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 at Sea for Coho Salmon (Oncorhynchus kisutch)

1990 ◽  
Vol 47 (9) ◽  
pp. 1765-1772 ◽  
Author(s):  
J. M. Emlen ◽  
R. R. Reisenbichler ◽  
A. M. McGie ◽  
T. E. Nickelson
Keyword(s):  
Density Dependence ◽  
Coho Salmon ◽  
Oncorhynchus Kisutch ◽  
Density Dependent ◽  
Density Dependent Mortality ◽  
Hatchery Fish ◽  
Statistical Assumptions ◽  
Diminishing Returns ◽  
Salmon Hatchery ◽  
Dependent Mortality

The success of expanded salmon hatchery programs will depend strongly on the degree of density-induced diminishing returns per smolt released. Several authors have addressed the question of density-dependent mortality at sea in coho salmon (Oncorhynchus kisutch), but have come to conflicting conclusions. We believe there are compelling reasons to reinvestigate the data, and have done so for public hatchery fish, using a variety of approaches. The results provide evidence that survival of these public hatchery fish is negatively affected, directly by the number of public hatchery smolts and indirectly by the number of private hatchery smolts. These results are weak, statistically, and should be considered primarily as a caution to those who, on the basis of other published work, believe that density-dependence does not exist. The results reported here also re-emphasize the often overlooked point that inferences drawn from data are strongly biased by investigators' views of how the systems of interest work and by the statistical assumptions they make preparatory to the analysis of those data.

scholarly journals Cycles, stochasticity and density dependence in pink salmon population dynamics

2010 ◽  
Vol 278 (1714) ◽  
pp. 2060-2068 ◽  
Author(s):  
Martin Krkošek ◽  
Ray Hilborn ◽  
Randall M. Peterman ◽  
Thomas P. Quinn
Keyword(s):  
Density Dependence ◽  
Disease Transmission ◽  
Pink Salmon ◽  
The Other ◽  
Oncorhynchus Gorbuscha ◽  
Stochastic Perturbations ◽  
Density Dependent ◽  
Density Dependent Mortality ◽  
Animal Populations ◽  
Dependent Mortality

Complex dynamics of animal populations often involve deterministic and stochastic components. A fascinating example is the variation in magnitude of 2-year cycles in abundances of pink salmon ( Oncorhynchus gorbuscha ) stocks along the North Pacific rim. Pink salmon have a 2-year anadromous and semelparous life cycle, resulting in odd- and even-year lineages that occupy the same habitats but are reproductively isolated in time. One lineage is often much more abundant than the other in a given river, and there are phase switches in dominance between odd- and even-year lines. In some regions, the weak line is absent and in others both lines are abundant. Our analysis of 33 stocks indicates that these patterns probably result from stochastic perturbations of damped oscillations owing to density-dependent mortality caused by interactions between lineages. Possible mechanisms are cannibalism, disease transmission, food depletion and habitat degradation by which one lineage affects the other, although no mechanism has been well-studied. Our results provide comprehensive empirical estimates of lagged density-dependent mortality in salmon populations and suggest that a combination of stochasticity and density dependence drives cyclical dynamics of pink salmon stocks.

MODELS OF PERIODIC INUNDATION OF PARASITOIDS FOR PEST CONTROL

1985 ◽  
Vol 117 (6) ◽  
pp. 705-716 ◽  
Author(s):  
Hugh J. Barclay ◽  
Imre S. Otvos ◽  
Alan J. Thomson
Keyword(s):  
Density Dependence ◽  
Pest Control ◽  
Ecological Factors ◽  
Host Population ◽  
Density Dependent ◽  
Density Dependent Mortality ◽  
Inundative Releases ◽  
Dependent Mortality

AbstractSeveral host–parasitoid models were examined to assess the feasibility of parasitoid inundation as a means of pest control or eradication. The approach is comparative, to assess independently the effects of various ecological factors on the ease of control by this means. For most of the models, there exists a critical inundation rate, I*, above which the host population is eradicated, provided inundative releases continue beyond the time of eradication. The existence of density-dependent mortality in the hosts reduces the time to eradication but does not affect I*. Density dependence in the parasitoids, however, usually increases I*. The existence of hyperparasitoids appears to have no effect on the ease of host eradication.

scholarly journals Enemies mediate distance- and density-dependent mortality of tree seeds and seedlings: a meta-analysis of fungicide, insecticide and exclosure studies

2021 ◽  
Vol 288 (1943) ◽  
pp. 20202352
Author(s):  
Xiaoyang Song ◽  
Richard T. Corlett
Keyword(s):  
Density Dependence ◽  
Natural Enemies ◽  
Natural Enemy ◽  
Plant Pathogens ◽  
Meta Analysis ◽  
Seedling Stage ◽  
Forest Community ◽  
Density Dependent ◽  
Density Dependent Mortality ◽  
Dependent Mortality

Conspecific negative distance- and density-dependence is often assumed to be one of the most important mechanisms controlling forest community assembly and species diversity globally. Plant pathogens, and insect and mammalian herbivores, are the most common natural enemy types that have been implicated in this phenomenon, but their general effects at different plant life stages are still unclear. Here, we conduct a meta-analysis of studies that involved robust manipulative experiments, using fungicides, insecticides and exclosures, to assess the contributions of different natural enemy types to distance- and density-dependent effects at seed and seedling stages. We found that distance- and density-dependent mortality caused by natural enemies was most likely at the seedling stage and was greater at higher mean annual temperatures. Conspecific negative distance- and density-dependence at the seedling stage is significantly weakened when fungicides were applied. By contrast, negative conspecific distance- and density-dependence is not a general pattern at the seed stage. High seed mass reduced distance- and density-dependent mortality at the seed stage. Seed studies excluding only large mammals found significant negative conspecific distance-dependent mortality, but exclusion of all mammals resulted in a non-significant effect of conspecifics. Our study suggests that plant pathogens are a major cause of distance- and density-dependent mortality at the seedling stage, while the impacts of herbivores on seedlings have been understudied. At the seed stage, large and small mammals, respectively, weaken and enhance negative conspecific distance-dependent mortality. Future research should identify specific agents of mortality, investigate the interactions among different enemy types and assess how global change may affect natural enemies and thus influence the strength of conspecific distance- and density-dependence.

scholarly journals Time lags and density dependence in age dependent two species competition

1982 ◽  
Vol 25 (2) ◽  
pp. 271-291 ◽  
Author(s):  
K. Gopalsamy
Keyword(s):  
Density Dependence ◽  
Linear Stability ◽  
Sufficient Conditions ◽  
Time Lags ◽  
Species Competition ◽  
Density Dependent ◽  
Density Dependent Mortality ◽  
Age Dependent ◽  
Time Lagged ◽  
Dependent Mortality

Sufficient conditions are obtained for the existence and linear stability of time independent age distributions in two species competition with age and time lagged density dependent mortality and fertility functions.

Sign in / Sign up

Export Citation Format

Share Document