Life‐history constraints on maximum population growth for loggerhead turtles in the northwest Atlantic

Conservation planning for protected species often relies on estimates of life‐history parameters. A commonly used parameter is the instantaneous maximum population growth rate (r_max) that can be used to limit removals and design recovery targets. Estimation of r_max can be challenging because of limited availability of species‐ and population‐specific data and life‐history information. We applied a method proposed by Neil and Lebreton, originally developed for birds, to loggerhead turtles. The method uses age‐at‐first‐reproduction and adult survival to estimate r_max. We used a variety of datasets and matrix population models to confirm an allometric assumption required by the method, and to generate estimates of age‐at‐first‐reproduction and adult survival. A meta‐analysis was applied to parameters from reported growth curves, which were then combined with the size distribution of neophyte nesters to derive estimates of age‐at‐first‐reproduction. Adult survival rates were obtained from an existing matrix population model. Monte Carlo simulation was then used to combine the estimates of the allometric coefficients, age‐at‐first‐reproduction, and adult survival to obtain a probability distribution of approximate r_max values. Estimated annual maximum population growth rates averaged 0.024, with a mode of 0.017 and a 95% highest density interval of 0.006–0.047. These estimates were similar to values reported by others using different methods and captured the variability in positive, annual change estimates across nesting beach sites for the northwest Atlantic loggerhead population. The use of life‐history parameters has a long history in wildlife and fisheries management and conservation planning. Our estimates of r_max, while having some biases and uncertainty, encompassed values presently used in recovery planning for loggerhead turtles and offer additional information for the management of endangered and threatened species.     

Presence of two host races of Aphis gossypii Glover (Hemiptera: Aphididae) collected in Turkey

The aphid, Aphis gossypii, is a primary pest of citrus, cotton, cucurbits and greenhouse‐grown vegetables in Turkey and throughout Europe. There is some previous empirical data suggesting that host‐adapted genotypes of this aphid exist which may in fact be host‐races. To determine if host races of A. gossypii are indeed present in the eastern Mediterranean region of Turkey, reciprocal host transfer experiments and life table analyses were performed with multiple asexual lineages (= clones) of the aphid collected from different hosts. The collection hosts included citrus, cucumber, eggplant, okra, sweet pepper and cotton. Aphid developmental times on the host from which the aphid was originally collected (= collection or natal host) were shorter (5.2–6.0 days) and had a higher intrinsic rate of population growth (r_m = 0.25–0.44) than the 6.6–7.3 days required when the aphid was reared on a non‐original collection host (= non‐collection host or non‐natal host) and had r_m = 0.03–0.30. Total immature mortality of the cotton clone, especially in the first nymphal stage, was high (51–100%) with low r_m (0–0.03) on cucumber, citrus and sweet pepper. Aphid populations transferred from citrus, eggplant and okra to cotton (r_m = 0.29–0.30) did not differ significantly in their performance from that of the cotton population on cotton (r_m = 0.34), whereas that from sweet pepper and cucumber populations (r_m = 0.22–0.24) were significantly lower. These data have allowed us to separate A. gossypii into two distinct biological groups: (a) a ‘generalist’ population obtained from cucumber, sweet pepper, citrus, eggplant and okra which exhibited statistically better development on cotton; versus (b) a population from cotton which, by comparison on reciprocal hosts, developed poorly on non‐natal hosts except on eggplant. Development of the cotton clone on cucumber and okra was not improved after four successive generations on the non‐natal host. The good development of A. gossypii from eggplant and cotton on these reciprocal hosts suggests that these particular clones were similar, if not identical, host races.     

Effects of elevated CO2 on life‐history traits of three successive generations of Frankliniella occidentalis and F. intonsa on kidney bean,Phaseolus vulgaris

The objective of this study was to determine how elevated CO₂ impacts on life‐history traits and life table parameters in three successive generations of invasive species Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) and its related native species, Frankliniella intonsa (Pergande), fed with kidney bean leaves grown in ambient CO₂. The oviposition period, sex ratio, net reproductive rate (R₀), intrinsic rate of increase (r_m), and finite rate of increase (λ) of F. occidentalis increased in elevated CO₂, and larval duration, survival rate, mean generation time (T), and population doubling time (DT) decreased. For F. intonsa, larval duration, survival rate, oviposition period, longevity of female adults, R₀, r_m, and λ decreased in elevated CO₂, whereas sex ratio, T, and DT increased. These results indicated that the effects of elevated CO₂ would be beneficial to F. occidentalis, whereas it would be detrimental to F. intonsa. However, the effects of elevated CO₂ on F. occidentalis and F. intonsa differed over generations. In elevated CO₂, larval duration, survival rate, oviposition period, sex ratio, r_m, and λ of F. occidentalis increased linearly through successive generations, whereas T and DT decreased linearly, which suggested that the effects of elevated CO₂ on F. occidentalis would be slowly accentuated over time. For F. intonsa, larval duration, survival rate, oviposition period, r_m, and λ decreased linearly over generations, whereas sex ratio, T, and DT increased linearly. This indicated that the effects of elevated CO₂ on F. intonsa would slowly accentuate over time. We conclude that F. occidentalis would be more adapted to elevated CO₂ than F. intonsa.     

Relationship between susceptibility to neonicotinoids and population dynamics of cotton aphid,Aphis gossypii Glover (Hemiptera: Aphididae)

Efficiency of imidacloprid and thiametoxam on population growth parameters of Aphis gossypii Glover (Hemiptera: Aphididae) was assessed using three bioassay methods including; residual, starvation and FAO dip methods. Aphids were assayed under laboratory conditions at 23 ± 2°C, photoperiod of 16:8 (L:D) and 70% relative humidity. Aphids were transferred to sprayed leaves and Petri dishes in residual and starvation methods, respectively. There was no feeding for the aphids in starvation method. In FAO dip method, insects were dipped for 5 s in pesticide solutions and then transferred to fresh leaves. Results revealed that LC₅₀ values calculated with the starvation and residual methods were respectively 15 and 11% more than FAO dip method (for imidacloprid) and 22 and 18% (for thiametoxam). The LC₅₀ value in starvation method was 3% more than the residual method. Calculated LC₅₀ in starvation and residual methods with imidacloprid respectively caused 160 and 34% increase in intrinsic rates of increase (r _m) and net reproductive rate (R ₀) in comparison with FAO dip method. Generation time (T) and doubling time (DT) were respectively 59 and 62% less than those in FAO dip method. In contrast, thiametoxam (LC₅₀ concentration) in starvation and residual method lead to 9 and 67% increase in r _m and R ₀ parameters compared to FAO dip method. However T and DT were respectively 65 and 92% less than mentioned parameters in FAO dip method. There was not any significant difference between life table parameters calculated by residual and starvation bioassay methods.     

The use and abuse of genetic marker‐based estimates of relatedness and inbreeding

Genetic marker‐based estimators remain a popular tool for measuring relatedness (r_xy) and inbreeding (F) coefficients at both the population and individual level. The performance of these estimators fluctuates with the number and variability of markers available, and the relatedness composition and demographic history of a population. Several methods are available to evaluate the reliability of the estimates of r_xy and F, some of which are implemented in the program COANCESTRY. I used the simulation module in COANCESTRY since assess the performance of marker‐based estimators of r_xy and F in a species with very low genetic diversity, New Zealand's little spotted kiwi (Apteryx owenii). I also conducted a review of published papers that have used COANCESTRY as its release to assess whether and how the reliability of the estimates of r_xy and F produced by genetic markers are being measured and reported in published studies. My simulation results show that even when the correlation between true (simulated) and estimated r_xy or F is relatively high (Pearson's r = 0.66–0.72 and 0.81–0.85, respectively) the imprecision of the estimates renders them highly unreliable on an individual basis. The literature review demonstrates that the majority of studies do not report the reliability of marker‐based estimates of r_xy and F. There is currently no standard practice for selecting the best estimator for a given data set or reporting an estimator's performance. This could lead to experimental results being interpreted out of context and render the robustness of conclusions based on measures of r_xy and F debatable.     

Resource partitioning in two coexisting cladocerans,Daphnia magna and Scapheloberis kingi (Anomopoda: Daphniidae), in north-eastern Algeria

Life-history traits of two coexisting cladocerans, Daphnia magna Straus and Scapheloberis kingi Sars, inhabiting a temporary pond in north-eastern Algeria were monitored in 2013 under laboratory conditions. Their life histories were compared for differences in traits such as age and size at first reproduction, size of neonates, brood size, number of broods per female, total life span and intrinsic rate of increase (r_m). Data were recorded during their entire life cycle. Daphnia magna, the larger species, could possibly be more successful in colonising temporary habitats than S. kingi because it allocates more energy to reproduction. Scapheloberis kingi, the smaller species, starts reproduction early, resulting in a smaller brood size and a shorter life span with fewer broods. Consequently, S. kingi produces a smaller number of neonates during its lifetime and has a lower r_m. In contrast, D. magna delays reproduction but produces a larger brood size and, because it is longer-lived, produces more broods and so produces a greater number of neonates and has a higher r_m over its lifetime.     

Did we miss some evidence of chaos in laboratory insect populations?

The collection and documentation of the experimental evidence of chaos in biological populations have always been elusive. We were puzzled by the observation that the most frequently computed demographic parameter for laboratory insect populations, the population intrinsic rate of increase (r _m), seems too small to induce chaotic dynamics. For example, when it is directly utilized as an approximation to the parameter (a) of the one-parameter discrete logistic model, the parameter seems well out of the chaotic range. In a recent reanalysis of our early laboratory demographic data of 1800 Russian wheat aphids (RWA), we discovered that a proper measure unit conversion should be performed to make the link between r _m and the discrete logistic model. We think that this conversion issue may have been ignored historically in biological literature since we are not aware of any uses of the r _m in the discussion of chaos. It should be noted that r _m is different from the r in discrete logistic model (e.g., May in Nature 261:459–467, 1976). Since extensive demographic data purported to estimate r _m have been accumulated in literature on population growth, the finding revealed with our RWA experiment data can easily be verified with the published data in literature. We near-arbitrarily surveyed 10 studies (containing 37 datasets of r _m) published in the literature and archived in JSTOR or BioOne databases to test the conversion, and the results confirmed our finding. The finding should significantly expand the evidence base of chaos in laboratory populations of insects and possibly microorganisms, too.     

Life history elasticity and the population-level effect of p-nonylphenol on Daphnia galeata

In order to evaluate population-level effects of p-nonylphenol on a cladoceran zooplankton (Daphnia galeata), the chronic effects on survival and reproduction were estimated with partial life table tests, which examined responses in life history characters until 3 weeks after birth. The observed responses in survival and reproduction were converted to reductions of the intrinsic rate of natural increase r. The population level EC₅₀, which is defined as the exposure concentration that reduces r by 50%, was estimated as 16.1 g l^–1. In order to examine the extent to which the population-level effect in terms of r is influenced by extra mortality in nature, which is induced by predation, starvation, etc., sensitivity (elasticity) measures of the intrinsic rate of natural increase to reductions in age-specific survival and reproduction were calculated under hypothetical predation schemes. The sensitivities of the intrinsic rate to changes in survival and reproduction invariably decline rapidly after the onset of reproduction irrespective of predation schemes. This implies that partial life cycle tests until 21 days after birth can provide reliable estimates of the population-level effects.     

Design and use of a simulation model to evaluate germplasm for antibiotic resistance to the greenhouse whitefly (Trialeurodes vaporariorum) and the sweetpotato whitefly (Bemisia tabaci)

SARAH (Software for theAssessment of antibioticResistance toAleyrodidae inHost plants) is a deterministic simulation model of whitefly population growth based on whitefly life-history components determined on individual plants. The life-history components recorded were oviposition rate, adult survival, pre-adult survival, developmental period, and sex ratio. The simulation model serves as a tool to combine these components and to obtain a single criterion for (antibiotic) resistance. The criterion used was the decrease in simulated intrinsic population growth rate, r _s , relative the r _s value determined on a susceptible control genotype. This model-based evaluation method was tested using the greenhouse whitefly,Trialeurodes vaporariorum Westwood, on tomato and the sweetpotato whitefly,Bemisia tabaci Gennadius, on tomato, eggplant, collard, and pepper. To study its consistency over time, the evaluation method was repeated six times forT. vaporariorum on a susceptible and a resistant tomato cultivar. Simulated intrinsic population growth rate was more consistent in indicating resistance than any of the individual life-history components. Of tenL. hirsutum accessions tested for resistance toT. vaporariorum, three exhibited r _s values that were significantly lower than those for the susceptible control. In addition, on these tenL. hirsutum accessions, a significant positive correlation was observed between r _s and sex ratio (# females/# males). Four host plant species (tomato, collard, eggplant, and pepper) were evaluated for resistance toB. tabaci. All life-history components and r _s values varied among host species, while a negative r _s value was observed forB. tabaci on pepper. A high correlation was found between results from a sensitivity analysis of SARAH and results from a sensitivity analysis of a validated whitefly population simulation model by Yanoet al. (1989a). Significant correlations were found for the relationships between oviposition rate, adult survival, or pre-adult survival and r _s , indicating that none of these life-history components can be omitted from the test procedure. This model-based evaluation method offers a standardized way to quantify levels of antibiotic resistance to whiteflies and will enhance efficiency in breeding programs.     

Estimating intrinsic growth rates of arthropods from partial life tables using predatory mites as examples

The intrinsic rate of natural increase of a population (r_m) has been in focus as a key parameter in entomology and acarology. It is considered especially important in studies of predators that are potential biological control agents of fast-growing pests such as mites, whiteflies and thrips. Life-table experiments under controlled laboratory conditions are standard procedures to estimate r_m. However, such experiments are often time consuming and may critically depend on the precise assessment of the developmental time and the fecundity rate early in the reproductive phase. Using selected studies of predatory mites with suitable life-table data, we investigated whether and how measurements of growth rates can be simplified. We propose a new method for estimating r_m from partial life tables, in which the researcher can choose a level of precision based on a stand-in measure of relative error. Based on this choice, the procedure helps the researcher to decide when a life-table experiment can be terminated. Depending on the chosen precision, significant amounts of experimental time can be saved without seriously compromising the reliability of the estimated growth parameter.

     

Fertility table and rate of population growth of the predator Supputius cincticeps (Heteroptera: Pentatomidae) on one plant of Eucalyptus cloeziana in the field

The reproductive potential and population growth (r_m and λ) of the predator Supputius cincticeps (Heteroptera: Pentatomidae) were evaluated using a life and fertility table. S. cincticeps was reared on one plant of Eucalyptus cloeziana in the field and fed with Tenebrio molitor (Coleoptera: Tenebrionidae) pupae. Females of this predator had a net reproductive rate (R₀) of 21.02 females/female; an intrinsic rate of population increase (r_m) of 0.041 and finite rate of increase (λ) of 1.042. This resulted in population growth of S. cincticeps in the eucalyptus plant with a doubling time of 17.01 days. This natural enemy can be reared under field conditions with alternative prey for use in biological control. Such individuals of S. cinticeps will be better adapted to field conditions when they are liberated.     

Importance of primary metabolites in canola in mediating interactions between a specialist leaf-feeding insect and its specialist solitary endoparasitoid

The role of primary plant chemistry on trophic interactions is not well studied. We examined the effect of primary plant metabolites, focusing on nitrogen, on several biological indices of second and third trophic level insects in a model tritrophic system, consisting of two strains of the crucifer, Brassica napus (canola) (SLM₀₄₆ and RGS₀₀₃), the specialist insect herbivore Plutella xylostella (L.) (Lepidoptera: Plutellidae), and its specialist koinobiont larval-pupal parasitoid Diadegma semiclausum (Hellén) (Hymenoptera: Ichneumonidae). In particular, we measured relative growth rate of the herbivore in relation to an index for plant quality (nitrogen content of leaf tissues), developmental time of the herbivore (sum of second, third, and fourth larval instars durations), and intrinsic rate of increase (r _m ) of the herbivore and the parasitoid. Tritrophic studies were conducted on development, survivorship curve analysis, reproductive potential, life history, parasitism, and several other fitness correlates of the parasitoid. The life table parameters of D. semiclausum were determined under laboratory conditions. The intrinsic rate of increase (r _m ) of the parasitoid was significantly higher on RGS₀₀₃ than SLM₀₄₆. In this tritrophic model, the results indicated that the bottom-up direct effect on the herbivore population growth rate was marginally as strong as the direct effect of top-down force due to the parasitoid population growth rate; but it was higher than its indirect counterpoint mediated with the parasitoid population growth rate. Consequently, D. semiclausum performed better on RGS₀₀₃, which was the most inferior host to P. xylostella in comparison with another plant cultivar and had the lowest content of nitrogen in its leaves.     

Patterns of aphid resistance in the genus Vicia

The performance of three aphid species, Aphis fubae, Acyrthosiphon pisum and Megoura viciae, was quantified on 22 taxonomically-selected host plant species from the genus Vicia (vetches), using intrinsic rate of increase (r_m) k standard errors. A. pisum proved to be the most successful aphid species, both in terms of highest potential population increase and widest host range; M. viciae was least successful, with most restricted host range and low r_m values on all but the closest relatives of Vicia faba. A wide range of antibiotic resistance was found within the genus, and host resistance to the three aphid species was found to be broadly related to classification patterns based on taxonomy and life-form. Analysis of the components of r_m revealed that nymphal survival rates were the most significant factor limiting host colonisation, not pre-reproductive period which is the most important factor in cultivars of V. faba. The consequences of aphid polyphagy on performance are discussed.     

An empirical test for a zone of canalization in thermal reaction norms

Theoretical models on the evolution of phenotypic plasticity predict a zone of canalization where reaction norms cross, and genetic variation is minimized in the environment a population most frequently encounter. Empirical tests of this prediction are largely missing, in particular for life‐history traits. We addressed this prediction by quantifying thermal reaction norms of three life‐history traits (somatic growth rate, age and size at maturation) of a Norwegian population of Daphnia magna and testing for the occurrence of an intermediate temperature (T_m) at which genetic variance in the traits is minimized. Size at maturation changed relatively little with temperature compared to the other traits, and there was no genetic variance in the shape of the reaction norm. Consequently, age at maturation and somatic growth rate were strongly negatively correlated. Both traits showed a strong genotype–environment interaction, and the estimated T_m was 14 °C for both age at maturation and growth rate. This value of T_m corresponds well with mean summer temperatures experienced by the population and suggests that the population has evolved under stabilizing selection in temperatures that fluctuate around this mean temperature. These results suggest local adaptation to temperature in the studied population and allow predicting evolutionary trajectories of thermal reaction norms under changing thermal regimes.     

Genetic drift outweighs natural selection at toll‐like receptor (TLR) immunity loci in a re‐introduced population of a threatened species

During population establishment, genetic drift can be the key driver of changes in genetic diversity, particularly while the population is small. However, natural selection can also play a role in shaping diversity at functionally important loci. We used a well‐studied, re‐introduced population of the threatened Stewart Island robin (N = 722 pedigreed individuals) to determine whether selection shaped genetic diversity at innate immunity toll‐like receptor (TLR) genes, over a 9‐year period of population growth following establishment with 12 genetic founders. We found no evidence for selection operating with respect to TLR diversity on first‐year overwinter survival for the majority of loci, genotypes and alleles studied. However, survival of individuals with TLR4_BE genotype was significantly improved: these birds were less than half as likely to die prior to maturity compared with all other TLR4 genotypes. Furthermore, the population frequency of this genotype, at a two‐fold excess over Hardy–Weinberg expectation, was increased by nonrandom mating. Near‐complete sampling and full pedigree and reproductive data enabled us to eliminate other potential causes of these patterns including inbreeding, year effects, density dependence, selection on animals at earlier life history stages or genome‐level association of the TLR4_E allele with ‘good genes’. However, comparison of observed levels of gene diversity to predictions under simulated genetic drift revealed results consistent with neutral expectations for all loci, including TLR4. Although selection favoured TLR4_BE heterozygotes in this population, these effects were insufficient to outweigh genetic drift. This is the first empirical study to show that genetic drift can overwhelm natural selection in a wild population immediately following establishment.     

Effects of seven diets on the population dynamics of laboratory culturedTisbe holothuriae Humes (Copepoda,Harpacticoida)

The harpacticoid copepodTisbe holothuriae was collected from Saronicos Gulf (Greece) and reared under constant laboratory conditions. In order to study the effects of food on the population dynamics, seven diets were tested: the seaweedUlva; five artificial compound feeds: the liquid Fryfood^® (Waterlife), a powder ofMytilus, yeast, soya andSpirulina, respectively; and a mixed diet consisting ofUlva and Fryfood. The life cycle parameters (mortality, sex ratio, generation time, offspring production) were measured, and the demographic variables [mean generation time (T), net reproductive rate (Ro), and intrinsic rate of natural increase (r_m)] were determined. As to their efficiency regarding population dynamics, the diets ranked as follows: (1)Ulva+Fryfood, (2),Ulva, (3) Fryfood, (4)Mytilus, (5) soya, (6) yeast, and (7)Spirulina. In this order they cause a progressive increase of both larval mortality and generation time, a progressive decrease of sex ratio, number of offspring per egg sac, number of egg sacs per female and, consequently, of Ro and r_m. The observed differences between diets were most pronounced with respect to offspring production. Of the compound diets, those containing animal extracts were more efficient than those containing vegetable materials.Ulva plays an important role in the nutrition ofT. holothuriae, favouring offspring production as well as larval survival, development and pigmentation.Ulva in combination with Fryfood led to a greater copepodid survival and offspring production. This mixed diet proved to be the most favourable for rearing the Greek population oft. holothuriae, resulting in an efficient intrinsic rate of natural increase (r_m=0.304) of the population.     

A life table study on three genetic strains of Ophryotrocha diadema (Polychaeta,Dorvilleidae)

A life-table study was performed on three strains of Ophryotrocha diadema. The wild type strain, YY (yellow eggs), was compared with a recessive mutant strain, ww (white eggs), and the F₁, hybrid, Yw.

The viability of the YY strain was greater than that of the ww strain. The hybrids were intermediate. Expectation of life. e., of zygotes were: YY 27.9, Yw 19.1, and ww 15.1 wk, respectively. The total outcome of reproduction followed the same pattern; the net reproductive rates, R ₀, were related as 1:0.62:0.47 for YY: Yw: ww.

Reproduction began in the fourth week. A maximum reproductive output during the next 4 wk was followed by a fast decline. The intrinsic rate of natural increase, r, was 0.880 per week for the YY strain, 0.903 for the Yw strain and 0.872 for the ww strain. For all strains, the first 7 wk of reproduction contributed more than 99% of the Lotka equation σ e ^?rx l _x m _x = l, i.e., l _x m _x values at older ages would not substantially affect population growth. In this 7–wk period (and the previous nonreproductive weeks), mortality differences were small among strains. During the period of maximum reproduction the average size of egg masses was approximately the same in all strains. The heterozygote superiority was due to shorter intervals between successive spawnings.

It is suggested that in the opportunistic species O. diadema deviations from an r–selected reproductive pattern are due to small adult size and to its ancestry from a mainly K–selected, very old polychaete group.

O. diadema has proven to be a useful test animal for marine pollution research. Observed effects on survival and reproduction have been summarized in a model to demonstrate population consequences of sublethal pollutant levels.     

Population Dynamics of Evolutionary Change: Demographic Parameters as Indicators of Fitness

I evaluated demographic parameters as indicators of fitness by calculating the net reproductive rate (R₀), exponential rate of change (r), lifetime reproductive success (LRS), and Malthusian parameter (m) for nine genotypes and four phenotypes (two alleles at each of two independent loci) of an age-structured population. The given starting conditions included age-specific survival rates of males and females and age-specific fecundity of females for each genotype (to simplify the problem I presumed no differences in survivorship or fecundity of genotypes with the same phenotype) and the same age structure for each genotype. The prevailing genotype had the greatestm, but it did not have the greatestr,R₀, or LRS, or even the greatest survivorship of either juveniles or adults, or the greatest fecundity. This result indicates thatmis the only correct measure of fitness (i.e., as a predictor of which genotype should prevail from among a group of genotypes) and that comparisons ofr,R₀, LRS, juvenile or adult survival rates, or fecundity may be misleading indicators of which genotype should prevail (i.e., be most “fit”) over time (i.e., be selected for).     

Equal nonbreeding period survival in adults and juveniles of a long‐distant migrant bird

In migrant birds, survival estimates for the different life‐history stages between fledging and first breeding are scarce. First‐year survival is shown to be strongly reduced compared with annual survival of adult birds. However, it remains unclear whether the main bottleneck in juvenile long‐distant migrants occurs in the postfledging period within the breeding ranges or en route. Quantifying survival rates during different life‐history stages and during different periods of the migration cycle is crucial to understand forces driving the evolution of optimal life histories in migrant birds. Here, we estimate survival rates of adult and juvenile barn swallows (Hirundo rustica L.) in the breeding and nonbreeding areas using a population model integrating survival estimates in the breeding ranges based on a large radio‐telemetry data set and published estimates of demographic parameters from large‐scale population‐monitoring projects across Switzerland. Input parameters included the country‐wide population trend, annual productivity estimates of the double‐brooded species, and year‐to‐year survival corrected for breeding dispersal. Juvenile survival in the 3‐week postfledging period was low (S = 0.32; SE = 0.05), whereas in the rest of the annual cycle survival estimates of adults and juveniles were similarly high (S > 0.957). Thus, the postfledging period was the main survival bottleneck, revealing the striking result that nonbreeding period mortality (including migration) is not higher for juveniles than for adult birds. Therefore, focusing future research on sources of variation in postfledging mortality can provide new insights into determinants of population dynamics and life‐history evolution of migrant birds.