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Competing Species (competing + species)
Selected AbstractsTrade-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] Interspecific interference and the functional response of four species of carnivorous stonefliesFRESHWATER BIOLOGY, Issue 9 2003J.M. Elliott Summary 1.,A previous study compared the functional responses to their prey and intraspecific interference in mature larvae of Perlodes microcephalus, Isoperla grammatica, Dinocras cephalotes and Perla bipunctata. The present study extends this work by assessing interspecific interference between pairs of these species in equal numbers (one, two or three larvae per species) to provide total predator densities of two, four or six larvae. Baetis larvae as prey were replaced as they were eaten, and their density per predator was varied between 20 and 200 larvae. 2.,The number of prey eaten by each competing species increased curvilinearly with prey density, the relationship being well described by a Type II model. Of the two constants in the model, handling time varied considerably between species, mean values being shortest for Perlodes, slightly higher for Isoperla, and much higher for Dinocras and Perla. It was not affected significantly either by predator density or the identity of the competing species. 3.,Attack rate also varied between species and decreased with predator density. This decrease was slight for Perlodes, and also for Dinocras and Perla in competition with Isoperla. The decrease in Dinocras and Perla was similar to that for intraspecific interference. 4.,The decrease in attack rate was described by a convex curve for Perlodes with the other three species and for Dinocras/Perla with Isoperla, but by a concave curve (negative power function) for Isoperla competing with the other three species, and for both Dinocras and Perla in competition with Perlodes. Prey consumption also decreased with predator density, the severity of competition with different species reflecting that for attack rate. 5.,A comparison with previous results for intraspecific interference showed that the latter was dominant for Perlodes in all contests and for Dinocras or Perla competing with Isoperla, whilst interspecific interference dominated for Isoperla in all contests and for Dinocras and Perla competing with Perlodes. Both types of interference were applicable to competition between Dinocras and Perla. Isoperla was the least, and Perlodes the most, aggressive of the four species with Dinocras and Perla intermediate. [source] Competition in variable environments: experiments with planktonic rotifersFRESHWATER BIOLOGY, Issue 6 2002KEVIN L. KIRK 1.,In a constant environment, competition often tends to reduce species diversity. However, several theories predict that temporal variation in the environment can slow competitive exclusion and allow competing species to coexist. This study reports on laboratory competition experiments in which two pairs of planktonic rotifer species competed for a phytoplankton resource under different conditions of temporal variability in resource supply. 2.,For both species pairs, Keratella cochlearis dominated under all conditions of temporal variability, and the other species (Brachionus calyciflorus or Synchaeta sp.) almost always went extinct. Increasing temporal variation in resource supply slowed competitive exclusion but did not change competitive outcome or allow coexistence. 3.,Rotifers show a gleaner,opportunist trade-off, because gleaner species have low threshold resource levels (R*) and low maximum population growth rates, while opportunist species have the opposite characteristics. In the competition experiments, the gleaner always won and the opportunists always lost. Thus, a gleaner,opportunist trade-off was not sufficient to facilitate coexistence under conditions of resource variability. Instead, the winning species had both the lowest R* and the greatest ability to store resources and ration their use during times of extreme resource scarcity. [source] Effects of Interspecific Interactions between Microcystis aeruginosa and Chlorella pyrenoidosa on Their Growth and PhysiologyINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 3 2007Min Zhang Abstract Interactions between Microcystis aeruginosa and Chlorella pyrenoidosa were analyzed by flow cytometry and by phytoplankton pulse-amplitude-modulated fluorimetry (Phyto-PAM) in joint cultures as well as in cultures separated by dialysis membranes. Results showed that the growth of C. pyrenoidosa was greater than that of M. aeruginosa, and that the growth of M.aeruginosa but not the growth of C. pyrenoidosa was significantly inhibited by the interactions between M. aeruginosa and C. pyrenoidosa. Culture filtrates of these two algae showed no apparent effects on the growth of the competing species. For M. aeruginosa, decreases in esterase activity, chlorophyll a fluorescence, and maximum quantum yield were observed in joint cultures, indicating that the metabolic activity and photosynthetic capacity of M.aeruginosa were suppressed. Light limitation from the shading effect of C. pyrenoidosa may be the main reason for such inhibition. For C. pyrenoidosa, esterase activity was suppressed in membrane-separated and joint cultures, suggesting that C.pyrenoidosa was probably affected by allelopathic substances secreted by M.aeruginosa. However, no significant difference was observed in the chlorophyll a fluorescence and maximum quantum yield of C. pyrenoidosa in the two cultures. In addition, interspecific interactions induced a reduction in size in both M. aeruginosa and C.pyrenoidosa, which may contribute to the development of C. pyrenoidosa dominance in the present study. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Sink habitats can alter ecological outcomes for competing speciesJOURNAL OF ANIMAL ECOLOGY, Issue 6 2005SEBASTIAN J. SCHREIBER Summary 1Species often compete for breeding sites in heterogeneous landscapes consisting of sources and sinks. To understand how the presence or absence of sink breeding sites influence ecological outcomes, we extend Pulliam's source,sink model to competing species. 2In a homogeneous landscape consisting of source sites, we prove that one species, the ,superior' competitor, competitively excludes the other. Dominance is determined by a simple rule: the species that at equilibrium acquires new breeding sites at a faster rate dominates. 3We prove that the inclusion of sink sites can alter this ecological outcome by either mediating coexistence, reversing competitive dominance, or facilitating a priority effect. 4Sink-mediated coexistence requires the species to exhibit asymmetries in acquiring sink sites, the ,inferior' species to have a competitive advantage on sink sites and the ratio of sink to source sites be sufficiently low. 5For example, if the sink breeding sites are competitive refuges for the ,inferior' competitor and not too low in quality, coexistence occurs if the number of sink sites lies below a threshold. Alternatively, when the number of sink sites exceeds this threshold, competitive dominance is reversed and the ,superior' competitor is displaced. 6Counter-intuitively, despite being unable to support species in isolation, sink habitats embedded in a geographical mosaic of sources and sinks can enhance biodiversity by mediating coexistence or alter species composition by reversing competitive interactions. [source] Influence of herbivory, competition and soil fertility on the abundance of Cirsium arvense in acid grasslandJOURNAL OF APPLIED ECOLOGY, Issue 2 2000G.R. Edwards Summary 1. ,The extent to which the weed Cirsium arvense (creeping thistle) may be controlled by manipulating interspecific competition and herbivory was examined in two factorial experiments in order to identify non-chemical herbicide-based control methods for the weed. 2. ,In the first experiment, a single spring cultivation of grassland intensively grazed by rabbits led to a 25-fold increase in C. arvense cover within 3 months, the effects of which were still present the following summer. As well as destroying the competing perennial vegetation, cultivation created and dispersed small root fragments (3,5 cm in length) from which almost all shoot recruitment occurred. 3. ,Fencing the cultivated plots against rabbits decreased the cover of C. arvense because ungrazed regrowth from palatable/grazing intolerant species reduced recruitment of C. arvense seedlings and shoots. Seedling competition, in the form of a wildflower seed mix sown soon after cultivation, reduced C. arvense cover on fenced plots to pre-cultivation levels. 4. ,In the second experiment, conducted in a permanent grassland, C. arvense shoot densities on plots fenced against rabbits and treated as a hay meadow were about one-eighth of those found on rabbit-grazed plots where competing vegetation was kept short. Adventitious shoot recruitment was greater on soil disturbances such as molehills and rabbit scrapes than in intact vegetation. Seedling recruitment occurred only on soil disturbances such as molehills. 5. ,Lime and nitrogen fertilizer application to the fenced grassland increased the standing biomass of competing species, which reduced C. arvense shoot density. Outside the fences, rabbit grazing was so concentrated on the competing species of the nitrogen-fertilized and limed areas that C. arvense benefited from competitive release, exhibiting increased shoot density. Cirsium arvense showed pronounced competitive release from grasses, with greater shoot densities where grasses were removed with selective herbicides than where no plant species were removed. 6. ,Exclusion of insects and molluscs with chemical pesticides had no effect on shoot or seedling recruitment or overall shoot density on cultivated soil or in permanent grassland. 7. ,It is concluded that combinations of management procedures that encourage interspecific competition, such as sowing crops soon after cultivation and delaying grazing of them, and nitrogen fertilizer application and non- or reduced grazing of intact grasslands, will help reduce C. arvense abundance. [source] Physiological effects of dominance hierarchies: laboratory artefacts or natural phenomena?JOURNAL OF FISH BIOLOGY, Issue 1 2002K. A. Sloman Studies of fish behaviour have demonstrated the existence of social interactions that result in dominance hierarchies. In environments in which resources, such as food, shelter and mates, are limited, social competition results in some fish becoming dominant and occupying the most profitable positions. This behaviour has been observed in natural environments and also in many laboratory-based experiments. When two fish have been confined in a small tank, one of them usually has exhibited behaviour that suggests it is dominant over the other submissive animal. Physiological consequences of social interaction can be seen in both dominants and subordinates but are more extreme in the subordinate. However, this scenario is without doubt an artificial situation. Fewer experiments have been conducted using laboratory experiments that are more socially and physically complex than those experienced by dyads in tanks. In simple fluvial tanks, through which water is recirculated, the physiological responses of fish to social competition have generally been qualitatively similar to those recorded among dyads. However, when environmental disturbances, complex resource distributions, increase in water flushing, presence of predators and competing species of fish have been included in experimen-tal designs, there have been fewer, diminished or no physiological dierences between dominant and subordinate fish. There have been very few studies of physiology in relation to dominance in natural habitats, and those that have been conducted suggest that under some circumstances hierarchies may cause less intense physiological responses than have been suggested based on results of laboratory studies in simple environments. Possible reasons for these variations are discussed. The need is identified for a well structured experimental approach to the investi-gation of the causes and consequences of hierarchies if the ecology of wild fish is to be modelled eectively based on physiological processes. It is also suggested that the further development and application of techniques for monitoring physiologies of fish in the wild is important. [source] Effects of browsing and grazing on cyclic succession in nutrient-limited ecosystemsJOURNAL OF VEGETATION SCIENCE, Issue 6 2001Jan Bokdam van der Meijden (1990) Abstract. This paper deals with browsing and grazing as forces driving cyclic succession. Between 1989 and 1994 reciprocal transitions between the dwarf shrub Calluna vulgaris and the grass Deschampsia flexuosa were monitored in permanent plots in a cattle grazed grass-rich Dutch heathland on podsolic soils in which tree encroachment was prevented. Heather beetles killed Calluna in four of the nine plots during 1991/1992. The monitoring revealed reciprocal transitions and cycles between Calluna and Deschampsia on a subplot scale. Beetles and cattle had additional and complementary effects on the two competing species. Defoliation by beetles and trampling by cattle-killed Calluna and favoured grass invasion. Grazing and gap creation by cattle in Deschampsia favoured the establishment and recovery of Calluna. Analysis of the causal mechanisms suggests that indirect, resource-mediated herbivory effects may be as important for the replacement processes as direct effects of defoliation and trampling. Herbivory created differential light and nutrient levels in Calluna and Deschampsia gaps. Grazing and browsing improved the resource-capturing abilities of Calluna and its resistance to herbivory and abiotic disturbances. The emerged Calluna-Deschampsia cycle and its driving forces are summarized in a conceptual triangular resource-mediated successional grazing cycle (RSGC) model, a limit cycle involving herbivore-plant-plant resource interactions. It offers a deterministic equilibrium model as alternative for stochastic transitions between the meta-stable states with dominance of Calluna and Deschampsia respectively. The validity range of the RSGC model and its management implications are briefly discussed. [source] Feeding success of African wild dogs (Lycaon pictus) in the Serengeti: the effects of group size and kleptoparasitismJOURNAL OF ZOOLOGY, Issue 2 2005C. Carbone Abstract Longer-term ecosystem level dynamics are often neglected in conservation studies involving single species. In this study, a retrospective analysis is presented on the feeding performance of African wild dogs Lycaon pictus in the Serengeti in relation to a competing species, the spotted hyena Crocuta crocuta, to test whether hyenas had an effect on feeding performance of wild dogs in this ecosystem. Our analysis is based on observations of over 700 wild dog kills recorded over a 20-year period (from 1964 to 1987) during which time there was a decline in wild dog numbers (ending with their local extinction in 1991) and a twofold increase in hyena density. Overall, the amount of time that dogs had access to the kill (access time) decreased with increasing numbers of hyenas attending kills, but access time increased with increasing hunting-group size of dogs and carcass mass. In addition, in the 1980s, dogs spent longer at kills than in the 1970s for a given set of conditions, including when hyenas were absent. Our analysis demonstrates a greater potential for group benefits than was found in a previous study (Carbone, Du Toit et al., 1997). Hunting-group sizes of between two and six dogs performed best when hyenas attended dog kills because the benefits of increased defence outweighed the costs of having to share the carcass with more dogs. Hunting-group sizes of wild dog and levels of hyena attendance at the kill broadly paralleled the population trends in these species, with hunting-group sizes of wild dog declining, followed by hyena attendance increasing. Despite the combined effects of increased hyena attendance and reduced hunting-group size, dogs in the 1980s typically spent longer feeding and consumed more of the carcass including the poorest sections. This suggests that dogs in the 1980s may have been under greater energetic stress. [source] Influence of predator-specific defense adaptation on intraguild predationOIKOS, Issue 3 2010Takefumi Nakazawa The persistence of intraguild predation (IGP), the prey,predator interaction between competing species, is puzzling because simple IGP models readily predict species extinction. In this study, we explored a mathematical model incorporating predator-specific defense adaptation of basal prey against intraguild prey and intraguild predator. The model explicitly described the dynamics of the defense effort against each predator under the assumption that anti-predator defense was associated with reducing effort allocated to reproduction. The model predicted that defense adaptation (i.e. the ability to reallocate defense effort) would facilitate coexistence, particularly when system productivity is high; at low productivity, coexistence would be facilitated or inhibited depending on initial effort allocation prior to defense adaptation. In addition, we found that three-species dynamics became more stable at higher adaptation rates. The results suggest that common behavioral changes, such as predator-specific defense adaptation, have significant implications for the community structure and dynamics of IGP systems. [source] | |||||||||||||