Mechanisms Of Interspecific Competition Research Articles

The fitness benefit of pyoverdine cross-feeding by Pseudomonas protegens Pf-5.

Under iron-limiting conditions, fluorescent pseudomonads acquire iron from the environment by secreting strain-specific, iron-chelating siderophores termed pyoverdines (PVD). The rhizosphere bacterium Pseudomonas protegens Pf-5 produces its own PVD but also can cross-feed on PVDs produced by other species. Previous work has found that Pf-5 continues to produce its own PVD when allowed to cross-feed, raising questions about the benefit of heterologous PVD utilisation. Here, we investigate this question using a defined, unidirectional P. protegens Pf-5/Pseudomonas aeruginosa PAO1 cross-feeding model. Quantifying the production of PVD in the presence of heterologous PVD produced by PAO1, we show that cross-feeding Pf-5 strains reduce the production of their own PVD, while non-cross-feeding Pf-5 strains increase the production of PVD. Measuring the fitness of cross-feeding and non-cross-feeding Pf-5 strains in triple coculture with PAO1, we find that cross-feeding provides a fitness benefit to Pf-5 when the availability of heterologous PVD is high. We conclude that cross-feeding can reduce the costs of self-PVD production and may thus aid in the colonisation of iron-limited environments that contain compatible siderophores produced by other resident microbes. Taken together, these results expand our understanding of the mechanisms of interspecific competition for iron in microbial communities.

Dispersal movements of non‐native and native terrestrial slugs in an urban environment

AbstractAnimal movement varies from undirected dispersal to directed migration. Movement rates may have implications for conservation and resource management, as well as pest control, and they play a key role in invasion success. In slugs, long‐distance dispersal is typically passive, whereas active movement is critical for local dispersal and determines access to resources such as food and shelter. Telemetry has recently been used to study individual slug movements in the wild, whereas movement in arena tests has explored mechanisms of interspecific competition and invasiveness in slugs. Studies that relate the performance of individual slugs in arena tests to their post‐release behavior in nature are lacking. We measured individual short‐term movement speed of commonly occurring native and non‐native slugs of the genera Arion and Limax in arena tests and tracked their post‐release dispersal movements in a garden by PIT telemetry. We demonstrate clear differences in movement behavior among the species, but non‐native slugs did not display higher movement rates than their native congeners. In the arena test, slugs of the genus Limax displayed a higher short‐term speed than slugs of the genus Arion, whereas in the field, individuals of Limax maximus showed lower dispersal rates compared to the other slug species. Moreover, there was a positive correlation between short‐term speed in the arena test and movement in the field among individuals of L. cinereoniger, indicating the possible existence of behavioral syndromes in slugs, which may link movement ecology, animal personality, and the invasion ecology of pest species.

Kinetics of phosphate uptake in the dinoflagellate Karenia mikimotoi in response to phosphate stress and temperature

Phosphate (Pi) and temperature are two important environmental factors affecting algal growth and the occurrence of red tide. In this paper, we conduct experiments on Karenia mikimotoi under different Pi concentrations and temperatures and propose a novel Pi uptake model by incorporating Arrhenius function and Pi-stress function into the two-stage model presented in one of our recent paper (Jiang et al. (2019)). In both Pi-replete and Pi-deplete, the model parameters are obtained by fitting the experimental data at 24 °C and validated by the experimental data at 20 °C, respectively. K. mikimotoi under low Pi condition entered into the exponential growth phase earlier compared with Pi-replete groups. Under the Pi-replete condition, K. mikimotoi continually increased, while the Pi-deplete condition showed a wave trend. The experimental results and the fitting of experimental data both show that K. mikimotoi has an obvious response to temperature. In both Pi-replete and Pi-deplete, the peak values of the cell quota of intracellular Pi and surface-adsorbed Pi at 24 °C were higher than those at 20 °C. Using the luxury coefficient and growth potential, interspecific competition between K. mikimotoi and Prorocentrum donghaiense is also discussed. These results and conclusions are helpful to understand the Pi uptake characteristics of algae at different Pi concentrations and temperatures, and could effectively explain mechanisms of interspecific competition and succession between different algae species during red tide.

Response of Poplar Leaf Transcriptome to Changed Management and Environmental Conditions in Pure and Mixed with Black Locust Stands

Mixed cropping in short rotation coppice can be an alternative to monocultures. To design optimized mixtures, field trials are needed. Poplar, as an economically important and fast-growing species, and black locust, as a nitrogen-fixing species, are promising candidates for such studies. RNA sequencing (RNA-seq) was used to monitor effects of mixed and pure cultivations on the gene expression of poplar along with growth measurements during 2017 and 2018. Both biomass production and leaf transcriptomes revealed a strong competition pressure of black locust and the abiotic environment on poplar trees. Gene expression differed between the two study sites and pure and mixed stands. Shading effects from black locust caused the downregulation of photosynthesis and upregulation of shade avoidance genes in mixed stands in 2017. As a result of higher light availability after cutting black locust, plant organ development genes were upregulated in mixed stands in 2018. Drought conditions during the summer of 2018 and competition for water between the two species caused the upregulation of drought stress response genes in mixed stands and at the unfavorable growing site. Further investigations are required to discover the mechanisms of interspecific competition and to develop stand designs, which could increase the success and productivity of mixed plantations.

Composition and niche of the existing herbaceous plants in the water-level-fluctuating zone of the Three Gorges Reservoir Area, China

To understand the usages of available resource by dominant plants, their niches and the mechanisms of inter-specific competition and co-existence in the water level fluctuation zone, we studied the spatial distributions and niche characteristics of existing dominant herbaceous species at a typical water-level-fluctuation site of the Three Gorges Reservoir Area, Zigui. The results showed that there were 39 herb species in total, which belonged to 18 families and 32 genera. Gramineae, Compositae, Polygonaceae and Euphorbiaceae were the dominant families. Cynodon dactylon, Setaria viridis, Bidentis tripartitae and Digitaria chrysoblephara were the dominant species, with high importance value and niche breadth. In addition, at 145-155 m, 155-165 m and 165-175 m altitude section, the three major species, expressing the highest ecological niche breadth, which were in order of C. dactylon ＞ Polygonum lapathifolium ＞ S. viridis, S. viridis ＞ D. chrysoblephara ＞ C. dactylon, and S. viridis ＞ B. tripartitae ＞ P. orientale, respectively. The niche overlap of the species between the different altitudes zone was relatively high. The species which had a broad niche could co-exist with those occupying narrow niche. The niche overlap could not be determined by niche breadth lonely. Furthermore, after seven times of water level fluctuations, most of the species were annual herbs, and the degree of niche differentiation was low in the area. Due to scarce resources and unstable habitats, the inter-specific competition was strong, and the vegetation was at the primary successional stage.

Mechanistic mechanisms of competition and biodiversity

AbstractThe nature of competition and biodiversity are open basic questions since Darwin. To investigate mechanisms of interspecific competition and their contribution in biodiversity as closely as possible we offer a white-box modelling method based on physically interpreted ecological axioms. These models are implemented as deterministic individual-based cellular automata and able to give a direct physico-mechanistic insight into studied phenomena. Competition of two trophically identical but fitness different species, competing for one limiting resource in one stable uniform habitat (which is closed for immigration, emigration, predation, herbivory and parasitism) has been investigated in conditions, which are the most unfavourable for their coexistence. The species are per capita identical in fecundity, ontogeny, regeneration features of microhabitats, and in habitat requirements. We have modelled following 8 mechanistic mechanisms of interspecific competition:1. A case of the competitive exclusion when competing species differ only in fitness.2. Coexistence based on periodic dominance changeovers as a consequence of environmental changes. Competing species differ only in fitness.3. A strong violation of the competitive exclusion principle due to the lowered fecundity of both competitors. Competing species differ only in fitness.4. Coexistence based on the competition–colonisation trade-off when greater fitness is compensated by r-strategy.5. A competition–colonisation trade-off based on differences in ontogeny.6. Competitive exclusion when recessive species drives out the dominant one having four times greater fecundity than the dominant one in stable environment (the greater fitness cannot compensate r-strategy).7. An inverted competitive exclusion when recessive species drives out the dominant one by strategy of anticipatory deprivation of resources for competitor’s offsprings propagation. Recessive species drives out the dominant one in stable environment and both competing species have identical fecundity (tripod neighbourhood). Paradoxically, but the greater fitness cannot save the dominant species when the all other parameters of the species are equal.8. Both competing species die because the regeneration of a limiting environmental resource takes too much time and they cannot propagate.The revealed mechanisms of competition can be useful not only in conservation biology, but also in economics and politics. Additionally, we speculate that the simplest way to maintain biodiversity is a controlled reduction of human fertility as the decrease in biodiversity occurs largely due to humankind overloading of biosphere resources.

Deterministic individual-based cellular automata modelling of single species population dynamics

AbstractThis presentation was created to characterise foundations of cellular automata modelling of single species population dynamics. We show models of single species population growth based on deterministic birth-death-regeneration process and demonstrate a relationship between fecundity rate and population growth rate. Our models provide mechanistic simulation of logistic-like and double logistic-like curves of population growth that is not possible in the classical Verhulst model (logistic growth model). This method is deterministic individual-based and is based on logical “if-then” statements only. As this method is bottom-up mechanistic and provides a direct visual insight into dynamics of complex systems, we used it to study mechanisms of interspecific competition in further experiments.

IMPORTANCE OF COMPETITION MECHANISMS IN SUCCESSIVE INVASIONS BY POLYPHAGOUS TEPHRITIDS IN LA RÉUNION

Understanding the strength and modes of interspecific interactions between introduced and resident species (native or previously introduced) is necessary to predict invasion success. We evaluated different mechanisms of interspecific competition among four species of polyphagous fruit flies (Diptera: Tephritidae) from the island of La Reunion: one endemic species, Ceratitis catoirii, and three exotic species, C. capitata, C. rosa, and Bactrocera zonata, that have successively invaded the island. Larval competition experiments, i.e., co-infestations of the same fruit, and behavioral interference experiments measuring the ability of one female to displace another from a fruit, were performed among all pairs of the four species. We observed asymmetric and hierarchical interactions among species in both larval and adult interference competition. In agreement with the hypothesis that invasion is competition-limited, the competitive hierarchy coincided with the temporal sequence of establishment on the island, i.e., each newly established species tended to be competitively dominant over previously established ones.

Natural Enemies of Gall-forming Sawflies on Willows (Salix spp) (Hymenoptera: Tenthredinidae: Euura, Phyllocolpa, Pontania)

Since 1981, the author has collected and reared more than 135,000 galls of the sawfly genera Pontania, Euura, and Phyllocolpa from 33 willow species in 249 natural sites of 10 European countries. The sites were situated along a gradient from the European arctic tundra to the mediterranean zone of Sicily (Southern Italy) over a geographic range of about 3,900 km. The communities of natural enemies associated with the gall formers consist of biologically different complexes of natural enemies, i.e parasitic inquilines (6 spp) and parasitoids (91 spp). The community of natural enemies of Pontania comprises six parasitic inquilines (Curculionidae: 3 spp, Tephritidae: 1 sp, Geometridae: 1 sp, Eurytomidae: I sp) and 70 parasitoid species (Braconidae: 22 spp, Ichneumonidae: 20 spp, Chalcidoidea: 27 spp, others: 1 sp). Euura species were attacked by four parasitic inquilines (Curculionidae: 3 spp, Eurytomidae: 1 sp) and 28 parasitoid species (Braconidae: 6 spp; Ichneumonidae: 9 spp; Chalcidoidea: 11 spp; others: 2 sp), whereas larvae of Phyllocolpa species were infested by only 17 parasitoid species (Braconidae: 3 spp; Ichneumonidae: 10 spp; Chalcidoidea: 4 spp). The mortality of host larvae caused by natural enemies differed widely between the species and genera as well as between sites, ranging from 12.9% to 88.3% in Pontania, 15.1% to 89.2% in Euura, and 2.4% to 34% in Phyllocolpa. Different guilds of parasitoids were found, most of which attacked young larvae and developed as ectoparasitic idiobionts. As the gall-making species of Euura, Pontania, and Phyllocolpa produce morphologically distinct gall-types, they are often attacked by their own typical enemy complex, dominated by specialists and a large number of rarer, polyphagous generalists. Among the specialists highly efficient attack strategies have evolved, maximizing the success of parasitoid attack of host larvae concealed within galls. The coexistence of natural enemies exploiting identical resources has been achieved through the development of diverse mechanisms minimizing interspecific competition: i.e: host specificity, differences in phenology or parasitizing strategies, or in morphological criteria like ovipositor length, limiting the success of parasitoid attack. Both, gallmaker and natural enemy populations, appear to be influenced by diverse 'bottom-up' effects rather than controlled by 'top-down' effects The driving variable is the abiotic environment that affects plant species and plant quality which govern the distribution and abundance of galls, and subsequently the pattern of parasitism. Carnivores may have 'top-down' effects on herbivores as well as abiotic or weather factors which may also control the community. Thus, three-trophic-level interactions and mechanisms of interspecific competition may have a combined effect in influencing the community structure of sawfly galls.

Mechanisms of interspecific competition among an invasive and two native fire ants

The mechanisms of interspecific competition among an invasive and two native Solenopsis fire ant forms were investigated in a series of laboratory experiments. In separate trials each with a different food resource, the native S. geminata×xyloni retrieved the greatest amount of a protein‐ and lipid‐rich artificial food resource and a high protein natural food resource, and the native S. geminata retrieved the greatest amount of a high carbohydrate food resource. In trials investigating aspects of interference competition at the colony level, the invasive S. invicta proved to be initially more aggressive than S. geminata, but less aggressive than S. geminata×xyloni. Solenopsis invicta eventually controlled more of the foraging arenas against both native forms when colonies were equivalent by worker biomass, but not when colonies were equivalent by worker number. When paired with S. invicta, S. geminata suffered a significantly greater proportional reduction in both workers and entire colonies when colonies were initially standardized by worker biomass, but not when colonies were standardized by worker number. When paired with S. invicta, a significantly greater proportional reduction of workers occurred in S. geminata×xyloni, regardless of how colonies were standardized. In pairwise trials at the individual level, majors always exhibited significantly less mortality than minors, regardless of the Solenopsis form. The majors of both native forms suffered significantly less mortality than those of S. invicta. Superiority in colony‐level interference ability appears to be an important mechanism allowing S. invicta to displace native Solenopsis forms. The ability of S. invicta to reach high population densities, because of intrinsic biological characteristics or an escape from natural enemies, plays an important contributory role. Similar mechanisms may underlie the success of other invasive ant species.

Indirect effects of phorid fly parasitoids on the mechanisms of interspecific competition among ants.

Indirect effects, which occur when the impact of one species upon another requires the existence of an intermediary species, are apparently very common and may be of greater magnitude than direct effects. Behaviorally mediated indirect effects occur when one species affects the behavior of a second, which in turn affects how that species interacts with a third. I studied behaviorally mediated indirect effects on the mechanisms of competition in two congeneric fire ant species in the presence and absence of parasitoid phorid flies, which parasitized only one ant species. In observational and experimental field studies, the presence of native Texas phorid flies in the genus Pseudacteon decreased food retrieval by their host, Solenopsis geminata (F.), by as much as 50%. In the presence of phorid flies, many S. geminata workers assumed a stationary, curled defensive posture and did not forage. Although the phorid parasitoids had a relatively large effect on exploitative competition, there was no measurable effect on interference competition. Fierce interspecific aggression was observed between S. geminata and S. invicta Buren, and the presence of phorids had no effect on the outcome of these contests. The indirect effects of Pseudacteon parasitoids on Solenopsis fire ant resource retrieval appear to be larger than the direct effect of mortality. Some aspects of the foraging behavior of these Solenopsis species may be, in part, evolutionary adaptations to phorid parasitoid pressure. Because of the relatively large indirect effects, South American Pseudacteon phorids may be promising biocontrol agents of imported fire ants, S. invicta, in the USA. In a laboratory study, a single South American Pseudacteon female was able to significantly decrease food retrieval rates of a North American population of the imported fire ant, S. invicta.

Mechanisms of interspecific competition that result in successful control of Pacific mites following inoculations of Willamette mites on grapevines.

We have successfully reduced populations of economically damaging Pacific mites by introducing another economically unimportant herbivorous mite to grapevines. Although this technique has proven successful in greenhouse and commercial applications, we had a poor understanding of why it worked. Experiments were conducted in a Zinfandel vineyard to assess the relative importance of different forms of competition between these two species and the importance of the timing of the introduction. The early season release of Willamette mites that occurred as shoots were first elongating reduced populations of Pacific mites, indicating that some form of competition occurred in this experiment. However, introductions of Willamette mites 4 weeks later did not reduce populations of Pacific mites. An early season release is essential for control. Control shoots did not receive additions of Willamette mites and had high population densities of Pacific mites. In contrast to this, Pacific mite populations were reduced on treatments with Willamette mites, regardless of whether the two species overlapped spatially or were separated by a barrier. This indicated that physical interference was not responsible, that induced resistance was involved, and that the effect was systemic throughout the shoot.

The Importance of the Mechanisms of Interspecific Competition

The Importance of the Mechanisms of Interspecific Competition

Indirect Mutualism: Variations on a Theme by Stephen Levine

Indirect Mutualism: Variations on a Theme by Stephen Levine

Numerical Taxonomy of Ecological Characteristics and the Niche Concept

In studies of interspecific competition of the bean weevils, Callosobruchus chinensis, and C. maculatus (Fujii, 1968; 1969), I employed the following eight geographical strains of both species: in C. chinensis, two strains collected in Kyoto, Japan, in 1936 (jC) and in 1965 (kC), a strain collected in -Iran in 1954 (iC), and a strain from Niigata Prefecture, Japan in 1964 (nC). In C. maculatus, two strains imported from the U.S.A. in 1946 (aQ) and in 1957 (cQ), a strain imported from Burma in 1954 (bQ), and a strain imported from the Near East in 1960 (tQ). For the analysis of the mechanisms of interspecific competition, I measured certain fundamental biological characteristics of each strain when cultured at 300 C. and 70% RH. Characteristics (1) through (7) as listed below are based on the means of measurements taken for individuals in each culture; those from (8) through (11) are based on counts or measurements obtained for the entire culture, during all generations of the study.

Competition for Food Between Redside Shiners (Richardsonius balteatus) and Rainbow Trout (Salmo gairdneri) in Two British Columbia Lakes

The distribution, movements, behaviour and food of trout and shiners in Paul and Pinantan Lakes were studied to determine the items and mechanisms of interspecific competition between them. Data from recent years were compared with data for years when trout alone inhabited the lakes.No interspecific aggression was observed. The possibility that the two species were competing for space was discounted. Stomach contents of shiners in Pinantan Lake revealed a marked qualitative diurnal food cycle. In Paul Lake, shiners have drastically reduced the Gammarus population relative to its pre-shiner abundance, forcing trout, as well as the shiners themselves, to shift their diets to other foods. This overgrazing was caused by the concentration of large numbers of shiners over the shoals where Gammarus are also present in their highest concentrations, and the ability of shiners to pursue food deeper into the weeds and to graze an area more thoroughly than trout. In Pinantan Lake, shiners have apparently reduced the density of Daphnia to a point where trout are unable to feed on them as rapidly as in pre-shiner years. The ability of both species to utilize many types of food tends to reduce the intensity of competition.The study demonstrates how false implications may arise from an appraisal of competition not initiated until after the effects of competition have been observed. If observations had not been made on Paul Lake until after competition had been observed, the importance of Gammarus as an item of competition would probably have been overlooked and the whole competitive relationship misconstrued.Environmental factors and behaviour were shown to be important influences on the dynamics of competition. The physical and biological environment and the distribution and behaviour of competitors may be in states of continual flux in which case the niches of the competitors cannot be considered constant.