Theory of Growth and Competition in Natural Populations

1953 ◽  
Vol 10 (5) ◽  
pp. 211-223 ◽  
Author(s):  
Gordon A. Riley
Keyword(s):  
Theoretical Analysis ◽  
Population Growth ◽  
Food Chain ◽  
Feeding Habits ◽  
Natural Populations ◽  
Individual Species ◽  
Ecological Groups ◽  
Reproductive Patterns ◽  
Complete Form

Classical theories of population growth and inter-species relations are briefly reviewed. It is shown how variations in feeding habits, reproductive patterns, and other aspects of population behaviour have required modifications of the basic theory in order to make it applicable to particular species. The role of the environment in population theory is also discussed, and this opens the way to a consideration of theoretical aspects of the ecology of natural populations. The latter are admittedly too complex to encourage the application of theory in its purest and most complete form. Practical attempts along these lines have simplified the problem by dealing with ecological groups—phytoplankton, zooplankton, etc.—rather than individual species. A review is presented of the methods, aims, and results of theoretical ecological investigations of the last few years. The significance of such work with respect to higher members of the food chain is discussed, and the paper concludes with remarks on some of the unsolved problems of theoretical analysis.

PERAN MASYARAKAT TERHADAP PEMBAYARAN RETRIBUSI SAMPAH DI KOTA SAMARINDA

2018 ◽  
Vol 2 (1) ◽  
pp. 33
Author(s):  
Abd Rachim AF,
Keyword(s):  
Waste Management ◽  
Population Growth ◽  
Frequency Analysis ◽  
Urban Areas ◽  
Relative Frequency ◽  
Environmental Problems ◽  
Living Standards ◽  
The Public ◽  
And Behavior

One of the environmental problems in urban areas is the pollution caused by garbage. The waste problem is caused by various factors such as population growth, living standards changes, lifestyles and behavior, as well as how the waste management system. This study aims to determine how the role of society to levy payments garbage in Samarinda. This research was descriptive; where the data is collected then compiled, described and analyzed used relative frequency analysis. The participation of the public to pay a "levy junk", which stated to pay 96.67%, for each month and the rates stated society cheap, moderate and fairly, respectively 46.08%, 21.21%, 21.04%. Base on the data , the role of the community to pay "levy junk" quite high.

scholarly journals Tick Ecdysteroid Hormone, Global Microbiota/Rickettsia Signaling in the Ovary versus Carcass during Vitellogenesis in Part-Fed (Virgin) American Dog Ticks, Dermacentor variabilis

2021 ◽  
Vol 9 (6) ◽  
pp. 1242
Author(s):  
Loganathan Ponnusamy ◽  
Haley Sutton ◽  
Robert D. Mitchell ◽  
Daniel E. Sonenshine ◽  
Charles S. Apperson ◽  
...  
Keyword(s):  
Hormonal Regulation ◽  
Natural Populations ◽  
Blood Feeding ◽  
Dermacentor Variabilis ◽  
Transovarial Transmission ◽  
Rickettsia Species ◽  
Adult Females ◽  
Dog Tick ◽  
Total Bacteria

The transovarial transmission of tick-borne bacterial pathogens is an important mechanism for their maintenance in natural populations and transmission, causing disease in humans and animals. The mechanism for this transmission and the possible role of tick hormones facilitating this process have never been studied. Injections of physiological levels of the tick hormone, 20-hydroxyecdysone (20E), into part-fed (virgin) adult females of the American dog tick, Dermacentor variabilis, attached to the host caused a reduction in density of Rickettsia montanensis in the carcass and an increase in the ovaries compared to buffer-injected controls. This injection initiates yolk protein synthesis and uptake by the eggs but has no effect on blood feeding. Francisella sp. and R. montanensis were the predominant bacteria based on the proportionality in the carcass and ovary. The total bacteria load increased in the carcass and ovaries, and bacteria in the genus Pseudomonas increased in the carcass after the 20E injection. The mechanism of how the Rickettsia species respond to changes in tick hormonal regulation needs further investigation. Multiple possible mechanisms for the proliferation of R. montanensis in the ovaries are proposed.

Plant Resistance in Some Modern Soybean Varieties May Favor Population Growth and Modify the Stylet Penetration of Bemisia tabaci (Hemiptera: Aleyrodidae)

2021 ◽  
Author(s):  
Mauricélia F Almeida ◽  
Clébson S Tavares ◽  
Euires O Araújo ◽  
Marcelo C Picanço ◽  
Eugênio E Oliveira ◽  
...  
Keyword(s):  
Population Growth ◽  
Bemisia Tabaci ◽  
Intrinsic Rate ◽  
Reproductive Rate ◽  
Genetically Engineered ◽  
Population Increase ◽  
Net Reproductive Rate ◽  
Bt Toxin ◽  
Demographic Performance

Abstract Complaints of severe damage by whiteflies in soybean fields containing genetically engineered (GE) varieties led us to investigate the role of transgenic soybean varieties expressing resistance to some insects (Cry1Ac Bt toxin) and to herbicide (glyphosate) on the population growth and feeding behavior of Bemisia tabaci (Gennadius) MEAM1 (Hemiptera: Aleyrodidae). In the laboratory, the whiteflies reared on the GE Bt soybeans had a net reproductive rate (R0) 100% higher and intrinsic rate of population increase (rm) 15% higher than those reared on non-GE soybeans. The increased demographic performance was associated with a higher lifetime fecundity. In electrical penetration graphs, the whiteflies reared on the GE soybeans had fewer probes and spent 50% less time before reaching the phloem phase from the beginning of the first successful probe, indicating a higher risk of transmission of whitefly-borne viruses. Data from Neotropical fields showed a higher population density of B. tabaci on two soybean varieties expressing glyphosate resistance and Cry1Ac Bt toxin. These results indicate that some GE soybean varieties expressing insect and herbicide resistances can be more susceptible to whiteflies than non-GE ones or those only expressing herbicide resistance. Most likely, these differences are related to varietal features that increase host-plant susceptibility to whiteflies. Appropriate pest management may be needed to deal with whiteflies in soybean fields, especially in warm regions, and breeders may want to consider the issue when developing new soybean varieties.

The role of S and Mo doping on the dissociation of water molecule on FeOCl surface: Experimental and theoretical analysis

2021 ◽  
pp. 131353
Author(s):  
Xiao Liu ◽  
Wenyi Zhang ◽  
Mingguo Peng ◽  
Guangqun Zhai ◽  
Linchao Hu ◽  
...  
Keyword(s):  
Theoretical Analysis ◽  
Water Molecule ◽  
Mo Doping

Effects of Natural Variation in Sex Ratio and Habitat Structure On Mate-Guarding Decisions in Amphipods (Crustacea)

Behaviour ◽  
1996 ◽  
Vol 133 (13-14) ◽  
pp. 985-996 ◽  
Author(s):  
Jaimie T.A. Dick ◽  
Robert W. Elwood
Keyword(s):  
Natural Populations ◽  
Mate Guarding ◽  
Reproductive Behaviour ◽  
Male Competition ◽  
Female Body Size ◽  
The Social ◽  
Size Assortment ◽  
Assortative Pairing ◽  
Study Species

AbstractWe employed field-based studies, with complementary laboratory-based studies, to investigate social and environmental influences on tactical mate-guarding decisions in amphipods (Crustacea). Firstly, we investigated variation in precopulatory mate-guarding duration in Cammarus duebeni celticus in relation to the social structure of natural populations. Variation in population density of up to two orders of magnitude had no effect on precopula duration, whereas guarding durations increased as the sex ratios of the populations became more male biased. That is, males have some ability to assess the probability of other males taking females into precopula and are prepared to guard for longer as this threat of male: male competition increases. A field demonstration of tactical shifts in reproductive behaviour in response to pertinent social conditions is thus provided. Secondly, the 'habitat segregation' hypothesis, which proposes that positive size-assortative pairing in amphipod populations arises due to variation in the use of micro-habitats, was tested in natural field populations and under laboratory conditions in Echinogammarus marinus. This was necessary in order to distinguish any purely environmental determinants of size-assortment from the role of active decisions by males concerning mate choice and male: male competition. The hypothesis was rejected on the grounds that size-assortative pairing arises under both heterogeneous and homogeneous environmental conditions. Further, in both study species, male and female body size were positively correlated with precopula duration. Thus, indirect competition for access to large, fecund females, based on the timing of male entry into precopula, together with direct aggression, provides the explanation for size-assortative pairing in amphipods.

scholarly journals Sex Differentiation in Amphibians: Effect of Temperature and Its Influence on Sex Reversal

2021 ◽  
pp. 1-11
Author(s):  
Adrián Ruiz-García ◽  
Álvaro S. Roco ◽  
Mónica Bullejos
Keyword(s):  
Sexual Differentiation ◽  
Sex Differentiation ◽  
Environmental Contaminants ◽  
Natural Populations ◽  
Sex Reversal ◽  
The Other ◽  
Effect Of Temperature ◽  
Amphibian Species ◽  
Expected Increase

The role of environmental factors in sexual differentiation in amphibians is not new. The effect of hormones or hormone-like compounds is widely demonstrated. However, the effect of temperature has traditionally been regarded as something anecdotal that occurs in extreme situations and not as a factor to be considered. The data currently available reveal a different situation. Sexual differentiation in some amphibian species can be altered even by small changes in temperature. On the other hand, although not proven, it is possible that temperature is related to the appearance of sex-reversed individuals in natural populations under conditions unrelated to environmental contaminants. According to this, temperature, through sex reversal (phenotypic sex opposed to genetic sex), could play an important role in the turnover of sex-determining genes and in the maintenance of homomorphic sex chromosomes in this group. Accordingly, and given the expected increase in global temperatures, growth and sexual differentiation in amphibians could easily be affected, altering the sex ratio in natural populations and posing major conservation challenges for a group in worldwide decline. It is therefore particularly urgent to understand the mechanism by which temperature affects sexual differentiation in amphibians.

scholarly journals Spontaneous Gac Mutants of Pseudomonas Biological Control Strains: Cheaters or Mutualists?

2011 ◽  
Vol 77 (20) ◽  
pp. 7227-7235 ◽  
Author(s):  
William W. Driscoll ◽  
John W. Pepper ◽  
Leland S. Pierson ◽  
Elizabeth A. Pierson
Keyword(s):  
Alternative Hypothesis ◽  
Natural Populations ◽  
Regulatory System ◽  
Wild Type ◽  
Content Type ◽  
The Public ◽  
Extracellular Metabolites ◽  
Mutualistic Interaction ◽  
Alternative Hypotheses

ABSTRACTBacteria rely on a range of extracellular metabolites to suppress competitors, gain access to resources, and exploit plant or animal hosts. The GacS/GacA two-component regulatory system positively controls the expression of many of these beneficial external products in pseudomonad bacteria. Natural populations often contain variants with defective Gac systems that do not produce most external products. These mutants benefit from a decreased metabolic load but do not appear to displace the wild type in nature. How could natural selection maintain the wild type in the presence of a mutant with enhanced growth? One hypothesis is that Gac mutants are “cheaters” that do not contribute to the public good, favored within groups but selected against between groups, as groups containing more mutants lose access to ecologically important external products. An alternative hypothesis is that Gac mutants have a mutualistic interaction with the wild type, so that each variant benefits by the presence of the other. In the biocontrol bacteriumPseudomonas chlororaphisstrain 30-84, Gac mutants do not produce phenazines, which suppress competitor growth and are critical for biofilm formation. Here, we test the predictions of these alternative hypotheses by quantifying interactions between the wild type and the phenazine- and biofilm-deficient Gac mutant within growing biofilms. We find evidence that the wild type and Gac mutants interact mutualistically in the biofilm context, whereas a phenazine-defective structural mutant does not. Our results suggest that the persistence of alternative Gac phenotypes may be due to the stabilizing role of local mutualistic interactions.

Evaluation-driven design of a robust coreference resolution system

2003 ◽  
Vol 9 (3) ◽  
pp. 281-306 ◽  
Author(s):  
ANDREI POPESCU-BELIS
Keyword(s):  
Working Memory ◽  
Theoretical Analysis ◽  
Coreference Resolution ◽  
Knowledge Sources ◽  
Narrative Texts ◽  
Data Annotation ◽  
Evaluation Measures ◽  
Optimal Behavior ◽  
Resolution System

In this paper, we describe a system for coreference resolution and emphasize the role of evaluation for its design. The goal of the system is to group referring expressions (identified beforehand in narrative texts) into sets of coreferring expressions that correspond to discourse entities. Several knowledge sources are distinguished, such as referential compatibility between a referring expression and a discourse entity, activation factors for discourse entities, size of working memory, or meta-rules for the creation of discourse entities. For each of them, the theoretical analysis of its relevance is compared to scores obtained through evaluation. After looping through all knowledge sources, an optimal behavior is chosen, then evaluated on test data. The paper also discusses evaluation measures as well as data annotation, and compares the present approach to others in the field.

Multigene Family of Ribosomal DNA in Drosophila melanogaster Reveals Contrasting Patterns of Homogenization for IGS and ITS Spacer Regions: A Possible Mechanism to Resolve This Paradox

Genetics ◽  
1998 ◽  
Vol 149 (1) ◽  
pp. 243-256 ◽  
Author(s):  
Carlos Polanco ◽  
Ana I González ◽  
Álvaro de la Fuente ◽  
Gabriel A Dover
Keyword(s):  
Drosophila Melanogaster ◽  
Concerted Evolution ◽  
Multigene Family ◽  
Natural Populations ◽  
Intergenic Spacer ◽  
Meiotic Pairing ◽  
Y Chromosomes ◽  
Mutation Distribution ◽  
Chromosome Exchanges

Abstract The multigene family of rDNA in Drosophila reveals high levels of within-species homogeneity and between-species diversity. This pattern of mutation distribution is known as concerted evolution and is considered to be due to a variety of genomic mechanisms of turnover (e.g., unequal crossing over and gene conversion) that underpin the process of molecular drive. The dynamics of spread of mutant repeats through a gene family, and ultimately through a sexual population, depends on the differences in rates of turnover within and between chromosomes. Our extensive molecular analysis of the intergenic spacer (IGS) and internal transcribed spacer (ITS) spacer regions within repetitive rDNA units, drawn from the same individuals in 10 natural populations of Drosophila melanogaster collected along a latitudinal cline on the east coast of Australia, indicates a relatively fast rate of X-Y and X-X interchromosomal exchanges of IGS length variants in agreement with a multilineage model of homogenization. In contrast, an X chromosome-restricted 24-bp deletion in the ITS spacers is indicative of the absence of X-Y chromosome exchanges for this region that is part of the same repetitive rDNA units. Hence, a single lineage model of homogenization, coupled to drift and/or selection, seems to be responsible for ITS concerted evolution. A single-stranded exchange mechanism is proposed to resolve this paradox, based on the role of the IGS region in meiotic pairing between X and Y chromosomes in D. melanogaster.

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