Population Regulation Research Articles

Assessing soil functioning: What is the added value of soil organic carbon quality measurements alongside total organic carbon content?

Soil organic carbon (SOC) content is the most widely used soil health indicator, but many soil functions are also influenced by the quality of SOC. Yet, standardized SOC quality parameters that can be used in soil health assessments in addition to SOC content are still in development. Here, we investigated the relationships between various SOC parameters (both quantity and quality) and soil functions.We collected 223 soil samples from arable fields in two contrasting Dutch soil types i.e., marine clay and sand. For each sample, we assessed three soil functions (i.e., biological population regulation, element cycling, and soil structure and water regulation) by measuring five indicators per function. We also analyzed SOC quality with four techniques (C:N-ratio, POX-C, Rock-Eval, POM-MAOM fractionation), resulting in 21 SOC quality parameters, and measured SOC content. We then determined for each soil type how much variation in each function indicator was explained by the SOC parameters and other measured intrinsic soil properties.We found that SOC parameters and intrinsic soil properties explained at most 30 ± 22% of the variation in soil function indicators. SOC content explained 9 ± 16% of the variation across functions and soil types. Including one single SOC quality parameter alongside SOC content never had significant added value in explaining soil functions. Only including multiple Rock-Eval parameters alongside SOC content significantly increased the explained variation compared to SOC content alone, as well as combining multiple parameters from the four different SOC quality techniques.We conclude that the relationships between the SOC quality parameters and soil functions are insufficiently straight-forward to add significant explanatory power to SOC content alone. We recommend that before including SOC quality parameters in soil health monitoring, more emphasis should be put on evaluating their relation to soil functions and their potential redundancy when used alongside SOC content.

Modelling decisions and density dependence in monarch butterflies: A comment on Meehan and Crossley (2023)

Abstract Decisions about which processes to include in a population model can have substantial impact on estimates of population trends and extinction risk. This is particularly important for species of conservation concern, whose conservation status is decided in part on the basis of these models. In their recent paper, Meehan and Crossley (2023) Insect Conservation and Diversity, 16, 566–573 revisit a time series of overwintering monarch butterfly abundances, which previous assessments had characterised as rapidly declining and at risk of extinction. The authors, in contrast, reported no evidence for declines in the past 10 years and characterised extinction risk as low. A primary reason for the difference between these conclusions was that Meehan and Crossley used a more complex model that included a parameter for density dependence. While negative density dependence may play a role in monarch population regulation, there are a variety of unresolved issues with how and if density dependence should be included in models of monarch populations, including widely known issues with separating observation error from density dependence in noisy time series and taxon‐specific issues with fitting models to data surveyed every fourth generation and pooled at continental scales. These issues make the conclusions of Meehan and Crossley about monarch population viability much less robust than implied in their article. They do not provide convincing evidence that density dependence reduces extinction risk in monarch butterflies. Our commentary supports their general conclusion that population viability projections depend on model assumptions, but the ways in which monarch butterfly populations are regulated remains an open question.

Urea regulates soil nematode population by enhancing the nematode-trapping ability of nematode-trapping fungi

As the most abundant animal in the soil, nematodes are directly or indirectly involved in almost all soil ecological processes. Studying soil nematode population regulation is essential to understanding soil ecological processes. This study found urea combines nematode-trapping fungi to regulate the population of soil nematodes. In soil, compared with no urea, adding 0.2 mg/mL urea after applying Arthrobotrys oligospora and Dactylellina ellipsospora reduced the number of nematodes by 34.7% and 31.7%. Further, the mechanism of urea couple nematode-trapping fungi to regulate the nematode population was explored in the medium environment. The results showed that the addition of 0.2 mg/ml urea accelerated the trap formation of A. oligospora and D. ellipsosporas by 50% and 46.5%, and increased the yield of traps of A. oligospora and D. ellipsosporas by 39.5% and 40.6%, thus, the predatory efficiency of A. oligospora and D. ellipsospora on nematodes was increased by 34.2% and 32.7%. In conclusion, urea regulates the predation ability of A. oligospora and D. ellipsosporas to regulate the soil nematode population. This study deepens the understanding of the regulatory pathways of the soil nematodes but also provides a potential new strategy for harmful nematode bio-control.

White-tailed deer population dynamics in a multipredator landscape shaped by humans.

Large terrestrial mammals increasingly rely on human-modified landscapes as anthropogenic footprints expand. Land management activities such as timber harvest, agriculture, and roads can influence prey population dynamics by altering forage resources and predation risk via changes in habitat, but these effects are not well understood in regions with diverse and changing predator guilds. In northeastern Washington state, USA, white-tailed deer (Odocoileus virginianus) are vulnerable to multiple carnivores, including recently returned gray wolves (Canis lupus), within a highly human-modified landscape. To understand the factors governing predator-prey dynamics in a human context, we radio-collared 280 white-tailed deer, 33 bobcats (Lynx rufus), 50 cougars (Puma concolor), 28 coyotes (C. latrans), and 14 wolves between 2016 and 2021. We first estimated deer vital rates and used a stage-structured matrix model to estimate their population growth rate. During the study, we observed a stable to declining deer population (lambda = 0.97, 95% confidence interval: 0.88, 1.05), with 74% of Monte Carlo simulations indicating population decrease and 26% of simulations indicating population increase. We then fit Cox proportional hazard models to evaluate how predator exposure, use of human-modified landscapes, and winter severity influenced deer survival and used these relationships to evaluate impacts on overall population growth. We found that the population growth rate was dually influenced by a negative direct effect of apex predators and a positive effect of timber harvest and agricultural areas. Cougars had a stronger effect on deer population dynamics than wolves, and mesopredators had little influence on the deer population growth rate. Areas of recent timber harvest had 55% more forage biomass than older forests, but horizontal visibility did not differ, suggesting that timber harvest did not influence predation risk. Although proximity to roads did not affect the overall population growth rate, vehicle collisions caused a substantial proportion of deer mortalities, and reducing these collisions could be a win-win for deer and humans. The influence of apex predators and forage indicates a dual limitation by top-down and bottom-up factors in this highly human-modified system, suggesting that a reduction in apex predators would intensify density-dependent regulation of the deer population owing to limited forage availability.

Population regulation and limitation-insights from lemming cycles: past, present and future.

Population regulation and limitation-insights from lemming cycles: past, present and future.

Dynamics of Indonesia's Population Regulation in the Child Identity Card Policy

Dynamics of Indonesia's Population Regulation in the Child Identity Card Policy

Ribosomal dormancy at the nexus of ribosome homeostasis and protein synthesis.

Dormancy or hibernation is a non-proliferative state of cells with low metabolic activity and gene expression. Dormant cells sequester ribosomes in a translationally inactive state, called dormant/hibernating ribosomes. These dormant ribosomes are important for the preservation of ribosomes and translation shut-off. While recent studies attempted to elucidate their modes of formation, the regulation and roles of the diverse dormant ribosomal populations are still largely understudied. The mechanistic details of the formation of dormant ribosomes in stress and especially their disassembly during recovery remain elusive. In this review, we discuss the roles of dormant ribosomes and their potential regulatory mechanisms. Furthermore, we highlight the paradigms that need to be answered in the field of ribosomal dormancy.

Genome-wide association study reveals candidate genes critical for skin pigmentation in common carp (Cyprinus carpio) strains including koi

The differentiation and variation of body color in fish is an important component of biological evolution and phylogenetic research, and is influenced by several factors such as heredity, nutrition, physiological hormones and rearing conditions, with heredity being the most critical factor. An improved comprehension of the genetic regulation in different carp populations will facilitate future applications of precision breeding and pigment cell development-related genes editing. In this study, we used restriction site-associated DNA sequencing (2d-RAD) to determine the distribution characteristics of single nucleotide polymorphisms (SNPs) in eight common carp strains including six koi strains, i.e., Kohaku (Hb), Taisho (Dz), Showa (Zh), Golden (Hj), Matsukawabake (Sch) and Five-color (Ws), and two genetically improved breeding strains, i.e., FFRC No. 2 strain (Fr) and red FFRC strain (Hfr), and then SNP markers to resolve genetic information on the population structure and skin color formation of these strains. We found that most individuals of eight strains were clearly divided into eight clades. Genetic diversity within Fr, Sch and Ws is relatively high, while it is low within Dz, Hb and Hfr. A comparison between the populations revealed that Hfr and Ws have the highest degree of genetic differences, while Hb and Dz have the lowest. The GWAS analysis for two strategies identified several SNPs that are significantly related to skin color variation and affect melanin synthesis (ephrinb2, slc22a23, herc2, ephb2), carotenoid metabolism (oca2, bcmo1, bco2) and circadian rhythm(cipc). To summarize, our study provides some information on the genetic structure and diversity of Japanese koi and Chinese FFRC carp. Furthermore, based on the data obtained on relevant genes related to skin color differentiation and pigmentation, it can provide a theoretical basis for the subsequent integration of dominant traits and precision breeding in carps.

Do wolves control their own numbers? Understanding and updating the long debate

The population dynamics of animals involve a complex interplay between intrinsic and extrinsic factors. Intrinsic regulation, characterized as population self‐regulation, encompasses mechanisms that moderate growth rates before reaching maximum food‐dependent densities. Conversely, extrinsically regulated populations are constrained by environmental variables such as food availability, predation, and disease. What regulates wolf populations has been debated for decades, with most publications concluding that wolves are extrinsically regulated, despite evidence of intrinsic mechanisms. This paper summarizes one perspective from a debate at the 'Wolves Across Borders' conference in Stockholm, Sweden in May 2023. Since this paper is a summary of a public debate, the paper is neither a review nor research paper, rather a research history and a recommendation on how the long‐term disagreement might be resolved. Wolf population regulation is likely an interplay between both intrinsic and extrinsic factors which is best studied longitudinally by monitoring one population through time.

Effects of Heavy Alcohol Use on Fasting Glucose and Insulin Resistance in Mid-Life Adults

Introduction: As our population ages, type 2 diabetes has become more prevalent in the United States and one in five mid-life adults (50-64 years) have type 2 diabetes. Unhealthy and heavy alcohol use (that exceeds recommended drinking limits) causes dysfunction of the liver and pancreas that can impact glucose control and thereby increase risks of type 2 diabetes. In young adults, we previously found that fasting glucose and insulin resistance were not associated with heavy alcohol use. However, it remains unclear if heavy alcohol use contributes to the development of type 2 diabetes in an aged population. Therefore, the purpose of this study is to determine the effect of heavy alcohol use on fasting glucose and insulin resistance in apparently healthy mid-life adults. Methods: Mid-life men (n=21) and postmenopausal women (n=28), non-smokers, free of obesity and major clinical diseases, were recruited from the community around the Dallas—Fort Worth metroplex. All participants underwent physical exam and fasting blood sampling. Alcohol use was assessed by the US Alcohol Use Disorders Identification Test (USAUDIT) and a dried blood spot phosphatidylethanol (PEth) test. A PEth cutoff of 20 ng/mL was used to define heavy drinkers. Insulin resistance was assessed by calculating HOMA-IR (Homeostatic model assessment for insulin resistance) as insulin (μU/L) x glucose (nmol/L)/22.5. Results: A total of 24 participants had PEth levels of <20 ng/mL (non-heavy drinkers; PEth ranged from <limit of quantification to 13 ng/mL; mean ± SEM for age: 58±1 years and body mass index: 25.2±0.6 kg/m2) and the other 25 participants had PEth levels ≥20 ng/mL (heavy drinkers; PEth ranged from 20 to 665 ng/mL; age: 57±1 years and body mass index: 25.7±0.5 kg/m2). Heavy drinkers had higher USAUDIT scores than non-heavy drinkers (11.3±1.4 vs. 3.3±0.5, p<0.001). No significant difference between these two groups were found in lipid values (P≥0.1) as well as renal (P≥0.3) and liver function values (P≥0.08). Compared to non-heavy drinkers, heavy drinkers had a higher level of fasting blood glucose (96±2 vs. 91±1 mg/dL, P=0.02), but similar blood insulin (9.2±2.5 vs. 5.5±0.5 μIU/L, P=0.2) and HOMA-IR (2.23±0.64 vs. 1.23±0.11, P=0.1). The results for stepwise linear regression model indicate that only USAUDIT score was an independent factor of fasting glucose (B=0.59, p<0.001). Conclusion: Our results indicate that compared to mid-life adult non-heavy drinkers, heavy drinkers had higher fasting blood glucose levels, despite similar renal and liver function. Our results also indicate that higher risks of alcohol use disorder were associated with higher levels of fasting glucose. These data suggest that heavy alcohol use may have negative effects on glucose regulation in aged populations and increase risks of type 2 diabetes. This work was supported by NIAAA AA028537 to CLH. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Deciphering visceral adipose tissue regulatory T cells: Key contributors to metabolic health.

Regulatory T cells (Tregs) within the visceral adipose tissue (VAT) play a crucial role in controlling tissue inflammation and maintaining metabolic health. VAT Tregs display a unique transcriptional profile and T cell receptor (TCR) repertoire, and closely interact with adipocytes, stromal cells, and other immune components within the local VAT microenvironment. However, in the context of obesity, there is a notable decline in VAT Tregs, resulting in heightened VAT inflammation and insulin resistance. A comprehensive understanding of the biology of VAT Tregs is essential for the development of Treg-based therapies for mitigating obesity-associated metabolic diseases. Recent advancements in lineage tracing tools, genetic mouse models, and various single cell "omics" techniques have significantly progressed our understandings of the origin, differentiation, and regulation of this unique VAT Treg population at steady state and during obesity. The identification of VAT-Treg precursor cells in the secondary lymphoid organs has also provided important insights into the timing, location, and mechanisms through which VAT Tregs acquire their distinctive phenotype that enables them to function within a lipid-rich microenvironment. In this review, we highlight key recent breakthroughs in the VAT-Treg field while discussing pivotal questions that remain unanswered.

Redefining 'state-of-the-art' for integrated population models with immigration.

Research Highlight: Christian, M., Oosthuizen, W. C., Bester, M. N., & de Bruyn, P. N. (2024). Robustly estimating the demographic contribution of immigration: Simulation, sensitivity analysis and seals. Journal of Animal Ecology. https://doi.org/10.1111/1365-2656.14053. Immigration can have profound consequences for local population dynamics and demography, but collecting data to accurately quantifying it is challenging. The recent rise of integrated population models (IPMs) offers an alternative by making it possible to estimate immigration without the need for explicit data, and to quantify its contribution to population dynamics through transient Life Table Response Experiments (tLTREs). Simulation studies have, however, highlighted that this approach can be prone to bias and overestimation. In their new study, Christian etal. address one of the root causes of this issue by improving the estimation of time variation in vital rates and immigration using Gaussian processes in lieu of traditionally used temporal random effects. They demonstrate that IPM-tLTRE frameworks with Gaussian processes produce more accurate and less biased estimates of immigration and its contribution to population dynamics and illustrate the applicability of this approach using a long-term data set on elephant seals (Mirounga leonida). Results are validated with a simulation study and suggest that immigration of breeding females has been central for population recovery of elephant seals despite the species' high female site fidelity. Christian etal. thus present new insights into population regulation of long-lived marine mammals and highlight the potential for using Gaussian process priors in IPMs. They also illustrate a suite of 'best practices' for state-of-the-art IPM-tLTRE analyses and provide an inspirational example for the kind of ecological modelling workflow that can be invaluable not just as a starting point for fellow ecologists picking up or improving their own IPM-tLTRE analyses, but also for teaching and in contexts where model estimates are used for informing management and conservation decision-making.

Adverse childhood experiences and insecure attachment: The indirect effects of dissociation and emotion regulation difficulties.

Difficulties with dissociation and emotion regulation are well-documented reactions to early adverse childhood experiences (ACEs). Although findings identify dissociation and emotion dysregulation as explaining the relationship between various forms of ACEs and adult psychopathology, less is known about their combined effect in the relationship between ACEs and insecure attachment in adulthood. This study examined the indirect effects of dissociation and emotion regulation difficulties in the relationship between early adverse experiences and insecure attachment traits. Participants (N = 260) completed an online questionnaire measuring ACEs, dissociation, emotion regulation difficulties, and anxious and avoidant attachment. Results indicated that, after controlling for mental health treatment, dissociation and emotion regulation difficulties explained the relationship between ACEs and insecure (anxious and avoidant) attachment. Emotion regulation difficulties were not a significant predictor of avoidant attachment. Findings provide support for greater research on mediating factors in the maintenance of insecure attachment across development and potential implications of dissociation and emotion regulation in clinical and nonclinical populations. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Long-term in vivo three-photon imaging reveals region-specific differences in healthy and regenerative oligodendrogenesis.

The generation of new myelin-forming oligodendrocytes in the adult central nervous system is critical for cognitive function and regeneration following injury. Oligodendrogenesis varies between gray and white matter regions, suggesting that local cues drive regional differences in myelination and the capacity for regeneration. However, the layer- and region-specific regulation of oligodendrocyte populations is unclear due to the inability to monitor deep brain structures in vivo. Here we harnessed the superior imaging depth of three-photon microscopy to permit long-term, longitudinal in vivo three-photon imaging of the entire cortical column and subcortical white matter in adult mice. We find that cortical oligodendrocyte populations expand at a higher rate in the adult brain than those of the white matter. Following demyelination, oligodendrocyte replacement is enhanced in the white matter, while the deep cortical layers show deficits in regenerative oligodendrogenesis and the restoration of transcriptional heterogeneity. Together, our findings demonstrate that regional microenvironments regulate oligodendrocyte population dynamics and heterogeneity in the healthy and diseased brain.

Bottom-up population regulation of Orthotomicus erosus on irrigated and fertilized Pinus eldarica: A comprehensive field study

The Mediterranean pine engraver, Orthotomicus erosus (Wollaston), is a destructive pest that has caused a significant threat to planted pine forests worldwide through feeding on phloem, disrupting sap flow and transmitting phytopathogens. This study investigated the bottom-up effects of different irrigation and fertilization treatments on the mean numbers of O. erosus immature stages (egg, larva and pupa) and adults in the pine forest of western Tehran, Iran. A total of 72 Pinus eldarica Medw. trees were selected in Chitgar Forest Park. The experiment was arranged as a split plot in a randomized complete block design with three replications. The irrigation treatments included non-irrigation, low-irrigation (30 liters of water per month) and high-irrigation (30 liters of water per two weeks) were assigned to main plots. Moreover, fertilizers of nitrogen 100 kg/ha, superphosphate 100 kg/ha and potassium sulfate 65 kg/ha were applied in subplots. Then, the total number of O. erosus life stages was counted under the bark samples (two 10 × 10 cm bark samples) separated from the pine trees. Results showed that irrigation and fertilization significantly affected the mean number of O. erosus from egg to adult stages. Irrigation had a more pronounced effect on the pest population than fertilization. The highest number of different life stages occurred in non-irrigated pines regardless of fertilization. Moreover, fertilizer effects were influenced by irrigation, where high irrigation negatively affected superphosphate + potassium sulfate fertilized pines and significantly increased the mean numbers of different O. erosus life stages compared to low-irrigation treatment. The lowest mean number of egg (11.95 ± 0.17), larva (8.62 ± 0.21), pupa (10.38 ± 0.13) and adult (9.04 ± 0.23) per bark samples occurred in superphosphate + potassium sulfate at low-irrigation plots. Interestingly, nitrogen fertilization increased pest density compared to unfertilized trees. Furthermore, despite the low mean number of different O. erosus life stages in superphosphate + potassium sulfate treatments, the nitrogen combination increased the pest density in both low and high-irrigation plots. These findings highlighted the importance of considering the interaction between irrigation and fertilizer types in the integrated pest management program for O. erosus.

Obese visceral adipose dendritic cells downregulate regulatory T cell development through IL-33.

Regulatory T cells (Tregs) residing in visceral adipose tissue (VAT) play a pivotal role in regulating tissue inflammation and metabolic dysfunction associated with obesity. However, the specific phenotypic and functional characteristics of Tregs in obese VAT, as well as the regulatory mechanisms shaping them, remain elusive. This study demonstrates that obesity selectively reduces Tregs in VAT, characterized by restrained proliferation, heightened PD-1 expression, and diminished ST2 expression. Additionally, obese VAT displays distinctive maturation of dendritic cells (DCs), marked by elevated expressions of MHC-II, CD86, and PD-L1, which are inversely correlated with VAT Tregs. In an in vitro co-culture experiment, only obese VAT DCs, not macrophages or DCs from subcutaneous adipose tissue (SAT) and spleen, result in decreased Treg differentiation and proliferation. Furthermore, Tregs differentiated by obese VAT DCs exhibit distinct characteristics resembling those of Tregs in obese VAT, such as reduced ST2 and IL-10 expression. Mechanistically, obesity lowers IL-33 production in VAT DCs, contributing to the diminished Treg differentiation. These findings collectively underscore the critical role of VAT DCs in modulating Treg generation and shaping Treg phenotype and function during obesity, potentially contributing to the regulation of VAT Treg populations.

Transcriptomic and proteomic profiles of fetal versus adult mesenchymal stromal cells and mesenchymal stromal cell-derived extracellular vesicles

BackgroundMesenchymal stem/stromal cells (MSCs) can regenerate tissues through engraftment and differentiation but also via paracrine signalling via extracellular vesicles (EVs). Fetal-derived MSCs (fMSCs) have been shown, both in vitro and in animal studies, to be more efficient than adult MSC (aMSCs) in generating bone and muscle but the underlying reason for this difference has not yet been clearly elucidated. In this study, we aimed to systematically investigate the differences between fetal and adult MSCs and MSC-derived EVs at the phenotypic, RNA, and protein levels.MethodsWe carried out a detailed and comparative characterization of culture-expanded fetal liver derived MSCs (fMSCs) and adult bone marrow derived MSCs (aMSCs) phenotypically, and the MSCs and MSC-derived EVs were analysed using transcriptomics and proteomics approaches with RNA Sequencing and Mass Spectrometry.ResultsFetal MSCs were smaller, exhibited increased proliferation and colony-forming capacity, delayed onset of senescence, and demonstrated superior osteoblast differentiation capability compared to their adult counterparts. Gene Ontology analysis revealed that fMSCs displayed upregulated gene sets such as “Positive regulation of stem cell populations”, “Maintenance of stemness” and “Muscle cell development/contraction/Myogenesis” in comparison to aMSCs. Conversely, aMSCs displayed upregulated gene sets such as “Complement cascade”, “Adipogenesis”, “Extracellular matrix glycoproteins” and “Cellular metabolism”, and on the protein level, “Epithelial cell differentiation” pathways. Signalling entropy analysis suggested that fMSCs exhibit higher signalling promiscuity and hence, higher potency than aMSCs. Gene ontology comparisons revealed that fetal MSC-derived EVs (fEVs) were enriched for “Collagen fibril organization”, “Protein folding”, and “Response to transforming growth factor beta” compared to adult MSC-derived EVs (aEVs), whereas no significant difference in protein expression in aEVs compared to fEVs could be detected.ConclusionsThis study provides detailed and systematic insight into the differences between fMSCs and aMSCs, and MSC-derived EVs. The key finding across phenotypic, transcriptomic and proteomic levels is that fMSCs exhibit higher potency than aMSCs, meaning they are in a more undifferentiated state. Additionally, fMSCs and fMSC-derived EVs may possess greater bone forming capacity compared to aMSCs. Therefore, using fMSCs may lead to better treatment efficacy, especially in musculoskeletal diseases.

A Systematic Review of Population Monitoring Studies of Sea Turtles and Its Application to Conservation

Sea turtles are keystone species in marine environments due to their essential role as seagrass grazers and population regulation of jellyfish and sponges in coral reefs. However, due to their predominant presence in coastal areas, sea turtle populations face significant threats due to the impact of human activities. In this systematic review, 655 peer-reviewed publications were analyzed to assess the extent of population monitoring for all seven sea turtle species. The analyses revealed that, although population monitoring studies have increased for sea turtles in the past four decades, these have been biased towards certain species and oceanic regions. Furthermore, sea turtle population monitoring has been undertaken primarily using field-based methods, with satellite tracking and nest surveys being the most commonly used methods; however, the implementation of genetic methods for population monitoring has increased since the 2000s. Direct conservation recommendations from this study include the urgent need to establish population monitoring studies in the Critically Endangered Kemp’s ridley and hawksbill and the Data Deficient flatback. Furthermore, population monitoring programs should be implemented in Southeast Asia and Northern and Central Africa, where knowledge on sea turtle populations is still limited. Finally, due to the long-distance movements of sea turtles, we also advocate for international cooperation and collaboration of local communities to protect these ecologically important and iconic marine species.

Post-settlement dynamics of Japanese flounder Paralichthys olivaceus in Tango Bay: Seasonal patterns in growth, mortality, and recruitment potential.

Japanese flounder Paralichthys olivaceus is one of the most valuable coastal flatfish species in East Asia. To investigate post-settlement growth and mortality, juveniles were sampled in Tango Bay (Japan) weekly throughout the settlement period in 2007 and 2008. Otolith (lapillus) microstructure analysis enabled the categorization of juveniles into six biweekly cohorts each year. Later cohorts exhibited higher growth rates possibly because of higher water temperatures. A key observation was the direct relationship between high mortality and high density in mid-season cohorts in both years, pointing to density-dependent mortality. This increased mortality may be attributed to predation, including cannibalism by earlier cohorts. Furthermore, growth-selective mortality was evident soon after settlement, underscoring the vulnerability of slow growers to predation during the early juvenile stage. Although earlier and later cohorts were less abundant but showed promising recruitment potential, the prospective contribution of mid-season cohorts to the adult population remained uncertain. The results clearly highlight the importance of density-dependent mortality in population regulation in post-settlement Japanese flounder.

Density‐dependence and competition between Tranosema rostrale and Elachertus cacoeciae, two parasitoids of the spruce budworm

AbstractCompetition between parasitoids for available hosts is common in insects. These interactions are often negative and are believed to reduce the overall impact of top‐down population regulation. In the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae), two parasitoid species are very common and often interact during the period of low‐density populations between outbreaks: the koinobiont endoparasitoid Tranosema rostrale (Brishke) (Hymenoptera: Ichneumonidae) and the idiobiont ectoparasitoid Elachertus cacoeciae (Howard) (Hymenoptera: Eulophidae). Data collected from field‐implanted larvae of spruce budworm exposed in summer during a 35‐year period between 1987 and 2022 were used to estimate the response of these two parasitoids to the density of their spruce budworm host, and the nature and importance of competitive interactions between them. It was found that both parasitoids are most effective at very low host population density, and that a strong, density‐dependent, and negative correlation of frequencies exists between them. This negative correlation is evident both among and within years and indicates that the parasitoids have developed seasonal history and host choice behaviors that tend to minimize the negative impact of direct competition on their respective performance. It appears that the koinobiont T. rostrale manages, through those adaptive strategies, to avoid direct competition inside a larval host with the competitively superior idiobiont E. cacoeciae.