Population Fecundity Research Articles

Fitness cost of imidacloprid resistance in generalist predator from northernmost and equatorial range in the tropics

AbstractLife‐history traits and population size of organisms may be affected by fitness costs associated with insecticide resistance. In this study, we examined the insecticide resistance and life‐history traits of Paederus fuscipes (Curtis), a common generalist predator, in field populations from Taiwan (high‐latitude region; 22° N–25° N) and Malaysia (low‐latitude region; 3° N–5° N). The results showed that Malaysian populations had higher imidacloprid resistance compared with Taiwanese populations. The fitness costs associated with imidacloprid resistance resulted in reduced fecundity, longer adult pre‐oviposition period, shorter egg length, and lighter pupal weight in the Malaysian populations, in contrast to the Taiwanese populations. However, the immature developmental time of the Malaysian populations was relatively short compared with the Taiwanese populations. The longevity of the Taiwanese populations was significantly shorter compared with the Malaysian populations. The fecundity of the adult populations increased in inverse proportion to longevity. The intrinsic rate of increase was significantly lower in the Malaysian populations compared with the Taiwanese populations. This regional‐scale study provided insights into the differences in life‐history traits and population growth of P. fuscipes as a result of fitness cost. However, it is worth noting that despite the high intrinsic rate of increase observed in the Taiwanese populations, among other factors, cannibalism may serve as a density‐dependent compensatory mechanism in regulating population size.

Forest harvest causes rapid changes of maternal investment strategies in ground beetles.

Species recovery following anthropogenic disturbances will depend on adaptations in survivorship and fecundity. Life-history theory predicts increased environmental stress will result in (1) shifts in resource allocation from fecundity to body growth/maintenance and (2) increased provisioning among offspring at the cost of reproductive output. For remnant populations that persist after forest harvesting, selection mediated through anthropogenic disturbances may affect resilience to additional stressors such as climate change. We tested how rapid changes in environmental conditions affected maternal investment strategies in two ground beetle species, Pterostichus pensylvanicus and Pterostichus coracinus, by comparing fecundity and survivorship in populations from recently clear-cut and uncut habitats. Using parents drawn from clear-cut or uncut stands, we reared progeny in both common garden and reciprocal transplant experiments. In P. pensylvanicus, we found that neither lineage nor rearing habitat affected the number of eggs laid per female or survivorship of offspring. However, eggs laid by females from clear-cuts were more likely to hatch and offspring reached maturity more quickly, suggesting increased provisioning per offspring. In P. coracinus, females from clear-cuts laid more eggs, and their eggs hatched more rapidly and had greater hatching success, suggesting increased investment in overall reproductive output and increased offspring provisioning. In the reciprocal transplant, we observed significant habitat by lineage interactions on survival in P. coracinus, with survivorship increasing when progeny were reared in novel habitats. In both species, increased maternal investment among offspring was not associated with a reduction in overall reproductive output, as anticipated. However, maternal investment among offspring declined with increasing female size, implying trade-offs between increased metabolic demand and fecundity. Taken together, our work suggests that females from more stressful, clear-cut habitats increased investment in fecundity, compared to females from uncut habitats, and may compensate for larval mortality. These changes were driven by smaller individuals, suggesting that increased environmental stress can influence the relationship between female size and maternal investment strategy. Additionally, reciprocal increases in offspring survivorship in habitats other than the parents suggest that adjacent areas between unharvested and clear-cut habitat may be useful in maintaining biodiversity under future climate stressors.

Temporal declines in fecundity: A study of southern Gulf of St. Lawrence Atlantic herring (Clupea harengus) and implications for potential reproductive output.

Individuals must reproduce to survive and thrive from generation to generation. In fish, the fecundity of individuals and estimates of total reproductive output are critical for evaluating reproductive success and understanding population dynamics. Estimating fecundity is an onerous task; therefore, many populations lack contemporary estimates of fecundity and size-fecundity relationships. However, reproductive dynamics are not static in time; therefore, it is important to develop contemporary fecundity estimates to better inform conservation and management action. To highlight the importance of contemporary fecundity estimates, we examined the fecundity of southern Gulf of St. Lawrence (sGSL) spring and fall spawning Atlantic herring in 2022, developed size-fecundity models, and compared these to historical fecundity estimates and models. Our results suggest that the average fecundity of sGSL spring and fall herring has undergone a substantial temporal decline of approximately 47% and 58%, respectively, since the 1970s and 1980s. The size-fecundity relationships for fall spawning herring have shifted, with fish of a given size exhibiting lower fecundity in 2022 compared to the 1970s. Alternatively, the size-fecundity relationships for spring spawning herring have remained relatively static. Furthermore, simulations highlighted a substantial reduction in potential reproductive output in 2022 compared to 1970 of approximately 32% and 68% for spring and fall spawners, respectively, based on a fixed number of mature females, which may have negative implications for stock rebuilding. Overall, our study provides support for periodic estimates of fecundity in fish populations to better understand temporal changes in reproductive and population dynamics.

Simulated reproductive allocation to fisheries-induced evolution among small yellow croaker populations in the Yellow and Bohai Seas

Fishery-induced evolution (FIE) affects the body size and reproduction of offspring, resulting in feedback regulation of fish survival and stock recruitment. Small yellow croaker (Larimichthys polyactis) is a species of high ecological and commercial importance in the Yellow and Bohai Seas, with large fluctuations in abundance linked to overfishing and environmental changes in recent decades. To better understand the maturation size and age, threshold reproduction cost, and energy trade-offs of small yellow croaker under environmental changes (e.g. conditions) and human impacts (e.g. fishing) in the Yellow and Bohai Seas, we utilised a two-pool uncertain growth model containing the growth threshold of reproductive energy and reproductive energy cost. The results showed that for growth, maturation age, and reproduction under the baseline scenario based on field survey data from the 1950 s, when resources for small yellow croaker were underexploited, the average age was 5–6 years old and the average body length was approximately 220 mm. As the model parameters for fishing pressure and condition mortality increased, small yellow croaker tended to mature earlier, had a smaller body size, and allocated more energy to reproduction, resulting in higher population fecundity but shorter lifespan. Higher reproductive costs led to a greater proportion of reproductive energy being allocated during the spawning period, resulting in an older age of sexual maturity, shorter lifespan for spawning populations, and poor physical conditions, resulting in higher post-reproductive mortality and a limited capacity for stock recruitment. The key life-history traits of small yellow croaker, including maturity age, mean age of the population, age-specific body weight, and spawn production at different age stages, can change under different conditions. The model represents the main life history strategies and energy allocation characteristics of small yellow croaker. The simulated age and body size were within the observed range and the predicted fecundity aligned with the observed values. This study provides a prediction tool for protecting the spawning and recruitment of small yellow croaker and establishes a biological reference for sustainable management of small yellow croaker populations in the Yellow and Bohai Seas in the future.

Fecundity of The Pine Processionary, Thaumetopoea Pityocampa (Denis & Schiffermüller, 1775) In The Case Of Reforestation In Moudjbara (Djelfa - Algeria)

A study of the fecundity of female populations of the pine processionary in the Moudjbara reforestation indicates that there are cyclical variations in the reproduction of this species. Descriptive analysis of pine processionary oviposition lengths showed greater significance for oviposition deposited on needles than for oviposition deposited on twigs. A very highly significant difference was noted between the lengths of the egg-laying supports from the Moudjbara reforestation (p=0.0001). The 195 pine processionary oviposition sites revealed a total of 37,272 eggs, with an average of 191 eggs per oviposition site. Analysis of the variance between the various categories of eggs showed a highly significant probability (p=0.0001). Three parasitoids were identified that emerged from oviposits collected at the Moudjbara reforestation site, with rates varying from year to year. T. embryophagum was encountered only sporadically in 2018, 2019 and 2021, with respective percentages not exceeding 2%. For the four pine processionary caterpillar populations studied, B. servadeii appeared to be more abundant than O. pityocampae. The number of B. servadeii adults observed reached 83.91% in 2020. Parasitoid activity was greater on eggs located at the ends of the clutch. It also appears that O. pityocampae mainly parasitizes the upper part of the egg, whereas B. servadeii shows a preference for the lower part.

Morphotype induced changes in the life history and population dynamics of an hippolytid shrimp

One of the most exceptional, loud paradigm of shape polymorphisms constitutes the “rostral loss” condition in hippolytid shrimps. The intertidal shrimp Hippolyte sapphica includes two conspecific morphotypes, one of which demonstrates a neotenic rostrum (morph-B). Morphs’ rostral elongation is controlled by a single genetic locus, with long rostra (morph-A) representing the recessive state and short, larval-like ones the completely dominant state. Geometrics morphometry on the species morphotypes revealed also the homozygous/heterozygous state of the gene site along with some induced body’ adaptations, which compete the micro-evolutionary disadvantage of the “rostral loss”. We found recently that females’ viability and maternal energy investment selectively favors morph-A. The present contribution detects and discuss comparatively demographic and reproductive traits in species mixed (both morphs) and unmixed populations. Our results show that this sharp dimorphic rostral condition is a sex-related marker and that the species is gonochoric. Presence of morph-B results to (a) lower egg production (b) higher seasonally males’ percentage (c) morph-A females’ earlier maturation and (d) higher fecundity in morph-A mixed populations. It seems that the “rostral loss” state induces complex adaptations between the two morphotypes through sex ratios equilibria, morphotypes’ growth rates, and morphs’ fecundity differentiate inputs throughout the seasons.

Implications of Warming on the Morphometric and Reproductive Traits of the Green Crab, Carcinus maenas

Understanding the relationship between environmental temperature and the biological traits of organisms is fundamental to inferring the potential impacts of climate change. In the case of marine poikilotherm species, seawater temperature is one of the main driving forces of biological processes, with consequences at higher levels of organization such as population and ecosystem. In this study, we analysed differences in maximum carapace width (CWmax), size at maturation, relative size at maturation, and duration of the reproductive season for the green crab (Carcinus maenas) along a temperature gradient. An extensive review of bibliographic data was performed on studies published between 1962 and 2020, gathering C. maenas data from 55 different populations, spread over 20 degrees of latitude and 14.2 °C of sea surface temperature (SST). In addition, green crab data were collected at five different lagoons and estuaries along the continental Portuguese coast. The relationship between average SST and CWmax, age of maturation, reduction of size at maturation, and duration of egg bearing was analysed to understand the role of SST in driving variation in these C. maenas characteristics across a latitudinal gradient. There was a significant relationship between SST and CWmax for males and SST and CW of females at maturation, respectively. The results extrapolate for each local projected temperature increase caused by climate change and suggest an effect on the morphometric and reproductive traits of C. maenas across regions. These changes comprise an overall reduction in C. maenas body size, an enlargement of the reproductive season, a shortening in the duration of larval developmental time, and a decrease in the relative size of crabs at maturation. Secondary consequences on the fecundity and connectivity of populations are discussed.

Use of Food Attractant to Monitor and Forecast Population Dynamics of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), a Long-Distance Migratory Pest

The rice leaf folder, Cnaphalocrocis medinalis, is a significant migratory pest that restricts rice production in Asia and Africa, and monitoring and early warning measures are the basis for its management. Based on its regional migratory path in China, the pest population dynamics were monitored from 2020 to 2021 using food attractants. In this study, we also used internal reproductive system dissection to determine the adult age and reproductive developmental state. The monitoring results indicated that the trapping dynamics of C. medinalis males using food attractants and sex pheromones were approximately similar. Both trapping methods yielded C. medinalis males of different ages, with an identical age structure for both trap types. Dissection analysis of the reproductive system of females trapped using the food attractants indicated that in 2020, the population of C. medinalis in Liling, Hunan Province, was indigenous, while populations in other monitoring sites mainly comprised migrants from other areas. The ovarian development level of females trapped using food attractants showed a positive correlation with the age of males, and there was also a significant positive correlation between the index of ovarian development of females and the mating time. Furthermore, a dynamic prediction method for fecundity in field populations was established based on the quantity of eggs held by the females. This study provides a new method for the monitoring and early warning of the existence of C. medinalis populations.

Age and Growth of Hedinichthys yarkandensis (Day, 1877) in the Hotan River

Hedinichthys yarkandensis (Day, 1877) has been highlighted in research and evaluated as a class II key protected aquatic wildlife in Xinjiang Uygur Autonomous Region. To enhance the study of fish resources in the Hotan River, further germplasm conservation of fishery resources specific to the Tarim River Basin should be carried out, and the development of the aquatic seed industry should be promoted. A total of 1275 H. yarkandensis individuals were collected from 2020–2021. Fish ecological methods were used to explore the population ecological characteristics and ecological habits of H. yarkandensis. We found that the age of H. yarkandensis ranged from one to seven based on lapillus otoliths, and two-plus individuals accounted for more. The age structure composition reveals stable genetic performance and good population fecundity. The fitting correlations of standard length and body weight reveal that H. yarkandensis in the Hotan River is a uniformly growing fish. The ratio of females to males is 0.87:1. The Fulton condition index of males was slightly higher than that of females due to individual miniaturization. The comparative study found that the growth parameters of the Hotan River population (L∞ = 302.772, W∞ = 310.8450, t0 = −0.4608) were higher than those of the other groups. The feeding demand of H. yarkandensis in the Hotan River was guaranteed because the effect of human activities was small in the watershed area and the watershed ecosystem was more stable, which resulted in stable germplasm resources in the Hotan River population.

Structure of the spawning herd and stocks of the Siberian vendace of the Yenisei River

The aim of the research is to evaluate the structural and biological parameters of the spawning stock of the turukhanskaya form of the Siberian vendace Coregonus sardinella (Valenciennes, 1848) from the Yenisei River and the state of the commercial stock of this fish species in the period from 2014 to 2021. Research methods: in the research used the ichthyological material collected in the period from 2014 to 2021 in the lower reaches of the Yenisei River (near the Dudinka town and the village of Levinsky Sands). Processing of ichthyological materials was carried out according to generally accepted methods. The number of spawning herds of Siberian vendace was calculated using a virtual population analysis in Galland’s modification. Instant natural mortality rates by age groups were calculated using the method of L. A. Zykov. Results: According to the control catches, the age of the spawning stock of the turukhanskaya form of Siberian vendace in the Yenisei River was 2+–9+ years. Fish aged 4+ years, which in different years constituted from 47 to 68 % of the spawning stock, dominated in the population. The average long-term age of the spawning population in the study period was 4.2 years. The ratio of females and males in the spawning herd was close to 1:1 on average. Individual absolute fecundity of fishes varied in the range from 1.9 to 12.5 thousand eggs, increasing with increasing age and size of females. The average population fecundity is 2.6–5.3 thousand eggs. The number and biomass of the spawning herd in different years varied from 11.0 to 30.5 thousand individuals and from 630 to 1738 tons, respectively. Practical significance: the obtained results about the dynamics and structure of the spawning stock of the semi-anadromous form of the Siberian vendace from Yenisei River for the period from 2014 to 2021 will be used for prognostic purposes in the preparation of materials substantiating the volumes of the recommended catch in the basin of the Yenisei River. Conclusion: Based on the results of the analysis of the age, size-weight and sex structure, it was shown that the state of stocks of the semi-anadromous turukhanskaya form of the Siberian vendace in the Yenisei River is currently in a satisfactory condition.

Two-Sex Life Table Analysis of the Predator Arma chinensis (Hemiptera: Pentatomidae) and the Prediction of Its Ability to Suppress Populations of Scopula subpunctaria (Lepidoptera: Geometridae)

Scopula subpunctaria (Herrich-Schaeffer) (Lepidoptera: Geometridae) is a leaf-eating pest in tea plantations that often causes serious economic losses. Arma chinensis (Fallou) (Hemiptera: Pentatomidae) as a polyphagous insect has become one of the main biological control agents for tea plantation pests due to its wide feeding habit, predatory ability, and adaptability. However, studies related to the predation using A. chinensis on the third instar S. subpunctaria have not been reported. In this study, we used the age-stage, two-sex life table method to analyze the developmental duration and fecundity of S. subpunctaria fed on tea, and A. chinensis fed on third instar S. subpunctaria larvae, under a 25 °C regime. The growth, development, survival, fecundity, and predation rates of the insect populations were investigated. The results showed that the predator and the prey can complete their respective life histories, but the developmental durations at each stage were different, and the developmental stages overlapped significantly. In addition, we used the computer program TIMING-MSChart to project the stage structure and the total population size of A. chinensis and S. subpunctaria. We also simulated the population changes of S. subpunctaria using an A. chinensis intervention. These results showed that S. subpunctaria can support A. chinensis to finish its life history and A. chinensis has great potential to control S. subpunctaria. This study contributes to the understanding of the biological characteristics of S. subpunctaria and provides a theoretical basis for releasing A. chinensis in the field to suppress S. subpunctaria.

Fecundity of the narrow-clawed crayfish Pontastacus leptodactylus in the water bodies of Belarus

Pre-larvae hatching fecundity and ovarian fecundity of narrow-clawed crayfish populations were estimated in the lakes and reservoirs of Belarus. Statistically significant differences in the fecundity of females from various water bodies were noted only for Lake Kichino. For all other water bodies, the fecundity dependence on the length of females did not differ statistically and was described by one equation. The greatest loss of eggs was noted during the spawning period (oviposition), insemination and attachment to pleopods of the female. During this short period (2–3 hours), egg mortality of females 120 mm TL is 30 %, it decreases for small females and increases for large ones. During the gestation period, egg mortality averages 8 %.

Sweepstakes reproduction facilitates rapid adaptation in highly fecund populations.

Adaptation enables natural populations to survive in a changing environment. Understanding the mechanics of adaptation is therefore crucial for learning about the evolution and ecology of natural populations. We focus on the impact of random sweepstakes on selection in highly fecund haploid and diploid populations partitioned into two genetic types, with one type conferring selective advantage. For the diploid populations, we incorporate various dominance mechanisms. We assume that the populations may experience recurrent bottlenecks. In random sweepstakes, the distribution of individual recruitment success is highly skewed, resulting in a huge variance in the number of offspring contributed by the individuals present in any given generation. Using computer simulations, we investigate the joint effects of random sweepstakes, recurrent bottlenecks and dominance mechanisms on selection. In our framework, bottlenecks allow random sweepstakes to have an effect on the time to fixation, and in diploid populations, the effect of random sweepstakes depends on the dominance mechanism. We describe selective sweepstakes that are approximated by recurrent sweeps of strongly beneficial allelic types arising by mutation. We demonstrate that both types of sweepstakes reproduction may facilitate rapid adaptation (as defined based on the average time to fixation of a type conferring selective advantage conditioned on fixation of the type). However, whether random sweepstakes cause rapid adaptation depends also on their interactions with bottlenecks and dominance mechanisms. Finally, we review a case study in which a model of recurrent sweeps is shown to essentially explain population genomic data from Atlantic cod.

Sweepstakes reproductive success via pervasive and recurrent selective sweeps.

Highly fecund natural populations characterized by high early mortality abound, yet our knowledge about their recruitment dynamics is somewhat rudimentary. This knowledge gap has implications for our understanding of genetic variation, population connectivity, local adaptation, and the resilience of highly fecund populations. The concept of sweepstakes reproductive success, which posits a considerable variance and skew in individual reproductive output, is key to understanding the distribution of individual reproductive success. However, it still needs to be determined whether highly fecund organisms reproduce through sweepstakes and, if they do, the relative roles of neutral and selective sweepstakes. Here, we use coalescent-based statistical analysis of population genomic data to show that selective sweepstakes likely explain recruitment dynamics in the highly fecund Atlantic cod. We show that the Kingman coalescent (modelling no sweepstakes) and the Xi-Beta coalescent (modelling random sweepstakes), including complex demography and background selection, do not provide an adequate fit for the data. The Durrett-Schweinsberg coalescent, in which selective sweepstakes result from recurrent and pervasive selective sweeps of new mutations, offers greater explanatory power. Our results show that models of sweepstakes reproduction and multiple-merger coalescents are relevant and necessary for understanding genetic diversity in highly fecund natural populations. These findings have fundamental implications for understanding the recruitment variation of fish stocks and general evolutionary genomics of high-fecundity organisms.

Viability Selection at Linked Sites

Evolutionary ecology may be described as explaining ecology through evolution and vice versa, but one may also view it as an integration of the two fields, where one takes the view that ecology and evolution are inseparable, and one can only begin to understand the biology of organisms by synthesizing the two fields. An example of such a synthesis is the biology of high fecundity and the associated concept of sweepstakes reproduction, or skewed individual recruitment success. As an illustration, we consider selection at linked sites under various dominance and epistasis mechanisms in a diploid population evolving according to random sweepstakes and experiencing recurrent bottlenecks. Using simulations, we give a few examples of the impact of the stated elements on selection. We show that depending on the dominance mechanisms, random sweepstakes can shorten the time to fixation (conditional on fixation) of the fit type at all sites. Bottlenecks tend to increase the fixation time, with random sweepstakes counteracting the effects of bottlenecks on the fixation time. Understanding the effect of random sweepstakes, recurrent bottlenecks, dominance mechanisms and epistasis on the fate of selectively advantageous mutations may help with explaining genetic diversity in natural highly fecund populations possibly evolving under sweepstakes reproduction.

Alternative food sources for Amblydromella caudiglans (Phytoseiidae) and effects on predation.

The addition of supplemental food sources for natural enemies is a growing component of conservation and augmentative biological control. Supplemental foods can be used to retain natural enemies when prey are scarce and to promote survival, fecundity, longevity, and development of natural enemy populations, especially generalist natural enemies. Amblydromella caudiglans (Schuster) (Acari: Phytoseiidae) is one of the most abundant predatory mites found in commercial apple orchards in Washington, USA, and contributes to spider mite control. However, because its widespread presence in commercial apple orchards was only recently discovered, how supplementary food sources affect its performance is unknown. In laboratory studies, we evaluated the performance (fecundity, retention, prey consumption) of the generalist phytoseiid A. caudiglans on commercially available supplemental food sources, including factitious prey (Ephestia eggs and Artemia brine shrimp cysts), and pollens of apple, pear, and cattail. We determined that A. caudiglans will not consume Ephestia eggs and performs best on cattail and pear pollens. Combinations of food sources did not enhance the performance of this predator compared to the best performing single-sources. The presence of alternative food sources did not decrease A. caudiglans predation of twospotted spider mite nymphs, except for Artemia brine shrimp cysts, which had a substantial handling time. These results lay the groundwork for identifying a way to promote and retain this natural enemy in tree fruit cropping systems through the use of food resource applications or floral plantings.

The energetic cost of early reproductive development in juvenile Antarctic krill at the Western Antarctic Peninsula

The overwinter survival mechanisms of Antarctic krill, Euphausia superba, are poorly characterized, especially for juveniles. It has been suggested that juveniles adopt a mix of strategies characteristic of both larvae and adults. Like larvae, they may feed opportunistically throughout winter when food is available, and like adults they may be able to suppress their metabolism when food is scarce. In this study we look at the overwinter strategies of juvenile krill and how their reproductive development changes when energy input exceeds what is necessary for survival. We take a closer look at how the sexual maturation of juvenile krill progresses in response to different environmental conditions throughout the fall and winter. We exposed juvenile Antarctic krill to four different “food environment scenarios”, supplementing them with various diets from May to September 2019 that were representative of environmental conditions that they may encounter in different regions of the Western Antarctic Peninsula during autumn and winter. Each month, we measured the physiology and condition of the krill, and assessed the reproductive development of females. We found that when female juvenile krill have greater energy reserves than what is needed to survive the winter, they will begin to sexually mature. Further, when there are sufficient levels of the fatty acids eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and 16:4 (n-1), krill are likely to be in a more reproductive advanced stage. However, when lipids, EPA, DHA and 16:4 (n-1) are depleted throughout the winter, juvenile female krill lose their ability to develop reproductively. We also found that sexual development is an energy intensive process that requires high respiration rates in juvenile krill. Furthermore, when juvenile females expend energy maturing, their physiological condition declines. This trade-off between early reproductive development and condition in juvenile female krill has important implications for individual health and population fecundity. Gaining a better understanding of the mechanisms behind juvenile krill winter survival strategies and their consequences will allow us to predict how future change at the western Antarctic Peninsula may affect krill population dynamics, especially in light of a warming climate.

Brood parasitism of Hooded Warblers by Brown-headed Cowbirds: Severe impact on individual nests but modest consequences for seasonal fecundity and conservation

Abstract Brood parasitism by Brown-headed Cowbirds (Molothrus ater) often has pronounced negative effects on host nests. However, the extent to which parasitism reduces annual reproduction and presents conservation challenges for host species is unclear. We address this issue with data from a color-banded population of Hooded Warblers (Setophaga citrina) in Pennsylvania, where Hooded Warblers have increased dramatically despite frequent nest parasitism. Our analysis is based on both an extensive dataset (8 years, 847 nests) on the per-nest impacts of cowbird parasitism and female-based stochastic simulations that accurately reflect the reproductive biology and parasitism rate (30%) of our study population. Cowbird parasitism has multiple negative consequences for Hooded Warbler nests, including (1) reduced host clutch size; (2) increased nest abandonment; (3) increased risk of complete failure due to predation; and (4) in surviving nests increased egg loss, hatching failure, and nestling mortality. We estimate that parasitism reduces success of Hooded Warbler nests 68%, from 1.29 to 0.41 fledglings per nest. For females and populations, however, the consequences of nest parasitism are considerably less extreme; female annual fecundity decreases 25% for each nesting attempt parasitized, and population-level fecundity drops 5.6% for each 10% increase in the frequency of parasitism. These more modest impacts are attributable to (1) steep declines in rates of cowbird parasitism as the nesting season progresses, (2) rapid renesting following abandonment or failure of parasitized nests, and (3) regular double brooding, with second broods initiated in late June and July when the incidence of cowbird parasitism is low. Our results help resolve the paradox of how cowbird parasitism can have both severe consequences for individual host nests but more modest and sustainable conservation impacts on the seasonal fecundity of females and populations. They further underscore the importance of determining population-level effects of brood parasites before investing in costly management efforts.

Using Bayesian state-space models to understand the population dynamics of the dominant malaria vector, Anopheles funestus in rural Tanzania

BackgroundIt is often assumed that the population dynamics of the malaria vector Anopheles funestus, its role in malaria transmission and the way it responds to interventions are similar to the more elaborately characterized Anopheles gambiae. However, An. funestus has several unique ecological features that could generate distinct transmission dynamics and responsiveness to interventions. The objectives of this work were to develop a model which will: (1) reconstruct the population dynamics, survival, and fecundity of wild An. funestus populations in southern Tanzania, (2) quantify impacts of density dependence on the dynamics, and (3) assess seasonal fluctuations in An. funestus demography. Through quantifying the population dynamics of An. funestus, this model will enable analysis of how their stability and response to interventions may differ from that of An. gambiae sensu lato.MethodsA Bayesian State Space Model (SSM) based on mosquito life history was fit to time series data on the abundance of female An. funestus sensu stricto collected over 2 years in southern Tanzania. Prior values of fitness and demography were incorporated from empirical data on larval development, adult survival and fecundity from laboratory-reared first generation progeny of wild caught An. funestus. The model was structured to allow larval and adult fitness traits to vary seasonally in response to environmental covariates (i.e. temperature and rainfall), and for density dependency in larvae. The effects of density dependence and seasonality were measured through counterfactual examination of model fit with or without these covariates.ResultsThe model accurately reconstructed the seasonal population dynamics of An. funestus and generated biologically-plausible values of their survival larval, development and fecundity in the wild. This model suggests that An. funestus survival and fecundity annual pattern was highly variable across the year, but did not show consistent seasonal trends either rainfall or temperature. While the model fit was somewhat improved by inclusion of density dependence, this was a relatively minor effect and suggests that this process is not as important for An. funestus as it is for An. gambiae populations.ConclusionThe model's ability to accurately reconstruct the dynamics and demography of An. funestus could potentially be useful in simulating the response of these populations to vector control techniques deployed separately or in combination. The observed and simulated dynamics also suggests that An. funestus could be playing a role in year-round malaria transmission, with any apparent seasonality attributed to other vector species.

Dispersal and life history of brown widow spiders in dated invasive populations on two continents

Theory and empirical work suggest that behaviours such as dispersal and exploration are predictors of invasive success, and that behaviours may shift predictably after invasive populations have established and spread. However, there are limited data on temporal patterns in the distribution of behavioural traits linked to the timeline of establishment of invasive species. We examined dispersal and exploration, along with life history traits that may be linked to behaviour, across multiple invasive populations of the brown widow spider, Latrodectus geometricus. This global invader has established populations across the United States and Israel. Using this temporal and spatial variation, we tested predictions about changes in suites of traits over establishment time. We compared trait distributions of four U.S. populations of L. geometricus to patterns in four populations in Israel. We predicted that selective filters during the invasion process would result in more dispersive, more exploratory spiders that are larger and more fecund in recently established populations, but, if trade-offs occur, dispersal would be favoured at the expense of fecundity and size in recent populations. We found more frequent and faster dispersal in more recently established populations in Israel, but not the United States. Spiders in more recently established populations in Israel were larger than those in older populations, but there were no consistent patterns across U.S. populations. However, there was evidence in both the U.S. and Israel for differing trade-offs among fecundity, dispersal and size. In more recently established populations, spiders were more variable in resource allocation to eggsacs. The results suggest that in some populations, trade-offs underlying dispersal, fecundity and body size are shaped by the time interval, and thus the number of generations, since establishment, with implications for the role of evolutionary processes in invasion success.