Age-specific Reproductive Values Research Articles

How fitness consequences of early‐life conditions vary with age in a long‐lived seabird: A Bayesian multivariate analysis of age‐specific reproductive values

Evolutionary theory suggests that individuals can benefit from deferring the fitness cost of developing under poor conditions to later in life. Although empirical evidence for delayed fitness costs of poor developmental conditions is abundant, individuals that die prematurely have not often been incorporated when estimating fitness, such that age-specific fitness costs, and therefore the relative importance of delayed fitness costs are actually unknown. We developed a Bayesian statistical framework to estimate age-specific reproductive values in relation to developmental conditions. We applied it to data obtained from a long-term longitudinal study of common terns Sterna hirundo, using sibling rank to describe variation in developmental conditions. Common terns have a maximum of three chicks, and later hatching chicks acquire less food, grow more slowly and have a lower fledging probability than their earlier hatched siblings. We estimated fitness costs in adulthood to constitute c. 45% and 70% of the total fitness costs of hatching third and second, respectively, compared to hatching first. This was due to third-ranked hatchlings experiencing especially high pre-fledging mortality, while second-ranked hatchlings had lower reproductive success in adulthood. Both groups had slightly lower adult survival. There was, however, no evidence for sibling rank-specific rates of senescence. We additionally found years with low fledgling production to be associated with particularly strong pre-fledging selection on sibling rank, and with increased adult survival to the next breeding season. This suggests that adults reduce parental allocation to reproduction in poor years, which disproportionately impacts low-ranked offspring. Interpreting these results, we suggest that selection at the level of the individual offspring for delaying fitness costs is counteracted by selection for parental reduction in brood size when resources are limiting.

Definitions of fitness in age-structured populations: Comparison in the haploid case

Fisher׳s (1930) Fundamental Theorem of Natural Selection (FTNS), and in particular the development of an explicit age-structured version of the theorem, is of everlasting interest. In a recent paper, Grafen (2015a) argues that Fisher regarded his theorem as justifying individual rather than population fitness maximization. The argument relies on a new definition of fitness in age-structured populations in terms of individual birth and death rates and age-specific reproductive values in agreement with a principle of neutrality. The latter are frequency-dependent and defined without reference to genetic variation. In the same paper, it is shown that the rate of increase in the mean of the breeding values of fitness weighted by the reproductive values, but keeping the breeding values constant as in Price (1972) is equal to the additive genetic variance in fitness. Therefore, this partial change is obtained by keeping constant not only the genotypic birth and death rates but also the mean age-specific birth and death rates from which the age-specific reproductive values are defined. In this paper we reaffirm that the Malthusian parameter which measures the relative rate of increase or decrease in reproductive value of each genotype in a continuous-time age-structured population is the definition of fitness used in Fisher׳s (1930) FTNS. This is shown by considering an age-structured asexual haploid population with constant age-specific birth and death (or survival) parameters for each type. Although the original statement of the FTNS is for a diploid population, this simplified haploid model allows us to address the definition of fitness meant in this theorem without the complexities and effects of a changing genic environment. In this simplified framework, the rate of change in mean fitness in continuous time is expected to be exactly equal to the genetic variance in fitness (or to the genetic variance in fitness divided by the mean fitness in discrete time), which can be seen as a generalized growth-rate theorem. This theorem is shown to hold with the Malthusian parameter used as the definition of fitness. Moreover, in the same framework, it is shown that a discrete-time version of Grafen׳s definition may lead to a decrease in mean fitness. In the limit of weak selection with the unit of time proportional to the inverse of the intensity of selection, however, this definition predicts the right population dynamics in agreement with the growth-rate theorem. This clarifies the domain of application of the new definition, at least as far as population dynamics is concerned, and reconciles the new definition with the original one.

Fitness prospects: effects of age, sex and recruitment age on reproductive value in a long-lived seabird.

Reproductive value is an integrated measure of survival and reproduction fundamental to understanding life-history evolution and population dynamics, but little is known about intraspecific variation in reproductive value and factors explaining such variation, if any. By applying generalized additive mixed models to longitudinal individual-based data of the common tern Sterna hirundo, we estimated age-specific annual survival probability, breeding probability and reproductive performance, based on which we calculated age-specific reproductive values. We investigated effects of sex and recruitment age (RA) on each trait. We found age effects on all traits, with survival and breeding probability declining with age, while reproductive performance first improved with age before levelling off. We only found a very small, marginally significant, sex effect on survival probability, but evidence for decreasing age-specific breeding probability and reproductive performance with RA. As a result, males had slightly lower age-specific reproductive values than females, while birds of both sexes that recruited at the earliest ages of 2 and 3years (i.e. 54% of the tern population) had somewhat higher fitness prospects than birds recruiting at later ages. While the RA effects on breeding probability and reproductive performance were statistically significant, these effects were not large enough to translate to significant effects on reproductive value. Age-specific reproductive values provided evidence for senescence, which came with fitness costs in a range of 17-21% for the sex-RA groups. Our study suggests that intraspecific variation in reproductive value may exist, but that, in the common tern, the differences are small.

Population statistics and biological traits of Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae) affected by LC30 of thiamethoxam and pirimicarb

Although selective pesticides are recommended to use in integrated pest management (IPM) programmes, they could adversely affect biological agents. So, the aim of the current study was to investigate the LC30 of pirimicarb and thiamethoxam on Hippodamia variegata. Two pesticides, pirimicarb and thiamethoxam, when applied at concentrations of 1522.8 and 251.3 mg (ai)/L, respectively, on the third instar larvae of the insect, produced 30% mortality. Also, results showed that neither pirimicarb nor thiamethoxam affect stage age distribution (cx), fecundity (eggs/female) and adult development time. These two pesticides extended preadult duration significantly (p < 0.0001, F = 31.22, df = 122). Also, survival rate (lx) and age-specific reproductive value (vx) decreased and some changes in age-specific life expectancy (ex) happened. Generally, more adverse effects were found in the population treated by thiamethoxam. The results showed that pirimicarb and thiamethoxam have potential to harm the predatory ladybird in IPM programme, though in sublethal doses.

Age-Dependent Fecundity and Life-Fertility Tables forEuborellia annulipes(Lucas) (Dermaptera: Anisolabididae) a Cotton Boll Weevil Predator in Laboratory Studies with an Artificial Diet

Little information regarding the biology and ecology of dermapteran predators has been reported. For possible use of Euborellia annulipes (Lucas) (Anisolabididae) in biological control programs against the cotton boll weevil Anthonomus grandis grandis Boheman (Curculionidae), it is important to know the effect of temperature on reproduction in this predator. Our objective was to evaluate the reproductive potential and the longevity of females of E. annulipes under laboratory conditions using an artificial diet, at 25 and 30°C, and to estimate life-fertility tables and growth rates. Fecundity began to decline on day 84 at 25°C and on day 74 at 30°C of adult age and ended with the death of the females at both temperatures. Females of E. annulipes oviposited an average of 206 and 306 eggs, and had a mean longevity of 198 and 149 d at 25 and 30°C, respectively. The gross reproductive rates were 89.2 at 25°C and 91.4 at 30°C; the net reproductive rates were 65.3 at 25°C and 40.3 at 30°C; the generation times were 195.2 d at 25°C and 142.9 d at 30°C; the doubling time was 33.0 d at 25°C and 26.7 d at 30°C; the intrinsic rates of increase were 0.02 at 25°C and 0.03 at 30°C, and the finite rates of increase were 1.02 at 25°C and 1.03 at 30°C. The predator population increased by 52 at 25°C and 20 at 30°C adult progeny per female per generation in the laboratory. The best age for inoculative releases of E. annulipes against cotton boll weevil populations is the age with the highest age-specific reproductive values, that is, newly emerged females at 25 or 30°C.

An explicit approach to evolutionarily stable dispersal strategies: no cost of dispersal

The evolution of dispersal is examined by looking at evolutionarily stable strategies (ESS) for dispersal parameters in discrete time multisite models without any cost of dispersal. ESS are investigated analytically, based on explicit results on sensitivity analysis of matrix models. The basic model considers an arbitrary number of sites and a single age class. An ESS for dispersal parameters is obtained when the spatial reproductive values, calculated at the density-dependent population equilibrium, are equal across sites. From this basic formulation, one derives equivalently that all local populations should be at equilibrium in the absence of migration, and that dispersal between sites should be balanced, i.e., the numbers of individuals arriving to and leaving a site are equal. These results are then generalized to a model with several age classes. Equal age-specific reproductive values do not however imply balanced dispersal in this case. Our results generalize to any number of sites and age classes those available [M. Doebeli, Dispersal and dynamics, Theoret. Popul. Biol. 47 (1995) 82] for two sites and one age class.

Spawning in the nick of time? Effect of adult demographics on spawning behaviour and recruitment in Chesapeake Bay striped bass

Striped bass (Morone saxatilis) is an iteroparous anadromous species that spawns dispersive offspring into freshwater habitats and exhibits a high fecundity and high embryo and larval mortality rates. Field studies indicate that temperature differentially affects spawning behaviour and larval survival, and periods of high egg production are often mis-timed for optimal larval survival. I hypothesize that age structure of females may be an important determinant in reducing variability in recruitment through its influence on spawning behaviour. Age diversity of Chesapeake Bay female striped bass is indexed according to expectations of age-specific reproductive values in an unexploited population. The age diversity index was positively correlated to spawning dispersion (egg presence ratio) and 0+ juvenile abundance during the recent period of population recovery (1985–1995). Diversity in age structure and spawning behaviour may contribute to a storage effect, because in most years minority behaviours would result in sustained recruitment. A diverse age structure may thus contribute to an accumulation of spawning stock biomass and increase the future likelihood of dominant year classes.

An explicit approach to evolutionarily stable dispersal strategies with a cost of dispersal

The evolution of dispersal is examined by looking at evolutionarily stable strategies (ESS) for dispersal parameters in discrete time multisite models without any cost of dispersal. ESS are investigated analytically, based on explicit results on sensitivity analysis of matrix models. The basic model considers an arbitrary number of sites and a single age class. An ESS for dispersal parameters is obtained when the spatial reproductive values, calculated at the density-dependent population equilibrium, are equal across sites. From this basic formulation, one derives equivalently that all local populations should be at equilibrium in the absence of migration, and that dispersal between sites should be balanced, i.e., the numbers of individuals arriving to and leaving a site are equal. These results are then generalized to a model with several age classes. Equal age-specific reproductive values do not however imply balanced dispersal in this case. Our results generalize to any number of sites and age classes those available [M. Doebeli, Dispersal and dynamics, Theoret. Popul. Biol. 47 (1995) 82] for two sites and one age class. ” 2000 Elsevier Science Inc. All rights reserved.

Simple Methods for Calculating Age‐Based Life History Parameters for Stage‐Structured Populations

Stage—classified matrix models are important analytical and theoretical tools for the study of population dynamics; in particular, these models may be appropriate for populations in which survivorship and fecundity are dependent on size or developmental stage, populations in which the age of individuals is difficult to determine, and populations in which there are multiple types of newborns. Nevertheless, methods for analyzing the implications of a population's stage—transition matrix have been limited in comparison to methods available for age—structured models (life tables or Leslie matrices). In this paper we show that all of the standard age—based measures of life history traits can be derived from a stage—transition model. By decomposing the transition matrix into separate birth, survival, and fission matrices we derive simple, direct formulas for age—based life history traits such as the discrete survivorship function, lx, maternity function, fx, mean age at maturity, and net reproductive rate, Ro, and also population parameters, including the stable age distribution, age—specific reproductive value, and generation time. These provide a common set of parameters for comparing age—structured and stage—structured populations or comparing populations with differently structured life cycles. In addition, we define four measures of age and life—span that summarize the relationship between stage and age in a stage—structured population: age distribution and mean age of residence for each stage class, expected remaining life—span for individuals in each stage class, and total life—span conditional on reaching a given stage class. We illustrate the use of our methods to address specific ecological questions by applying them to several previously published demographic data sets. These questions include: (1) what are the demographic effects of crowding on the tropical palm Astrocaryum mexicanum?; (2) how important is the initial rosette size in determining life history of teasel, Dipsacus sylvestris?; and (3) how old are reproducing adults in a stage—classified population of pink lady's—slipper, Cypripedium acaule? Our results may also be useful for evaluating the adequacy of a given stage—transition model.

Demographic Attributes of Tribolium freemani HINTON : Coleoptera : Tenebrionidae

Demographic studies were carried out for Tribolium freemani HINTON on a wheat shorts or wheat flour medium under a laboratory condition (32.5°C and 73% r.h.). The sex ratio determined at pupal stage was 1 : 1. The mean lonevity of females and males was 329.1 and 346.7 days, respectively. The survivorship curves for both sexes were negatively skewed rectangular type. A female produced ca 1, 000 eggs during her enitre life. The intrinsic rate of increase (rm) was 0.073 per day, the net reproductive rate (R0) was 351 and the mean generation time (T) 80.6 days. T.freemani had a relatively low age specific reproductive value (vx) which was retained for a long period. Ecological and pest status of T. freemani, in comparison with other Tribolium species ofstored-product pests, was discussed.

A Population Dynamics Model of Black Bears in Eastcentral Ontario

A population model was developed to estimate demographic parameters and abundance of a black bear (Ursus americanus) population in eastcentral Ontario, using data from a 12-year mark-recapture program. The model enables the separation of natural and hunting mortality and allows for immigration to the study area. Parameter fitting was done by a nonlinear least-squares criterion. Abundance estimates using the 0-truncated Poisson, Petersen, and Jolly-Seber procedures allowed comparison of the different methods. The population growth rate was estimated as 2.9%/year for the female segment. Age-specific reproductive value was calculated, and its significance for black bear conservation is discussed. J. WILDL. MANAGE. 50(4):602-612 The black bear is one of Ontario's most familiar and widely distributed large mammals. Traditionally it was regarded as a predator and a nuisance, and a provincial bounty was paid from 1942 to 1961. In 1961, the species was recognized as a valuable wildlife resource with removal of the bounty and elevation to game animal status (Clarke 1961). During recent years, increased hunter pressure in many areas and invasion of black bear habitat by nonconsumptive users intensified the need for information about population densities and behavior. Although important studies of black bear demography have been conducted in a variety of habitats (Jonkel and Cowan 1971, Poelker and Hartwell 1973, Rogers 1977, Beecham 1980, Lindzey and Meslow 1980, Young and Ruff 1982), none have been carried out in the conifer-deciduous forests of eastern Canada. This paper presents the results of an extensive mark-recapture program carried out in eastcentral Ontario from 1969 to 1980. Objectives of the study were to: (1) estimate population abundance; (2) estimate age-specific natural mortality; (3) estimate immigration into the study area; and (4) use this information, together with reproductive data obtained during the study, to estimate the intrinsic growth rate of the population and the age-specific reproductive value of female bears. This project was supported in part by the Nat. Sci. and Eng. Res. Counc. Can. under Grant A7775.

Comparative Demography of Littorina rudis, L. Nigrolineata and L. Neritoides on Three Contrasted Shores in North Wales

(1) A possible relationship between reproductive mode and demography was sought between species of Littorina that brood young, lay benthic egg masses and broadcast planktonic larvae. Population size-frequency and density and cohort survivorship were monitored for Littorina rudis on a sheltered saltmarsh, L. rudis and L. nigrolineata on a boulder shore and for L. rudis and L. neritoides on an exposed cliff face. (2) Adult size classes formed a single broad peak and, except in L. neritoides, young recruits formed a second peak each summer. (3) In the saltmarsh, L. rudis population density fell from a maximum after summer recruitment to a minimum in spring; this was less evident in L. rudis and L. nigrolineata on the boulder shore and undetectable in the cliff populations of L. rudis and L. neritoides. (4) Spring densities fluctuated between years by maximum factors of 7, 6, 9, 9 and 2 in saltmarsh L. rudis, boulder shore L. rudis, cliff L. rudis, L. neritoides and L. nigrolineata respectively. (5) There was no evidence of density dependence in any of the population trajectories. (6) Artificial crevices increased the local density of L. rudis and L. neritoides on the cliff by attracting snails seeking shelter, but did not affect the total population size. (7) Mortality rate diminished progressively through the juvenile phase to a constant rate in adults. (8) Generation times were 24, 18, 18, 25 and 41 months for the saltmarsh L. rudis, boulder shore L. rudis, L. nigrolineata, cliff L. rudis and L. neritoides respectively. (9) Age-specific reproductive value increased beyond the age of first sexual maturity and declined only when growth had almost ceased. (10) All populations except that of L. nigrolineata had values of R0 < 1. Isoclines of juvenile versus adult survivorship for R0 = 1 were used to assess the reliability of the observed survivorship values. (11) Apart from a possible advantage of oviparity versus ovoviviparity during phases of population expansion, no relationship between demography and reproductive method could be found. Oviparity may be advantageous where egg survivorship is high and ovoviviparity in the converse situation. Broadcasting of planktonic larvae by L. neritoides may be correlated with the temporal and spatial unpredictability of microhabitat quality between shores.