植物地上竞争与地下竞争研究进展

植物地上光竞争和地下水分与营养的竞争过程十分复杂,并且与竞争机制密切相关。从地上和地下竞争理论、两种竞争过程的相互作用机制以及分离地上和地下竞争的研究方法和表达指标等几个方面综述和分析目前的研究状况,以期为国内研究者在本领域进一步展开实验提供理论依据和实验设计参考。总结了与地上、地下相对竞争强度有关的优化分配理论,地上、地下竞争随生产力梯度的变化,资源异质性对地上、地下竞争机制的影响。介绍了地上竞争和地下竞争相互作用类型以及目前提出的两种作用机制。对常用的3种分离地上、地下竞争的方法:盆分隔、间植分隔和目标植分隔法以及表达竞争强度和竞争重要性的指标和公式进行了归纳。提出未来的研究内容,认为在开展此类研究时,应考虑到实验植物的生理学特性、发育状况、立地生产力跨度范围以及竞争持续时间等方面因素,并认为发展地下竞争研究、深入探讨根系间相互作用的影响因子和过程是当前的研究热点。     

Intensity and Importance of Competition for a Grass (Festuca rubra) and a Legume (Trifolium pratense) Vary with Environmental Changes

How plant competition varies across environmental gradients has been a long debate among ecologists. We conducted a growth chamber experiment to determine the intensity and importance of competition for plants grown in changed environmental conditions. Festuca rubra and Trifolium pratense were grown in monoculturs and in two- and/or three-species mixtures under three environmental treatments. The measured competitive variations in terms of growth (height and biomass) were species-dependent. Competition intensity for Festuca increased with decreased productivity, whilst competition importance displayed a humpback response. However, significant response was detected in neither competition intensity nor importance for Trifolium. Intensity and importance of competition followed different response patterns, suggesting that they may not be correlated along an environmental gradient. The biological and physiological variables of plants play an important role to determine the interspecific competition associated with competition intensity and importance. However, the competitive feature can be modified by multiple environmental changes which may increase or hinder how competitive a plant is.     

Temperature‐dependence of minimum resource requirements alters competitive hierarchies in phytoplankton

Resource competition theory is a conceptual framework that provides mechanistic insights into competition and community assembly of species with different resource requirements. However, there has been little exploration of how resource requirements depend on other environmental factors, including temperature. Changes in resource requirements as influenced by environmental temperature would imply that climate warming can alter the outcomes of competition and community assembly. We experimentally demonstrate that environmental temperature alters the minimum light and nitrogen requirements – as well as other growth parameters – of six widespread phytoplankton species from distinct taxonomic groups. We found that species require the most nitrogen at the highest temperatures while light requirements tend to be lowest at intermediate temperatures, although there are substantial interspecific differences in the exact shape of this relationship. We also experimentally parameterize two competition models, which we use to illustrate how temperature, through its effects on species’ traits, alters competitive hierarchies in multispecies assemblages, determining community dynamics. Developing a mechanistic understanding of how temperature influences the ability to compete for limiting resources is a critical step towards improving forecasts of community dynamics under climate warming.     

Testing the mechanisms by which source-sink dynamics alter competitive outcomes in a model system

Dispersal among sites can affect within-site competitive outcomes via source-sink dynamics. Source-sink dynamics are thought to affect competitive outcomes primarily via spatial subsidies: by redistributing individuals from sources to sinks, source-sink dynamics can alter competitive outcomes in both sources and sinks. However, dispersal also can affect competitive outcomes via demography modification, which occurs when dispersal alters the parameters governing species' per capita demographic rates. For instance, dispersal of exploitative competitors might cause extinction of some of the resources for which competition occurs, thereby altering the competition coefficients. I used protist microcosms as a model system to test whether spatial subsidies alone could explain the effects of source-sink dynamics on competitive outcomes. I examined the long-term outcome of exploitative competition among three bacterivorous ciliate protists in microcosms of high enrichment (sources) and low enrichment (sinks) in both the presence and the absence of dispersal. Dispersal altered competitive outcomes. Fitting mathematical models to the population dynamics revealed that spatial subsidies were insufficient to account for the effects of dispersal. Fitting alternative models strongly suggested that demography modification was an important determinant of competitive outcomes. These results provide the first evidence that dispersal does not simply redistribute competitors but can alter their per capita demographic rates.     

A shift from exploitation to interference competition with increasing density affects population and community dynamics

Intraspecific competition influences population and community dynamics and occurs via two mechanisms. Exploitative competition is an indirect effect that occurs through use of a shared resource and depends on resource availability. Interference competition occurs by obstructing access to a resource and may not depend on resource availability. Our study tested whether the strength of interference competition changes with protozoa population density. We grew experimental microcosms of protozoa and bacteria under different combinations of protozoan density and basal resource availability. We then solved a dynamic predator–prey model for parameters of the functional response using population growth rates measured in our experiment. As population density increased, competition shifted from exploitation to interference, and competition was less dependent on resource levels. Surprisingly, the effect of resources was weakest when competition was the most intense. We found that at low population densities, competition was largely exploitative and resource availability had a large effect on population growth rates, but the effect of resources was much weaker at high densities. This shift in competitive mechanism could have implications for interspecific competition, trophic interactions, community diversity, and natural selection. We also tested whether this shift in the mechanism of competition with protozoa density affected the structure of the bacterial prey community. We found that both resources and protozoa density affected the structure of the bacterial prey community, suggesting that competitive mechanism may also affect trophic interactions.     

Size-asymmetric competition and size-asymmetric growth in a spatially explicit zone-of-influence model of plant competition

Size-asymmetric competition among plants is usually defined as resource pre-emption by larger individuals, but it is usually observed and measured as a disproportionate size advantage in the growth of larger individuals in crowded populations (“size-asymmetric growth”). We investigated the relationship between size-asymmetric competition and size-asymmetric growth in a spatially explicit, individual-based plant competition model based on overlapping zones of influence (ZOI). The ZOI of each plant is modeled as a circle, growing in two dimensions. The size asymmetry of competition is reflected in the rules for dividing up the overlapping areas. We grew simulated populations with different degrees of size-asymmetric competition and at different densities and analyzed the size dependency of individual growth by fitting coupled growth functions to individuals. The relationship between size and growth within the populations was summarized with a parameter that measures the size asymmetry of growth. Complete competitive symmetry (equal division of contested resources) at the local level results in a very slight size asymmetry in growth. This slight size asymmetry of growth did not increase with increasing density. Increased density resulted in increased growth asymmetry when resource competition at the local level was size asymmetric to any degree. Size-asymmetric growth can be strong evidence that competitive mechanisms are at least partially size asymmetric, but the degree of size-asymmetric growth is influenced by the intensity as well as the mode of competition. Intuitive concepts of size-asymmetric competition among individuals in spatial and nonspatial contexts are very different.     

Get the shovel: morphological and evolutionary complexities of belowground organs in geophytes

Herbaceous plants collectively known as geophytes, which regrow from belowground buds, are distributed around the globe and throughout the land plant tree of life. The geophytic habit is an evolutionarily and ecologically important growth form in plants, permitting novel life history strategies, enabling the occupation of more seasonal climates, mediating interactions between plants and their water and nutrient resources, and influencing macroevolutionary patterns by enabling differential diversification and adaptation. These taxa are excellent study systems for understanding how convergence on a similar growth habit (i.e., geophytism) can occur via different morphological and developmental mechanisms. Despite the importance of belowground organs for characterizing whole-plant morphological diversity, the morphology and evolution of these organs have been vastly understudied with most research focusing on only a few crop systems. Here, we clarify the terminology commonly used (and sometimes misused) to describe geophytes and their underground organs and highlight key evolutionary patterns of the belowground morphology of geophytic plants. Additionally, we advocate for increasing resources for geophyte research and implementing standardized ontological definitions of geophytic organs to improve our understanding of the factors controlling, promoting, and maintaining geophyte diversity.     

Seasonal variation in the strength of interference competition among headwater stream predators

1. Vertebrate communities in headwater streams are assumed to be regulated through competitive and predatory interactions. Although documented predation is rare, studies regularly report competitive dominance by fish that, as larger competitors reliant on aquatic habitat, exclude semi-aquatic salamanders to marginal stream habitat. However, it is unclear whether fish interact with stream-breeding salamanders through indirect effects such as competition for resources (e.g. food or cover) or fear (i.e. threat of predation) nor is it known whether these interactions are consistent through time.
2. This study used a novel caging approach to determine if competitive outcomes between a headwater fish and salamanders were regulated primarily through resource depletion (exploitative competition) or behavioural avoidance (interference competition).
3. We paired banded sculpin (Cottus carolinae) and larval red salamanders (Pseudotriton ruber) of similar body size in independent flow through mesocosms with intra- and inter-specific pairs allowed to interact physically or non-physically. The experiment was repeated in the autumn and in the spring when stream salamander larvae begin to transform into terrestrial juveniles.
4. Banded sculpin negatively influenced growth of red salamanders regardless of whether they were allowed to physically interact, suggesting interference competition and behavioural avoidance. This asymmetrical effect was strongest in the spring when salamanders underwent metamorphosis at higher rates in the presence of fish. However, in the autumn, the effects were more balanced between the two species with salamanders impacting fish through exploitative competition.
5. By studying the temporal relationships between two competitors and using a caging method novel to competition studies, we established that the outcomes of competition are dependent on season and may vary in type relative to the timing of life-history events. For this community, these results suggest that outcomes of competition are highly dependent on season and could indicate a biotic mechanism maintaining headwater salamander distributions through source–sink dynamics. Our results also suggest that, in this species interaction, it may be unwarranted to assume that the outcomes of competition at one time represent the complex relationships regulating community interactions.

     

“Cancer Reviews 2021” series: Cell competition in intratumoral and tumor microenvironment interactions

Tumors are complex cellular and acellular environments within which cancer clones are under continuous selection pressures. Cancer cells are in a permanent mode of interaction and competition with each other as well as with the immediate microenvironment. In the course of these competitive interactions, cells share information regarding their general state of fitness, with less‐fit cells being typically eliminated via apoptosis at the hands of those cells with greater cellular fitness. Competitive interactions involving exchange of cell fitness information have implications for tumor growth, metastasis, and therapy outcomes. Recent research has highlighted sophisticated pathways such as Flower, Hippo, Myc, and p53 signaling, which are employed by cancer cells and the surrounding microenvironment cells to achieve their evolutionary goals by means of cell competition mechanisms. In this review, we discuss these recent findings and explain their importance and role in evolution, growth, and treatment of cancer. We further consider potential physiological conditions, such as hypoxia and chemotherapy, that can function as selective pressures under which cell competition mechanisms may evolve differently or synergistically to confer oncogenic advantages to cancer.     

Influence of resource levels,organic compounds and laboratory colonization on interspecific competition between the Asian tiger mosquito Aedes albopictus (Stegomyia albopicta) and the southern house mosquito Culex quinquefasciatus

The mosquitoes Aedes albopictus (Stegomyia albopicta) (Skuse) and Culex quinquefasciatus (Say) (Diptera: Culicidae) are common inhabitants of tyres and other artificial containers, which constitute important peridomestic mosquito breeding habitats. We tested the hypotheses that interspecific resource competition between the larvae of these species is asymmetrical, that the concentration of chemicals associated with decomposing detritus affects the competitive outcomes of these species, and that wild and colonized strains of Cx. quinquefasciatus are affected differently by competition with Ae. albopictus. We conducted two laboratory competition experiments wherein we measured survivorship and estimated population growth (λ′) in both species under multiple mixed‐species densities. Under varying resource levels, competition was asymmetrical: Ae. albopictus caused competitive reductions or exclusions of Cx. quinquefasciatus under conditions of limited resources. In a second experiment, which used both wild and colonized strains of Cx. quinquefasciatus, organic chemical compounds associated with decomposing detritus did not affect the competitive outcome. The colonized strain of Cx. quinquefasciatus had greater survivorship and adult mass, and faster development times than the wild strain, but both strains were similarly affected by competition with Ae. albopictus. Competition between these species may have important consequences for vector population dynamics, especially in areas in which tyres and artificial containers constitute the majority of mosquito breeding habitats.     

Predation, competition, and nutrient recycling: a stoichiometric approach with multiple nutrients

A model for two competing prey species and one predator is formulated in which three essential nutrients can limit growth of all populations. Prey take up dissolved nutrients and predators ingest prey, assimilating a portion of ingested nutrients and recycling or respiring the balance. For all species, the nutrient contents of individuals vary and growth is coupled to increasing content of the limiting nutrient. This model was parameterized to describe a flagellate preying on two bacterial species, with carbon (C), nitrogen (N), and phosphorus (P) as nutrients. Parameters were chosen so that the two prey species would stably coexist without predators under some nutrient supply conditions. Using numerical simulations, the long-term outcomes of competition and predation were explored for a gradient of N:P supply ratios, varying C supply, and varying preference of the predator for the two prey. Coexistence and competitive exclusion both occurred under some conditions of nutrient supply and predator preference. As in simpler models of competition and predation these outcomes were largely governed by apparent competition mediated by the predator, and resource competition for nutrients whose effective supply was partly governed by nutrient recycling also mediated by the predator. For relatively small regions of parameter space, more complex outcomes with multiple attractors or three-species limit cycles occurred. The multiple constraints posed by multiple nutrients held the amplitudes of these cycles in check, limiting the influence of complex dynamics on competitive outcomes for the parameter ranges explored.     

The interaction between predation and competition: a review and synthesis

This review discusses the interface between two of the most important types of interactions between species, interspecific competition and predation. Predation has been claimed to increase, decrease, or have little effect on, the strength, impact or importance of interspecific competition. There is confusion about both the meaning of these terms and the likelihood of, and conditions required for, each of these outcomes. In this article we distinguish among three measures of the influence of predation on competitive outcomes: short‐term per capita consumption or growth rates, long‐term changes in density, and the probability of competitive coexistence. We then outline various theoretical mechanisms that can lead to qualitatively distinct effects of predators. The qualitative effect of predators can depend both on the mechanism of competition and on the definition of competitive strength/impact. In assessing the empirical literature, we ask: (1) What definitions of competitive strength/impact have been assumed? (2) Does strong evidence exist to support one or more of the possible mechanisms that can produce a given outcome? (3) Do biases in the choice of organism or manipulation exist, and are they likely to have influenced the conclusions reached? We conclude by discussing several unanswered questions, and espouse a stronger interchange between empirical and theoretical approaches to this important question.     

Interspecific competition in bats: state of knowledge and research challenges

1. Interspecific competition (IC) is often seen as a main driver of evolutionary patterns and community structure. Bats might compete for key resources, and cases of exaggerated divergence of resource-related characters or trait overdispersion in bat assemblages are often explained in terms of current or past interspecific competition. However, other pressures leading to patterns that mimic the outcome of competition cannot always be ruled out.
2. We present the state of knowledge on IC among bats, providing a critical evaluation of the information available and identifying open questions and challenges.
3. We reviewed 100 documents addressing potential or actual IC in bats and categorised them in terms of the resource for which bats compete (food, foraging habitat, roosts, water, and acoustic space). We also examined the ecomorphological and behavioural traits considered therein to highlight responses to IC or niche partitioning.
4. We found that: although resources should be limiting in order for competition to occur, this is seldom tested; sympatry is sometimes taken as synonymous of syntopy (yet sympatric species that are not syntopic will never experience competition); comparisons between sympatry and allopatry are rare; and testing of objective criteria exploring the existence of niche partitioning or character displacement is not commonly adopted.
5. While morphological examination of food remains in droppings has often led to coarse-grained analysis that proved insufficient to establish the occurrence of food niche overlap or partitioning, new frontiers are being opened by state-of-the-art molecular dietary analysis.
6. A better understanding of IC in bats is paramount, since distributional changes leading to novel bat assemblages driven by climate change are already taking place, and the dramatic decline in insect availability, as well as the global loss or alteration of foraging habitat, may generate new competitive interactions or exacerbate existing interactions in the Anthropocene, and into the future.

     

植物竞争研究综述

概述了竞争的概念、理论 (包括最大生长率理论、最小资源需求理论和资源动态两阶段说 )、特性 (主要有竞争不对称性和环境相关性 )及其影响因素 ,竞争与群落组成、结构和动态的关系。并对近几十年来生态学上关于植物竞争的争论焦点作了论述 ,即竞争对个体生长、繁殖和存活及群落演替的相对重要性 ,主要介绍了Grime、Newman&Tilman和Deborah&Ariel的 3种观点 ,其中Grime认为竞争不重要 ,相反Newman&Tilman认为竞争比较重要 ,Deborah&Ariel则提出了资源动态两阶段说 ,认为竞争重要与否取决于两个条件 :一为植物对土壤资源的吸收利用与非生物因素两者分别在多大程度上决定了资源可利用性的渐次降低 ;二为资源正波动期因竞争引起的生长量减少在多大程度上决定了资源负波动期个体的存活率     

Resource competition and adaptive radiation in a microbial microcosm

Theory predicts that competition for shared resources in a monomorphic population generates divergent selection for adaptation to alternative resources. Experimental tests of this hypothesis are scarce. We selected populations of the bacterium Pseudomonas fluorescens in spatially homogeneous microcosms containing a complex mixture of resources. Initially, all populations consisted of two isogenic clones. The outcome of selection was the evolution of a diverse community of genotypes within each population. Sympatric genotypes exhibited differentiation in metabolic traits related to resource acquisition and frequency‐dependent trade‐offs in competitive ability, as we would expect if different genotypes consumed different resources. These results are consistent with the hypothesis of adaptive radiation driven by resource competition. Reconciling the results of this study with those of earlier experiments provides a new interpretation of the ecological causes of adaptive radiation in microbial microcosms.     

Variation in the relative magnitude of intraspecific and interspecific competitive effects in novel versus familiar environments in two<Emphasis Type="Italic">Drosophila</Emphasis> species

Models of competitor coevolution, especially the genetic feedback hypothesis, suggest that a negative correlation between intraspecific and interspecific competitive effects may be important in sustaining competitor coexistence, and can give rise to oscillatory dynamics with repeated reversals of competitive superiority. I reanalyzed previously published census data from an experiment in which populationsof Drosophila melanogaster andD. simulans underwent competitive coevolution in one familiar and two novel environments, to specifically look for any evidence of a negative relationship between intraspecific and interspecific competitive effects on population growth rates, and for any indication of short period cycling in the relative magnitude of intraspecific and interspecific competitive effects. While there was considerable variation in the relative magnitude of intraspecific and interspecific competitive effects over generations, among both populations and environments, there was no clear evidence supporting the genetic feedback hypothesis. Intraspecific and interspecific competitive effects on population growth rates were strongly positively correlated in novel environments, and uncorrelated in the familiar environment. Data from the familiar environment indicated that indices of competition of populations of the initially superior competitor,D. melanogaster, might be showing some cyclic behaviour, but I argue that this is likely to be transient, and not suggestive of sustained oscillatory dynamics predicted by the genetic feedback model. I discuss the results in the context of the importance of the genetic architecture of intraspecific and interspecific competitive abilities in determining the coevolutionary trajectory of competitive interactions.     

Population regulation of territorial species: both site dependence and interference mechanisms matter

Spatial patterns of site occupancy are commonly driven by habitat heterogeneity and are thought to shape population dynamics through a site-dependent regulatory mechanism. When examining this, however, most studies have only focused on a single vital rate (reproduction), and little is known about how space effectively contributes to the regulation of population dynamics. We investigated the underlying mechanisms driving density-dependent processes in vital rates in a Mauritius kestrel population where almost every individual was monitored. Different mechanisms acted on different vital rates, with breeding success regulated by site dependence (differential use of space) and juvenile survival by interference (density-dependent competition for resources). Although territorial species are frequently assumed to be regulated through site dependence, we show that interference was the key regulatory mechanism in this population. Our integrated approach demonstrates that the presence of spatial processes regarding one trait does not mean that they necessarily play an important role in regulating population growth, and demonstrates the complexity of the regulatory process.     

Phenotypic and genetic integration of personality and growth under competition in the sheepshead swordtail,Xiphophorus birchmanni

Competition for resources including food, physical space, and potential mates is a fundamental ecological process shaping variation in individual phenotype and fitness. The evolution of competitive ability, in particular social dominance, depends on genetic (co)variation among traits causal (e.g., behavior) or consequent (e.g., growth) to competitive outcomes. If dominance is heritable, it will generate both direct and indirect genetic effects (IGE) on resource‐dependent traits. The latter are expected to impose evolutionary constraint because winners necessarily gain resources at the expense of losers. We varied competition in a population of sheepshead swordtails, Xiphophorus birchmanni, to investigate effects on behavior, size, growth, and survival. We then applied quantitative genetic analyses to determine (i) whether competition leads to phenotypic and/or genetic integration of behavior with life history and (ii) the potential for IGE to constrain life history evolution. Size, growth, and survival were reduced at high competition. Male dominance was repeatable and dominant individuals show higher growth and survival. Additive genetic contributions to phenotypic covariance were significant, with the G matrix largely recapitulating phenotypic relationships. Social dominance has a low but significant heritability and is strongly genetically correlated with size and growth. Assuming causal dependence of growth on dominance, hidden IGE will therefore reduce evolutionary potential.     

Evolutionary significance of genotypic variation in developmental reaction norms for a perennial grass under competitive stress

The developmental reaction norm (DRN) represents the set of ontogenetic trajectories that can be produced by a genotype exposed to different environmental conditions. Genetic variation in the DRN for growth traits and in the patterns of biomass allocation is critical to phenotypic evolution in heterogeneous environments. The DRN and patterns of biomass allocation were investigated in 11 clones of the caespitose, corm-forming, perennial grass Phleum pratense in relation to competitive stress imparted by Lolium perenne in a 16 week glasshouse experiment. A separate experiment assessed the ability of basal buds flanking a corm to sprout and the relationship of corm mass to sprout mass for the same clones. Corm fresh mass varied among clones and was significantly correlated with the dry mass of the tillers that sprouted from basal buds. In the competition experiment, clones in competitive environments varied significantly from those in non-competetive environments in terms of their DRNs for number of tillers and shoot dry mass. Thus, selection of DRNs would favour different genotypes in the two environments and at different times. Significant negative genetic correlations were detected for tiller number and mean tiller mass in the noncompetitive, but not the competitive, environment. Biomass allocation to stem bases was significantly greater for clones under competitive stress. Allocation to storage tissues such as corms may be adaptive if it enhances persistence in the competitive field environments typically occupied by caespitose grasses. Root and shoot allocation showed a significant clone by competition interaction. For P. pratense, genotypic variation in growth trajectories plays an important role in determining variation in individual performance, a condition necessary for the continued evolution of the DRN.     

Implications of body size for interspecific interactions and assemblage organization among coral-reef fishes

Abstract Population size-structure is often ignored in assemblage-level studies of reef fishes, which usually rely on static and dynamic patterns of relative total abundance to infer what mechanisms organize those assemblages. However, body size has substantial effects on processes that affect competitive relationships between species: (i) small, recently recruited fish, which usually(?) suffer high mortality, can dominate total abundance and strongly influence the dynamics of the relative total abundances of different species, while having little effect on interspecific biomass relations; (ii) numeric abundance and biomass of a species can vary independently, due to habitat variation in population size-structure resulting from variation in mortality and growth, as well as habitat selection; and (iii) population size-structure affects the potential for and outcome of interspecific competition due to (a) ontogenetic change in types of resources used, (b) levels of resource needs being dependent on individual and species biomass rather than numbers, (c) advantages due to large size in behavioural contests, (d) variation in population size-structure being linked to habitat preference, which affects expression of competitive dominance, and (e) size dependency in the development of interspecific resource-sharing relationships. Assemblage-level analyses that ignore such size effects may fail to detect important effects of interspecific interactions.