Interspecific competition in Drosophila I. Reversal of competitive superiority due to varying concentration of ethanol

The experiments reported here were designed to investigate the outcome of interspecific competition between Drosophila melanogaster and D. simulans in environments varying in one factor only. The factor chosen was ethanol concentration in the medium; the strains used were D. melanogaster SM5 (Series I), D. melanogasterw, b , (Series II) and D. simulans v (both Series).
The results of competition over a number of generations, the longest experiment lasting 100 days, showed clear differences in the relative competitive abilities of the two species between the different environments. With no ethanol, D. simulans won in all replicates; with 896 ethanol, D. melanogaster won in all replicates; at intermediate (496) concentration, the winning species was not consistent. Experiments in Series II showed very similar results to their counterparts in Series I despite distinct genetic differences between the strains of D. melanogaster used.
These results tie in with published work, on (i) the relative susceptibility of single–species cultures of D. melanogaster and D. simulans to high ethanol concentrations, and (ii) distributional patterns observed in some field populations exposed to alcohols in their environment.     

Competitive interactions and persistence of two nematode species that parasitize Drosophila recens

Drosophila recens is parasitized in the wild by two nematodes, Howardula aoronymphium , a host generalist, and Parasitylenchus nearcticus , a host specialist known only from D .  recens . In order to understand how these two parasite species coexist, we compared their ability to infect and grow in D .  recens , their effects on host fecundity and survival, and whether one parasite species was competitively superior in double infections. The specialist nematode P. nearcticus had greater rates of infection and reproduction than the generalist H. aoronymphium , and completely sterilized females in single and mixed infections. The specialist was competitively superior in mixed infections, as generalist motherworms were significantly smaller than in single infections. These results suggest that P. nearcticus might competitively exclude H. aoronymphium if D. recens were the only host available. It is likely that H. aoronymphium persists in D. recens by transmission from other, more suitable host species.     

Interspecific competition in perennial sedentary organisms: An individual-based model

We investigated a mathematical model of the dynamics of the ecological system consisting of two competing perennial species, each of which leads a sedentary life. It is an individual-based model, in which the growth of each individual is described. The rate of this growth is weakened by competition from neighboring individuals. The strength of the competitors' influence depends on their size and distance to them. The conditions, in which the competitive exclusion of one of the competitors and the coexistence of both competitors take place are provided. The influence of the parameters responsible for the strength of competition, the degree of competitive asymmetry, and consideration of the importance of specific elements of the spatial structure of this ecological system on the results of the competition were analyzed. Both species co-exist when they are equal competitors. Permanent coexistence is possible only when interspecific competition is weaker than intraspecific. When interspecific competition is stronger, the coexistence of equal interspecific competitors is random. Both species have equal probability of extinction. If species are not equal competitors, the stronger one wins. This result can be modified by different strengths of intraspecific competition. The weaker interspecific competitor can permanently coexist with stronger one, when its individuals suffer stronger intraspecific competition.     

Diauxic lags explain unexpected coexistence in multi‐resource environments

How the coexistence of species is affected by the presence of multiple resources is a major question in microbial ecology. We experimentally demonstrate that differences in diauxic lags, which occur as species deplete their own environments and adapt their metabolisms, allow slow‐growing microbes to stably coexist with faster‐growing species in multi‐resource environments despite being excluded in single‐resource environments. In our focal example, an Acinetobacter species (Aci2) competitively excludes Pseudomonas aurantiaca (Pa) on alanine and on glutamate. However, they coexist on the combination of both resources. Experiments reveal that Aci2 grows faster but Pa has shorter diauxic lags. We establish a tradeoff between Aci2’s fast growth and Pa’s short lags as their mechanism for coexistence. We model this tradeoff to accurately predict how environmental changes affect community composition. We extend our work by surveying a large set of competitions and observe coexistence nearly four times as frequently when the slow‐grower is the fast‐switcher. Our work illustrates a simple mechanism, based entirely on supplied‐resource growth dynamics, for the emergence of multi‐resource coexistence.     

Interspecific competition among urban cockroach species

The aim of this study was to quantify and to compare the effects of intraspecific and interspecific competition among pairs of urban cockroaches [Blatta orientalis L., Periplaneta americana (L.), and Periplaneta australasiae Fabricius (Dictyoptera: Blattodea)] in relation to the limitation of resources such as shelter or food. Our approach was to assess whether the presence of one species affected the resource exploitation of another. A reduction in access to shelters or to food for one species revealed dominant/subordination relationships among species and induced spatial segregation in shelters and temporal segregation during food exploitation. The fragmentation of available resources facilitated spatial segregation and the access of more individuals of the subordinate species. Individuals of each species were aware of the presence of non‐conspecifics. The outcome of interspecific competition under laboratory conditions should help us to understand how segregated spatial distributions occur under natural conditions in urban areas.     

Temporal resource partitioning mitigates interspecific competition and promotes coexistence among insect parasites

A key to understanding life's great diversity is discerning how competing organisms divide limiting resources to coexist in diverse communities. While temporal resource partitioning has long been hypothesized to reduce the negative effects of interspecific competition, empirical evidence suggests that time may not often be an axis along which animal species routinely subdivide resources. Here, we present evidence to the contrary in the world's most biodiverse group of animals: insect parasites (parasitoids). Specifically, we conducted a meta-analysis of 64 studies from 41 publications to determine if temporal resource partitioning via variation in the timing of a key life-history trait, egg deposition (oviposition), mitigates interspecific competition between species pairs sharing the same insect host. When competing species were manipulated to oviposit at (or near) the same time in or on a single host in the laboratory, competition was common, and one species was typically inherently superior (i.e. survived to adulthood a greater proportion of the time). In most cases, however, the inferior competitor could gain a survivorship advantage by ovipositing earlier (or in a smaller number of cases later) into shared hosts. Moreover, this positive (or in a few cases negative) priority advantage gained by the inferior competitor increased as the interval between oviposition times became greater. The results from manipulative experiments were also correlated with patterns of life-history timing and demography in nature: the more inherently competitively inferior a species was in the laboratory, the greater the interval between oviposition times of taxa in co-occurring populations. Additionally, the larger the interval between oviposition times of competing taxa, the more abundant the inferior species was in populations where competitors were known to coexist. Overall, our findings suggest that temporal resource partitioning via variation in oviposition timing may help to facilitate species coexistence and structures diverse insect communities by altering demographic measures of species success. We argue that the lack of evidence for a more prominent role of temporal resource partitioning in promoting species coexistence may reflect taxonomic differences, with a bias towards larger-sized animals. For smaller species like parasitic insects that are specialized to attack one or a group of closely related hosts, have short adult lifespans and discrete generation times, compete directly for limited resources in small, closed arenas and have life histories constrained by host phenology, temporal resource subdivision via variation in life history may play a critical role in allowing species to coexist by alleviating the negative effects of interspecific competition.     

Interspecific competition in metapopulations

The assumptions and predictions of metapopulation models for competing species are discussed in relation to empirical studies of colonization and extinction in metapopulations. In three species of Daphnia in rockpools, interspecific competition increased local extinction rates, while no effects on colonization rates were detected. Distributional patterns were consistent with several predictions of the competition model; for example, the number of species on an island increased with the number of pools and the proportion of pools occupied by each species decreased with increasing species number. It is concluded that interspecific competition is important for the distributional dynamics of Daphnia species in rockpools, but the question whether the coexistence of these species depends on metapopulation dynamics is still unresolved. Other studies on the effects of interspecific competition on colonization and extinction rates are discussed.     

Interspecific interactions in phytophagous insects revisited: a quantitative assessment of competition theory

The importance of interspecific competition is a highly controversial and unresolved issue for community ecology in general, and for phytophagous insects in particular. Recent advancements, however, in our understanding of indirect (plant- and enemy-mediated) interactions challenge the historical paradigms of competition. Thus, in the context of this rapidly developing field, we re-evaluate the evidence for interspecific competition in phytophagous insects using a meta-analysis of published studies. Our analysis is specifically designed to test the assumptions underlying traditional competition theory, namely that competitive interactions are symmetrical, necessitate spatial and temporal co-occurrence, and increase in intensity as the density, phylogenetic similarity, and niche overlap of competing species increase. Despite finding frequent evidence for competition, we found very little evidence that plant-feeding insects conform to theoretical predictions for interspecific competition. Interactions were highly asymmetrical, similar in magnitude within vs. between feeding guilds (chewers vs. sap-feeders), and were unaffected by the quantity of resources removed (% defoliation). There was mixed support for the effects of phylogeny, spatial/temporal separation, and the relative strength of intra- vs. interspecific competition. Clearly, a new paradigm that accounts for indirect interactions and facilitation is required to describe how interspecific competition contributes to the organization of phytophagous insect communities, and perhaps to other plant and animal communities as well.     

病原体感染对物种间资源竞争的影响——基于资源竞争理论

病原体感染对种间竞争的影响可能是因为改变了宿主的资源利用过程,然而竞争模型（Lotka-Volterra）由于参数化竞争系数而忽略了资源的动态变化过程,因此基于此类模型的研究无法揭示病原体对宿主资源利用的影响。基于Tilman的资源竞争理论构建了病原体感染一个物种的资源竞争模型,通过分析宿主物种资源利用效率的变化探讨了病原体对种间竞争的影响。结果表明：（1）病原体降低了宿主对资源的消耗率（消费矢量变短）,抬高了对资源的最低需求（零等倾线上移）,这意味着宿主的竞争力减弱;（2）虽然感染影响了竞争物种的密度,但不会改变共存物种的共存状态;（3）病原体可以使宿主物种的竞争对手更容易入侵,形成共存局面,极大地扩大了竞争物种共存的参数范围,本质上促进了物种多样性维持;（4）病原体的传播率和毒性也复杂地影响了竞争物种共存,传播率越大越能促进物种共存,而中等强度毒性最能促进物种共存。研究结果明确了病原体对物种资源利用模式的潜在改变,强调了病原体在物种共存和生物多样性维持中的重要性。     

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.

     

沙区植物种的一类种间竞争模型及应用

以沙坡头人工固沙植物油蒿和柠条为研究对象,针对水分是沙坡头植物生r长的限制因子的现实,研究了在水分条件限制下两种植物的种间关系,建立了混播油蒿、柠条种间竞争模型,验证了油蒿、柠条既竞争又稳定共存的关系,其目的为充分有效利用水资源、稳定人工生态系统提供科学依据。     

Intraspecific variation for resource use in Drosophila

Individuals within natural populations of Drosophila tripunctata and D. falleni varied significantly in their responses to alternative types of food baits; no such variation was detected in D. putrida. The food type at which laboratory-reared D. melanogaster tended to settle in the field was influenced by the type of food on which they had been kept prior to release. Although flies apparently forgot their previous experience within hours, its effect on their behaviour can be manifested for at least 1 day in the field. Mark -recapture experiments on wild flies are shown to be very inefficient at detecting individual variation in behaviour.     

荒漠草原主要植物种间关系对降水年型变化的响应

该研究采用内蒙古短花针茅荒漠草原长期试验平台2004~2015年期间不同降水年型(丰水、平水、欠水)下的植被数据,分析研究区7个主要植物21个种对的种间关系及其对降水年型的响应;应用方差比率法确定物种间的总体联结性,基于χ^2检验测定种对间的联结性,采用联结系数AC判断种对间联结的正负,运用共同出现百分率PC、Ochiai指数、Dice指数分析种对相伴出现的几率,以明确荒漠草原主要物种间的关系,揭示降水对种群间相互作用的影响机制。结果表明:(1)样方内的平均物种数在平水年达到最大,主要物种的总体联结性在丰水年呈显著正相关、平水年呈不显著正相关、欠水年呈不显著负相关,表明年降水量的下降致使种对间的关系由共存为主转变为竞争为主。(2)降水年型的变化使部分种对间的联结性发生改变,丰水年正联结的种对占57.1%,平水年降至52.4%,欠水年降至33.3%,也表明干旱胁迫导致协同共存的种对数减少,相互竞争的种对数增加。(3)降水年型的变化主要影响狭叶锦鸡儿与其他物种的共同出现几率,并以平水年最大,而对其他种对间的正相互作用无影响。     

Rapid evolution of ecological sexual dimorphism driven by resource competition

Sex differences in ecologically important traits are common in animals and plants, and prompted Darwin to first propose an ecological cause of sexual dimorphism. Despite theoretical plausibility and Darwin's original notion, a role for ecological resource competition in the evolution of sexual dimorphism has never been directly demonstrated and remains controversial. I used experimental evolution in Drosophila melanogaster to test the hypothesis that resource competition can drive the evolution of sex differences in diet. Following just three generations of adaptation, offspring from flies evolved in low-resource, high-competition environments show elevated sexual dimorphism in diet preference compared to both the ancestor and populations evolved on high-resource availability. This increased sexual dimorphism was the result of divergence in male sucrose intake and female yeast intake consistent with the differential nutritional requirements of the sexes. These results provide the first real-time direct evidence for evolution of sexual dimorphism driven by resource competition.     

Role of interspecific competition in the coexistence ofApodemus argenteus andA. speciosus (Rodentia: Muridae)

Reciprocal-removal experiments with two replicates were conducted to test for the role of interspecific competition in the coexistence ofApodemus argenteus andA. speciosus. Population density, rate of appearance of new (unmarked) individuals, reproduction, survival rate and habitat use were monitored during pre- and removal periods. In both removal experiments, the removal ofA. argenteus had little effect onA. speciosus, while that ofA. speciosus affected several population characteristics ofA. argenteus. Namely, the removal ofA. speciosus shifted the distribution ofA. argenteus to the habitat with a denser shrub cover in one experiment. Also, the removal increased the population densities and appearance rates of new individuals ofA. argenteus in another experiment. Interspecific interactions between the two species appeared to be a one-way action fromA. speciosus toA. argenteus. In removal periods in both experiments, the rates of appearance of new individuals in each species were the highest on the grid where that species was removed. These results suggest that, though interspecific competition occurred between the two species, intraspecific competition had greater effects than interspecific competition on the abundance and habitat use ofA. argenteus andA. speciosus. This implies that the fundamental niches ofA. argenteus andA. speciosus differ potentially, which may play an important role in the coexistence of the two species.     

Interspecific competition among macroparasites in a density-dependent host population

 We analyze the dynamics of a community of macroparasite species that share the same host. Our work extends an earlier framework for a host species that would grow exponentially in the absence of parasitism, to one where an uninfected host population is regulated by factors other than parasites. The model consists of one differential equation for each parasite species and a single density-dependent nonlinear equation for the host. We assume that each parasite species has a negative binomial distribution within the host and there is zero covariance between the species (exploitation competition). New threshold conditions on model parameters for the coexistence and competitive exclusion of parasite species are derived via invadibility and stability analysis of corresponding equilibria. The main finding is that the community of parasite species coexisting at the stable equilibrium is obtained by ranking the species according t! o th e minimum host density H ^* above which a parasite species can grow when rare: the lower H ^* , the higher the competitive ability. We also show that ranking according to the basic reproduction number Q ₀ does not in general coincide with ranking according to H ^* . The second result is that the type of interaction between host and parasites is crucial in determining the competitive success of a parasite species, because frequency-dependent transmission of free-living stages enhances the invading ability of a parasite species while density-dependent transmission makes a parasite very sensitive to other competing species. Finally, we show that density dependence in the host population entails a simplification of the portrait of possible outcomes with respect to previous studies, because all the cases resulting in the exponential growth of host and parasite populations are eliminated.. Received: 24 June 1996 / Revised version: 28 April 1998     

Geographical distributions,relative abundance and coexistence of Drosophila aldrichi and Drosophila buzzatii in Australia

Abstract Climatic data and collection records for the cactophilic Drosophila aldrichi and Drosophila buzzatii for 97 localities were used to examine the effects of geographical location, season, host plant species and climatic factors on their range and relative abundance. Temporal variation in relative abundance was assessed from monthly collections over 4 years at one locality. Effects of weather variables over the 28 days before each collection were examined. A generalized linear model of the spatial data showed significant geographical variation in relative abundance, and significant climatic effects, with the proportion of D. aldrichi higher in the warm season, and increasing as temperature variation decreased and moisture indices increased. The temporal data gave generally concordant results, as D. aldrichi proportion was higher in summer and autumn, and increased as maximum and minimum temperatures increased, and as variation in maximum temperature decreased. In a laboratory competition experiment, D. aldrichi eliminated D. buzzatii at 31°C, but was itself eliminated at 18°C and 25°C. The range of D. buzzatii is constrained only by availability of its host plant, Opuntia species, although its relative abundance is reduced in the northern part of its distribution. The range of D. aldrichi, from central Queensland to northern NSW, Australia, is entirely within that of D. buzzatii, and its relative abundance decreases from north to south. Both climate and weather, particularly temperature variability, have direct effects on the relative abundances of the two species, and both likely act indirectly by influencing the outcome of interspecific competition.     

Interspecific Infanticide and Infant‐Directed Aggression by Spider Monkeys (Ateles hybridus) in a Fragmented Forest in Colombia

Interspecific aggression amongst nonhuman primates is rarely observed and has been mostly related to scenarios of resource competition. Interspecific infanticide is even rarer, and both the ultimate and proximate socio‐ecological factors explaining this behavior are still unclear. We report two cases of interspecific infanticide and five cases of interspecific infant‐directed aggression occurring in a well‐habituated primate community living in a fragmented landscape in Colombia. All cases were initiated by male brown spider monkeys (Ateles hybridus) and were directed toward infants of either red howler monkeys (Alouatta seniculus: n = 6 cases) or white‐fronted capuchins (Cebus albifrons: n = 1 case). One individual, a subadult spider monkey male, was involved in all but one case of interspecific infanticide or aggression. Other adult spider monkeys participated in interspecific aggression that did not escalate into potentially lethal encounters. We suggest that competition for food resources and space in a primate community living in high population densities and restricted to a forest fragment of ca. 65 ha might partly be driving the observed patterns of interspecific aggression. On the other hand, the fact that all but one case of interspecific infanticide and aggression involved the only subadult male spider monkey suggests this behavior might either be pathological or constitute a particular case of redirected aggression. Even if the underlying principles behind interspecific aggression and infanticide are poorly understood, they represent an important factor influencing the demographic trends of the primate community at this study site. Am. J. Primatol. 74:990‐997, 2012. © 2012 Wiley Periodicals, Inc.