Relative Competitive Strength Research Articles

How relative competitive strength moderates stock price responses after European soccer tournaments

Stock price responses of soccer clubs to national and international tournaments have been interpreted in light of fan investors who are prone to emotions. We employ Champions League and Europa League fixtures between 2004 and 2020 to investigate whether postmatch stock price responses are driven by emotions. We argue that a soccer club’s relative competitive strength can be a proxy for investors’ emotions, such as rage and disappointment, after losing against a strong opponent, which then leads to abnormal decreases in stock prices. While we find several factors, such as the percentage of shares held by institutional investors less subject to emotions, whose effects on postmatch abnormal returns are in line with rational information processing, our evidence also suggests that the effect of a club’s relative competitive strength on stock performance is driven by investor emotion. We outline the general applicability of stock price responses arising from relative competitive strength in corporate finance settings.

Dynamics of a discrete-time pioneer\u2013climax model

We present a simple mathematical model for the dynamics of a successional pioneer–climax system using difference equations. Each population is subject to inter- and intraspecific competition; population growth is dependent on the combined densities of both species. Nine different geometric cases, corresponding to different orientations of the zero-growth isoclines, are possible for this system. We fully characterize the long-term dynamics of the model for each of the nine cases, uncovering diverse sets of potential behaviors. Competitive exclusion of the pioneer species and of the climax species are both possible depending on the relative strength of competition. Stable coexistence of both species may also occur; in two cases, a coexistence state is destabilized through a Neimark–Sacker bifurcation, and an attracting invariant circle is born. The invariant circle eventually disappears into thin air in a heteroclinic or homoclinic bifurcation, leading to the sudden transition of the system to an exclusion state. Neither global bifurcation has been observed in a discrete-time pioneer–climax model before. The homoclinic bifurcation is novel to all pioneer–climax models. We conclude by discussing the ecological implications of our results.

Evaluation of Marketing Management using WSM Method

Marketing Management. More work goes into becoming an effective marketing leader than that. Any marketing management expert will agree that strategy, planning, execution, and analysis go hand in hand. Why is clear to see? Compared to their counterparts who do not have a written strategy, marketing professionals with one are 313% more likely to be successful. What then is the function of marketing management in a broader corporate context, and how does it assist firms in future planning, customer understanding, process improvement, and the development of valuable goods and services? In our marketing management handbook, you may learn more about all of this. Marketing management analyses the market environment in which the company operates using economic and competitive strategy techniques. Among Porter's five forces are value chain analysis, competitive strategic group analysis, and others. Marketers use SWOT analysis to focus on the relative competitive strengths and weaknesses of each competitor in the market as they create extensive profiles of each competitor. Marketing managers look at a competitor's cost structure, profit sources, available resources, product differentiation, degree of vertical integration, past responses to market changes, and other aspects. Weighted Sum works by multiplying the designated field values Marketing Management alternatives Analysis in an Internet video, Web, email, and data, File sharing, Online gaming Evaluation parameters in 2015, 2016, 2017, 2018, 2019, 2020. Internet video, Web, email, and data, File sharing, Online Gaming. 2015, 2016, 2017, 2018, 2019, 2020. Web, email, and data get the first rank whereas File sharing has the lowest rank.

Interspecific social dominance networks reveal mechanisms promoting coexistence in sympatric charr in Hokkaido, Japan.

Coexistence of species requires equalizing mechanisms that minimize fitness differences, which are balanced by stabilizing mechanisms that enhance negative intraspecific interactions versus interspecific ones. Here, we develop a simple theoretical framework that allows measuring the relative strength of intraspecific versus interspecific competition in dominance hierarchies. We use it to evaluate mechanisms promoting coexistence between two congeneric charr that compete for foraging positions, which strongly influence density-dependent growth and survival. Agonistic interactions (n=761) among 71 Dolly Varden Salvelinus malma and whitespotted charr Salvelinus leucomaenis were measured by snorkelling in two pools in the sympatric zone of a Hokkaido stream during two summers. Interspecific dominance hierarchies, analysed using three methods, were closely correlated with fish length but the species treated each other equally. Ranks for the most dominant fish in each pool, determined directly by knockout experiments, were also virtually identical to ranks by length. Similarly, exponential random graph modelling of the social networks provided no evidence that either species was dominant over the other. Instead, larger fish were more likely to win contests, especially over fish of the next lower ranks. These results demonstrated that the two species were nearly ecological equivalents in accessing key resources in this sympatric zone. Nearly identical growth and stable densities over 4years further supported this inference, although Dolly Varden were a minority (29% of the assemblage), a sign of some fitness difference. Detailed foraging observations coupled with two concurrent studies revealed an effective stabilizing mechanism. Dolly Varden shifted to feeding directly from the benthos when drifting invertebrates declined, a behaviour enhanced by morphological character displacement, thereby partitioning food resources and enhancing intraspecific competition while avoiding agonistic encounters with whitespotted charr. The plurality of evidence indicates that fitness differences between these ecologically equivalent species are small in this local assemblage, and balanced by resource partitioning, a modest stabilizing mechanism that promotes coexistence. The theoretical framework presented here is a useful tool to evaluate the strength of interspecific versus intraspecific competition, which combined with information on trade-offs in ecological performance can contribute to a mechanistic understanding of species coexistence.

Plant traits and species interactions along gradients of N, P and K availabilities

Abstract Plant performance is driven by nutrient availability. So far, studies on plant nutrient relationships mostly focused on nitrogen (N) and phosphorus (P), whereas potassium (K) received less attention. We evaluated whether plant responses to variation in nutrient availability are similar or different for the nutrients N, P and K and whether the same plant traits are decisive for the competitive ability of species along gradients of N, P and K availabilities. We studied plant trait responses of three temperate perennial grass species (Alopecurus pratensis, Agrostis capillaris and Anthoxanthum odoratum, each dominant under N limitation, P limitation and K limitation, respectively). Each gradient consisted of eight treatments (N1–N8, P1–P8, K1–K8), with N:P:K supply rates being 1:0.8:6 (N1), 128:0.8:6 (N8), 12:0.075:6 (P1), 12:9.6:6 (P8), 12:0.8:0.56 (K1) and 12:0.8:72 (K8) (total supply per plant individual in mg). Plant individuals were kept either in single‐species pots (intraspecific competition) or in mixed‐species pots (interspecific competition). After 2 months, plant biomass, leaf and root traits and root enzyme activity were measured. Most below‐ground traits (e.g. total root length, root diameter) responded most strongly to competition as predictor variable and only secondly to the type of nutrient or their supply rates (unlike RGRTotal and SLA). Leaf chlorophyll content and root enzyme activity responded most strongly to supply rate of nutrients and the interaction of nutrient type and supply rate, respectively. In line with our prediction, A. pratensis was the superior competitor under N limitation and A. odoratum was the superior competitor under K limitation (assessed by relative dominance [RD] and relative competitive strength [RCS]). Both species showed high investment in total root length. Opposite to our expectation, A. capillaris was a bad competitor under P limitation, with low root length but higher root phosphatase activity. Our results indicate that below‐ground plant traits are decisive in nutrient‐related competition between plant species. Further, competitive strength is determined by a high total root length per soil volume both under N and K limitation. Under P limitation, the model species A. capillaris showed a weak competitive performance either because it was lacking colonization with mycorrhiza and/or the high investment in phosphatase activity posed a trade‐off with higher N investment in phosphatase production. A free Plain Language Summary can be found within the Supporting Information of this article.

Consequences of hybridization during invasion on establishment success

Initial colonization by non-native species sometimes occurs in regions already occupied by closely related species, and subsequent hybridization is often inevitable. However, there are several different ways that such hybridization might affect the successful establishment of the non-native species, but many of these remain insufficiently explored. Although there is growing evidence in support of improved local adaptation by genetic rescue, we demonstrate here another way that closely related species can facilitate invasions in which hybridization assists the invading species to overcome Allee effects arising from mate-finding failure. We explore this phenomenon using a simple mathematical model of two closely related diploid insect species, native and non-native, exhibiting differences in mate searching efficacy, relative strength of competition, and mate preference. We find that when the carrying capacity in the invading species is higher than in the native species, invasion success is facilitated. Invasion is also facilitated under parameterization for high hybrid fitness and severe competition between natives and hybrids. In light of these results, we discuss general patterns of how invasion success is affected by the manner in which native, non-native, and hybrids interact with each other and note situations where such conditions might occur in nature.

Facilitation among plants can accelerate density‐dependent mortality and steepen self‐thinning lines in stressful environments

The speed and slope of plant self‐thinning are all affected by plant–plant interactions across environmental gradients. Possible mechanisms driving the self‐thinning dynamics include the relative strength of root versus shoot competition, and the interplay between competition and facilitation. Although these mechanisms often act in concert, their relative importance has not yet been fully explored. We used both a one‐layer and a two‐layer zone‐of‐influence (ZOI) model to examine how competition and facilitation drive self‐thinning across stress gradients. As a development of the traditional ZOI model, the two‐layer version explicitly models shoot and root growth and neighbor interactions, and thus the overall size‐symmetry of competition is regulated by the relative strength of root versus shoot competition. One‐layer model simulations revealed that increasingly asymmetric competition accelerated thinning, and steepened (slope ranged from about –1 to –4/3) and lowered self‐thinning lines. Stress slowed down density‐dependent mortality considerably when competition was not completely symmetric. Stress significantly decreased the self‐thinning intercept, while facilitation simply counteracted stress effects. Both stress and facilitation showed little effect on the slope. In the two‐layer model, both stress and facilitation affected mortality in the same way as in the one‐layer version when competition was not completely symmetric. Different from the one‐layer model, the two‐layer version showed that the effects of stress and facilitation on the self‐thinning slope were mediated by the asymmetry of competition. As stress increased, the overall asymmetry of competition shifted from asymmetric to symmetric due to increased relative strength of root competition. High stress thus dramatically flattened self‐thinning lines, whereas the inclusion of facilitation counteracted stress and led to steeper self‐thinning lines. Our two‐layer model is based on the current knowledge of plant–plant interactions, and better represents ecological realities. It can help elaborate experiments for testing the role of competition and facilitation in driving plant population dynamics.

Field manipulations of resources mediate the transition from intraspecific competition to facilitation.

Population density affects individual performance, though its effects are often mixed. For sessile species, increases in population density typically reduce performance. Still, cases of positive density-dependence do occur in sessile systems and demand explanation. The stress gradient hypothesis (SGH) predicts that under stressful conditions, positive effects of facilitation may outweigh the negative effects of competition. While some elements of the SGH are well studied, its potential to explain intraspecific facilitation has received little attention. Further, there have been questions regarding whether the SGH holds if the stressor is a resource. Most studies of interactions between the environment and intraspecific facilitation have relied on natural environmental gradients; manipulative studies are much rarer. To test the effects of intraspecific density and resources, we manipulated resource availability over natural population densities for the marine bryozoan Watersipora subtorquata. We found negative effects of density on colony performance in low resource environments, but mainly positive density-dependence in high resource environments. By adding resources, competition effects were reduced and the positive effects of facilitation were revealed. Our results suggest that resource availability mediates the relative strength of competition and facilitation in our system. We also suggest that intraspecific facilitation is more common than may be appreciated and that environmental variation may mediate the balance between negative and positive density-dependence.

Expanding vaccine efficacy estimation with dynamic models fitted to cross-sectional prevalence data post-licensure

The efficacy of vaccines is typically estimated prior to implementation, on the basis of randomized controlled trials. This does not preclude, however, subsequent assessment post-licensure, while mass-immunization and nonlinear transmission feedbacks are in place. In this paper we show how cross-sectional prevalence data post-vaccination can be interpreted in terms of pathogen transmission processes and vaccine parameters, using a dynamic epidemiological model. We advocate the use of such frameworks for model-based vaccine evaluation in the field, fitting trajectories of cross-sectional prevalence of pathogen strains before and after intervention. Using SI and SIS models, we illustrate how prevalence ratios in vaccinated and non-vaccinated hosts depend on true vaccine efficacy, the absolute and relative strength of competition between target and non-target strains, the time post follow-up, and transmission intensity. We argue that a mechanistic approach should be added to vaccine efficacy estimation against multi-type pathogens, because it naturally accounts for inter-strain competition and indirect effects, leading to a robust measure of individual protection per contact. Our study calls for systematic attention to epidemiological feedbacks when interpreting population level impact. At a broader level, our parameter estimation procedure provides a promising proof of principle for a generalizable framework to infer vaccine efficacy post-licensure.

Coordination Chemistry of Microbial Iron Transport.

ConspectusThis Account focuses on the coordination chemistry of the microbial iron chelators called siderophores. The initial research (early 1970s) focused on simple analogs of siderophores, which included hydroxamate, catecholate, or hydroxycarboxylate ligands. The subsequent work increasingly focused on the transport of siderophores and their microbial iron transport. Since these are pseudo-octahedral complexes often composed of bidentate ligands, there is chirality at the metal center that in principle is independent of the ligand chirality. It has been shown in many cases that chiral recognition of the complex occurs. Many techniques have been used to elucidate the iron uptake processes in both Gram-positive (single membrane) and Gram-negative (double membrane) bacteria. These have included the use of radioactive labels (of ligand, metal, or both), kinetically inert metal complexes, and Mössbauer spectroscopy. In general, siderophore recognition and transport involves receptors that recognize the metal chelate portion of the iron–siderophore complex. A second, to date less commonly found, mechanism called the siderophore shuttle involves the receptor binding an apo-siderophore.Since one of the primary ways that microbes compete with each other for iron stores is the strength of their competing siderophore complexes, it became important early on to characterize the solution thermodynamics of these species. Since the acidity of siderophores varies significantly, just the stability constant does not give a direct measure of the relative competitive strength of binding. For this reason, the pM value is compared. The pM, like pH, is a measure of the negative log of the free metal ion concentration, typically calculated at pH 7.4, and standard total concentrations of metal and ligand. The characterization of the electronic structure of ferric siderophores has done much to help explain the high stability of these complexes.A new chapter in siderophore science has emerged with the characterization of what are now called siderocalins. Initially found as a protein of the human innate immune system, these proteins bind both ferric and apo-siderophores to inactivate the siderophore transport system and hence deny iron to an invading pathogenic microbe. Siderocalins also can play a role in iron transport of the host, particularly in the early stages of fetal development. Finally, it is speculated that the molecular targets of siderocalins in different species differ based on the siderophore structures of the most important bacterial pathogens of those species.

VirtualCom: a simulation model for eco‐evolutionary community assembly and invasion

Summary What is the relative importance of environmental filtering and competition in community assembly and invasion? At large spatial scales and for species‐rich systems, this question can be answered by studying functional and phylogenetic diversity patterns. The greater availability of community composition surveys, functional trait data bases and/or phylogenies from across a wide range of ecosystems has led to a significant increase in studies based on the analysis of diversity patterns. However, the underlying conceptual and methodological assumptions have recently been put into question, requiring rigorous evaluation of their reliability. In order to test these underlying assumptions, we need to be able to compare diversity patterns with their true underlying processes. For empirical data, we usually do not know these underlying processes, but for virtual data generated by simulation models, this information is available. Using two illustrative examples, we introduce VirtualCom, a simulation model that generates such data sets. Integrating both ecological and evolutionary processes, VirtualCom simulates the evolution of the pool of regionally occurring species, the process‐based assembly of native communities and the invasion of novel species into native communities. The model provides functionalities for a variety of processes. Most importantly, in the simulation of the species pool, different trait evolution models allow the generation of clustered and random trait distributions in the phylogeny (resulting in varying strength of phylogenetic signal). Additionally, when the species assemble from the species pool into local communities based on their trait values, the relative strength of environmental filtering and competition can be set independently. By offering possibilities for a broad range of simulation‐based modelling experiments, VirtualCom is a simple and readily usable tool that will help to resolve theoretical and methodological issues in community ecology.

Trait‐based community assembly of aquatic macrophytes along a water depth gradient in a freshwater lake

Summary Trait‐based approaches provide a framework for integrating the distribution of functional traits associated with ecological strategies into the responses of plant community dynamics along environmental gradients. We used a trait‐based approach to unravel the processes governing macrophyte community assembly along a water depth gradient. We sampled 42 plots and 1513 individual plants and measured 12 functional traits and abundance of 17 macrophyte species. The results showed significant evidences of habitat filtering (i.e. a significant reduction in the range and variance of trait values) and of niche differentiation (i.e. trait values distributed more evenly than expected), both of which affected the functional responses of macrophyte communities associated with different sets of traits in significant different patterns along the gradient. Habitat filtering effects increased significantly for specific leaf area and leaf carbon content along the gradient. Niche differentiation effects increased significantly for leaf dry mass content, but decreased for ramet size, shoot height and leaf carbon content with increasing water depth, implying that the relative strength of biotic competition in a specific functional niche would vary with water depth. Intraspecific trait variability promoted significantly the detection of habitat filtering effects on stem diameter, lamina thickness and stem dry mass content, and niche differentiation effects on specific leaf area, leaf dry mass content, shoot height, stem diameter, stem dry mass content and ramet size. Community assembly processes shape the functional trait distribution within communities along environmental gradients through hierarchical effects of habitat filtering and niche differentiation. Our study highlights that niche differentiation plays a structuring role in macrophyte community assembly and that intraspecific trait variability is an important factor influencing macrophyte community dynamics.

Market driving behaviour in organisations: Antecedents and outcomes

Previous research suggests that the market driving behaviour of firms is linked to exceptional performance. However, the elements of market driving, its antecedents and outcomes, have so far not been empirically measured. The primary objectives of this study are to identify factors that describe market driving, develop a conceptual model, and then consider influencing factors and performance indicators drawn from the entrepreneurship and marketing literature. The model has been empirically tested using a sample of managers in the South African healthcare industry. A fully structured questionnaire was used to address the objective of this study. The realised sample of n=328 was used to analyse the conceptual model applying a partial least squares path modelling approach (PLS-PM). The results revealed that market driving is a firm behaviour and is distinguished by three distinct concepts: market sensing, influencing customer preferences and alliance formation. Three out of four antecedents: strategic orientation, entrepreneurial capital and entrepreneurial behaviour, influenced market driving ability positively. The study also demonstrated that market driving behaviour positively influences firm performance and relative competitive strength

Microbial transformations of nitrogen, sulfur, and iron dictate vegetation composition in wetlands: a review.

The majority of studies on rhizospheric interactions focus on pathogens, mycorrhizal symbiosis, or carbon transformations. Although the biogeochemical transformations of N, S, and Fe have profound effects on vegetation, these effects have received far less attention. This review, meant for microbiologists, biogeochemists, and plant scientists includes a call for interdisciplinary research by providing a number of challenging topics for future ecosystem research. Firstly, all three elements are plant nutrients, and microbial activity significantly changes their availability. Secondly, microbial oxidation with oxygen supplied by radial oxygen loss from roots in wetlands causes acidification, while reduction using alternative electron acceptors leads to generation of alkalinity, affecting pH in the rhizosphere, and hence plant composition. Thirdly, reduced species of all three elements may become phytotoxic. In addition, Fe cycling is tightly linked to that of S and P. As water level fluctuations are very common in wetlands, rapid changes in the availability of oxygen and alternative terminal electron acceptors will result in strong changes in the prevalent microbial redox reactions, with significant effects on plant growth. Depending on geological and hydrological settings, these interacting microbial transformations change the conditions and resource availability for plants, which are both strong drivers of vegetation development and composition by changing relative competitive strengths. Conversely, microbial composition is strongly driven by vegetation composition. Therefore, the combination of microbiological and plant ecological knowledge is essential to understand the biogeochemical and biological key factors driving heterogeneity and total (i.e., microorganisms and vegetation) community composition at different spatial and temporal scales.

Reversing invasion in bistable systems

In this paper, we discuss a class of bistable reaction-diffusion systems used to model the competitive interaction of two species. The interactions are assumed to be of classic "Lotka-Volterra" type and we will consider a particular problem with relevance to applications in population dynamics: essentially, we study under what conditions the interplay of relative motility (diffusion) and competitive strength can cause waves of invasion to be halted and reversed. By establishing rigorous results concerning related degenerate and near-degenerate systems, we build a picture of the dependence of the wave speed on system parameters. Our results lead us to conjecture that this class of competition model has three "zones of response". In the central zone, varying the motility can slow, halt and reverse invasion. However, in the two outer zones, the direction of invasion is independent of the relative motility and is entirely determined by the relative competitive strengths. Furthermore, we conjecture that for a large class of competition models of the type studied here, the wave speed is an increasing function of the relative motility.

Price Competition and Endogenous Valuation in Search Advertising

This article studies how to endogenously assess the value of a “superior” advertising position in the price competition and examines the resulting location competition outcomes and price dispersion patterns. The authors consider a game-theoretic model in which firms compete for advertising positions and then compete in price for customers in a product market. Firms differ in their competence, and positions are differentiated in their prominence, which reflects consumers' online search behavior. They find that when endogenously evaluated within the product market competition, a prominent advertising position might not always be desirable for a firm with competitive advantage, even if it is cost-free. The profitability of a prominent advertising position depends on the trade-off between the extra demand from winning the position and the higher equilibrium prices when the weaker competitor wins it. Furthermore, the authors show that the bidding outcome might not align with the relative competitive strength, and an advantaged firm might not be able to win the prominent position even when it values that position. They derive two-dimensional equilibrium price dispersion with the realized prices at the same position varying and the expected prices differing across different positions. They find that the expected price in the prominent position might not always be higher, implying that an expensive location does not necessarily lead to expensive products.

Patterns and mechanisms of conspecific and heterospecific interactions in a dry perennial grassland

Summary 1. Models of local stable coexistence require negative feedbacks, i.e. intraspecific interactions must be more negative than interspecific interactions. However, most competition experiments, often done in the glasshouse, have found evidence for competitive hierarchies. Measurement of interactions under realistic field conditions is necessary to assess their contribution to community dynamics, and explicit measurement of intermediaries thought to be important in interactions may allow studies to account for any variation in experimental results. 2. In this study, we compare conspecific and heterospecific interactions in a field experiment in a dry sand prairie in Michigan. We study the four dominant species at two different stages, germination and adult growth. Using seed addition and adult transplant experiments, we ask whether plants perform best in natural field monocultures of conspecifics, heterospecifics or no neighbour plots. We also measure abiotic environmental characteristics associated with each neighbourhood type and test whether performance can be explained by environmental effects. We hypothesize that plants will create competitive hierarchies because our experimental design is similar to classic competition experiments. 3. Neighbour species created consistent hierarchies in their effects on germination of all four target species, which is likely due to light limitation. However, interestingly, adult plant biomass for two of the three species (one species did not survive) was lower in conspecific monocultures compared to heterospecific or no neighbour plots, thus producing negative feedbacks. For two species, the effects of neighbours on adult growth are likely due to reduction of light and soil nitrate; for the third, however, resources could not explain the pattern that conspecific interactions were more negative than heterospecific. 4. Synthesis. These results suggest that patterns in the relative strength of conspecific and heterospecific competition depend on life‐history stage. Moreover, resource uptake could explain some, but not all, of the interactions among species, suggesting that other factors such as microbial communities or other forms of niche partitioning may play a role and that field experiments are necessary to gauge their relative importance.

Biodiversity and belowground interactions mediate community invasion resistance against a tall herb invader

Species-rich plant communities are hypothesized to be more resistant against plant invasions because they use resources in a more efficient way. However, the relative contributions of aboveground competition and belowground interactions for invasion resistance are still poorly understood. We compared the performance of Knautia arvensis transplants growing in plots differing in plant diversity both under full competition and with shoots of neighbors tied back to determine the relative strength of aboveground competition in suppressing this test invader without the confounding effect of shading. In addition, we assessed the effects of belowground competition and soil-borne pathogens on transplant performance. Both aboveground competition and plant species richness strongly and independently affected invader performance. Aboveground biomass, height, leaf mass per area and flowering of transplanted individuals of K. arvensis decreased with increasing species richness of the host community. Species-rich and species-poor communities both imposed equally strong aboveground competition on K. arvensis. However, belowground interactions (especially belowground root competition) had strong negative effects on transplant performance. In addition, the presence of grasses in a plant community further reduced the performance of K. arvensis. Our results suggest that belowground competition can render species-rich host communities more suppressive to newly arriving species, thus enhancing community invasion resistance.

Size at hatching determines population dynamics and response to harvesting in cannibalistic fish

We hypothesize that size at hatching strongly affects population dynamics of cannibalistic fish species and is a crucial determinant of how populations respond to selective removal of large individuals (harvesting). We use a mechanistic mathematical model to study the relation between hatching size and response to harvesting mortality, using Eurasian perch ( Perca fluviatilis ) as a model organism. We show how hatching size determines dynamics through its effect on the relative strength of cannibalistic mortality and resource competition as mechanisms of population regulation. In populations with intermediate and large hatching size, cannibalistic mortality is an important determinant of population dynamics, and harvesting destabilizes population dynamics. When hatching size is small, population stability is less sensitive to this type of harvesting. Populations hatching at small size are regulated by competition, and harvesting large individuals affects such populations less. Harvesting can also induce the growth of very large individuals, absent in unharvested populations. Our results show that harvesting in cannibalistic lake fish populations can strongly alter population dynamics in ways that can only be anticipated on the basis of mechanistic knowledge about how populations are regulated.

The shifting balance of facilitation and competition affects the outcome of intra- and interspecific interactions over the life history of California grassland annuals

Trait-based resource competition in plants, wherein more similar plants compete more strongly for resources, is a foundation of niche-based explanations for the maintenance of diversity in plant communities. Alternatively, neutral theory predicts that community diversity can be maintained despite equivalent resource requirements among species. We examined interactions at three life history stages (germination, survival, and juvenile-adult growth) for three native and three exotic California annual species in a glasshouse experiment. We varied plant density and species composition in small pots, with pots planted with either intraspecific seeds or in a three species mix of intra- and interspecific neighbors. We saw a range of facilitative, neutral, and competitive interactions that varied significantly by species, rather than by native or exotic status. There were more competitive interactions at the emergence and juvenile-adult growth stages and more facilitative interactions for survival. Consequently, the relative strength of competition in intraspecific versus mixed-species communities depended on whether we considered only the juvenile-adult growth stage or the entire life history of the interacting plants. Using traditional analysis of juvenile-adult growth only, all species showed negative density-dependent interactions for final biomass production. However, when the net effect of plant interactions from seed to adult was considered, which is a prediction of population growth, two native species ceased to show negative density dependence, and the difference between intraspecific and mixed-species competition was only significant for one exotic species. Results were consistent with predictions of neutral, rather than niche, theory for five of six species.