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 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     

Interspecific competition enhances nitrogen fixation in an actinorhizal shrub

In forest understory restoration, the establishment of reintroduced species may be strongly linked to their ability to compete for belowground resources. In this study, we provide isotopic and morphological evidence for competition-induced increases in nitrogen fixation by Morella cerifera (L.) Small (wax myrtle) when planted with Pinus palustris Mill (longleaf pine). Compared to a competition-free treatment, we found no significant differences in tissue N concentrations for M. cerifera. However, ¹⁵N enrichment in leaves, stems and roots, as well as whole-plant values for nitrogen derived from fertilizer were significantly lower when the plants were subject to interspecific competition from P. palustris. Plants in the competition treatment also allocated a significantly greater percentage of belowground biomass to root nodules than those in the competition-free treatment (0.65 vs. 0.41%). This strongly suggests that M. cerifera is capable of upregulating nitrogen fixation in response to interspecific competition. This may help explain why M. cerifera outperformed non-nitrogen-fixing species reintroduced on the same site.     

Interspecific competition constrains local abundance in highly suitable areas

Sites with high environmental suitability for species’ occurrence, in terms of abiotic conditions, may hold populations with higher local abundances by increasing reproductive and survival rates and decreasing extinction rate. Interspecific competition, however, may affect this relationship. Here we tested the hypothesis that local abundance of the gray slender opossum Marmosops incanus is affected by the local richness of potential competitors and environmental suitability derived from ecological niche models (ENMs). We also discuss the ability of distinct modelling methods to predict species’ abundance. We compiled occurrence records and information about M. incanus’ relative abundance from museums and published articles. Environmental suitability was derived from five algorithms using seven environmental predictors. To assess our hypothesis, we chose the best statistical models among generalised linear models and quantile regressions, and then tested whether the effects of richness of competitors on local abundance are stronger under highly suitable conditions. We found that environmental suitability given by presence-only methods are positively related to the maximum abundance of M. incanus. That is, species’ local abundance is low when suitability is low but can be either low or high when suitability is high. The richness of competitors, in turn, explains the abundance variation within sites with high environmental suitability. We strongly recommend that the relationship between abundance and suitability must be carefully interpreted when using ENMs to predict species’ distribution because biotic interactions can be the main driver of local abundance within highly suitable environments.     

Interspecific competition alters leaf stoichiometry in 20 grassland species

The extensive use of traits in ecological studies over the last few decades to predict community functions has revealed that plant traits are plastic and respond to various environmental factors. These plant traits are assumed to predict how plants compete and capture resources. Variation in stoichiometric ratios both within and across species reflects resource capture dynamics under competition. However, the impact of local plant diversity on species‐specific stoichiometry remains poorly studied. Here, we analyze how spatial and temporal diversity in resource‐acquisition traits affects leaf elemental stoichiometry of plants (i.e. the result of resource capture) and how flexible this stoichiometry is depending on the functional composition of the surrounding community. Therefore, we assessed inter‐ and intraspecific variations of leaf carbon (C), nitrogen (N), and phosphorus (P) (and their ratios) of 20 grassland species in a large trait‐based plant diversity experiment located in Jena (Germany) by measuring leaf elemental concentrations at the species‐level along a gradient in plant trait dissimilarity. Our results show that plants showed large intra‐ and interspecific variation in leaf stoichiometry, which was only partly explained by the functional group identity (grass or herb) of the species. Elemental concentrations (N, P, but not C) decreased with plant species richness, and species tended to become more deviant from their monoculture stoichiometry with increasing trait dissimilarity in the community. These responses differed among species, some consistently increased or decreased in P and N concentrations; for other species, the negative or positive change in P and N concentrations increased with increasing trait difference between the target species and the remaining community. The strength of this relationship was significantly associated to the relative position of the species along trait gradients related to resource acquisition. Trait‐difference and trait‐diversity thus were important predictors of how species’ resource capture changed in competitive neighbourhoods.     

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。     

Interspecific competition in Drosophila II. Competitive outcome in some 2–resource environments

Populations of Drosophila metanogaster and D. simulans were made to compete in a number of 2– resource environments. The resources used were all based on a standard Drosophila medium and differed from each other only in their concentrations of ethanol. Each experiment comprised three cages started at a species–frequency of 0.8 D. melanogaster and three at 0.2 D. melanogaster. This enabled screening for a wide range of equilibria.
Reversal of competitive superiority was achieved (unintentionally) by raising the alcohol level of one of the resources. Thus while D. simulans won in an environment with media containing 0 and 896 ethanol, D. melanogaster won if the ethanol concentrations were 0 and 10%, or 0 and 12%. This parallels the reversal of dominance reported earlier for single–resource systems. However, in none of the 2–resource systems studied was there a stable equilibrium in species–frequency–in fact there was no significant frequency–dependence at all.
An artificial selection experiment produced a stock of D. melanogaster ovipositing a higher proportion of eggs on the alcoholic resource. Thus, this stock was more divergent from D. simulans , in at least one aspect of resource use, than was the original stock of D. melanogaster. However, competition between stock D. simulans and selected D. melanogaster showed no frequency–dependence. Again, reversal of competitive dominance was unintentionally achieved.
The implications of these results are discussed, and the need for a comprehensive study of resource–utilization in a pair of competing species is stressed.     

Interspecific competition in small rodents: from populations to individuals

The role of interspecific competition in shaping animal and plant communities has formed one of the major issues in ecology for decades. Small mammals, mainly rodents, have been among the model systems used for research on interspecific competition. Most studies within small mammal systems in the past have examined effects of competition on population attributes such as on population size, habitat use, or population dynamics. Population-level responses are the cumulative effects of individual responses, however, the influence of competition on individual life-history traits has rarely been studied. Research on life-histories may bridge gaps between population biology and effects of competition on individual behaviour. In this paper, we review recent research approaches to interspecific competition in rodents based on census data and species assemblages, that use regression analysis, time series analysis, removal and exclusion experiments, and showcase our own experimental research on the effects of interspecific competition on individual life-history traits in boreal voles.     

Interspecific competition limits larders of pygmy owls Glaucidium passerinum

To test whether competitive and predatory interactions limit larder size we erected pygmy owl Glaucidium passerinum nest-boxes for hoarding with 45 mm entrance diameter near and far (>2 km) from Tengmalm's owl Aegolius funereus nest-boxes with >80 mm entrance diameter during early autumn. We found larders of pygmy owls in similar frequency in both near and far plots (41 vs. 42% of plots), but in near plots the number and biomass of cached prey by pygmy owls were lower. These results suggest that there is competition for food between these two owl species and/or that food caching behaviour of pygmy owls is disturbed by larger Tengmalm's owls.     

Interspecific competition between two field populations of grass-feeding bugs

Abstract. 1. We tested the hypothesis that interspecific competition between two grass-feeding stenodemine bug species ( Notostira elongata Geoffroy and Megaloceraeu recticornis Geoffroy) was capable of causing population-scale mortality in the field.
2. N.elongata nymphs were added to two field enclosures in which the M.recti-cornis population was to hatch. In one of these enclosures the grass Arrhena-therum elatius L., on which only M.recticornis can feed, was also added. Population changes of the bug species were then monitored. An unmanipulated enclosure and an unfenced plot of grassland were used as controls.
3. The results demonstrated that N.elongata lowered the survival of M.recticornis and that this effect was removed by the addition of A.elatius . The results also suggested that N.elongata suffered less from the effects of competition with M.recticornis when the latter had access to the refuge foodplant.
4. Interspecific competition was rare among members of the grass-feeding stenodemine guild in the area studied. Only one out of fifteen possible pairs competed, and this competition occurred only under special circumstances.     

Interspecific competition between two species of the bean weevil

---

Contributions from the Entomological Laboratory, Kyoto University, No. 110.     

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.     

小麦/大豆间作中作物种间的竞争作用和促进作用

春小麦／春大豆间作是西北一熟制灌区广泛采用的高产种植形式．本文采用田间小区和微区根系分隔试验研究了这种种植形式作物种间的竞争作用和促进作用．结果表明,小麦／大豆间作具有明显的间作优势．土地当量比为１．２３～１．２６．小麦为优势种,竞争力强于大豆,具有明显的间作边行优势．小麦边行优势的１／３贡献来自于地下部．小麦收获后,大豆生长具有恢复作用,认为这种恢复作用是间作优势的机制之一．间作相对于单作两种作物的收获指数均有显著提高．收获指数的种间促进作用是间作优势的另一机制．     

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.

     

Interspecific competition between two species of Trichogrammatidae III The analytical study on the competition

The experiment was carried out in order to analyze the results of interspecific competition which were mentioned in the previous reports (Sasaba 1964, 1965). The following definite tendencies were obtained and an account was given with regard to the process of competition. (1)T. minutum had a higher reproductive rate than T. japonicum at a lower density of the parent wasps. (2) The parasitic efficiency of T. minutum was high as compared with T. japonicum. (3)T. japonicum was consistently superior to T. minutum in the interspecific competition at larval stage.     

Interspecific competition between the ichneumonid Campoletis chlorideae and the braconid Microplitis mediator in their host Helicoverpa armigera

We investigated interspecific competition between Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) and Microplitis mediator (Haliday) (Hymenoptera: Braconidae) in their host, the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) under laboratory conditions. Cotton bollworm larvae were allowed to be parasitized by both wasp species simultaneously or sequentially at different time intervals. When host larvae were parasitized simultaneously by both parasitoids, the majority of the cocoons produced were of M. mediator. When host larvae were parasitized initially by M. mediator followed by C. chlorideae at 12 or 24 h, parasitoids emerging from the multiparasitized hosts were mainly M. mediator. In contrast, when host larvae were parasitized initially by C. chlorideae, followed by M. mediator 12 or 24 h later, parasitoids emerging from the multiparasitized hosts were mainly C. chlorideae. Dissections of host larvae at various time intervals after parasitization by the two parasitoids showed that first instars of M. mediator could physically attack the larvae of C. chlorideae, but not the eggs of C. chlorideae. When a host was parasitized by both wasp species sequentially, more host larvae died and the number of wasp offspring was significantly reduced compared to a host parasitized by only one wasp. Conversely, in simultaneous multiparasitism, the host mortality and wasp offspring production were not significantly different from those parasitized by single wasp species.     

Interspecific variation of sperm morphology in the Australian rodent genus Zyzomys

The sperm head morphology and tail length of two species of Australian rock rats, Zyzomys argurus and Zyzomys pedunculatus, are presented. In Z. argurus the sperm head has an apical hook together with two ventral processes extending from the upper concave surface that are largely composed of cytoskeletal material, and the sperm tail is about 135 µm in length. By contrast, in Z. pedunculatus the sperm head is paddle‐shaped with the nucleus capped by an acrosome that has a large apical segment and is surrounded by a thin layer of cytoskeletal material, and the sperm tail is only around 85 µm in length. Since the structure of the spermatozoon of Z. argurus is similar to that of most of the old endemic Australian rodents it is presumed to be the ancestral condition within the Zyzomys genus with that of Z. pedunculatus being highly derived and showing convergence with the sperm structure in some other orders of mammals.     

游猎蛛在茶尺蠖高峰日的种间竞争作用

为了合理保护和充分利用天敌,明确茶园游猎蛛天敌捕食茶尺蠖Ectropis obliqua hypulina的种间竞争力及其差异。本文运用通经分析法、灰色关联度分析法、竞争系数分析法及竞争强度指数分析法对龙井43、黄山大叶种、乌牛早、安吉白茶、平阳特早和农抗早6类茶园中茶尺蠖高峰日时的7种游猎蛛捕食茶尺蠖的种间竞争作用进行分析。结果表明,按相关系数比较,乌牛早茶园茶尺蠖与条纹蝇虎Plexippus setipet的相关系数为-0.888,平阳特早茶园茶尺蠖与三突花蟹蛛Misumenops tricuspidatus和斜纹猫蛛Oxyopes Sertatws的相关系数分别为0.981和-0.902,均达相关水平,天敌间鞍型花蟹蛛Xysticus ephippiafus、三突花蟹蛛、斑管巢蛛Clubiona reichlini和斜纹猫蛛均与黑色跳蛛Plexippus paykulli相关,鞍型花蟹蛛、粽管巢蛛Clubiona japonicola和黑色跳蛛均与三突花蟹蛛相关。用灰色关联度法分析,与茶尺蠖数量上关系密切的前4种天敌依次是三突花蟹蛛、粽管巢蛛、黑色跳蛛和鞍型花蟹蛛。按竞争系数大小...     

The risk of inter-specific competition in Australian short-necked turtles

Freshwater turtles are threatened globally; however, short-necked turtles in Eastern Australia have been particularly successful in exploiting natural and man-made permanent water bodies. The catchments of eastern Australia offer a unique opportunity to compare the diets of species in habitats where both genera co-exist, but only one genus is usually locally dominant. We compared the diets of species of Emydura and Myuchelys and Flaviemys in inland and coastal catchments in eastern Australia to determine the breadth of diets. We also conducted a more in depth study of the ecology and habitat preferences of the Bellinger River Emydura (Emydura macquarii macquarii) and Myuchelys georgesi. We found that diets of short-necked turtles on the east coast of Australia are separated by water conditions, and largely independent of species and location. Species of Myuchelys and Emydura are omnivorous. A high proportion of their food is from benthic macro-invertebrate communities in clear water. Terrestrial invertebrates and filamentous algae are present more in the diets of species inhabiting turbid water. Competition between species of Emydura and Myuchelys/Flaviemys is likely to occur when in sympatry, because species of Emydura can adapt their diets to various habitats and water quality. Myuchelys georgesi is restricted to, but common in, the Bellinger River. Interspecific competition may occur between E. m. macquarii and M. georgesi because of similar habitat preferences, diets and life histories. Emydura m. macquarii is not unique to the Bellinger River and hybridization with the endemic M. georgesi is a threatening process.