Find research datasets worth reusing

Data from: Experimental tests of the function and flexibility of song consistency in a wild bird

Measures of bird song that capture aspects of motor performance, such as consistency, have become a major focus in understanding sexual selection on song. Despite accumulating evidence that consistency is related to reproductive success in many species, the relative importance of male–male interactions and female–male interactions is still unclear. We studied the function and flexibility of song consistency and song rate in common yellowthroat warblers (Geothlypis trichas). A previous study of this population found that song consistency—measured as the amount of variability within a bout of songs—was positively correlated with the likelihood of siring extrapair young. In this study, we conducted two experiments aimed at testing (1) the role of song consistency and rate in mediating male–male and male–female interactions and (2) whether song effort is flexibly adjusted to changes in social context. In the first experiment, we simulated a male territorial intrusion with song playbacks that varied in consistency and rate; focal males responded aggressively to playbacks, but their response did not differ with playback consistency or rate. In the second experiment, we presented focal males with a taxidermic female mount and female vocalizations; focal males approached the speaker, but continued to sing and did not perform the aggressive rattle vocalization observed during male encounters. Immediately after the simulated female encounter, focal males increased in song consistency. Taken together, our results are most consistent with the hypothesis that song consistency in common yellowthroats is primarily a female-directed signal that is actively adjusted in response to rapidly changing social conditions.

Data from: Using experimentation to understand the 10-year snowshoe hare cycle in the boreal forest of North America

1. Population cycles have long fascinated ecologists from the time of Charles Elton in the 1920s. The discovery of large population fluctuations in undisturbed ecosystems challenged the idea that pristine nature was in a state of balance. The 10-year cycle of snowshoe hares (Lepus americanus Erxleben) across the boreal forests of Canada and Alaska is a classic cycle, recognized by fur traders for more than 300 years. 2. Since the 1930s ecologists have investigated the mechanisms that might cause these cycles. Proposed causal mechanisms have varied from sunspots to food supplies, parasites, diseases, predation, and social behaviour. Both the birth rate and the death rate change dramatically over the cycle. Social behaviour was eliminated as a possible cause because snowshoe hares are not territorial and do not commit infanticide. 3. Since the 1960s large-scale manipulative experiments have been used to discover the major limiting factors. Food supply and predation quickly became recognized as potential key factors causing the cycle. Experiments adding food and restricting predator access to field populations have been decisive in pinpointing predation as the key mechanism causing these fluctuations. 4. The immediate cause of death of most snowshoe hares is predation by a variety of predators, including the Canada lynx (Lynx canadensis Kerr). The collapse in the reproductive rate is not due to food shortage as was originally thought, but is a result of chronic stress from predator chases. 5. Five major issues remain unresolved. First, what is the nature of the predator-induced memory that results in the prolonged low phase of the cycle? Second, why do hare cycles form a travelling wave, starting in the centre of the boreal forest in Saskatchewan and travelling across western Canada and Alaska? Third, why does the amplitude of the cycle vary greatly from one cycle to the next in the same area? Fourth, do the same mechanisms of population limitation apply to snowshoe hares in eastern North American or in similar ecosystems across Siberia? Finally, what effect will climatic warming have on all the above issues? The answers to these questions remain for future generations of biologists to determine.

Data from: Higher species richness enhances yield stability in intensively managed grasslands with experimental disturbance

Climate models predict increased frequency and severity of drought events. At an Irish and Swiss site, experimental summer droughts were applied over two successive years to grassland plots sown with one, two or four grassland species with contrasting functional traits. Mean yield and plot-to-plot variance of yield were measured across harvests during drought and after a subsequent post-drought recovery period. At both sites, there was a positive relationship between species richness and yield. Under rainfed control conditions, mean yields of four-species communities were 32% (Wexford, Ireland) and 51% (Zürich, Switzerland) higher than in monocultures. This positive relationship was also evident under drought, despite significant average yield reductions (-27% at Wexford; -21% at Zürich). Four-species communities had lower plot-to-plot variance of yield compared to monoculture or two-species communities under both rainfed and drought conditions, which demonstrates higher yield stability in four-species communities. At the Swiss but not the Irish site, a high degree of species asynchrony could be identified as a mechanism underlying increased temporal stability in four-species communities. These results indicate the high potential of multi-species grasslands as an adaptation strategy against drought events and help achieve sustainable intensification under both unperturbed and perturbed environmental conditions.

opencc-zeroDec 2014View details →

Data from: Experimental manipulation of avian social structure reveals segregation is carried over across contexts

Our current understanding of animal social networks is largely based on observations or experiments that do not directly manipulate associations between individuals. Consequently, evidence relating to the causal processes underlying such networks is limited. By imposing specified rules controlling individual access to feeding stations, we directly manipulated the foraging social network of a wild bird community, thus demonstrating how external factors can shape social structure. We show that experimentally imposed constraints were carried over into patterns of association at unrestricted, ephemeral food patches, as well as at nesting sites during breeding territory prospecting. Hence, different social contexts can be causally linked, and constraints at one level may have consequences that extend into other aspects of sociality. Finally, the imposed assortment was lost following the cessation of the experimental manipulation, indicating the potential for previously perturbed social networks of wild animals to recover from segregation driven by external constraints.

opencc-zeroDec 2018View details →

Data from: Effects of fleas on nest success of Arctic barnacle geese: experimentally testing the mechanism

Parasites have detrimental effects on their hosts' fitness. Therefore, behavioural adaptations have evolved to avoid parasites or, when an individual is already in contact with a parasite, prevent or minimize infections. Such anti-parasite behaviours can be very effective, but can also be costly for the host. Specifically, ectoparasites can elicit strong host anti-parasite behaviours and interactions between fleas (Siphonaptera) and their hosts are one of the best studied. In altricial bird species, nest fleas can negatively affect both parent and offspring fitness components. However, knowledge on the effects of fleas on precocial bird species is scarce. Research on geese in the Canadian Arctic indicated that fleas have a negative impact on reproductive success. One possible hypothesis is that fleas may affect female incubation behaviour. Breeding females with many fleas in their nest may increase the frequency and/or duration of incubation breaks and could even totally desert their nest. The aim of our study was to 1) determine if a similar negative relationship existed between flea abundance and reproductive success in our study colony of Arctic breeding barnacle geese Branta leucopsis and 2) experimentally quantify if such effects could be explained by a negative effect of nest fleas on female behaviour. We compared host anti-parasite and incubation behaviour between experimentally flea-reduced and control nests using wildlife cameras and temperature loggers. We found that flea abundance was negatively associated with hatching success. We found little experimental support, however, for changes in behaviour of the breeding female as a possible mechanism to explain this effect.

Data from: Whether larval amphibians school does not affect the parasite aggregation rule: testing the effects of host spatial heterogeneity in field and experimental studies

Almost all macroparasites show over-dispersed infections within natural host populations such that most parasites are distributed among a few heavily-infected individuals. Despite the importance of parasite aggregation for understanding system stability, the potential for population regulation, and super-spreading events, many questions persist about its underlying drivers. Theoretically, aggregation results from heterogeneity in host exposure, resistance, and tolerance. However, few studies have examined how host spatial arrangement – which likely affects both parasite encounter and density-dependent interactions – influences infection and dispersion, representing a critical gap in our current knowledge regarding the possible drivers of parasite aggregation. Using field data from over 165 ponds and 8,000 hosts, we evaluated how the spatial clustering of amphibian larvae within ponds 1) varied among different amphibian species, and 2), affected the distribution of parasites within the host population using Taylor's Power Law. A complementary mesocosm experiment used field-guided manipulations of the spatial arrangement of larval amphibians to create a gradient in host clustering while controlling host density, thereby testing for spatial effects on both infection success and aggregation by three different trematode species. Our field data indicated that larval amphibians exhibited significant spatial clustering that was well captured by Taylor's Power Law (R2 0.92 to 0.97 for different host species), but the residual variation only weakly correlated with observed patterns of trematode parasite over-dispersion. Correspondingly, experimental manipulation of host clustering had no effects on parasite infection success or the degree of parasite aggregation among cages or mesocosms. Given the importance of parasite over-dispersion for host populations and disease dynamics, we advocate for further investigations of host and parasite spatial aggregation, particularly studies that incorporate and/or control for heterogeneity in exposure and susceptibility.

Data from: Effects of experimental warming on biodiversity depend on ecosystem type and local species composition

Climatic warming is a primary driver of change in ecosystems worldwide. Here, we synthesize responses of species richness and evenness from 187 experimental warming studies in a quantitative meta-analysis. We asked 1) whether effects of warming on diversity were detectable and consistent across terrestrial, freshwater and marine ecosystems, 2) if effects on diversity correlated with intensity, duration, and experimental unit size of temperature change manipulations, and 3) whether these experimental effects on diversity interacted with ecosystem types. Using multilevel mixed linear models and model averaging, we also tested the relative importance of variables that described uncontrolled environmental variation and attributes of experimental units. Overall, experimental warming reduced richness across ecosystems (mean log-response ratio = –0.091, 95% bootstrapped CI: –0.13, –0.05) representing an 8.9% decline relative to ambient temperature treatments. Richness did not change in response to warming in freshwater systems, but was more strongly negative in terrestrial (–11.8%) and marine (–10.5%) experiments. In contrast, warming impacts on evenness were neutral overall and in aquatic systems, but weakly negative on land (7.6%). Intensity and duration of experimental warming did not explain variation in diversity responses, but negative effects on richness were stronger in smaller experimental units, particularly in marine systems. Model-averaged parameter estimation confirmed these main effects while accounting for variation in latitude, ambient temperature at the sites of manipulations, venue (field versus lab), community trophic type, and whether experiments were open or closed to colonization. These analyses synthesize extensive experimental evidence showing declines in local richness with increased temperature, particularly in terrestrial and marine communities. However, the more variable effects of warming on evenness were better explained by the random effect of site identity, suggesting that effects on species' relative abundances were contingent on local species composition.

Data from: Linking species abundance and overyielding from experimental communities with niche and fitness characteristics

1) So far, the principal force shaping local plant abundance patterns remains unclear. Rarity can result from poor competitive ability or from small vegetative or generative reproduction, but also from strong self-limitation. The same mechanisms can drive species-specific overyielding, i.e. increased species productivity at high community diversity. Rare species can then benefit more (i.e. overyield to a larger extent) from growing in species-rich communities because of altered competitive hierarchies or smaller conspecific frequencies. Here we test which mechanism is the most important determinant of species rarity and of species-specific productivity across a diversity gradient ranging from one- to 60-species plots. 2) For that we measured vegetative growth, competitive ability (competitive effect), and negative frequency dependence for 49 perennial grassland species from Central Europe. We then linked these characteristics with species abundance (measured as species biomass from 60-species plots) and with species-specific overyielding in The Jena Experiment. 3) Species with higher rates of vegetative growth (when grown without neighbors) were also more abundant in the Jena Experiment. Larger species-specific overyielding was then associated with a stronger negative frequency dependence. As species with greater vegetative growth were also more self-limited, larger overyielding in species-rich communities was characteristic for common rather than for rare species, refuting our initial hypothesis. Finally, path analysis indicated that species with poor capacity to suppress neighbors also profited more from growing in diverse communities. 4) Synthesis. Our results identify key mechanisms driving abundance and productivity of species in synthetic communities differing in species richness. While vegetative reproduction was closely associated with abundance, intraspecific interactions (strength of negative frequency dependence) shaped species productivity across a richness gradient. Our study sheds light on the abundance patterns of species and their influence on community functions, such as biomass production, of species-rich and -poor vegetation.

opencc-zeroDec 2013View details →

Data from: Evolutionary relatedness does not predict competition and co-occurrence in natural or experimental communities of green algae

The competition-relatedness hypothesis (CRH) predicts that the strength of competition is the strongest among closely related species and decreases as species become less related. This hypothesis is based on the assumption that common ancestry causes close relatives to share biological traits that lead to greater ecological similarity. Although intuitively appealing, the extent to which phylogeny can predict competition and co-occurrence among species has only recently been rigorously tested, with mixed results. When studies have failed to support the CRH, critics have pointed out at least three limitations: (i) the use of data poor phylogenies that provide inaccurate estimates of species relatedness, (ii) the use of inappropriate statistical models that fail to detect relationships between relatedness and species interactions amidst nonlinearities and heteroskedastic variances, and (iii) overly simplified laboratory conditions that fail to allow eco-evolutionary relationships to emerge. Here, we address these limitations and find they do not explain why evolutionary relatedness fails to predict the strength of species interactions or probabilities of coexistence among freshwater green algae. First, we construct a new data-rich, transcriptome-based phylogeny of common freshwater green algae that are commonly cultured and used for laboratory experiments. Using this new phylogeny, we re-analyse ecological data from three previously published laboratory experiments. After accounting for the possibility of nonlinearities and heterogeneity of variances across levels of relatedness, we find no relationship between phylogenetic distance and ecological traits. In addition, we show that communities of North American green algae are randomly composed with respect to their evolutionary relationships in 99% of 1077 lakes spanning the continental United States. Together, these analyses result in one of the most comprehensive case studies of how evolutionary history influences species interactions and community assembly in both natural and experimental systems. Our results challenge the generality of the CRH and suggest it may be time to re-evaluate the validity and assumptions of this hypothesis.

opencc-zeroDec 2013View details →

Data from: Experimentally increased reproductive effort alters telomere length in the blue tit (Cyanistes caeruleus)

Telomeres have recently been suggested to play important role in ageing and are considered to be a reliable ageing biomarkers. The life history theory predicts that costs of reproduction should be expressed in terms of accelerated senescence, and some empirical studies do confirm such presumption. Thus, a link between reproductive effort and telomere dynamics should be anticipated. Recent studies have indeed demonstrated that reproduction may trigger telomere loss, but actual impact of reproductive effort has not received adequate attention in experimental studies. Here, we experimentally manipulated reproductive effort by increasing the brood size in the wild blue tit (Cyanistes caeruleus). We show that parents attending enlarged broods experienced larger yearly telomere decay in comparison to control birds attending unaltered broods. In addition, we demonstrate that the change in telomere length differs between sexes, but this effect was independent from our treatment. To our knowledge, this is the first experimental study in the wild revealing that telomere dynamics may be linked to reproductive effort. Thus, telomere shortening may constitute one of the potential proximate mechanisms mediating the costs of reproduction.

opencc-zeroDec 2011View details →

Data from: Biomass responses to elevated CO2, soil heterogeneity and diversity: an experimental assessment with grassland assemblages

While it is well-established that the spatial distribution of soil nutrients (soil heterogeneity) influences the competitive ability and survival of individual plants, as well as the productivity of plant communities, there is a paucity of data on how soil heterogeneity and global change drivers interact to affect plant performance and ecosystem functioning. To evaluate the effects of elevated CO2, soil heterogeneity and diversity (species richness and composition) on productivity, patterns of biomass allocation and root foraging precision, we conducted an experiment with grassland assemblages formed by monocultures, two- and three-species mixtures of Lolium perenne, Plantago lanceolata and Holcus lanatus. The experiment lasted for 90 days, and was conducted on microcosms built out of PVC pipe (length 38 cm, internal diameter 10 cm). When nutrients were heterogeneously supplied (in discrete patches), assemblages exhibited precise root foraging patterns, and had higher total, above- and belowground biomass. Greater aboveground biomass was observed under elevated CO2. Species composition affected the below:aboveground biomass ratio and interacted with nutrient heterogeneity to determine belowground and total biomass. Species richness had no significant effects, and did not interact with either CO2 or nutrient heterogeneity. Under elevated CO2 conditions, the two- and three-species mixtures showed a clear trend towards underyielding. Our results show that differences among composition levels were dependent on soil heterogeneity, highlighting its potential role in modulating diversity–productivity relationships.

Data from: Ectomycorrhizal and saprotrophic fungi respond differently to long-term experimentally increased snow depth in the High Arctic

Changing climate is expected to alter precipitation patterns in the Arctic, with consequences for subsurface temperature and moisture conditions, community structure, and nutrient mobilization through microbial belowground processes. Here, we address the effect of increased snow depth on the variation in species richness and community structure of ectomycorrhizal (ECM) and saprotrophic fungi. Soil samples were collected weekly from mid-July to mid-September in both control and deep snow plots. Richness of ECM fungi was lower, while saprotrophic fungi was higher in increased snow depth plots relative to controls. [Correction added on 23 September 2016 after first online publication: In the preceding sentence, the richness of ECM and saprotrophic fungi were wrongly interchanged and have been fixed in this current version.] ECM fungal richness was related to soil NO3-N, NH4-N, and K; and saprotrophic fungi to NO3-N and pH. Small but significant changes in the composition of saprotrophic fungi could be attributed to snow treatment and sampling time, but not so for the ECM fungi. Delayed snow melt did not influence the temporal variation in fungal communities between the treatments. Results suggest that some fungal species are favored, while others are disfavored resulting in their local extinction due to long-term changes in snow amount. Shifts in species composition of fungal functional groups are likely to affect nutrient cycling, ecosystem respiration, and stored permafrost carbon.

opencc-zeroJul 2019View details →

Data from: Experimental evolution of response to anoxia in Drosophila: recovery of locomotion following CO2 or N2 exposure

Many insects enter coma upon exposure to anoxia, a feature routinely exploited by experimentalists to handle them. But the genetic and physiological bases of anoxic coma induction and recovery are only partially understood, as are the long-term consequences for the animal's performance. We examined three populations of Drosophila melanogaster (designated B) that have been inadvertently under selection for rapid recovery from CO2 exposure for nearly 40 years (around 1,000 generations) resulting from routine maintenance practices. We contrasted CO2 and N2 (presumed a less reactive gas) knockdown and recovery times of these B flies with six populations of common ancestry (A and C populations) that were not exposed to CO2 over the same period. We found that B populations showed faster and more consistent locomotor recovery than A or C populations after CO2 knockdown, a result also observed with N2 knockdown. A and C populations showed much higher variance in recovery time after CO2 exposure than after N2 exposure, suggesting gas-specific effects on pathways associated with locomotor recovery. While these selection treatments result in considerable variation in life history attributes and body size, with the characteristic intermediacy of B populations, their superiority in resistance to gas exposure and locomotor recovery suggests that it is a direct consequence of prior repeated exposure to anoxia, broadly, and CO2, specifically. Hence we describe a powerful new evolutionary model for the genetic and physiological investigation of anoxic coma in insects.

Data from: An experimental test of local adaptation among cytotypes within a polyploid complex

The geographic distributions of polyploids suggest they can have distinct and sometimes broader niches compared to diploids. However, relatively few field experiments have investigated whether range differences are associated with local adaptation or reflect other processes, such as dispersal limitation. In three years of transplants across the elevational ranges of five cytotypes in the Claytonia perfoliata complex, we found evidence for local adaptation. In at least one study year germination was higher within the natural range for each cytotype, and four of the five cytotypes attained larger biomass within their natural range. Fitness within and beyond range varied across years, with two instances of cytotypes showing higher fitness beyond the range, highlighting a potential role of temporal variability in cytotype differentiation. Polyploids as a group did not outperform diploids, but the cytotype with highest fitness across environments was a hexaploid reported to be invasive. Our results suggest that differences in geographic ranges within the C. perfoliata complex reflect local adaptation of cytotypes. Although we did not find a general polyploid advantage, our findings support the idea that occasional polyploid cytotypes exhibit high fitness relative to other cytotypes, and contribute to growing evidence supporting ecological differentiation of cytotypes within polyploid complexes.

Data from: Experimental evaluation of the robustness of the growth-stress tolerance trade-off within the perennial grass Dactylis glomerata

1. A core tenet of functional ecology is that the vast phenotypic diversity observed in the plant kingdom could be partly generated by a trade- off between the ability of plants to grow quickly and acquire resources in rich environments vs. the ability to conserve resources and avoid mortality under stress. However, experimental demonstrations remain scarce and potentially blurred by phylogenetic constraints in cross-species analyses. Here we experimentally decoupled growth potential and stress survival by applying an off-season stress on contrasting populations of the perennial grass Dactylis glomerata exhibiting a range of seasonal dormancy. 2. Seventeen populations of D. glomerata, originating from a latitudinal gradient from Norway to Morocco, were subjected to three types of dehydration stress: winter frost in Norway, summer drought, and early spring (off-season) drought stress in the south of France. Growth rate, and two leaf traits (leaf width and leaf dry matter content) suspected to be involved in the adaptation to dehydration stress, were monitored under optimal conditions. We quantified plant dehydration survival as the amount of plant recovery after a severe stress. 3. Nordic populations were found to be winter dormant. Winter and summer dormant populations better survived frost and summer drought, respectively. However, no trade-off between growth potential and dehydration survival was detected in non-dormant plants in early spring when dehydration occurred unseasonably for all populations. Furthermore, Mediterranean populations better survived an early spring drought. 4. Our results highlight the importance of assessing plant growth potential as a response to seasonal environmental cues. They suggest that growth potential and stress survival trade-off when plants exhibit seasonal dormancy but can be functionally independent at other seasons. Consequently, the growth-stress survival relationship could be better described as a dynamic linkage rather than a constant and general trade-off. Moreover, leaf trait values, such as thinner and more lignified leaves reflecting drought adaptation, may have contributed to the improved drought-stress survival without resulting in a cost to growth. 5. Further exploration of the growth-stress survival relationship should permit deciphering the suite of plant traits and trait covariations involved in plants' responses to increasing stress.

Data from: Exclusion of invertebrates influences saprotrophic fungal community and wood decay rate in an experimental field study

1. Decomposer communities perform an essential ecosystem function by recycling nutrients. However, the effect of higher trophic levels on microbial decomposer communities and rate of decomposition is poorly understood. We therefore conducted an exclusion experiment to test the effect of invertebrates on fungal decomposer communities in dead wood, repeated at 30 sites in two landscapes, and measured wood density to assess effect on decay rate. 2. Invertebrates were excluded from recently cut logs by cages with a 1 mm mesh net, and fungal communities in caged logs were compared to logs accessible to invertebrates by DNA metabarcoding analyses. Accessible logs included control logs, cage control logs and positive control logs. 3. We found that exclusion of invertebrates had a significant effect on fungal community composition. For example, the wood decay fungi Trametes versicolor and T. ochracea were significantly more abundant in accessible logs than in caged logs. The strongest effect on fungal community composition, however, was attributed to differing baseline conditions in the individual trees. When accounting for these baseline differences, caged logs had significantly higher wood density than control logs after two years, indicating lower rates of wood decay in caged logs. 4. Further studies, spanning several years, are required to fully understand the influence of invertebrates on fungi and wood decay. However, our results indicate that invertebrates influence both the composition of saprotrophic communities in dead wood and their decomposition function, which is vital to forest ecosystems.

Data from: Biodiversity as insurance for sapling survival in experimental tree plantations

Biodiversity can insure ecosystems against declines in their functioning by increasing the mean level of ecosystem processes and decreasing the spatial or temporal variance of these processes. On this basis, mixing tree species is expected to be an effective management strategy to reduce the risk of planting failure in young plantations. We examined the effects of biodiversity insurance on sapling survival in three tree diversity experiments across Belgium. Based on the survival scoring of 89 254 saplings, planted in 126 plots with up to four-species mixtures, we tested two hypotheses: (i) variability in plot-level survival is lower for mixtures compared to monocultures due to compensation among the species (i.e. buffering effect) and (ii) mean survival is higher due to facilitation (i.e. performance-enhancing effect). Variation in plot-level survival decreased strongly with diversity, indicating a buffering effect. The risk of severe planting failure was reduced in mixtures because species exhibit different survival rates; therefore, mixing ensures that not all trees in the plantation are equally susceptible to environmental stressors. In contrast, the mean plot-level survival did not increase with diversity, and thus, an overall performance-enhancing effect was lacking. However, species-level analyses did show performance-enhancing effects, where some species profited from mixing while others did not. Synthesis and applications. We conclude that biodiversity through mixing tree species insures young experimental plantations against planting failure and is therefore highly recommended as a planting management strategy. The risk of large mortality gaps is reduced if tree plantation saplings are mixed at the scale of individual trees or small cells of trees.

Data from: Tree species diversity alters plant defence investment in an experimental forest plantation in Southern Mexico

The effects of plant species diversity on plant traits conferring herbivore resistance (e.g., chemical defences), as well as the mechanisms underlying such effects, have received little attention. One potential mechanism for diversity effects on plant defences is that increased plant growth at high diversity could lead to reduced investment in defences via growth-defence trade-offs. We measured tree growth (diameter at breast height) and collected leaves for quantification of total phenolics on 2.5-year old plants of six tropical tree species (N = 597 plants) in a young experimental plantation in southern Mexico. Selected plants were distributed across 23 plots (21 x 21 m each) classified as monocultures of one species (N = 13, 2-3 plots per species) or polycultures (N = 10) represented by mixtures of four out of the six species. We found a significant negative effect of tree species diversity on total phenolics, where polycultures exhibited a 13 percent lower mean concentration than monocultures. However, there was marked variation among tree species in diversity effects on defences, where some species exhibited strong reductions in phenolics in mixtures, whereas others were unresponsive. Further, we found no effect of tree species diversity on growth and results indicated that the negative effect of diversity on chemical defences was not mediated by a growth-defence trade-off. These results demonstrate that tree diversity can alter investment in chemical defences in long-lived tree species, which has important implications for predicting effects on consumers and ecosystem function.

Data from: Yield of temperate forage grassland species is either largely resistant or resilient to experimental summer drought

Due to climate change, an increasing frequency and severity of drought events are expected to impair grassland productivity, particularly of intensively managed temperate grasslands. To assess drought impacts, a common field experiment to manipulate precipitation was set up at three sites (two Swiss and one Irish) using monocultures and mixtures with two and four key forage species. Species differed in their functional traits: a shallow-rooted non-legume (Lolium perenne L.), a deep-rooted non-legume (Cichorium intybus L.), a shallow-rooted legume (Trifolium repens L.) and a deep-rooted legume (Trifolium pratense L.). A nine-week summer drought was simulated and soil water status and above-ground biomass yield were compared to a rainfed control. Based on soil water measurements, the drought induced severe stress at both Swiss sites and extreme stress at the Irish site. Under severe drought, the legumes were more drought-resistant and showed an average change in above-ground biomass (CAB, compared to rainfed control) of only -8% and -24% (for the two Swiss sites) while the non-legumes had an average CAB of -51% and -68%. However, under extreme drought, all species were substantially impaired, with an average CAB of -85%. During a six-week post-drought period with adequate water supply (Swiss sites), formerly drought-stressed species were highly resilient and attained (legumes) or clearly outperformed (non-legumes) the yield level of the rainfed controls. As a result, aggregated over the drought and the post-drought periods, a negative drought impact was largely absent. Significant overyielding by multi-species mixtures was evident under rainfed control (+38% predicted CAB across all sites, P < 0.05) and persisted under severe drought conditions (+50%, P < 0.05). This overyielding was so large that drought-stressed mixtures at least attained the same yield as the average of the rainfed monocultures. Yields of selected species of intensively managed temperate grasslands are either resistant to a single severe drought or are highly resilient as soon as soil moisture levels recover after the drought event. Combining species in mixtures can compensate for yield reductions caused by severe drought and it offers a practical management tool to adapt forage production to climate change.

Data from: Dispersal and diversity in experimental metacommunities: linking theory and practice

There has been a recent rise in the number of experiments investigating the effect of dispersal on diversity, with many of the predictions for these tests derived from metacommunity theory. Despite the promise of linking observed relationships between dispersal and diversity to underlying metacommunity processes, empirical studies have faced challenges in providing robust tests of theory. We review experimental studies that have tested how dispersal affects metacommunity diversity to determine why shortcomings emerge, and to provide a framework for empirical tests of theory that capture the processes structuring diversity in natural metacommunities. We first summarize recent experimental work to outline trends in results and to highlight common methods that cause a misalignment between empirical studies and the processes described by theory. We then identify the undesired implications of three widely used experimental methods that homogenize metacommunity structure or species traits, and present alternative methods that have been used to successfully integrate experiments and theory in a biologically relevant way. Finally, we present methodological and theoretical insights from three related ecological fields (coexistence, food web and priority effects theory) that, if integrated into metacommunity experiments, could help isolate the independent and joint effects of local interactions and dispersal on diversity, and reveal the mechanisms underlying observed dispersal–diversity patterns. Together, these methods can provide stronger tests of existing theory and stimulate new theoretical explorations.