Rates of increase in age-structured populations: a lesson from the European harbour seals

2002 ◽  
Vol 80 (9) ◽  
pp. 1498-1510 ◽  
Author(s):  
Tero Härkönen ◽  
Karin C Harding ◽  
Mads-Peter Heide-Jørgensen
Keyword(s):  
Survival Rates ◽  
Natural Populations ◽  
Structured Populations ◽  
Population Increase ◽  
Biological Removal ◽  
Harbour Seals ◽  
Rate Of Increase ◽  
Population Structures ◽  
Age Structured ◽  
Age And Sex

Behavioural differences among population segments coupled with the transient dynamics of perturbed population structures lead to severely biased estimates of the intrinsic rates of increase in natural populations. This phenomenon is expected to occur in most populations that are structured by age, sex, state, or rank. The 1988 epizootic in European harbour seals (Phoca vitulina) perturbed the population composition radically. Detailed documentation of mass mortality, 20 years of population surveys, and data on age- and sex-specific behaviour were used to quantify biases in the observed rate of increase (λobs.), which in many areas substantially exceeded the "maximum rate of increase". This is serious, since λobs. is a key parameter, for example, in estimating potential biological removal or modelling population dynamics. For populations where the underlying age and sex composition is unknown, we suggest that data on fecundity and survival rates be used to find the upper theoretical rate of population increase. We found that the intrinsic rates of increase (λ1) in populations of true seals with even sex ratios and stable age structures cannot exceed 13% per year (λ1max. = 1.13). Frequently reported larger values are indicative of nonstable population structures or populations affected by migrations.

Spatial structure of harbour seal populations and the implications thereof

2001 ◽  
Vol 79 (12) ◽  
pp. 2115-2127 ◽  
Author(s):  
T Härkönen ◽  
K C Harding
Keyword(s):  
Population Dynamics ◽  
Site Fidelity ◽  
Phoca Vitulina ◽  
Population Increase ◽  
Dynamic Processes ◽  
Term Study ◽  
Long Term Study ◽  
Harbour Seals ◽  
Age And Sex

A long-term study of freeze-branded harbour seals (Phoca vitulina) revealed explicit site fidelity. Individuals were followed up to 14 years of age and none of the 163 branded animals were observed to haul out beyond a 32-km distance from the site where they were branded as pups. Within this range, striking spatial segregation by age and sex prevailed. While females' site fidelity increased with age, males spent less time at their natal site with increasing age. These findings have consequences for understanding the population dynamics of harbour seals, since single "colonies" will act as partly isolated "subpopulations" in some contexts but not in others. The differing migration tendencies of the population segments lead to spatially segregated sex and age ratios of subpopulations and create a complex pattern of connectivity among these subpopulations. Ignoring the spatial scale will lead to severe misinterpretations of analyses of basic population-dynamic processes, especially rates of population increase, rates of gene flow, and the dynamics of the spread of diseases. We suggest that when studies have different aims, these should be addressed by encompassing different numbers of subpopulations.

Survival of radio-collared caribou (Rangifer tarandus caribou) from the George River herd, Nouveau-Québec – Labrador

1990 ◽  
Vol 68 (2) ◽  
pp. 276-283 ◽  
Author(s):  
Brian J. Hearn ◽  
Stuart N. Luttich ◽  
Michel Crête ◽  
Maria B. Berger
Keyword(s):  
Cause Of Death ◽  
Rangifer Tarandus ◽  
Survival Rates ◽  
Rangifer Tarandus Caribou ◽  
Annual Survival ◽  
Lower Survival ◽  
Fecundity Rate ◽  
Rate Of Increase ◽  
George River ◽  
Age And Sex

Between September 1983 and June 1987, 175 caribou (Rangifer tarandus caribou) from the George River caribou herd were captured and radio-collared. By October 1987, 42 of those had died: 15 were apparently killed by predators, 8 were legally shot, 4 appeared to have died proximally from malnutrition, 1 died from an accident, and cause of death could not be determined for 14 others. Seasonal and annual survival rates were estimated most precisely for adult (≥ 24 months) females, but a consistent trend towards lower survival at the end of the study period was evident in all age and sex groups. Decreasing summer survival was responsible for the lowering of annual survival rates, as winter survival was relatively constant over the study period. Using our calculated age-specific survival rates, and estimates of age-specific fecundity, the survival–fecundity rate of increase (rs) for the female segment of the herd was 0.12 for 1983–1984 and −0.01 for 1986–1987. Decreasing summer survival thus appears to have been of greatest importance in reducing rs to zero and halting the growth of the herd. Density-dependent mechanisms acting on the George River caribou herd appear different from those described for caribou herds regulated by winter forage.

On the quantitative genetics of correlated characters under directional selection in age-structured populations

1991 ◽  
Vol 331 (1260) ◽  
pp. 213-223 ◽  
Keyword(s):  
Quantitative Genetics ◽  
Evolutionary Dynamics ◽  
Natural Populations ◽  
Directional Selection ◽  
Structured Populations ◽  
Short Term ◽  
Age Structured ◽  
Correlated Characters ◽  
Selection Differentials ◽  
Non Equilibrium

The evolution of correlated characters in natural populations depends on the demographic structure of these populations. This is often considerably more complicated than the structure of populations typically addressed by quantitative genetics, involving overlapping generations, age-dependent vital rates, and large fluctuations in recruitment from year to year. It is important to know more about such evolution because human exploitation of natural populations such as fishes is selective and has the potential to cause major changes in their properties. Here the theory of quantitative genetics of correlated characters under directional selection is extended to incorporate some demographic properties of non-equilibrium age structured populations. Short-term evolution is described in terms of changes in a matrix of mean breeding values of the traits at each age, and depends on the selection differentials in operation, together with the variances and covariances of breeding and phenotypic values. Because the selection differentials depend on the current mean phenotypic values which are themselves changing as each cohort grows older, the dynamics of mean phenotypic values within cohorts are also followed. Together, the changes in mean breeding and phenotypic values are sufficient to predict the short-term transient evolutionary dynamics of correlated characters in non-equilibrium age-structured populations. The predictions are compared with the dynamics observed in some randomly generated populations, and the application of the theory to evolution in commercially exploited populations of fish is discussed.

scholarly journals Does Larval Rearing Diet Lead to Premating Isolation in Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae)?

Insects ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 203
Author(s):  
Xue-Yuan Di ◽  
Bin Yan ◽  
Cheng-Xu Wu ◽  
Xiao-Fei Yu ◽  
Jian-Feng Liu ◽  
...  
Keyword(s):  
Mate Choice ◽  
Spodoptera Litura ◽  
Artificial Diet ◽  
Survival Rates ◽  
Intrinsic Rate Of Increase ◽  
Larval Rearing ◽  
Population Parameters ◽  
Premating Isolation ◽  
Behavioral Isolation ◽  
Rate Of Increase

Host plant preference during the larval stage may help shape not only phenotypic plasticity but also behavioral isolation. We assessed the effects of diet on population parameters and mate choice in Spodoptera litura. We raised larvae fed on tobacco, Chinese cabbage, or an artificial diet, and we observed the shortest developmental time and highest fecundity in individuals fed the artificial diet. However, survival rates were higher for larvae on either of the natural diets. Population parameters including intrinsic rate of increase and finite rate of increase were significantly higher with the artificial diet, but this diet led to a lower mean generation time. Copulation duration, copulation time, and number of eggs reared significantly differed between diets. In terms of mate choice, females on the artificial diet rarely mated with males fed on a natural host. Our results support the hypothesis that different diets may promote behavioral isolation, affecting mating outcomes. Thus, findings for populations fed an artificial diet may not reflect findings for populations in the field.

scholarly journals Frequency responses of age-structured populations: Pacific salmon as an example

2010 ◽  
Vol 78 (4) ◽  
pp. 239-249 ◽  
Author(s):  
Lee Worden ◽  
Louis W. Botsford ◽  
Alan Hastings ◽  
Matthew D. Holland
Keyword(s):  
Pacific Salmon ◽  
Structured Populations ◽  
Frequency Responses ◽  
Age Structured

Inbreeding effects among inbred and outbred laboratory colonies of Peromyscus maniculatus

1992 ◽  
Vol 70 (4) ◽  
pp. 820-824 ◽  
Author(s):  
David O. Ribble ◽  
John S. Millar
Keyword(s):  
Performance Measures ◽  
Reproductive Performance ◽  
First Generation ◽  
Peromyscus Maniculatus ◽  
Survival Rates ◽  
Natural Populations ◽  
Outbreeding Depression ◽  
Sibling Pairs ◽  
Laboratory Colonies ◽  
And Control

We examined the effects of sibling matings upon reproductive performance among inbred and outbred laboratory colonies of Peromyscus maniculatus. The inbred colony was founded by 12 females collected from one locality in Alberta and bred for 20 generations, with 35–45 pairs each generation. The outbred colony consisted of first-generation mice born of wild-caught females from diverse areas in Alberta. Consistent with theoretical expectations, there were no differences in reproductive performance between sibling and control (outbred) pairs within the inbred colony of mice. In contrast, sibling pairs had significantly fewer young per litter than control pairs within the outbred colony. Reproductive performance measures (proportion breeding, days from pairing to first litter, number of litters, and total number of offspring produced) were also significantly lower among sibling pairs from the outbred colony than among sibling pairs from the inbred colony. Lastly, we predicted that reproductive performance of the control pairs from the outbred colony would be less than that of control pairs from the inbred colony, due to outbreeding depression. Contrary to our predictions, average litter survival rates were greatest among the outbred colony control pairs. We suggest that the benefits of inbreeding or outbreeding extend broadly across the inbreeding–outbreeding continuum in natural populations of northern Peromyscus.

scholarly journals The effect of life-history and mode of inheritance on neutral genetic variability

2001 ◽  
Vol 77 (2) ◽  
pp. 153-166 ◽  
Author(s):  
BRIAN CHARLESWORTH
Keyword(s):  
Sequence Variation ◽  
Adult Mortality ◽  
Structured Populations ◽  
Human Populations ◽  
Effective Population ◽  
Transmission Modes ◽  
Population Sizes ◽  
Age Structured ◽  
Infinite Sites Model ◽  
Site Diversity

Formulae for the effective population sizes of autosomal, X-linked, Y-linked and maternally transmitted loci in age-structured populations are developed. The approximations used here predict both asymptotic rates of increase in probabilities of identity, and equilibrium levels of neutral nucleotide site diversity under the infinite-sites model. The applications of the results to the interpretation of data on DNA sequence variation in Drosophila, plant, and human populations are discussed. It is concluded that sex differences in demographic parameters such as adult mortality rates generally have small effects on the relative effective population sizes of loci with different modes of inheritance, whereas differences between the sexes in variance in reproductive success can have major effects, either increasing or reducing the effective population size for X-linked loci relative to autosomal or Y-linked loci. These effects need to be accounted for when trying to understand data on patterns of sequence variation for genes with different transmission modes.

Invalid estimates of rate of population increase from Glossina (Diptera: Glossinidae) age distributions

1988 ◽  
Vol 78 (1) ◽  
pp. 155-161 ◽  
Author(s):  
J. Van Sickle
Keyword(s):  
Sampling Error ◽  
Age Distribution ◽  
Population Increase ◽  
Sampling Errors ◽  
True Rate ◽  
Survivorship Curve ◽  
A Value ◽  
Tsetse Population ◽  
Rate Of Increase ◽  
Highly Sensitive

AbstractSeveral published reports have presented estimates of the rate of increase, r, based on sampled ovarian age distributions from Glossina populations throughout Africa. These estimates are invalid, because an age distribution sampled at one point in time can be equated to a survivorship curve only if r = 0. When such a survivorship curve and a corresponding fecundity schedule are then used to estimate r via the Euler-Lotka equation, the result is a value of r near zero, regardless of the population's true rate of increase. Synthetic sampling from a hypothetical tsetse population confirmed that estimates computed in this fashion are entirely the products of sampling error. Valid estimates of r can sometimes be obtained from an age distribution, using an alternative method, but such estimates are highly sensitive to sampling errors in the distribution.

Evolution in Age-Structured Populations.

1995 ◽  
Vol 83 (3) ◽  
pp. 548
Author(s):  
Tom J. de Jong ◽  
B. Charlesworth
Keyword(s):  
Structured Populations ◽  
Age Structured
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