Mechanisms Of Population Regulation Research Articles

A general, resource‐based explanation for density dependence in populations of large herbivores

AbstractThe discipline of ecology seeks to understand how ecosystems, communities, and populations are regulated. A ubiquitous mechanism of population regulation of consumers is that capturing energy and nutrients in sufficient quantities for survival and reproduction becomes more difficult as population density increases. Extensive evidence has revealed that populations of large herbivores are often regulated by density dependence, defined as the reduction in the per‐capita population growth rate that occurs as populations grow large. Diminished body mass of individuals has been repeatedly observed in high‐density populations, implicating compromised nutrition as the primary cause of density dependence. However, there is no general explanation for why these nutritional deficiencies occur. Recent work demonstrated that reduced food intake rates resulting from the functional response of herbivores to depleted plant biomass does not provide a sensible explanation for density dependence because rates of food intake of herbivores are often insensitive to changes in plant biomass. A new model of feedbacks from plant biomass to herbivores shows how reduced nutrition of herbivores can result from increased dilution of nutrients in the plant tissue they consume as populations grow, even when their rate of consumption of plants remains constant. The model contains parameters that can be scaled to body mass, allowing unusually general predictions. The model shows that convex, concave, and linear relationships between the per‐capita growth rate and population density can arise from the effects of depletion of plant biomass by herbivore foraging. The model is the first to explicitly include spatial variance in the nutritional quality of plants as a general driver of herbivore population dynamics. I show how regulation of herbivore abundance by plant nutrients can occur, even when a large fraction of the consumable plant biomass remains uneaten, providing a simple, mechanistic explanation for bottom‐up control of population dynamics of primary consumers in a “green world.”

Ecological Mechanisms of Sus Scrofa Population Regulation in Modern Conditions

Wild boar population (Sus scrofa) has been growing rapidly in most countries of the world over the past decades. The invasive species has high reproduction rates and well-developed adaptive responses, which allows it to successfully expand the boundaries of its habitat, create significant economic losses to agriculture and horticulture, urban ecosystems, and threatens the loss of biological diversity and the spread of zoonotic infections. The purpose of the paper was to analyse the factors that contribute to the expansion of the Sus scrofa species in the world, to determine the ecological mechanisms of population regulation against the background of rapid anthropogenic transformation of the habitat and global climatic anomalies; to assess changes in the dynamics of population size in hunting farms of Ukraine for the period from 2010 to 2020 in the Chernihivska oblast, in particular. Conventional methods of retrospective analysis, synthesis, environmental, general biological, and epizootic research were used. The paper analyses the world experience and identifies the main factors of low effectiveness of strategies for controlling the rapidly growing population of wild boar in agroecosystems, mixed forest and urban ecosystems. Due to the unique features of forming a life strategy, the Sus scrofa species demonstrate successful development, expansion of the range of available food resources, effective use of daily diversification of ecological niches in the conditions of transformed ecosystems, etc. It is established that the reason for the inefficiency of ecological mechanisms of pressure on the population of the species in the "predator-prey" system is the absence of large predators in the forest ecosystems of Chernihivska oblast. At the same time, the absence of deterrent mechanisms in the predator-prey system ensured the manifestation of next-level mechanisms, namely, the appearance of foci of African swine fever along the forest cycle in the natural biocenoses of the region. Response – the response of populations was manifested by a rapid short-term decrease in the population of Sus scrofa, as a temporary deterrent effect with a subsequent recovery trend. The results obtained can be used in the development of practical recommendations for biological monitoring, environmental control, and the development of effective forest management measures to prevent biological safety associated with the uncontrolled distribution of Sus scrofa and African swine fever based on universal ecological mechanisms of population regulation

Sex ratio in the mother's environment affects offspring population dynamics: maternal effects on population regulation.

Classic population regulation theories usually concern the influence of immediate factors on current populations, but studies investigating the effect of parental environment factors on their offspring populations are scarce. The maternal environments can affect offspring life-history traits across generations, which may affect population dynamics and be a mechanism of population regulation. In cyclical parthenogens, sexual reproduction is typically linked with dormancy, thereby providing a negative feedback to population growth. In this study, we manipulated population sex ratios in the mother's environment to investigate whether this factor affected future population dynamics by regulating offspring sexual reproduction in the rotifer Brachionus calyciflorus. Compared with females in male-biased environments, those in female-biased environments produced fewer mictic (sexual) offspring, and their amictic (asexual) offspring also produced a lower proportion of mictic females at a gradient of population densities. Moreover, populations that were manipulated under male-biased conditions showed significantly smaller population sizes than those under female-biased conditions. Our results indicated that in cyclical parthenogens, mothers could adjust the sexual reproduction of their offspring in response to the current population sex ratio, thus providing fine-scale regulation of population dynamics in addition to population density.

Sex-biased demography modulates male harm across the genome.

Recent years have seen an explosion of theoretical and empirical interest in the role that kin selection plays in shaping patterns of sexual conflict, with a particular focus on male harming traits. However, this work has focused solely on autosomal genes, and as such it remains unclear how demography modulates the evolution of male harm loci occurring in other portions of the genome, such as sex chromosomes and cytoplasmic elements. To investigate this, we extend existing models of sexual conflict for application to these different modes of inheritance. We first analyse the general case, revealing how sex-specific relatedness, reproductive value and the intensity of local competition combine to determine the potential for male harm. We then analyse a series of demographically explicit models, to assess how dispersal, overlapping generations, reproductive skew and the mechanism of population regulation affect sexual conflict across the genome, and drive conflict between nuclear and cytoplasmic genes. We then explore the effects of sex biases in these demographic parameters, showing how they may drive further conflicts between autosomes and sex chromosomes. Finally, we outline how different crossing schemes may be used to identify signatures of these intragenomic conflicts.

A missing cog in the wheel: an Allee effects perspective in biological invasion paradigm.

Environmental stochasticity and invasive species demographical factors are considered to be fundamental aspects of species invasion. Population size, density, and intraspecific competition are the important determinants of species range expansion. Allee effects, interesting density-dependent phenomena, act as 'mechanism of population regulation' during species expansion. The study intends to understand the trend of published researches and identify research gaps pertaining to biological invasions and Allee effects with the help of bibliometric analysis. Content and citation analysis using key words 'Allee effects' AND 'biological invasion' was conducted on research articles published over a period of two and a half decades from Scopus database for global and Indian context. Understanding of Allee effects dynamics in context of biological invasion is limited, especially in India. Integrating the emerging trends pertaining to Allee effects in the biological invasion framework will strengthen the understanding on species range expansion. It is emphasized that Allee effects can emerge as an important tool to manage invasive species range expansion.

Direct evidence of a prey depletion “halo” surrounding a pelagic predator colony

Colonially breeding birds and mammals form some of the largest gatherings of apex predators in the natural world and have provided model systems for studying mechanisms of population regulation in animals. According to one influential hypothesis, intense competition for food among large numbers of spatially constrained foragers should result in a zone of prey depletion surrounding such colonies, ultimately limiting their size. However, while indirect and theoretical support for this phenomenon, known as "Ashmole's halo," has steadily accumulated, direct evidence remains exceptionally scarce. Using a combination of vessel-based surveys and Global Positioning System tracking, we show that pelagic seabirds breeding at the tropical island that first inspired Ashmole's hypothesis do indeed deplete their primary prey species (flying fish; Exocoetidae spp.) over a considerable area, with reduced prey density detectable >150 km from the colony. The observed prey gradient was mirrored by an opposing trend in seabird foraging effort, could not be explained by confounding environmental variability, and can be approximated using a mechanistic consumption-dispersion model, incorporating realistic rates of seabird predation and random prey dispersal. Our results provide a rare view of the resource footprint of a pelagic seabird colony and reveal how aggregations of these central-place foraging, marine top predators profoundly influence the oceans that surround them.

Reproduction Ecology of the Bank Vole Myodes (Clethrionomys) glareolus Schreb. at the Northern Periphery of the Range: Communication 2. Sexual Maturation and Fertility of Adults and Juveniles

Over many years of field studies (1958–2017), we determined that, under the conditions of the northern periphery of the range, the rate of sexual maturation of bank vole juveniles depends on the calendar date of birth more than on the absolute age. It was noted that individuals can reproduce as early as 25–30 days after birth. The earlier the animals are born, the faster they grow and develop and the earlier they mature and begin to reproduce. It was established that males and females born later than June do not generally mature in the year of birth and reproduce only the next spring, after wintering, and although among them there are mature individuals (mainly July broods), their number does not exceed 21%. It was found that the rapidly developing underyearlings of early broods, almost without exception participating in reproduction in the year of birth, provide population growth by the fall of the current year, and those born in the second half of summer serve as a population reserve for the next breeding season. We registered the age-related differences in the quality of the population and a clear “distribution of responsibilities” between individual generations, which are quite labile and serve as one of the most important mechanisms of population regulation. It was also noted that the fertility of adult and breeding new females depends not only on the environmental conditions, but also on their numbers in spring.

ВЛИЯНИЕ УРОВНЯ ЗАЛЕСЁННОСТИ НА ИЗМЕНЕНИЕ ЧИСЛЕННОСТИ ЛОСЯ В НЕКОТОРЫХ РАЙОНАХ КУЗБАССА

Forests are a unique environmental phenomenon, since their space serves as the fundamental basis for the life of an innumerable number of biological species. Significant integral limited territories of forests are important ecosystems of our planet and have a significant impact on climate and biological processes. Mixed or single-breed, mountain or plain, dense or well-groomed, the forest as a self-regulating system with its life cycle is directly related to the natural balance. Currently, fragmentation, degradation and loss of natural habitats of animals are recognized as serious threats to the conservation of wildlife around the world. First of all, these changes are anthropogenic in nature and directly affect forests as a sphere of existence of the animal world. This issue is updated in the works of modern domestic and foreign scientists. Fragmentation, deterioration, and destruction of natural animal habitats are major threats to global wildlife conservation. The article introduces some results of monitoring the existing data on the layout chart, exportation, and protection of hunting grounds on the territory of the Kemerovo region (Kuzbass). The data were provided by the Kemerovo Regional Department of Wildlife Protection. The article focuses on the population of large game species, e.g. elks. The research covered two municipalities, namely Krapivinsky and Topkinsky municipal districts. The study proved that monitoring data analysis can provide reliable initial assessment of the changes that happen to the hunting grounds and the local biodiversity as a result of natural and man-induced processes. A comparative analysis of game population in several economic zones of the Kemerovo region revealed a strong connection between the uneven growth and / or decrease in the animal population on the hunting grounds and the level of forest coverage. Based on the study of monitoring data, analysis of comparative material on the number of hunting species in different economic zones of the Kemerovo region revealed the existence of natural connections between uneven growth and/or reducing the number of animals on the hunting grounds, and’s forest coverage rate. The study confirms and complements the research of Russian and foreign researchers on the complex influence of anthropogenic and biological factors on changes in the parameters of the population of hunting species (elk). The obtained results contribute to modern research on the mechanisms of population regulation. To improve the efficiency of hunting resources use, it is necessary to conduct on-farm management with the introduction of new methods of land quality assessment based on forest management materials in geoinformation systems. These points fit into the prospects of our further research.

Проблема безработицы в цифровой экономике

The article analyzes a special type of unemployment, the occurrence of which is associated with the development of the digital economy. Shown are the main problems that digital can bring to social life and the fate of an individual worker. Chief among these problems is that with the further digital transformation of the economy, more and more jobs may be threatened with extinction, and the disappearance of old jobs this time will not be accompanied by the emergence of new ones. A situation may arise when workers released due to digitalization will become not only unemployed, but also generally inoperable. A global question arises — what to do with those who do not work, and how to support them? It also examines the related measures of population regulation and global mechanisms for managing demographic processes.

Density-induced social stress alters oxytocin and vasopressin activities in the brain of a small rodent species.

It is known that social stress could alter oxytocin (OT) and arginine‐vasopressin (AVP) expression in specific regions of brains which regulate the aggressive behavior of small rodents, but the effects of density‐induced social stress are still unknown. Brandt's voles (Lasiopodomys brandtii) are small herbivores in the grassland of China, but the underlying neurological mechanism of population regulation is still unknown. We tested the effects of housing density of Brandt's voles on OT/AVP system with physical contact (allowing aggression) and without physical contact (not allowing aggression) under laboratory conditions. Then, we tested the effects of paired‐aggression (no density effect) of Brandt's voles on OT/AVP system under laboratory conditions. We hypothesized that high density would increase aggression among animals which would then increase AVP but reduce OT in brains of animals. Our results showed that high housing density induced more aggressive behavior. We found high‐density‐induced social stress (with or without physical contact) and direct aggression significantly increased expression of mRNA and protein of AVP and its receptor, but decreased expression of mRNA and protein of OT and its receptor in specific brain regions of voles. The results suggest that density‐dependent change of OT/AVP systems may play a significant role in the population regulation of small rodents by altering density‐dependent aggressive behavior.

Effects of chronic exposure to a pharmaceutical mixture on the three-spined stickleback (gasterosteus aculeatus) population dynamics in lotic mesocosms

Pharmaceutical substances are ubiquitous in the aquatic environment and their concentration levels typically range from ng/L up to several μg/L. Furthermore, as those compounds are designed to be highly biologically active, assessing their impacts on non-target organisms is important. Here, we conducted a mesocosm experiment testing a mixture of five pharmaceuticals (diclofenac, carbamazepine, irbesartan, acetaminophen and naproxen) on fish, three-spined stickleback (Gasterosteus aculeatus). The mixture concentration levels were chosen on the basis of the contamination of the Meuse river in Belgium which had been measured previously during a monitoring campaign undertaken in 2015 and 2016. Three nominal mixture concentration levels were tested: the lowest concentration level mixture was composed by environmentally-relevant concentrations that approximate average realistic values for each pharmaceuticals (Mx1); the two other levels were 10 and 100 times these concentrations. Although no impact on stickleback prey was observed, the mixture significantly impaired the survival of female fish introduced in the mesocosms at the highest treatment level without causing other major differences on fish population structure. Impacts on condition factors of adults and juveniles were also observed at both individual and population levels. Using a modelling approach with an individual-based model coupled to a bioenergetic model (DEB-IBM), we concluded that chronic exposure to environmentally-relevant concentrations of five pharmaceuticals often detected in the rivers did not appear to strongly affect the three-spined stickleback populations. Mechanisms of population regulation may have counteracted the mixture impacts in the mesocosms.

Neoliberalismo, inserción internacional y financiarización: una comparación entre Argentina y Portugal

El presente trabajo intenta analizar el neoliberalismo periférico financiarizado (NPF) como forma específica del neoliberalismo. Tras presentar cuatro formas diferentes y criterios para delimitarlas, se estudian las características generales del NPF. Se destacan una matriz común de políticas, un modelado similar de estructuras productivas centradas en la acumulación financiera y una articulación común a los procesos de valorización internacionales. Comparando dos países que ejemplifican el NPF (Argentina y Portugal), se corrobora la caracterización general. Pero también se observan especificidades en la regulación monetaria, la inserción internacional y los mecanismos de la regulación poblacional, que le dan al modelo cadencias específicas, importantes para analizar las crisis y las alternativas para estructurar políticas de desarrollo diferentes.

Predation risk and resource abundance mediate foraging behaviour and intraspecific resource partitioning among consumers in dominance hierarchies

Dominance hierarchies and the resulting unequal resource partitioning among individuals are key mechanisms of population regulation. The strength of dominance hierarchies can be influenced by size‐dependent tradeoffs between foraging and predator avoidance whereby competitively inferior subdominants can access a larger proportion of limiting resources by accepting higher predation risk. Foraging‐predation risk tradeoffs also depend on resource abundance. Yet, few studies have manipulated predation risk and resource abundance simultaneously; consequently, their joint effect on resource partitioning within dominance hierarchies are not well understood. We addressed this gap by measuring behavioural responses of masu salmon Oncorhynchus masou ishikawae to experimental manipulations of predation risk and resource abundance in a natural temperate forest stream. Responses to predation risk depended on body size and social status such that larger fish (often social dominants) exhibited more risk‐averse behaviour (e.g. lower foraging and appearance rates) than smaller subdominants after exposure to a simulated predator. The magnitude of this effect was lower when resources were elevated, indicating that dominant fish accepted a higher predation risk to forage on abundant resources. However, the influence of resource abundance did not extend to the population level, where predation risk altered the distribution of foraging attempts (a proxy for energy intake) from being skewed towards large individuals to being skewed towards small individuals after predator exposure. Our results imply that size‐dependent foraging–predation risk tradeoffs can weaken the strength of dominance hierarchies by allowing competitively inferior subdominants to access resources that would otherwise be monopolized.

How density-dependence and climate affect guanaco population dynamics

The guanaco (Lama guanicoe) is one of the two South American native wild camelid species, and despite its important ecological role and economic value conservationists are in a permanent conflict with sheep ranchers. Currently, management programs are being developed in Argentina and Chile to guarantee guanaco and grassland conservation. We developed a non-linear simulation, three stages-structured matrix model of guanaco population dynamics, with climatic and density-dependence effects, that can be used as a tool to devise optimal management interventions. We estimated population parameters using a 41-year time-series data from a guanaco population in Tierra del Fuego (Chile). We conducted a multivariate multiple regression analysis between matrix demographic parameters (survival at each stage and fertility) as dependent variables, and climatic variables and population density as independent variables.Guanaco density was significantly correlated with female newborn and adult annual survival while annual precipitation correlated significantly with the fertility (females born per female per year), in contrast to population regulation mechanisms commonly seen in other ungulate species. This guanaco model allows the evaluation of the effects of different events (e.g. offtake, particular dry or wet years, poaching) on specific sexes and life stages which is the field information commonly available.

Comparative diets and foraging strategies of subyearling Atlantic salmon, brown trout, and rainbow trout during winter

Over-winter survival of salmonids in streams is thought to be an important population regulation mechanism. Yet because of the difficulty of conducting field studies due to adverse weather or ice conditions, compared to other seasons, salmonid ecology during winter is least understood. Consequently, we sought to examine interspecific feeding associations of an important salmonid stream assemblage in the Lake Ontario watershed during winter. The diets of Atlantic salmon (Salmo salar) parr, brown trout (S. trutta) parr, and rainbow trout (Oncorhynchus mykiss) parr were significantly different in February but not in March. Salmonid diets differed from the benthos and the drift during both months. Dipterans (chironomids, simuliids, and tipulids) and ephemerellids were the major prey taxa consumed. All three species fed more heavily on prey items from the benthos than from the drift. The diet of Atlantic salmon had the highest similarity to the benthos whereas the diet of brown trout had the lowest similarity to the drift. All three salmonid species generally selected ephemerellids, limnephilids, and chironomids and avoided elmids. These winter feeding observations are the first reported for this specific salmonid assemblage and will help managers better understand interspecific associations during this critical period.

Effects of the Ordering of Natural Selection and Population Regulation Mechanisms on Wright-Fisher Models.

We explore the effect of different mechanisms of natural selection on the evolution of populations for one- and two-locus systems. We compare the effect of viability and fecundity selection in the context of the Wright-Fisher model with selection under the assumption of multiplicative fitness. We show that these two modes of natural selection correspond to different orderings of the processes of population regulation and natural selection in the Wright-Fisher model. We find that under the Wright-Fisher model these two different orderings can affect the distribution of trajectories of haplotype frequencies evolving with genetic recombination. However, the difference in the distribution of trajectories is only appreciable when the population is in significant linkage disequilibrium. We find that as linkage disequilibrium decays the trajectories for the two different models rapidly become indistinguishable. We discuss the significance of these findings in terms of biological examples of viability and fecundity selection, and speculate that the effect may be significant when factors such as gene migration maintain a degree of linkage disequilibrium.

Population dynamics of Telenomus fariai (Hymenoptera: Scelionidae), a parasite of Chagas' disease vectors. V. Parasite size and vital space.

Some ecological aspects of the developmental process of the endophagous egg parasite Telenomus fariai when reared in Triatoma phyllosoma pallidiPennis eggs, have been investigated. It was shown that mortality among pupae and last instar larvae does not account for the constancy in parasite progeny emergence per host egg, suggesting that if there is any population regulation mechanism based on larval competition, it would be operating among the youngest instars. Simple and multiple linear correlations between parasite size and host egg volume, and progeny production per host egg show that both factors are relevant in determing parasite size, but the effect of progeny production per host egg is on the average three times as important as host egg volume. Vital space (mm3 of host egg volume available per parasite) shows an extremely high correlation (0.970) with parasite size. The elasticity function of vital space on parasite size shows that with increasing values of the former, there is always a higher percentile increase of the latter.

Spatial patterns at host and forest stand scale and population regulation of the pine processionary mothThaumetopoea pityocampa

Different spatial processes are likely to generate variability at different scales. Thus, the explanation of patterns may be facilitated by knowledge about the spatial scales where variation in patterns occurs. In the present study, the link between spatial patterns of the pine processionary moth Thaumetopoea pityocampa Den. & Schiff. (Lepidoptera, Notodontidae) at two different scales, as well as its population dynamics, was assessed. First, the spatial patterns of T. pityocampa population were assessed at the forest stand scale by surveying the distribution of larval colonies within the pine forest, indicative of adult dispersion. Second, egg-laying patterns across individual host-plants, indicative of female oviposition choices, were assessed, as well as their impact on the survival of immature stages. It was found that T. pityocampa presents a gregarious distribution in homogeneous pine forests, over distances of a few dozen metres. At the pine tree scale, females tend to aggregate their egg batches, whereas aggregation increases with population density. Natural enemies such as parasitoids do not appear to play an important role in regulating the population dynamics of the species. At the same time, aggregation in individual hosts leads to increased mortality in the period from hatching to the third instar, which is notable at high population densities. A patchy distribution in the landscape over short distances has a potentially positive effect on population dynamics of the species, avoiding the Allee effect, and allowing for a rapid increase in population, even where initial numbers are low, leading to localized outbreaks. At the same time, increased mortality as a result of egg-batch clumping at high population densities is a potential density-dependent mechanism of population regulation.

Vespa velutina nest distribution at a local scale: An 8-year survey of the invasive honeybee predator.

Vespa velutina is an invasive species that was observed for the first time in France and Europe in 2004, which rapidly threatened domestic honeybees with active predation. For the first time in this study, we analyzed the distribution of V. velutina nests at a local scale to understand the pattern of nesting, and in 8 years of monitoring, a total of 528 nests were surveyed. With the exception of 2 years, the nests of V. velutina were randomly distributed within the monitored area, which suggested that intraspecific competition for nesting sites and/or food was unlikely. When the data for all years were combined, an aggregated distribution of nests at the seafront in the vicinity of the oyster farm and sportfishing activities was observed. This distribution suggested that seafood, attractive to vespids, might provide a valuable alternative food source that favored colony development. We also tested the effect of spring queen trapping of V. velutina on the distribution of nests in 2014, which was the year with the greatest number of colonies within the area; the position of the traps did not influence the distribution of the nests. For the first time, this study showed that (i) intraspecific competition was unlikely to be a mechanism for population regulation, (ii) some areas were more likely favored for hornet nests, and (iii) spring queen wasp trapping was inefficient as a method to limit the distribution of the V. velutina population.

Stress-host-parasite interactions: a vicious triangle?

The potential for synergy between host physiological condition and infection has recently been recognised. Here we review the evidence to support the idea that stress may play a key role in the interplay between host and parasite, integrating a three-way circular synergistic interaction between stressors, infections and host response: chronic stress can elicit responses that impoverish the host’s physiological condition (including its immune function), which predisposes to infection, which results in more stress, and so on. We argue that this introduces additional explanatory power to previous ideas posited by the authors, by including stress as a third interacting factor that intervenes in the synergy between condition and infection. This in turn, may have important implications. In nature, evolutionary forces appear to select against stress-related disease or exacerbated parasite virulence. Nonetheless, under certain circumstances, parasites and (other) stressors interact generating a vicious spiral that may affect host fitness and survival. At high host densities, this becomes a mechanism of population regulation. Also, anthropogenic stressors may cause this mechanism to misfire, with significant implications for biological conservation and public health.