LOGARITHMIC REGRESSION AS AN INDEX OF RESPONSES TO POPULATION DENSITY: COMMENT ON A PAPER BY M. P. HASSELL AND C. B. HUFFAKER

1969 ◽  
Vol 101 (4) ◽  
pp. 361-364 ◽  
Author(s):  
R. F. Morris ◽  
T. Royama
Keyword(s):  
Theoretical Model ◽  
Population Density ◽  
Density Dependence ◽  
Functional Significance ◽  
Natural Populations ◽  
Biological Significance ◽  
Host Density ◽  
Regression Coefficients ◽  
Forest Insects ◽  
Simulation Exercises

AbstractRegression coefficients derived from the Nicholson–Bailey parasite mode) by Hassell and Huffaker (1969) are interpreted, and their conclusions about the biological significance of changes in slope are shown to be invalid. It is demonstrated that the term "delayed density-dependence" has no functional significance because it includes density responses that range from inverse to direct, depending upon the particular theoretical model that is selected for simulation exercises. In natural populations of a number of forest insects, the net response of parasitism to host density is direct, not inverse.

RELATION OF MORTALITY CAUSED BY PARASITES TO THE POPULATION DENSITY OF HYPHANTRIA CUNEA

1976 ◽  
Vol 108 (11) ◽  
pp. 1291-1294 ◽  
Author(s):  
R. F. Morris
Keyword(s):  
Nova Scotia ◽  
Population Density ◽  
New Brunswick ◽  
Parasite Species ◽  
Natural Populations ◽  
Host Density ◽  
Delayed Response ◽  
Hyphantria Cunea ◽  
Cent Mortality ◽  
The Relationship

AbstractParasitism in natural populations of Hyphantria cunea Drury was measured in New Brunswick and Nova Scotia, 1957–1973. Thirteen parasite species were recovered during this period but only a few caused an appreciable degree of mortality. The per cent mortality showed an immediate rather than a delayed response to host density, the relationship being direct up to a density of about 10 host colonies per mile, then inverse. Possible reasons for this sort of relationship are discussed.

scholarly journals Natural variation in social conditions affects male mate choosiness in the amphipod Gammarus roeselii

2021 ◽  
Author(s):  
Konrad Lipkowski ◽  
Sophie Steigerwald ◽  
Lisa M Schulte ◽  
Carolin Sommer-Trembo ◽  
Jonas Jourdan
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Natural Variation ◽  
Natural Populations ◽  
Social Background ◽  
Social Conditions ◽  
Background Information ◽  
Male Mating ◽  
Natural Environments ◽  
Male Mate

Abstract The extent of male mate choosiness is driven by a trade-off between various environmental factors associated with the costs of mate acquisition, quality assessment and opportunity costs. Our knowledge about natural variation in male mate choosiness across different populations of the same species, however, remains limited. In this study, we compared male mate choosiness across 10 natural populations of the freshwater amphipod Gammarus roeselii (Gervais 1835), a species with overall high male mating investments, and evaluated the relative influence of population density and sex ratio (both affecting mate availability) on male mate choosiness. We investigated amplexus establishment after separating mating pairs and presenting focal males with a novel, size-matched female from the same population. Our analysis revealed considerable effects of sex ratio and (to a lesser extent) population density on time until amplexus establishment (choosiness). Male amphipods are able to perceive variable social conditions (e.g., sex ratio) and modify their mating strategy accordingly: We found choosiness to be reduced in increasingly male-biased populations, whereas selectivity increases when sex ratio becomes female biased. With this, our study expands our limited knowledge on natural variations in male mate choosiness and illustrates the importance of sex ratio (i.e., level of competition) for male mating decisions in natural environments. Accounting for variation in sex ratios, therefore, allows envisioning a distinctive variation of choosiness in natural populations and highlights the importance of considering social background information in future behavioral studies.

Parasite infection and host dynamics in a naturally fluctuating rodent population

2012 ◽  
Vol 90 (9) ◽  
pp. 1149-1160 ◽  
Author(s):  
J.C. Winternitz ◽  
M.J. Yabsley ◽  
S.M. Altizer
Keyword(s):  
Population Density ◽  
Experimental Studies ◽  
Host Density ◽  
Positive Association ◽  
Population Cycles ◽  
Host Population ◽  
Reproductive Status ◽  
Vole Cycles ◽  
Host Infection ◽  
The Impact

Parasites can both influence and be affected by host population dynamics, and a growing number of case studies support a role for parasites in causing or amplifying host population cycles. In this study, we examined individual and population predictors of gastrointestinal parasitism on wild cyclic montane voles ( Microtus montanus (Peale, 1848)) to determine if evidence was consistent with theory implicating parasites in population cycles. We sampled three sites in central Colorado for the duration of a multiannual cycle and recorded the prevalence and intensity of directly transmitted Eimeria Schneider, 1875 and indirectly transmitted cestodes from a total of 267 voles. We found significant associations between host infection status, individual traits (sex, age, and reproductive status) and population variables (site, trapping period, and population density), including a positive association between host density and cestode prevalence, and a negative association between host density and Eimeria prevalence. Both cestode and Eimeria intensity correlated positively with host age, reproductive status, and population density, but neither parasite was associated with poorer host condition. Our findings suggest that parasites are common in this natural host, but determining their potential to influence montane vole cycles requires future experimental studies and long-term monitoring to determine the fitness consequences of infection and the impact of parasite removal on host dynamics.

scholarly journals GENES AFFECTING PRODUCTIVITY IN NATURAL POPULATIONS OF DROSOPHILA MELANOGASTER

Genetics ◽  
1975 ◽  
Vol 80 (4) ◽  
pp. 807-819
Author(s):  
Takao K Watanabe ◽  
Seido Ohnishi
Keyword(s):  
Drosophila Melanogaster ◽  
Japanese Population ◽  
Natural Populations ◽  
Regression Coefficients ◽  
Average Productivity ◽  
Partial Sterility

ABSTRACT Two hundred second chromosomes were extracted from a Japanese population in October of 1972, and the viabilities and productivities of homozygotes and heterozygotes from them were examined. Viability was measured by the Cy method and productivity by the number of progeny produced per female. The frequency of lethal-carrying chromosomes was 0.315. When the average heterozygote viability was standardized as 1.000, the average homozygote viability was 0.595 including the lethal lines, and 0.866 excluding them. The frequency of recessive sterile chromosomes among 131 non-lethal lines was 0.092 in females and 0.183 in males. There were two instances in which homozygosis for the second chromosome caused sterility in both sexes, which was close to the number expected (2.2) on a random basis of 0.092 × 0.183 × 131. When the average heterozygote productivity of 200 lines was standardized as 1.000, the average homozygote productivity was 0.532 including female steriles, and 0.584 excluding them. The ratio of detrimental load to lethal load was 0.383, while the ratio of partial sterility load to complete sterility load was 5.767. The average viability of lethal heterozygotes was slightly, but not significantly, lower than that of lethal-free heterozygotes, while the average productivity of lethal heterozygotes was significantly lower than that of lethal-free heterozygotes. There was a significant association of sterility in either sex with low viability of homozygotes. However, no statistically significant differences in viability and productivity were detected between sterile heterozygotes and non-sterile heterozygotes. The heterozygous effects of viability and productivity polygenes were examined by regressions of the heterozygotes on the sum of corresponding homozygotes. The regression coefficients were slightly positive for both viability and productivity if lethal and sterile chromosomes were excluded. The correlation between viability and productivity in homozygotes was significantly positive when sterile chromosomes were included, but the significance disappeared when the sterile chromosomes were excluded. In the heterozygotes there were no detectable correlations between them.

scholarly journals Balancing selection maintains polymorphisms at neurogenetic loci in field experiments

2017 ◽  
Vol 114 (14) ◽  
pp. 3690-3695 ◽  
Author(s):  
Eija Lonn ◽  
Esa Koskela ◽  
Tapio Mappes ◽  
Mikael Mokkonen ◽  
Angela M. Sims ◽  
...  
Keyword(s):  
Reproductive Success ◽  
Population Density ◽  
Arginine Vasopressin ◽  
Field Experiments ◽  
Balancing Selection ◽  
Regulatory Region ◽  
Natural Populations ◽  
Myodes Glareolus ◽  
Sexual Antagonism ◽  
Reproductive Behaviors

Most variation in behavior has a genetic basis, but the processes determining the level of diversity at behavioral loci are largely unknown for natural populations. Expression of arginine vasopressin receptor 1a (Avpr1a) and oxytocin receptor (Oxtr) in specific regions of the brain regulates diverse social and reproductive behaviors in mammals, including humans. That these genes have important fitness consequences and that natural populations contain extensive diversity at these loci implies the action of balancing selection. In Myodes glareolus, Avpr1a and Oxtr each contain a polymorphic microsatellite locus located in their 5′ regulatory region (the regulatory region-associated microsatellite, RRAM) that likely regulates gene expression. To test the hypothesis that balancing selection maintains diversity at behavioral loci, we released artificially bred females and males with different RRAM allele lengths into field enclosures that differed in population density. The length of Avpr1a and Oxtr RRAMs was associated with reproductive success, but population density and the sex interacted to determine the optimal genotype. In general, longer Avpr1a RRAMs were more beneficial for males, and shorter RRAMs were more beneficial for females; the opposite was true for Oxtr RRAMs. Moreover, Avpr1a RRAM allele length is correlated with the reproductive success of the sexes during different phases of reproduction; for males, RRAM length correlated with the numbers of newborn offspring, but for females selection was evident on the number of weaned offspring. This report of density-dependence and sexual antagonism acting on loci within the arginine vasopressin–oxytocin pathway explains how genetic diversity at Avpr1a and Oxtr could be maintained in natural populations.

Density-Dependent Population Growth

2020 ◽  
pp. 29-46
Author(s):  
Michael J. Fogarty ◽  
Jeremy S. Collie
Keyword(s):  
Population Density ◽  
Population Growth ◽  
Density Dependence ◽  
Multiple Equilibria ◽  
Dynamical Behavior ◽  
Logistic Growth ◽  
Density Dependent ◽  
Per Capita ◽  
Discrete Time Models ◽  
Complex Dynamical Behavior

The observation that no population can grow indefinitely and that most populations persist on ecological timescales implies that mechanisms of population regulation exist. Feedback mechanisms include competition for limited resources, cannibalism, and predation rates that vary with density. Density dependence occurs when per capita birth or death rates depend on population density. Density dependence is compensatory when the population growth rate decreases with population density and depensatory when it increases. The logistic model incorporates density dependence as a simple linear function. A population exhibiting logistic growth will reach a stable population size. Non-linear density-dependent terms can give rise to multiple equilibria. With discrete time models or time delays in density-dependent regulation, the approach to equilibrium may not be smooth—complex dynamical behavior is possible. Density-dependent feedback processes can compensate, up to a point, for natural and anthropogenic disturbances; beyond this point a population will collapse.

Distinguishing error from chaos in ecological time series

1990 ◽  
Vol 330 (1257) ◽  
pp. 235-251 ◽  
Keyword(s):  
New York ◽  
Population Density ◽  
Sampling Error ◽  
Natural Populations ◽  
Real Data ◽  
Environmental Stochasticity ◽  
Population Variation ◽  
Data Sets ◽  
Spatial Effects ◽  
Low Dimensional

Over the years, there has been much discussion about the relative importance of environmental and biological factors in regulating natural populations. Often it is thought that environmental factors are associated with stochastic fluctuations in population density, and biological ones with deterministic regulation. We revisit these ideas in the light of recent work on chaos and nonlinear systems. We show that completely deterministic regulatory factors can lead to apparently random fluctuations in population density, and we then develop a new method (that can be applied to limited data sets) to make practical distinctions between apparently noisy dynamics produced by low-dimensional chaos and population variation that in fact derives from random (high-dimensional)noise, such as environmental stochasticity or sampling error. To show its practical use, the method is first applied to models where the dynamics are known. We then apply the method to several sets of real data, including newly analysed data on the incidence of measles in the United Kingdom. Here the additional problems of secular trends and spatial effects are explored. In particular, we find that on a city-by-city scale measles exhibits low-dimensional chaos (as has previously been found for measles in New York City), whereas on a larger, country-wide scale the dynamics appear as a noisy two-year cycle. In addition to shedding light on the basic dynamics of some nonlinear biological systems, this work dramatizes how the scale on which data is collected and analysed can affect the conclusions drawn.

THE APPRAISAL OF DELAYED AND DIRECT DENSITY-DEPENDENCE

1969 ◽  
Vol 101 (4) ◽  
pp. 353-361 ◽  
Author(s):  
M. P. Hassell ◽  
C. B. Huffaker
Keyword(s):  
Density Dependence ◽  
Predictive Value ◽  
Biological Significance ◽  
Population Models ◽  
Dependent Types ◽  
Density Dependent ◽  
Morris Method ◽  
Density Dependent Mortality ◽  
Linear Regressions ◽  
Dependent Mortality

AbstractOf the methods designed to detect and measure the intensity of direct and delayed density-dependent types of mortality acting on populations, that of Morris has gained considerable acceptance. While this method of analysis has predictive value and provides a means of estimating direct density-dependence, it seems inappropriate to the detection and measurement of a delayed density-dependent mortality such as that normally associated with entomophagous parasites. The biological significance of the slopes of the linear regressions calculated in the Morris method is discussed, and population models based on the theory of Nicholson and Bailey are presented in support of the argument.

Density dependence, regulation and variability in animal populations

1990 ◽  
Vol 330 (1257) ◽  
pp. 141-150 ◽  
Keyword(s):  
Density Dependence ◽  
Population Regulation ◽  
Time Series Data ◽  
Complex Dynamics ◽  
Natural Populations ◽  
Single Species ◽  
Abundant Species ◽  
Series Data ◽  
Animal Populations ◽  
The Common

This paper reviews a series of approaches to the study of density dependence, regulation and variability in terrestrial animals, by using single-species, multispecies and life table time series data. Special emphasis is given to the degree of density dependence in the level of variability, which is seldom discussed in this context, but which is conceptually related to population regulation. Broad patterns in density dependence, regulation and variability in vertebrates and arthropods are described, with some more specific results for moths and aphids. Vertebrates have generally less variable populations than arthropods, which is the only well documented, consistent pattern in population variability. The degree of density dependence of variability is negatively correlated with the average level of variability, suggesting that generally the more regulated populations are less variable. Most population studies, especially on insects, have involved outbreak species with complex dynamics, which may explain the common failures to detect density dependence in natural populations. In British moths, density dependence is less obvious in the more abundant species. The study of uncommon and rare species remains a major challenge for population ecology.

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