ANALYSIS OF LIFE TABLES FOR THE LARCH CASEBEARER (LEPIDOPTERA: COLEOPHORIDAE) IN OREGON

1986 ◽  
Vol 118 (12) ◽  
pp. 1255-1263 ◽  
Author(s):  
R.B. Ryan
Keyword(s):  
Density Dependence ◽  
Introduced Species ◽  
Adult Mortality ◽  
Life Tables ◽  
Density Dependent ◽  
Delayed Density Dependence ◽  
Coleophora Laricella ◽  
Key Factor ◽  
Expanding Population ◽  
High Range

AbstractLife tables for Coleophora laricella (Hübner) at three locations in Oregon were completed for six generations from overwintering larvae in 1978–1979 through overwintering larvae in 1984–1985. Egg densities (per 100 buds) were high (range 279–1038) at Catherine Creek, moderate (49–705) at Tollgate, and low (14–200) at Emigrant Springs. Mortality of early stages was in the order CC>T>ES and tended to equalize overwintering densities. Ten within-generation mortalities (k-values) were calculated. Adult mortality (or reduced fecundity) was always highest. The key factor at Tollgate was mortality of needleminers along with winter-to-spring disappearance. At Catherine Creek, the key factor was mortality of fall casebearers. At Emigrant Springs, the expanding population of an introduced parasite, Agathis pumila (Ratz.), indicated a change in the key factor from mortality of needleminers to parasitism. Mortality of fall casebearers at Emigrant Springs was density dependent. Parasitism caused by A. pumila and another introduced species, Chrysocharis laricinellae (Ratz.), showed characteristics of delayed density dependence.

scholarly journals Increased natural mortality at low abundance can generate an Allee effect in a marine fish

2014 ◽  
Vol 1 (2) ◽  
pp. 140075 ◽  
Author(s):  
Anna Kuparinen ◽  
Jeffrey A. Hutchings
Keyword(s):  
Population Dynamics ◽  
Population Growth ◽  
Density Dependence ◽  
Gadus Morhua ◽  
Allee Effect ◽  
Population Regulation ◽  
Atlantic Cod ◽  
Adult Mortality ◽  
Natural Mortality ◽  
Density Dependent

Negative density-dependent regulation of population dynamics promotes population growth at low abundance and is therefore vital for recovery following depletion. Inversely, any process that reduces the compensatory density-dependence of population growth can negatively affect recovery. Here, we show that increased adult mortality at low abundance can reverse compensatory population dynamics into its opposite—a demographic Allee effect. Northwest Atlantic cod ( Gadus morhua ) stocks collapsed dramatically in the early 1990s and have since shown little sign of recovery. Many experienced dramatic increases in natural mortality, ostensibly attributable in some populations to increased predation by seals. Our findings show that increased natural mortality of a magnitude observed for overfished cod stocks has been more than sufficient to fundamentally alter the dynamics of density-dependent population regulation. The demographic Allee effect generated by these changes can slow down or even impede the recovery of depleted populations even in the absence of fishing.

scholarly journals Influence of delayed density and ultraviolet radiation on caterpillar granulovirus infection and mortality

2021 ◽  
Author(s):  
Adam Pepi ◽  
Vincent Pan ◽  
Richard Karban
Keyword(s):  
Ultraviolet Radiation ◽  
Viral Infection ◽  
Density Dependence ◽  
Infection Rate ◽  
Population Cycles ◽  
Viral Disease ◽  
Environmental Persistence ◽  
Density Dependent ◽  
Delayed Density Dependence ◽  
Occlusion Bodies

AbstractInfectious disease is an important potential driver of population cycles, but this must occur through delayed density-dependent infection and resulting fitness effects. Delayed density-dependent infection by baculoviruses can be caused by environmental persistence of viral occlusion bodies, which can be influenced by environmental factors. In particular, ultraviolet radiation is potentially important in reducing the environmental persistence of viruses by inactivating viral occlusion bodies.Delayed density-dependent viral infection has rarely been observed empirically at the population level although theory predicts that it is necessary for these pathogens to drive population cycles. Similarly, field studies have not examined the potential effects of ultraviolet radiation on viral infection rates in natural animal populations. We tested if viral infection is delayed density-dependent with the potential to drive cyclic dynamics and if ultraviolet radiation influences viral infection.We censused 18 moth populations across nearly 9° of latitude over two years and quantified the effects of direct and delayed density and ultraviolet radiation on granulovirus infection rate, infection severity, and survival to adulthood. Caterpillars were collected from each population in the field and reared in the laboratory.We found that infection rate, infection severity, and survival to adulthood exhibited delayed density-dependence. Ultraviolet radiation in the previous summer decreased infection severity, and increased survival probability of the virus. Structural equation modelling found that the effect of lagged density on moth survival was mediated through infection rate and infection severity, and was 2.5 fold stronger than the effect of ultraviolet radiation on survival through infection severity.Our findings provide clear evidence that delayed density dependence can arise through viral infection rate and severity in insects, which supports the role of viral disease as a potential mechanism, among others, that may drive insect population cycles. Furthermore, our findings support predictions that ultraviolet radiation can modify viral disease dynamics in insect populations, most likely through attenuating viral persistence in the environment.

scholarly journals Conspecific negative density dependence and why its study should not be abandoned

2020 ◽  
Author(s):  
Joseph A. LaManna ◽  
Scott A. Mangan ◽  
Jonathan A. Myers
Keyword(s):  
Density Dependence ◽  
Latitudinal Gradient ◽  
Null Model ◽  
Statistical Bias ◽  
Fitness Components ◽  
Density Dependent ◽  
Statistical Errors ◽  
Negative Density Dependence ◽  
Model Approach

AbstractRecent studies showing bias in the measurement of density dependence have the potential to sow confusion in the field of ecology. We provide clarity by elucidating key conceptual and statistical errors with the null-model approach used in Detto et al. (2019). We show that neither their null model nor a more biologically-appropriate null model reproduces differences in density-dependent recruitment between forests, indicating that the latitudinal gradient in negative density dependence is not an artefact of statistical bias. Finally, we suggest a path forward that combines observational comparisons of density dependence in multiple fitness components across localities with mechanistic and geographically-replicated experiments.

Anadromous Sturgeons: Habitats, Threats, and Management

2007 ◽  
Keyword(s):  
Density Dependence ◽  
Simulation Study ◽  
White Sturgeon ◽  
Acipenser Transmontanus ◽  
Snake River ◽  
Spawning Habitat ◽  
Density Dependent ◽  
Hydrologic Conditions ◽  
Genetic Results ◽  
New Alleles

<em>Abstract.</em>— This paper describes a simulation study of reconnection options for white sturgeon <em>Acipenser transmontanus</em> subpopulations in adjacent river segments above and below CJ Strike Dam on the Snake River, Idaho, USA. In contrast to the downstream river segment, the upstream river segment is long and has areas that are suitable for spawning during normal and wet hydrologic conditions. We evaluated demographic and genetic consequences of upstream and downstream passage using different model assumptions about trashrack spacing and density-dependent effects on the spawning interval. Our genetic results predict that, although reconnection would introduce new alleles to the upstream subpopulation, it would also preserve alleles from the downstream subpopulation by propagating them in the larger subpopulation above the dam. Our demographic results predict that halving the space between trashracks would have large and unequivocal benefits, whereas the predicted effects of reconnection were smaller and more sensitive to model assumptions. Simulated upstream passage tended to benefit both subpopulations only in the absence of density-dependent limitation. In the presence of density dependence, the combination of halved trashrack spacing and upstream and downstream passage produced the best results. Narrower trashracks kept spawning adults in the upstream segment with spawning habitat, while allowing their progeny to migrate downstream. Screening appears to be the best option for such a species in this configuration of a long river segment acting as a demographic source above a short one acting as a demographic sink.

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.

scholarly journals Territorial landscapes: incorporating density-dependence into wolf habitat selection studies

2019 ◽  
Vol 6 (11) ◽  
pp. 190282 ◽  
Author(s):  
Shawn T. O'Neil ◽  
Dean E. Beyer ◽  
Joseph K. Bump
Keyword(s):  
Habitat Selection ◽  
Density Dependence ◽  
Temporal Dynamics ◽  
Wildlife Habitat ◽  
Population Increase ◽  
Habitat Availability ◽  
Functional Responses ◽  
Model Framework ◽  
Selection Probability ◽  
Density Dependent

Habitat selection is a process that spans space, time and individual life histories. Ecological analyses of animal distributions and preferences are most accurate when they account for inherent dynamics of the habitat selection process. Strong territoriality can constrain perception of habitat availability by individual animals or groups attempting to colonize or establish new territory. Because habitat selection is a function of habitat availability, broad-scale changes in habitat availability or occupancy can drive density-dependent habitat functional responses. We investigated density-dependent habitat selection over a 19-year period of grey wolf ( Canis lupus ) recovery in Michigan, USA, using a generalized linear mixed model framework to develop a resource selection probability function (RSPF) with habitat coefficients conditioned on random effects for wolf packs and random year intercepts. In addition, we allowed habitat coefficients to vary as interactions with increasing wolf density over space and time. Results indicated that pack presence was driven by factors representing topography, human development, winter prey availability, forest structure, roads, streams and snow. Importantly, responses to many of these predictors were density-dependent. Spatio-temporal dynamics and population changes can cause considerable variation in wildlife–habitat relationships, possibly confounding interpretation of conventional habitat selection models. By incorporating territoriality into an RSPF analysis, we determined that wolves' habitat use in Michigan shifted over time, for example, exhibiting declining responses to winter prey indices and switching from positive to negative responses with respect to stream densities. We consider this an important example of a habitat functional response in wolves, driven by colonization, density-dependence and changes in occupancy during a time period of range expansion and population increase.

Geographic variation in population cycles of Canadian muskrats (Ondatra zibethicus)

2000 ◽  
Vol 78 (6) ◽  
pp. 1009-1016 ◽  
Author(s):  
John Erb ◽  
Nils Chr. Stenseth ◽  
Mark S Boyce
Keyword(s):  
Density Dependence ◽  
Trophic Interactions ◽  
Dynamic Properties ◽  
Population Cycles ◽  
Period Length ◽  
Ondatra Zibethicus ◽  
Delayed Density Dependence ◽  
Relative Contribution ◽  
Arctic Regions ◽  
Harvest Data

We investigated the dynamic properties of population cycles in Canadian muskrats (Ondatra zibethicus). Ninety-one historic time series of muskrat-harvest data obtained from the Hudson's Bay Company Archives were analyzed. Most series were 25 years in length (1925–1949) and were distributed primarily throughout five ecozones. For each series, we estimated period length and coefficients for a second-order autoregressive model. Estimated period length varied between 3 and 13 years, with 3- to 5-year periods located in Subarctic-Arctic ecozones. We hypothesize that the 4-year cycles are largely a result of predation by red fox (Vulpes vulpes), which exhibit 4-year cycles in Arctic regions. The remaining ecozones generally averaged 8–9 years in period length. However, the relative contributions of direct and delayed density dependence varied along a latitudinal gradient. We hypothesize that both social and trophic interactions are necessary to produce the observed dynamics, but that shifts in the nature of mink predation were responsible for the changes in the relative contribution of direct and delayed density dependence. Essentially, there is a tension between population-intrinsic and trophic interactions that may bound the length of the cycle.

Density dependent ambient ammonium as the key factor for optimization of stocking density of common carp in small holding tanks

Aquaculture ◽  
2006 ◽  
Vol 261 (3) ◽  
pp. 952-959 ◽  
Author(s):  
J.K. Biswas ◽  
D. Sarkar ◽  
P. Chakraborty ◽  
J.N. Bhakta ◽  
B.B. Jana
Keyword(s):  
Common Carp ◽  
Stocking Density ◽  
Density Dependent ◽  
Key Factor ◽  
Small Holding
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