Population Dynamics Of Species Research Articles

Diet quality and conspecific larval density predict functional trait variation and performance in a polyphagous frugivorous fly

AbstractDiet quality and the presence and abundance of conspecifics feeding on the same food resource are critical factors that affect functional traits of many animal species and influence ecological processes.We hypothesized that in insects whose larvae live in groups of varying sizes in ephemeral and nutritionally variable environments, extreme macronutrient content in the feeding substrate is a barrier for optimal performance that can be overcome by the collective feeding behaviour of large numbers of larvae.We experimentally examined how multiple immature and adult traits of the polyphagous tephritid fruit fly,Anastrepha ludens, vary as a function of the quality of its larval diet (protein + carbohydrate [P + C] content of 8.0%–12.6% w/w, and protein‐to‐carbohydrate [P/C] ratio of 1.8–0.11) across extreme levels of conspecific larval densities (60–600 larvae/60 g of diet).Overall, we found positive effects on survival of immature and adult stages, the duration of the larval stage, pupal weight and adult emergence of flies, as dietary P + C content increased, followed by negative effects when the diet had extremely high carbohydrate‐biased macronutrient content. Larval density had positive, negative and curvilinear effects depending on the macronutrient composition of the food, resulting in a range of fly responses through a continuous scale of macronutrient content and larval density combinations. Optimal performance ofA.ludens, in terms of larval development time, body weight and survival to adulthood, was found when the diet consisted of low P + C content and high P/C ratios, and low larval densities.Our findings point to a diet‐mediated relationship between density and survival to the adult stage, suggesting that large numbers (up to a point) of larvae can balance negative effects of conspecific competition when food is characterised by high macronutrient content and low P/C ratios. We conclude that diet quality and conspecific density interact in complex ways to shape trait expression and performance in a frugivorous fly. Addressing this interaction is key to advance the understanding of the mechanisms behind changes in population dynamics in insect species living in groups confined in isolated and ephemeral resources.Read the freePlain Language Summaryfor this article on the Journal blog.

Morphological and molecular identification reveals a high diversity of Anopheles species in the forest region of the Cambodia\u2013Laos border

BackgroundTo develop an effective malaria vector intervention method in forested international border regions within the Greater Mekong Subregion (GMS), more in-depth studies should be conducted on local Anopheles species composition and bionomic features. There is a paucity of comprehensive surveys of biodiversity integrating morphological and molecular species identification conducted within the border of Laos and Cambodia.MethodsA total of 2394 adult mosquitoes were trapped in the Cambodia–Laos border region. We first performed morphological identification of Anopheles mosquitoes and subsequently performed molecular identification using 412 recombinant DNA–internal transcribed spacer 2 (rDNA-ITS2) and 391 mitochondrial DNA–cytochrome c oxidase subunit 2 (mtDNA-COII) sequences. The molecular and morphological identification results were compared, and phylogenetic analysis of rDNA-ITS2 and mtDNA-COII was conducted for the sequence divergence among species.ResultsThirteen distinct species of Anopheles were molecularly identified in a 26,415 km2 border region in Siem Pang (Cambodia) and Pathoomphone (Laos). According to the comparisons of morphological and molecular identity, the interpretation of local species composition for dominant species in the Cambodia–Laos border (An. dirus, An. maculatus, An. philippinensis, An. kochi and An. sinensis) achieved the highest accuracy of morphological identification, from 98.37 to 100%. In contrast, the other species which were molecularly identified were less frequently identified correctly (0–58.3%) by morphological methods. The average rDNA-ITS2 and mtDNA-COII interspecific divergence was respectively 318 times and 15 times higher than their average intraspecific divergence. The barcoding gap ranged from 0.042 to 0.193 for rDNA-ITS2, and from 0.033 to 0.047 for mtDNA-COII.ConclusionsThe Cambodia–Laos border hosts a high diversity of Anopheles species. The morphological identification of Anopheles species provides higher accuracy for dominant species than for other species. Molecular methods combined with morphological analysis to determine species composition, population dynamics and bionomic characteristics can facilitate a better understanding of the factors driving malaria transmission and the effects of interventions, and can aid in achieving the goal of eliminating malaria.Graphical

Variation in population dynamics and abundance of the bigeye croaker Micropogonias megalops in the Northern Gulf of California

The bigeye croaker Micropogonias megalops is an endemic Sciaenidae fish species of the Gulf of California. Although it is a stock that has been exploited for nearly three decades, its biological and fishery information has been limited over time. Therefore, its recent and current population status is poorly known. This study analyzed biological and fishery data for M. megalops in the Northern Gulf of California for the period 1995–2020. Variation of species population dynamics has been analyzed for years with biological information (2000, 2010, and 2020), finding points in time with relative decreases and increases in growth and natural mortality values. An interannual abundance analysis was performed, obtaining biological reference points for the resource through two surplus production models, the Monte Carlo (CMSY+) and the Bayesian state–space Schaefer surplus production model (BSM) methods. The results for management (based on the BSM analysis) indicated that the currently relative stock biomass level is at 79% of virgin biomass (k), which means a recovery compared to the 2017 biomass level (64% k) that has been the lowest in this fishery history. According to the Kobe phase plot, the resource has been harvested in a healthy way, showing a maximum sustainable yield of 8 248.52 t and current status of sub-exploited.

Five decades (1972-2020) of zooplankton monitoring in the upper San Francisco Estuary.

We present the longest available dataset (by 15 years) of estuarine zooplankton abundance worldwide. Zooplankton have been monitored throughout the upper San Francisco Estuary from 1972 -present due to its status as a central hub of California water delivery and home to commercially important and endangered fishes. We integrated data from five monitoring programs, including over 300 locations, three size-classes of zooplankton targeted with different gears, over 80,000 samples, and over two billion sampled organisms. Over the duration of this dataset, species invasions have driven community turnover, periodic droughts have occurred, and important fishes have declined, likely due in part to reduced food supply from zooplankton. Data from the individual surveys have been used in prior studies on issues related to species invasions, flows, fish diets and population dynamics, zooplankton population dynamics, and community ecology. Our integrated dataset offers unparalleled spatio-temporal scope to address these and other fundamental ecological questions.

Prescriptions for the Control of a Clonal Invasive Species Using Demographic Models.

Until recently, little research has focused on determination of the population dynamics of invasive species and evaluating their genetic variation. Consequently, not much is known of what drives clonal invasive species and their demography. Here, we describe the population dynamics of Kalanchoe delagoensis (Crassulaceae), considered invasive to several countries. We quantified the demography of a population in central Mexico using integral projection models (IPM) in a population that reproduced asexually exclusively through plantlets. The effect of clonal recruitment on population growth rate () was evaluated by changing plantlet survival and simulating management scenarios that used previous data of watering and seven experimental herbicide treatments. The finite rate of population increase indicated that this Kalanchoe delagoensis population is growing (above one) and with water availability, growth rates will only accelerate. The IPM showed that plantlet survival and recruitment were the most critical steps in the cycle for the population, and simulations of different management scenarios showed that reducing plantlet survival significantly decreased only in two out of the seven herbicides used.

Local population collapse of Ross's and lesser snow geese driven by failing recruitment and diminished philopatry

Dynamics of free‐ranging animal populations can result from complex interplays of survival, recruitment and movement. Yet incomplete understanding of demography impedes conservation strategies intended to modify population dynamics of focal species. We estimated survival and per capita production of young, as well as emigration and immigration, from 1997 to 2017 in Ross's goose Anser rossii and lesser snow goose Anser caerulescens caerulescens, which are sympatric species of migratory birds that nest in the central Canadian Arctic at one of the largest breeding colonies in North America. We formed age‐structured integrated population models (IPMs) for each species that jointly analyzed live and dead encounter data as well as breeding adult population size and fecundity data to understand drivers of population dynamics. We compared the demography between species because both species increased during the 1990s and early 2000s yet thereafter snow geese declined, while Ross's geese continued to increase, then stabilized and similarly declined. Declines in Ross's and snow goose populations were caused by reduced per capita production of young, and juvenile survival, as well as increased adult and juvenile emigration. Stronger declines in juvenile survival in snow geese explain their earlier population decline compared to Ross's geese. Despite the divergence in population trends in Ross's and snow geese, we found strong synchrony in demographic rates which suggested substantial emigration from this colony and similar responses to environmental conditions. Direct estimation of demographic patterns in the IPM framework permitted hypothesis testing and inference about the role of immigration, even though immigrant sources were unsampled. We provide a novel m‐array implementation specific to a multi‐state Burnham model which greatly improved computational efficiency and convergence of posterior estimates. Our findings are an important reminder of the role that permanent movements can play in animal demography and metapopulation structure.

Low heritability and high phenotypic plasticity of salivary cortisol in response to environmental heterogeneity in a wild pinniped.

Individuals are unique in how they interact with and respond to their environment. Correspondingly, unpredictable challenges or environmental stressors often produce an individualized response of the hypothalamic‐pituitary‐adrenal (HPA) axis and its downstream effector cortisol. We used a fully crossed, repeated measures design to investigate the factors shaping individual variation in baseline cortisol in Antarctic fur seal pups and their mothers. Saliva samples were collected from focal individuals at two breeding colonies, one with low and the other with high density, during two consecutive years of contrasting food availability. Mothers and pups were sampled concurrently at birth and shortly before weaning, while pups were additionally sampled every 20 days. We found that heritability was low for baseline cortisol, while within‐individual repeatability and among‐individual variability were high. A substantial proportion of the variation in baseline cortisol could be explained in pups and mothers by a combination of intrinsic and extrinsic factors including sex, weight, day, season, and colony of birth. Our findings provide detailed insights into the individualization of endocrine phenotypes and their genetic and environmental drivers in a wild pinniped. Furthermore, the strong associations between cortisol and life history traits that we report in fur seals could have important implications for understanding the population dynamics of species impacted by environmental change.

Joint Effects of Dispersal and Trophic Interactions on the Biodiversity of Species

Local dispersal and trophic interactions are thought to have important influences on species range limits (i.e., the boundaries of locations where species is found) across geographical regions. To better understand this problem, we perform a numerical bifurcation analysis of a partial differential equations model. This system consists of prey-predator interactions, environmental suitability, and local dispersal terms. The main objective of this investigation is to examine the combined effects of distinct ecological factors on species population dynamics. In the absence of dispersal, our results show that variations in abiotic environments and handling times of predator lead to different outcomes of species interactions (i.e., stable limit cycles, species coexistence, and species exclusion). The inclusion of dispersal into this system reduces the predation pressure and stabilizes this ecological community to mediate species biodiversity. Local dispersal also induces intriguing dynamical behaviour in the system such as bistability and unstable limit cycles.

The Effect of Temperatures and Hosts on the Life Cycle of Spodoptera frugiperda (Lepidoptera: Noctuidae).

Simple SummaryFall armyworm (FAW), Spodoptera frugiperda (J E Smith) (Lepidoptera: Noctuidae) is an invasive worldwide agricultural pest that seriously threatens the safety of grain production. Temperatures and hosts play vital roles in the performance of S. frugiperda. In this study, we studied the effects of three different temperatures (20, 25, and 30 °C) and three different host plants (maize (Zea mays L. (Poaceae)), sorghum (Sorghum bicolor (L.) Moench), and coix seed (Coix lacryma-jobi L.)) on the whole life cycle of S. frugiperda. The results showed that both temperatures and host plants significantly influenced the mortality, developmental time, reproduction, and population parameters of FAW. In the treatment with host plants, the developmental period of S. frugiperda at each stage shortened significantly with the increasing of temperatures. At each temperature, the type of host plant did not affect the development time of S. frugiperda eggs. However, there was no significant difference when S. frugiperda 1st to 6th instar larvae were fed different host plants at 20 °C, while 2nd to 5th instar larvae developed rapidly on maize at 25 and 30 °C. Moreover, there were no significant differences in the longevity of FAW when fed sorghum and coix seed at 20 and 25 °C, but a significant difference in the longevity was observed at 30 °C. Feeding on maize achieved a higher intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rate (R0) of S. frugiperda at 25 and 30 °C than those FAW fed on sorghum and coix seed.The interactions between ambient temperatures and host plants are central to the population dynamics of invasive animal species. Despite significant research into the effects of temperatures, the performance of invasive species is also influenced by host plants. The effects of different temperatures (20, 25, and 30 °C) and host plants (maize, sorghum, and coix seed) were tested on the mortality, development, reproduction, and population parameters of the fall armyworm (FAW), Spodoptera frugiperda (J E Smith) (Lepidoptera: Noctuidae), using an age-stage, two-sex life table. The results support the hypothesis that temperature and the species of the host plant significantly influences the performance of FAW. Feeding on maize at 30 °C resulted in a lower mortality rate, a shorter developmental time and longevity, a higher fecundity, intrinsic rate of natural increase (r), finite rate of increase (λ), and net reproductive rate (R0). However, at 20 °C, the host plant could eliminate temperature-mediated synergism in FAW performance, which did not reach statistical significance at 20 °C. Similar results induced by a relatively low temperature (20 °C) on different host plants were also found in the age-stage specific survival curves (sxj), fecundity (mx), maternity (lxmx), and reproductive value (vxj) curves of FAW. Consequently, we also need to pay more attention to FAW outbreaks on different host plants mediated by relatively low temperatures.

Mosquito population structure, pathogen surveillance and insecticide resistance monitoring in urban regions of Crete, Greece.

BackgroundIn Greece vector borne diseases (VBD) and foremost West Nile virus (WNV) pose an important threat to public health and the tourist industry, the primary sector of contribution to the national economy. The island of Crete, is one of Greece’s major tourist destinations receiving annually over 5 million tourists making regional VBD control both a public health and economic priority.MethodologyUnder the auspices of the Region of Crete, a systematic integrative surveillance network targeting mosquitoes and associated pathogens was established in Crete for the years 2018–2020. Using conventional and molecular diagnostic tools we investigated the mosquito species composition and population dynamics, pathogen infection occurrences in vector populations and in sentinel chickens, and the insecticide resistance status of the major vector species.Principal findingsImportant disease vectors were recorded across the island including Culex pipiens, Aedes albopictus, and Anopheles superpictus. Over 75% of the sampled specimens were collected in the western prefectures potentially attributed to the local precipitation patterns, with Cx. pipiens being the most dominant species. Although no pathogens (flaviviruses) were detected in the analysed mosquito specimens, chicken blood serum analyses recorded a 1.7% WNV antibody detection rate in the 2018 samples. Notably detection of the first WNV positive chicken preceded human WNV occurrence in the same region by approximately two weeks. The chitin synthase mutation I1043F (associated with high diflubenzuron resistance) was recorded at an 8% allelic frequency in Lasithi prefecture Cx. pipiens mosquitoes (sampled in 2020) for the first time in Greece. Markedly, Cx. pipiens populations in all four prefectures were found harboring the kdr mutations L1014F/C/S (associated with pyrethroid resistance) at a close to fixation rate, with mutation L1014C being the most commonly found allele (≥74% representation). Voltage gated sodium channel analyses in Ae. albopictus revealed the presence of the kdr mutations F1534C and I1532T (associated with putative mild pyrethroid resistance phenotypes) yet absence of V1016G. Allele F1534C was recorded in all prefectures (at an allelic frequency range of 25–46.6%) while I1532T was detected in populations from Chania, Rethymnon and Heraklion (at frequencies below 7.1%). Finally, no kdr mutations were detected in the Anopheles specimens included in the analyses.Conclusions/SignificanceThe findings of our study are of major concern for VBD control in Crete, highlighting (i) the necessity for establishing seasonal integrated entomological/pathogen surveillance programs, supporting the design of targeted vector control responses and; ii) the need for establishing appropriate insecticide resistance management programs ensuring the efficacy and sustainable use of DFB and pyrethroid based products in vector control.

Conservation genomics and systematics of a near-extinct island radiation.

Conservation benefits from incorporating genomics to explore the impacts of population declines, inbreeding, loss of genetic variation and hybridization. Here we use the near-extinct Mariana Islands reedwarbler radiation to showcase how ancient DNA approaches can allow insights into the population dynamics of extinct species and threatened populations for which historical museum specimens or material with low DNA yield (e.g., scats, feathers) are the only sources for DNA. Despite their having paraphyletic mitochondrial DNA (mtDNA), nuclear single nucleotide polymorphisms (SNPs) support the distinctiveness of critically endangered Acrocephalus hiwae and the other three species in the radiation that went extinct between the 1960s and 1990s. Two extinct species, A. yamashinae and A. luscinius, were deeply divergent from each other and from a third less differentiated lineage containing A. hiwae and extinct A. nijoi. Both mtDNA and SNPs suggest that the two isolated populations of A. hiwae from Saipan and Alamagan Islands are sufficiently distinct to warrant subspecies recognition and separate conservation management. We detected no significant differences in genetic diversity or inbreeding between Saipan and Alamagan, nor strong signatures of geographical structuring within either island. However, the implications of possible signatures of inbreeding in both Saipan and Alamagan, and long-term population declines in A. hiwae that pre-date modern anthropogenic threats require further study with denser population sampling. Our study highlights the value that conservation genomics studies of island radiations have as windows onto the possible future for the world's biota as climate change and habitat destruction increasingly fragment their ranges and contribute to rapid declines in population abundances.

Experimental evidence suggesting temperature-driven dormancy in the planktotrophic larvae of the sea cucumber Isostichopus fuscus

ABSTRACT While larval ecology is central to the population dynamics of marine benthic species with multiphasic life histories, the adaptations of larvae to environmental variability remain incompletely understood in many species. Using the holothuroid echinoderm (sea cucumber) Isostichopus fuscus, we examined how a planktotrophic species can use pre-competency plasticity to withstand suboptimal conditions of temperature over extended periods. Five cohorts of propagules (embryos/larvae) were exposed to temperature treatments (28–29, 24–25 and 20–22°C) in standardized culture settings. Under the coldest temperatures (typical of offshore upwelling areas), development mirrored that obtained under warmer temperatures until the early auricularia stage, where development was arrested for ~5 months in a manner consistent with quiescence. When temperature was increased again, larvae quickly resumed development and settled; no lasting negative impact was noted. The findings suggest that the larvae can use a form of dormancy to withstand suboptimal oceanic conditions for indefinite periods of time until successful delivery to appropriate inshore locations, the habitat were I. fuscus is exclusively found.

Growth and mortality of the European hake Merluccius merluccius (Linnaeus, 1758) from the North of Moroccan Atlantic coasts

Growth and mortality studies on fish are considered crucial to the comprehension of species biology and population dynamics. This work aims to study the growth and mortality of Merluccius merluccius (Linnaeus, 1758) from the North Atlantic coasts of Morocco. A total of 1001 European hakes was sampled from trawler’s fishery during the period from August 2017 to August 2018. Growth parameters were computed for the European hake males and females by applying the von Bertalanffy growth formula. The asymptotic lengths (L∞), growth coefficients (k) and the theoretical age at zero-length (t0) for females and males were; L∞ = 80.19 cm, k = 0.27 year−1, t0 = –0.472 year−1, and L∞ = 69.15 cm, k = 0.31 year−1, t0 = –0.426 year−1, respectively. The total mortality rate (Z), natural (M) and fishing mortality (F) were estimated as Z = 1.49, M = 0.51 and F = 0.98 for combined sexes. The estimated exploitation ratio (E = 0.66), indicated overexploitation of the M. merluccius in the North Atlantic coasts of Morocco.

Problems seeded in the past: lagged effects of historical land-use changes can cause an extinction debt in long-lived species due to movement limitation

ContextLand-use change is one of the main threats to biodiversity on the global scale. Legacy effects of historical land-use changes may affect population dynamics of long-lived species, but they are difficult to evaluate through observational studies alone. We present here an interdisciplinary modelling approach as an alternative to address this problem in landscape ecology.ObjectivesAssess effects of agricultural abandonment and anthropisation on the population dynamics of long-lived species. Specifically, we evaluated: (a) how changes in movement patterns caused by land-use change might impact population dynamics; (b) time-lag responses of demographic variables in relation to land-use changes.MethodsWe applied an individual-based and spatial-explicit simulation model of the spur-tighed tortoise (Testudo graeca), an endangered species, to sequences of real-world landscape changes representing agricultural abandonment and anthropisation at the local scale. We analysed different demographic variables and compared an “impact scenario” (i.e., historical land-use changes) with a “control scenario” (no land-use changes).ResultsWhile agricultural abandonment did not lead to relevant changes in demographic variables, anthropisation negatively affected the reproductive rate, population density and the extinction probability with time-lag responses of 20, 30 and 130 years, respectively, and caused an extinction debt of 22%.ConclusionsWe provide an understanding of how changes in animal movement driven by land-use changes can translate into lagged impacts on demography and, ultimately, on population viability. Implementation of proactive mitigation management are needed to promote landscape connectivity, especially for long-lived species for which first signatures of an extinction debt may arise only after decades.

Spatiotemporal variations in the population dynamics of a few prominent brittle star species (Echinodermata: Ophiuroidea) from the intertidal flat of the Veraval coast, Gujarat, India

The present communication reports the spatiotemporal variation in the population dynamics of three prominent Ophiuroidea species: Amphipholis squamata, Ophiactis savignyi and Ophiocomella sexradia at the rocky intertidal zone at Veraval (21°35’ N, 69°36’ E) Gujarat, off the Arabian Sea. The two sampling areas with different substratum and community structures were investigated from April 2019 to March 2020. Brittle stars were found inhabited in the coralline bed, zoanthid bed, algal holdfast, rock pool crevices and underneath rocks in the studied coastal areas. A. squamata was the most abundant species followed by O. savignyi and O. sexradia at the Veraval coast. The current study described a few remarkable revelations between the patches of coralline algae and Ophiuroidea abundance. Brittle star population revealed major spatial variations between both sampling sites. Cluster analysis and nMDS support population abundance in a seasonal pattern distribution.

Anthropogenic fire practices only ‘best’ if they promote a large seed buildup: comment on the conservation needs of a fire-killed grevillea

Fire regimes control the population dynamics of fireprone plant species. Here, I re-analyse the data acquired in a study of the conservation requirements of a rare, fire-killed grevillea. I conclude that specific knowledge is required on the rate at which seeds accumulate in the soil, and the effect of fire frequency on population dynamics for a comprehensive understanding of the conservation biology of this species. Modelling indicates that fires at intervals in the order of multiple decades and covering at least 60% of the ground surface are optimal for this species, independently of the type of fire employed.

Intensive Fishing Effort and Market Controls as Management Tools for Invasive Aquatic Species: A Review

Invasive aquatic species may disrupt ecosystems and cause socioeconomic damage. Biosecurity protocols were developed to prevent transport and unintended introductions of invasive species, but less attention has been paid to management once they become established. The use of classical fisheries stock assessment to determine levels at which selectively targeted fisheries elicit recruitment overfishing is discussed. Case studies of several species of invasive aquatic organisms, including lionfish Pterois spp. two species of mytilids and three species of crayfish, including Faxonius rusticus (Girard, 1852), are discussed as examples. Fecundity as measured by egg production rate (EPR) is a key factor determining how the various species react to fishing pressure. Ecosystem modelling of predatorprey relations between indigenous and invasive aquatic species suggests that restricting fishing effort on indigenous predators of invasive prey may be as effective in managing invasive species in lieu of directly increasing fishing effort on the targeted species itself. Invasive mytilids Dreissena polymorpha (Pallas, 1771) and Mytella strigata (Hanley, 1843) may not be effectively controlled by intensive fishing effort due to high EPR values. However, crayfish that brood offspring and exhibit much lower EPR values may be ideal candidates for stock assessment and setting fishing effort targets to promote recruitment overfishing. Recommendations for managing invasive aquatic species include: collecting data on population dynamics of the invasive species; assessing predator populations; developing fisheries that target the invasive species; and collecting socioeconomic data to understand the human dimensions of the impacts of the invasive species and inform subsequent policy development.

New survey of Clare Island. Volume 9: Birds ed. by T.K. Kelly

Reviewed by: New survey of Clare Island. Volume 9: Birds ed. by T.K. Kelly Joe Furphy New Survey of Clare Island. Volume 9: Birds T.K. Kelly (ed.) (Royal Irish Academy; 166 pp; €35) ISBN: 978–1–911479–41–3 Any published work must be seen as a picture of a particular time and place, but one of the strengths of New Survey of Clare Island. Volume 9: Birds is the way in which comparisons are made with other locations and species. While it is particularly interesting to see the tables in the Appendices giving comparative statistics for several Irish islands, for many readers their fascination will be with the unanswered questions on bird population make-up and the differences between Clare Island and other islands, especially where habitats, food resources and land use etc., appear superficially similar. An early chapter lists the avian species so far recorded on Clare Island. Some are given longer descriptions, contributing towards an understanding of relationships not only inter-specifically, but also spatially in relation to the situation on the nearby mainland, although few direct comparisons to topography or land use are made. The Clare Island avifauna benefits from a lack of general human interference; only two species are listed as deliberate introductions: Canada goose Branta canadensis and Pheasant Phasianus colchius; ironically, throughout Europe both species are often unwelcome; questions therefore need to be asked about their effects on the native populations on Clare Island. Separate chapters are devoted to seabirds, land birds and water birds. The seabirds chapter raises several interesting and relevant questions regarding the population dynamics of several species. Contrasts with population changes in other seabird colonies not only make interesting reading but also pose questions as to why there is so much variation in numbers in colonies that externally appear similar in terms of habitat and available food supplies. By way of example, Gannets did not nest on Clare Island until 1978 but the numbers have dramatically increased, while the number of Fulmars, similarly open-sea feeders and cliff-nesters, has decreased. Fortunately, there have been several national and European censuses of seabirds, so there are sufficient data available to allow basic comparisons to be made and research projects instituted to ascertain reasons for such discrepancies. However, a full analysis of the causes for fluctuations in bird population requires evidence from a large range of parameters, several of which are not readily available. In considering the distribution and population changes in land birds, proximity to the mainland is a factor, and it is postulated that the changes on Clare Island may be related to fluctuations on the adjacent Mayo shores. Much of the land area of Ireland has been subject to changes in land use and land management, factors with profound effects on the distribution and population dynamics of land birds. Clare Island is fortunate in that it has been spared most of the recent changes, with the result that bird numbers and their distribution can be related much more to naturally induced fluctuations than in most of mainland Ireland. The major 21st-century survey involved a series of transects, after which estimates were made of the populations of the various species throughout the island. Most groups are open-habitat and generalist species, and it is noted that hole-nesting birds are absent, despite the presence of woodland. The absence of rooks is similarly remarked upon, and a chapter devoted to examining possible reasons for this concludes that the island is simply not large enough to sustain a colony of this species. The limitations of conducting detailed survey work on farmland are mentioned, especially the necessity to avoid walking on cropped land or through flocks of animals. A chapter is devoted to the land birds (excepting raptors) of other Irish islands. As well as producing a series of fascinating graphs, diagrams and lists, we learn about the difficulties in making accurate deductions on many aspects of the inter-island contrasts, due to the lack of statistics on which any conclusions can be based. The chapter on waterbirds highlights the difficulties in surveying breeding populations in certain locations, partly due to the secretive behaviour of several species during the...

Global population dynamics of a single species structured with distinctive time-varying maturation and self-limitation delays

<p style='text-indent:20px;'>We consider the classical Nicholson's blowflies model incorporating two distinctive time-varying delays. One of the delays corresponds to the length of the individual's life cycle, and another corresponds to the specific physiological stage when self-limitation feedback takes place. Unlike the classical formulation of Nicholson's blowflies equation where self-regulation appears due to the competition of the productive adults for resources, the self-limitation of our considered model can occur at any developmental stage of an individual during the entire life cycle. We aim to find sharp conditions for the global asymptotic stability of a positive equilibrium. This is a significant challenge even when both delays are held at constant values. Here, we develop an approach to obtain a sharp and explicit criterion in an important situation where the two delays are asymptotically apart. Our approach can be also applied to the non-autonomous Mackey-Glass equation to provide a partial solution to an open problem about the global dynamics.</p>

The relationship between the Acoustic Complexity Index and avian species richness and diversity: a review

ABSTRACT Technologies to monitor species are constantly evolving including the use of acoustic recordings to determine species presence, activity patterns and population dynamics. The Acoustic Complexity Index (ACI) aims to determine ecologically relevant changes in the soundscape by measuring the variability within biotic sounds whilst remaining insensitive to anthrophony. Previous findings relating to this index and its correlations with avian species richness and diversity, environmental and anthropogenic factors were amalgamated in this review to guide the future use of this monitoring technique. A total of 25 papers were returned following a literature search in June 2020 targeting studies in which these relationships were analysed. Current literature shows inconclusive relationships between the ACI and avian species richness and diversity. Also, those studies analysing relationships between the index, environmental and anthropogenic factors provided contrasting results due to the lack of replication between studies. The future implementation of a standardised approach towards data collection should lead to more compelling conclusions. Relationships between the soundscape and the environment should be evaluated on an individual site basis due to the influence species composition has on the acoustic environment. Further study is required to determine the relationship between anthropogenic factors, the ACI and avian assemblages.