Limited Food Sources Research Articles

An age-structured population model with state-dependent delay: Dynamics

We consider an age-structured population model with distinct immature and adult stages, wherein the populations at each stage consume different limited food sources. This gives rise to a model composed of the McKendrick-Von Förster partial differential equation, a nonlinear boundary condition describing the birth rate, and a threshold condition that yields a state-dependent delay. The state-dependence re?ects the changing age of maturity stemming from an intuitive accounting of the maturation time due to competition for resources within the immature population. Properties of solutions to this model are derived and the dynamics are compared to the corresponding constant delay case when state-dependence is ignored. As a parameter involved in birth rate is increased, we numerically observe a bifurcation from an extinction steady state to an endemic steady state, and observe both monotonic and oscillatory approaches to equilibrium.

Fifty Fertile Years: Anthropologists' Studies of Reproduction in High Altitude Natives

Early European colonists of the Andes had difficulties in reproducing, a fact that underpins the hypothesis that reproduction is impaired amongst all humans at high altitudes. Yet a 16th century missionary wrote, "… the Indians are healthiest and where they multiply the most prolifically is in these same cold air-tempers, … [yet most children of the Spaniards] when born in such regions do not survive." These observations suggest that humans at high altitudes are subjected to strong natural selection from hypoxia, cold and limited food sources and, furthermore, that human populations can and have adapted, and continue to adapt, to these conditions. Informed by multiple approaches and theoretical frameworks, anthropologists have investigated to what extent and precisely how high altitude environments impact human reproductive functioning and fertility. Analyses of the proximate determinants of natural fertility suggest that behaviors (breast/infant feeding practices in the Andes, and marriage practices and religious celibacy in the Himalaya) are major determinants of fertility in high altitude populations. Furthermore, data from Project REPA (Reproduction and Ecology in Provincía Aroma), a longitudinal study in rural Bolivia, demonstrate that fecundity is not impaired in this indigenous altiplano population, and that the risk for early pregnancy loss (EPL) is not elevated by environmental hypoxia but does vary seasonally with the agricultural cycle (contra to the assumption that EPLs are due almost entirely to genetically flawed concepti). This review discusses these and other findings that reveal the complex and dynamic adaptations of human reproductive functioning in high altitude environments.

Regional differences in foraging behaviour of invasive green crab (Carcinus maenas) populations in Atlantic Canada

Invasive green crab populations initially established in Canada within the Bay of Fundy, New Brunswick in the 1950s and were present in all five Atlantic provinces by 2007. Genetic evidence suggests that the Atlantic Canadian populations originated from two separate introductions with differences in time of establishment among regions and possible population-level behavioural differences. In this study, we examine intraspecific foraging behaviour among crabs from different populations, and interspecific foraging behaviour between genetically similar crabs and juvenile lobsters. Both sets of foraging experiments involved competition for a limited food source over a 1-h period. In intraspecific match-ups, recent invaders from Newfoundland (NL) were significantly superior foragers than long-established invaders from Nova Scotia (NS) and New Brunswick (NB) populations; however, we found no differences between NL and Prince Edward Island (PE) invaders. Crabs from PE were better competitors than those from NS and NB, but these differences were not significant. Interspecific competition experiments indicated that the feeding behaviour of recent invaders (NL) and genetically similar, but long-established invaders (NS), differed in the presence of juvenile lobsters. Our study documents striking behavioural differences among populations of green crab from a small geographic region, which may reflect a combination of both genetic differences and time since establishment. These differences may result in varying impacts on newly invaded habitats.

Biological vs. Physical Mixing Effects on Benthic Food Web Dynamics

Biological particle mixing (bioturbation) and solute transfer (bio-irrigation) contribute extensively to ecosystem functioning in sediments where physical mixing is low. Macrobenthos transports oxygen and organic matter deeper into the sediment, thereby likely providing favourable niches to lower trophic levels (i.e., smaller benthic animals such as meiofauna and bacteria) and thus stimulating mineralisation. Whether this biological transport facilitates fresh organic matter assimilation by the metazoan lower part of the food web through niche establishment (i.e., ecosystem engineering) or rather deprives them from food sources, is so far unclear. We investigated the effects of the ecosystem engineers Lanice conchilega (bio-irrigator) and Abra alba (bioturbator) compared to abiotic physical mixing events on survival and food uptake of nematodes after a simulated phytoplankton bloom. The 13C labelled diatom Skeletonema costatum was added to 4 treatments: (1) microcosms containing the bioturbator, (2) microcosms containing the bio-irrigator, (3) control microcosms and (4) microcosms with abiotic manual surface mixing. Nematode survival and subsurface peaks in nematode density profiles were most pronounced in the bio-irrigator treatment. However, nematode specific uptake (Δδ13C) of the added diatoms was highest in the physical mixing treatment, where macrobenthos was absent and the diatom 13C was homogenised. Overall, nematodes fed preferentially on bulk sedimentary organic material rather than the added diatoms. The total C budget (µg C m−2), which included TO13C remaining in the sediment, respiration, nematode and macrobenthic uptake, highlighted the limited assimilation by the metazoan benthos and the major role of bacterial respiration. In summary, bioturbation and especially bio-irrigation facilitated the lower trophic levels mainly over the long-term through niche establishment. Since the freshly added diatoms represented only a limited food source for nematodes, the macrobenthic effect was more pronounced in niche establishment than the negative structuring effects such as competition.

Plumage Colouration, Age, Testosterone and Dominance in Male Red Bishops (Euplectes orix): A Laboratory Experiment

AbstractVisual signals such as plumage characteristics in birds often play a key role in the establishment of dominance in contests by acting as a badge of status that can be used to assess individual fighting ability. We studied the role of plumage colouration in males of the red bishop (Euplectes orix), a sexually dimorphic and polygynous weaverbird species occurring in sub‐Saharan Africa and breeding in dense colonies around water. Males are highly territorial and often engage in competition over limited resources such as breeding sites and potential mates. By experimentally staging male–male contests over a limited food source, we wanted to determine whether the orange–red breeding plumage in this species serves as a dominance signal between individuals, with males with redder plumage being dominant over those with duller plumage. In the first set of experiments, we staged contests between unfamiliar and unmanipulated males. The setup of the second set of experiments was identical to the first, with the exception that those males with the lowest chroma and hue values had their plumage experimentally reddened within the range of the natural variation. In addition to plumage colouration, we incorporated testosterone levels, body condition and age into the analysis of factors contributing to contest outcome. Our results show a consistent and strong age effect in both sets of experiments, which seems to be independent of plumage colouration, testosterone and body condition. This suggests that in the red bishop, the outcome of male–male competitions over limited resources is determined by age‐related acquired experience rather than by status signalling through plumage colouration.

Knowledge and Usage Patterns of Folic Acid amongst Physician Assistant Students at the University of Texas Medical Branch at Galveston.

Physician Assistant (PA) students are educated that 400 micrograms (μg) of daily folic acid (FA) is a vital component of prenatal care to reduce fetal development abnormalities. Studies have shown that higher education level is correlative with the use of daily FA in women of reproductive age. The objective of this study was to assess PA students' knowledge of the physiologic implications of FA supplementation, the recommended dosage and intake regimen, and how having this knowledge impacted their behavior. A knowledge-based questionnaire was given to 59 first year female PA students and 39 third year female PA students at the University of Texas Medical Branch at Galveston (UTMB). Overall FA use amongst female UTMB PA students is 66.3%. Furthermore, 40% of the third year students consumed 400 μg of FA daily as opposed to 7.8% of the first year students. One-hundred percent of the third year students knew that FA deficiency caused NTDs, and 86.4% of the first year students recognized this causation. There was poor compliance for following the United States Preventative Services Task Force (USPSTF) recommended FA regimen amongst students in the UTMB PA program. The results in our study were comparable to the previous publications, finding that the majority of women in both our study and the general population acknowledged the importance of FA supplementation. BACKGROUND AND SIGNIFICANCE Folate, Vitamin B9, is a naturally occurring water-soluble vitamin. Foods containing folate include leafy green vegetables, oranges, legumes, and liver (Brown et al., 1997). Due to the poor bioavailability and limited food sources of folate, a synthetic form was developed: FA (Winkels, Brouwer, Siebelink, Katan, & Verhoef, 2007). The U.S. Public Health Service issued a recommendation in 1992 stating “all women of reproductive age in the U.S., capable of becoming pregnant, should consume 400 μg of FA daily to reduce the risk of having a pregnancy affected by [neural tube defect] NTD” (Prue, Flores, Panissidi, & Lira, 2008). The Food and Drug Administration (FDA) utilized this recommendation in 1998, and mandated that all enriched grains be fortified with FA (CDC, 2007). In 2005 the Dietary Guidelines for Americans (DGA) made an effort to inform the general population about these new recommendations, and advocated women consume 400 μg of FA daily in multivitamin or supplement form in addition to the FA provided by enriched foods (Cena et al., 2008). In May 2009, the USPSTF recommended “all women planning or capable of pregnancy take a daily supplement containing 400 μg – 800 μg of FA” (U.S. Preventative Services Task Force, 2009). The importance of FA is annually recognized by the Department of Health and Human Services, the Centers for Disease Control, and the National Birth Defects Prevention Network during January’s National Birth Defects Prevention Month (Center for Disease Control and Prevention, 2007). Lifetime healthcare costs for children suffering from spina bifida can exceed two million dollars per child for medical and surgical care of the individual (Spina Bifida Association, 2009). It is important for women of reproductive age to be proactive regarding their health and the health of a potential

Opine-BasedAgrobacteriumCompetitiveness: Dual Expression Control of the Agrocinopine Catabolism (acc) Operon by Agrocinopines and Phosphate Levels

Agrobacterium tumefaciens strain C58 can transform plant cells to produce and secrete the sugar-phosphate conjugate opines agrocinopines A and B. The bacterium then moves in response to the opines and utilizes them as exclusive sources of carbon, energy, and phosphate via the functions encoded by the acc operon. These privileged opine-involved activities contribute to the formation of agrobacterial niches in the environment. We found that the expression of the acc operon is induced by agrocinopines and also by limitation of phosphate. The main promoter is present in front of the first gene, accR, which codes for a repressor. This operon structure enables efficient repression when opine levels are low. The promoter contains two putative operators, one overlapping the -10 sequence and the other in the further upstream from it; two partly overlapped putative pho boxes between the two operators; and two consecutive transcription start sites. DNA fragments containing either of the operators bound purified repressor AccR in the absence of agrocinopines but not in the presence of the opines, demonstrating the on-off switch of the promoter. Induction of the acc operon can occur under low-phosphate conditions in the absence of agrocinopines and further increases when the opines also are present. Such opine-phosphate dual regulatory system of the operon may ensure maximum utilization of agrocinopines when available and thereby increase the chances of agrobacterial survival in the highly competitive environment with limited general food sources.

Long-term trends in food habits of a relict brown bear population in northern Spain: the influence of climate and local factors

Relict endangered populations may be especially vulnerable to the effects of climate change. A data series for the period 1974–2003 was used to examine shifts in brown bear Ursus arctos food habits in its south-westernmost European population. This focused on the hyperphagic season, when bears gain the fat that is essential for winter dormancy and reproduction. General climatic indicators were predictors of diet trends. Other variables potentially able to modify brown bear food habits at the local scale were accounted for by considering two areas where local conditions changed in different ways during the study period. General climatic indicators such as temperature and the winter North Atlantic Oscillation index were good predictors of some diet trends, although local factors seemed to modulate the potential response of food habits to recent climate change. Boreal and temperate food items decreasingly contributed to brown bear diet, replaced by increasing contributions of southern foods, which suggested that warmer temperatures might determine the occurrence of some food items in the diet of Cantabrian brown bears through effects on plant distribution and phenology. At the local scale, high cattle density in one of the study areas limited food sources available for brown bears. Important food sources for brown bears, such as heath-like Vaccinium formations and old-growth oak forest in the Cantabrian Mountains, require increased levels of protection.

Erythrocyte Riboflavin for the Detection of Riboflavin Deficiency in Pregnant Nepali Women

Riboflavin deficiency is common among chronic alcoholics, the elderly, and vegetarians (1)(2)(3)(4), but intake in the United States is generally adequate(5)(6), unlike the widespread deficiency in regions of the world with limited animal food sources(7)(8). Riboflavin status has been assessed from measurements in urine, plasma, and erythrocytes(9)(10)(11). The erythrocyte glutathione reductase activity coefficient (EGRAC) is the commonly used test and reflects the adequacy of riboflavin to support enzyme function(10). In this assay, the stimulation of erythrocyte glutathione reductase by FAD is measured in vitro, and a higher activity coefficient reflects a larger amount of unsaturated glutathione reductase apo-enzyme resulting from lack of FAD. The EGRAC cutoffs(12) are based on observational studies in well-nourished American school children (n = 431) and adult men (n = 6) and a depletion–repletion study in Indian adults (n = 8)(13)(14)(15). These cutoffs are usually ≥1.4 for deficiency status, 1.2 to <1.4 for marginal status, and <1.2 for acceptable status. Although erythrocyte riboflavin concentration is seldom used to assess riboflavin status, Hustad et al. (16) showed that the sum of erythrocyte flavin mononucleotide and FAD is correlated with the EGRAC and might be a useful indicator of riboflavin status in population studies. The elderly Irish persons (n = 122) in their study had marginal riboflavin status (mean EGRAC, 1.26), but no erythrocyte riboflavin cutoffs were evaluated. In healthy Californian adults (n = 22), we previously determined the 5th percentile of erythrocyte riboflavin concentration to be 170 nmol/L (range, 169–289 nmol/L) but did not measure the EGRAC in the same samples (L.H. Allen, unpublished data). The purpose of our study was to compare erythrocyte riboflavin concentrations against the EGRAC in a group of …

Spatial, temporal and competition effects on size and weight of caddisflies (Insecta, Trichoptera) in emergence traps

Size, weight and abundance of eleven species of caddisfly collected in four emergence traps from 1983-1991 at the Breitenbach (Germany) were analyzed for spatial and temporal patterns. Scrapers were abundant and small, shredders rare but large, predators were in between. Individual weights of most species increased downstream. No weight change along the stream was detected in A. fimbriata, T. rostocki, P. conspersa and R. fasciata. At low discharge, specimen numbers of A. fimbriata and C. villosa decreased, but it increased in P. conspersa. No correlation between discharge and any weight measure occurred. Intra- and interspecific competition was detected only between the scrapers A. fuscipes, A. fimbriata and D. annulatus, with negative effects on size and weight of other species and of competitors. Similar findings in the shredder C. villosa were effects of site specific temperature patterns, not of direct competition. It was evident that dependencies or interactions discovered at individual sites generally did not occur at all sites simultaneously. Inter- and intraspecific competition for a limited food source was detected only in scrapers during periods of low flow. No effects of food shortage was discovered in shredders or predators. Thus, based on the individual and population success of caddisflies, it is argued that the stream community in the Breitenbach was mainly driven by physical forces, temperature and discharge. Only under particular spatial and temporal conditions competition effects do become evident.

YELLOW JACKETS MAY BE AN UNDERESTIMATED COMPONENT OF AN ANT-SEED MUTUALISM

Abstract Yellow jackets (Hymenoptera: Vespidae) are attracted to the typically ant-dispersed seeds of trilliums and will take seeds from ants in the genus Aphaenogaster. To determine if yellow jacket, Vespula maculifrons (Buysson), presence interferes with seed foraging by ants, we presented seeds of Trillium discolor Wray to three species (A. texana carolinensis Wheeler, Formica schaufussi Mayr, and Solenopsis invicta Buren) of seed-carrying ants in areas where vespids were present or excluded. We found that interspecific aggression between yellow jackets and ants is species specific. Vespid presence decreased average foraging time and increased foraging efficiency of two of the three ant species studied, a situation that might reflect competition for a limited food source. We also found that yellow jackets removed more seeds than ants, suggestive that vespids are important, albeit underestimated, components of ant-seed mutualisms.

Stable isotope analysis of macroinvertebrates and their food sources in a glacier stream

1. Food sources and trophic structure of the macroinvertebrate community along a longitudinal gradient were examined in a glacier stream of the Swiss Alps (Val Roseg). Analysis of multiple stable isotopes (δ13C and δ15N) and measurement of C : N ratios were used to differentiate between allochthonous and autochthonous organic matter.2. Although isotopic signatures of algae varied widely among sites and dates, it was possible to discriminate between allochthonous and autochthonous food sources using a site‐specific approach.3. Dominant food sources of herbivorous invertebrates in all main channel sites were epilithic diatoms and the filamentous gold alga Hydrurus foetidus. Allochthonous organic matter was of some importance only in a groundwater‐fed stream close to the floodplain margin.4. Seasonal changes in the δ13C signature of the macroinvertebrates corresponded with seasonal changes in δ13C of the gold alga H. foetidus. This indicated that the energy base remains autochthonous throughout the year.5. Because of limited food sources, feeding plasticity of the invertebrate community was high. Both grazers and shredders fed predominantly on algae, whereas gatherer‐collectors seemed to be omnivorous.6. The overall enrichment of δ15N was 2.25‰ (r2=0.99) per trophic level. On a gradient from the glacier site to a downstream forested site trophic enrichment was constant but variation in δ15N within trophic levels decreased.

Agonistic Tactics and Size Asymmetries between Opponents in Blattella germanica (L.) (Dictyoptera: Blattellidae)

AbstractIn this paper we investigated the influence of size differences between opponents on the occurrence of different agonistic attack and response tactics displayed during encounters between Blattella germanica (L.) cockroaches of all developmental stages, competing for a limited food source. The two main results were: 1) attack and response tactics varied during development and 2) size asymmetries between contestants influenced agonistic tactics. Developmental stage of initiator influenced the frequency distribution of the three types of attack patterns (Bite, Kick and Jump) and of the four types of response patterns (Retaliation, Escape, Resettle and No Response). The proportion of kicks increased gradually with developmental stage of the initiator whereas the proportion of bites declined during development. In addition, cockroaches adapted their attack tactics to the developmental stage of their opponent. Similarly the response displayed varied in relation to the developmental stage of the attacked individual, the developmental stage of the initiator and the type of attack displayed. During an interaction, animals appeared to be able to evaluate the relative size of their opponent and to evaluate the consequences of the behavioural pattern they displayed. Larger animals tended to minimize the intensity of the agonistic act they initiated. Escalation in interactions was rare and smaller individuals tended to escape when attacked by larger ones. Wrong estimations of the relative size of opponent, when a smaller animal retaliated after being attacked by a larger animal or when a larger animal fled after being attacked by a smaller one, represented only 6% of the records.

Agonistic interactions and exploitation of limited food sources in Blattella germanica (L.)

The importance of size asymmetries between contestants that engage in agonistic interactions at a limited food source were investigated. Rates of agonistic interactions at the experimental food sources were not density-dependent. Most of the interactions concerned dyads either of the same developmental stage or of close developmental stages. Larvae interacted more frequently with an animal of the same developmental stage whereas adults interacted more frequently with an adult of the other sex or with a large, instar 6, larva. According to the composition of the feeding group, the number of acts initiated per individual per unit time varied with developmental stage. A factorial analysis of correspondence, followed by a cluster analysis, enabled us to define three categories of interacting groups according to group structure. Feeding group structure influenced the level of individual aggression, particularly in adults. We show how a slight change in group structure modified intensity and direction of aggressiveness, particularly in males and in females.

Effects of Mulches on Foraging Behaviour of Microtermes Obesi and Odontotermes Spp. in India

Termites are important agricultural pests in the semi-arid tropics. Conventional methods of control have relied on persistent organochloride insecticides with accompanying health and environmental problems. In contrast, cultural control methods provide untested, but environmentally sound options to farmers. This study reports results from three experiments on the use of mulches to reduce Microtermes obesi and Odontotermes spp. damage with relevance to groundnut production in India.Termites scarification of groundnut was 80–90% lower for pods dried in neem cake or Ipomoea fistulosa mulches than for pods dried directly on the soil. Similarly, subterranean attack by termites on bamboo baits was 20–40% lower in mulched plots than in controls. However, mulches were ineffective in protecting bullock manure from removal by termites.Successful use of mulches in termite control may be related to food source concentration. Termite location of concentrated food sources, such as bullock manure, was followed by recruitment of workers and construction of protected runways. In contrast, termites foraging on limited food sources, such as groundnut pods, did not construct runways and had greater exposure to mulches.

Testing the Behavioural Dominance and Dispersal Hypothesis in Pochard

Wintering flocks of diving ducks often show a great disparity in sex ratio with males predominating. The behavioural dominance and dispersal hypothesis explains this phenomenon by arguing that males dominate and exclude females from limited food sources, forcing them to migrate further south. Our study of a wild flock of Pochard Aythya ferina under manipulated feeding conditions, provides some support for this hypothesis. Male attacks were directed more at females (74%) than at other males (26%) even though the sex-ratio favoured males 4.7 to 1. Male dominance appeared to influence the timing of female foraging activity rather than foraging location. Females appeared to feed after the requirements of males were fulfilled. We suggest, that in the long run, feeding second may be energetically expensive to females and cause them to migrate further, where food supply may be more abundant and male competition less.

Weight Changes in Relation To Social Hierarchy in Captive Flocks of Silvereyes, Zoster Ops La Teralis

Abstract1. A flock of ten silvereyes kept under regular food deprivation of one hour per day exhibited a dominance hierarchy resulting from aggressive encounters. The weight gain of these birds in six weeks of winter was significantly less than that of the control flock of ten birds kept with uninterrupted food supply. 2. In the experimental flock the omega bird lost weight whereas the two most aggressive birds gained considerably less weight than the others. This was interpreted to mean that both agonistic behaviour and the resultant social organisation have biological significance in the survival of individuals. 3. It is proposed that winter flocking serves a conservation function in exploiting limited food sources and that agonistic behaviour is an integrating factor in the organisation of the flock.

Quantitative observations on feeding behavior inSaguinus geoffroyi (callithricidae, primates)

Feeding behavior of a six-animal group of marmosets,Saguinus geoffroyi, was observed under field conditions in the Panama Canal Zone. The order of feeding was recorded as the marked animals fed from a limited access food source. A combined distribution of observed visitations to the food source was shown to be significantly non-random (p<.005). The juveniles of the group were seen to feed at the source before adults on the average.

Seasonal Changes in the Chemical Composition and Food Reserves of the Freshwater Triclad Dugesia tigrina (Platyhelminthes: Turbellaria)

Changes in the food reserves and chemical constituents of a population of Dugesia tigrina (Girard, 1850) from Grenadier Pond, Toronto, Ont., have been followed over a 13-month period from October 1968 through October 1969. The parameters examined were individual worm dry weight, protein nitrogen, nonprotein nitrogen, lipid nitrogen, lyo-glycogen, desmo-glycogen, and total lipid.Whereas the nitrogen, lipid, and desmo-glycogen fractions remained relatively constant when expressed on a weight-to-unit-weight basis, irrespective of changes in the number and size of individual worms, the lyo-glycogen fraction decreased exponentially with an increase in the number of worms in the population. This decrease mirrored the relation between the size of individual worms and the number of worms in the population. The negative regression coefficient of lyo-glycogen on population biomass was statistically significant (P &lt; 0.05).The changes at different times of the year in the chemical constituents and food reserves of D. tigrina have been correlated with variations resulting from the life cycle of D. tigrina in both the size of the population and the size of the individual members comprising the population.The results are consistent with Reynoldson's (1966) hypothesis that triclad populations show restricted fluctuations in numbers because the population size is regulated by intra-specific competition for a limited food source. The significance of a limited food resource is demonstrated by showing that, as the population size increased, intraspecific competition resulted in decreases in the lyo-glycogen food reserves at both the individual and population level.