been developed for perennials based on the avoidance strategy, can thus be extended to annuals based on escape, a finding that should facilitate projecting consequences of global change in drylands dominated by annuals. [ABSTRACT FROM AUTHOR]

Climate and litter quality drive litter decomposition, but there is currently little consensus on their relative importance, likely because studies differ in the duration, the climatic gradients and variability in litter‐trait values. Understanding these drivers is important because they determine the direct and indirect (via vegetation composition) effects of climate change on decomposition and thereby on carbon and nutrient cycling.We studied how microclimate (soil moisture and temperature) and litter traits interactively affect litter mass loss, by using a reciprocal litter translocation experiment along a large climatic gradient in Chile. We followed decomposition for 2 years and used 30 plant species with a wide spectrum of functional‐trait values.Litter traits had a strong impact on litter decomposition across the gradient, while an increase in decomposition with soil moisture was observed only in the wettest climates. Overall, soil moisture increased considerably in importance, relative to trait effects, at later decomposition stages, from c. 15% of the importance of traits after 3 and 6 months to c. 110% after 24 months. Moreover, analysing subsets of the 30 species showed that trait effects on litter decomposition gained in importance when including a greater variation in trait values.Synthesis. The relative effects of litter traits and climate on decomposition depend on the ranges in climate and litter traits considered and change with time. Our study emphasizes the critical role of representative ranges in climate and functional trait values for understanding the drivers of litter decomposition and for improving predictions of climate‐change effects on this important ecosystem process. [ABSTRACT FROM AUTHOR]

Rapid evolution of traits and of plasticity may enable adaptation to climate change, yet solid experimental evidence under natural conditions is scarce. Here, we imposed rainfall manipulations (+30%, control, −30%) for 10 years on entire natural plant communities in two Eastern Mediterranean sites. Additional sites along a natural rainfall gradient and selection analyses in a greenhouse assessed whether potential responses were adaptive. In both sites, our annual target species Biscutella didyma consistently evolved earlier phenology and higher reproductive allocation under drought. Multiple arguments suggest that this response was adaptive: it aligned with theory, corresponding trait shifts along the natural rainfall gradient, and selection analyses under differential watering in the greenhouse. However, another seven candidate traits did not evolve, and there was little support for evolution of plasticity. Our results provide compelling evidence for rapid adaptive evolution under climate change. Yet, several non‐evolving traits may indicate potential constraints to full adaptation. [ABSTRACT FROM AUTHOR]

Summary: Global warming and reduced precipitation may trigger large‐scale species losses and vegetation shifts in ecosystems around the world. However, currently lacking are practical ways to quantify the sensitivity of species and community composition to these often‐confounded climatic forces. Here we conducted long‐term (16 yr) nocturnal‐warming (+0.6°C) and reduced precipitation (−20% soil moisture) experiments in a Mediterranean shrubland. Climatic niche groups (CNGs) – species ranked or classified by similar temperature or precipitation distributions – informatively described community responses under experimental manipulations. Under warming, CNGs revealed that only those species distributed in cooler regions decreased. Correspondingly, under reduced precipitation, a U‐shaped treatment effect observed in the total community was the result of an abrupt decrease in wet‐distributed species, followed by a delayed increase in dry‐distributed species. Notably, while partially correlated, CNG explanations of community response were stronger for their respective climate parameter, suggesting some species possess specific adaptations to either warming or drought that may lead to independent selection to the two climatic variables. Our findings indicate that when climatic distributions are combined with experiments, the resulting incorporation of local plant evolutionary strategies and their changing dynamics over time leads to predictable and informative shifts in community structure under independent climate change scenarios. [ABSTRACT FROM AUTHOR]

Water is one of the major drivers determining distribution and abundance of plant species. Namely, plant species’ presence and location in the landscape can be explained using metrics of soil water because plant species are restricted to a species-specific range of soil water conditions, i.e. their hydrological niche. However, little is known about the specific traits that determine the hydrological niche of a plant species. To investigate the relationship between plant functional traits, community structure and hydrological niche segregation, we developed a new generic individual-based model PLANTHeR which describes plant functional trait abundance as a function solely of soil water potentials and individual behavior. An important innovation is that there are no a priori defined trade-offs so that the model is neither restricted to a certain set of species nor scaled to a specific ecosystem. We show that PLANTHeR is able to reproduce well-known ecological rules such as the self-thinning law. We found that plant functional traits and their combinations (plant functional types − PFTs) were restricted to specific ranges of soil water potentials. Furthermore, the existence of functional trait trade-offs and correlations was determined by environmental conditions. Most interestingly, the correlation intensity between traits representing competitive ability and traits promoting colonization ability changed with water stress intensities in a unimodal fashion. Our results suggest that soil water largely governs the functional composition, diversity and structure of plant communities. This has consequences for predicting plant species’ response to changes in the hydrological cycle due to global change. We suggest that PLANTHeR is a flexible tool that can be easily adapted for further ecological-modelling studies. [ABSTRACT FROM AUTHOR]

The success of invasive plants has often been attributed to their rapid evolution at the introduced range. In particular, release from native enemies has been suggested to select for an evolutionary shift in resource allocation patterns from herbivore defence to increased size. Such evolutionary processes can take place not only between the native and invasive ranges but also within the invasive range over time, but this premise has been very seldom studied., In this study, we examined the potential for post-invasion evolution in two traits hypothesized to facilitate plant invasion success, that is herbivore resistance and allelopathic ability. We studied these traits in the invasive plant Impatiens glandulifera by comparing plants from its native populations and from populations across its invasion chronosequence., Results of common-garden experiment and chemical analyses revealed that plants from native populations or older populations within the invasive range show greater resistance to the generalist herbivore, Deilephila elpenor, coupled with greater production of the secondary defence compound 2-methoxy-1,4-naphthoquinone glycoside. In contrast, no differences were found between populations in their allelopathic effect on the germination of the co-occurring neighbour, Urtica doica. Finally, results from a field survey suggested that older populations within the invasive range incur greater attack rates from local herbivores compared to more recently established populations., Synthesis. Our findings support the idea that the selection pressure of enemy release at the introduced range might attenuate over time, leading to the evolutionary recovery of enemy resistance. This study emphasizes the importance of incorporating the effect of time since introduction when examining evolutionary or ecological processes of plant invasions. [ABSTRACT FROM AUTHOR]

The number of individuals within a population or community and their body size can be associated with changes in resource supply. While these relationships may provide a key to better understand the role of abiotic vs. biotic constraints in animal communities, little is known about the way size and abundance of organisms change along resource gradients. Here, we studied this interplay in ants, addressing two hypotheses with opposite predictions regarding variation in population densities along resource gradients- the ‘productivity hypothesis’ and the ‘productivity-based thinning hypothesis’. The hypotheses were tested in two functional groups of ground-dwelling ants that are directly primary consumers feeding on seeds: specialized seed-eaters and generalist species. We examined variations in colony density and foraging activity (a size measurement of the forager caste) in six ant assemblages along a steep productivity gradient in a semi-arid region, where precipitation and plant biomass vary 6-fold over a distance of 250km. An increase in the density or foraging activity of ant colonies along productivity gradients is also likely to affect competitive interactions among colonies, and consequently clinal changes in competition intensity were also examined. Ant foraging activity increased with productivity for both functional groups. However, colony density revealed opposing patterns: it increased with productivity for the specialized seed-eaters, but decreased for the generalist species. Competition intensity, evaluated by spatial partitioning of species at food baits and distribution of colonies, was uncorrelated with productivity in the specialized seed-eaters, but decreased with increasing productivity in the generalists. Our results provide support for two contrasting hypotheses regarding the effect of resource availability on the abundance of colonial organisms- the ‘productivity hypothesis’ for specialized seed-eaters and the ‘productivity-based thinning hypothesis’ for generalist species. These results also stress the importance of considering the role of functional groups in studies of community structure. [ABSTRACT FROM AUTHOR]

Background and Aims A common hypothesis to explain plants' invasive success is that release from natural enemies in the introduced range selects for reduced allocation to resistance traits and a subsequent increase in resources available for growth and competitive ability (evolution of increased competitive ability, EICA). However, studies that have investigated this hypothesis have been incomplete as they either did not test for all aspects of competitive ability or did not select appropriate competitors. Methods Here, the prediction of increased competitive ability was examined with the invasive plant Lythrum salicaria (purple loosestrife) in a set of common-garden experiments that addressed these aspects by carefully distinguishing between competitive effect and response of invasive and native plants, and by using both intraspecific and interspecific competition settings with a highly vigorous neighbour, Urtica dioica (stinging nettle), which occurs in both ranges. Key Results While the intraspecific competition results showed no differences in competitive effect or response between native and invasive plants, the interspecific competition experiment revealed greater competitive response and effect of invasive plants in both biomass and seed production. Conclusions The use of both intra- and interspecific competition experiments in this study revealed opposing results. While the first experiment refutes the EICA hypothesis, the second shows strong support for it, suggesting evolutionarily increased competitive ability in invasive populations of L. salicaria. It is suggested that the use of naturally co-occurring heterospecifics, rather than conspecifics, may provide a better evaluation of the possible evolutionary shift towards greater competitive ability. [ABSTRACT FROM PUBLISHER]

1. Interactions among neighbouring plants are often mediated by foraging choices of pollinators. For example, the presence of a conspicuous species may increase the number of pollinators attracted to its vicinity, indirectly increasing visitation rates also to neighbouring plants. Because pollinator choices are frequently density-dependent, the presence of a conspicuous species at high densities may also increase competition for pollination services. Additionally, models predict that plant density will interact with spatial distribution in manipulating the pollinator behaviour, yet experimental evidence for this effect is missing. 2. We performed a field experiment in which we introduced a highly conspicuous species in different densities and spatial configurations in a full-factorial manner into a species-rich meadow and studied its effect on neighbouring plants. 3. We showed that the highly conspicuous species strongly contributed to the attractiveness of its local patch and thus benefited its neighbours. However, because of the strong density effect, the conspicuous species changed its role and became a competitor for pollinators when its density increased. 4. We supported our theoretical assumptions and showed that when the introduced conspicuous species was regularly distributed among other plants in the patch, it increased visitation rate, and in some cases also seed set, to conspicuous neighbours relative to when it was aggregated, at least at low densities. 5. Synthesis. We suggest that complex interactions between density and spatial distribution of plant species at the patch scale are highly relevant for the interpretation of pollinator behaviour and therefore should be treated as factors of floral attractiveness in future studies. [ABSTRACT FROM AUTHOR]

Disturbances' role in shaping communities is well documented but highly disputed. We suggest replacing the overused two-trait trade-off approach with a functional group scheme, constructed from combinations of four key traits that represent four classes of species' responses to disturbances. Using model results and field observations from sites affected by two highly different disturbances, we demonstrated that popular dichotomous trade-offs are not sufficient to explain community dynamics, even if some emerge under certain conditions. Without disturbances, competition was only sufficient to predict species survival but not relative success, which required some escape mechanism (e.g., long-term dormancy). With highly predictable and large-scale disturbances, successful species showed a combination of high individual tolerance to disturbance and, more surprisingly, high competitive ability. When disturbances were less predictable, high individual tolerance and long-term seed dormancy were favored, due to higher environmental uncertainty. Our study demonstrates that theories relying on a small number of predefined trade-offs among traits (e.g., competition-colonization trade-off) may lead to unrealistic results. We suggest that the understanding of disturbance-community relationships can be significantly improved by employing sets of relevant trait assemblies instead of the currently common approach in which trade-offs are assumed in advance. [ABSTRACT FROM AUTHOR]

Desert species respond strongly to infrequent, intense pulses of precipitation. Consequently, indigenous flora has developed a rich repertoire of life-history strategies to deal with fluctuations in resource availability. Examinations of how future climate change will affect the biota often forecast negative impacts, but these--usually correlative--approaches overlook precipitation variation because they are based on averages. Here, we provide an overview of how variable precipitation affects perennial and annual desert plants, and then implement an innovative, mechanistic approach to examine the effects of precipitation on populations of two desert plant species. This approach couples robust climatic projections, including variable precipitation, with stochastic, stage-structured models constructed from long-term demographic datasets of the short-lived Cryptantha flava in the Colorado Plateau Desert (USA) and the annual Carrichtera annua in the Negev Desert (Israel). Our results highlight these populations' potential to buffer future stochastic precipitation. Population growth rates in both species increased under future conditions: wetter, longer growing seasons for Cryptantha and drier years for Carrichtera. We determined that such changes are primarily due to survival and size changes for Cryptantha and the role of seed bank for Carrichtera. Our work suggests that desert plants, and thus the resources they provide, might be more resilient to climate change than previously thought. [ABSTRACT FROM AUTHOR]

Question: Can wild ungulates efficiently maintain and restore open habitats? Location: Brandenburg, NE Germany. Methods: The effect of wild ungulate grazing and browsing was studied in three successional stages: (1) Corynephorus canescens-dominated grassland; (2) ruderal tall forb vegetation dominated by Tanacetum vulgare; and (3) Pinus sylvestris-pioneer forest. The study was conducted over 3 yr. In each successional stage, six paired 4 m2-monitoring plots of permanently grazed versus ungrazed plots were arranged in three random blocks. Removal of grazing was introduced de novo for the study. In each plot, percentage cover of each plant and lichen species and total cover of woody plants was recorded. Results: Wild ungulates considerably affected successional pathways and species composition in open habitats but this influence became evident in alteration of abundances of only a few species. Grazing effects differed considerably between successional stages: species richness was higher in grazed versus ungrazed ruderal and pioneer forest plots, but not in the Corynephorus sites. Herbivory affected woody plant cover only in the Pioneer forest sites. Although the study period was too short to observe drastic changes in species richness and woody plant cover, notable changes in species composition were still detected in all successional stages. Conclusion: Wild ungulate browsing is a useful tool to inhibit encroachment of woody vegetation and to conserve a species-rich, open landscape. [ABSTRACT FROM AUTHOR]

1. A positive relationship between seed size and subsequent offspring survival is a key assumption in ecological theory concerning life-history strategies. Yet, this relationship is uncertain in respect to lifetime survival because sound evidence only exists for early seedling stages. Furthermore, the effect of environmental variation in space and time, and of contrasting plant functional groups, on this relationship has been scarcely examined. 2. Here, we investigated survival and between-year variation therein. We tested for both whether their relationship to seed size (i) is maintained up until reproduction, (ii) changes along environmental gradients and (iii) differs between functional groups (grasses, legumes, forbs). 3. Survival was monitored from established seedlings to reproductive plants in 49 annual species under natural conditions during 7 years in three sites along a steep rainfall gradient. We then related average survival per species and between-year variation in survival to seed size, site along the gradient and functional group. 4. Larger seed size was associated with higher survival and lower between-year variation. Across the rainfall gradient, we detected no difference in the seed size–survival relationships; however, variation between years was lowest in the most mesic site where no relationship for between-year variation with seed size was observed. Legumes showed lower survival and higher between-year variation than grasses. 5. Our findings indicate that larger seed size provides survival advantages beyond seedling establishment up until reproduction among annual species. Larger seed size also provides a bet-hedging strategy in temporally unpredictable environments. Increased abiotic favourability along environmental gradients may have little effect on survival rates but reduces survival variation between years and thus reduces the bet-hedging benefit of larger seed size. We suggest that the contrasting response of legumes and grasses may partly result from their disparity in seed dormancy. 6. Synthesis. Current plant life-history theory can be refined by accounting for both benefits of larger seed size, higher survival rates and bet-hedging. Studies along environmental gradients are needed to generalize findings across ecosystems and to predict patterns of plant traits and plant performance under changing environmental conditions. [ABSTRACT FROM AUTHOR]

1. An unresolved question in plant ecology is how the balance between positive and negative interactions changes with environmental conditions. Recently, the debate has been expanded by Brooker & Kikvidze (2008) , reintroducing the importance, rather than the intensity, of interactions as the appropriate concept for empirical studies. Importance is the difference in performance with interactions relative to all affecting factors. 2. Positive interactions among plants (facilitation) are common in nature. However, the advocated importance indices fail to address facilitation and can thus not be applied to studying shifts in the balance between positive and negative interactions. The deficiencies of the current importance indices are both conceptual as well as mathematical. In particular, their maximum performance estimator is based on the assumption that it can only be attained in the absence of neighbours. 3. We suggest two major improvements. First, we use the target’s overall maximum performance as a surrogate for the plant optimum, i.e. we allow the possibility of higher performance with neighbours (i.e. facilitation). Second, we propose an alternative approach to treat the factors affecting measured performance. The new index is limited in its range [−1, 1], is symmetrical for competition and facilitation, and it preserves the intuitive nature of the original index by Brooker & Kikvidze (2008) . 4. Synthesis. The concept of interaction importance is useful for studying interactions along environmental gradients. In contrast to previous indices, our index accommodates facilitative interactions and thus offers a significant conceptual and methodological advancement. We advocate its use in future empirical studies. [ABSTRACT FROM AUTHOR]

1. Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field. 2. We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant–plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research. 3. With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies. 4. There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non-transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity. 5. Certain ecological modelling approaches (e.g. individual-based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes. 6. Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re-assessment of the evolution of plant growth forms. 7. Improved understanding of facilitation processes has direct relevance for the development of tools for ecosystem restoration, and for improving our understanding of the response of plant species and communities to environmental change drivers. 8. Attempts to apply our developing ecological knowledge would benefit from explicit recognition of the potential role of facilitative plant–plant interactions in the design and interpretation of studies from the fields of restoration and global change ecology. 9. Synthesis: Plant facilitation research provides new insights into classic ecological theory and pressing environmental issues. Awareness and understanding of facilitation should be part of the basic ecological knowledge of all plant ecologists. [ABSTRACT FROM AUTHOR]