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Competitive Ability (competitive + ability)
Kinds of Competitive Ability Selected AbstractsCompetitive ability and the coexistence of anuran larvae in freshwater rock-poolsFRESHWATER BIOLOGY, Issue 2 2000Anssi Laurila Summary 1I examined the competitive ability of larval common frogs (Rana temporaria) and common toads (Bufo bufo) in a laboratory experiment by manipulating the number and size of Rana and the number of Bufo. 2Bufo was the most active tadpole type, whereas small Rana was more active than large Rana. 3Especially at high food availability, the growth rate of large Rana at metamorphosis was reduced in the presence of small Rana, whereas that of small Rana was not affected by larger conspecifics. 4Both size classes of Rana were negatively affected by the presence of Bufo. Size at metamorphosis of Bufo was greater when large Rana was present. These results suggest that activity level is important in determining competitive ability. 5To study competition in the field, tadpoles of Bufo were introduced to small rock-pools that did not support Bufo naturally, but were with or without Rana. 6In the experimental pools, there were no interspecific effects on the growth rate of either species. However, the growth rate of Bufo was lower in the experimental pools than in pools inhabited naturally. Futher, survival of Bufo was low in small pools. Lower food availability or physical factors associated with small pools, rather than interspecific competition, may be the reason why Bufo avoids breeding in small rock-pools. [source] Interspecific carbon exchange and cost of interactions between basidiomycete mycelia in soil and woodFUNCTIONAL ECOLOGY, Issue 2 2002J. M. Wells Summary 1.,The outcome of interactions between wood decay basidiomycete fungi is affected by the size of territory held by a mycelium. We investigated the outcomes of interactions between the cord-forming saprotrophs Phanerochaete velutina (DC: Pers.) Parm., Phallus impudicus (L.) Pers. and Hypholoma fasciculare (Huds: Fr) Kumner over 152,155 days, determined as ability to capture or share territory in soil and wood, in terms of decay partitioning and the carbon cost of interactions. 2.,The outcome of interactions in wood alone differed from those in which the fungi competed for an opponents' inoculum in soil microcosms. Competitive ability (the ability to capture or co-occupy an opponent's inoculum) varied according to species and inoculum age. In wood block pairings in the absence of soil there was evidence that P. velutina opportunistically utilized C previously mobilized within an opponent's inoculum. 3.,In soil systems, short-term (28-day) respiratory losses of preloaded 14C (supplied as glucose) indicated that interaction could have a substantial C cost, depending on the resource quality of the opponents' inocula. Phallus impudicus inocula accumulated 14C from opponents' mycelia during ,deadlock' interactions, although reciprocal interspecific 14C transfer was not observed. 4.,Saprotrophic cord-forming basidiomycetes are considered to be highly conservative of acquired nutrients, representing a significant nutrient reservoir in woodland ecosytems. Here we demonstrate that a potential major pathway for nutrient mineralization by this group is nutrient loss during competitive interactions in soil. [source] Competitive ability not kinship affects growth of Arabidopsis thaliana accessionsNEW PHYTOLOGIST, Issue 1 2010Frédéric Masclaux Summary ,In many organisms, individuals behave more altruistically towards relatives than towards unrelated individuals. Here, we conducted a study to determine if the performance of Arabidopsis thaliana is influenced by whether individuals are in competition with kin or non-kin. ,We selected seven pairs of genetically distinct accessions that originated from local populations throughout Europe. We measured the biomass of one focal plant surrounded by six kin or non-kin neighbours in in vitro growth experiments and counted the number of siliques produced per pot by one focal plant surrounded by four kin or non-kin neighbours. ,The biomass and number of siliques of a focal plant were not affected by the relatedness of the neighbour. Depending on the accession, a plant performed better or worse in a pure stand than when surrounded by non-kin plants. In addition, whole-genome microarray analyses revealed that there were no genes differentially expressed between kin and non-kin conditions. ,In conclusion, our study does not provide any evidence for a differential response to kin vs non-kin in A. thaliana. Rather, the outcome of the interaction between kin and non-kin seems to depend on the strength of the competitive abilities of the accessions. [source] More plant biomass results in more offspring production in annuals, or does it?OIKOS, Issue 9 2008Marina S. Neytcheva Competitive ability in plants has been previously measured almost exclusively in terms of traits related to growth (biomass) or plant size. In this study, however, we used a multi-species competition experiment with six annuals to measure relative competitive ability in terms of reproductive output, i.e. the number of offspring produced for the next generation. Under greenhouse conditions, plants of each species were started in pots from germinating seeds and were grown singly (free of competition) and at high density in both monocultures and in mixtures with all study species. Several traits traditionally regarded as determinants of competitive ability in plants were recorded for each species grown singly, including: seed mass, germination time, early growth rate and potential plant size (biomass and height). Under competition, several traits were recorded as indicators of relative performance in both monocultures and mixtures, including: biomass of survivors, total number of survivors, number of reproductive survivors, and reproductive output (total seed production) of the survivors. As expected, species that grew to a larger biomass in isolation had higher seed production in isolation. However, none of the traditional plant growth/size-related traits, measured either in isolation or under competition, could predict between species variation in reproductive output under competition in either monocultures or mixtures. In mixtures, 97% of this variation in reproductive output could be explained by between-species variation in the number of reproductive survivors. The results indicate that traits measured on plants grown singly may be poor predictors of reproductive output under competition, and that species' rank order of competitive ability in terms of the biomass of survivors may bear no relationship to their rank order in terms of the number of offspring produced by these survivors. This has important implications for the interpretation of mechanisms of species coexistence and community assembly within vegetation. [source] Genetic and phenotypic differences between thistle populations in response to habitat and weed management practicesBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2010RICCARDO BOMMARCO Rapid evolutionary change is increasingly being recognized as commonplace, but the evolutionary consequences for species and ecosystems under human-induced selection regimes have not been explored in detail, although many species occur in such environments. In a common garden experiment and with amplified fragment length polymorphism markers, we examined whether genetic differentiation has taken place between spatially intermixed populations of creeping thistles Cirsium arvense (Asteraceae) collected from a natural habitat (maritime shores), a semi-natural habitat (road verges) and arable fields under two management regimes: conventional and organic farming. Populations of C. arvense have altered genetically and locally adapted their growth patterns with changed land use. Although plants from different habitats showed similar total biomass production, shoot and root production was higher for maritime populations, suggesting selection for increased competitive ability. Competitive ability then declined in the order semi-natural, conventional farms and organic farms. Thistles in arable fields may be more selected for tolerance against disturbances from herbicides and mechanical weed control. In addition, early shoot sprouting and genetic analysis showed differentiation between plants originating from conventional farms and farms that were converted to organic 9,30 years ago, suggesting some adaptation to altered crop cultivation practices. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 797,807. [source] Waterlogging and canopy interact to control species recruitment in floodplainsFUNCTIONAL ECOLOGY, Issue 4 2010Wiktor Kotowski Summary 1.,The extent to which seedling recruitment contributes to local functional diversity depends on the environmental filters operating in a plant community. Classical community assembly models assume that habitat constraints and competition act like hierarchical filters with habitat filtering as the dominant one. Alternative models assume a synergic interaction since responses to environmental stress and competition may impose physiological trade-offs in plants. 2.,River floodplains are an ideal system to test the relationship between habitat and competition filtering in community (re)assembly, as flooding causes changes in both habitat stress (waterlogging, resulting in anoxia and toxicity) and competition (dieback of vegetation) on one hand and acts as an effective seed dispersal vector on the other hand. 3.,We conducted a mesocosm experiment on early community assembly from a pool of 34 floodplain species covering a wetness gradient. Seed mixtures were sown in a full factorial design with water level, canopy and mowing as controlling factors. We measured the biomass of all species after one growing season and determined germination and seedling growth traits, both outside (response to waterlogging/no waterlogging) and in a growth-chamber (response to light/darkness). 4.,Species recruitment was analysed in relation to the controlling factors and measured functional traits using co-inertia analysis. Furthermore we analysed the effects of the controlling factors on several aspects of functional diversity. 5.,There was no establishment in grass sward, unless mowing was applied. Species-rich communities only developed when germination and early establishment phases occurred on waterlogged bare soil. High water level did not suppress establishment but reduced the total biomass and lowered inter-specific competition. The effect of mowing on species richness depended upon the interplay between waterlogging and canopy. 6.,Establishment success under canopy required seedling strategies to tolerate shade. The elimination of typical wetland specialists from oxic mesocosms was clearly an effect of their poorer and/or slower germination and lower competitive abilities in comparison to non-wetland plants, leading to their disappearance in this low-stress environment. 7.,Our results indicate that single stress factors can enhance species richness and functional diversity through limiting competition but a synergic interaction of different stresses can lead to reduced richness. [source] The effect of pea cultivar and water stress on root and shoot competition between vegetative plants of maize and peaJOURNAL OF APPLIED ECOLOGY, Issue 1 2001Tzehaye Semere Summary 1Improvements in intercrop yields may be achieved through an understanding of yield advantages due to above-ground or below-ground interactions. 2Forage maize and two morphologically contrasting cultivars of pea (leafy cv. Bohatyr and semi-leafless cv. Grafila) were grown alone and in additive mixtures, under two contrasting levels of soil moisture (± water stress). 3The mechanism of competition between maize and pea was studied by separating the effects of root competition and shoot competition, using soil and aerial partitions. Plants were grown in rectangular tanks in a glasshouse. 4Leafy pea cv. Bohatyr was as competitive as maize, both below-ground and above-ground, whereas semi-leafless pea cv. Grafila was less competitive than maize or pea cv. Bohatyr. The greater competitive ability of the leafy pea, both above- and below-ground, was probably due to its greater growth rate, associated with its greater leaf area. 5The competitive ability of maize, relative to peas, was considerably reduced by water stress. Both the root and shoot competitive abilities of pea were greater under water stress, compared with those of maize. 6Relative yield total (RYT) values were significantly greater when maize and pea were subjected to shoot competition only (RYT = 1·76) than when subjected to root competition (RYT = 1·17) or when subjected to both shoot and root competition (RYT = 1·13). This reflects the fact that the effects of root competition were greater than those of shoot competition. 7Root competition decreased the shoot dry weights, plant height and leaf area of both maize and pea, whereas shoot competition had no significant effect on these attributes, indicating that soil resources, i.e. mineral nutrients and water, were more limiting than light. [source] Differential genetic influences on competitive effect and response in Arabidopsis thalianaJOURNAL OF ECOLOGY, Issue 5 2005JAMES F. CAHILL JR Summary 1Competition plays an important role in structuring populations and communities, but our understanding of the genetic basis of competitive ability is poor. This is further complicated by the fact that plants can express both competitive effect (target plant influence upon neighbour growth) and competitive response (target plant growth as a function of a neighbour) abilities, with these ecological characteristics potentially being independent. 2Using the model plant species Arabidopsis thaliana, we investigated patterns of intraspecific variation in competitive effect and response abilities and their relationships to other plant traits and resource supply rates. 3Both competitive effect and response were measured for 11 genotypes, including the Columbia ecotype and 10 derived mutant genotypes. Plants were grown alone, with intragenotypic competition, and with intergenotypic competition in a replicated blocked design with high nutrient and low nutrient soil nutrient treatments. We quantified competitive effect and response on absolute and per-gram bases. 4Competitive effect and response varied among genotypes, with the relative competitive abilities of genotypes consistent across fertilization treatments. Overall, high rates of fertilization increased competitive effect and competitive response abilities of all genotypes. Both competitive effect and response were correlated with neighbour biomass, though genotype-specific traits also influenced competitive response. 5At the genotype level, there was no correlation between competitive effect and response in either fertilization treatment. Overall patterns in competitive response appeared consistent among inter- and intragenotypic competition treatments, indicating that a target genotype's response to competition was not driven by the genetic identity of the competitor. 6These findings indicate that within A. thaliana, there is the potential for differential selection on competitive effect and response abilities, and that such selection may influence different sets of plant traits. The concept of a single competitive ability for a given plant is not supported by these data, and we suggest continued recognition of these dual competitive abilities is essential to understanding the potential role of competition in influencing intra- and interspecific processes. [source] Food-dependent individual growth and population dynamics in fishes,JOURNAL OF FISH BIOLOGY, Issue 2006L. Persson It is long since well established that growth and development in fish individuals are heavily dependent on food intake. Yet, this dependence of individual development on food levels has only to a limited extent been taken into consideration when studying fish population and community processes. Using the modelling framework of physiologically structured population models and empirical data for a number of species configurations, how different size-dependent processes may affect fish population dynamics and community structures are reviewed. Considering competitive interactions, cohort interactions will often give rise to cohort cycles driven by an inequality in competitive abilities between differently sized individuals. The addition of cannibalism may dampen these cycles, the extent to which is dependent on life-history characteristics of the cannibals. The circumstance that individuals change their trophic position over their life cycle as a result of an increase in size gives rise to life history omnivory. In such omnivorous systems, food-dependent growth demotes the potential for predatory and prey fishes to coexist. In tritrophic food chains, food-dependent growth in the intermediate consumer may lead to the presence of bistability including sensitivity to catastrophic behaviour. These results shed new light on the drastic decreases observed in the stocks of many marine fish top predators including their inability to recover after fishing moratoria, and on the suggested presence of alternative states in freshwater fish communities. [source] Oscillating vegetation dynamics in a wet heathlandJOURNAL OF VEGETATION SCIENCE, Issue 1 2005Katharina E. Urban Abstract. Question: The significance of disturbances caused by periodical inundation was investigated with respect to its effects on vegetation dynamics, species richness and fluctuations, and to the relevance of certain plant properties. Location and Method: At a sod-cut stand within nutrient-poor inland sand dunes, permanent plots along a transect were surveyed over a period of up to nine years after sod cutting. Results: In contrast to never inundated plots, periodically inundated plots were characterized by low vegetation cover and by high numbers of species belonging to many different communities, each of them with a low cover. Periodical inundations favoured the presence of pioneers, species tolerant of disturbances, species adapted to wet conditions and stoloni-ferous species. Furthermore, annual fluctuations of species within each plot were higher and most species occurred only sporadically. Discussion: A comprehensive model is presented describing the relevant processes identified in the littoral zone. Changing water tables result in the creation of gaps. The re-colonization of these gaps follows mainly from vegetative regeneration and less to the dispersion of diaspores. Highest species numbers in the zone of moderate disturbances result from a high rate of re-colonization in spite of local extinctions following each disturbance event. It is suggested that colonization abilities are among the most important features for species occurrence at a site rich in disturbances (more important than competitive abilities and more important than a slow rate of displacement). For nature conservation such sites are very important, because they allow (rare) pioneer species to survive for longer periods of time. [source] Experiments on growth interactions between two invasive macrophyte speciesJOURNAL OF VEGETATION SCIENCE, Issue 1 2004Marie-Hélène Barrat-Segretain Tutin et al. (1980) Abstract. The success of invasive species has been attributed to the ability to displace other species by direct competition. We studied growth and possible competition between the two macrophyte species Elodea nuttallii and E. canadensis, because the former has been observed to replace the latter in the field. Additional experiments were conducted in aquaria with mixed plantings of Elodea species. Species growth was measured and competitive abilities of each species determined by applying the reciprocal yield model to mean plant weight and length. In monocultures the growth rates of the two species were similar, while in mixtures the growth rate of E. canadensis was significantly lower than that of E. nuttallii. E. canadensis was more sensitive to intraspecific than to interspecific neighbours, whereas E. nuttallii was indifferent to the presence of neighbours. Differential growth characteristics of Elodea species can explain the displacement of E. canadensis by E. nuttallii under eutrophic field conditions. [source] Competitive ability not kinship affects growth of Arabidopsis thaliana accessionsNEW PHYTOLOGIST, Issue 1 2010Frédéric Masclaux Summary ,In many organisms, individuals behave more altruistically towards relatives than towards unrelated individuals. Here, we conducted a study to determine if the performance of Arabidopsis thaliana is influenced by whether individuals are in competition with kin or non-kin. ,We selected seven pairs of genetically distinct accessions that originated from local populations throughout Europe. We measured the biomass of one focal plant surrounded by six kin or non-kin neighbours in in vitro growth experiments and counted the number of siliques produced per pot by one focal plant surrounded by four kin or non-kin neighbours. ,The biomass and number of siliques of a focal plant were not affected by the relatedness of the neighbour. Depending on the accession, a plant performed better or worse in a pure stand than when surrounded by non-kin plants. In addition, whole-genome microarray analyses revealed that there were no genes differentially expressed between kin and non-kin conditions. ,In conclusion, our study does not provide any evidence for a differential response to kin vs non-kin in A. thaliana. Rather, the outcome of the interaction between kin and non-kin seems to depend on the strength of the competitive abilities of the accessions. [source] A competitive coexistence principle?OIKOS, Issue 10 2009Cathy Neill Competitive exclusion , n species cannot coexist on fewer than n limiting resources in a constant and isolated environment , has been a central ecological principle for the past century. Since empirical studies cannot universally demonstrate exclusion, this principle has mainly relied on mathematical proofs. Here we investigate the predictions of a new approach to derive functional responses in consumer/resource systems. Models usually describe the temporal dynamics of consumer/resource systems at a macroscopic level , i.e. at the population level. Each model may be pictured as one time-dependent macroscopic trajectory. Each macroscopic trajectory is, however, the product of many individual fates and from combinatorial considerations can be realized in many different ways at the microscopic , or individual , level. Recently it has been shown that, in systems with large enough numbers of consumer individuals and resource items, one macroscopic trajectory can be realized in many more ways than any other at the individual , or microscopic , level. Therefore, if the temporal dynamics of an ecosystem are assumed to be the outcome of only statistical mechanics , that is, chance , a single trajectory is near-certain and can be described by deterministic equations. We argue that these equations can serve as a null to model consumer-resource dynamics, and show that any number of species can coexist on a single resource in a constant, isolated environment. Competition may result in relative rarity, which may entail exclusion in finite samples of discrete individuals, but exclusion is not systematic. Beyond the coexistence/exclusion outcome, our model also predicts that the relative abundance of any two species depends simply on the ratio of their competitive abilities as computed from , and only from , their intrinsic kinetic and stoichiometric parameters. [source] On the importance of the negative selection effect for the relationship between biodiversity and ecosystem functioningOIKOS, Issue 4 2008Lin Jiang Much of our knowledge on biodiversity and ecosystem functioning comes from studies examining the effects of biodiversity on biomass production within a trophic group. A large number of these studies have found that increasing biodiversity tends to increase biomass production, leading many ecologists to believe that there exists a general positive relationship between biodiversity and ecosystem functioning. Here we argue that such a positive relationship may not be general, particularly for ecosystem functions other than biomass. Our argument centers on the potential importance of the negative selection effect, which operates where competitively dominant species do not contribute significantly to the function of interest. We suggest that negative selection effects may be potentially common for non-biomass functions, for which species competitive ability may often be a poor indictor of its functional impact. We conclude that diverse (positive, negative, and neutral) BEF relationships are possible for non-biomass functions and that for a particular function, the exact form of the BEF relationship may depend on how species functional impacts relate to their competitive abilities in the community. [source] Species-specific limitation of vole population growth by least weasel predation: facilitation of coexistence?OIKOS, Issue 1 2008Elina Koivisto Interspecific competition is usually understood as different species competing directly with each other for limited resources. However, predators can alter such competitive interactions substantially. Predation can promote the coexistence of species in a situation where it would otherwise be impossible, for example if a tradeoff between the competitive abilities and predation resistance of the prey species exists. The field vole Microtus agrestis and the sibling vole M. rossiaemeridionalis are sympatric grassland species, which compete for the same resources. At the population level sibling voles are suggested to be superior competitors to field voles, yet more vulnerable to predation. We tested the effects of predation on the two species in 0.5 ha outdoor enclosures by exposing vole populations to radio-collared freely-hunting least weasels Mustela nivalis nivalis for three weeks. Lethal and non-lethal impacts of predation limited population densities of both species during and after the experimental period, but the effect was more pronounced in sibling voles in which population densities decreased markedly during the treatment period and even after that. Field vole population densities remained stable under weasel predation, while densities increased in controls. Survival in both species was lower in treatment populations compared to controls, but the effect tended to be more pronounced in sibling voles and in females of both species. The average mass of adults in both species declined in the treatment populations. These results suggest that predation by least weasels can limit vole populations locally, even during favourable summer conditions, and have extended negative effects on the dynamics of vole populations. In addition, predation alleviated interspecific competition between the vole species and is, therefore, a potential factor enabling the coexistence of them. [source] Foraging capacities and effects of competitive release on ontogenetic diet shift in bream, Abramis bramaOIKOS, Issue 2 2002Anders Persson Bream (Abramis brama) undergo ontogenetic diet shift from zooplankton to benthic macroinvertebrates, but the switching size may be highly variable. To unravel under what conditions bream are pelagic versus benthic foragers, we experimentally determined size-dependent foraging capacities on three prey types from the planktivory and benthivory niche; zooplankton, visible and buried macroinvertebrates. From these data we derived predictions of size-dependent diet preferences from estimates of prey value and competitive ability, and tested these predictions on diet data from the field. Planktivorous foraging capacity described a hump-shaped relationship with bream length that peaked for small bream of 67 mm total length. Benthivory capacity increased with increasing bream size, irrespective if benthic prey were visible on the sediment surface or buried in the sediment. From the experimental data and relationships of metabolic demand we calculated minimum resource requirement for maintenance (MRR) for each of the prey categories used in experiments. MRR increased with bream size for both zooplankton and visible chironomids, but decreased with bream size for buried chironomids, suggesting that intermediate sized bream (120,300 mm) may be competitively sandwiched between small and large bream that are more competitive planktivores and benthivores, respectively. Prey value estimates and competitive abilities qualitatively predicted diet shift in a bream population being released from competition. Competitive release did not change the diet of the largest size-class feeding on an optimal diet of benthic invertebrates both before and after competitive release. However, profound diet shifts towards benthic macroinvertebrates were recorded for intermediate size-classes that fed on a suboptimal diet prior to competitive release. Thus, laboratory estimates of size-dependent foraging capacity of bream in planktivorous and benthivorous feeding niches provided useful information on size-specific competitive ability, and successfully predicted diet preference in the field. [source] Offshore spatial segregation in giant petrels Macronectes spp.: differences between species, sexes and seasonsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2007J. González-Solís Abstract 1.Investigations were made to determine whether the two giant petrel species segregate by gender and species in relation to the stage of the annual cycle. The individual foraging behaviour of 14 male and 11 female northern giant petrels (Macronectes halli) and 13 male and 15 female southern giant petrels (M. giganteus) breeding at South Georgia were tracked over 1 year using geolocators (global location sensing loggers). 2.Males of both species showed a flexible foraging strategy, switching from coastal to pelagic habits, probably governed by spatio-temporal changes in carrion availability. In contrast, marine areas exploited by females were more consistent over the year and similar for the two species, with most foraging locations concentrated over the same pelagic waters. 3.This study provides support for the differences in foraging between sexes as the main mechanism reducing intraspecific competition. Although the two species are morphologically similar and can easily access each other's foraging habitat, they differ in the foraging areas exploited. Thus, interspecific competition seems mainly relaxed by spatial segregation, particularly between males in winter, probably mediated by different competitive abilities and physical tolerances to temperature and winds. Foraging southern giant petrels from South Georgia were not restricted to the areas within the line of equidistance to other colonies, but their foraging range overlapped with feeding grounds of conspecifics breeding in the Falkland Islands and the Antarctic Continent. 4.Taken together, these findings suggest that foraging selection on marine habitat heterogeneity reduces interspecific competition, whereas carrion availability reduces intersexual competition, in giant petrels. Copyright © 2008 John Wiley & Sons, Ltd. [source] Introduced plants of the invasive Solidago gigantea (Asteraceae) are larger and grow denser than conspecifics in the native rangeDIVERSITY AND DISTRIBUTIONS, Issue 1 2004Gabi Jakobs ABSTRACT Introduced plant species that became successful invaders appear often more vigorous and taller than their conspecifics in the native range. Reasons postulated to explain this better performance in the introduced range include more favourable environmental conditions and release from natural enemies and pathogens. According to the Evolution of Increased Competitive Ability hypothesis (EICA hypothesis) there is a trade-off between investment into defence against herbivores and pathogens, and investment into a stronger competitive ability. In this study, we conducted field surveys to investigate whether populations of the invasive perennial Solidago gigantea Ait (Asteraceae) differ with respect to growth and size in the native and introduced range, respectively. We assessed size and morphological variation of 46 populations in the native North American range and 45 populations in the introduced European range. Despite considerable variation between populations within continents, there were pronounced differences between continents. The average population size, density and total plant biomass were larger in European than in American populations. Climatic differences and latitude explained only a small proportion of the total variation between the two continents. The results show that introduced plants can be very distinct in their growth form and size from conspecifics in the native range. The apparently better performance of this invasive species in Europe may be the result of changed selection pressures, as implied by the EICA hypothesis. [source] Seasonal spatial dynamics and causes of nest movement in colonies of the invasive Argentine ant (Linepithema humile)ECOLOGICAL ENTOMOLOGY, Issue 5 2006NICOLE E. HELLER Abstract 1.,Colony organisation and movement behaviour of the Argentine ant (Linepithema humile) was studied over 3 years in field populations in California and in captive colonies in the laboratory. This invasive species is highly polydomous and unicolonial; colonies consist of expansive and fluid networks of nests and trails. The spatial and temporal organisation of colonies may contribute to ecological dominance. 2.,Argentine ant nests and inter-nest trails shift in size, abundance, and location, so that colony networks are spatially contracted in the winter and expanded spring to autumn. Colonies occupy permanent sites; ants migrated to and from the same winter nest locations year after year, and occupied 30% of the same nests repeatedly during seasonal migrations. 3.,Nests were moved on average 2,3 m. Forty-two per cent were occupied less than 1 month, 4% the entire study, and the other 54% lasted 3.9 ± 2.3 months (mean ± SD). 4.,Nests were located within 2,4 m of woody plants, in warm sites in the winter and cool sites in the summer. Both humidity and food availability influenced nest-site choice in laboratory colonies. However, when faced with a trade-off between factors, the ants chose humid nest boxes over nest boxes near food, and ants moved nests only in response to changes in humidity and not distance to food. 5.,The results indicate that L. humile colonies are seasonally polydomous, and that nest movements are driven by changes in microclimate. Colony organisation maintains high local density and increases food supply, which may improve the competitive ability of L. humile colonies and reduce opportunities for species coexistence. [source] Phorid fly parasitoids of invasive fire ants indirectly improve the competitive ability of a native antECOLOGICAL ENTOMOLOGY, Issue 5 2004Natasha J. Mehdiabadi Abstract., 1.,The red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), is an invasive species of south-eastern U.S.A. Since its introduction from South America approximately 70 years ago, this pest has devastated natural biodiversity. 2.,Due to such ecological costs, Pseudacteon phorid fly parasitoids (Diptera: Phoridae) from South America are being introduced into the U.S.A. as a potential biological control agent. Here, the indirect effects of these specialised parasitoids on an interspecific native ant competitor, Forelius mccooki (Hymenoptera: Formicidae), are evaluated. 3.,Over the course of a 50-day laboratory experiment, the results show that the native ant improved aspects of exploitative, but not interference, competition when S. invicta -attacking flies were present compared with when they were absent. 4.,Forelius mccooki colonies from the phorid treatment had approximately twice as many foragers at food baits relative to controls; however, there was no significant difference in interference aspects of competition or native ant colony growth between the two treatments. 5.,These results suggest that the S. invicta -specialised parasitoids help shift the competitive balance more in favour of F. mccooki than if these flies were not present; however, this competitive advantage does not translate into increased colony growth after 50 days. These laboratory findings are interpreted with regard to the more complex interactions in the field. [source] Trade-offs and the evolution of life-histories during range expansionECOLOGY LETTERS, Issue 10 2010Olivia J. Burton Ecology Letters (2010) Abstract During range-advance, individuals on the expanding edge of the population face a unique selective environment. In this study, we use a three-trait trade-off model to explore the evolution of dispersal, reproduction and competitive ability during range expansion. We show that range expansion greatly affects the evolution of life-history traits due to differing selection pressures at the front of the range compared with those found in stationary and core populations. During range expansion, dispersal and reproduction are selected for on the expanding population front, whereas traits associated with fitness at equilibrium density (competitive ability) show dramatic declines. Additionally, we demonstrate that the presence of a competing species can considerably reduce the extent to which dispersal is selected upwards at an expanding front. These findings have important implications for understanding both the rate of spread of invasive species and the range-shifting dynamics of native species in response to climate change. [source] Simple rules for the coexistence and competitive dominance of plants mediated by mycorrhizal fungiECOLOGY LETTERS, Issue 3 2005James Umbanhowar Abstract Mycorrhizal fungi have been demonstrated to be important in the makeup of plant communities. Likely, their most important role is in altering mineral nutrition of plants, which, in turn, is thought to be among the most important determinants of plant competitive ability. Using mathematical models we examine what role these fungi can play in determining the competitive outcome between two plants in competition for one mineral resource. Depending on different relationships between the benefit accrued to the plant and the fungi, the presence of mycorrhizal fungi can (i) have no impact on which plant wins in competition, (ii) change the order of competitive dominance or (iii) enable coexistence when compared with the system in the absence of mycorrhizal fungi. Furthermore, environmental conditions, such as light and nutrient levels, can determine if coexistence is possible. We describe the necessary biological trade-offs for coexistence and experimental tests for these trade-offs. [source] Invasive aliens and sampling biasECOLOGY LETTERS, Issue 4 2003Andrew M. Simons Abstract Two hypotheses have been proposed to explain the observation of increased vigour of invasive alien plants in their nonindigenous ranges: phenotypic plasticity, and the post-invasion evolution of increased competitive ability (EICA). Here I specify how a general pattern of increased vigour may result from sampling bias. Ignoring failed invasions can account for the illusion of increased vigour over a broad range of assumptions. Plasticity and EICA need not be viewed as explanations for a general pattern of increased vigour even if they are the mechanisms underlying every occurrence. [source] Herbivore and pathogen damage on grassland and woodland plants: a test of the herbivore uncertainty principleECOLOGY LETTERS, Issue 4 2002Stefan A. Schnitzer Researchers can alter the behaviour and ecology of their study organisms by conducting such seemingly benign activities as non-destructive measurements and observations. In plant communities, researcher visitation and measurement of plants may increase herbivore damage in some plant species while decreasing it in others. Simply measuring plants could change their competitive ability by altering the amount of herbivore damage that they suffer. Currently, however, there is only limited empirical evidence to support this `herbivore uncertainty principle' (HUP). We tested the HUP by quantifying the amount of herbivore and pathogen damage in 13 plant species (> 1400 individuals) at four different visitation intensities at Cedar Creek Natural History Area, Minnesota, USA. Altogether, we found very little evidence to support the HUP at any intensity of visitation. Researcher visitation did not alter overall plant herbivore damage or survival and we did not detect a significant visitation effect in any of the 13 species. Pathogen damage also did not significantly vary among visitation treatments, although there was some evidence that high visitation caused slightly higher pathogen damage. Based on our results, we question whether this phenomenon should be considered a `principle' of plant ecology. [source] Genetic differences in growth of an invasive tree speciesECOLOGY LETTERS, Issue 6 2001Evan Siemann Invasive plants are often more vigorous in their introduced ranges than in their native ranges. This may reflect an innate superiority of plants from some habitats or an escape from their enemies. Another hypothesis proposes that invasive plants evolve increased competitive ability in their introduced range. We present the results of a 14-year common garden experiment with the Chinese Tallow Tree (Sapium sebiferum) from its native range (Asia), place of introduction to North America (Georgia) and areas colonized a century later (Louisiana and Texas). Invasive genotypes, especially those from recently colonized areas, were larger than native genotypes and more likely to produce seeds but had lower quality, poorly defended leaves. Our results demonstrate significant post-invasion genetic differences in an invasive plant species. Post-introduction adaptation by introduced plants may contribute to their invasive success and make it difficult to predict problem species. [source] Predicting competition coefficients for plant mixtures: reciprocity, transitivity and correlations with life-history traitsECOLOGY LETTERS, Issue 4 2001R.P. Freckleton There are few empirical or theoretical predictions of how per capita or per individual competition coefficients for pairs of plant species should relate to each other. In contrast, there are a considerable number of general hypotheses that predict competitive ability as a function of a range of ecological traits, together with a suite of increasingly sophisticated models for competitive interactions between plant species. We re-analyse a data set on competition between all pairwise combinations of seven species and show that competition coefficients relate strongly to differences between the maximum sizes, root allocation, emergence time and seed size of species. Regressions suggest that the best predictor of competition coefficients is the difference in the maximum size of species and that correlations of the other traits with the competition coefficients occur through effects on the maximum size. We also explore the patterns of association between coefficients across the competition matrix. We find significant evidence for coefficient reciprocity (inverse relationships between the interspecific coefficients for species pairs) and transitivity (numerically predictable hierarchies of competition between species) across competition matrices. These results therefore suggest simple null models for plant community structure when there is competition for resources. [source] Interspecific Differences in Responses to Predation Risk May Confer Competitive Advantages to Invasive Freshwater Turtle SpeciesETHOLOGY, Issue 2 2008Nuria Polo-Cavia The nature of competitive interactions between native and introduced invasive species is unclear. In the Iberian Peninsula, the introduced red-eared slider (Trachemys scripta elegans) is an invasive species that is competing and displacing the endangered native Spanish terrapin (Mauremys leprosa). We hypothesized that interspecific differences in antipredatory behavior might confer competitive advantages to introduced T. scripta. We examined whether interspecific differences in responses to predation risk affect the time that turtles remained hidden in the shell before using an active escape to water. Both turtle species adjusted hiding times by balancing predation threat, microhabitat conditions and the costs of remaining hidden. However, introduced T. scripta showed longer hiding times before escaping than native M. Leprosa, which, in contrast, switched from waiting hidden in the shell to escape to deep water as soon as possible. These interspecific differences might result from the risk of facing different types of predators in different microhabitats (land vs. water) in their original habitats. However, in anthropogenically altered habitats where predators have been greatly reduced, T. scripta may avoid potential costs of unnecessary repeated escape responses to water (e.g. interruption of basking). These behavioral asymmetries could contribute to the greater competitive ability of introduced T. scripta within anthropogenically disturbed environments. [source] Multiple Cues in Status Signalling: The Role of Wingbars in Aggressive Interactions of Male House SparrowsETHOLOGY, Issue 10 2006Veronika Bókony During aggressive interactions, animals may signal their competitive ability by various ornaments referred to as badges of status. The use of a single badge predicting dominance rank occurs in many vertebrate species. However, animals often display multiple ornaments that may convey information about either different or the same aspects of the signaller's quality, or alternatively, may serve as signal amplifiers. We observed the fighting behaviour of male house sparrows in two captive flocks to investigate whether they may use multiple cues in status signalling during aggressive interactions. Beside the status-signalling bib, male sparrows possess a conspicuous white wingbar that they often display upon aggressive encounters. We tested whether bib size and the wingbar's conspicuousness (i.e. its achromatic contrast with the neighbouring dark feathers) or its area predicted success in various aspects of fighting. We found that bib size strongly predicted overall fighting success (i.e. proportion of fights won) and defence success (i.e. proportion of successful defences out of all attacks received). Wingbar conspicuousness was positively related to defence success after controlling for the effect of bib size in multivariate analyses. Furthermore, displaying the wings also tended to improve the birds' success in defence but not in attack. Wingbar area was unrelated to any measured aspect of fighting ability. We suggest that bib size and wingbar conspicuousness may convey multiple messages on fighting abilities, specifically on overall aggressiveness and defending potential, respectively. Alternatively, wingbars may serve as amplifiers for the wing displays of aggressive motivation. Thus, male sparrows may use multiple cues in assessing the competitive ability of opponents during social interactions. [source] Impact of Environmental Disturbance on the Stability and Benefits of Individual Status within Dominance HierarchiesETHOLOGY, Issue 5 2006Lynne U. Sneddon Changes in environmental conditions affect social interactions and thus may modify an individual's competitive ability within a social group. We subjected three-spined sticklebacks, Gasterosteus aculeatus, housed in groups of four individuals, to environmental perturbations to assess the impact on dominance hierarchy stability. Hierarchy stability decreased during increased turbulence or lowered water levels (,simulated drought') whereas control hierarchies became more stable in a constant environment. The dominant individual either became more aggressive and remained dominant during the environmental manipulation or was usurped by a lower rank member. Only simulated drought affected rates of aggression where levels of aggression were higher after the water level was dropped which may be the result of an increased encounter rate in these conditions. When there were large size differences between the group members, the dominant individual performed the greatest amount of aggression and ate the largest proportion of food and there was little aggressive behaviour from the lower ranks. In groups of similar-sized individuals, aggression was much higher. The benefit of being dominant was to gain weight over the experimental period whereas ranks 2 and 3 lost weight. The lowest rank, 4, actually gained weight over the experimental period. This study suggests that it would benefit an individual to be dominant, highly aggressive and gain weight or be submissive, avoid aggressive interactions and, by sneakily obtaining access to food, also gain weight. Altering environmental conditions has a profound effect on social behaviour in this study. [source] Strophe Length in Spontaneous Songs Predicts Male Response to Playback in the Hoopoe Upupa epopsETHOLOGY, Issue 5 2004Manuel Martín-Vivaldi Hoopoe (Upupa epops, Coraciformes) males produce a very simple song during the breeding season in order to attract females and repel intruders. Strophes vary in length (i.e. number of elements) both within and between males, and previous studies have shown that this song cue is positively correlated with male condition and breeding success. In the present study we tested whether strophe length of males influences male behaviour during intra-sexual contests, in a colour-ringed population in southeast Spain. Paired males were presented with a recorded song with long strophes during the pre-laying period, while they were near their mates, in order to provoke male mate-defence behaviour. Most males responded to the playback, but the strategy of defence adopted depended on their own strophe length in spontaneous songs recorded before the experiments. While singing responses were common to most of the males, only those using long strophes adopted the most risky strategy of approaching the loudspeaker. However, the males that approached produced abnormal songs during playback, that were shorter and with fewer strophes than those of males that did not approach, and used shorter strophes in comparison with spontaneous songs before the experiment. These differences in quality of the song produced in response to the playback suggest that long-strophe males were basing their response mainly on attacking rather than singing, while short-strophe males tried to resolve the contest at a distance by means of their song. These results show that strophe length reflects some component of the competitive ability of males (either physical strength or aggressiveness) in the hoopoe, which together with previous results regarding its role for female choice, show that it is a sexual signal with dual function. [source] | |||||||||||||||||||||||||||||||||||||