Flow, food supply and acorn barnacle population dynamics

This paper reports the effects of food supply, predation and the interaction between them on the population dynamics of root voles, Microtus oeconomus, by adopting factorial experiments in field enclosures. This two‐factor experiment proved the general hypothesis that food supply and predation had independent and additive effects on population dynamics of root voles. The experimental results proved the following predictions: (1) predation reduced population density and recruitment significantly; (2) food supply increased population density; (3) predation and food supply influenced spacing behavior of root voles separately and additively: Exposure to predation reduced long movements of root voles between trapping sessions; additional food supply reduced aggression level and home range size of root voles. Less movement of individuals that exposed to predators possibly reduced their opportunity of obtaining food and lessened population survival rate, which led population density to decrease. Smaller home range and lower aggression level could make higher population density tolerable. The interactive effect of predation and food on home range size was highly significant (P=0.0082<0.01). The interactive effect of food and predation on dispersal rate was significant (P<0.01). From the experimental results, we conclude that the external factors (predation, food supply) were more effective than internal factors (spacing behavior) in determining population density of root voles – under the most favorable external conditions (−P, +F treatment), the mean density and mean recruitment of root vole population was the highest; under the most unfavorable external conditions (+P, −F treatment), the mean density and mean recruitment of root vole population was the lowest.

In the Chironomus tentans 10-d growth test, changes in larval growth relative to sediment contamination are often ascribed ecological relevance by assuming that such changes become manifest at the population level through effects on reproductive output even though the relationship between growth and reproduction is poorly understood. The objective of this study was to evaluate the relationship between growth and reproduction in C. tentans and to use these data in a demographic model to predict the growth and size of a theoretical population. Growth was manipulated by varying food supply (0.29, 0.33, 0.38, 0.42, 0.46, and 0.5 mg/individual per d). The test was initiated with 12 newly hatched larvae per replicate and carried through one complete generation. Larval growth and survival were determined at 20 d, and reproduction was monitored daily during emergence. Food supply did not significantly affect survivorship at any life stage; survival of larvae at 20 d, pupae, and adults exceeded 83%, while survival of larvae in the reproduction replicates exceeded 65%. Both larval and adult dry weight declined significantly with a reduction in food supply. Total emergence was reduced at the lowest feeding level only, whereas the rate of emergence declined at food supplies below 0.42 mg/individual per d. Based on the relationship between larval and adult dry weight, a minimum larval tissue mass of between 0.5 and 0.6 mg dry weight/individual appears to be necessary before emergence can take place. The number of eggs/female declined significantly with a decrease in food supply below 0.42 mg/individual per d. Above this level (corresponding to larval dry weight of ∼ 1.5 mg/individual), the addition of more food had no effect on reproductive output. Fecundity (number of daughters/female) and expected number of progeny declined linearly with reduced food supply. Application of the data in a demographic model showed that the growth and predicted size of a population would decline significantly with a decline in larval growth and reproductive output. These results demonstrate that changes in growth, positive or negative, can be used to make meaningful predictions regarding reproduction and population dynamics in the midge C. tentans.

Modeling oyster populations. V. Declining phytoplankton stocks and the population dynamics of American oyster ( Crassostrea virginica) populations

The application of size-frequency distribution and energy flow in paleoecologic analysis: An example using parautochthonous death assemblages from a variable salinity bay

Cold-water corals and sponges form iconic and globally occurring benthic communities, provide important habitats for a diverse associated fauna and thrive in environmental conditions with often large temporal and spatial variations in near-bottom currents, food availability and other environmental parameters. We investigate the variability of near‐bottom currents and physical processes from simulations with a nested hydrodynamic modelling framework at two seamounts rich in benthic fauna along the Northeast Walvis Ridge, Valdivia Bank and Ewing Seamount. Our aim is to obtain new insights on physical drivers of observed occurrences and distribution of benthic suspension feeders (cnidarians and sponges) in this data‐poor area. We use dynamic downscaling of high-resolution implementations of the ROMS-AGRIF model in combination with high-resolution bathymetry and open boundary forcing from the basin-scale model INALT20 and the OSU inverse tidal model to explore the fine-scale physical processes and mechanisms that potentially drive a continuous or episodic food supply to the benthic communities.  Over a three-year period, we analysed how near-bottom currents vary in space and time and assess potential connections between the distribution of filter-feeding fauna and the surrounding physical marine environment. We identified a close link between flow dynamics, internal tide dynamics and faunal species distributions. We propose that physical processes such as kinetic energy dissipation and internal wave dynamics could serve as functional indicators of food supply and particle encounter rates in future species distribution and habitat suitability models for important deep-sea taxa, such as those that represent vulnerable marine ecosystems. Our results also show little impact of mesoscale eddies from the Agulhas Leakage as they propagate north-westward into the southeast Atlantic along a well-defined corridor, which only occasionally extends as far north as the Valdivia Bank and Ewing Seamount.

In this paper we review and integrate key aspects of behavioral and life history traits, food supply and population dynamics of the white-footed mouse (Peromyscus leucopus), a species that is abundant and widely distributed across much of eastern North America. Results are based largely on a 33-year mark-and-recapture study in a forest fragment in northwest Ohio, USA. Behavioral plasticity in such reproductive traits as mating system and parental care allows this species to adjust quickly to changing environments. The species has a relatively "fast" life history, with rapid attainment of sexual maturity and high fecundity in the face of high mortality rates. Maximal reproductive effort early in life enables a rapid population response. Food supply, in the form of mast, determines the size of the reproducing population in early spring, which, in turn, influences the size of the late summer peak population. The peak population size is also affected by short-term weather events possibly acting via the food supply. The effects of weather and food on population growth are in part mediated through competition, including defense of space and suppression of reproduction. The inelasticity of female territories appears to set an upper limit to population density.

The population ecology of grey squirrels Sciurus carolinensis living in a 9-ha oak Quercus robur wood in southern England was studied between 1976 and 1987 using live-trapping techniques. Trapping was carried out in winter, spring and summer. The availability of tree seeds during the autumn of each year, and the severity of cold weather over each winter were also measured to examine their effects on squirrel population dynamics. Capture probabilities of squirrels in winter, and to a lesser extent in spring, were inversely related to food availability and data from these two seasons were not considered dependable. The analyses concentrated on the summer populations. The long-term average summer density of squirrels was high at 8.8 ha -1 (SE 3.41 ha -1 ) demonstrating that the oak wood was high quality habitat for grey squirrels. Over 10 of the 12 years, summer densities were remarkably similar, ranging between 7 ha -1 and 10 ha -1 (mean 8.5 ha -1 , SE 0.95 ha -1 ). However, numbers were driven upwards in 1977 to a density approaching 18 ha -1 and downwards in 1982 to a density of about 3 ha -1 : a 6-fold difference. In good seed years, breeding starts in December, in poor seed years the start of breeding is deferred until the spring. There was no or very little spring breeding in 5 years when food supplies were poor. Female reproductive success was positively associated with food availability. Partial correlation analysis showed that the level of association was not improved when the effects of winter weather were taken into account. The number of new adult females in the summer population was positively associated with food availability but there was no association between new males and food. This suggests that food availability is more important to breeding females than breeding males. Persistence from summer to winter was positively associated with food availability, but persistence from summer to spring and to the following summer were not. Partial correlation analyses showed that the severity of winter weather tended to mask the effects of food availability on persistence and the partial correlation coefficients were higher when the effects of weather were held constant. Adult females had the highest persistence between summers (52%, n = 11, SE 6%), followed by juvenile females (38%, n = 7, SE 8%), adult males (36%, n = 11, SE 4%), and juvenile males (21%, n = 7, SE 7%). The persistence of adult males but not females was inversely related to the initial number of males present. In males, there was no significant difference in winter body mass between years and winter body mass was not associated with food availability, although there were very few data for winters when the food supply was good. In 7 years when the food supply was poor to moderate, there was an increase in mean body mass between summer and winter in 4 years, and a decrease in 3 years. The data were explored using ordination techniques; first a standardized principal component analysis and then the canonical form of principal component analysis or redundancy analysis. The analysis was carried out on years derived from MNA of males and females and various combinations of the environmental variables: food availability (FOOD) and the severity of winter weather (TEMP). The ordination biplots clearly showed the high correlation between MNA males and MNA females and that FOOD was the most important environmental variable. TEMP on its own had no effect but FOOD x TEMP was important. Following on the exploratory data analysis and for predictive purposes, a general linear model between the numbers of squirrels in the summer populations and sex, FOOD and FOOD x TEMP as explanatory variables accounted for 77% the variance in squirrel numbers among years. This study shows that tree seed availability is the most important factor limiting grey squirrel densities, but this factor both positively and negatively interacts with the severity of w

Context Feral pigs (Sus scrofa) are highly fecund, and populations can increase rapidly under favourable conditions. Population size can also fluctuate widely, driven largely by changes in juvenile mortality in response to food availability, but these relationships have only been explored on a limited number of sites and over short periods. Aims The present study aimed to investigate and quantify the numerical response of feral pig populations to changes in their food supply in north-eastern Australia. Methods Pig population densities were determined from aerial surveys conducted over a 21-year period on 10 regional blocks (~2000–6000 km2) throughout the Queensland rangelands. Densities were used to calculate annual exponential rates of increase (r), which were then corrected for anthropogenic mortality (baiting and commercial harvesting). Six proxy measures of annual food supply, including rainfall, pasture biomass and pasture growth (using the AussieGRASS model), were calculated for each survey block, and assessed as predictors of corrected r. The rates of increase predicted from the first half of the data series were then applied to initial population densities to estimate successive pig densities during the second period in each bioregion. Key results The most parsimonious model of the numerical response had parameters common to three bioregions, with rainfall in the 12 months between surveys being the best predictor variable. Modelled densities for each bioregion were a good fit to actual, observed densities. Relationships between r and each measure of food supply at the individual block level were inconsistent. Conclusions Using rainfall as a measure of food supply, the numerical response relationship provides a method for predicting the dynamics of feral pig populations at the bioregional scale. Predicting population dynamics at any one site using this relationship is less precise, suggesting that differences in landscape composition affect utilisation of resources supporting population growth. Implications The results from the present study could be used to predict feral pig population changes at the bioregional level, supplementing or reducing the need for more frequent, expensive population surveys. This improved ability to predict fluctuations in regional feral pig populations can help guide future management actions.

This article aims to analyze the repercussions of food trade between China and various regions of the world to understand the dynamics of food flows and offer a novel perspective on the contemporary globalization process. Understanding these flows involves analyzing the global production and commercialization of food and the effects of these movements on exporting and importing countries in economic terms and food security. The concept of unequal caloric exchange is applied to the case of China, which allows for an understanding of how its economic growth and participation in international trade have transformed its global and internal commercial dynamics by establishing links with self-sufficiency and the composition of its population’s diet. The results show that China is increasingly dependent on international markets for its food supply. From 1961 to 2021, food consumption in China has tripled in calories and experienced qualitative changes, with a reduction in high-quality carbohydrates and vegetable proteins and an increase in cereals, vegetable oils, alcohol, and vegetables. This dietary transformation is related to economic growth and greater dependence on international trade. From 1987 to 2022, China has shown a growing deficit in the food trade balance, with imports exceeding exports in volume, value, and calories, although it maintains favorable terms of trade. Food self-sufficiency has decreased from 95% in 1961 to 76% in 2022, and the diet has diversified, replacing traditional foods with products demanded in international trade.

Nonlinear population dynamics: Complex Population Dynamics: A Theoretical/Empirical Synthesis by Peter Turchin. Princeton University Press, 2003. £19.95 pbk (536 pages) ISBN 0 691 09021 1

AimWe studied dynamics of four populations of New Zealand forest birds for 5–9 years after reintroduction to islands. We primarily aimed to predict whether these populations were viable, and what, if any, management was needed to maintain them. However, the small scale of these islands also provided an opportunity to study density‐dependent population growth over a short time frame.LocationWe studied New Zealand robin (toutouwai,Petroica australis) and stitchbird (hihi,Notiomystis cincta) populations reintroduced to Tiritiri Matangi, a 220‐ha offshore island near Auckland, and saddleback (tieke,Philesturnus carunculatus) and stitchbird populations reintroduced to Mokoia, a 135‐ha island in Lake Rotorua. These islands are free of mammalian predators, but have highly modified habitat following clearing and regeneration.MethodsWe closely monitored each population, individually marking all or most of the birds and in some cases experimentally manipulated population density or food supply. We used model selection procedures to understand factors affecting survival, fecundity and dispersal, and developed stochastic simulation models.ResultsThe Tiritiri Matangi robin and Mokoia saddleback populations grew without management and appear to be viable. Both showed strong evidence of density‐dependent growth, with fecundity (saddlebacks) and juvenile survival (both populations) declining with increasing density. Neither stitchbird population appears viable without management and supplementation experiments showed reproduction and/or survival to be limited by food supply. The Tiritiri Matangi population appears viable as long as supplementary feeding continues. However, the Mokoia population has a high mortality rate regardless of supplementary feeding, resulting in tenuous viability even with intensive management. Mokoia stitchbirds suffer from infection byAspergillus fumigatus, a pathogenic fungus that is prevalent in highly modified habitats and more abundant on Mokoia than Tiritiri Matangi.Main conclusionsSome forest birds can thrive in regenerating forest on islands and strong evidence of density dependence can be detected in such populations in as little as 5 years. This allows density‐dependent models to be developed, providing guidance when island populations are harvested for further translocations. Other species are limited by food supply in regenerating environments, a problem potentially overcome by management. However, prevalence ofA. fumigatusmay render highly modified environments uninhabitable by some species regardless of management.

In a population convergence experiment, the initial densities of adults of the predatory backswimming bug Notonecta hoffmanni were set above and below a putative equilibrium density in stock tanks. The experiment was done at two constant rates of food supply (wingless Drosophila) for the larger instars (in natural pools Notonecta feed mainly on terrestrial arthropods that fall on the water surface). It was predicted that the densities of the resulting populations would converge on an equilibrium set by the rate of food supply for the larger instars. The tanks also contained zooplankton (mainly Daphnia), which were the main food supply for the smaller instars of Notonecta. The resulting overwintering populations converged towards the appropriate equilibrium densities, via density—dependent and food—dependent fecundity and then cannibalism. However, the populations overshot their equilibria, producing overconvergence. In natural populations such overconvergence might tend to produce 2—yr cycles in abundance. Overconvergence resulted from the insensitivity of the survivorship of the original adults (at least over the short term) to differences in food supply between treatments, allowing them to continue to affect (via cannibalism and reproduction) the eventual density of the new overwintering population. Because Notonecta population density was determined by the externally supplied, locally uncoupled food supply, even though the early instars depended for food largely upon dynamic populations of zooplankton, the dynamics of the Notonecta population were simpler than a description of the food web might suggest.

Influence of bacterial type and density on population growth of bacterial-feeding nematodes

Cover provides shelter, food, nesting opportunities and protection from predators. The behavioural response of small mammals to reduced cover has been well documented. However, very little is known about the effect of cover on community and population dynamics. Australian small mammals generally inhabit extremely dynamic ecosystems, where cover and food supplies are greatly affected by fire. Species are described as early or late seral specialists, generally returning to a disturbed area once their habitat requirements are met. Habitat requirements have loosely been interpreted as cover and food supply, however, these factors are not mutually exclusive and few studies have attempted to determine the driving factors behind small mammal succession. In this study, we manipulated specific aspects of cover in the eucalypt forests of Fraser Island and show that the behaviour and population dynamics of small mammals were greatly affected. A reduction of cover from grass‐trees (Xanthorrhoea johnsonii) did not affect small mammal species composition, however, the abundance and size structure distribution of the dominant species (Rattus fuscipes) decreased. Patch use by rodents also decreased after cover was reduced. Rattus fuscipes must trade‐off remaining in an environment with increased risk of predation, or disperse to an area with greater cover but increased competition. Juveniles dominated (>60%) populations of R. fuscipes after cover was reduced, however, size distributions of control sites were relatively more even (<25% juvenile). While adult R. fuscipes are either killed by predators or disperse to other areas, juveniles that remained or immigrated to an area of reduced cover gained a selective advantage over those in control sites, because reduced competition with adults increased body condition of juvenile R. fuscipes.

Some common ideas about environmental factors that determine the patterns of migration (including timing) and stock dynamics of walleye pollock are critically analyzed with particular attention to the Bering Sea. There is shown that the conception of the migration timing dependence on food supply in the northern Bering Sea does not represent the real facts, as well as the conception of year-class strength dependence on winter mortality of fingerlings determined by food supply, especially in conditions of its deficiency. Periodicity of the pollock stocks dynamics associated with global changes of climatic and oceanographic factors is also called in question. Role of provincial factors in dynamics of the pollock populations is discussed and emphasized.