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194 results for “Competitive effect”
Data for: Effect of heterospecific and conspecific competition on individual differences in tadpole behavior
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Stage-mediated priority effects and season lengths shape long-term competition dynamics
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Data from: Compounding negative effects of leaf litter absence and belowground competition from an invasive spring ephemeral on native spring ephemeral growth and reproduction
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Data and code from: The functional form of specialized predation affects whether Janzen-Connell effects can prevent competitive exclusion
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Competitive interactions modify the direct effects of climate
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A general approach for quantifying microbial effects on plant competition
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Data from: Multiple facets of diversity effects on plant productivity: species richness, functional diversity, species identity and intraspecific competition
<p>1. Deciphering the mechanisms that drive variation in biomass production across plant communities of contrasting species composition and diversity is a main challenge of biodiversity-ecosystem functioning research. Niche complementarity and selection effect have been widely investigated to address biodiversity-productivity relationships. However, the overlooking of the specific role played by key species have limited so far our capacity to comprehensively assess the relative importance of other potential drivers of biodiversity effects.</p> <p>2. Here, we conducted a grassland diversity-productivity experiment to test how four potential facets of biodiversity effects, namely species richness, functional diversity, species identity and the relaxation of intraspecific competition, account for variations in above and root biomass production.</p> <p>3. We grew six plant species in monoculture, as well as in every combinations of two, three and six species. Plant density was kept constant across the richness gradient but we additionally grew each species in half-density monoculture to estimate the strength of intraspecific competition for each studied species. We characterized eight functional traits, including root traits, related to nutrient and light acquisition and computed both the functional dissimilarity and the community weighted mean (CWM) of each trait. We further partitioned aboveground biodiversity effect into complementarity and selection effects.</p> <p>4. We observed strong positive biodiversity effects on both aboveground and root biomass as well as strong positive complementarity effect. These arose largely from the presence of a particular species (<i>Plantago lanceolata</i>) and from CWM trait values more than from a higher functional dissimilarity in plant mixtures. <i>P. lanceolata</i> displayed the highest intraspecific competition, which was strongly relaxed in species mixtures. By contrast, the presence of <i>Sanguisorba minor</i> negatively affected the productivity of plant mixtures, this species suffering more from interspecific than intraspecific competition.</p> <p>5. This study provides strong evidences that the search for key species is critical to understand the role of species diversity on ecosystem functioning and demonstrates the major role that the balance between intraspecific and interspecific competition plays in biodiversity-ecosystem functioning relationships. Developing more integrative approaches in community and ecosystem ecology can offer opportunities to better understand the role that species diversity plays on ecosystem functioning.</p>
Data from: Cascading effects of a top predator on intraspecific competition at intermediate and basal trophic levels
1. Predators can impact competition among prey by altering prey density via consumption or by causing prey to modify their traits or foraging behavior. Yet, differences between these two mechanisms may lead to different cascading impacts on lower trophic levels. 2. Using a crab-snail-barnacle rocky intertidal food chain, we tested the effects of predation risk from crabs (top predators) on intraspecific competition among snails (intermediate consumers) and emergent indirect effects on the density of and competition between barnacles (basal resources). 3. The per capita foraging and growth rates of snails declined with high conspecific density. Predation risk from crabs, which caused even larger reductions in snail foraging and growth, weakened competition among snails, whereas a 45% increase in barnacle density had no detectable effect on snail competition. 4. Intraspecific competition between barnacles, however, depended on the interactive effects of barnacle density, snail density, and crab predation risk. Barnacles developed hummocking morphologies as they grew and competed for space. Hummock formation (a proxy for competition) increased as a result of either greater initial barnacle density or reduced snail foraging pressure, but these effects depended on predation risk. 5. The effects of crab predation risk on snail foraging behavior weakened an otherwise strong relationship between barnacle density and hummock development: hummocking increased with barnacle density in the absence of crabs but remained relatively high when crabs were present. In communities with similar final barnacle densities, hummocking was more common in those with crabs than those without crabs. 6. The extent to which predators can drive trophic cascades by suppressing the foraging rates of their prey is highly context-dependent: the positive trait-mediated indirect effect of predators on basal resource abundance is stronger when many prey respond simultaneously to the threat of predation. However, our results demonstrate that top predators can also enhance competition among basal resources even when their indirect effect on resource abundance is relatively weak. Hence, the cascading effects of predators on competition within lower trophic levels may play an important but underappreciated role in the dynamics of basal resource populations and the communities they support.
Data from: Effects of condition and sperm competition risk on sperm allocation and storage in neriid flies
<p>Ejaculate traits can be sexually selected and often exhibit heightened condition-dependence. However, the influence of sperm competition risk in tandem with condition-dependent ejaculate allocation strategies is relatively unstudied. Because ejaculates are costly to produce, high-condition males may be expected to invest more in ejaculates when sperm competition risk is greater. We examined the condition-dependence of ejaculate size by manipulating nutrient concentration in the juvenile (larval) diet of the neriid fly Telostylinus angusticollis. Using a fully factorial design we also examined the effects of perceived sperm competition risk (manipulated by allowing males to mate first or second) on the quantity of ejaculate transferred and stored in the three spermathecae of the female reproductive tract. To differentiate male ejaculates, we fed males non-toxic rhodamine fluorophores (which bind to proteins in the body) prior to mating, labelling their sperm red or green. We found that high-condition males initiated mating more quickly and, when mating second, transferred more ejaculate to both of the female's posterior spermathecae. This suggests that males allocate ejaculates strategically, with high-condition males elevating their ejaculate investment only when facing sperm competition. More broadly, our findings suggest that ejaculate allocation strategies can incorporate variation in both condition and perceived risk of sperm competition.</p>
Data from: Contrasting per-gram competitive and soil resource effects in grasses and woody plants
1. Plant species differ in their competitive effects by decreasing resource availability via uptake, but in some cases may increase resource availability via non-uptake pathways. Here we explore differences between grasses and woody plants in their competitive effects, and relate these to differences in resource effects. 2. We grew five species each of grasses and woody plants in monocultures for eight years. In the final two growing seasons, competitive effects were measured by growing transplants in all monocultures and in plots without neighbours. 3. Total competitive effects were significantly greater for woody plants than grasses. In contrast, the competitive effect per gram of grasses was about 17 times greater than that of woody plants. 4. For grasses, soil water and soil available N decreased significantly with increasing biomass. In contrast, for woody plants, soil water and soil available N increased significantly with increasing biomass. The results suggest that the intense per-gram competitive effects in grasses is related to the uptake of soil resources, and that the significantly lower per-gram competitive effects of woody plants may be related to their positive effects on soil resources. 5. Synthesis. The results link differences in competitive effects between grasses and woody plants to differences in the direction of their effects on soil resources. These differences may contribute to the entrainment of negative feedback in grasslands, excluding trees by means of strong competition, and the entrainment of positive feedback beneath woody plants establishing in grasslands, resulting in a state change from grassland to woody vegetation.
Competition for nitrogen between plants and microorganisms in grasslands: Effect of nitrogen application rate and plant acquisition strategy
<p>Several studies have investigated how nitrogen (N) addition changes N competition between focal plant species and soil microorganisms; still, the impact on community-level plant-microbial N competition and the underlying mechanisms remain unclear. We conducted a short-term (4 h) <sup>15</sup>N labeling experiment in an alpine meadow subjected to 7 years of NH<sub>4</sub>NO<sub>3 </sub>additions (0, 5, 10, and 15 g N m<sup>−2</sup> year<sup>−1</sup>), by monitoring changes in soil properties (e.g., pH, Al<sup>3+</sup>, NH<sub>4</sub><sup>+</sup>, NO<sub>3</sub><sup>−</sup>), microbial biomass (MB), plant community composition, root traits (e.g., root length, root area, specific root length), as well as the plant (nine focal species and at the community level) and microbial N uptake. Change in the N competition between the nine focal plant species and microorganisms following N addition depended on the species. At the community level, the N addition rate did not affect plant-microbial competition for NH<sub>4</sub> <sup>+</sup> and NO<sub>3</sub> <sup>−</sup> (<em>P </em>> 0.05). Nitrogen addition directly decreased NH<sub>4</sub><sup>+</sup>competition (β= −0.700) but indirectly increased because of improved plant uptake due to increased N availability(β=1.214). Competition for NO<sub>3</sub><sup>−</sup> was dependent on microbial uptake (β= −0.953) and was influenced by opposing effects of increased N availability (β=1.342) and reduced MB (β= −0.439). Thus, the effects of increased soil N availability and suppressed MB on plant and microbial N competition offset each other, while the plant community had a negligible impact. Such responses should be taken into account for better predictions of the effect of N addition on net primary productivity and ecosystem stability.</p>
The effects of microplastics on crop variation depend on polymer types and their interactions with soil nutrient availability and weed competition
<p>Microplastics pollution of agricultural soil is a global environmental concern because of its potential risk to food security and human health. Although many studies have tested the direct effects of microplastics on growth of <em>Eruca sativa</em> Mill., little is known about whether these effects are regulated by fertilization and weed competition in field management practices.</p> <p>Here, we performed a greenhouse experiment growing <em>E. sativa</em> as target species in a three-factorial design with two levels of fertilization (low versus. high), two levels of weed competition treatments (weed competition versus no weed competition) and five levels of microplastic treatments (no microplastics, Polybutylene adipateco-terephthalate [PBAT], Polybutylene succinate [PBS], Polycaprolactone [PCL] or Polypropylene [PP]).</p> <p>Compared to the soil without microplastics, PBS and PCL reduced aboveground biomass and leaf number of the <em>E. sativa</em>. PBS also resulted in increased root allocation and thicker roots in <em>E. sativa</em>. In addition, fertilization significantly mitigated the negative effects of PBS and PCL on aboveground biomass of <em>E. sativa</em>, but weed competition significantly promoted these effects. Although fertilization alleviated the negative effect of PBS on aboveground biomass, such alleviation became weaker under weed competition than when <em>E. sativa</em> grew alone.</p> <p>The results indicate that the effects of specific polymer types on <em>E. sativa</em> growth could be regulated by fertilization, weed management, and even their interactions. Therefore, reasonable on-farm management practices may help in mitigating the negative effects of microplastics pollution on <em>E. sativa</em> growth in agricultural fields.</p>
Radiation-Induced Stem Cell Competition and Dose-Rate Effect
<p>A radiation biological effect of a given dose generally decreases with decreasing radiation dose rate, which is known as a “dose-rate effect”. The dose-rate effect demonstrated by many cellular and animal studies. Additionally, recent epidemiological study in high background radiation area in Kerala, India showed that cancer incidence did not increase with increasing cumulative dose (Jayalekshmi et al. Radiat Environ Med 2021). Tissue stem cells have been considered as a target of radiation-induced carcinogenesis. Radiation biological effect could be reduced if damaged stem cells are eliminated by stem cell competition. ICRP described that stem cell competition at the tissue level leaves an ample possibility for a dose-rate effective factor (DREF) value larger than unity, as in the case of the current dose and dose-rate effective factor (DDREF) value (ICRP Publication 131).</p> <p>Cells expressing Lgr5 are one of the major components of intestinal stem cells. Intestinal organoids are three-dimensional cultured tissue model generated from intestinal stem cells. To evaluate a radiation-induced stem cell competition, we established a quantitative method using mixed-organoid derived from two independent fluorescent protein-expressing Lgr5 stem cells, which one of stem cells were irradiated, for mimicking heterogeneous exposure under low-dose-rate irradiation. The organoid-forming potential (OFP) is one of the indices of the abilities of self-renewal, proliferation, and differentiation of stem cells. We found that irradiated stem cells exhibited a growth disadvantage in the mixed organoid, whereas the OFP of irradiated cells per se did not decrease significantly from that of non-irradiated cells.</p> <p>Additionally, we constructed a mathematical model to assess stem cell competition under low-dose-rate irradiation condition. In our model, a stem cell pool, containing a constant number of cells, was assumed, and changed through transition and turnover event. The intact cells turned into damaged cells through transition event which was assumed as the effect of radiation exposure. In the turnover event, a single cell was divided, and a single cell was eliminated from the stem cell pool. The probability of cell division and elimination depended on the properties of cells. The properties of damaged cells were different from that of intact cells. Under very low-dose-rate conditions, the radiation damage was suppressed when the damaged cells were less reproductive and tended to be eliminated compared to the intact cells.</p> <p>These results suggest the radiation-induced stem cell competition can be occurred in the intestine, and the stem-cell competition plays an important role in suppress carcinogenesis under low-dose-rate irradiation condition.</p>
Effects of community richness and competitive asymmetry on protozoa evolution in Sarracenia purpurea leaves
<p>Predicting evolution in natural systems will require understanding how selection operates in multispecies communities. We predicted that the amount that traits evolve in multispecies mixtures would be less than the amount that would be predicted from the additive contributions of the pair-wise interactions and that subordinate species will be more likely to evolve in competitive systems than dominant species. We conducted an experimental test of these predictions using a guild of protozoans found in the water-filled leaves of the pitcher plant <em>Sarracenia purpurea</em>. The response to selection did not significantly change as we increased richness from monocultures to two- and four-species mixtures. In accordance with our second prediction, subordinate species demonstrated greater growth in competition after selection than before, while dominant species generally showed no response to selection. Monod-type experiments to determine minimum resource levels found that the dominant species had much higher resource requirements than the subordinate species and that the minimum resource requirements evolved to be higher in the subordinate species. Importantly, these results suggest that subordinate species evolve to become more similar to dominant species, which may involve resource-use convergence. Our findings and other recent works suggest that community diversity can affect evolution in surprising ways that warrant further investigation.</p>
Effects of nest-site availability on male-male competition and the foraging costs associated with paternal care in a resource-defense species
<p><strong>Effects of nest-site availability on male-male competition and associated costs of nest site maintenance and paternal care in a resource-defense species</strong></p> <p>This repository contains the .csv files used for the statistical analyses of the study "Effects of nest-site availability on male-male competition and associated costs of nest site maintenance and paternal care in a resource-defense species". In case of questions, please email Laís A. Grossel: <a href="mailto:laisgrossel@gmail.com">laisgrossel@gmail.com</a></p> <p><strong>Data files and structure</strong></p> <p>We have files for the analysis with field and experimental data.</p> <p>With the file <strong>field.csv</strong> we tested the probability of males obtaining a nest and receiving eggs from females. In this file, we have the headers:</p> <ul> <li><strong>maleID:</strong> identity of males in the field</li> <li><strong>DSW:</strong> dorsal scute width, in mm</li> <li><strong>mass:</strong> to the nearest 0.001 g</li> <li><strong>nest_possession:</strong> with 2 levels: 0 if the male did not possess a nest and 1 if the male possessed a nest</li> <li><strong>nest_opening:</strong> in cm</li> <li><strong>parental_status:</strong> with 3 levels: 0 if the male did not have a nest, 1: if the male had a nest but no eggs, and 2: if the male had a nest and eggs</li> </ul> <p>With the file <strong>experiment_nests.csv</strong> we tested predictions related with the nest possession. In this file, we have the headers:</p> <ul> <li><strong>terrariaID:</strong> identity of the 14 terraria (containing 4 or 8 nests)</li> <li><strong>exp_group:</strong> experimental group, with 2 levels of nests availability: low (4 nests per terraria) and high (8 nests per terraria)</li> <li><strong>nestID:</strong> identity of the nests</li> <li><strong>occupation:</strong> if the nest was once occupied during the experiment, with 2 levels: 0 if it was never occupied and 1 if it was occupied at least once</li> <li><strong>occupied_scans:</strong> number of scans with any male inside the nest</li> <li><strong>vacant_scans:</strong> number of scans without any male inside the nest</li> <li><strong>total_scans:</strong> total number of observation scans </li> <li><strong>owners:</strong> number of different owners of the nest (at least 6 consecutive scans)</li> <li><strong>turnover:</strong> if there was at least a substitution of the nest owner without figths, with 2 levels: 0 if there was not any substitution and 1 if there was a substitution</li> <li><strong>turnovers_number:</strong> number of substitutions of the nest owner without figths</li> <li><strong>takeover:</strong> if there was at least a takeover attempt of the nest after figths, with 2 levels: 0 if there was not any attempt and 1 if there was an attempt</li> <li><strong>takeovers_number:</strong> number of takeover attempts of the nest after figths</li> <li><strong>fight:</strong> if there was at least a figth inside or close to the nest, with 2 levels: 0 if there was not any figth and 1 if there was a figth</li> <li><strong>fights_number:</strong> number of figths inside or close to the nest</li> <li><strong>canibalism:</strong> if there was at least a cannibalism event inside the nest, 2 levels: 0 if there was not any cannibalism event and 1 if there was a cannibalism event</li> <li><strong>canibalism_number:</strong> number of cannibalism events inside the nest</li> </ul> <p>With the file <strong>experiment_males.csv</strong> we tested predictions related to the males owners. In this file, we have the headers:</p> <ul> <li><strong>terrariaID:</strong> identity of the 14 terraria (containing 4 or 8 nests)</li> <li><strong>exp_group:</strong> experimental group, with 2 levels of nests availability: low (4 nests per terraria) and high (8 nests per terraria)</li> <li><strong>maleID:</strong> identitity of the males</li> <li><strong>DSW:</strong> dorsal scute width, in mm</li> <li><strong>nest_possession:</strong> with 2 levels: 0 if the male never possessed a nest during the experiment and 1 if the male possessed a nest at least once (6 consecutive scans)</li> <li><strong>nestID:</strong> identity of the nest possessed by the male</li> <li><strong>inside_scans:</strong> number of scans with the male inside his nest</li> <li><strong>outside_scans:</strong> number of scans with the male outside his nest</li> <li><strong>total_scans:</strong> total number of scans in which the male was the owner of the nest</li> <li><strong>takeover:</strong> if the male suffered a takeover attempt of his nest, with 2 levels: 0 if the male did not suffer any attempt and 1 if the male suffered an attempt</li> <li><strong>eggs:</strong> if the male received eggs from a female, with 2 levels: 0 if the male did not receive eggs and 1 if the male received eggs</li> <li><strong>eggs_number:</strong> number of eggs received </li> <li><strong>cannibalism:</strong> if the owner male cannibalized the eggs inside the nest, 2 levels: 0 if the male did not cannibalize eggs and 1 if the male cannibalized eggs</li> <li><strong>cannibalism_number:</strong> number of cannibalism events by the owner male </li> </ul> <p>With the file <strong>fights-takeovers.csv</strong> we tested predictions related with nest takeovers. In this file, we have the headers:</p> <ul> <li><strong>terrariaID:</strong> identity of the 14 terraria (containing 4 or 8 nests)</li> <li><strong>exp_group:</strong> experimental group, with 2 levels of nests availability: low (4 nests per terraria) and high (8 nests per terraria)</li> <li><strong>nestID:</strong> identity of the nest possessed by the male</li> <li><strong>focalID:</strong> identitity of the focal males (the owner nest)</li> <li><strong>DSW:</strong> dorsal scute width, in mm</li> <li><strong>fight:</strong> if the male was involved in at least a figth, with 2 levels: 0 if the male was not involved in any figth and 1 if the male was involved in a figth</li> <li><strong>takeover:</strong> if the male suffered a takeover attempt of his nest, with 2 levels: 0 if the male did not suffer any attempt and 1 if the male suffered an attempt. Obs: the nest takeover always happens after a fight. If there was a takeover, then there was a fight too.</li> <li><strong>res_focal: </strong>result of the figth or takeover for the focal male, with 2 levels: 0 if the focal male did not lose the figth or the nest and 1 if the focal male lost the figth or the nest</li> <li><strong>intruderID:</strong> identity of the intruder male involved in the figth or the takeover with the owner male</li> <li><strong>intruder_DSL: </strong>dorsal scute width of the intruder male, in mm</li> <li><strong>dyad:</strong> identity of the two individuals involved in the figth or takeover (owner male and intruder male)</li> <li><strong>DSW_difference:</strong> difference between the dorsal scute width of the dyad (focal male minus intruder male)</li> </ul> <p>With the file <strong>foraging.csv</strong> we tested a prediction related with males foraging. In this file, we have the headers:</p> <ul> <li><strong>terrariaID:</strong> identity of the 14 terraria (containing 4 or 8 nests)</li> <li><strong>exp_group:</strong> experimental group, with 2 levels of nests availability: low (4 nests per terraria) and high (8 nests per terraria)</li> <li><strong>nestID:</strong> identity of the nest possessed by the male</li> <li><strong>maleID:</strong> identitity of the males</li> <li><strong>parental_status:</strong> with 2 levels: 0 if the male did not have eggs in the nest and 1: if the male had eggs</li> <li><strong>inside_scans:</strong> number of scans with the male inside his nest</li> <li><strong>outside_scans:</strong> number of scans with the male outside his nest</li> <li><strong>total_scans:</strong> total number of scans in which the male was the owner of the nest</li> </ul>
WBES2023 data for paper entitled "The effect of informal competition on family firms' performance: The case of three Western Balkans candidates for EU membership"
<p>WBES2023 data for paper entitled "The effect of informal competition on family firms’ performance: The case of three Western Balkans candidates for EU membership"</p>
Data from: The effects of competition on fitness depend on the sex of both competitors
<p>In intraspecific competition, the sex of competing individuals is likely to be important in determining the consequences of competition, both for the immediate outcome of competitive interactions, and for long-term effects of competition during development on adult fitness traits. Previous studies have explored differences between males and females in their response to intraspecific competition. However, few have tested how the sex of the competitors, or any interactions between focal and competitor sex, influence the nature and intensity of competition. We set up larval seed beetles <i>Callosobruchus maculatus</i> to develop either alone or in the presence of a male or female competitor, and measured a suite of traits: development time, emergence weight; male ejaculate mass, copulation duration and lifespan; and female lifetime fecundity, offspring egg-adult survival and lifespan. We found effects of competition and competitor sex on the development time and emergence weight of both males and females, and also of an interaction between focal and competitor sex: females but not males responded differently to competitor sex. There was little effect of larval competition on male and female adult fitness traits, with the exception of the effect of a female competitor on a focal female's offspring survival rate. Our results highlight the importance of directly measuring the effects of competition on fitness traits, rather than distant proxies for fitness, and suggest that competition with the sex with the greater resource requirements (here females) might have a strong effect in driving trait evolution. We also found that male-male competition during development resulted in shorter copulation times than male-female competition, a result that remained when controlling for the weight of competitors. Although it is difficult to definitively tease apart the effects of social environment and access to resources, this result suggests that something about the sex of competitors other than their size is driving this pattern.</p>
Data for: Light competition drives herbivore and nutrient effects on plant diversity
<p>Nutrient enrichment and loss of herbivores are assumed to cause plant diversity loss in grassland ecosystems because they increase plant cover that decreases understory light. Empirical tests of the role of competition for light in natural systems are based on indirect evidence and have contributed to strong debates over the last 40 years. Using illumination by LED-lamps, we demonstrate that experimentally restoring light to understory plants in a natural grassland mitigated the loss of plant diversity caused either by nutrient enrichment or the absence of mammalian herbivores. The initial effect of light addition on restoring diversity under fertilization was transitory and outweighed by the greater effect of herbivory on light levels, highlighting herbivory as a major factor controlling diversity, partly via light. Our results provide the first direct experimental demonstration in a natural system that competition for light is a major mechanism contributing to biodiversity loss under cessation of mammalian herbivory. Our results also demonstrate that herbivore effects can outpace fertilization effects on competition for light. Management practices that target maintaining grazing by native or domestic herbivores may have applied utility for protecting biodiversity in grassland ecosystems because they alleviate competition for light in the understory.</p>
Data from: Quantifying neighbour effects on tree growth: are common "competition" indices biased?
<p>1. Interactions among neighbouring plants are key determinants of plant growth. To characterise the cumulative effect of all neighbours on the growth of a focal plant, neighbourhoods are often described by 'competition' indices. Common competition indices calculate the summed size of neighbour plants (focal-independent index) whilst others include the summed ratio of the neighbour size relative to focal plant size (focal-dependent). A frequently overlooked statistical artifact is that focal-dependent indices may lead to biased estimates of neighbourhood effects on plant growth when growth is size-dependent.</p> <p>2. Here, we conduct a literature search to determine the most common index types used to explain neighbour effects on tree growth. We then assess the ability of two common index types – focal-dependent and focal-independent – to correctly infer neighbourhood effects in (1) observations of tree growth in an experimental forest in south-east Tasmania, Australia, and (2) an artificially created dataset where tree growth is unrelated to the neighbourhood.</p> <p>3. Both indices detected the competitive neighbourhood effect on tree growth observed in our own dataset but differed in their conclusion regarding neighbour effects in the simulated data. Despite the simulated dataset being generated so there was no relationship between tree growth and their neighbourhood, the focal-dependent index detected strong, competitive neighbourhood effects when intrinsic growth was incorrectly related to tree size. In contrast, when we considered the focal-independent index as the neighbourhood metric, we correctly did not detect any neighbourhood effects in the simulated data regardless of how size-dependent growth was described.</p> <p>4. <em>Synthesis</em>. 'Competition' indices are a useful method to characterise the cumulative neighbourhood effect on plant growth, however, we demonstrate that indices which include the size of the focal plant in their calculation can be biased by an inherent relationship between tree growth and initial size. Whilst this bias typically overstates the strength of competition in determining focal tree growth, we show that it can be mitigated by correctly describing intrinsic growth. We discuss the limitations of both index types, provide recommendations for performing statistical modelling, and outline how to check for accurate neighbour inference.</p>
Stronger effect of individual species' traits than shading on aquatic plant community productivity and interspecific competition
<p>Competition is one of the major factors structuring plant communities. Species with similar traits generally compete more intensely and have more similar yield than functionally dissimilar species, which often respond differently to environmental change. Little is known about how the interacting species' traits influence the effect of environmental change on interspecific competition. However, theory predicts that environmental change should lead to more asymmetric competition, by favouring the species best adapted to the particular environmental change. Here we used a mesocosm experiment with three common aquatic plant species from the Baltic Sea (Northern Europe), to test how community productivity and competition asymmetry were affected by functional dissimilarity, individual species' traits, and a common stressor: shading. Competition asymmetry was defined as the absolute difference in reductions in yield relative to monocultures of two interacting species. Community productivity decreased and competition asymmetry increased with functional dissimilarity of the interacting species, possibly explained by the traits of the superior species, which had higher specific leaf area, maximum canopy height, and primary production rate than the subordinate species. Community productivity was not affected by shading, contrary to our expectation, while competition asymmetry was higher in shaded than ambient conditions. Individual species yield depended on species identity and species combination. Only the shortest species was negatively affected by shading. Thus, by favouring tall-growing species, shading can alter interspecific competition. Together, these findings suggest that non-random species loss following environmental change can be caused by competitive exclusion, in addition to a direct effect of abiotic filtering.</p>
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